SBPMat
BRAZIL-MRS
2nd Brazilian MRS Meeting
October 26-29, 2003
Symposium A:
Current trends in Nanostructured
Materials and Systems II
Symposium Organizers:____________________________________________________
Fernando Lázaro Freire Jr. (PUC-Rio)
Guillermo Solórzano (PUC-Rio, SBPMat)
Israel Baumvol (UFRGS)
Wander Vasconcelos (UFMG)
1
INVITED PRESENTATIONS
A-I1
SELF-ASSEMBLING SYSTEMS AND SURFACE PATTERNING STRATEGIES FOR
NANOTECHNOLOGIES
Giovanni Marletta, Dipartimento di Scienze Chimiche - University of Catania - Viale A.Doria 6 - I95125 Catania – Italy
The need for very large scale planar integration of different functions in multifunctional devices
including electronic devices, arrays of biosensors, highly integrated optoelectronic devices, etc.., is
driving a growing effort towards techniques for surface patterning. Two basically different
philosophies of patterning have been extensively developed, respectively exploiting selforganization properties of matter (bottom-up approach), and radiation-based lithography (top-down
approach).
In the present paper we report a number of case studies dealing with the use of techniques as
Langmuir-Blodgett deposition (LB), SPM tip-writing and focused-ion beam activation of surfaces
to obtain micro- and nanoscale spatially resolved structures. In particular, we will report specific
cases of unusual self-structuring of LB-deposited monolayers on solid surfaces, of tip-induced
chemical patterning of organic monolayers on silicon, and spontaneous protein aggregation on ionirradiated polymer dots. The formation of various structures, as variously shaped domains, stripes,
fibers and dots, will be related to the molecular structure of the employed compounds, the
deposition parameters, and the substrate composition and properties obtained by Near Field
Microscopies (NFM), X-ray Photoelectron Spectroscopy (XPS), Imaging ToF-SIMS, Dynamic
Contact angle measurements, Surface Enhanced Raman Spectroscopy (SERS) and theoretical
simulations. The perspective of the employed techniques in the context of the developing patterning
technologies will be given with respect to the state-of-art of the field.
A-I2
TEACHING “OLD” MATERIALS “NEW” TRICKS: SITE- AND SHAPE-SPECIFIC
NANOPATTERNING OF FUNCTIONAL NANOSTRUCTURES
Vinayak P. Dravid, Professor, Materials Science & Engineering, Director, NUANCE Center
Northwestern University, Evanston, IL 60208 USA
At Northwestern, we are working towards designing the intricate architecture of functional
nanostructures, as well as using them as building blocks for device systems for sensing, diagnostics
and therapeutics. Embedded in this scheme are several nanopatterning approaches, some are based
on the original invention of Dip-Pen Nanolithography (DPN) developed at Northwestern. The
original DPN approach is modified to pattern, at the nanoscale, templates for inorganic and
organic-inorganic complexes of arbitrary shape/size on arbitrary substrates, thus extending the
efficacy and elegance of DPN.
The talk will outline sol-based precursor “inks” as an enabling approach to pattern and characterize
magnetic, electronic, chemical- and optical active nanostructures at the nanoscale. Success is
already evident for magnetic oxides, inorganic mesoporous structures, ferroelectrics and opticallyactive nanostructures.The real need for characterizing structure/crystallography/chemistry, as well
as unambiguous measurement of their local properties, will be emphasized. The prospects for
patterning at single-molecule resolution, especially for bioactive molecules, both by themselves and
as templates for inorganics, will also be discussed.
A-I3
MOLECULAR ORIGINS OF BIO(IN)COMPATIBILITY : MATERIALS DESIGN ISSUES AND
2
CHALLENGES AT THE NANOSCALE
C. Ortiz, Department of Materials Science and Engineering, Massachusetts Institute of Technology,
Cambridge, MA USA
To produce truly bioinert or bioactive surfaces a detailed knowledge of the nanoscale morphology,
mechanical properties, physical and chemical interactions with the biological environment is
needed. Using the powerful technique of high resolution force spectroscopy (HRFS), we have
measured the intermolecular interaction forces between a nanosized probe tip covalently bound
with human serum albumin (HSA), the most abundant blood plasma protein in the human body,
and various well-defined chemically modified surfaces including; COO- and CH3-terminated
alkanethiol self-assembling monolayers and end-grafted poly(ethylene oxide) mushrooms. By
varying the solution conditions and using molecular-level theoretical models this net interaction
was deconvoluted into the individual constituent interactions including; electrostatic double layer,
configurational entropy, H-bonding, and van der Waals forces. A series of chemically advantageous
molecular attributes was formulated and based on this information, new glycocalyx-mimetic
oligosaccharide-functionalized surfaces were chosen and studied using HRFS.
A-I4
PATTERNED ASSEMBLY OF EPITAXIAL SEMICONDUCTOR NANOSTRUCTURES
R. Hull; S. Atha, J.L. Gray, M. Kammler, A. Portavoce, N. Singh, D.M. Elzey, Dept. of Mat. Sci.,
Univ. of Virginia, Charlottesville, VA 22904, USA; F.M. Ross, IBM Yorktown Heights Research
Center, NY, USA; X. Luo, G. Snider, Dept of Elec. Eng., Notre Dame Univ., IN, USA; J.A. Floro,
Sandia National Laboratories, NM, USA.
Substantial progress has been described in the literature with respect to the synthesis of ordered
semiconductor quantum dot (QD) arrays with single spatial frequencies, through control of elastic
interactions during epitaxial growth. For most nano-electronic architectures, more complex
patterns are required. For example, in the quantum cellular automata concept, QD quadruplets are
charged in bistable configurations, with quadruplet cells arranged in more complex patterns to
enable the functions of digital logic. We will describe two experimental approaches for achieving
accurate surface placement of quantum dots in the epitaxial Ge(Si)/Si system: 1) Creation of
localized topography, chemistry and strain on the substrate surface using focused ion beams for
seeding of QD nucleation. 2) Synthesis of QD quadruplet molecules, where molecules selfassemble through cooperative nucleation around nano-scaled surface pits formed during epitaxial
growth. Combined focused ion beam / electron beam lithography methods for coupling these QD
architectures into nano-electronic test structures will also be presented.
A-I5
A-I6
MAPPING 3D ALLOYING OF Ge:Si (001) DOMES
G.Medeiros-Ribeiro, S. Kycia; LNLS, Campinas, SP; A. Malachias, R. Magalhães-Paniago; Depto.
de Física, UFMG, Belo Horizonte, MG; T. I. Kamins, and R. Stanley Williams; Hewlett-Packard
Labs, Palo Alto, CA
The issue of Si diffusion into Ge islands grown on Si(100) has been addressed by several
independent studies with electron microscopy and x-ray techniques. Alloying is a significant factor
in determining the shape and size distribution of an island ensemble. All experiment evidences
support the existence of a distinct SiGe vertical composition variation, with most of the Si
concentrated at the base of the island. Different growth conditions produce distinct lateral profiles.
Hence, the assessment of lateral composition profiles is important to both identify the dominant
growth mechanisms and model the confining potential of quantum dots. We report Grazing
Incidence Angle X-ray Scattering (GIAXS) measurements on an ensemble of Ge domes with a
uniform size distribution. We determined the (average) three-dimensional composition of the
domes from an analysis of the anomalous scattering reciprocal space intensity maps near the Ge K
absorption edge by first segmenting the domes into a stack of layers and then mapping the lateral
concentration of Ge in each layer. Finally, we performed selective-etching experiments and
qualitatively confirmed our proposed structural model. The significance of the analysis and
procedure presented is key for the realistic modeling of quantum dot confining potentials, as this
work presents a solution for imputing lateral composition profiles with its associated strain. This
work was funded by FAPESP (contract 98/14757-4) and HP Brazil.
ON THE NATURE OF Mn IN SEMICONDUCTORS*
3
Adalberto Fazzio, Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970, São
Paulo-SP, Brazil
We have performed a systematic study of the nature of Mn in semiconductors, using total energy ab
initio calculations within the density-functional theory. We will discuss results for Mn in GaAs and
in Si, Ge and SiGe. Our results for Ga1-xMnxAs diluted magnetic semiconductors (DMS)
unambiguously show that the effective Mn-Mn coupling is always ferromagnetic, thus non-RKKY,
and it is intermediated by the antiferromagnetic coupling of each Mn spin to the holes. We then
address the following question: can there be a MnxSi1-x ferromagnetic semiconductor, similarly to
MnxGe1-x? Since the main difference between Mn in Si and Ge is the fact that it prefers to be
interstitial in Si, whereas it is substitutional in Ge, we investigate the origin of this difference. For
that, we study the properties of interstitial and substitutional Mn impurities in both Si and Ge bulk
crystals, as well as in the alloy Si1-xGex. We conclude that the main reason behind the different
behavior of Mn in Si and Ge has a chemical origin, indicating that a Ge-rich neighborhood will
stabilize a substitutional Mn in the Si1-xGex. Assuming that in order to obtain a Si based DMS it is
fundamental to have substitutional Mn impurities, we investigate the possibility of incorporating
MnSi using some sort of non-equilibrium growth procedure. Studying a variety of interstitial and
substitutional sites for a Mn impurity on the Si(100) bare and hydrogenated surface, we find a
substitutional Mn surface site with a formation energy similar to the interstitial surface site,
suggesting that it might be possible to grow, probably through low temperature MBE, Mn xSi1-x
samples with a high enough concentration of substitutional Mn.
*
This work was done in collaboration with Antônio J. R. da Silva, Raimundo R. dos Santos, Luiz E.
de Oliveira, Alex Antonelli and Gustavo M. Dalpian, supported by the Brazilian agencies FAPESP
and CNPq.
A-I7
NANOPARTICLES-BASED CHEMICAL GAS SENSORS FOR OUTDOOR AIR QUALITY
MONITORING MICROSTATIONS
M.-I. Baraton, SPCTS CNRS, University of Limoges, France; L. Merhari, CERAMEC R&D,
Limoges, France
Due to the growing concern worldwide about the consequences of urban air pollution on public
health, the official organizations in charge of environment protection are strengthening the
regulations and have set the maximum authorized concentrations of pollutants at very low levels.
Current cost-effective semiconductor sensors used to monitor indoor air quality are not suitable for
outdoor air quality monitoring due to their insufficient sensitivity and to their cross-sensitivity to
humidity.
We present here some of our consolidated results on the optimisation of chemical gas sensors based
on metal oxide semiconductors. In order to increase sensitivity and selectivity while keeping
fabrication at low cost, three major research directions have been considered: 1) the use of
semiconductor nanoparticles in the fabrication of screen-printed gas sensors to increase the
sensitivity; 2) the printing of sensitive layers on alumina tiles using a simple mechanical layer-bylayer technique to further increase the sensitivity; 3) the control and tailoring of surface chemistry
of nanoparticles proved to be a critical step for further device optimisation. We will finally show
how our prototype devices which are capable of detecting O3 and NOx concentrations down to 20
ppb and 50 ppb respectively, and CO concentrations down to 3ppm in air, can be used as sensing
elements in novel and cost-effective air monitoring micro-stations. This work has been financially
supported by the European Community.
A-I8
SURFACE CHARGE INDUCED NANOSCALE MANIPULATION OF MOLECULAR FILMS
4
Francisco Nart and Frederico Cunha, Instituto de Química de São Carlos, Universidade de São
Paulo, Av. Trabalhador Saocarlense, 400 - 13566-690 - São Carlos, SP – Brazil
The adsorption mechanism of organic molecules on metallic surfaces depends upon several factors
that include molecular structure, concentration, temperature and surface charge. The careful
control of some of these variables allows one to manipulate the adsorption geometry of these
molecules leading to dissimilar packing structures, which can be followed by in situ STM and
vibrational spectroscopy. The construction of nanostructured materials following a layer-by-layer
approach is the final objective of this work. The molecular probe of choice is a series of derivatives
of Uracil. These molecules present a variety of possibilities in adsorption geometries and ready
availability. We found that the packing depends on the surface charge on the electrode and on the
atom substituted in position 5 of the Uracil base molecule. We used also a silver electrode to
investigate the charge induced restructuring of Uracil based molecules by Raman Spectroscopy,
since SERS measurements on gold were not possible.
A-I9
SPUTTERED NANOSCALE MAGNETIC MATERIALS
Antonio Azevedo, F.M. de Aguiar and S.M. Rezende, Departamento de Física, Univ. Federal de
Pernambuco, 50670-901 Recife, PE, Brazil.
New properties and phenomena in magnetism have emerged from the ability to artificially prepare
nanoscale magnetic materials. The assembling of nanometer-sized magnetic structures with desired
properties have resulted in a forthcoming age for electronic devices, named spintronics. The
investigation of the structure and magnetic properties of nanoscale magnetic materials such as thin
films, multilayers, particulate and thin film recording media, exchange biased films, GMR spinvalves, magnetic tunneling junctions, and so on has been driven by the demanding requirements of
this new area of research. Here, it will be presented a description of some challenging problems and
exciting applications envisioned for nanomagnetic materials. Particular attention will be devoted to
some activities in this area that are being pursued at the Magnetism and Magnetic Materials group,
in Recife. The magnetic properties of multilayers, exchange coupled bilayers, GMR spin-valves
and spin injection will be discussed. The correlation between structure, growth conditions and
magnetic properties will be emphasized. Dynamic and static properties investigated by Brillouin
light scattering, ferromagnetic resonance, ac-susceptibility, dc-magnetometry, etc. are going to be
also discussed.
Supported by FINEP, CNPq and CAPES (Brazilian agencies)
A-I10
THERMODYNAMICS OF NANOPARTICLES
Miguel Jose Yacaman, Texas materials Institute and Chemical Engineering department University
of Texas- Austin Austin TX 79705 USA
Metallic particles in the nanosized regime show a thermodynamic behavior, which is very different
from that of the macroscopic systems. This is reflected in many properties such as strange
minimum energy configurations, shape instabilities, wetting properties and unique alloy structures.
This is the result of the complex energy landscape in the nano systems. This is increased when two
metals are present .we make a review of recent work by our group in this area and present new data
on the alloy behavior of bimetallic systems such as Au-Pd and Au-Cu .we demonstrate both
experimentally and theoretically that that the eutectic structure and the core shell structures are
favored in nano-alloy systems. In addition we discuss the interactions of nanoparticles of metals
and semiconductors with carbon nanotubes and onions new ways to form one-dimensional
structures are found.
Finally we show that when nanoparticles are in a carbon substrate collective phenomena are
produced resulting in new chemical properties at the nanolevel.
A-I11
SYNCHROTRON RADIATION SAXS STUDIES OF NANOSTRUCTURED MATERIALS
5
Aldo F. Craievich, Institute of Physics, University of São Paulo, C. P. 66318, 05315-970 São
Paulo, Brazil
A set of recent in situ synchrotron radiation SAXS studies of nano-structured materials will be
reviewed. The experiments were carried out at the synchrotron laboratory LNLS, Campinas, Brazil.
The first investigation deals with the formation and growth of liquid Bi nano-droplets embedded in
a borate glass [Phys. Rev. B, 67, 0854051 (2003)]. Measurements performed in absolute scale
allowed us to quantitatively characterize the mechanisms of growth and coarsening, and determine
the diffusion coefficient and the activation energy of Bi atoms. The second investigation to be
reported concerns the clustering mechanism for the formation of fractal aggregates in several
sulfate-zirconia colloidal solutions [J. Phys. Chem. B. 107, 3390 (2003)]. The experimental results
lead to a unified model of the clustering process consisting of an initial 1D growth of colloidal
chains followed by a 3D cross-linking and further coarsening. Finally, the first results of an ongoing study of ordered nanoporous materials and self-organized precursor sols, for applications in
catalysis, will be described [in progress (2003)]. This study provided useful insight about the
nanostructure of several sols and also about the resulting porous powders, which are expected to
mimic the structure of the precursor systems. Since the properties of nanomaterials not only depend
on the atomic structure but also, and strongly, on the shape and size of their basic building blocks,
SAXS characterizations - such as those reported here - are expected to provide useful information
for new materials design.
AI-12
MICRO-RAMAN STUDIES OF CARBON NANOTUBES USING TUNABLE LASERS
M. A. Pimenta, A. Jorio, C. Fantini, M. Souza, Departamento de Física – UFMG, Brasil; R. Saito,
Tohoku University, Japan; G. Dresselhaus and M. S. Dresselhaus, MIT, USA
Resonant Raman scattering is a very useful tool to investigate carbon nanotubes since it can probe
both the phonon spectra and the one-dimensional (1D) electronic structure. We will present results
of the Raman spectra of different samples of carbon nanotubes (bundles of nanotubes, isolated
nanotubes in aqueous surfactant suspensions, isolated nanotubes deposited on a Si/SiO2 substrate),
using tunable lasers in the range of laser energies from 1.5 to 2.7 eV. We will show that the 1D
electronic structure formed by van Hove singularities can be obtained from the resonant Raman
spectra. We will also present a detailed investigation of the intermediate frequency Raman modes,
between 600 and 1100 cm-1. These intermediate frequency modes exhibit a step-like dispersive
behavior, that can be explained by a 1D double resonance mechanism, involving acoustic and
optical phonons.
A-I13
APPLICATIONS OF ANALYTICAL TRANSMISSION ELECTRON MICROSCOPY IN
NANOSCIENCE AND NANOTECHNOLOGY
Joachim Mayer, Central Facility for Electron Microscopy, Aachen University, 52074 Aachen,
Germany
Nanoscale characterisation and analysis are indispensable to establish the structure/property
relationship and thus the scientific basis for nanoscience and nanotechnology. Transmission
electron microscopy (TEM), in particular in combination with site-specific focused ion beam (FIB)
specimen preparation, has become a more and more important tool with unique capabilities for the
study of the chemistry, crystallography and local electronic structure of interfaces and nanoscale
features. To highlight the experimental possibilities, recent examples from three areas of
application will be discussed: (1) The study of the structure and chemistry of metal/ceramic
interfaces, (2) the application of Au quantum dots in nanoelectronic devices based on the Coulomb
Blockade effect and (3) the investigation of the tunnel barriers in magnetic tunnel junctions (MTJ)
used as MRAM test devices. In all the cases, structural and chemical information from the TEM
investigations could directly be linked to the materials and device properties. Furthermore, we will
present new ideas of how to employ the focused ion beam technology to create model devices in
nanoscience. Finally, we will discuss the needs for future developments in the TEM and FIB area.
A-I14
UNDERSTANDING DEFECT NUCLEATION THROUGH NANOSCALE EXPERIMENTS
6
AND COMPUTATIONS
Krystyn J. Van Vliet, Children's Hospital and Harvard Medical School, Boston, MA USA and
Subra Suresh, Massachusetts Institute of Technology, Cambridge, MA USA
Nanoscale contact experiments and atomistic modeling thereof is presented as a means to
investigate the onset and early stages of plasticity in metals. Although this work focuses on
homogeneous defect nucleation far from grain boundaries, it will enable subseuqent development
of heterogeneous nucleation near and at grain boundaries--a key phenomenon in the mechanical
deformation of nanocrystalline materials. An energetic, position-sensitive defect nucleation
criterion is developed to predict the site and slip character of nucleated defects. This criterion is
validated explicitly in the context of dislocation nucleation, using nanoindentation both as a means
to concentrate applied force and to measure accurately the onset of dislocation activity.
Molecular dynamics (MD) modeling of Bragg-Nye soap bubble raft indentation experiments
confirm the accuracy and potential of this appoach. In addition, a new nonlinear finite element
approach is developed to guide large-scale computational studies by an intrinsically atomic-scale
defect nucleation criterion. With these tools, we demonstrate the effects of microstructural features
such as grain size and macrostructural features such as film thickness and line width on the
initiation and early stages of plastic deformation.
A-I15
TEM STUDIES OF INDIVIDUAL AND AGGLOMERATED NANOPARTICLES
C. Barry Carter*, Christopher R. Perrey, William M. Mook, William W. Gerberich, Siri
Thompson1, Ameya Bapat1, Uwe Kortshagen1, Rajesh Mukherjee1, Xiaoliang Wang1, Jami Hafiz1,
Peter McMurry1, Joachim Heberlein1, and Steven Girshick1
Department of Chemical Engineering and Materials Science, University of Minnesota,
Minneapolis, MN; 1 Department of Mechanical Engineering, University of Minnesota,
Minneapolis, MN; * cbcarter@umn.edu
In the 1-100 nm size regime, the properties of materials can differ significantly from those of their
bulk counterparts. Recent work has reported nanospheres of Si with hardnesses much higher than
that of bulk Si; other studies have described similarly advantageous electronic and chemical
properties of nanoparticles. The unique relationships between nanoscale structure, morphology,
chemistry, and crystallography to the properties observed must be understood for successful
incorporation into commercial applications. Because of the inherently small size of these nanoscale
structures, the transmission electron microscope (TEM) is an essential tool for this analysis of both
individual nanoparticles and agglomerated nanoparticles. Using the TEM, nanoparticles from three
distinctly different plasma-generation methods have been investigated. Nanoparticles of Si, Ti, and
SiC have been observed and led to interesting discoveries on nanoparticle surface structure,
formation processes, oxidation, and planar defects in nanoparticles. Similar work involving
nanoparticle agglomerates provides the opportunity to observe the behavior of sintering and
coagulation at the nanoscale. These observations of nanoparticle systems can then be compared to
that of previously studies bulk systems for a greater understanding of these processes across
different length scales.
A-I16
USING
NATURE'S
TOOLS
TO
DESIGN
7
NOVEL
HYBRID
NANOSTRUCTURED
MATERIALS
Angela M. Belcher*, Brian Reiss*, Seung-Wuk Lee* and Chuanbin Mao; University of Texas at
Austin and *Massachusetts Institute of Technology
Peptides capable of specific recognition and nucleation of semiconductor and magnetic materials
were isolated and engineered into advanced biological viral templates and long range-ordering viral
liquid crystal systems. Peptides selected through an evolutionary screening process that exhibit
control of composition, size and phase during nanoparticle nucleation were exploited for these
materials-directing structures. The incorporation of specific, nucleating peptides into the generic
scaffold of the M13 coat structure provides a viable template for the directed synthesis of
semiconducting and magnetic materials. The engineered viruses were exposed to semiconductor
precursor solutions, and the resultant nanocrystals that were templated along the viruses to form
nanowires were extensively characterized using high resolution analytical electron microscopy and
photoluminescence. Removal of the viral template via annealing promoted oriented aggregationbased crystal growth, forming individual single crystal nanowires. We report a virus based scaffold
for the synthesis of crystalline ZnS and the first free standing L10 CoPt nanowires. The unique
ability to interchange substrate specific peptides into the linear self-assembled filamentous
construct of the M13 virus introduces a material tunability not seen in previous synthetic routes.
Additionally, liquid crystal systems were used for the fabrication of a highly ordered composite
material composed of genetically engineered M13 bacteriophage and inorganic nanocrystals.
A-I17
MECHANICAL PROPERTIES OF BULK METALLIC GLASS-BASED COMPOSITES
W.J. Botta F., A.M. Jorge Júnior, C.Bolfarini, C.S. Kiminami, LabNano, DEMa, UFSCar, cp 676,
13565-905, São Carlos, SP, Brazil; A.R. Yavari, Institut National Polytechnique de Grenoble,
LTPCM (CNRS umr 5614), BP 75, St-Martin-d’Hères Campus, 38402, France
Despite the large values of elastic strain range (2% as compared with 0.2% for conventional metals)
and excellent values of fracture stress, applications of bulk metallic glasses (BMG) are limited by
the lack of plasticity since they fail catastrophically by strain softening or a shearing off
mechanism. However, more recently, it was discovered that the strain-softening mechanisms that
lead to the shear instability and rapid plastic failure of BMGs can be overcome in BMG-based
composites of appropriate microstructural length-scales, leading to the emergence of roomtemperature ductility and plastic deformations of the order of 10% beyond their usual 2% elastic
deformation range. In this paper, the controlled partial crystallisation by direct heating processing
of bulk metallic glasses is reported. Fully amorphous Zr55Ti5Cu22Ni8A110 samples have been
annealed by a direct electrical current heating system for the formation of nanocrystals, whose
transformation is controlled by the analyses of the thermal variation of the bulk sample resistivity.
Mechanical properties results are discussed as a function of the presence of crystalline phase and its
interaction with the shear bands which penetrate or branch-off when reaching the micro-nano
particles in the BMG matrix.
ORAL PRESENTATIONS
8
A-O1
SHAPE STABILITY OF SELF-ASSEMBLED InAs/InP NANOSTRUCTURES
H.R. Gutiérrez, M.A.Cotta, J.R.R. Bortoleto; IFGW, DFA/LPD, UNICAMP, CP 6165,13081-970
Campinas-SP, Brazil. R. Magalhaes-Paniago; Departamento de Física, Universidade Federal de
Minas Gerais, C.P. 702, CEP 30123-970 Belo Horizonte, MG, Brazil
InAs nanostructures in an InP matrix have received much attention in the last years. Recently, we
have reported the conditions that determine the InAs shape transition -from wires to dots – for films
grown on (100) InP substrates by Chemical Beam Epitaxy. The grown of such self-assembled
nanostructures requires a complete understanding and control of the formation mechanisms. In this
sense we have obtained a complete picture of the InAs nanostructures formation. InAs growth
evolution was monitored by Reflection High Energy Electron Diffraction (RHEED). The samples
were analyzed by Atomic Force Microscopy (AFM) and High Resolution Transmission Electron
Microscopy (HRTEM). The strain distribution was characterized by grazing incidence x-ray
scattering, an accurate method sensitive to both local lattice parameter variations and nanostructure
lateral size. These measurements were correlated with Atomic Force Microscopy and Transmission
Electron Microscopy data. A remarkable anisotropy was observed for strain distributions parallel
and perpendicular to the wires. Here we report the three-dimensional map of the strain distribution
in these nanostrucutres, for crystalline directions parallel and perpendicular to the wires.
A-O2
EFFECT OF DISORDER ON OPTICAL BAND EDGE OF RANDOM DOPED GaAs/AlGaAs
SUPERLATTICES
Yu.A.Pusep, F.E.G.Guimarães, M.B.Ribeiro, H. Arakaki, C.A. de Souza, Instituto de Fisica de São
Carlos, Universidade de São Paulo, 13560-970 São Carlos, SP, Brazil; S.Malzer, G.H.Döhler,
Institut für Technische Physik I, Universität Erlangen, D-91058 Erlangen, Germany
The optical broadenings studied by the photoluminescence in the intentionally disordered
GaAs/AlGaAs superlattices were compared with the broadenings of the individual electron states
measured by the Shubnikov-de Haas oscillations. It was shown that the combined effect of the
electron and hole energy blurrings is to decrease the optical broadening with respect to the
individual state broadenings resulting in very sharp optical edges even in highly disordered
superlattices. It was also found that the impurities almost equally influence the electron and hole
scattering potentials, contrary to what happens due to the structural superlattice disorder. The
anisotropy of the scattering potentials, additional to that one caused by the vertical intentional
disorder, was found due to the segregation of impurities near interfaces.
A-O3
HIGH-PRESSURE
EFFECTS
ON
P-PHENYLENEDIAMINE/SILICA
AND
PANISIDINE/SILICA HYBRID XEROGELS
S. V. M. de Moraes, M. T. Laranjo, M. Zat, C. C. Moro, T. M. H. Costa, E. V. Benvenutti, Instituto
de Química, UFRGS, CP 15003, 91501-970, Porto Alegre, RS, Brazil, M. R. Gallas, Instituto de
Física, UFRGS, CP 15051, 91501-970, Porto Alegre, RS, Brazil
The hybrid xerogels p-phenylenediamine/silica and p-anisidine/silica were prepared with different
surface area and porosity and they were processed at high-pressure, at 7.7 GPa in a quasihydrostatic medium, at room temperature. The morphology of the materials were studied before
and after the high-pressure treatment by using N2 adsorption desorption isotherms, scanning
electron microscopy and infrared thermal analysis. The porous hybrid p-phenylenediamine/silica
presented after the high-pressure treatment, a surface area reduction and an entrapment of organics
in closed pores. However the less porous hybrid p-anisidine/silica showed a surprising behavior, a
pressure-induced increase in surface area with opening of pores. We propose a mechanism based on
the inhibition of the cold sintering process by the organics to explain these results.
A-O4
ORDERED MESOPOROUS SILICA: MICROWAVE PROCESS
9
M. C. A. Fantini, IF-USP, CP 66318, 05315-970, São Paulo, Brazil; J. R. Matos, L. C. Cides da
Silva, L. P. Mercuri, G. O. Chiereci, IQ-USP, CP 26077, 05599-970, São Paulo, Brazil; Mietek
Jaroniec, Department of Chemistry, Kent State University, Kent, Ohio 44240, USA.
Triblock copolymers are used as templates for the synthesis of ordered mesoporous silica, due to
the fact that they allow the growth of different morphological structures, besides their reasonable
commercial cost and biodegradability. These silicas are synthesized at temperatures lower than 550
o
C and are useful for applications running from microelectronics to medical diagnosis, opening up a
wide variety of utilities beyond the traditional areas of materials for catalysis and absorbers.
Depending on the polymers used as template and synthesis process, mesoporous cubic and
hexagonal silicas are formed, with pores between 10 nm and 30 nm. The structural differences are
suitable for each specific application. In this work we report on FDU-1 type ordered mesoporous
silicas, synthesized with the triblock copolymer "B50-6600" [1]. The microwave heating was used,
varying the process time, and it was compared with results obtained with hydrothermal treatment.
This new procedure succeeded in producing ordered cubic face centered, diamond like, mesoporous
structures even at 15 min. of heating. The best result was obtained for 1 h. treatment. The X-ray
diffraction, gas adsorption and electron microscopy results were compared to characterize the
material.
1. J. R. Matos; L. P. Mercuri; M. Kruk; M. Jaroniec; Langmuir 18 (2002) 884.
Acknowledgements: FAPESP, CNPq, CAPES, Brazil.
A-O5
OPTICAL CHARACTERISTICS OF SOL-GEL SILICA GLASSES CONTAINING COPPER
N.F. de Sales, V.C.Costa, W.L.Vasconcelos, Dep. de Eng. Metalúrgica e de Materiais, UFMG,
30160-030, Belo Horizonte, Brazil
We evaluated the influence of reagents concentration and temperature on structural properties of
sol-gel silica glasses doped with copper nitrate.
Optical absorption and transmission were followed using visible-near infrared spectroscopy
(VIS/NIR) and Fourier transform infrared spectroscopy (FTIR). The density was obtained via
helium picnometry and porosity was measured by nitrogen gas adsorption (BET). The gels
analysed were dried at 80C and 120C had molar ratios of TEOS/Cu of 1/0.0084, 1/0.042 and
1/0.084. The molar ratios of TEOS/H2O/EtOH/HNO3 used for the three samples was
1/3.8/3.8/0.005. We observed a increase in the energy of Si-O(H) with the evolution of the drying
process and a decrease in the energy with increasy of reagents concentration. The color of the
glasses shifted from blue to green between 80C and 120C due to changing on the environment
coordination of Cu2+ ions related to the hidroxyl groups.
A-O6
OBTENTION OF SELECTIVE MEMBRANES FOR WATER AND HYDROPHOBIC LIQUIDS
10
BY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION
P. Bankovic, MD student, Laboratory of polymers, Department of Metallurgy and Materials
Engineering, USP, 2463, Prof. Mello Moraes Av., 05508-900 São Paulo, Brazil, N. R. Demarquette
PhD, Associate Professor, Department of Metallurgy and Materials Engineering, USP, 2463, Prof.
Mello Morães Av., 05508-900 São Paulo, Brazil, M. L. P. da Silva PhD, Laboratório de Sistemas
Integráveis, Department of Electrical Engineering, USP 158, Prof. Luciano Gualberto Av., 05508900 São Paulo, Brasil
In this work, the possibility of obtaining selective membranes for water and hydrophobic liquids by
Plasma Enhanced Chemical Vapor Deposition (PECVD) of Hexamethyldisilasane (HMDS), or
double layers of HMDS and n-hexane using a capacitive plasma reactor, on porous substrates was
investigated. The porous substrates used were filter paper, diatomite and textiles of polyester,
aramide and nylon. The films were characterized by Electron Spectroscopy of Chemical analysis
(XPS) and Infrared Spectroscopy (FTIR) and measuring the contact angle formed by drops of water
on their surface. The membranes obtained were characterized by mercury porosimetry and Cobb
test. Their efficiency to separate hydro carbonates from water was evaluated through filtration
experiments and Karl Fisher titration. The reagents used in the filtration experiments were: CHCl 3,
n-hexane, n-heptane or C6H6. The modified porous substrates were tested with solutions of water
and ethanol. The porosity of the different substrates was shown to be unchanged by the deposition
of the films. The contact angles formed by drops of water on the film surface and water adsorption
measured by Cobb Test for all the substrates were above 12 g.m-2 and reduced to around 15 g.m-2
respectively, showing the hydrophobic character of the modified surfaces. The Karl Fisher titration
indicated that between 90 and 500 ppm (depending on the reagent used) of water remained in the
hydro carbonate after filtration. Addition of ethanol to water that was retained on the top of the
membrane resulted in a change of hydrophobic character of the membrane and resulted in a
hydrophilic substrate. The results are explained in light of XPS and FTIR analysis.
A -O7
AB INITIO INTERPRETATION OF PHOTOLUNINESCENCE IN PEROVSKITE STRONTIUM
AND BARIUM TITANATE
E. Orhan, J. A. Varela, Instituto de Química, Universidade Estadual Paulista, 14801-907,
Araraquara-SP, Brazil
C. D. Pinheiro, M. F. C. Gurgel, M. A. dos Santos, F. M. Pontes, Elson Longo, Laboratório
Interdisciplinar de Eletroquímica e Cerâmica (LIEC), Departamento de Quimica, Rod. Washington
Luis, km 235, Universidade Federal de São Carlos, 13565-905 São Carlos – SP
P. S. Pizani, T. M. Boschi, C. E. M. Campos, Departamento de Física, Universidade Federal de São
Carlos, Caixa Postal 676, 13565-905, São Carlos – SP
First principles quantum mechanical techniques, based on density functional theory (B3LYP level)
were employed to study the electronic structure of ordered and deformed periodic models for
Ba0.5Sr0.5TiO3. Electronic properties are analyzed in the light of the measured photoluminescence
properties. The presence of localized electronic levels in the band gap, due to the symmetry break,
together with the coexistence of a charge gradient between TiO6 and TiO5 clusters in the deformed
model would be responsible for the visible photoluminescence of the amorphous compound at
room temperature.
(FAPESP-CEPID, CNPq, CAPES)
A -O8
QUANTUM DYNAMICS SIMULATIONS OF INTERFACIAL ELECTRON TRANSFER IN
11
SENSITIZED SEMICONDUCTORS.
L.G.C. Rego, Depto. de Física, UFPR, Curitiba, CP 19044, 81531-990; V.S. Batista, Dept. of
Chemistry, Yale University, 06520-8107, USA.
Ab initio-DFT molecular dynamics simulations are combined with semi-empirical quantum
dynamics calculations of electronic relaxation to study interfacial electron transfer processes in
sensitized semiconductor nanostructures. Realistic models are used to investigate the dynamics of
electron-injection from the adsorbed catechol molecule to the conduction bands of TiO 2 (anatase).
This is a fundamental process in surface physical-chemistry, relevant to a broad range of
technological applications. It is found that the primary process in the interfacial electron transfer
involves an ultrafast (1  6 fs) electron-injection event that localizes the charge in the Ti4+ surface
ions next to the catechol adsorbate. The primary event is followed by charge delocalization (i.e.,
carrier diffusion) through the TiO2 crystal, an anisotropic diffusional process that can be up to an
order of magnitude slower along the [-101] direction than carrier relaxation along the [010] and
[101] directions in the anatase crystal. It is shown that both the mechanism of electron injection and
the time scales for interfacial electron transfer are quite sensitive to the symmetry of the electronic
state initially populated in the adsorbate molecule. The thermal effects due to the lattice (nuclear)
dynamics are considered in the simulations. Possible applications of this mechanism to molecular
electronics are considered. (J. Am. Chem. Soc. 125, 7989 (2003)).
A -O9
INTRABAND TRANSITIONS IN Si/SiO2 QUANTUM DOTS
J. S. de Sousa, V. N. Freire, Universidade Federal do Ceará, Depto. de Física, CX Postal 6030,
60455-970 Fortaleza-CE, Brazil; E. F. da Silva Jr., Universidade Federal de Pernambuco, Depto.
De Física, Cidade Universitária, 50670-901 Recife-PE, Brazil
Semiconductor quantum dots (QD’s) have been considered one of the nanotechnology building
blocks because their electronic structure can be tailored by controlling their shape, size and charge
state. As intraband transitions usually occur in the infrared (IR) spectral range, night vision systems
and IR radiation detectors figure among the main applications of this technology, which are
important to a variety of fields like military and surveillance. Even though the interest in intraband
transitions in quantum dots have recently increased [1], the number of papers in this matter is still
small. Moreover, they are limited to few systems like III-V compounds and almost inexistent for
the Si/SiO2 systems. Here, we address the investigation of the intraband transitions in Si/SiO2
QD’s, by using a 3D quantum mechanical model, which has the ability to capture the coupling of
the Si band structure anisotropy and QD geometry, and different alignment of the Si
crystallographic orientation [2]. We observed that Si/SiO2 QD’s have efficient transitions and that
QD size, shape and crystallographic orientations strongly affect the oscillator strength of the optical
transitions. Moreover, smaller QD’s exhibit a larger energy range of efficient transitions in
comparison to larger ones.
[1] G. Allan and C. Delerue, Phys. Rev. B 66, 233303 (2002); [2] J. S. de Sousa et al., Appl. Phys.
Lett. 82, 2685 (2003)
A-O10
Fe SPIN STRUCTURE IN Fe/MnF2 EXCHANGE-BIASED BILAYERS
12
W. A. A. Macedo, Lab. de Física Aplicada, Centro de Desenvolvimento da Tecnologia Nuclear,
Belo Horizonte, Brazil; B. Sahoo, V. Kuncser, W. Keune, Institut für Physik, Universität DuisburgEssen, Duisburg, Germany; J. Eisenmenger, Ivan K. Schuller, Physics Department, University of
California - San Diego, La Jolla, Ca, USA; I. Felner, Racah Institute of Physics, The Hebrew
University, Jerusalem, Israel; J. Nogués, Institutió Catalana de Recerca i Estudis Avançats
(ICREA) and Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain; K.
Liu, Department of Physics, University of California – Davis, Ca, USA.
The spin structure of the ferromagnetic (F) Fe layer at different depths in Fe films exchangecoupled to twinned (110) MnF2 antiferromagnetic (AF) layers has been probed by 57Fe probe layer
Mössbauer spectroscopy. Conversion electron Mössbauer spectroscopy (CEMS), above (80 K), and
below (18 K) the Nèel temperature of the AF layer (T N = 67 K for MnF2), was carried out in
remanence, after applying an in-plane magnetic field of 0.4 T at room temperature, which results in
an exchange bias of –54 Oe at 10 K and zero-field cooling. We find that exchange bias induces a
significant in-plane rotation of the average orientation of the Fe magnetic moments at the interface
and inside the Fe film, consistent either with the onset of an in-plane rotation of the average Fe spin
orientation or with an increase of in-plane Fe spin fanning, away from the remanent magnetization
direction. Out-of-plane spin canting in the Fe layer is ruled out.
A -O12
PARTICLE SIZE AND DISORDER IN GMR CO-CU SYSTEMS STUDIED BY EXAFS
J.C.Cezar, H.C.N.Tolentino, LNLS, CP 6192, 13084-971 Campinas, SP, Brazil; M.Knobel, LMBT,
IFGW, UNICAMP, Campinas, SP, Brazil
Granular magnetic systems are made of small particles of a magnetic material embedded in a non
magnetic one. Produced beyond the solubility limit, their properties are controlled by suitable
annealing. We have studied the structural, magnetic and transport properties of Co nanoparticles
embedded in a Cu matrix using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy,
magnetization and transport measurements of samples containing 3, 10, 12 and 25 at % Co,
annealed under different conditions. We have observed by EXAFS a systematic contraction of the
average distance around Co atoms, with the increasing Co content and annealing, related to the
growing of small nanoparticles. Based on a simple structural model, we have deduced particle sizes
ranging from 1 nm to more than 8 nm. We have found that the particle diameter for the maximum
giant magnetoresistance (GMR) is about 4.4 nm. This corresponds to nearly 30 % of the Co atoms
at the interface with the Cu matrix, which optimizes GMR because the particles are sufficiently
large to change orientation under an applied magnetic field and have a large amount of surface to
scatter the conducting electrons responsible for the transport properties. Moreover, we have
observed that the disorder is significantly reduced around that size, due to the hardening of Co
bonds, further favoring the GMR.
Cezar et al., Phys. Rev. B 68, 054404 (2003)
A -O13
LOCAL DISTORTION AND CHARGE LOCALIZATION IN MIXED MANGANITE THIN
13
FILMS
N. M. Souza-Neto, A. Y. Ramos, H. C. N. Tolentino, LNLS, C.P. 6192, 13084-971, Campinas SP,
Brazil ; L. Ranno, E. Favre-Nicolin, Laboratoire Louis Néel, Grenoble, France.
Mixed manganite films have received special attention due to their potential application for a new
generation of magneto-electronic devices. In these systems the external biaxial strain resulting of
epitaxial growth could be used, as cation doping, to tune the magnetism and transport properties. In
this context it is important to explicit the consequence of strain-induced distortion on the local
structure. We report on an angular resolved X-ray Absorption Spectroscopy study of the local
atomic structure around the manganese atoms in La07Sr03MnO3 thin films (25-60nm) grown on
tensile and compressive substrates. We derive a model of local biaxial anisotropic distortion of the
coordination octahedrum around the manganese atoms, without modification of the tilt angle MnO-Mn among the octahedra. This distortion, tending to localize the charge carriers, is the driving
parameter in the modifications of the magnetic and transport properties observed in thin films with
respect to bulk systems. An additional distortion in the plane of the film suggest that cooperative
distortion is still more energetically favorable than isotropic planar expansion of the Mn-O
distance.
A -O14
QUANTUM TRANSPORT PROPERTIES OF MAGNETIC NANOWIRES
V. Rodrigues, J. Bettini, P.C. Silva, D. Ugarte, Lab. Nac. de Luz Síncrotron, C.P. 6192, 13084-971
Campinas SP, Brazil.
The development of spintronics has rendered the influence of low dimensionality and/or reduced
size on the magnetic properties of materials a fundamental issue. There is a large amount of work
on metal nanowires, however it is surprising that magnetic nanowires have not yet been studied in
detail. In this work, we have analyzed the electronic transport properties of atomic-size metallic
wires made of magnetic and non-magnetic metals using an ultra-high-vacuum mechanically
controllable break junction system. In addition, the atomic structure of NWs has been studied using
independent experiments based on time-resolved high-resolution transmission electron microscopy.
We have observed that just before rupture, the ultimate Co wires adopt a suspended chain of atoms
configuration, which shows a conductance of half the conductance quantum. Then, our results
suggest that a fully spin polarized current is spontaneously generated even at room temperature and
zero magnetic field. Similar behavior has been observed for Pd (a quasi-magnetic 4d metal) and Pt
(a non-magnetic 5d metal) atom chains. These results open new opportunities to get a deeper
understanding of spin effects in nanostructures.
A -O15
A -O16
FORMATION OF EXTENDED DEFECTS AFTER He+ IMPLANTATION AT ELEVATED
TEMPERATURES
D.L. da Silva, M.J. Mörsbacher, E. Oliviero, M. Behar, Instituto de Física-UFRGS, Caixa Postal
15051, 91501-970 Porto Alegre, Brasil; P.F.P. Fichtner, Departamento de Metalurgia-UFRGS,
Caixa Postal 15051, 91501-970 Porto Alegre, Brasil
In the present contribution we study on the formation of {311} defects in Si(100) which occurs
concomitantly with the formation of nano-bubbles during He implantations at 150 and 300°C
(implantation energies of 15 and 40 keV and fluences between 1 and 2x10 16 He cm-2). The as
implanted samples were analyzed using Rutherford Backscattering/ Channeling, Elastic Recoil
Detection Analysis and Transmission Electron Microscopy. After the implantation, independently
of the energy, spherical-like nano-bubbles (1 to 3 nm in diameter) and {311} type defects are
formed. The sizes of the bubbles and the defects increase with the implantation temperature. In
addition, the defect morphology depends on the implanted fluence. Single {311} defects are
observed for the lower fluences while ribbon-like defects resulting from the agglomeration of the
single {311}’s start to appear for the high fluence cases. We propose a mechanism correlating the
formation of the defects and the He bubbles and discuss the effects of the implantation temperature
on the point defect fluxes. The present results also demonstrate that {311}-type defects can be
formed and dissolved at temperatures about 300°C lower that what is know in the literature.
TOWARDS STRAINED SILICON: STRAIN RELAXED Si1-xGex BUFFER LAYERS
14
PRODUCED BY He+ ION IMPLANTATION
B. Holländer, S. Mantl, St. Lenk, D.M. Buca, N. Hüging M. Luysberg, ISG/IFF
Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany,
Th. Hackbarth, H.-J. Herzog, DaimlerChrysler Forschungszentrum Ulm, D-89013 Ulm, Germany,
R. Loo, M. Caymax IMEC, B-3001 Leuven, Belgium, M. Mörschbächer, P.F.P. Fichtner, UFRGS,
BR-91501-970 Porto Alegre, Brazil
Strain relaxed Si1-xGex layers serve as virtual substrates for the growth of strained Si, a material
with superior electronic properties. Strained Si will be used for the fabrication of advanced
microelectronic devices in the near future. We report on the strain relaxation of pseudomorphic Si1+
xGex layers (x=0.10 ... 0.30) grown by MBE and CVD on Si(100) and SOI after subsequent He
implantation and annealing. Implantation with energies between 10 keV and 50 keV and doses
between 7x1015 cm-2 and 2x1016 cm-2 promotes the generation of strain relieving misfit dislocations
during subsequent annealing. The samples were investigated by Rutherford backscattering and ion
channeling, X-ray diffraction and transmission electron microscopy and Raman spectrometry. The
amount of strain relaxation and threading dislocation density will be discussed as a function of
implantation and annealing conditions. n-MODFETs grown on these relaxed layers showed
excellent results comparable to structures grown thick, graded Si1-xGex buffer layers. The
alternative use of other light ions for the promotion of strain relaxation will be addressed.
A -O17
EFFECTS OF NITROGEN INCORPORATION INTO Al2O3 FILMS ON Si FOR ADVANCED
MOS DEVICES
R.P. Pezzi, K.P. Bastos, L. Miotti, G.V. Soares, C. Driemeier, E.B.O. da Rosa and J. Morais
Instituto de Física - UFRGS, CP 15051 Porto Alegre 91501-970 – Brazil; I.J.R. Baumvol, Centro
de Ciências Exatas e Tecnológicas - UCS Av. Francisco G. Vargas 1130, 95070-560 Caxias do Sul
– Brazil.
There is a frenetic search for an alternative material with higher dielectric constant than that of
SiO2, which can be able to replace it as the gate dielectric in MOSFET devices. Thermal stability
during post- deposition annealings at high temperatures is one of the mandatory requirements this
new material, called high-k, must satisfy. Some previous works have shown that the addition of
nitrogen into the high-k material can have beneficial effects. In this work we report on the
investigation of thermal stability (atomic mobility and chemical reaction) of Al2O3 films deposited
on Si substrates by remote plasma-enhanced chemical vapor deposition, followed by remote
plasma-assisted nitridation in 15N2. This structure was submitted to thermal annealings in either
inert or oxidizing atmospheres. Areal densities and concentration profiles of the species of interest
were addressed using ion beam techniques, namely resonant and non-resonant nuclear reaction
analysis, while the chemical environment was investigated by X-ray photoelectron spectroscopy.
A-O18
A -O20
PHOTONIC CRYSTALS FORMATION BY SELF-ASSEMBLE TECHNIQUE
D. S. Raimundo and W. J. Salcedo, Laboratório de Microeletrônica da Escola Politécnica da USP,
Av. Prof. Luciano Gualberto Travessa 3, n.158, Caixa Postal 61548, São Paulo, Brazil.
The present work reports the 2-D and 3-D photonic crystals formation by self-assemble process of
the polymeric micro-spheres (polystyrene). These photonic crystals were fabricated from
dispersible solution of polystyrene micro-spheres. The glass substrates were immersed into the
solution in vertical configuration after that, the cell was heated at temperature of 50 oC in order to
have a controllable evaporation process of the solvent. At these conditions, the hydrodynamic
forces drove the formation of self-assemble structure. The Scanning Electron Microscopy imagines
of samples showed the hexagonal compact periodic array with lattice constant of ca. 0.666 m in
agreement with the minimum of Gibbs energy as reported in the literature. The 2-D photonic
crystals were obtained preferentially when glass surface was in hydrophilic condition. However,
hydrophobic surface condition drove to 3-D photonic crystal formation preferentially. The optical
transmittance spectra of the samples showed the existence of band gaps in 1376 nm to 1517 nm
(near infrared region).
STRESS CONTROL IN DIAOMONDLIKE CARBON FILMS BY ENERGETIC IONS.
15
Othon R. Monteiro(1) and Marie-Paule Delplancke-Ogletree(2); (1)Lawrence Berkeley national
Laboratory, University of California, Berkeley, Berkeley, CA 94720; (2) Universite Libre de
Bruxelles , Brussels, Belgium
High level of intrinsic stresses has prevented, to a large extent, the use of such films to applications
where thick coatings are required. The magnitude of intrinsic stresses in diamondlike carbon
(DLC) films is directly related to the sp 3 content in the films, which bears a strong dependence on
the energetics of the deposition process. We have used in-situ monitoring of the stress to determine
its evolution during deposition of DLC films, and to guide us in altering process conditions so that
thick DLC films are produced with virtually no intrinsic stresses, while maintaining a high fraction
of sp3 bonding. Stress measurements was carried out by using the laser deflection technique. The
process parameter used for relaxation was the energy of the depositing ions. Deflection of the laser
beam induced by changes in the radius of curvature of the substrate was measured with a position
sensitive detector (PSD). The mechanisms of stress-relaxation in DLC are discussed in view of the
results obtained.
A-O21
NANOMANIPULATOR FOR IN-SITU STUDIES IN A FEG-SEM
D. Nakabayashi, P. C. Silva, V. Rodrigues, D. Ugarte, LNLS – Laboratório Nacional de Luz
Síncrotron, C.P. 6192, 13084-971, Campinas, SP, Brazil; H. Gutiérrez, M.A. Cotta, UNICAMP IFGW - DFA/LPD, C.P. 6165, 13081-970, Campinas, SP, Brazil.
Nanosystems are attracting a huge interest; nevertheless the controlled characterization and
manipulation are still a challenge. High-resolution capabilities of electron microscopy techniques
render them a preferred tool for studying nano-objects, however electron microscopy methods are
usually static. Here, we describe the development of manipulation system operating inside a FEGSEM; the nanomanipulator has three independent axes, each one with coarse and fine movements.
The coarse movements are driven by picomotors and piezo elements slabs are responsible by
precise displacements. We have already used the manipulator to measure the mechanical properties
of individual nanosystems showing a high aspect ratio by measuring resonance vibration modes
excited by AC voltages. We have also produced Atomic Force Microscopy (AFM) tips based on
carbon nanotubes in a controlled way. These tips have shown a high performance, allowing a
significant improvement of the AFM image quality.
A-O22
SYNTHESIS OF CARBON NANOTUBES BY CVD
S. A. Moshkalyov, J. W. Swart, UNICAMP, CCS, C.P. 6061, Campinas, SP, Brazil
Results of carbon nanotubes (CNTs) synthesis, employing methane and acetylene based gas
mixtures, are presented. Two different catalytic high-temperature (up to 900 C) CVD techniques
were used: microwave plasma-enhanced low-pressure CVD and atmospheric-pressure thermal
CVD. Multi-walled CNTs with tube diameters from ~ 10 to 100 nm were obtained and analyzed
using high-resolution SEM. Thin Ni films (1-40 nm) were used as a catalyst material. After
deposition, the films were thermally treated (~700 C) in a N2 or H2 atmosphere to provide
formation of separate catalyst nanoparticles. The CNTs growth process depends critically on the
catalyst thickness. For thicker films, large diameter (up to 100 nm) tubes, apparently with high
content of amorphous carbon were grown. For thin films, it was possible to grow long (up to 30
m) and small diameter (~10 nm) CNTs. The study of CNTs CVD using another catalysts is in
progress.
A-O23
PHOTOCURRENT AND PHOTOLUMINESCENCE STUDIES OF RESONANT TUNNELING
16
DIODES
L.F. dos Santos, A. Vercik, Y. Galvão Gobato, Universidade Federal de São Carlos , CP 676, São
Carlos - SP, 13560-970 ; M. J. S. P. Brasil, Universidade de Campinas, CP 6165, Campinas-SP,
13083-970, Brazil.
In this work, we have investigated the transport and optical properties of a GaAs/GaAlAs doublebarrier diode. Current-voltage (I-V) characteristics and photoluminescence (PL) spectra were
measured as a function of applied voltage, laser intensity and temperature on symmetric
GaAs/Al0.35Ga0.65As double barrier resonant tunneling diodes. We have observed an unexpected
enhancement of the photoluminescence intensity with increasing temperature, which depends on
applied voltage and laser intensity. This enhancement is followed by a decrease of PL intensity at
higher temperatures, associated to more effective nonradiative mechanisms and a consequent
decrease of radiative recombination, reducing the quantum efficiency. The integrated PL spectra
versus temperature curves present a peak, whose position depends on the applied voltage in the
structure. We have observed a similar temperature-dependent behavior of the photocurrent,
measured in the same voltage and temperature range. This effect is associated to the transport of
holes in the collector contact which controls the minority carrier supply for tunneling into the well
A-O24
HARDNESS AND ELASTIC MODULUS MEASUREMENTS BY NANOINDENTATION OF
ALUMINUM IMPLANTED WITH CARBON
C.E. Foerster, F.C. Serbena, A. Assmann, Defis, UEPG, 84030-900, Ponta Grossa, PR, Brazil,
C.M. Lepienski, Defis, UFPR, CP 19044, 81531-990 ,Curitiba, PR, Brazil, T. Fitz, E. Richter, W.
Moeller, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf,
Germany
In this work the mechanical properties of pure Al samples implanted with C+ ions at 25 keV and
fluences ranging from 1 x 1017 to 20 x 1017 C+.cm-2 at room temperature were measured. The near
surface region after low C+ fluence revealed a structure of Al4C3 as embedded precipitates in
addition to C-C clusters that changed to an amorphous Al4C3 structure together the C-C clusters at
higher C+ fluences. To measured the surface mechanical properties, load/unload curves were
performed using a nanoindenter and from the Oliver and Pharr method, the hardness and elastic
modulus profiles were determined. The results showed a hardening process due to the presence of
Al4C3 and C-C clusters. The hardness increased from 0.3 GPa for the bulk Al up to 9 GPa at the
highest C+ fluence. At same time, the elastic modulus increased from approximately 70 GPa (bulk
Al) to 100 GPa. Subsequent annealing at 500°C produced a little decrease in these values, meaning
that hardness and elastic modulus are determined by the presence of Al 4C3 and C-C clusters. The
surface morphology and structure were previously analyzed by elastic recoil detection analysis
(ERDA), Raman spectroscopy, grazing incidence X-Ray diffraction analysis (GIXRD) and high
resolution electron microscopy (HRTEM).
Financial support: CAPES
A-O25
SPECTROSCOPIC CHARACTERISTICS OF DOPED ALUMINUM OXIDE NANOPOROUS
17
W. M. de Azevedo, D. D. de Carvalho, Departamento de Química Fundamental, UFPE-PE 50670901, Recife, Brasil; H.J. Khoury Departamento de Energia Nuclear UFPE-PE 50740-540, Recife,
Brasil;E.F. da Silva Júnior, Departamento de Física UFPE-PE 50670-901, Recife, Brasil
In nanotechnology research, fabricating functional nanoscale structures and devices in a wellcontrolled way represents one of the most difficult challenges facing today’s researchers and
engineers. The means to organize nanoelements into device structures to realize their desired
functionalities using inexpensive fabrication techniques is essential from a technological point of
view. Aluminum anodization is one of the most controllable self-assembly processes, and
nanoporous anodic aluminium oxide has been employed to synthesize a variety of nanoparticles
and nanowires through a template-mediated approach. From the point of view of luminescent
properties, it is interesting to note that colloidal Al2O3 does not exhibit any photoluminescence
whereas polymeric aluminum oxide exhibit photoluminescence at 420 nm. In this work we present
the luminescence characterization of porous aluminum oxide synthesized by anodization process in
several solvents. We found that the luminescence of porous aluminum doped with rare earth ions
strongly depends on the synthesis medium, in inorganic acid only rare earth luminescence is found,
whereas aluminum oxide synthesized in organic solvent presents two strong unexpected
luminescence emission, one at 4200 A and the second at 4900 A when excited in the UV region,
with quit long decay time, it is worthwhile to mention that porous aluminum oxide synthesized in
inorganic acid presents no fluorescence at all
POSTER PRESENTATIONS
18
A-P01
THE ROLE OF COMPOSITIONAL MODULATION IN INGAP LAYER SURFACE
PROPERTIES
J.R.R.Bortoleto, H.R.Gutiérrez, M.A.Cotta, and M.M.G.de Carvalho; Instituto de Física Gleb
Wataghin, DFA/LPD, UNICAMP, CP 6165,13081-970 Campinas-SP, Brazil. J.Bettini; Laboratório
Nacional de Luz Síncrotron, C.P. 6192, 13084-971 Campinas-SP, Brazil
In this work, we investigate InGaP layer properties leading to preferential nucleation sites to
Stranski-Krastanov dot overgrowth. Our experimental results indicate that a periodic strain field
can be formed within the InGaP layer via surface processes. We have investigated the presence of
CuPt ordered regions and compositional modulation phenomena in our samples, since these bulk
properties are both surface-activated. TEM plan-view images from InGaP layers shows bright
domains organized into a bidimensional pattern. Such patterns have been extensively credited to
compositional modulation on InGaP films. On the other hand, cross-sectional TEM micrographs
with g=(½,½,½) shows random, weak CuPt domains for our samples. This fact rules out any
correlation between CuPt phenomena and the periodic strain field. But, cross section TEM images
with g=(2,-2,0) show a clear correlation between InP dots positioning with the contrast
modulation in the InGaP buffer layer. Thus the compositional modulation indeed gives rise to
preferential sites to dot nucleation, allowing the in situ formation of InP dot arrays. We have
extended this concept to create a bidimensional array of InAs/GaAs quantum dots using the InP
array as a template for lateral ordering .
A-P03
PRESSURE-INDUCED
CHANGES
ON
THE
OPTICAL
PROPERTIES
AND
MICROSTRUCTURE OF SILICA-GEL MATRICES DOPED WITH RHODAMINE 6G
T. M. H. Costa, H. S. Hoffmann, E. V. Benvenutti, V. Stefani, Instituto de Química, UFRGS, CP
15003, 91501-970, Porto Alegre, RS, Brazil, M. R. Gallas, Instituto de Física, UFRGS, CP 15051,
91501-970, Porto Alegre, RS, Brazil
Sol-gel method and the high-pressure technique were associated to produce rhodamine 6G doped
silica compacts with a very low porosity. It was studied the state of R6G dye molecules in the silica
sol-gel monolith/powder and in the compacted powders obtained at 7.7 GPa and room temperature.
The excitation-emission fluorescence spectra were measured, in order to investigate pressureinduced changes in the optical properties of R6G embedded in closed pores of the silica matrix.
Measurements of surface areas and pore size distribution, using the N2 isotherms were performed,
showing a great reduction in surface area and porosity. The dye entrapped in the compacted silica
maintain its optical properties similar to that in ethanolic solutions, which means that the dye is
dispersed in a molecular level. Additionally, these samples are optically transparent, hard and
resistant to dye leaching and to chemical attacks, being a promising material to be used in optical
devices.
A-P04
NANOSTRUCTURAL EVOLUTION OF STRUCTURAL BRICKS
J. Calabria, W. L Vasconcelos; Laboratório de Materiais Cerâmicos – UFMG, Rua Espírito Santo,
35, sala 206, 30160-030,Belo Horizonte, Brazil
In this work we studied the nanostructure of clay and two types of bricks. One brick was made
using the same clay analysed and the material was fired at around 900C. The second brick was
kept in a non-fired condition, becoming similar to an adobe. We evaluated the nanostructure of the
particles using X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy
and chemical adsorption. We described the evolution of the nanostructure, associating it to different
conditions of processing.
A-P05
PROCESSING AND CHARACTERIZATION OF α-SILICON CARBIDE NANOPOWDERS
19
M. A. P. Santos, Grupo de Materiais, IPqM, Ilha do Governador, Rio de Janeiro, Brazil; C. A.
Costa, Centro de Tecnologia, Bl. F/210, Cidade Universitária, CEP 21945-970, Rio de Janeiro,
Brazil
The use of nanopowders in sintering process has been increasing very fast and the resulting
products possess very good mechanical properties. Brazil process -silicon carbide (SiC) powders
with mean particle size around 5 m, which is very large for sintering application.
In this study, the national -SiC was comminuted by high energy milling process and the mean
particle size was reduced to nanometer size. The analysis of the powders milled for ½, 2, 4 and 6
hours were conducted by sedigraphy, BET, laser and X-ray diffraction methodologies. The results
showed that precise measurement was not achieved, but the size range was in between 0,1 and 0,5
m. The difficulty in measuring fine particles is that they tend to cluster very fast and strongly.
A-P06
VIBRATIONAL PROPERTIES OF OXIDATED SINGLE-WALL CARBON NANOTUBE
BUNDLES
E.B. Barros, and V. Lemos, Departamento de Física, UFC, C.P. 6030, Fortaleza, CE, M. Herbst, ,
Instituto de Física, FRJ, Rio de Janeiro, RJ, C.A. Luengo, Instituto de Física “Gleb Wataghin”,
UNICAMP, Campinas, SP, J.G Huber, 501 N. Boulevard, #7 Richmond, VA 23220, USA
Single-wall carbon nanotubes, SWNTs, prepared by arc discharge using Zr(Fe 0.5Ni0.5)2 as catalyst,
were oxidated and filtered. Both samples, before and after the treatment, were analyzed by using
Raman scattering and Scanning Electron Microscopy. The raw material was found to consist of
bundles of SWNTs in an heterogeneous, nearly uniform distribution of nanoparticle clusters. In the
treated material the SWNTs seemed less abundant but the bundles appear in small regions quite
defect free. Raman spectra reveal that nanotubes are present in the raw as well as in the treated
sample. The spectra, however, differ in several aspects. The radial breathing mode, RBM, structure
for the treated material is upshifted by a few wavenumbers. Two additional higher frequency peaks
appear in the spectrum for the raw material. As no nanotube Raman feature is expected in the
position of those features they are supposed to be due to vibrations involving metal particles. As
they do not appear in the treated sample spectrum it is possible to infer that the metal particles are
quite removed from the bundles. After treatment the tangential modes, besides upshifted, appear
with two shoulders at lower and higher wavenumber sides of the band. The overall Raman
modifications are typical of intercalation of HNO 3 molecules into the bundles.
A-P07
HELIUM REDISTRIBUTION IN AS-IMPLANTED SILICON AND Si0.8Ge0.2/Si
HETEROSTRUCTUES
M.J. Mörschbächer, D.L. da Silva, E. Oliviero, M. Behar, F.C. Zawislak, Instituto de FisicaUFRGS, C.P. 15051, 91501-970 Porto Alegre, RS, Brasil; P.F.P. Fichtner, Departamento de
Metalurgia-UFRGS, Porto Alegre, RS, Brasil; M. Luysberg, Institut für Festkörperforschung,
Forschungszentrum Jülich, Jülich, Germany; B. Holländer, S. Mantl, Institut für Schichten und
Grenflächen, Forschugszentrum Jülich, Jülich, Germany; R. Loo, M. Caymax, IMEC, Leuven,
Belgium.
In the present contribution we report experimental results on the retention of implanted He atoms in
Cz (100) Si wafers and in 80 nm thick Si0.8Ge0.2 pseudomorphic heterostructures, grown by CVD
on a Si(100) wafer, as a function of the implantation energy. The implantations were performed at
room temperature using energies from 5 to 60 keV and fluences within 1 to 4x1016 cm-2. The
implanted samples were analyzed by Elastic Recoil Detection (ERD), Rutherford
Backscattering/Channeling Spectrometry (RBS/C) and Transmission Electron Microscopy (TEM).
The fraction of the implanted He fluence that is retained increases from 5% at 5 keV to 100% for
E  40 keV. The retained He fraction is independent of the implanted fluence, of the accumulated
lattice damage or of the presence of TEM observable bubbles. The present results are applied to
optimize the He assisted strain relaxation process of pseudomorphic ultra thin SiGe/Si (100) buffer
layers with low threading dislocation densities.
A-P08
NANOCAVITIES FORMATION IN ION IMPLANTED SILICON
20
E. Oliviero, S. Peripolli, L. Amaral, Instituto de Física, Universidade Federal do Rio Grande do Sul,
P.O. Box 15051, 91501-970 Porto Alegre, RS, Brazil; P. F. Fichtner, Departamento de Metalurgia,
Universidade Federal do Rio Grande do Sul, P.O. Box 15051, 91501-970 Porto Alegre, RS, Brazil.
The formation of nanocavities in Si is considered as a microstructure engineering tool to form very
efficient gettering sites for metallic impurities thus improving device performance. This is usually
achieved by room temperature He implantation at sufficiently high fluences followed by thermal
annealings, thus allowing the formation of a nano-bubble system which interact and modify the
point defect fluxes in the matrix and therefore affect the obtained extended defects. In the present
contribution we have expanded our previous studies to the case of Ne implanted into (100) Cz
silicon wafers. The Ne ions were implanted at 50 keV with fluences ranging from 1x10 15 cm-2 to
5x1016 cm-2. The implantations were carried out at a temperature of 250°C to avoid target
amorphization. As implanted and annealed samples were investigated by Rutherford Backscattering
Spectrometry under channeling conditions (RBS/C) and by Transmission Electron Microscopy
(TEM) to quantify and characterize the lattice damage. In the as implanted samples we observe the
formation of a continuous buried layer containing a high density of Ne nano-bubbles (1 to 5 nm in
diameter) as well as small clusters of interstitials. Upon annealing at temperatures higher than 400
C, the bubbles coarsen and extended defects of {311} type are formed. The results are discussed in
comparison to the case of He, accounting for the distinct diffusivity, solubility as well as and
implantation damage of Ne in Si. On the basis of the present results we propose a method to
significantly reduce the thermal budget required for the formation of local impurity gettering layers
in Si matrix.
A-P09
METAL LAYER MASK PATTERNIG BY FORCE MICROSCOPY LITHOGRAPHY
H.D. Fonseca Filho, C.R. Ponciano, R. Prioli, Depto. de Física, PUC-Rio, Caixa Postal 38071, Cep
22452-970, Rio de Janeiro, Brazil; M.H.P.Maurício, Depto. de Ciência dos Materiais, PUC-Rio,
Caixa Postal 38008, Cep 22453-970, Rio de Janeiro, Brazil
In this work a nanolithography process is developed with the use of an atomic force microscope
equipped with a diamond tip while operated in contact mode. The presented process starts with a
deposition of an a-As2S3 thin film by PVD on a Si substrate. A metallic layer is then deposited on
the top of the a-As2S3 surface. The AFM is used to draw a pattern, in a controlled way, on the
surface of the metallic layer with the use of a nanoscript program, leaving the As2S3 surface
exposed. The photosensitive surface of the a-As2S3 film is illuminated and chemically etched. This
leaves now the Si surface exposed with the pattern draw by the tip. A final layer is then deposited,
filling the lithographed pattern. A last chemical etching is performed in order to remove all the
remaining a-As2S3 from the substrate, leaving only the desired pattern on the substrate surface.
An analysis of the As2S3 surface roughness as a function of film thickness is presented and it is
shown that films with thickness of 40nm are suitable to the lithography. The influence of the tipsurface normal force on the lithography process is also presented. It is shown that the depth of the
lithographed pattern increses with the rise of the applied normal force. Furthermore, the scanning
velocity have influence on the AFM patterning process. As the scanning velocity increases the
pattern depth decreases. The possible use of the presented process to create nanostructures are
discussed.
A-P10
NANOINDENTATION STUDIES OF NATURAL RUBBER
21
Mariselma Ferreira, Ciência e Engenharia de Materiais-USP, Caixa Postal 369, São Carlos, SP,
Brazil; Luiz Henrique Capparelli Mattoso, Embrapa Instrumentação Agropecuária, Caixa Postal
741, São Carlos, SP, Brazil; Christine Ortiz, Massachusetts Institute of Technology, 77
Massachusetts Avenue, Cambridge, MA, USA
In recent years, the importance of natural rubber has increased due to the need for environmentally
friendly materials and improved properties relative to synthetic materials. In this context, Embrapa
Agricultural Instrumentation, in collaboration with Agronomic Institute of Campinas, has initiated a
research program to study the mechanical, chemical, and physical properties and to assess the
quality of the natural rubber in São Paulo State, which is the largest rubber producer in Brazil. As
one component of this program, the technique of nanoindentation has been employed to
characterize the compressive normal load versus displacement properties of natural rubber in nm
thick films yielding information on nanomechanical properties such as viscoelasticity and energy of
dissipation. The nanoindentation force curves show forces near to 50 nm and displacements up to
500 nm and reveal a huge amount of mechanical hysteresis indicating viscoelastic deformation.
This novel technique has great potential to yield insights into the molecular origins of macroscopic
mechanical properties and material performance.
FUNDING: FAPESP, CAPES, CNPQ
A-P11
INVESTIGATION OF DOMAIN STRUCTURE AND GRAINS IN Pb(Zr 1-x Tix)O3
FERROELECTRIC THIN FILMS BY PIEZORESPONSE MICROSCOPY
V.B.Nunes1, S.I.Zanette1, A.O.Caride1, E.B. Araújo2, J.A.Eiras3 M.P.Albuquerque1,
M.P.Albuquerque1 and A.G.Mello1; 1Centro Brasileiro de Pesquisas Físicas, Rua Dr.Xavier Sigaud,
150-Urca, 22290-180, Rio de Janeiro, RJ – Brazil; 2Universidade Estadual Paulista, Dpto.de Física
e Química, Caixa Postal 31, Ilha Solteira, São Paulo – Brazil; 3Universidade Federal de São Carlos,
Dpto de Física, Grupo de Cerâmicas Ferroelétricas, Caixa Postal 676, 13565-670, São Carlos, SP –
Brazil
Ferroelectric Pb(Zr 1-x Tix)O3 (PZT) thin films were prepared by rapid thermal annealing and
investigated by piezoresponse (PFM) using a commercial atomic force microscope (AFM,
TopoMetrix, Discoverer TMX 2010) connected to a lock-in amplifier (EG&G Instruments, 7265).
The AFM tips were made of Si3N4 coated with TiO2 . Standard Si cantilevers were used with spring
constant k=2 N/m and resonant frequency of 105 kHz. Topography and piezoresponse images were
taken simultaneously across the PZT thin films. An ac modulation voltage of 10 V pp at 10 kHz was
applied to the tip during imaging. Regions of dark and white contrast show opposite directions of
polarization. The films also show a structure with grains of different sizes depending on the
crystallization temperature. The image processing of ferroelectric domains consists in grain
delimitation by watershed technique, entropic segmentation and histogram computation of dark and
white regions. This analysis quantifies the ferroelectric domain distribution for each grain.
A-P12
SYNTHESIS OF MoS2 NANOTUBES
22
O.P. Ferreira, O.L. Alves, Laboratório de Química do Estado Sólido LQES, IQ–UNICAMP,
Campinas, SP, Brazil. http://lqes.iqm.unicamp.br
The discovery of carbon nanotubes in 1991 has stimulated intense experimental and theoretical
studies in such tubular structures. A great deal of effort has also been dedicated to the synthesis of
different kinds of nanotubes. Metal sulfide nanotubes (MSN) are the most studied inorganic
nanotubes due to their promising electronic, catalytic and mechanical properties. In this work we
report the synthesis of MoS2 nanotubes by thermal decomposition of thiomolybdates [(NH 4)2MoS4
and (NH4)2Mo2S12] under argon flow. Different conditions of decomposition were investigated such
as heating temperature (250-1100oC), heating rate and annealing time (0.5-8h). The reaction
products were characterized by SEM, TEM, XRD and Raman. The XRD patterns of the as prepared
samples showed the presence of reflections characteristic of 2H-MoS2. The SEM and TEM images
showed nanotubes with outer diameter in the range of 50-100 nm. The MSN showed inner diameter
about 10 nm. Nanorods and spherical nanoparticles were also observed in TEM images. The
Raman spectra obtained for MoS2, prepared in this work, showed bands with frequencies similar to
the bulk MoS2, whose spectrum is characterized by bands at 380, 405 and 450 cm-1. To our
knowledge this is the first time MoS2 nanotubes were prepared by solid reaction under inert
atmosphere. [CNPq and Millennium Institute of Complex Materials]
A-P13
QUANTUM CONDUCTANCE OF COPPER NANOWIRES
J. C. González, V. Rodrigues, J. Bettini, D. Ugarte, Laboratório Nacional de Luz Síncrotron, C.P.
6192, 13084-971 Campinas, SP, Brazil; A. R. Rocha, Department of Physics, Trinity College
Dublin, Dublin 2, Dublin, Ireland; L. G. C. Rego, Departamento de Física, Universidade Federal do
Paraná, Curitiva, PR, Brazil.
In this work, we present a study of the correlation between atomic structure and quantum
conductance of atomic size Cu nanowires (NWs).
Time resolved high resolution transmission electron microscopy was used to study the formation,
elongation, and rupture of Cu NWs produced by mechanical stretching. One-atom-thick chains
were observed for NWs generated along [111], [100] and [110] directions. Rod-like NWs that
evolve to one-atom-thick chains were also observed for NWs generated along the [100] and [110]
directions.
Quantum conductance of Cu NWs was studied using a mechanically controllable break junction
(MCBJ) system operating at room temperature in ultra high vacuum. MCBJ experiments showed
conductance values around 1 G0, 2.4 G0 and 4.5 G0.
Molecular orbital calculations were implemented to calculate the quantum conductance of Cu NWs
with face centered cubic (fcc) structure. These calculations revealed that one-atom-thick chains
display conductance close to 1 G0, regardless of NWs direction. Rod-like [100] and [110] NWs
show conductance at 4.5 G0 and 2.4 G0, respectively. However in order to explain all the
conductance evolution observed in the MCBJ experiments [110] NWs with pentagonal structure
(none fcc) must also be considered. Quantum conductance calculations of these NWs explain our
experimental results, demonstrating the formation of relaxed atomic arrangements in Cu NWs.
A-P14
SYNTHESIS AND CHARACTERIZATION OF FREE-STANDING SEMICONDUCTOR
23
NANOWIRES
J. C. González, J. Bettini, D. Zanchet, D. Ugarte, Laboratório Nacional de Luz Síncrotron, Caixa
Postal 6192, 13084-971 Campinas SP, Brazil; H. R. Gutiérrez, M.A. Cotta, Instituto de Física Gleb
Wataghin, DFA/LPD, UNICAMP, CP 6165, 13081-970 Campinas-SP, Brazil; F. M. Matinaga,
Departamento de Física, UFMG, CP 702, 30123-970, Belo Horizonte, MG, Brazil.
In this work, we report the synthesis and characterization of free-standing semiconductor
nanowires. III-V wires were grown by the Vapor-Liquid-Solid (VLS) method in a Chemical Beam
Epitaxy (CBE) reactor. Au nanoparticles (NPs) were used as seeds to catalyze the growth process.
Using this method nanowires of InP, GaP, GaAs and InAs were grown with diameters around 50
nm and several microns long. The wires may also be generated to include heterostructures (ex.
InP/InAs/InP).
The morphology, crystal structure and chemical composition of the wires were characterized by
Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy
(TEM), Electron Diffraction (ED) and Energy Dispersive X-ray Spectroscopy (EDS). The
nanowires were found to be stoichiometric, single crystal with a tapered morphology and mainly
oriented along the [100] and [110] crystallographic directions.
Low temperature Photoluminescence (PL) experiments in undoped and Si doped InP NWs revealed
a small quantum confinement in the wires and confirmed the good crystalline quality of the wires,
as observed by TEM.
A-P15
MORPHOLOGICAL CHARACTERIZATION OF NANOPARTICLES OF SnO2
WITH
ADDITIVES Ni AND Fe
Pilar Hidalgo1, Douglas Gouvêa1, Daniela Zanchet2, Jefferson Bettini2; 1 Department of
Metallurgical and Materials Engineering- USP, Av. Professor Mello Moraes, 2463, 05580-900. S.P.
Brazil; 2 National Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil.
Recently studies on ceramic powders have shown that microestrutural modifications take place
when the system reaches the lowest surface energy. Indirectly this decrease is related to the
segregation of the additive onto the surface powder.
This work intends to study the segregation of additives in two interesting system: F 2O3-SnO2 and
NiO-SnO2, prepared by Pechini´s method. Morphological characteristics were performed using
Transmission Electron Microscopic (TEM), X-ray diffraction (XRD), Specific Surface Area (S BET)
and Mössbauer Spectroscopy.
The segregation of ions Fe or Ni on the surface the matrix phase (SnO 2) was observed even in
specimens with 30 mol% of additive. After, with increasing of ions Fe or Ni (50 and 80 mol %) has
been observed nucleation of second phase: magnetite (Fe3O4) and NiO respectively. Perhaps SnO2
has persuaded epitexial growing for these phase. This was confirmed better joining EDX results
and TEM.
A-P16
A-P18
NANOMECHANICAL PROPERTIES OF THE SUPERCONDUCTORS JOINTS
P. R. JUNIOR, Universidade Estadual de Ponta Grossa – DEFIS, Ponta Grossa, Brazil; C. M.
LEPIENSKI, A. S. DUBIEL, Universidade Federal do Paraná - DEFIS, Centro Politécnico, Caixa
Postal 19044, CEP 81531-990, Curitiba, Brazil
The determination of the mechanical properties of nanostructured material is a new and very
interesting area. In the present work the nanomechanical properties of the superconductors joints
from YBCO system were studied. The samples processed had YBCO-123, YBCO-211 and Ag
particles. The YBCO with silver was used as solder agent because its melting point is lower than
YBCO-123. The method to obtain hardness and elastic modulus by load-displacement curves with
a load and depth-sensing indentation consists in using a diamond indenter, with triangular base to
penetrate some few nanometers into the material surface. In these samples the Berkovich indenter
applied a peek load of 400 mN and its maximum penetration into material was 1600 nm. The
hardness and the elastic modulus obtained were 16-10 GPa and 200 GPa respectively. In
displacements until 400 nm the hardness was 16 GPa decreasing to a constant value of 10 GPa. The
elastic modulus value was constant in all displacements. The difference on the hardness value can
be an effect of the mechanical polishing on the sample before the indentation test.
STUDY OF CARBON NANOTUBES GROWTH BY MICROWAVE PLASMA WITH NICKEL
24
AND IRON CATALYST
E.F.Antunes, E.J.Corat, A.F.Beloto, V.J.T.Airoldi, Instituto Nacional de Pesquisas Espaciais –
INPE, Laboratório Associado de Sensores e Materiais – LAS, Grupo de Diamantes e Materiais
Relacionados – DIMARE, Avenida dos Astronautas, 1758, Jd. da Granja - São José dos Campos/
SP- Brasil CEP 12.245-970, Caixa Postal 515, ericafa@las.inpe.br
Carbon nanotubes have been investigated by many research groups of around the world due its
greats properties, mainly about field emission capacity. In this work, we have studied the
morphology of carbon nanotubes thin films produced by microwave plasma chemical vapor
deposition. For this, nickel and iron thin film (5nm) have been used as catalyst, deposited by
electron beam evaporator on silicon substrates covered by silicon oxide (50nm). Microwave plasma
has been used to promote island formation of diameter of tens of nanometers on the metallic films,
and in a further step the carbon nanotubes have been nucleated. In the step of island (clusters)
formation only N2 and H2 are inserted in the plasma chamber and then CH4, which is the carbon
source to form the nanotubes. The plasma conditions are studied (pressure, power, gas mixture).
External heating is necessary to control substrate temperature. Cluster and nanotubes have been
characterized by AFM (atomic force microscopy), SEM (scanning electron microscopy) and
Raman spectroscopy.
[1] Ph. Mauron , Ch. Emmeneger, A. Züttel, Ch. Nützenadel, P. Sudan, L. Schlapbach. Carbon 40
(2002)1339-1344
[2] U. Kim, R. Pcionek, D. M. Aslam, D. Tománek. Diamond and Related Materials 10
(2001)1947-195
[3] Qing Zhang, S. F. Yoo, J. Ahn, B. Gan ,Rusli , M.-B. Yu. J. of Physics and Chemistry of Solids
61(2000)1179-1183
[4] J. H. Huang, C. C. Huang, C. H. Tsai. Microelectronic Engineering 1(2003) 000-000
[5] S. G. Wang, Qing Zhang, S. F. Yoon, J. Ahn. Scripta Materialia 48 (2003) 409-412
[6] C. H. Lin, H. L. Chang, M. H. Tsai, C. T. Kuo. Diamond and Related Materials 11 (2002) 922
-926
A-P19
CARBON NANOTUBES PRODUCTION BY ARC DISCHARGE IN AQUEOUS SOLUTION
R. C. Z. Lofrano, L. A. Montoro and J. M. Rosolen. Depto. de Química da FFCLRP - USP
Avenida dos Bandeirantes, 3900 CEP 14 040-901 Ribeirão Preto/SP, Brasil
A lot of progress has been reported in the synthesis of carbon nanotubes (CNT) in recent years.
Different authors have successfully produced carbon onions and nanotubes in large quantities by
arc discharge in water. They have shown that arc discharge in water technology simplifies the
traditional. We have studied the products of pyrolise of graphite in an arc-discharge reactor in
metavanadic acid solutions. The graphite bars were filled with a mixture of Ni/Co powder and the
arc was formed in DC conditions (25V, 60A). The samples were characterized using Raman and
microscopy techniques (SEM and HRTEM). The carbon produced is presents bundles
interconnected by many segments of solid materials like foil. The length and diameter of bundles is
in the range 1.0 –
-50nm, respectively. The Co, Ni and V are presents in these
structures, inside the bundles and solid materials. Vanadium oxide traces was detected in the
samples. The Raman spectra show that the composite carbon present features of multi-wall carbon
nanotubes. Acklowledments LME/LNLS and FAPESP.
A-P20
STRUCTURAL
AND
NANOSCALE
25
FRICTION
MODIFICATIONS
INDUCED
BY
NITROGEN INCORPORATION INTO HARD AMORPHOUS FLUORINATED CARBON
FILMS
C.M.T. Sanchez, M.E.H. Maia da Costa, R.R.M. Zamora, R. Prioli , F.L. Freire Jr. and L.G.
Jacobosohn* ; Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Caixa
Postal 3807, Rio de Janeiro, RJ 22453-970, Brazil; *- Los Alamos National Laboratory, P.O.Box
1663 Los Alamos, NM 87545, USA
Plasma enhanced chemical vapor deposition (PECVD) technique was used to study the nitrogen
incorporation into fluorinated amorphous carbons films by decomposition of CH 4-CF4-N2 mixtures.
The gas mixture was (CH4-CF4)1-x (N2)x where x was varied from 0 to 0.6. The CH4:CF4 ratio was
fixed at 1:2. All the films were deposited at 10 Pa. The structural and chemical characterizations of
the films were performed by ion beam analysis (RBS, ERD and NRA), Raman spectroscopy and XRay photoelectron spectroscopy. The results show that nitrogen incorporation occurs at the expense
of the carbon contents of the films. It results in an increase of the size and the number of the
graphictic domains. The nitrogen was incorporated into aromatic rings and as terminator radicals,
as observed in XPS measurements. The nanofriction behavior of the films was investigated by
atomic force microscopy. The direct correlation of the nitrogen incorporation with the contact angle
and the friction coefficient were was investigated.
A-P21
ENHANCEMENT OF THE HYDROPHOBICITY OF POLYPROPYLENE AND TEFLON BY
SF6 PLASMA TREATMENT
Rita C. C. Rangel, Elidiane C. Rangel, Nilson C. Cruz , Laboratório de Plasmas, Av. Dr. Ariberto
Pereira da Cunha, 333, Guaratinguetá / SP, Brazil DFQ/FEG/UNESP
Low water affinity materials are interesting in many scientific and technological areas. In
biomaterial field, for instance, abdominal wall prostheses are made from hydrophobic materials to
avoid bowels adherence onto the implant surface. In this work, polypropylene and Teflon have
been exposed to SF6 plasmas in order to enhance their hydrophobicity. It has been investigated the
influence of exposure time, applied power and discharge pressure on the contact angle, , of such
polymers. Plasmas were generated by applying radiofrequency power (13.56 MHz) to two metallic
electrodes external to a cylindrical glass vacuum chamber. Contact angles were evaluated using an
automated goniometer comprised by a CCD camera which digitizes the image of a water drop, of
about 0.2 l in volume, placed onto the polymer surface by micro-syringe. A dedicated software
analyzes that image and determines . We have observed that the treatments resulted in
considerable enhancement in . For instance, under certain conditions the contact angle of
polypropylene increased from 93, as measured in the pristine material, to about 125.
A-P22
LATERAL FORCE MICROSCOPY OF HYDROPHILIC SURFACES
26
R.R.M.Zamora , R.Prioli, Departamento de Física, Pontifícia Universidade Católica do Rio de
Janeiro, Cx. Postal 38071, 22452-970 Rio de Janeiro Brasi.
In the quantitative measurement of friction with AFM, it is important to take into account the
calibration of the lateral photodiode and the cantilever spring constants. In this work we present a
procedure for the AFM cantilever and photodetector calibration. The proposed calibration
procedure is focused on the calculation of the cantilever normal and lateral spring constants as a
function of the cantilevers dimensions. The relationship between the torsion signal (lateral force)
and the normal bending signal (normal force) is obtained by an analysis of the AFM optical
detection system. It is shown here that the position of the laser on the cantilever strongly influences
the lateral force measurement. To analyze the reproducibility of the lateral force data, we have
measured the lateral force between the Si3N4 and SiO2 for ten cantilevers in a first set and ten
independent measurements with the same cantilever in a second set. We show that, in spite of the
fact that both sets presents the same lateral force, the error in the first set of measurements is up to
50% higher then for the second set.
The calibrated microscope was used to study the influence of the humidity in the adhesion and
lateral forces between the AFM tip and an hydrophilic sample. It is shown that at very low
humidities, the Van der Waals forces are responsible for the tip-surface adhesion, while at
humidities higher than 10% the capilary condensation of water is responsible for the adhesion. The
lateral forces are shown to be strongly dependent on the environmental conditions. At low
humidities a multiasperity regime is observed wihle at higher humidities a single asperity friction is
observed. The friction coeficient is shown to decrease with the increase of humidity.
A-P24
WEAR OF AMORPHOUS FLUORINATED CARBON FILMS IN NANO AND MICROSCALES
P. Ayala, M.E.H. Maia da Costa, R. Prioli, F.L. Freire Jr.; Departamento de Física, Pontifícia
Universidade Católica do Rio de Janeiro, Caixa Postal 3807, Rio de Janeiro, RJ 22453-970, Brazil.
Amorphous fluorinated carbon films were deposited by plasma enhanced chemical vapor
deposition (PECVD) to study the wear in nanoscale and microscale. For nanoscale wear, an atomic
force microscopy was used and for microscale a sliding sphere test. The films microstructure and
chemical composition were also investigated. Density measurements, Raman and x-ray
photoelectron spectroscopy showed that films became polymeric-like upon fluorine incorporation.
It was shown that the wear marks produced with a microscope diamond tip are strongly related to
the film hardness and microstructure. The wear depth on a polymeric-like film was greater than that
obtained from hard amorphous carbon and carbon fluorinated films. At nanometer scale, the
minimum force necessary to scratch the films increased with the film hardness, while the wear rate
decreased. Similar behaviors were observed in both nano and microscale wear experiments
A-P25
STRUCTURAL CHARACTERIZATION, MECHANICAL PROPERTIES AND THERMAL
27
STABILITY OF HARD AMORPHOUS CARBON-FLUORINE FILMS DEPOSITED BY
PECVD USING C2H2-CF4 GAS MIXTURES
M. E. H. Maia da Costa and F.L.Freire Jr. , Departamento de Física, Pontifícia Universidade
Católica do Rio de Janeiro, Caixa Postal 3807, Rio de Janeiro, RJ 22453-970, Brazil.
Fluorinated amorphous carbon films (a-CF) were deposited by PECVD in C2H2-CF4 gas mixtures
at a pressure of 10 Pa. The first series of samples were prepared fixing the self-bias voltage at 350V and changing the ratio of the partial pressure of C2H2 and CF4. The idea is to investigate the
effects of the fluorine incorporation on the film properties. The acetylene partial pressure was
varied from 100% to 20% of the total pressure. The second series of samples was deposited at a
fixed self-bias voltage (–350V) and partial pressure ratio of C2H2-CF4 of 1:2. Films deposited in
pure acetylene atmosphere were also deposited. In order to investigate the thermal stability of a-CF
films, samples of these second series were annealed in vacuum without any kind of sequential
annealing for 30 minutes. The range of temperature was 200 oC to 600oC. Ion beam techniques
(RBS and ERD) were used to determine the chemical composition and, when combined with the
film thickness, the atomic density of the films. Structural modifications were investigated by
Raman spectroscopy, while X-ray Photoelectron Spectroscopy probed the chemical bonds. The
internal stress and the hardness were also measured. Contact angle measurements were made to
evaluate the hidrophobicity of the samples. Films with hidrophobicity comparable to that of the
polytetrafluoroethylene (PTFE) were obtained for films with high fluorine content. However, the
film hardness is much higher compared to PTFE. The films were thermally stable up to 300 oC. For
higher annealing temperatures, strong fluorine loss and structural changes were observed.
A-P26
PRODUCTION AND CHARACTERIZATION OF HYDROGENATED AMORPHOUS
CARBON THIN FILMS DEPOSITED IN METHANE PLASMAS DILUTED BY NOBLE
GASES
G. Capote and F.L. Freire Jr. ; Departamento de Física, Pontifícia Universidade Católica do Rio de
Janeiro, Rua Marquês de São Vicente, 225 – Gávea, Caixa Postal 38071, Rio de Janeiro, 22452970, Brazil.
The effects of the dilution of the precursor methane atmosphere by three noble gases (Ar, Ne and
He) on the mechanical properties and the microstructure of hydrogenated amorphous carbon films
(a-C:H) are presented. The influence of the precursor atmosphere and the variation of the self-bias
voltage are studied. The influence of the substrate temperature also is studied for three temperatures
250 K, 300 K and 420 K for films deposited in atmospheres of 100% CH 4 and 2% CH4 + 98% Ar.
The films were deposited by Plasma Enhance Chemical Vapor Deposition (PECVD). The
mechanical and structural properties were investigated with the use of the nuclear techniques
(Rutherford backscattering and elastic recoil detection analysis), infrared and Raman
spectroscopies, atomic force microscopy, contact angle measurements, internal stress and hardness
measurements. The results shown that the precursor atmosphere dilution by noble gases did not
induce substantial modifications in the microstructure or in the mechanical properties of the films.
On the other side, the composition, the microstructure and the mechanical properties of the films
are strongly dependent on the ion bombardment regime. The dependence of the mechanical and
structural properties of the films as a function of the substrate temperature was also investigated.
Experimental results had been obtained from the film roughness measurements using atomic force
microscopy. These results suggest the transition from predominantly adsorption/diffusion
mechanisms to the predominance of the ballistic processes in the formation mechanisms of the aC:H films.
A-P27
SURFACE MODIFICATION OF PLASMA POLYMERIZED THIN FILMS BY PLASMA
28
IMMERSION ION IMPLANTATION
D. C. R. Santos, R. P. Mota, R. Y. Honda, M. E. Kayama, E. C. Rangel, FE-UNESP, Av. Ariberto
P. da Cunha, 333, Guaratinguetá, 12516-410, SP, Brazil.
Surface modification of metal, ceramic and polymeric materials is a study of great interest for
several engineering and biomedical areas. Improvements of the surface properties can increase the
lifetime and the functionality of those materials. Plasma Immersion Ion Implantation (PIII) is an
effective method to do it. It is relatively cheaper than the conventional ion implantation and,
furthermore, it overcomes the difficulties of that technique. In this work, we investigated the PIII
effect in plasma polymer films, varying the exposure time from 1800 to 9000 s. The films were
deposited from the mixture of acethylene and argon gas, submitted to radiofrequency plasma (RF,
13.56 MHz, 100 W) in low pressure regime. Then, the films were polarized by high voltage
negative pulses (10 kV, 30 Hz) and bombarded by ions created from RF nitrogen plasmas (13.56
MHz, 70 W). Contact angle measurements were performed to evaluate the wettability and surface
energy. Age of the films was accompanied by periodical measurements of the contact angle after
the treatment. Etching rate was evaluated after exposing the films to oxygen reactive plasmas. After
the implantation, the contact angle droped for all samples. However, there was not stability of
them. In spite of that, the films showed better oxidation resistance.
A-P28
AMORPHOUS CARBON FILMS WITH VERY LOW HYDROGEN CONTENT PREPARED
BY RF PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION
E. F. Motta and I. Pereyra Departamento de Engenharia de Sistemas Eletrônicos, Escola
Politécnica, Universidade de São Paulo, CP: 61548 CEP: 05424-970, São Paulo, SP, Brazil
Research on tetrahedral amorphous carbon (taC), is still at a young stage, in the sense that film
preparation and characterization as well as practical applications have yet to be proven. In this way,
the relationship between the deposition conditions, the growth mechanisms, the microstructure and
the electronic density of states of films prepared by PECVD from hydrocarbon gaseous precursors
are not fully understood [1-3]. Therefore, in this work, we perform a systematic study by means of
several complementary characterization techniques to determine the correlation of the material
microstructure and optical properties with the deposition conditions for taC samples deposited by
radio-frequency glow discharge from methane and argon gaseous mixtures at  25 degrees C. The
studied deposition parameters were the plasma Rf power, the deposition pressure and the argon
flow rate. Raman scattering and FTIR results indicate that high argon flows and optimized
intermediate chamber pressure favor the deposition of tetrahedral amorphous carbon films with low
hydrogen content. On the other hand high deposition pressure and low flows induce the growth of
diamond like films with much higher hydrogen incorporation.
A-P29
PRE-IRRADIATION
EFFECTS
ON
THE
29
PHOTOLUMINESCENCE
AND
CLUSTER
COARSENING PROPERTIES OF GE-IMPLANTED SIO2 LAYERS
J. M J. Lopes, F.C. Zawislak, M. Behar, Instituto de Física – UFRGS, Porto Alegre, Brazil;
P.F.P. Fichtner, Escola de Engenharia - UFRGS, Porto Alegre, Brazil; L. Rebohle, Nanoparc
GmbH, Dresden, Germany; W. Skorupa, Rossendorf e.V. , Dresden, Germany
SiO2/Si(100) films were irradiated with He+, Si+, Au+ and Kr++ ions as function of the amount of
electronic and nuclear deposited energy density by the beams. After the irradiation, the SiO 2 layers
were implanted with 120 keV Ge+ ions at a fluence of
1.2  1016 cm-2. Thermal annealings in
the 400800C temperature range were performed to allow the formation of a Ge-nanoclusters,
characterized by transmission electron microscopy. The photoluminescence (PL) and PL excitation
properties of the pre-irradiated Ge-implanted layers were investigated and compared with those
from non pre-irradiated samples. The results showed that, in both situations, PL emissions are
observed in the blue-violet and ultra-violet spectral regions. At 800C the blue-violet PL intensity
of the Ge-implanted layer pre-irradited with Si+ ions is about 65% higher than in the non-irradiated
Ge-implanted layer while for the Au-irradiated layer a decrease by a factor of 6 was observed.
Furthermore, we also observe that the mean cluster sizes are affected by the pre-irradiation. For the
Au+ irradiation case, the Ge mean cluster size is 2 times smaller than to the non pre-irradiated
sample. These results indicate a pre-irradiation memory effect on the PL intensity and on the cluster
growing. The results are discussed in terms of a new model correlating the formation of PL
luminescent centers with the cluster coarsening behavior.
A-P30
CHARACTERIZATION OF Si1-xCx:H THIN FILMS DEPOSITED BY PECVD ON Si AND
Si/INSULATOR SUBSTRATES
N. A. E. Forhan and I. Pereyra, Escola Politécnica da USP - PEE – LME, Av. Prof. Luciano
Gualberto, 158, Trav. 3 - CEP05508-900, São Paulo - SP - Brazil
In this work we investigate the structural properties of amorphous hydrogenated silicon carbide thin
films (-Si1-xCx:H) deposited by PECVD on silicon and silicon covered with an insulator layer
substrates, before and after thermal annealing for crystallization. The SiC-on-insulator
heterojuntion allows its use in high temperature, high power, high frequency, smart-sensors, and
micromechanical applications. Here, we analyze -Si1-xCx:H films deposited on silicon covered
with different kind of insulator capping layer: high temperature (1100 oC) thermal SiO2, low
temperature (300oC) PECVD SiO2, SiOxNy, and Si3N4. These insulators were chosen due to their
great interest for optoelectric and microelectronic applications. The infrared studies have shown
that samples deposited on silicon covered with an insulator layer have a better coordination among
Si and C atoms. Post-growth thermal annealing leads to the crystallization for all the amorphous
films. Raman scattering spectroscopy measurements exhibit a weak C-C bond vibration, after
annealing, only for samples deposited on PECVD insulator. The structural properties and the
mechanical internal stress of the -Si1-xCx:H films are studied, before and after thermal annealing,
by X-Ray Diffraction and Stoney method, respectively.
A-P31
ANNEALING OF DEFECTS AND NANOPORES PRODUCED ON SiO2 THIN FILMS BY
30
MEANS OF ION BOMBARDMENT
C.Milanez1 , J.M.J.Lopes2 , P.F.P.Fichter3 , R.M.Papaléo1
1
Faculdade de Física, PUCRS, Av Ipiranga 6681, 90619-900 Porto Alegre; 2Instituto de Física,
UFRGS; 3Dep. Metalurgia, Escola de Engenharia, UFRGS, Cx Postal 15051, 91501-970 Porto
Alegre-RS.
Nanometer-sized conical pores of high aspect ratio were produced on SiO 2 thin films thermally
grown on Si (100) wafers by irradiation with Au MeV ions followed by chemical etching. Such
holes are formed because of the enhanced etching rate around the site of ion penetration, as
compared to undamaged zones of the material. The number of defects produced by the MeV ions
and their spatial distribution are key to the final shape and size of the pores. Thermal annealing of
the bombarded oxide was performed at temperatures T a ranging from 150˚C to 900˚C for 30 min
under dry N2 flux, before pore opening by etching in aqueous HF solution. Thermal treatment
results in a substantial decrease in the pore size, even at T a as low as 150˚C. For example, while
pore diameters were around 150nm on unannealed samples, their average values decrease to 
50nm for Ta = 250˚C and to  25nm for Ta = 500˚C. Pores are not seen on samples annealed at
900˚C, probably because of a complete recovery of the defects in the ion track. We note that the
pore dimensions on the etched SiO2 films are unchanged even after annealing at 800˚C for 1h, i.e.
once formed the pores show an excellent thermal stability.
A-P32
EVIDENCE OF CLUSTERS SIZE DEPENDENT PHOTOLUMINESCENCE ON SILICONRICH SILICON OXYNITRIDE FILMS
R.A.R. Oliveira, M. Ribeiro, I. Pereyra and M.I. Alayo; University of São Paulo, CP 61548, CEP
5424-970, São Paulo, SP, Brazil
In recent years, photoluminescent materials for optical and microelectronic integration have
received great attention. Among these, silicon nanocrystals in a SiO x matrix is considered very
promising due to its stability and high luminescence intensity after annealing at high temperatures
[1,2].
This work reports on the growth of silicon clusters within silicon oxynitride (SiO xNy) matrices by
Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. The films were characterized
by Fourier transform infrared spectroscopy (FTIR), Raman scattering and photoluminescence
before and after thermal annealing at various temperatures. The results indicate the presence of
silicon clusters in as-deposited and the evolution of clusters size after annealing. Also, the
photoluminescence measurements, show that as-deposited films already present high luminescence
intensities. These results are in accordance with soft X-ray absorption spectroscopy (XANES)
measurements at Si K-edge which demonstrate the silicon phase segregation on these films.
[1] M. Ribeiro, I.Pereyra, M.I. Alayo, Thin Solid Films 426 (2003) 200.
[2] L. Pavesi et. al., Nature 408 (2000) 440.
A-P33
STUDY OF PECVD MATERIALS FOR TFT APLICATION
31
K.F.Albertin; I.Pereyra and M.N.P.Carreño, LME, EPUSP, University of São Paulo, CEP 05508900, CP 61548, São Paulo,SP, Brazil
The application of thin film transistors (TFT’s) in image sensors and displays is widespread and
the amorphous silicon technology has shown to be mature and thus a-Si:H TFTs are widely used
for individually switched display elements (pixels) in flat panel displays[1].
However the mobility of amorphous silicon is in the 0.5-1.0 cm2.V-1.s-1range and higher values are
needed for some applications, such as: high resolution large area displays, requiring complementary
metal – insulator – semiconductor operation (CMOS). CMOS operation however is out of reach for
a-Si:H since its hole mobility is insufficient for p channel operation. In this way research is now
directed to semiconductors materials with higher mobilities than amorphous silicon, as
nanocrystaline (nc-Si), microcrystaline (uc-Si) and policrystaline (Poly-Si) silicon films.
In this work we fabricate TFT’s utilizing a-Si:H and c-Si:H as active layer and with insulating
layer of SiOxNy and a-SiC:H all obtained by the PECVD technique at low temperatures (~300 oC).
The TFT’s are caracterized by Ids xVds and Ids x Vgs measurements, and these results are correleted
with the physical properties of the materials which are characterized by Raman, XRD and FTIR
measurements.
[1] R.E.I Schropp, B.Stannowski, J.K. Rath. Journal of Non-Crystalline Solids 299 – 302 (2002)
1304.
A-P34
STRUCTURAL ANALYSIS OF SILICON OXYNITRIDE FILMS DEPOSITED BY PECVD
D. Criado, M.I. Alayo, I. Pereyra, M.C.A. Fantini ; University of São Paulo, CEP 5424-970 CP
61548, São Paulo, SP, Brazil
Silicon oxynitride films have nowadays assumed great importance for the development of various
microelectronic and optical devices, such as: waveguides, TFT transistors, and micro-electromechanical systems (MEMS) [1]. The main characteristic of these materials is the possibility of
tuning the physical and optical properties when adequate growth parameters are varied [2]. This
work reports on the deposition and characterization of silicon oxynitride films deposited by Plasma
Enhanced Chemical Vapor Deposition at low temperatures from different N 2, N2O and SiH4
gaseous flow ratio. Fourier Transform Infrared Spectroscopy, Rutherford Backscattering
Spectroscopy and Soft X-Ray Absorption Near Edge Structure (XANES) performed at the Si-K
edge show that depending on the deposition parameters it is possible to grow materials with a
homogeneous structure between silicon dioxide and silicon nitride obeying a Random Bonding
Model (RBM). Furthermore, analysis of XANES at N-K edge demonstrate two edges which are
attributed to the different nitrogen neighborhoods, nitrogen in a Si 3N4 matrix and nitrogen
substituting the O in a SiO2 matrix.
[1] K.C. Mohite et. al. Materials Letters 4494 (2003) 1; [2] M.I. Alayo et. al. Thin Solid Films 402
(2002) 154.
A-P35
PECVD-SILICON OXYNITRIDE FILMS FOR FABRICATION OF OPTICAL WAVEGUIDES
M.I. Alayo, M.N.P. Carreño, D. Criado, I. Pereyra; University of São Paulo, CEP 5424-970, CP
61548, São Paulo, SP, Brazil
Silicon oxynitride films have nowadays assumed great importance in the fabrication of optical
devices mainly due to that this material permits the integration of optical and microelectronic
devices in a single chip because the same infra-structure is used by the fabrication of both devices
[1]. Furthermore, the properties of these materials are strongly dependent on the deposition
parameters, so tunability of the refractive index over a wide range can be obtained (n = 1.46 - 2)
resulting in a large degree of freedom for integrated optics design [2].
In this work were fabricated optical waveguides with different compositions PECVD silicon
oxynitride films and optical attenuation measurements in these devices were realized. On the other
hand, in order to correlate the optical characteristics of these devices with the optical, physical and
chemical characteristics of the films utilized as core and cladding, materials characterization such
as: Fourier Transform Infrared Spectroscopy (FTIR), Ellipsometry and Rutherford Backscattering
Spectroscopy (RBS) were realized.
[1] M. Modreanu et. al. Optical Materials 17 (2001) 145; [2] M.I. Alayo et. al. Thin Solid Films 402 (2002) 154.
A-P36
ELECTRICAL
PROPERTIES
OF
32
LOW-TEMPERATURE
PECVD
SiC/c-Si
HETEROSTRUCTURES
A.R. Oliveira*, M.N.P. Carreño and I. Pereyra; Department of Electronic Systems, Polytechnic
School of the University of São Paulo - CP 61548, CEP 05424-970, São Paulo – SP, Brazil
The electrical properties of the SiC/Si heterostructure based on stoichiometric a-SiC:H thin films
grown by r.f. plasma chemical vapor deposition at low-temperature (320 ºC) on Si(100) substrates
have been investigate. Films deposited with different chemical and structural orders and annealed at
550 ºC for 2 hours were obtained in the so-called “silane starving plasma” condition, from SiH 4,
CH4 and H2 gaseous mixture. In order to assess the applicability of these films, the electrical
properties were evaluated from current-voltage and capacitance-voltage characteristics curves. It
was found that electrical properties of the heterojunction formed with optimized deposition
condition and subsequent annealing step show the better electrical performance, exhibiting good
rectifying properties.
A-P37
MICRO-RAMAN STRESS CHARACTERIZATION OF POLYCRYSTALLINE SILICON
FILMS GROWN AT HIGH TEMPERATURE
R. C. Teixeira; I. Doi, M. B. P. Zakia, J. A. Diniz, and J. W. Swart; School of Electrical and
Computer Engineering (FEEC), and Center for Semiconductor Components (CCS), State
University of Campinas (UNICAMP), C.P. 6101, 13083-970 Campinas-SP, Brazil
Polycrystalline Silicon (poly-Si) is widely used in microelectronics and micro-electro-mechanical
systems (MEMS). In MEMS, poly-Si is used as structural material for a variety of applications such
as pressure transducers and micro-switches. The performance and control of the dimensions of the
micro-structural elements are critically dependent on the mechanical stress in the films. The stress
is controlled during deposition process, as the processing parameters affects significantly the
mechanical and electrical characteristics of devices. Poly-Si obtained by low pressure chemical
vapor deposition (LPCVD) is used in surface micromachining applications, however, a high
residual stress are inherent in as-deposited poly-Si, requiring further annealing steps to achieve
minimum residual stress. In this paper we present the residual stress characterization and analysis
of the poly-Si grown at high temperature in a vertical pancake type LPCVD reactor by MicroRaman spectroscopy. The samples were prepared on Si (100) substrates coated with 50nm of SiO 2
at pressure of 5 and 10 Torr in the temperature range between 750°C to 900°C. The results show
that residual stress decreases with temperature, thus with crystalline amount of the films. All the
samples exhibited less than 250 Mpa tensile stress at temperatures above 800°C. These results
indicate that a high quality, low strained, and highly crystalline poly-Si films, can be obtained in
this type of reactor at high temperature.
A-P38
A-P39
STRUCTURAL AND OPTICAL CHARACTERIZATION OF SILICON NANOCRYSTALS
OBTAINED BY ÍON IMPLANTATION
S. N. M. Mestanza, J. E. C.Queiroz, H. R. Gutierrez, A. A. R. Neves, G. O. Dias, I. Doi and J. W.
Swart; Centro de Componentes Semicondutores CCS/FEEC-UNICAMP, CP6165, 13083-970
Campinas, SP, Brazil; nilo@led.unicamp.br
In spite of high efficiency emitter devices can be obtained from III-V semiconductor compounds;
its integration in the current Si planar technology is very complex and often ineffective. On the
other hand silicon is a very poor emitter due to it indirect bandgap. However, in nanocrystal form
(Si-nano), silicon properties change drastically presenting a direct bandgap with emission in the
wavelength range of 600-1000 nm, depending on the nanocrystal size distribution.
In this work, different samples with Si nanocrystals were prepared by implantation and annealing.
Thermal silicon oxides with  300nm, were grown on (100) n-Si and p-Si wafers. 28Si+
implantation was performed with energies of 100Kev. The implantation energies were chosen from
Monte Carlo simulation, using the TRIM code. Conventional photoluminescence (PL) spectra were
obtained at room temperature, showing a broad luminescence band in the red region for all the
samples. We have studied the behavior of PL emission peak and full wide at half maximum
(FWHM) with the annealing time. The nanocrystal size distribution was determined by crosssection Transmission Electron Microscopy measurements.
THERMAL STABILITY OF Hf-BASED HIGH-K FILMS ON SILICON FOR ADVANCED
33
CMOS DEVICES
K.P. Bastos, R.P. Pezzi, L. Miotti, G.V. Soares, C. Driemeier and J. Morais, Instituto de Física UFRGS, CP 15051 91501-970 Porto Alegre – Brazil; I.J.R. Baumvol, Centro de Ciências Exatas e
Tecnológicas – UCS, Av. Francisco G. Vargas 1130, 95070-560 Caxias do Sul – Brazil
The use of metal oxide and silicate films with higher dielectric constant than that of silicon oxide
(high-k materials) as a substitute for SiO2 as gate dielectric presents several difficulties. Some of
them include chemical and structural instabilities in further thermal processing following gate
deposition, such as oxidation of the Si substrate, migration of metallic species into the active
semiconductor region, transport of Si into the high-k film, and crystallization of the initially
amorphous film. This work reports on the thermal stability investigation of HfO 2/SiOxNy/Si,
HfSiO/Si and HfSiON/Si structures submitted to various combinations of rapid thermal annealings
in either inert or oxidizing atmospheres. The areal densities and the concentration profiles of the
species of interest were determined before and after rapid thermal annealings by resonant and nonresonant nuclear reaction analysis and Rutherford backscattering spectrometry. The incorporation
of nitrogen into hafnium oxide and hafnium silicate films, either during deposition or during postdeposition thermal treatments, provided substantial improvements in the thermal stability of the
films.
A-P40
ANNEALING STUDIES IN JVD HIGH-K OXIDE SYSTEMS
E. A. de Vasconcelos, J. A. A. Fotius, J. B. Oliveira Jr., E. F. da Silva Jr., Departamento de Física,
Universidade Federal de Pernambuco, 50670-901 Recife, PE, Brazil; H. Boudinov, Instituto de
Física, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil; T. P. Ma,
Department of Electrical Engineering, Yale University, New Haven, CT 06520, USA.
High-k oxides are promising materials for ultra-thin gate dielectrics in advanced MOS technologies
and the development of their fabrication techniques has been actively investigated in the last few
years. The Jet-Vapor-Deposition (JVD) process is one of the methods proposed for fabrication of
these materials. In this work, we report on the effects of gaseous, ultra-violet and ion-irradiation
annealing on the interfacial and bulk properties of Jet-Vapor-Deposited high-k oxides. MOS
capacitors with high-k oxides (HfO2, HfAlO) were fabricated and I-V, C-V, voltage and current
stress tests have been performed. The results indicate that it is possible to improve significantly the
oxide properties by an appropriate selection and combination of the annealing techniques above.
We will discuss the details of the techniques and discuss the mechanisms involved.
A-P41
A-P42
MORPHOLOGY AND STRESS STUDY OF NANOSTRUCTURED POROUS SILICON AS A
SUBSTRATE FOR PbTe THIN FILMS GROWTH BY ELECTROCHEMICAL PROCESS
C.R.B. Miranda1,2, P.G. Abramof1,3, F.C.L. Melo2, N.G. Ferreira2; 1Instituto Nacional de Pesquisas
Espaciais INPE/LAS, CP 515, 122245-970, São José dos Campos, SP, Brasil; 2Centro Técnico
Aeroespacial – Divisão de Materiais - AMR/IAE /CTA, 12228-904, São José dos Campos, SP,
Brasil ; 3Centro de Desenvolvimento de Tecnologia e Recursos Humanos - CDT, 12242-800, São
José dos Campos, SP, Brasil
Porous silicon layers (PSL) were produced by stain etching using a solution of HF:HNO 3 500:1
with etching time varying from 1 up to 10 min. The samples have presented nanometric porosity as
a function of etching time, characteristic of heavily doped p type silicon. The residual stress and the
correlation length of the layers were obtained through the analysis of the micro-Raman spectra
using a phonon confinement model including a term to account for the amorphous phase. The
correlation length, which corresponds to the crystallite size, is found to decrease as the etching time
increases, and agrees with the values obtained by Atomic Force Microscopy (AFM) analysis. The
residual compressive stress tends to increase with etching time, as expected by the smaller
crystallite size. PbTe thin films were electrodeposited on PSL from aqueous alkaline solutions of
Pb(CH3COO)2, disodium salt of ethylendiaminetetraacetic acid (EDTA) and TeO2 by galvanostatic
and potentiostatic method. It was also obtained nanostructured PbTe thin films with polycrystalline
morphology evidenced by X-Ray Diffraction (XRD) spectra. Scanning Electron Microscopy (SEM)
analysis has demonstrated good films reproducibility with an average grain size of 100 nm.
EXPERIMENTAL AND THEORETICAL STUDY OF POROUS SILICON ELASTIC
34
PROPERTIES
A. B. S. Camussi, R. J. M. da Fonseca, Grupo de Ótica e Propriedades Físicas de Materiais – DEQ,
Instituto de Física, UERJ, R. São Francisco Xavier, 524 sala D-3030, 20550-013 Rio de Janeiro,
Brazil; J. Attal, Laboratoire d’Analyse des Interfaces et de Nanophysique – URA CNRS 1881 Université Montpellier II 34095, Montpellier CEDEX 05 – France
Porous silicon (PS) has been extensively studied since it exhibits strong visible luminescence at
room temperature, suggesting promising applications in silicon-based optoeletronic devices,
dielectric isolation of integrated circuits and epitaxial growth of heterostructures on Si substrate.
Great part of this research has been focussed in the investigation of optical and electronic properties
of PS layers. However, for many pratical applications, it is important to characterize the mechanical
behaviour of them. For this purpose, we apply the scanning acoustic microscopy (acoustic imaging
and V(z) signature) to measure the acoustic wave velocities and elastic characteristics of this
material (Young’s modulus and Poisson coefficient) with different porosity. This is a powerful
technique for non-destructive and non-contact measurements, specially when small volumes are
involved. The investigated samples have a porosity range of 20% to 60% and thickness of 30 µm to
120 µm. So, in this work, we present V(z) curves and acoustical images and a comparision between
theoretical and experimental results using Biot’s theory which describes the propagation of elastic
waves in a system composed of a porous elastic solid saturated by a fluid.
A-P44
STRUCTURAL CHARACTERIZATION OF Ge NANOCRYSTALS IN SILICA
G. de M. Azevedo1,2, A. Cheung2, M. C. Ridgway2, C. J. Glover2, D. J. Llewellyn2, R.G. Elliman2,
G. J. Foran3; 1Laboratório Nacional de Luz Síncrotron, Campinas-SP, Brazil; 2Australian National
University, Research School of Physical Sciences and Engineering, Canberra, Australia;
3
Australian Nuclear Science and Technology Organisation, Menai, Australia
Germanium nanocrystals encapsulated in silica display size-dependent photo luminescence, with
possible applications in the fabrication of optical devices. Given the influence of nanocystal size
and structure on the optical properties, characterization of the geometrical structure as a function of
the preparation conditions is crucial to fully understand and exploit their optical properties. In this
contribution, ion implantation followed by annealing was utilized synthesize nanocrystals in the
near surface region of 5 micron-thick silica layers. Samples were produced with a variety of ion
doses and annealing temperatures. The resulting size distributions were estimated by transmission
electron microscopy (TEM) and the local environment surrounding Ge atoms was investigated with
EXAFS. The highest dose and annealing temperatures resulted in samples containing nearly
spherical nanocrystals with average diameter of 14 nm. Simulations with the FEFF8.0 code indicate
precipitates of such a size with bulk like parameters should yield bulk-like spectra. Our
experimental results indicate the first nearest neighbor shell in the annealed sample is essentially
identical to that of the bulk standard. None-the-less, the amplitudes of the second and greater
nearest neighbor shells are considerably reduced. We attribute this reduction to distortions in both
bond-length and bond-angle distributions relative the bulk phase. The potential causes of the
observed perturbations will be discussed.
A-P45
TRANSPORT VIA EXCITONIC COMPLEXES IN RESONANT TUNNELING STRUCTURES.
35
A. Vercik, Y. Galvão Gobato, Universidade Federal de São Carlos, CP 676, São Carlos - SP,
13560-970, Brazil; M. J. S. P. Brasil, Universidade de Campinas, CP 6165, Campinas-SP, 13083970, Brazil.
The Coulomb interaction can bind an electron to a hole forming a neutral exciton. When a second
electron is involved, negatively charged excitons are formed, also known as trions. These systems
have attracted much interest and their properties continue to be subject of intense debate. These
complexes can participate in charge transport, creating an intermediate state in the quantum well of
a double barrier structure, through which electrons can tunnel resonantly. Because of the binding
energy of the excitons or trions, the excitonic intermediate level must be located at a lower energy
than the resonant level.
In this work we study the formation of neutral and negatively charged excitons in double barrier
diodes under bias, and how they contribute to transport. We observe a pre-resonance shoulder in the
current-voltage curve, which is associated to trion-assisted tunneling of electrons. We analyze this
phenomenon by measuring also the quantum-well photoluminescence emission. This trion-assisted
mechanism is terminated when trion complexes are dissociated either by thermal excitation or by
scattering with free carriers in the quantum well. A simple phenomenological rate equation model
allows us confirming the hypothesis of charge transport via a trion state and the proposed methods
of termination.
A-P46
RELAXATION OF NANODEFORMATIONS PRODUCED ON PMMA THIN FILMS NEAR
THE GLASS TRANSITION
R. Leal , R. M. Papaléo; Faculdade de Física, PUCRS, Av Ipiranga 6681, 90619-900 Porto Alegre;
-RS, Brasil.
Individual heavy ions impacting polymers and other organic materials at high energies leave at the
surface nanometer-sized craters often surrounded by a raised region of displaced material (rims). In
this work, we report on measurements of relaxation times of such features near the glass transition.
PMMA thin films were bombarded by 20 MeV Au ions at grazing angles at different temperatures
(75, 84, 91, 93, 95 and 100°C) and low fluences (~10 9 ions/cm-2). The targets are kept at the
irradiation temperature for a certain period of time before the samples are quenched to room
temperature (where PMMA is a glass and structural relaxation of the chains is virtually stopped).
By irradiating a series of samples at a fixed temperature, each annealed during a different time, the
average dimensions of the crater and rims can be extracted from SFM images and plotted as a
function of annealing time, t. The relaxation of the protusions follows roughly an exponential law
( exp(-t/), where  is identified as an average characteristic relaxation time. Extracted values of 
were smaller than 2s at 100°C and around 48h at 75°C, in accordance to what is expected for
macroscopic deformations in PMMA. Some parts of the rims surrounding the middle of craters
relax much more slowly, probably because of the severe chemical modification of the chains in the
core of the impact.
A-P47
PHOTOLUMINESCENCE OF NANOCRYSTALLINE TUNGSTEN DOPED ZT
36
Rubens S.G.1, Zaghete M.A2, Sidey J.L.R.3, Santos D. M.4, Paiva_Santos C.O2 , Siqueira J. R.R4,
Varela J.A.2, Longo E.6
1
Department of Mechanical and Material (DMM) - Centro Federal de Educação Tecnológica do
Maranhão (CEFET-MA) - São Luís, MA, Brazil; 2 Centro Multidisciplinar de Desenvolvimento
de Materiais Cerâmicos (CMDMC) - Instituto de Química- UNESP, C.Postal 355,14801-970
Araraquara,SP, Brazil; 3 Departamento de Química Geral e Inorgânica - Instituto de QuímicaUNESP, Araraquara,SP, Brazil; 4 Universidade Federal do Maranhão (UFMA); São Luís, MA,
Brazil ; 5 Universidade Estadual de Mato Grosso do Sul (UEMS), Brazil; 6 Centro Multidisciplinar
de Desenvolvimento de Materiais Cerâmicos (CMDMC) - Department of Chemistry, Universidade
Federal de São Carlos, C.Postal 676 13565-905, São Carlos, SP, Brazil.
Photoluminescence studies of tungsten doped ZT powders are presented. The polymeric precursor
method was used to synthesize the ZT powders. The polyester precursor was decomposed at low
temperature to obtain the “amorphous” phase. The experimental results suggest that the visible
photoluminescence emission, at room temperature, could be related to the disorganization of the
atoms in the structure. Which is in the interface between amorphous and crystalline state. The
photoluminescence properties were investigated and correlated with amount of dopant and
annealing temperature. The optical gap and the energy constant were calculated using the Wood
and Tauc method whereas the absorption coefficient,, was obtained Kubelka-Mulk model. Both
constants were calculated using the UV_vis data. The powders were also characterized by DRX,
IR.
Keywords: none structured, ZT, Photoluminescence, amorphous structure, optical gap
A-P48
STUDY OF NiFe/WTi MULTILAYERS BY XMCD
V. P. Nascimento, 1A. D. Alvarenga, M. Morales, E. Baggio Saitovitch, Centro Brasileiro de
Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, RJ, 22290-180; A. Biondo, Depto. de Física do
CCE/UFES, Av. Fernado Ferrari, Campus de Goiabeira, Vitória, ES, 29060-900; A.R.B. de Castro,
LNLS, Rua Giuseppe Máximo Scolfaro 10000, Campinas, SP, 13083-100; Universidade Estadual
de Campinas – UNICAMP, Campinas, SP, Brazil.
The investigation of spin-dependent phenomena in magnetic materials has being intensively
enhanced by the use of circularly polarized synchrotron radiation. Here we report investigations on
the magnetism of NiFe/WTi multilayers prepared by Magnetron Sputtering. These multilayers have
great interest for magnetoresistive devices based on antiferromagnetic coupling and giant
magnetoresistance, which depend sensitively on interface structure and film morphology. XMCD
measurements were performed in order to study the interfacial spin configuration. The XMCD
experiments gives a magnetic depth profile; few layers of material are removed by in situ
sputtering, followed by XMCD measurements at the Fe and Ni L2, 3 edges. For complementary
analysis X-ray diffraction, magnetization (VSM), magnetoresistance and ferromagnetic resonance
(FMR) measurements are also discussed. The results give evidence of a NiFe dead layer at the
interface.
A-P49
NEW ELECTRODE MATERIAL FOR THE ELECTROCHEMICAL DETERMINATION OF 2,4
37
DICLOROPHENOXYACETIC ACID HERBICIDE (2,4D)
*F. R. Simões1,2, 1Programa Interunidades em Ciência e Engenharia de Materiais- IFSC-USP
Caixa Postal: 369. 13560-970 São Carlos, SP, Brasil. C. M. P. Vaz2, 2Embrapa Instrumentação
Agropecuária Caixa Postal:741, CEP:13560-970
São Carlos, SP, Brasil.
Conducting polymers have been used in many technological and scientific research applications.
Due to the necessity of active materials and great demand for different applications, the conducting
polymer allows an increasing of versatility for the construction of sensors. In agriculture, in
particular, the uncontrolled use of pesticide has been causing a great environmental impact, as for
example the groundwater and surface water contamination. The most popular methods of pesticide
analysis are the chromatographics mainly the HPLC and gas chromatography. These methods are
sensible and selective, but they are laborious and expensive. Electroanalytical techniques have also
been used as methods for pesticides determination in natural waters, soils, vegetables, fruits and
other matrices. The main advantage of this method is the possibility of determining its
concentration without previous treatments or separations. This work presents a new modified
electrode for the determination of the herbicide 2,4 diclorophenoxyacetic acid (2,4D). This
compound is known as not electroactive in electrodes as mercury, platinum and carbon (glassy,
fiber or paste), but a new composite material consisting of carbon paste electrode and the
conducting polymer polyaniline (PANI) was prepared, showing electroactivy and therefore, the
possibility of the pesticide determination using electrochemical techniques. The analyses of the
herbicide was carried out through cyclic voltammetry (C.V) in different pHs. The results showed
good sensitivity and selectivity.
*Correspondências devem ser enviadas no endereço abaixo:
R. Carlos S. Rodrigues n.75 apto 21. CEP 13574-580 São Carlos, SP, Brasil.
A-P50
POLYMER-LIGHT EMITTING DIODES IN ITO/MEH-PPV/Al STRUCTURES
J. A. R. Neves, E. A. T. Dirani, F. J. Fonseca, A. M.Andrade; Av. Luciano Gualberto, travessa 3, nº
158, Cidade Universitária, São Paulo/SP, CEP 05424-970, jrocha@lme.usp.br
This work, is aimed to study and develop electroluminescence polymeric devices, such as polymer
light emitting diodes (PLEDs). These devices are of interest because of their comercial application,
for example, in the manufacturing of large area, slim, light and flexible displays. They can also
offer potential low cost compared to the present available technology. All devices presented in this
work were processed in matricial shape, using photolithography techniques, in order to study and
develop procedures for displays production. The polymer used as emissive coating of the device
was the poly (2-methoxy 5-(2’-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and the
process of coating deposition was made by spin casting of liquid solution on substrate. For the
device manufacturing, it was necessary to study the characteristic of the various coating
components through optical and electrical measurements. The process variables analysed were the
polymeric film thickness, deposition uniformity, polymeric solution concentration, superficial
roughness of the hole injector electrode and device packaging. In these processed devices, the best
obtained electrical characteristics for the structure formed by ITO/MEH-PPV/Al were the operation
voltage about 7 volts with currents close to 0.2 mA. These results show that the improvment in the
PLED’s characteristics is associated to the uniformity and thickness of the polymeric coating
(MEH-PPV), carrier injection and device packaging.
A-P51
IONENE-MODIFIED BENTONITE AS A TOOL IN THE ADSORPTION OF ORGANIC
38
POLLUTANTS
A.P.Costa Filho*1,2; A.S.Gomes; and F.E.Lucas. 1Instituto de Macromoléculas, Centro de
Tecnologia, Universidade Federal do Rio de Janeiro, Bloco J, Ilha do Fundão, Rio de Janeiro, C. P.
68525, CEP 21945-570, Brasil. 2Tecnologia Química, Universidade Federal do Maranhão-CT,
Campus do Bacanga S/N, São Luís, Maranhão, Brasil.* araofilho@terra.com.br
The adsorption of organic pollutants in polycation-modified clays is a well known technique. In this
work, a sodium bentonite, (having CEC= 96 meq/100 g clay as determined by X-Ray fluorescence)
was treated with ionene-like polycations containing different spacers, those being synthesized
according to the Menshutkin reaction. Those polymers were characterized using FT-IR, NMR 1H,
13
C and UV visible (for assessing the molecular weight), TGA and elemental analysis.The modified
clays were analyzed by FT-IR, TGA, fluorescence and X-Ray diffraction. Data confirm polymer
intercalation in the clay, configuring a polymeric net between the mineral interlamellar spaces.
These materials find potential application in the absorption of organic pollutants such as benzene,
toluene, p-nitrophenol, and the like.
Acknowledgments:CAPES/UFMA/FINEP/CTPETRO, CNPQ/RENAMI
A-P52
SIMULATION ENVIRONMENT FOR INVESTIGATING ADSORPTION MECHANISMS IN
LAYER-BY-LAYER FILMS.
Linder C. DaSilva, Osvaldo N. Oliveira Jr. and Luciano da F. Costa. IFSC – USP , Caixa Postal
369, São Carlos, SP, 13570-970 Brazil
A computational environment is described which is aimed at simulating adsorption processes in
layer-by-layer films obtained via physical adsorption of charged polymers. Consistent with
experimental data, the mechanism of adsorption is treated at the nanoscopic level, with adsorption
of polymer aggregates as they appear in an aqueous solution. Simulations can be made for
aggregates of any shape and with a generic polydispersity for circular particles. When the ballistic
deposition is applied, interpenetration between adjacent layers occurs, which may explain
adsorption data for polyelectrolytes. The morphological characteristics of simulated films such as
porosity, degree of interpenetration and roughness are obtained by defining the film/air interface
with the Euclidean distance transform. These features allow the verification of scaling laws.
Correlation can also be made between the morphological properties of the aggregates and the shape
functionals of individual particles as a means to predict the overall properties of the film. The
system is generic and may be extended to any process of surface growth. The tools are developed
under the Scilab environment incorporating C routines for the bottleneck processing. A graphicinteractive interface will be developed to foster collaboration with material scientists.
A-P53
A-P54
ELECTRICAL PERCOLATION DURING GELATION OF LITHIUM-DOPED SILOXANEPOLY(OXYETHYLENE) HYBRIDS
A.P Sacco, Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil; K. Dahmouche,
Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil; C.V Santilli, Instituto de Química,
UNESP, C.P 355, Araraquara-SP, Brazil; S.H Pulcinelli, Instituto de Química, UNESP, C.P 355,
Araraquara-SP, Brazil
Gelation mechanisms of lithium-doped Siloxane-Poly(oxyethylene) (PEO) hybrids containing
polymer of two different molecular weight (500 g/mol and 1900 g/mol) were investigated through
the evolution of the electrical properties of the materials during the sol-gel transition. The electrical
investigation, performed by in-situ complex impedance spectroscopy, was correlated with the local
coordination and the dynamical properties of the lithium ions during the process performed by 7Li
NMR measurements. For both hybrids sols, a decrease of the conductivity is observed at the initial
gelation stage, due to the existence of an inverted percolation process consisting of the progressive
separation of solvent molecules containing conducting species in isolated islands during the solid
network formation. An increase of conductivity occurs at more advanced stages of gelation and
aging, attributed to the increasing connectivity between PEO chains promoted by the formation of
crosslinks of siloxane particles at their extremities, favoring hopping motions of lithium ions along
the chains.
NYLON-6 / CLAY (NANO)COMPOSITES PREPARED BY MELT INTERCALATION
39
T. J. A. Mélo; E. M. Araújo; M. P. Baracuhy, L. H. Carvalho, Departamento de Engenharia de
Materiais, Universidade Federal de Campina Grande, Av. Aprígio Veloso, 882, Bodocongó, Caixa
Postal 10034, 58109-970 Campina Grande, Brazil. tomas@dema.ufcg.edu.br
Nanocomposites of nylon-6 were prepared by melt blending the polymer with imported Na+
montmorillonite and montmorillonite modified by quaternary ammonium salt. The nanocomposites
were obtained by mixing in a Haake closed mixer at 240°C and 60 rpm for 10min, with 3wt% of
clay. The effects of the incorporation of clay were observed by X-ray diffraction, Fourier transform
infrared (FTIR) analysis and mechanical properties. The results from X-ray and FTIR suggest that
has occurred intercalation of the salt but the mechanical properties no showed significant changes.
This might be due the processing conditions are not enough to provide an appropriate nanometric
dispersion of clay layers and an homogeneous distribution of the clay in the samples.
A-P55
INFLUENCE OF ORGANO-BENTONITE CLAY ON THE PROCESSING AND
MECHANICAL PROPERTIES OF NYLON 6 AND POLYSTYRENE COMPOSITES
E.M. Araújo 1; T.J.A. Mélo 1; L.N.L. Santana 1; G.A. Neves 1; H.C. Ferreira1; H.L. Lira 1; L.H
Carvalho1; M.M. A’vila Jr.,2; M.K.G. Pontes, 2; I.S. Araújo,2; 1DEMa/CCT/UFCG – C.Postal
10034, CEP 58109-970, Campina Grande, PB edcleide@dema.ufcg.edu.br; 2 Students of the
Materials Engineering/UFCG
The development and characterisation of nanostructured polymer-clay composites has received
special attention in recent years. Organoclays consist of a clay that has been modified with
quaternary amine cations. Influence of organoclay on the processing and mechanical properties of
nylon 6 and polystyrene was investigated. A bentonite sample from Boa Vista/PB, Northeast of
Brazil, was treated by ion exchange with alkyldimethylbenzylammonium chloride quaternary
ammonium salts. After the modifying, the powder was characterised by infrared spectroscopy,
analysis chemistry, thermal analysis and X-ray diffraction. Composites were prepared using a
Haake Blucher Torque Rheometer. The results evidence the effective intercalation of quaternary
ammonium salt in the structure of bentonite and show that the organo-bentonite produced
significant changes on the processing of the nylon 6 with increase in the viscosity and rigidity.
However, the mechanical properties of polystyrene/organoclay system no showed significantly
changes.
A-P56
A-P57
CHARACTERISTICS OF ELECTRICAL TRANSPORT IN SOL-GEL DIP-COATING SnO2
EXCITED BY ULTRAVIOLET SOURCES
V. Geraldo 1, T. J. Pereira2, L. V. A. Scalvi 2, P.B. Miranda 1 and C. V. Santilli3 ; 1 I. Física de S.
Carlos–USP, C.P. 369, 13560-970 S. Carlos SP; 2 D.Física – Fac. Ciências, UNESP, C. P. 473,
17033-360 Bauru SP; 3 I. Química -UNESP, C. P. 355, 14801-970, Araquarara SP,Brazil
Technological interest on tin dioxide has grown due to large application in devices. Our films are
deposited via sol-gel with nanocrystalline grains (3-7 nm), and present n-type conduction, due to
oxygen vacancies and/or Sb doping, and interesting nanoscopic transport properties. In this
communication we report photoconductivity of SnO2 film, excited in the range 70-200 K, by using
the fourth harmonic of a Nd:YAG laser (266nm). The conductivity increases up to 40 times under
laser irradiation until practically saturates. After removing the illumination, the conductivity
remains unchanged as long as the temperature is kept constant. Film conductivity only changes
when the temperature is increased. The return to original values after a few hours discharge
possibilities of local structural effects such as laser induced burns. The photocurrent spectra in the
range 200-400nm, obtained by using a deuterium source, yields a band around 240nm, which is
temperature dependent. The explanation for these results is related to optical absorption of SnO 2 in
conjunction with recombination of photogenerated electron-hole pairs with grain boundary
adsorbed oxygen. Adsorbed oxygen recombines with holes and the resulting gaseous specimen is
continuously eliminated from the system by the vacuum pumping.
EFFECT OF GAMMA IRRADIATION ON OPTICAL PROPERTIES OF POLY(P-
40
PHENYLENEVINYLENE) SOLUTIONS
Eric A. B Silva.;. C F. O. Graeff.; . P Nicolucci;. T. G Netto; Faculdade de Filosofia Ciências e
Letras de Ribeirão Preto, Univ. São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto- SP/Brazil
R. F Bianchi; R. M. Farias, D. T. Balogh; Instituto de Física de São Carlos, Univ. São Paulo, São
Carlos-SP, Brazil
Conjugated polymers have nowadays a vast field of technological applications, however there are
still few applications of them in medicine as sensors and detectors of ionizing radiation, for
example. In this work we use a conducting polymer: poly[2-methoxy,5-(2-ethyl-hexyloxy – p phenylenevinylene] (MEH-PPV) for the detection of ionizing radiation, by means of spectroscopic
methods such as: (Uv-vis) absorption, photoluminescence (PL) and (FTIR) infrared absorption. The
samples have being prepared in films, deposited by spin-coating as well as in solution dissolved in
CHCL3. We have found that oxygen plays an important rule in the process of photo-degradation of
the material exposed to ionizing radiation. It was found a displacement in the absorption band
proportional to radiation dose absorbed from 493 nm up 467 nm for a dose between 0 and 45Gy.
This displacement is followed by other changes in the UV-VIS absorption spectra, attributed to the
replacement of C=C by C=O bonds. Both FTIR absorption and photoluminescence spectroscopy
confirmed this substitution. These results suggest the potential of this material as ionizing radiation
detectors.
A-P58
ORGANO-INORGANIC
NANOCOMPOSITE
ALTERNATING
-GERMANIUM
HYDROGENPHOSPHATE LAYERS AND NYLON-6 CHAINS
R. Romano, O. L. Alves, Laboratótio de Química do Estado Sólido, Instituto de Química,
UNICAMP, CP 6154, 13083-970, Campinas, SP, Brasil.
A two-dimensional organo-inorganic nanocomposite was obtained by direct intercalation and
polymerization of the monomer -aminocaproic acid inside the interlayer spaces of -germanium
hydrogenphosphate. The inorganic host was prepared by refluxing germanium oxide and
phosphoric acid during 125 hours, giving rise to a layered material showing an interlayer distance
of 7,8 Å. The intercalation reaction was performed by sealing the host and the monomer inside an
ample and heating the mixture firstly above the melting point of the later (230 oC), and then to the
polymerization temperature (300 oC). The product presented a brown flocculated aspect suggesting
external polymerization of the monomer. The solid was washed with formic acid, an acid capable
of dissolving the external polymer, leading to a white powder. The removed polymer was
characterized as nylon-6 by FTIR spectroscopy, while the white powder showed a new interlayer
distance of 11,2 Å. The increment of 3.4 Å was consistent with the intercalation of a single chain of
this polymer. The FTIR spectroscopy confirms the presence of intercalated chain of nylon-6 by
detecting characteristic bands and the maintenance of the chemical nature of the layered phosphate.
A-P59
THE INFLUENCE OF SOLVENT ANNEALING TIME TO PULLING DOWN OF ADSORBED
CYLINDRICAL MICELLES.
M. A. Pereira-da-Silva, IFSC/USP, CP 369, 13560-970, São Carlos SP Brasil; S. S. Sheiko, Univ N
Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA
Block copolymers form micelles which shape depends on the relation between the degree o
polymerization of the two components. The adsorption of micelles to a solid substrate and the
atomic force microscopy visualization technique give the possibility to image and 3D measure the
micelle shape evolution during pulling down process under influence of solvent annealing. In this
work it was used a block copolymer composed by polystyrene and polyisoprene being different
polymerization degree(PD): PDPS=404 for polystyrene and PDPI=147 for polyisoprene. To obtain a
micelle from a copolymer solution it is needed to find a solvent that is a good solvent for only one
of the two parts of block copolymer. For this work it was chosen the N-heptane, which is a good
solvent for polyisoprene and a bad solvent for polystirene. Therefore, the formed micelle should
show a central portion of polystyrene and a polyisoprene corona. In the present work, PD PS/PDPI =
2.75, we verified that formed micelles are cylinder shaped. This work shows the quantitative shape
evaluation during pulling down process under influence of solvent annealing
A-P60
PALLADIUM-SILICA AND PALLADIUM-TITANIUM COMPOSITES PREPARED BY THE
41
SOL-GEL METHOD: EFFECT OF THE SUPPORT AND OF THE THERMAL TREATMENT
ON THE CATALYTIC ACTIVITY
E. V. Gusevskaya; José Aílton Gonçalves, Departamento de Química, UFMG, Belo Horizonte,
MG; P.A. Robles-Dutenhefner; D. L. Nunes, V. K. Moreira; M. G. Speziali and E. M. B. Sousa,
Centro de Desenvolvimento da Tecnologia Nuclear, CDTN/CNEN, R. Mario Werneck s/n, Campus
Universitário, 30123-970, Belo Horizonte, MG.
Composites of silica and titanium doped with palladium were prepared by the sol-gel method. The
materials were characterized by a powder X-Ray diffraction, nitrogen adsorption and scanning
electronic microscopy. Catalytic behavior of the gels was investigated in the oxidation of limonene
with dioxygen, in acetic acid solutions. For the sample treated at 300 and 1100 oC, the XRD patterns
showed the presence of metallic palladium dispersed in amorphous matrix of the silica.The XRD
patterns for the sample treated at 500 and 900 oC showed the presence of the palladium oxide phase.
The catalysts treated at 500 and 900oC showed a catalytic activity in the limonene oxidation. The
main products are cis and trans- carveyl acetate. The relation between cis/trans carveyl acetate is
influenced by the support.
(CNPQ, FAPEMIG)
A-P61
PALLADIUM-TITANIUM COMPOSITES OBTAINED BY SOL-GEL METHOD: CATALYTIC
ACTIVITY IN THE CICLOOCTADIENE (COD) HYDROGENATION
P. A. Robles-Dutenhefner, D. L. Nunes, V. K. Saraiva, M. G. Speziali and E. M. B. Sousa, Centro
de Desenvolvimento da Tecnologia Nuclear–CDTN/CNEN. Rua Professor Mário Werneck, s/n.
Campus Universitário – Belo Horizonte – MG, CEP 30.123-970, Brazil
In this work, composites of palladium were prepared via sol-gel method. The samples were
obtained from tetraethylorthosilicate (TEOS) or from tetraisopropylorthotitanate (TIOT) and the
palladium was added in the proportions 1 and 3% (w/w). Gels samples were dried at 110 C and
then thermally treated at 300, 500, 900 and 1100 C. The structural characteristics were studied by
scanning electronic microscopy (SEM), X-ray diffraction (XRD) and nitrogen gas adsorption
(BET). The catalytic activity of these materials was tested in the hydrogenation of ciclooctadiene as
a model of polyunsaturated olefin. The samples treated at 300 and 1100 oC showed catalytic activity
due the presence of metallic palladium phase according to the XRD patterns. Although, the
selectivity to ciclooctadiene (monohydrogenated product) have been affected by morphology of the
catalyst.
A-P63
EFFECT OF PRESENCE OF AN ACID CATALYST ON STRUCTURE AND PROPERTIES OF
IRON-DOPED SILOXANE-POLYOXYETHYLENE NANOCOMPOSITES PREPARED BY
SOL-GEL
L. A. Chiavacci, Instituto de Química, UNESP, Araraquara-SP, Brazil; K. Dahmouche, Instituto de
Química, UNESP, Araraquara-SP, Brazil; N.J.O. Silva, Departamento de Física, Universidade de
Aveiro, Aveiro, Portugal; L. D. Carlos, Departamento de Física, Universidade de Aveiro, Aveiro,
Portugal; C.V. Santilli, Instituto de Química, UNESP, Araraquara-SP, Brazil; V. Briois, LURE,
Université Paris-Sud, Orsay, France, A.F. Craievich, Instituto de Física, USP, São Paulo-SP, Brazil.
In this work we investigate the effect of addition of hydrochloric acid (HCl) on the structure and on
the thermal and magnetic properties of iron-doped siloxane-polyoxyethylene (POE) hybrids
prepared by sol-gel route. X-ray powder diffraction (XRD) and X-ray absorption near edge
structure (XANES) results reveal the predominance of ferrihydrite nanoparticles and a mixture of
this phase with FeCl4- species in the hybrid prepared without and with HCl, respectively. Thermal
analysis reveals the existence of two polymeric crystalline phases in the hybrid prepared with HCl,
whereas hybrids prepared without HCl are amorphous. The existence of 105 and 60 Å sized
ferrihydrite nanoparticles was detected by small-angle X-ray scattering (SAXS) analysis of the
composites prepared without and with HCl, respectively. The magnetic results suggest that in both
samples antiferromagnetic nanoparticles coexist with small clusters/isolated ions. In the sample
without HCl addition, larger particles dominate the magnetic behaviour, while the opposite occurs
for the sample prepared using HCl catalyst.
A-P64
SYNTHESIS OF THIOL FUNCTIONALIZED TITANIA-SILICA WITH NANOPORES BY
42
USING POLYMERIC SPHERES AS TEMPLATE
Robson Fernandes de Farias 1 and Cláudio Airoldi 2; 1 Departamento de Química, UFRR 69310270 Boa Vista, RR; 2 Instituto de Química, UNICAMP
The sol-gel process have been successfully employed to the preparation of a series of doublé oxides
with regular nanostructure [1-4], including titânia, due to its many applications, such as
photocatalyst. In this work is reported the synthesis of a titania-silica inorganic-organic hybrid
matrix, functionalized with thiol groups. Such matrix exhibits a porous nanostructure, with pores
from 200 to 500 nm. The matrix is obtained through sol-gel process, by using titanium and thiol
functionalized silicon alkoxydes. The porous nanostructure is achieved by using polymeric spheres
as template. The main purpose of such preparations is to obtain a hybrid matrix with several
functions, able to act as photocalalyst, as well as soft metals sequestrating agent.
[1] R. de Faria, et al., J. Phys. Chem. Solids, in press. [2] R. F. de Farias, Int. J. Inorg. Mater., 2001,
3, 825. [3] R. F. de Farias, J. Non-Cryst. Solids, 2001, 288, 218, [4] R. F. de Farias, C. Airoldi, J.
Solid State Chem., 2001, 158, 134.
A-P65
MAGNETIC PROPERTIES OF ACICULAR Fe1-XREX (RE = Nd, Sm, Eu, Tb; x = 0, 0.05, 0.15)
METALLIC NANOPARTICLES.
L.C. Varanda, M. Jafelicci Jr, Instituto de Química, UNESP, CP 355, Araraquara, 14801-970 SP,
Brazil; G.F. Goya, Instituto de Física, USP, CP 66318, São Paulo 05315-970 SP, Brazil; M.
Imaizumi, Depto de Física FC, UNESP, Av. Luiz Edmundo Carrijo Coube, s/n, Bauru 17033-360
SP, Brazil; M.P. Morales, C.J. Serna, Instituto de Ciencia de Materiales de Madrid, CSIC,
Cantoblanco 28049, Spain.
Acicular monodispersed Fe1-xREx (RE= Nd, Sm, Eu, Tb; x = 0, 0.05, 0.15) metallic nanoparticles
60±5 nm in lenght and axial ratio ~6 have been obtained by reduction of alumina-coated goethite
nanoparticles containing the RE elements under hidrogen flow at 450 oC/10 h. Metallic
nanoparticles were protected against synthering by alumina thin layer on particle surface and
stabilized against surface oxidation with nitrogen-containing ethanol vapor atmosphere at room
temperature. Al and RE additions were obained by sucessive heterocoagulation reactions. Narrow
particle size distribution was observed by TEM and the presence of Al and RE elements were
confirmed by ICP analysis. X-ray diffraction, Mössbauer and magnetization data are in agreement
with the nanosized -Fe core, having a spinel structure, -Fe2O3, on particle surface. Main magnetic
parameters show decreasing in the saturation magnetization and significative increasing in the
coercivity with the increase in the RE compositions. Magnetic properties of the particles, ~40%
smaller than those commercially available, suggest a decrease in the bit-size for high density
magnetic or magneto-optic recording media application.
Fapesp
A-P66
MAGNETIC AND STRUCTURAL PROPERTIES OF NANOESTRUCTURED FeAlNiMn
43
QUATERNARY ALLOY OBTAINED BY HIGH-ENERGY MECHANICAL MILLING
J.F.M. Borges, Departamento de Física - UEPG, Av. Carlos Cavalcanti, 4748, Uvaranas, Ponta
Grossa, PR, Brazil,CEP:84030-900, fborges@uepg.br; C.Larica, Departamento de Física- UFES,
Av.Fernando Ferrari, Campus Goiabeiras, Vitória, ES, Brazil, A. Paesano Jr., Departamento de
Física - UEM, Av. Colombo, 5790 – CEP: 87.020-900, Maringá – PR – Brazil.
Due to a high degree of structural complexity, quaternary alloys present an interesting field for
investigation of phase formation and magnetic behaviour. On the other side, the high-energy ballmilling is a powerful method to prepare supersaturated or granular alloys, amorphous materials and
metastable phases. This technique also provides the conditions for the formation of disordered
crystalline phases with grain size of some nanometers. In this sense, this work shows preliminary
results of a structural and magnetic characterization of a FeAlNiMn quaternary alloy obtained by
high-energy ball-milling. The samples were prepared with high purity iron, aluminum, nickel and
manganese powders, with nominal composition of 25 at.% for each element, and manipulated
inside a glove box under high purity argon atmosphere. At regular intervals during the milling
process, small amounts of the milled samples were collected from the vial. The structural, hyperfine
and magnetic characterizations of the milled materials were performed by X-ray Diffraction,
Vibrating Sample Magnetometry and Mössbauer Spectroscopy, at room temperature. It can be
observed, from the X-ray diffractometry results, a possible interdiffusion of aluminum in the ironnickel alloy. In addition, the broadening of the FeNi diffraction peaks suggests a grain size
reduction with increasing milling time. From the Mössbauer spectra, it was also identified a
paramagnetic contribution, which suggests an interdifusion of aluminium in the iron clusters.
A-P67
UNIDIRECTIONAL
ANISOTROPY
AND
COERCIVITY
ENHANCEMENT
IN
NANOCRYSTALLINE POWDERS OF MnO/-FeCo
Eduardo Padrón Hernández, Daniel R. Cornejo , Sergio M. Rezende; Laboratório de Magnetismo e
Materiais Magnéticos, Departamento de Física, UFPE, 50670-901, Recife, PE, Brasil, PósGraduação em Ciência de Materiais, UFPE CEP 50670-901, Recife, PE, Brasil
Isotropic nanocrystalline heterogeneous magnetic powders of MnO + FeCo were obtained by
mechanical alloying in normal atmosphere from high-purity Mn, Fe and Co elements. After to
milling, the material consists of micrometric particles with exchange-coupled nanocrystalline grains
of MnO and -Fe40Co60 as determined by x-ray diffraction and Mössbauer spectroscopy. The
hysteresis loop obtained by VSM in the as-milled powder showed clear unidirectional anisotropy
phenomena when the temperature of the sample is smaller than the Néel temperature of the MnO,
approximately 120 K. The as-milled powders were cold pressed and annealed at 700 K for different
times in vacuum. Although the exchange-bias field is smaller in the annealed materials, samples
with times of annealing below to three hours show a noticeable improvement of the coercivity,
even to room temperature. The mechanism for this coercivity enhancement effect can be linked to
the substantially high anisotropy field produced by the unidirectional anisotropy, and the favorable
fine structure originated during the milling process. Also, a strong effect the spin wave stiffness
constant of the ferromagnetic FeCo, induced by the antiferromagnetic ordering of the MnO at 120
K was observed. A modified Preisach model was implemented in order to describe the hysteresis
behavior of these exchange-biased materials.
A-P68
DIPOLAR MAGNETIC INTERACTIONS AMONG MAGNETIC WIRES
44
R. Piccin, A. E.P. de Araújo and M. Knobel, Universidade Estadual de Campinas, C.P. 6165,
13.083-970 Campinas, São Paulo, Brazil
In an amorphous magnetic wire produced by quenching melt technique, the magnetic domain
configuration consists of an axial core in a remnant state and an outer shell with a bamboo-like
structure. In the axial direction these wires present single and large Barkhausen jump. Such
characteristics allow us to use several ferromagnetic wires as an analogous of an array of spins. The
stray fields couple the magnetizations of the wires, affecting their magnetic state. Although this
system seems to be rather simple, it displays a variety of interesting aspects that apply to magnetic
systems. In this work, we present a study of the magnetic properties of arrays formed by
Fe77.5Si7.5B15 wires. The array presents jumps and plateau on their hysteresis loops due the
dipolar interaction among the wires [1]. The jumps correspond to the inversion of the core
magnetization in each wire. Theoretical calculations were also performed applying a single model
concerning the effective field, applied field plus the dipolar field produced by the neighbor wires,
during the magnetization process. Such results are discussed in comparison with experimental data.
The authors thank to FAPESP by the financial support.1 - L.C. Sampaio, E.H.C.P. Sinnecker,
G.R.C. Cernicchiaro, M. Knobel, M. Vazquez and J. Velazquez, Phys. Rev. B 61 (13) 8976 (2000).
A-P69
STRUCTURAL AND MAGNETOTRANSPORT PROPERTIES OF Co/SiO2 GRANULAR
MULTILAYERS
J.C. Denardin, L. M. Socolovsky, M. Knobel, Unicamp, PO Box 6165, Campinas (SP) 13083-970 –
Brazil; L.S. Dorneles, L.F. Schelp, Departamento de Física, CCNE, UFSM, Santa Maria, RS,
Brazil
The increase of density requirements in the magnetic data storage has motivated the research of
nanostructured magnetic devices. Granular films consisting of magnetic nanoparticles in an
insulating matrix could present promising features for ultrahigh density magnetic recording media,
respecting the superparamagnetic limit and the effect of dipolar interactions. Cosputtering or
coevaporation is a common method to fabricate these granular solids. It usually results in a random
distribution of clusters in the matrix, with a large dispersion of grain sizes and distances. We have
used an alternative method to fabricate granular multilayer, consisting of successive planes of
nanosized cobalt clusters embedded in SiO2 and produced by sequential deposition. Varying the
nominal thickness of Co and SiO2 layers we obtained several different samples, ranging from
insulating to metallic. Transmission electon microscopy (TEM) images show that the most
insulating samples are composed of periodicaly arranged, and almost monodisperse, Co
nanoparticles with 3nm in diameter. Measurements of resistivity vs. temperature, Hall effect,
magnetoresistance and magnetization were made in the temperature range of 5 - 300 K, and fields
up to 7 T. Relationships between the nanostructure and magnetotransport properties are discussed
and compared with previous results obtained in cosputtered films.
A-P70
PRODUCTION OF MAGNETIC NANOSTRUCTURED MATERIALS USING HOLOGRAPHIC
45
LITHOGRAPHY
L.M. Socolovsky, A.E.P. de Araújo, W. O. Rosa, M. Knobel, E.J. Carvalho and L. Cescato, IFGW
UNICAMP Cx. Postal 6165 CEP 13085-970 Campinas, SP.
The study of the magnetic interactions of the structures in the nanometric scale gives important
contributions to improvement of the nanotechnologies. In this work we present the development of
a technique to grow magnetic periodic patterns using holographic lithography. An advantage of this
technique is the large area of the pattern which can has an aspect ratio smaller than 30 nm in an
area up to of the order of 1000 cm2 [1]. It is based on the selective exposing of a resistive layer to
an interference pattern from two coherent lasers. For Usually to produce metallic samples we need
to combine this technique with electroplating. The idea is to use the fotoresistent resin as the
building block for the magnetic patterned material. We prepared two kinds of samples, one using
Nd-Fe-B powder and the other one with Fe-Cu powder. For the Nd-Fe-B we obtained powder of
500 nm and in the case of iron we use an additional Cu powder to obtain grains smaller than 50 nm.
These powders were mixed with the fotoresine and deposited in a glass substrate using a spinner.
After this we characterize the distribution of the grain dimensions with an electronic scanning
microscope, and the transport and magnetization measurements were made using a SQUID
magnetometer. The effect of the grain size in the line-patterned material on the magnetic properties
will be discussed. The authors thank to FAPESP by the financial support. [1] J.I. Martín et al, J.
Magn. Magn. Mater. 256 (2003) 449.
A-P71
FLASH EVAPORATED PbTe THIN FILMS IN DIFFERENT STOICHIOMETRY FOR
THERMAL INFRARED SENSORS APLICATIONS
J. M. K. Assis1,2, S. Guimarães1; F. C. L. Melo1, N. G. Ferreira1; 1) Instituto Nacional de Pesquisas
Espaciais INPE/LAS, CP 515, 12245-970, São José dos Campos, SP, Brazil; 2) Centro Técnico
Aeroespacial CTA/IAE/AMR, Pça Marechal Eduardo Gomes, 50, Cep 12228-904, São José dos
Campos, SP, Brazil.
Flash Evaporation is an easer and cheaper method for depositing compound such as GaAs and
PbTe when compared to Hot Wall Epitaxy or Molecular Beam Epitaxy techniques. In this process
the constituents have a high vapor pressure and where it is important to maintain the deposit
stoichiometry. PbTe thin films were deposited on silicon and porous silicon substrates. Porous
samples were obtained by stain etching technique on (100) p +- type boron doped wafer, which
produces a nanostructured surface with a lower stress. This procedure is important for relaxing the
natural stress between PbTe films and monocrystalline silicon, mainly due to the lattice mismatch.
Semiconductors PbXTeX-1 stoichiometry in the range of x= 0.504 up to 0.508 are flash evaporated by
keeping evaporation pressure of around 10-5 torr. Similar films were also evaporated on Si wafer
with high resistivity (103 to 6 x 103 .cm) in order to characterize the type of epilayer using Hall
Effect measurements. Film morphology and crystalline quality were also analyzed by Scanning
Electron Microscopy (SEM) and X-Ray Diffraction, respectively. Film thickness may be estimated
with the weigh of the evaporated material and is confirmed by using Fourier Transformed Infrared
(FTIR) and Perfilometry techniques.
A-P72
A-P73
ACCURATE MEASUREMENT OF Ag+/K+ ION-EXCHANGED GLASS WAVEGUIDES BY
EDS, M-LINE AND DNS-B METHODS UP TO THE NEAR-SURFACE REGION
M.B. Pereira, F. Horowitz, PGCIMAT and Instituto de Física, UFRGS, Campus do Vale, CP
15051, 91501-970 Porto Alegre, RS, Brasil
In the description of the refractive index profile of ion-exchanged waveguides, we evaluate the
accuracy of the standard m-line method (micro-probing range) by comparing its results with those
from Energy Dispersion Spectroscopy (EDS) and Direct Near-Surface/Extended Brewster-Pfund
(DNS-B) Method (nano-probing range). Looking at single and double-exchange processes, the
comparison shows three major situations: (i) the m-line accuracy is validated by the other two
methods; (ii) discontinuity of ion-concentration does not allow the assumption of a continuous
refractive index profile; or (iii) although the overall m-line profile is compatible with results from
the other two methods, these may significantly depart by a near-surface inflection – in which case,
the DNS-B Method can be used with the m-line experimental data to produce a more accurate
index profile, including the nanometric near-surface region.
GROWTH OF METALLIC Ag PARTICLES IN FLUOROBORATE GLASSES
46
Luz P. N. Riano1, Marcos A. Couto dos Santos4, Fred Cunha4, Oscar L. Malta2, Petrus Santa Cruz2
and Cid B de Araújo3; 1Programa de Ciência dos Materiais / Universidade Federal de Pernambuco,
50670-901, Recife, PE, Brazil; 2Departamento de Química Fundamental / Universidade Federal de
Pernambuco, 50670-901, Recife, PE, Brazil; 3Departamento de Física / Universidade Federal de
Pernambuco, 50670-901, Recife, PE, Brazil; 4Departamento de Física/UFS, 49100-000, São
Cristóvão, SE, Brazil.
Ag-Eu and Ag-Pr doped fluoroborate glasses have been prepared following the procedure of
powder fusion and thermal annealing. The presence of the Ag species and thermal annealing at 550
and 650 °C originate the growth of metallic Ag particles. The thermal-annealing time and
corresponding particles sizes are different for each doped glass. Optical absorption, excitation and
fluorescence were used for analysis of the plasmon band formation. Electronic microscopy was
used to determine the particle concentration and their size distributions. The techniques used
allowed to identify the presence of silver particles with diameter in the range of 70-200 nm.
A-P74
EVOLUTION OF THE CRYSTALLINITY Ni DOPED ZT
Santos D.M1, Paiva_Santos C.O2, Siqueira J. R.R1, Rubens S.G4, Zaghethe M.A2, Varela J.A2,
Longo E2; 1Universidade Federal do Maranhão (UFMA); São Luís, MA, Brazil; 2 CMDMC Instituto de Química- UNESP, C.Postal 355,14801-970 Araraquara,SP, Brazil. Departamento de
química, UFSCars, C.P.676, 13565-905 São Carlos, São Paulo, Brazil; 3 DMM - CEFET-MA - São
Luís, MA, Brazil
Abstract. Recently, pure and doped zirconium titanate, ZrTiO4, ceramics have attracted great
interest as dielectric resonators for satellite telecommunication ranging from cellular telephones to
global positioning systems and as precursor for synthesis of lead zirconium (PZT). The effects of
Ni concentration on powder of ZT prepared by polymeric precursor method have been studied. Xray diffraction (XRD) and thermogravimetric analysis (TG) showed that powders with high
crystallinity (>90%) are obtained after calcination at 750oC for 3 h. At 550oC, the XRD pattern
shows a broad peak indicating nucleation of the ZT phase. With increasing calcination temperature,
an increase in ZT crystallinity is observed. The Rietveld method was applied to determine
significant variation in the crystallite size and microstrain of Ni doped ZT samples.
Key words: ZT, dielectric, chemical synthesis, XRD, nanostructures.
A-P75
A-P76
NIOBATE EXFOLIATION: A PROMISING ROUTE FOR HOLLOW TUBES SYNTHESIS
A. L. Shiguihara, M. A. Bizeto and V. R. L. Constantino, Departamento de Química Fundamental Instituto de Química, Universidade de São Paulo, CP 26077, 05513-970, São Paulo – SP, Brazil
We have been studying the exfoliation of the layered phase H 2K2Nb6O17 promoted by alkyl amines.
The exfoliated lamellas can coil producing an hollow tubes depending on the pH and ionic strength
of the medium. These tubes have interesting promising applications such as template for porous
mesostructures, nanocasting, membranes for separation etc. In this work, the niobate exfoliation
process was evaluated in aqueous solution of propylamine, n-butylamine and n-hexylamine at
different concentrations. For each experiment two fractions were isolated: a solid fraction that
remains seated after the exfoliated process and an aqueous dispersion of niobate particles. The
characterization of each one of these systems was performed by x-ray diffraction, thermal analysis,
electronic spectroscopy and scanning electron microscopy.
It was observed that the formation of the exfoliated niobate particles dispersion is close related to
the amine / H+-niobate ratio and carbon chain length. For each amine used, there is an optimal ratio
where the exfoliation is more favorable than the intercalation process. The amine also seems to play
an important role in the dispersion stabilization.
Acknowledgments: FAPESP and CNPq
AB INITIO CALCULATION OF THE PHOTOLUMINES-CENCE PROPERTIES OF SrO-
47
DEFICIENT STRONTIUM TITANATE
M. A. dos Santos, E. Orhan, F. M. Pontes C. D. Pinheiro, M. F. C. Gurgel, E. Longo, Laboratório
Interdisciplinar de Eletroquímica e Cerâmica (LIEC), Departamento de Química, Universidade
Federal de São Carlos, São Carlos-SP, Brazil. A Beltrán, J. Andrés, Departamento de Ciències
Experimen-tals, Universitat Jaume I; PO Box 6029, Castelló, Spain
SrO-deficient Sr1-xTiO3-x powders (ST) was synthesized using polymeric precursor method and its
photoluminescence (PL) properties were measured. The samples present an intensive PL at room
temperature, due to a combinated radiative and non radiative decay process. First principles
quantum mechanical technics were used to calculate the electronic structure of two ST periodic
models in the light of the PL results. The first model stands for the crystalline stoichiometric phase,
the second for the deficient one. The comparison of the DOS and band diagrams for both models
gives keys to understand the PL of those deficient ST compounds. (FAPESP-CEPID, CNPq, CAPES)
A-P77
PREPARATION OF POROUS GLASS-CERAMICS WITH CALCIUM ORTHOVANADATE
SKELETON USING VANADIUM PHOSPHATE GLASS AS PRECURSOR
I.O. Mazali, O.L. Alves, Laboratório de Química do Estado Sólido – LQES, IQ – UNICAMP,
Campinas, SP, Brazil
http://lqes.iqm.unicamp.br
The aim of this work was the preparation and characterization of porous glass-ceramics with
skeleton of Ca3(VO4)2. This material has ferroelectric and luminophoric properties. Porous materials
are important in several fields (catalysis, separation sciences, sensors) showing cooperative
interactions when reactions are performed in confined porous ambient. Glass-ceramics (GC) were
prepared by controlled crystallization of the glass system Li2O-V2O5-CaO-P2O5. The production of
the porous glass-ceramic (PGC) involves the acid leaching of the soluble phases, to achieve a porous
structure formed by the insoluble phase. The XRD data suggested the presence of the -Ca2P2O7 (CPP), -Ca2V2O7 (-CPV) and LiCaPO4 phases. The acid leaching of the -CPP and -CPV phases
was confirmed by the absence of bands at 725 cm-1 (IR) and at 880 cm-1 (Raman), respectively. The
PGC exhibit bright green color due to residual -CPV. The IR and Raman data indicate that the
skeleton of the PGC is constituted of Ca3(VO4)2, due to the presence of a very strong band at 898 cm1
, attributed to (V-O) stretching mode of the VO43- groups and, additionally, vanadyl phosphate, as
minor phase. The SEM/EDX micrographs confirmed the porous structure of the monolithic
Ca3(VO4)2. [This is a contribution of Millennium Institute of Complex Materials]
A-P78
A-P79
MORPHOLOGICAL AND STRUCTURAL CHARACTERISTICS OF DIAZODYES AT THE
AIR-WATER INTERFACE. IN-SITU BREWSTER ANGLE MICROSCOPY AND POLARIZED
UV/VIS ANALYSIS
Yamaki, S. B.; Andrade, A. A.; Mendonça, C. R.; Oliveira Jr., N. O.; Instituto de Física de São
Carlos, Universidade de São Paulo, CP 369, CEP 13560-970, São Paulo, SP, Brazil.
+550162713616; Atvars, T. D. Z.; Instituto de Química, Unicamp, Caixa Postal 6154, Campinas,
13084-971, SP, Brazil
The morphological analysis of Langmuir films from the diazodyes Sudan 4 (S4), Sudan 3 (S3) and
Sudan Red (SR), using Brewster angle microscopy (BAM), indicates that stable nonmonomolecular structures are formed at the air/water interface which is denoted as a plateau in the
pressure-area isotherms. Monolayer domains are formed even before the pressure starts to rise,
which grow in size until reaching a condensed monolayer with a contrastless image in the
beginning of the plateau. This behavior resembles that of Langmuir films from simple aromatic
fatty acids. The films from all the azodyes display similar features, according to the surface
potential isotherms and in situ polarized UV/VIS. spectroscopy. The only exception was in the
larger area per molecule occupied by S4 and SR, which is attributed to the presence of CH 3 groups
that cause steric hindrance, and in the organization of diazodye molecules at the air/water interface.
UV/VIS polarized absorption spectroscopy showed that S4 and S3 have a preferential orientation
on the water surface while SR molecules lie isotropically. For the three diazodyes, film absorption
was negligible at very large areas per molecule, only becoming non-zero at a critical area that
coincides with the onset of surface potential. This is attributed to the formation of a H-bonded
network between water molecules and headgroups of the diazodyes.
NANOSTRUCTURAL EVOLUTION AND SPECTRAL IMAGING OF Cu-Al2O3
48
NANOCOMPOSITES PREPARED BY IN-SITU REDUCTION AND THERMO-MECHANICAL
PROCESSED
M. Motta, I.G. Solórzano, E.A. Brocchi, and P.K. Jena , Department of Materials Science and
Metallurgy, Catholic University of Rio de Janeiro (PUC-Rio), Brazil
The uniform dispersion of Al2O3 particles in a copper matrix provides unique characteristics to the
material, enabling its use in high temperature applications. In recent years, it has been experienced
that the physical and mechanical properties of these composites are improved significantly if the
dispersion of the constituents is homogeneous and the particle sizes are in nano-scale. Previous
results have shown that the microstructure of the nanocomposites is formed by a copper matrix,
with grains in the sub-micron scale, and a homogeneous dispersion of Al2O3 particles in nano-scale
size. HRTEM observations have show that the Al2O3 particles are in the range of 10 to 60/70 nm,
but mostly in the lower range up to 30 nm. By comparing a computer generated X-Ray STEM
elemental mapping with experimental ones taken at very high magnifications it is possible to
achieve a better understanding of the real composition of the Cu/Al2O3 interface and also to assess
the formation of a third phase in the consolidated material. Finally, studies on thermo-mechanical
processing have shown that, even after cold-rolling down to 50% of reduction in thickness and
annealing at 900oC for one hour, a high density of dislocations and sub-grain boundaries have still
remained in the microstructure. This is an important information about the structural stability of the
composite when considering possible future technological applications.
A-P80
CRYSTALLOGRAPHIC PROPERTIES OF THE KSr2Nb5O15 SOLID SOLUTION
M. A. L. Nobre, C. X. Cardoso, S. Lanfredi, Faculdade de Ciências e Tecnologia – FCT,
Universidade Estadual Paulista- UNESP, C. P. 467, CEP 19060-900, Presidente Prudente, SP,
Brazil
The rapid progress in microwave telecommunications satellite broadcasting and other related
devices has demanded the search of new ferroelectric materials for industrial applications. This
work presents the synthesis and structural characterization of a lead-free ferroelectric ceramic
derived from KSr2Nb5O15. Nanostructured KSr2Nb5O15 oxide was synthesized by the polymeric
precursor method, a chemical synthesis route derived from Pechini’s method. The thermal
decomposition of the precursor was followed by differential analysis (DTA) and differential
scanning calorimeter (DSC). The XRD pattern of the calcined powder at 1000 oC were performed
over the angular range 5  2  120o with a 0.02o step and a fixed counting time of 30 s. The XRD
data were analyzed by Rietveld refinements using the software FullProf. The data obtained showed
a tetragonal system with the tetragonal tungsten bronze structure – TTB type (a = 12.4577 (3) Å
and c = 3.9403 (9) Å, V = 611,52 (2) Å3. The refinements were determined on the basis of a polar
group P4bm. The best refinements were provided with pentagonal site occupied by equal quantities
of K+ and Sr2+ ions and square site occupied by Sr2+ ion.
A-P81
NANOSIZED BaSO4 POWDER FOR Ba2Ti9O20 CERAMICS FABRICATION
49
Yu. Koldayeva, M. C. A. Nono, C. Kuranaga, S. T. Fonseca, Associated Laboratory of Sensors and
Materials (LAS), National Institute for Space Research (INPE), São José dos Campos, SP, C.P. 515
- 12201-970, Brazil, (P. J. Castro, Associated Laboratory of Plasma (LAP), São José dos Campos,
SP, C.P. 515 - 12201-970, Brazil.)
Barium nanotitanate (Ba2Ti9O20) ceramic is good to be used as dielectric resonators (DRs) for
microwave applications because of it high quality factor, high dielectric constant, and a low
temperature coefficient of resonant frequency. It is complicate to obtain Ba2Ti9O20 stable crystalline
phase near the room temperature due to the narrowness of it phase-pure stability region. As usual
the BaCO3 and TiO2 powders are used to obtain barium nanotitanate ceramics but the size and
shape anisotropy of BaCO3 particles difficult phase formation as well. In this work the BaSO 4 and
TiO2 powders were mixed in estequiometric proportions to obtain the Ba2Ti9O20 ceramic and the
influence of different sintering temperatures and times on the phase formation and microstructure
were studied. BaSO4 powder was obtained from BaCO3 by precipitation. The result was a drastic
reduction of medium size of particles from 10 m to less than 500 nm. BaSO4 and TiO2 dried
mixture was pressed on uniaxial and isostatic press to form cylindrical pellets and then they were
synthesized and sintered at the same stage in air atmosphere. This raw material substitution permits
diminish of the sintering temperature and time. The finished ceramics were characterized by
scanning electronic microscopy (SEM) and X-ray diffraction (XRD).
A-P82
MICROSTRUCTURES AND MECHANICAL PROPERTIES OF CE-TZP CERAMICS FROM
MIXTURES OF NANO AND MICROSIZED POWDERS
M. C. A. Nono Associated Laboratory of Sensors and Materials (LAS), National Institute for Space
Research (INPE), São José dos Campos, SP, C.P. 515 - 12201-970, Brazil
The fabrication of a nanostructured ceramic materials will undoubtedly involves preparing of a
nanosized ceramic powder, which may then then be consolidated to a high sintered density at a
relatively lower sintering temperature. Many of desirable microstructural features may therefore be
realized, including the improved sintered density, refined grain size, narrow grain size distribution
and minimized degree of structural defects. In this work are reported and discussed the
microstructures and mechanical properties of a tetragonal ceria-zirconia (Ce-TZP) ceramics
prepared from mixtures of nanosized and microsized powders. These mixtures These powders were
obtained from dehydratation with isopropilic and ethylic alcohols of zirconium an cerium
coprecipitated sulphates (liquid-liquid extraction). Sintered ceramics were fabricated from powder
mixtures containing different CeO2 content (8 to 16 mol %). The microstructures of the sintered
ceramic was analysed by SEM and X-rays diffraction. The mechanical properties of the sintered
ceramic were measured by Vickers indentation to obtain the surface microhardness and fracture
toughness, and 4-point bending test to get the rupture strength values. These results were correlated
with tetragonal (t) to monoclinic (m) phase transformation. These results were discussed and
compared to those published in international literature.
A-P83
ORGANOMETALLIC
CHEMICAL
50
VAPOR
DEPOSITION
OF
COMPOUND
SEMICONDUCTORS
M. Grassi1, A.A.A. de Queiroz1, A .H. A .Bressiani2, J.C. Bressiani2 1DFQ/ICI, Universidade
Federal de Itajubá, alencar@efei.br; 2CCTEM, Instituto de Pesquisas Energéticas e Nucleares.
The organomethallic chemical vapor deposition (OMCVD) of compound semiconductors
represents the one of the most important research area of nanotechnology. It provides an efficient
synthetic rout for the production of materials in nanometric scale with desirable physical properties,
which are often inaccessible by conventional materials synthesis. In this work, we report the
development of sulfonated polystyrene (PSSO3H) as a new precursor to OMCVD techniques. The
mechanisms of the interaction macromolecule-metal complex were investigated using quantum
chemistry calculations. Semiempirical calculations for the PSSO3H and PSSO3H:M (M=
Ni+2,Zn+2,Cu+2) charge transfer complexes using the PM3 parametrization were performed with the
program MOPAC 2000. The PSSO3H:M structures were obtained by direct minimization of the
total energies in a classical molecular mechanic methods with respect to all geometrc variables, i.e.
bond lengths and angles. The experimental results suggest a growth mechanism that involves
transfer of hydrogen from the polymeric ligand to surface resulting in the oxide crystal growth at
polymeric interface (SEM, Phillips XL30) micrograph. The quantum chemical calculations indicate
that the stability of the polymer-metal complexes increase in the order Zn+2>Cu+2>Ni+2. This results
leads to the known of the decomposition chemistry on the surface leading to a better control of
impurities and providing the tools necessary to quantify OMCVD reaction mechanisms.
A-P84
SYNTHESIS AND CHARACTERIZATION OF NANOSTRUTURED THIN FILMS
P.S. Gouveia1, N.L.V. Carreño1, M. Mescote1, G.F. Goya2, R.F. Jardim2, E.R. Leite1, E.
Longo1; 1 CMDMC-LIEC, Department of Chemistry, UFSCar, Via Washington Luiz, km 235, São
Carlos, SP, Brazil; 2 institute of Physics, USP, SP, Brazil; P.S. Gouveia, CMDMC-LIEC,
Department of Chemistry, UFSCar, Via Washington Luiz, Km 235, CP 13565-905, São Carlos, SP,
Brazil
This work describes a new route for the preparation of Ni-nanoparticles embedded in a SiO2 matrix
thin film. We have produced Ni-SiO2 films with 3% and 6% wt of Ni by the polymeric precursor
method, which were deposited on Si(100) substrates by spin coating, and annealed at a
temperatures of 550 oC in a N2 atmosphere. X-Ray Diffraction, Scanning Electron Microscopy,
Atomic Force Microscopy and Magnetization characterization were performed in these films.
The microstructural characterization suggested that these films display Ni-nanoparticles with an
average diameter of ~3nm. Magnetization measurements (ZFC and FC processes) revealed a
blocking temperature, TB close to 7.2 K for the most diluted sample. Also, magnetization data
showed the expected scaling of the M/Ms vs. H/T curves for superparamagnetic particles.
A-P85
INFLUENCE OF HEAT TREATMENT ON CERAMIC POWDERS OF COBALT FERRITES
51
N. D. S. Mohallem, Laboratório de Materiais, Depto de Química, UFMG, 31270-901, Belo
Horizonte, MG, Brazil; Walter de Brito, CDTN/CNEN, 31270-901, Belo Horizonte, MG, Brazil,
Juliana B Silva, CDTN/CNEN, 31270-901, Belo Horizonte, MG, Brazil.
Nanosized crystalline CoFe2O4 powder was synthesized by a coprecipitation process using metallic
nitrates in aqueous media as precursors and NH4OH as precipitant. The as-prepared powder was
washed, dried at 80°C and heat-treated at various temperatures for 2 hours for crystallization of the
material. The influence of heat treatment on the structure, texture and saturation magnetization was
studied. The average crystallite size of the powders varied from 17 to 100 nm with annealing
temperature and the corresponding saturation magnetization (Ms) values ranged from 20 to 60
emu/g. The material obtained under optimal condition by this process reached a value of
spontaneous magnetization around of 90% (80 emu/g) of the theoretical magnetization of a
stoichiometric ferrite.
A-P86
CORRELATION BETWEEN TEXTURAL AND MORPHOLOGICAL PROPERTIES OF
ALUMINA PREPARED BY VARIOUS PROCESSES
Cristina Fontes Diniz, Laboratório de Materiais, Depto de Química, UFMG, 31270-901, Belo
Horizonte, MG, Brazil; N. D. S. Mohallem, Laboratório de Materiais, Depto de Química, UFMG,
31270-901, Belo Horizonte, MG, Brazil.
Alumina (Al2O3) is a well-known ceramic material used as refractory, coating material, and
ceramic composite matrix, among others. Recently, porous alumina has attracted much attention
due to its potential use in nanotechnology. In this work, we synthesized porous alumina by
coprecipitation and sol-gel processes, using variations in the drying procedures (liofilization,
controlled, and hypercritic drying) and temperatures. The structural, textural and morphological
changes in the obtained material were studied by powder X-ray diffraction, infrared spectroscopy,
scanning electronic microscopy, nitrogen adsorption, and thermal analysis.
A-P87
A-P88
PREPARATION OF SiO2-TiO2 FILMS CONTAINING CdS NANOPARTICLES
Costa, V. C., Santos, A.M., Lameiras F. S., Center of Nuclear Technology Development, CP 941,
Belo Horizonte, MG, Brazil, 30123-970; Sansiviero, M. T. Department of Chemistry, UFMG,
Pampulha, Belo Horizonte, Brazil; Simões, A. B., Vasconcelos, W. L. Mettalurgical and Materials
Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
Titania-silica materials have been extensively used as catalysts and supports for a wide variety of
reactions. In the present work, silica-titania thin films containing up to 20 mol% TiO 2 were
prepared by sol-gel process. The solutions were prepared through a two-stage hydrolysis, where
tetraethoxysilane (TEOS) and titanium isopropoxide (Ti(OPr) 4) were used as precursors. Small
sized CdS particles were incorporated in the silica-titania films by a complex formation reaction
using cadmium acetate and thiourea, SC(NH2)2. The films were thermally treated at 300-400 oC.
The preparation process and properties of the films were investigated through UV-Visible
absorption, IR and Raman spectroscopy, X-ray diffraction and atomic force microscopy (AFM)
HIGH-PRESSURE ANNELING EFFECT ON THE STRUCTURAL PROPERTIES OF
52
NANOSTRUCTUREDPbTiO3 COMPOUNDS
M. T. Escote, E. R. Camargo, E. R. Leite, and E. Longo, CMDMC – LIEC, Depto. De Química,
UFSCar, São Carlos, SP, Brazil; R. F. Jardim, Instituto de Física, USP , São Paulo, SP, Brazil.
We have produced polycrystalline PbTiO3 (PT) by the called oxidant peroxo method (OPM).
These compounds were heat-treated at temperatures varying from 450 to 700 °C in air and under
oxygen pressure of PO2 ~ 60 bar. The structural and microstructural properties were characterized
by X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron
microscopy (HR-TEM). The XRD and Raman spectroscopy revealed that the oxygen pressure
annealing enhances the thermal stability of the amorphous solids. In fact, a comparison among the
XRD data shows that the application of the external pressure results in increase of the
crystallization temperature. Moreover, HR-TEM images, carry out after each heat treatment,
suggested that we have produced nanostructured PT compounds with size particles of the order of 7
to 14 nm. Through these images, we believe that these samples displayed two different crystalline
phases: (a) pyroclore Pb2Ti2O6 meta-stable phase for the samples heat-treated at low temperature (T
~ 450 °C); and (b) the PT for sample annealed at 700 °C.
A-P89
LACTOSE INTERCALATION IN THE NANOMETRIC INTERLAYER SPACE OF A
SMECTITIC CLAY MINERAL
L. C. Morais, Departamento de Engenharia Química-Escola Politécnica-USP, Rua do Lago250,
Prédio Semi-Industrial, Cidade Universitária, São Paulo, Brazil, leandro.morais@poli.usp.br
F.R. Valenzuela Díaz, Laboratório de Matérias-Primas Particulados e Sólidos Não-Metálicos,
PoliUSP, São Paulo, Brazil.: e-mail: frrvdiaz@usp.br; J. Dweck, Laboratório de Análises
Térmicas, Bloco E do CET – DPI, Fundos, Escola de Química, UFRJ, Rio de Janeiro, Brazil.: email: dweck@eq.ufrj.br; P. M. Büchler, Departamento de Engenharia Química(PQI-USP),
PoliUSP, São Paulo, Brazil. e-mail: pedro.buchler@poli.usp.br
The treatment of the effluents of dairy product industries containing lactose is done by a biological
process, which reduces considerably the original amount of that sugar. Although the final residual
content of lactose after treatment is small, it may cause the eutrophication and/or the
superfertylization of the water, which provokes vegetation growth on the water surface, hindering
the navigability of the rivers where the treated effluent is thrown, and decreasing significantly the
content of the dissolved oxygen necessary to the life of the fishes therein.
The objective of this paper is to present a study of the intercalation of lactose in the nanometric
interlayer space of a smectitic clay, and to compare these results with those of the adsorption of the
residual lactose in aqueous solutions by an organophylic clay, which was prepared from a sodium
bentonite, after an ion exchange procedure with an organic cation of a quaternary ammonium
chloride. This chemical modification transforms the originally hydrophilic clay to an organophilic
one, as well as it changes the characteristics and sorption properties of the nanometric interlayer
space of the clay structure. The equilibrium lactose concentrations after organophilic clay sorption
are measured by the change of the total organic carbon (TOC) present in the original aqueous
solution . The characterization of the lactose, the original clay and the organophilic clay is done by
thermal analysis techniques and X-ray diffraction.
A-P90
BRAZILIAN ORGANOCLAYS AS NANOSTRUCTURED SORVENTES OF PETROLEUM
53
DERIVED HIDROCARBONS
K. R. O. Pereira1, R. A. Hanna 1, M. M. G. Ramos Vianna 1, M. G. F. Rodrigues 2, F. R.
Valenzuela-Díaz 1; 1 Laboratório de Matérias-Primas Particuladas e Sólidos Não Metálicos, Rua do
Lago, 250, Cidade Universitária, São Paulo, Brazil; 2 Laboratório de Novos Materiais, Rua Aprígio
Veloso, 882, Campina Grande, Brazil
Smectitic clays, also known as bentonites, find several different industrial uses, being the largest
group in terms of utilization and the most interesting group of clays minerals. However, it is
necessary to submit them to chemical treatments to develop their real potentialities. Polluted areas
by organic pollutants are of great concern in terms of environmental control. Several types of
sorvent materials have been studied to remediate these areas. Among them, organoclays obtained
from smectitic clays and quaternary ammonium salts, containing at least a 12-carbon chain between
their layers, represent a featured promising material. For the preparation of the organophilic clays
was used a smectitic clay from Boa Vista city, Paraíba State, and two quaternary ammonium salts.
The obtained materials were characterized by X-ray diffraction and infrared spectroscopy. The
results showed good capability for the adsorption of gasoline, toluene, diesel fuel and kerosene.
A-P91
MOKE STUDY OF Fe MONOLAYERS ON ZnSe(001)/GaAs(001)
M. D. Martins, P. L. Gastelois, L. H. F. Andrade, W.A.A. Macedo, Lab. de Física Aplicada, Centro
de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Brazil; V. H. Etgens, LMCP,
Universitè Paris VI-VII, Paris, France.
Hybrid ferromagnetic/semiconductor materials have attracted great attention to new spintronic
devices. The Fe-ZnSe is one promising system due to the good quality of epilayers and absence of
reactivity at the interface. We have studied the structural and magnetic properties of ultrathin Fe
films, from the submonolayer regime up to 10 monolayers thick grown by molecular beam epitaxy
on ZnSe(001). Fe monolayers have been deposited at 180 oC on c(2x2) Zn-rich ZnSe/GaAs(001)
surfaces. The substrate, growth and structure of the Fe films were well characterized by reflection
high-energy electron diffraction (RHEED), Auger electron spectroscopy, and low energy electron
diffraction (LEED). The magnetic properties were determined by magneto-optical Kerr effect
(MOKE), in situ, in ultrahigh vacuum. We have studied the thickness dependence of the MOKE
hysteresis loops in the longitudinal geometry, at 150 K and under magnetic fields up to 0.1 T
applied along the [110] and [1-10] directions of the ZnSe(001). Clear hysteretic loops were
obtained only starting from ~4 monolayers (ML) Fe. The onset of an uniaxial magnetic anisotropy
with [110] magnetic easy axis has been observed at ~ 7 ML Fe. Our results suggest that the in-plane
magnetic anisotropy develops after partial relaxation of the in-plane structural anisotropy, as
determined by RHEED.
A-P92
IMPEDANCE SPECTROSCOPY ANALYSIS OF BIMEVOX SOLID ELECTROLYTES
C. H. Hervoches and R. Muccillo, Centro Multidisciplinar para o Desenvolvimento de Materiais
Cerâmicos, CCTM - Instituto de Pesquisas Energéticas e Nucleares, Av. Lineu Prestes 2242,
Cidade Universitária, São Paulo, SP, 05508-900, Brazil
The so-called BIMEVOXes are a group of fast oxide ion conductors at fairly low temperature.
They are structurally related to the Aurivillius materials consisting of perovskite blocks sandwiched
between fluorite-like (Bi2O2)2+ sheets. The parent compound Bi4V2O11 has three structural domains
,  and , the last one presenting high ionic conductivity between 840 and 1150 K. Here we
present results about several BIMEVOX materials prepared by the citrate and combustion
techniques. These methods present the advantage over solid state reaction of lower processing
temperature and the formation of materials with finer grains size. Different sintering processes
allowed us to synthesize materials with various grains size. The physical properties of the
BIMEVOX materials prepared have been studied using impedance spectroscopy (IS) and compared
with results obtained by other methods of synthesis. The influence of grain size on the conductivity
and relative influence of the bulk and grain boundaries have been analyzed.
A-P93
EXPERIMENTAL AND THEORETICAL STUDY OF POROUS SILICON ELASTIC
54
PROPERTIES
A. B. S. Camussi, R. J. M. da Fonseca, Grupo de Ótica e Propriedades Físicas de Materiais – DEQ,
Instituto de Física, UERJ, R. São Francisco Xavier, 524 sala D-3030, 20550-013 Rio de Janeiro,
Brazil; J. Attal, Laboratoire d’Analyse des Interfaces et de Nanophysique – URA CNRS 1881 Université Montpellier II 34095, Montpellier CEDEX 05 – France
Porous silicon (PS) has been extensively studied since it exhibits strong visible luminescence at
room temperature, suggesting promising applications in silicon-based optoeletronic devices,
dielectric isolation of integrated circuits and epitaxial growth of heterostructures on Si substrate.
Great part of this research has been focussed in the investigation of optical and electronic properties
of PS layers. However, for many pratical applications, it is important to characterize the mechanical
behaviour of them. For this purpose, we apply the scanning acoustic microscopy (acoustic imaging
and V(z) signature) to measure the acoustic wave velocities and elastic characteristics of this
material (Young’s modulus and Poisson coefficient) with different porosity. This is a powerful
technique for non-destructive and non-contact measurements, specially when small volumes are
involved. The investigated samples have a porosity range of 20% to 60% and thickness of 30 µm to
120 µm. So, in this work, we present V(z) curves and acoustical images and a comparision between
theoretical and experimental results using Biot’s theory which describes the propagation of elastic
waves in a system composed of a porous elastic solid saturated by a fluid.
A-P94
MORPHOLOGICAL CHARACTERIZATION OF NANOPARTICLES OF SnO2
WITH
ADDITIVES Ni AND Fe
Pilar Hidalgo1 Douglas Gouvêa1 Daniela Zanchet2, Jefferson Bettini2 ; 1Department of
Metallurgical and Materials Engineering- USP. Av. Professor Mello Moraes, 2463, 05580-900. S.P.
Brazil; 2 Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil.
Recently studies on ceramic powders with additives have shown that microestrutural modifications
take place when the system reaches the lowest surface energy. It has been suggested that this
decrease is related to the segregation of the additive onto the surface powder.
This work presents the study of segregation of additives in two interesting system: Fe 2O3-SnO2 and
NiO-SnO2, prepared by Pechini´s method. Morphological analysis was performed using
Transmission Electron Microscopic (TEM), X-ray diffraction (XRD), Specific Surface Area (S BET)
and Mössbauer Spectroscopy.
The segregation of Fe or Ni ions to the surface of the matrix phase (SnO 2) was observed in
specimens with 30 mol% of additive. Above that (50 and 80 mol %), it has been observed for both
Fe and Ni the nucleation of a second phase: Fe3O4 and NiO respectively. The analysis revealed that
SnO2 has a strong influence on the structure of the second phase, suggesting an epitaxial process.
A-P95
PREPARATION OF POROUS GLASS-CERAMICS WITH CALCIUM ORTHOVANADATE
55
SKELETON USING VANADIUM PHOSPHATE GLASS AS PRECURSOR
I.O. Mazali, O.L. Alves, Laboratório de Química do Estado Sólido – LQES; IQ – UNICAMP,
Campinas, SP, Brazil
http://lqes.iqm.unicamp.br
The aim of this work was the preparation and characterization of porous glass-ceramics with
skeleton of Ca3(VO4)2. This material has ferroelectric and luminophoric properties. Porous materials
are important in several fields (catalysis, separation sciences, sensors) showing cooperative
interactions when reactions are performed in confined porous ambient. Glass-ceramics (GC) were
prepared by controlled crystallization of the glass system Li2O-V2O5-CaO-P2O5. The production of
the porous glass-ceramic (PGC) involves the acid leaching of the soluble phases, to achieve a porous
structure formed by the insoluble phase. The XRD data suggested the presence of the -Ca2P2O7 (CPP), -Ca2V2O7 (-CPV) and LiCaPO4 phases. The acid leaching of the -CPP and -CPV phases
was confirmed by the absence of bands at 725 cm-1 (IR) and at 880 cm-1 (Raman), respectively. The
PGC exhibit bright green color due to residual -CPV. The IR and Raman data indicate that the
skeleton of the PGC is constituted of Ca3(VO4)2, due to the presence of a very strong band at 898 cm1
, attributed to (V-O) stretching mode of the VO43- groups and, additionally, vanadyl phosphate, as
minor phase. The SEM/EDX micrographs confirmed the porous structure of the monolithic
Ca3(VO4)2. [This is a contribution of Millennium Institute of Complex Materials]
56