ASEVA WORKSHOPS 2008
WS-22:
Gas and Radiation
Sensors: Properties,
Characterisation. Thin
Films Based Sensors
Salamanca, Spain. July 7-9, 2008
Faculty of Science- University of Salamanca
Abstract Book
Editors:
K. Schierbaum
University of Düsseldorff
J. L. de Segovia
Instituto de Ciencia de Materiales
1
ASEVA Copyright-2008
2
FOREWORD
The goal of the workshop is to review the state-of-the art of thin
film sensors for detection of gases and electromagnetic radiation and
to reflect the latest advances in materials´ developments and
deposition technologies.
WS-22 will feature six invited lectures by leading researchers in the
field as well as oral and poster sessions.
The workshop aims to bring together researchers from the sensor
community and from related fields of thin film growth and
characterisation techniques. It intends to be a forum for the
exchange of recent scientific developments and for the discussion of
new trends. The scope of the workshop includes all aspects of gas
and radiation sensing from fundamental and applied research.
Topics of primary interest include
Preparation and characterisation of sensing films and
nanostructures, Growth and epitaxy of sensing materials,
Electrical and sensing properties,
Multiple methods for the characterisation of complex micro- and
nanostructures,
Functional materials through doping,
Ultrathin films for sensors, applications to novel devices
Properties of new materials.
3
notes
4
MoM-INV-1
CONCEPTS FOR CARBON NANOTUBE SENSORS
Christofer Hierold, Thomas Helbling, Lukas Durrer, Matthias Muoth,
and Nanosystems, Department of Mechanical and
Cosmin Roman, Micro
Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland
Carbon Nanotubes (CNT) are intensively studied as a new functional material for sensors, nanosystems and electronic
systems. Single-walled carbon nanotubes (SWNTs) for example show unique mechanical and electromechanical properties
and they change electronic properties by interacting with the environment (e.g. for chemical and biochemical sensing).
Therefore CNTs are very promising candidates for active elements in future nanoscaled transducers. Concepts for carbon
nanotube sensors for mechanical and chemical quantities are presented. We focus on single-walled carbon nanotubes as
"simple" macro molecular functional structures with an option for low scale integration in micro and nano
electromechanical systems (MEMS and NEMS).
Transducer
Type Model
Sensitivity
Nano electromechanical
Piezoresistance of SWNTs by straindependent band gap in semiconducting
and small band gap SWNTs
Gauge factor depends on the tube’s
chirality: gauge factors up to 3000
measured in pre-strained tubes possible.
Nano balance in preferably pre-strained
SWNT resonators
Resonance frequency change due to mass
increase by adsorbed gas molecules; low
SWNT’s mass results in high sensitivity;
SWNT structural control not important
Adsorption of molecules on the tube’s
surface or chemisorption at defect sites
and charge transfer, resulting in Fermi
level shift
Shift of threshold voltage of gated SWNT
transistors; high surface to volume ratio
results in high sensitivity at very low
power consumption for room
temperature measurements; radius
control of the SWNT enough for bandgap
control.
Adsorption of molecules on metal
contacts or gate structures, resulting in
work function modulation of contacts or
gates and thus modulating Schottky
barriers on the tubes’ contacts or
threshold voltage shifts
Shift of transistor conductance or
threshold voltage shift of gated SWNT
transistors; low power consumption for
room temperature measurement; radius
control of the SWNT enough for bandgap
control.
Nano chemical
Nano chemical / biochemical
Acknowledgments
We thank the operational teams of ETH Zurich’s clean room facilities (FIRST and FIRSTCLA) and EMEZ for support, Prof. Victor Bright, University of Colorado at Boulder, for
many helpful discussions and for supporting the project with ALD alumina substrates.
We also thank Dr. Siegmar Roth and Dirk Obergfell from MPI of Solid State Research,
Stuttgart, for support with SWNTs and SWNT dispersion. Support of the nanotransducers
research program by ETH Zurich (TH 18/03-1, TH 13/05-3) and by Swiss National Science
Foundation (20021-108059/1) is gratefully acknowledged.
5
notes
6
MoM-IA-1
FIBER OPTIC NANOSENSORS BASED ON SINGLE WALL CARBON
NANOTUBES: PERSPECTIVES AND CHALLENGES
Andrea Cusano and Marco Consales. Optoelectronic Division – Engineering
University of Sannio, C.so Garibaldi 107, 82100 Benevento, Italy
Michele Giordano. Institute for Composite and Biomedical Materials, National
(IMCB-CNR), P.le Enrico Fermi 1, 80055 Porti, Italy.
Department,
Research
Council
This contribution reviews the development of high performance opto-chemical nanosensors based on the integration of
carbon nanotubes as advanced sensitive coatings with the optical fiber technology. The Langmuir-Blodgett technique has
been chosen for the deposition of nanometer-scale thin films of single-walled carbon nanotubes (SWCNTs) upon the distal
end of standard silica optical fibers, in order to form a low finesse Fabry-Perot (FP) interferometer working in reflectometric
configuration. The sensing principle relies on the possibility provided by this configuration to monitor the concentration of
chemicals present within the environment through changes in the overlay refractive index and thickness induced by its
interaction with the gas molecules. An extensive investigation of structural and morphological characteristics of the SWCNT
overlays has been carried out by means of X-ray diffraction and Raman Spectroscopy analyses, High-Resolution
Transmission Electron Microscopy and Scanning Electron Microscopy observations, which confirmed their nanostructured
dimensions as well as the successful integration with the optical fibers. The excellent sensing capabilities of the realized
chemical nanosensors have been demonstrated against gaseous H2 at cryogenic temperature (particularly suitable for
aerospace applications), for which detection limits below the explosion limit in air (4%) have been observed, and against
NO2 in air at room temperature where ppm and sub-ppm detection limits have been estimated. In addition, in both cases
the sensors demonstrated good recovery and reversibility features as well as fast responses. Furthermore, novel SWCNTsbased nanocomposites have also been exploited as sensitive fiber optic coatings to enhance the sensing performance and
improve the adhesion of carbon nanotubes to the fiber surface. The experimental results revealed the strong potentiality
of such nanocomposites to be successfully employed for chemical sensing. Finally, the peculiarity of SWCNTs-based optochemical nanosensors to exhibit responses of opposite sign in case of gases or volatile organic compound detection could
be usefully exploited to improve the discrimination ability of the proposed fiber optic transducers, thus enabling the
realization of high performance optoelectronic noses.
7
notes
8
MoM-IA-3
NANOSTRUCTURE MATERIALS FOR SENSORS
L. Lozzi and S. Santucci. Department of Physics, University of L’Aquila, I-67100 L’Aquila, Italy
Since the discovery of the sensing properties of carbon nanotubes there was a strong interest in the research activities for
the realization of new sensors based on nanostructured materials [1].
In this talk the activity on this field that we are carrying out using different nanostructured materials will be reviewed.
Using supported multiwalled carbon nanotubes (MWCNT), grown on a patterned substrate by means of Plasma Enhanced
Chemical Vapour Deposition (PECVD), we prepared an NO2 sensor with quite high sensitivity (up to 10 ppb) [2]. On these
MWCNT we studied, using soft X-ray photoemission spectroscopy, the effects on the density of states close to the Fermi
edge of the adsorption of NO2 molecules, showing a decrease of these states when the MWCNT are exposed to these
molecules [3]. This spectroscopic evidence, supported by theoretical calculations that underline the effects of structural
defects on the MWCNT walls, is in agreement with the variation of the electrical conductivity of these sensors.
More recently we started to prepare new sensor devices based on nanostrutured metal oxides, in particular WO3
nanowires. Using the electrospinning technique we deposited onto a patterned substrate tungsten oxide nanofibers, having
a mean diameter of about 100-200 nm. Because of their very high surface-to-volume ratio, these nanofibers show a quite
high sensitivity. These nanofibers show a polycrystalline structure and a stoichiometric chemical composition [4].
Finally the evolution of this deposition technique, the near-filed electrospinning, that we are using for growing well ordered
metal oxide nanofibers, will be also presented [5].
J. Kong, N.R. Franklin, C. Zhou, M.G. Chapline, S. Peng, K. Cho, and H. Dai, Science 287, 622 (2000).
L. Valentini, I. Armentano, J.M. Kenny, C. Cantalini, L. Lozzi, and S. Santucci, Appl. Phys. Lett. 82, 961 (2003).
L. Lozzi, S. Picozzi, I. Armentano, L. Valentini, J.M. Kenny, S. La Rosa, M. Coreno, M. De Simone, B. Delley, and S. Santucci, J.
Chem. Phys. 123, 034702 (2005).
S. Piperno, M. Passacantando, S. Santucci, L. Lozzi, and S. La Rosa, J. Appl. Phys. 101, 124504 (2007).
D. Sun, C. Chang, S. Li, and L. Lin, Nano Lett. 6, 839 (2006).
9
notes
10
Mo-M-INV-2 Mathur
11
notes
12
MoM-IA-4
INTEGRATION OF METAL OXIDE NANOWIRES IN ELECTRONIC DEVICES FOR
GAS SENSING AND UV PHOTODETECTION
R. Jimenez-Diaz.
EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat de
Barcelona, Barcelona, Spain.
J. D. Prades. EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat de
Barcelona,
Barcelona, Spain.
F. Hernandez-Ramirez. EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat
de Barcelona, Barcelona, Spain.
S. Barth.
Department of Nanocrystalline Materials and Thin Film Systems, Leibniz
Institute of New Materials, Saarbruecken, Germany. Department of Chemistry, Wuerburg
University, Wuerzburg, Germany.
O. Casals.
EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat de Barcelona,
Barcelona, Spain.
A. Romano-Rodriguez.
EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat
de Barcelona, Barcelona, Spain.
Juan Ramon Morante.
EME/XaRMAE/IN2UB, Departament d’Electrònica, Universitat
de Barcelona, Barcelona, Spain.
S. Mathur. Department of Nanocrystalline Materials and Thin Film Systems, Leibniz
Institute of New Materials, Saarbruecken, Germany. Department of Chemistry, Wuerburg
University, Wuerzburg, Germany.
Research on 1-D nanomaterials is a subject of great interest due to the possibility of using them as building blocks of
devices with innovative properties. However, the development of new nanodevices has been restrained by the difficulties in
the formation of electrical contacts with high stability, low contact resistances and ohmic behaviour. In this work, we
present the electrical access to individual nanomaterials by means of the fabrication of platinum nanocontacts with a
Focused Ion Beam (FIB) system, following a process which combines both electron and ion assisted depositions. The
characterisation of these contacts is analyzed to determine the optimal configuration for the measurement of the
electrical, optical and gas sensing properties of metal oxide nanowires.
In order to modify the response of these nanowire-based sensors, some nanowires are dispersed over a microhotplate with
interdigitaded microelectrodes and integrated heaters. This allows the fast and reproducible control of the temperature of
the nanowires which plays a prominent role in the sensing capabilities of metal oxides as well as in the performance in the
photodetection of electromagnetic radiation.
We also demonstrate that these devices can be operated with low-cost electronics controlled by a personal computer or a
PDA through an ordinary USB connection, overcoming the cost and size limitations of lab-class equipments. Finally, new
strategies for large-scale fabrication will be discussed such as nanomanipulation and self-alignment of individual
nanowires.
13
notes
14
MoA-IA-5
NOVEL TECHNIQUE FOR THE DEPOSITION OF NANOSTRUCTURED THIN
FILMS BASED ON RARE-EARTH BISPHTHALOCYANINES
M. Gay Martín, M.L Rodríguez-Méndez, Dpto. Química Física y Química Inorgánica.
E.T.S. Ingenieros Industriales. Paseo del Cauce s/n, 47011Universidad de Valladolid.
Spain.
José Antonio De Saja Sáez, Dpto. Física de la Materia Condensada, Facultad de
Ciencias. Prado de la Magdalena s/n, 47011 Universidad de Valladolid. Spain
The Langmuir-Blodgett technique is the classical method traditionally used to fabricate nanostructured bisphthalocyanine
thin films. Compared with this method, the electrophoretic deposition (EDP) technique can be an alternative way with low
cost and short time.
In this work, films of a series of rare earth bisphthalocyanines (GdPc2, DyPc2 and LuPc2) have been prepared with the EDP
technique. Indium/tin oxide (ITO) coated glass and Platinum plates were used as the cathodic and anodic electrodes,
respectively. The electrophoretic solution consisted on bisphthalocyanine diluted on trifluoroacetic acid and chloroform.
Using this technique, it has been possible to obtain nanostructures consisting in nanowires.
Depending on the conditions used during deposition (type of bisphthalocyanine, concentration, voltage applied, distance
between electrodes or deposition time) the morphology of the obtained films can be modified (thickness and length of the
nanowires). The structure of the films has been characterised by UV-Vis, X-Ray diffraction and SEM.
The electrochemistry measures of these thin films showed that first oxidation potential increased almost linearly when
increasing the ionic radii of the central metal.
Fig1.SEM micrograph of GdPc2 nanostructured formed by electrophoretic deposition
References
1. M.L Rodríguez-Méndez , Encyclopedia of Sensors, American Scientific Publishers 9, 111-133, 2006.
2. Hong-Zheng Chen, Lei Cao, Han-Bo Zhou, et al, Journal of Crystal Growth, 281, 530-537 (2005)
15
notes
16
MoA-INV.3
SURFACE SCIENCE STUDIES OF GAS SENSING METAL OXIDES
Matthias Batzill
Department of Physics, University of South Florida, Tampa, FL 33620, USA
Single crystal surfaces of the gas sensing materials SnO2 and ZnO are used as model systems for atomic scale
characterization in ultra high vacuum.[1],[2] Mainly scanning tunneling microscopy and photoemission studies are
discussed to obtain structural and electronic information.
On SnO2 our studies show that the surfaces can reversibly change from a Sn(II)O to a Sn(IV)O2 charge state depending on
the gas phase oxygen chemical potential.[3],[4],[5] Interestingly, the reduced Sn(II)O surface is chemically less reactive
than the stoichiometric Sn(IV)O2, which we investigated by water adsorption.[6] We also demonstrate that the gas response,
i.e. the change in conductivity, can be assessed by photoemission spectroscopy.[7] Observed band bending upon adsorption
of molecules gives a direct measure of the gas response signal and this enables us to determine and compare the gas
response for different surfaces, e.g. Sn(II)O vs. Sn(IV)O2.
Studies on ZnO concentrate on H2S sensing on the two polar surfaces.[8] First we compare the clean surfaces of ZnO.
Surprisingly, the ZnO(000-1)-O surface exhibits a strong upward band bending at 600 K sample temperature. We discuss this
effect in the context of the stabilization mechanism of polar surfaces.[9] Interaction of ZnO with H2S reduces the band
bending on the O-side but induces upward band bending on the ZnO(0001)-Zn surface. At one monolayer sulfide coverage
(saturation coverage) both sides exhibit the same upward band bending relative to the Fermi level. These studies illustrate
that different surface orientations may exhibit different gas sensing behaviors that may be exploited in single crystal thin
film sensors.
Finally, we address the effects of surface sensitization of metal oxides by metal additives. We discuss the case of Cu
clusters on ZnO(0001)-Zn. The reduction/oxidation of supported Cu-clusters is investigated by XPS.[10] These studies allow
correlating the oxidation state of the Cu with the band bending in the ZnO gas sensing substrate and thus a description of
the sensitization mechanism. It is found that the interface between Cu and the oxide is easier oxidized than the remaining
cluster.
[1] M. Batzill, Sensors 6, 1345 ( 2006).
[2] M.Batzill, U. Diebold, Chem. Phys. Phys.Chem. 9, 2307 (2007).
[3] M.Batzill, U. Diebold, Prog. Surf. Sci 79, 47 (2005).
[4] M. Batzill, K. Katsiev, J.M. Burst, U. Diebold, A.M. Chaka, B. Delley, Phys. Rev. B 72, 165414 (2005).
[5] M.Batzill, A. M. Chaka, U. Diebold, Europhys. Lett. 65, 61 (2004).
[6] M.Batzill, W. Bergermayer, I. Tanaka, U. Diebold, Surf. Sci. Lett. 600, L29 (2006).
[7] M.Batzill, U. Diebold J. Phys.: Condens. Matter 18, L1 (2006).
[8] J. Lahiri and M. Batzill J. Phys. Chem. C 112, 4304 (2008).
[9] J. Lahiri and M. Batzill Phys. Rev. B submitted.
[10] P.Lazcano, M. Batzill, U. Diebold and P. Haberle Phys. Rev. B 77, 035435 (2008).
17
notes
18
Mo-A-IA-8
NANOSCOPIC PT PARTICLES ON TIO2(110): STM AND POINT CONTACT
INVESTIGATIONS ON O2 DETECTION CAPABILITY AND PHOTOSENSITIVITY
Micha Kölbach and Klaus Schierbaum
University of Düsseldorf, Institute of Experimental Condensed Matter Physics, Department of
Materials Science
Schottky diodes, revealing sensing properties, are known for silicon (PdAg/thin SiO2/Si for H2 sensing and Pd/SiC)[1] and
also for oxide seminconducting materials (e.g. Pt/ZnO for CO sensing)[2]. Recently, Somorjai and Xiaozhong Ji have
constructed a nanoscale Schottky diode, based upon a 150-nm-thick layer of TiO2 and a 5-nm-thick platinum film, which is
used to measure a continuous flow of hot electrons generated by catalytic surface reactions.[3] We have chosen singlecrystals of rutile-phase titanium dioxide (TiO2), terminated by the thermodynamically most stable (110) surface; rutile-TiO2
is one of the best investigated oxide and hence is regarded as a “prototypical” n-conducting transition metal oxide.[4]
TiO2
Fig. 1. Sketch of an STM arrangement to study Pt
nanoparticles on
Figure 1 indicates our experimental approach schematically; a tungsten tip, attached to the z-piezo tube of a scanning
tunneling microscope (STM), is used to “contact” a single Pt crystal on a TiO2(110) surface. We used the so-called “seeding
and growing” technique[5] to deposit small amounts of Pt on a clean TiO2(110) surface. By decreasing the cluster-tip
spacing from a start value z0 (typically at I = 0,6 nA), through the voltage applied to the z-piezo, one can form an intimate
electrical connection. The value z0 is the distance previously adjusted in the constant-current operation mode of the STM.
The effect of oxygen dosing and photo-induced effects to such a nanoscopic Schottky-diode arrangement is studied by
current-voltage curves. An electrochemical uhv oxygen source, devoloped for this purpose, was applied to expose the
“nanodiode” to O2. This gas has been found to strongly influence the I-V-curves of macroscopic Pt/TiO2 diodes, indicating
the sensor effect of related devices.
It shows that the structures behave like non-linear circuit units in uhv (as expected for reduced TiO2) but converts into
Schottky-diodes upon O2 interaction. The net effect corresponds to the behaviour of macroscopically Pt contacts on
TiO2(110) single crystals.[6] Apart from this O2 detection capability, the nanoscopic diode is also photosensitive, as studied
by radiation the structure with laser light.
[1] Hughes et al. Appl. Phys. A. 62 (1987) 1074
[2] Kang et al., Appl. Phys. A. 80 (2005) 259
[3] X. Ji, A. Zuppero, J. M. Gidwani, and G. A. Somorjai, Nano Lett. 5 (2005) 753
[4] U. Diebold, Surf. Sci. Rep. 48 (2003) 53
[5] J.Szöko, A.Berkó, Vacuum 71 (2003) 193–199
[6] U. Kirner, K.D. Schierbaum, W. Göpel, L. Leibold, N. Nicoloso, W. Weppner, D. Fischer and W. Chu, Sensors and Actuators B 1
(1990) 103 - 107
19
notes
20
Mo-A-DM-1
DISCUSSION PANEL 1
21
notes
22
TuM-INV-4
ATOMICALLY RESOLVED CHEMICAL PHYSICS ON PROTOTYPE METAL OXIDE
GAS SENSORS
Geoff Thornton (g.thornton@ucl.ac.uk)
London Centre for Nanotechnology & Chemistry Department,
University College London, London WC1H 0AJ, UK
Scanning probe methods have played a crucial role in allowing us to understand chemical and physical processes on oxide
surfaces. This talk will highlight some important advances in connection with TiO2 and CeO2 surfaces; both reducible oxides
the conductivity of which is modified by a variety of gases. The surface structure is an important place to start, since this
provides the basis for accurate modelling of the surface electronic structure. In this context, surface X-ray diffraction
results for the (110) and (011) surfaces of TiO2 will be presented. Attention will then first focus on imaging the water
surface chemistry of TiO2(110) as well as related reactions with O2 and SO2 for comparison with DFT calculations.
Reactions with TiO2(110) are dominated by oxygen vacancies. Moreover, on TiO2(110) the main point defects are oxygen
vacancies and surface hydroxyls. We have probed the reactivity of adsorbed surface hydroxyl towards molecular oxygen via
an interplay between scanning tunneling microscopy measurements and theoretical calculations. The surface hydroxyls are
removed upon exposure to molecular oxygen, forming gaseous water and depositing charged oxygen adatoms onto the
surface. The additional charge originates at oxygen vacancies. Such charged oxygen vacancies have not been previously
observed and atomically resolved scanning tunneling spectra are used to confirm their presence. The interaction of Pd with
CeO2(111) will be used to provide a bridge between the surface chemistry and surface engineering parts of the talk. Here
we are interested in the redox behaviour of the system, the results pointing to charge transfer from Pd to CeO2. This is
important in connection with the use of Pd/CeO2 as a CO both a sensor and an oxidation catalyst. The second part of the
talk will examine the potential for TiO2(110) to self-assemble Pd, guide the substrate structure of TiO2 through ultrathin
film growth and be modified by electron beams. Using scanning tunnelling microscopy and X-ray photoelectron microscopy
we show that it is possible to grow 1 µm long metallic wires of width 3 nm. Formation of reduced ultrathin films results in
well defined shear plane structures that offer the potential to template linear structures. Electron beams are shown to form
well defined reconstructed areas, with a mechanism that probably involves local heating.
23
notes
24
TuM-IA-9
OPPORTUNITIES AND LIMITATIONS IN USING COMBINED ELECTRICAL
METHODS TO CHARACTERISE METAL OXIDE SEMICONDUCTORS FOR GAS
SENSING APPLICATION: HOW AND TO WHICH EXTENT CAN BE EXPLOITED
THE INPUT FROM INVESTIGATIONS PERFORMED IN OPERANDO
CONDITIONS TOWARDS PERTINENT INFORMATION
A. Oprea, N. Bârsan, U. Weimar
Institute of Physical and Theoretical Chemistry, University of Tuebingen, Auf der
Morgenstelle 15, D-72076, Tuebingen, Germany
The presentation provides a critical assessment of the progresses made in the field of gas sensing metal oxide
semiconductors (MOX) based on combined measurement as main experimental data source. After focussing on the
morphologic and functional peculiarities of this type of materials, that differentiate them among the larger class of
polycrystalline, granular and porous semiconductors, the complications in defining and extracting the electrical parameters
of MOX, especially under operating conditions are considered. Different experimental solutions addressing Hall Effect and
conductance measurements on gas sensing MOX reported in the literature are then briefly addressed as
foundation of the discussions about the most utilised modelling procedures. Two main trends were identified, namely the
solid-state and, respectively, chemo-physical ones. The solid-state methods focus on the crystallite energy structure,
introducing the external influences, that is, the chemistry of the surface in interaction with the gaseous species, as model
parameters describing the interface trap distribution. The chemo-physical models firstly give a physical picture of the
chemical interaction of the ambient atmosphere with the solid-state surface by connecting the target gases partial
pressures with the surface trap concentration and energy and, afterwards, follow the formalism used by the solid-state
models. For each type of approach few representative examples and applicative illustrations are considered. A very short
overview of the data accessible in literature is also included.
25
notes
26
TuM-IA-10
CHEMICAL AND PHYSICAL PROPERTIES OF CARBON-BASED MATERIALS
APPLICABLE AS CHEMICAL SENSORS
Jerzy P Łukaszewicz*
Faculty of Chemistry, Nicholas Copernicus University, 87-100 Torun, Poland
Chemical sensors have become one of the most important branches of contemporary science and technology. Recently
there is growing interest in the application of fullerenes and carbon nanotubes in chemical sensors. However, the terms
“carbon”, “carbon-based” or “carbon-type” is not limited to fullerenes and nanotubes but also applicable to graphite,
carbon black, glassy carbon, or active carbon. The aim of this lecture is to review the basic types of carbon-based
materials, selected methods of “carbon” preparation, and the most recent announcements on application of carbon-based
materials to chemical sensing. Particular attention is paid to the fabrication of carbon-based films and their application to
chemical sensing. One intends to show how the chemical properties of the carbon surface can be controlled, and how the
properties influence possible application of “carbons” to the construction of chemical sensors. The paper describes:
types of carbon-based materials and the methods of their preparation,
chemical functionalization of carbon surfaces including CNTs,
porosity of various carbons as a kind physical functionalization,
basic electric properties of carbons.
All above mentioned preparative procedures are considered in light of the application of different carbon-based materials
to chemical sensors. Special attention is paid to the application of carbon nanotubes to chemical sensing of gases and
vapors of relatively strong acceptor and donor properties. The interaction with more (chemically) inert molecules with CNTs
is presented, too. Carbon-based sensors of several types are considered: chemoresitors, mass sensitive devices and
electrodes. The considered chemical functionalization of carbon-based sensing materials includes: formation of surface
oxygen and nitrogen containing functional groups, water solubilization, polymer grafting, inorganic oxide “wrapping”,
implantation of cations, metallization, fabrication of composite materials incorporating different carbon –based materials
and binders, bio-functionalization (DNA-modification, enzyme-modification, protein-modification). Beside CNTs (multiwalled and single-walled), sensing properties of polycrystalline semiconductor carbon films is considered in detail.
E-mail: lukaszju@chem.uni.torun.pl
27
notes
28
TuM-IA-11
NONAQUEOUS SOL-GEL ROUTES TO METAL OXIDES: VERSATILE
PREPARATION METHODS OF NANOPOWDERS AND FILMS FOR SENSING
APPLICATIONS
Giovanni Neri1* and Nicola Pinna2*
1Dept. of Industrial Chemistry and Materials Engineering, Univ. of Messina, 98166
Messina, Italy *Contrada di Dio, Vill. S. Agata, 98166 Messina. E-mail:
neri@ingegneria.unime.it
2Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
In order to sustain the positive trend observed in the last years in the growth of solid state gas sensors market and provide
new applications in relevant technological fields, improvements in the sensors properties are required. Especially, better
sensitivity and selectivity, faster response, together with low power consumption and high device reliability are sought. The
sensor performance can be enhanced by decreasing the grain size of the sensing material.
In this respect, our recent works were focused on the synthesis of semi-conducting metal oxides by surfactant-free
nonaqueous sol-gel approaches, involving the reaction of metal oxide precursors in organic solvents (e.g. benzyl alcohol) at
moderate temperature and pressure. Compared to aqueous sol-gel chemistry and surfactants-assisted routes, our nonaqueous sol-gel routes offer advantages such as high crystallinity of the as synthesized oxides, high purity, high
reproducibility and the ability to control the crystal/film growth. In fact, nonaqueous sol-gel approaches were found
particularly suitable for the preparation of metal oxide nanocrystals, ordered organic-inorganic hybrid materials and low
dimensional metal oxide structures, such as nanorods, nanowires, etc. The coating of various substrates, including carbon
nanotubes, with metal oxide films by using nonaqueous routes in conjunction with the ALD (Atomic Layer Deposition)
technique was also recently reported.
The synthesis and characterization of these materials as well as their sensing properties for the detection of important
gases such as carbon monoxide, ethanol, ammonia, nitrogen dioxide and oxygen will be presented.
29
notes
30
TuM-INV-5
ENHANCED REACTIVITY AND SENSITIVITY OF METAL-CONTAINING
MICROPOROUS MATERIALS
S. Mintova,* L. Delmotte, V. Valtchev, G. Chaplais, I. Yordanov
Laboratoire de Matériaux à Porosité Contrôlée, U.M.R.-7016 CNRS, 68093 Mulhouse,
France E-mail: Svetlana.Mintova@univ-mulhouse.fr
Controlling the structure and the function of materials at the nanometer scale often requires the use of novel strategies
such as self-assembly, non-covalent interactions, host-guest chemistry, and structural templates. Periodic nanoporous
materials such as zeolites or liquid-crystal-templated mesoporous materials offer many opportunities in this field. These
materials can serve as hosts for a large number of functional guests, stabilization of a variety of metallic species and
switchable dyes.
This presentation will cover the development of synthetic strategies for generation of structurally defined, functionalized
microporous crystals by incorporation of metal (Ag, Pt, Pd, Cu) and semiconductor (CdS) clusters, and further use for
assembling in thin films on sensor devices. First, the preparation of stable colloidal suspensions of discrete nanosized
zeolites (GIS, LTL, FAU, BEA and MFI/MEL-types) with metal clusters with emphasis on their complex crystallization
mechanism under hydrothermal synthesis conditions will be revealed. Second, the stabilization of metal containing
nanoparticles in coating suspensions follow by assembly into defined thin-to-thick films by chemical binding, microwave
induced crystallization and spin-patterned-deposition in multi-sensing layers will be discussed. The transport properties of
the self-organized materials with nanosized dimensions and preferred crystal orientation are bringing a large
improvement in their sensing performance. Finally, the focus will be on the preparation of chemical sensors with enhanced
reactivity and selectivity toward hydrocarbons and water. The microporous nanocrystals with dimension smaller than 100
nm, variable pore architecture and chemical composition (hydrophilic/hydrophobic) result in well-ordered films with
enhanced sensitivity toward polar compounds in comparison to disordered nanostructures. Non-destructive identification of
the thin microporous films using GID-X-ray diffraction, HRTEM, Raman, and UV-vis spectroscopes will be presented.
31
notes
32
TuM-IA-12
DISCRIMINATION OF VOLATILE COMPOUNDS THROUGH AN ELECTRONIC
NOSE BASED ON QUARTZ SAW SENSORS
M. Aleixandre, M.J. Fernández, J.L. Fontecha, I. Sayago, J. Gutiérrez, M.C. Horrillo. Instituto de
Física Aplicada, (CSIC), Serrano 144, 28006 Madrid, Spain
I. Gracia, C. Cané, Centro Nacional de Microelectrónica, (IMB-CSIC), 08193 Bellaterra, Spain
Volatile organic compounds (VOC) generated on industries and residential areas can produce degrading effects on the
environment or health problems in humans. Systems that are composed by an electronic nose can be an alternative to
other systems to detect them. The surface acoustic devices (SAW) use the change in the velocity of a surface acoustic wave
with the change of mass in that surface. The sensitive layer that adsorbs the VOCs is generally a polymer witch has shown
a good response to them. In this work we show the possibility of that kind of analysis with an array of SAW sensors built
over quartz. The 8 SAW sensors making the electronic nose consisted of delay lines (DL) with different polymer thin films of
various thicknesses. They were fabricated on ST-X cut quartz substrate. As sensitive layers we deposited
polyepichlorohydrin (PECH), polyetherurethane (PEUT) and a silicone polymer OV-225 of different thickness. The sensor
array was tested with different gases at different concentrations varying from 10 to 500 ppm. These gases were ammonia,
octane, methyethylketon and toluene. To see the results we plot the PCA analysis of the data measured in figure 1. We can
see that the PCA plot shows that the four gases can be separated even when different concentrations are analyzed at the
same time. To test the classification results we developed an Artificial Neural Network (ANN) that can classify the
measurements. The neural network gives a 98.7% of classification success.
33
notes
34
TuA-IA.13
USING AN ELECTRONIC NOSE TO DISCRIMINATE BETWEEN RED WINES
AGED IN OAK BARRELS AND WINES AGED USING PIECES OF WOOD.
N. Prieto1, M.L. Rodríguez-Mendez2, J.A. de Saja1.
1Dptm. of Condensed Matter Physics. Sciences Faculty. Prado de la Magdalena s/n. 47011 Valladolid,
University of Valladolid, Spain.
2Dptm. of Inorganic Chemistry. E.T.S. Ingenieros Industriales. Pº del Cauce s/n. 47011 Valladolid.
Spain.
In previous works, our group has developed an electronic nose, specifically dedicated to the analysis of red wines. The
system consists in an array of metal oxide (MOX) sensors, coupled to a Solid Phase Microextraction (SPME) system [1,2]. This
system has been able to discriminate among wines made using different varieties of grapes, or made using grapes of
different geographical origins. The system can also be used to follow the ageing process of wines. In this work, the
capability of the multisensor system has been used in oune of the most important problems of the wine industry, the
discrimination between red wines aged in oak barrels and red wines matured in steel tanks in contact with oak wood chips
and staves. The volatile compounds have also been analysed by gas chromatography (GC) coupled to mass spectrometry
(MS) connected to SPME [3]. Using chromatography certain compounds important in the ageing process ( 2-furaldehyde,
guaicol, cis/trans-whiky lactone and eugenol) have been quantified. The chromatographic method showed good linearity
over the concentration range tested, with correlations of the calibration coefficients higher than 0.99 for all studied
compounds.
Results obtained using the electronic nose have demonstrated that after six months of ageing, it is possible to discriminate
between wines aged using traditional methods from those aged using oak chips or staves. The capability of discriminations
was similar to that observed using chromatographic results.
The GC-MS results have been correlated with the sensor array responses using partial least squares (PLS). The PLS
correlation coefficients ranged from 0.72 to 0.97 have demonstrated a good-quality ability to establish prediction models
that are capable to infer the methodology used to age wines due to presence of genuine extractable oak wood compounds
in each type of aged. The best correlations have been found for the whisky lactone. The results confirmed the multivariate
relationships between the volatile compounds responsible of the aged wine aroma.
References
[1] M. L. Rodriguez Mendez, A. Arrieta, V. Parra, A. Bernal, A. Vegas, S. Villanueva, R. Gutiérrez-Osuna, Fusion of Three
Sensory Modalities for the Multimodal Characterization of Red Wines, IEEE Sensors Journal, 4 (2004) 348-354.
[2] S. Villanueva, A. Guadarrama, M.L. Rodr´ıguez-Mendez, J.A. de Saja, Use of an array of metal oxide sensors coupled
with solid phase microextraction for characterisation of wines. Study of the role of the carrier gas, Sensors and Actuators B:
Chemical (2007), doi:10.1016/j.snb.2008.01.035.
[3] José David Carrillo, Álvaro Garrido-López, Maria teresa Tena. Determination of volatile oak compounds in wine by
headspace solid.phase microextracion and gas chromatography-mass spectometry, Journal of chromatography A, 1102
(2006) 25-36.
Acknowlegedments.
Financial support from CICYT (Grant nº. AGL2006-05501/ALI), and the collaboration of Ibernam is gratefully acknowledge.
35
notes
36
Tu-A-IA-14
GAS SENSING PROPERTIES OF METAL-DECORATED OXYGEN-PLASMA
FUNCTIONALISED MULTIWALL CARBON NANOTUBE MICROARRAYS.
Eduard Llobet, Radouane Leghrib, MINOS, Departamento de Ingeniería Electrónica,
Universidad Rovira i Virgili, E-43007, Tarragona, Spain.
Alexandre Felten, Jean Jacques Pireaux, LISE, Université de Namur, B-5000, Namur,
Belgium
In the last few years, different studies have shown the excellent potential of carbon nanotubes (CNT) as sensitive material
for detecting biological and chemical molecules. Via a functionalisation of CNT side walls, an improved interaction between
a specific chemical species and the nanotube can be reached and the selectivity of the adsorption process can be enhanced.
Some properties of CNTs make them very attractive to produce small, wearable sensors for industrial and transport
environments:
The adsorption of a small quantity of chemical species can result in a dramatic change of the CNT conductivity. Therefore,
CNT are suited to detect species at low concentrations (e.g. low ppb level).
A sensor can be built using a simple transducer (comb electrodes) to monitor the electrical resistance of a CNT-based film.
They respond even when operated at room temperature, which is optimal for ultra-low power, wearable, battery-operated
devices. Such devices could easily meet the requirements of intrinsically safe operation, needed in industrial environments
where the occurrence of flammable/explosive atmospheres is possible.
Their intrinsic strength makes them suited for miniaturised sensors and usable on flexible substrates.
As an alternative to the usual functionalisation techniques that are employed to increase the reactivity of the CNT surface,
CNT can be decorated with metal nanoparticles. The concept of using CNTs decorated with metal clusters as the sensitive
material of a device where the metal cluster surfaces act as reactive sites for the adsorption of the target molecules has
been introduced recently in a theoretical study. The adsorption of a target gas may produce a substantial polarisation and
accumulation of charge in the region between the metal cluster and the nanotube. This charge transfer between the metal
cluster and the nanotube provides important information regarding the system’s electronic response. It affects the ionic
component of the bonding, alters the position of the Fermi level and the band alignment. Therefore, the variations in the
electrical conductance of the CNT-metal system are a measure of the sensitivity of chemical sensors based on these
materials. According to these preliminary theoretical results, CNTs decorated with metal clusters could be tailored for the
recognition of chemical species with high sensitivity and selectivity. The key concept is to use nano-clusters (small size is
essential to maximise the effect of adsorbates on metallic clusters) that donate or accept a significant amount of charge
upon adsorption of a target molecule, so that electron transport in the nanotube is affected.
In this presentation we will report on the use of multi-wall carbon nanotubes (MWCNT) decorated with nanoclusters of
different metals as gas sensitive materials. MWCNT were functionalised in oxygen R.F. plasma and decorated with metal
nanoclusters using electron beam evaporation. The decorated nanotubes were on micro-hotplate substrates that included
interdigited electrodes and a micro-heater. TEM, SEM and XPS analysis will be shown to discuss sample morphology and
composition. Their sensitivity towards different pollutant gases will be shown too and some gas sensing mechanisms will
be discussed.
This work is financially supported by Nano2Hybrids (EC-FP6-STREP-033311).
37
notes
38
TuA-DM.2
39
notes
40
WeM-INV-6
CONTRIBUTION OF CHEMICAL SENSORS IN ANIMIC EVALUATIONS
F.Javier Gutierrez, Mª.C Horrillo ,I.Sayago,M.J. Fernández,M.Aleixandre, .GRIDSEN
.IFA,CSIC,Serrano 144,28006 Madrid ,javiergutierrez@ifa.cetef.csic.es
The objective evaluation of emotions in humans and their cuantification is a subjet of a great interest not only for the
people concerned in health as : psychiatry , neurology and endocrinology .Today it has became in a important challenge
for the responsible on civic security that their interest is growing in order to detect , digitalize and integrate the
human responses for biometric identification purposes .
Different kinds of stress induce reactions in the humans as: sweating , conductive skin, sympathetic responses , hormonal
secretion in plasma and urine, body odours, changes in feeling, heart and respiration rate.
Several molecules and ions in human sweat excreted in abnormal amounts became a indication of a pathological disorder:
Lactate , Ph, amines , are analytes present on skin and excreted, are good markers for diagnostic test of stress. Human
saliva contains many products of interest as: proteins, amylase, Na, K, lactate, and cortisol .All markers measured and
quantified by non invasive methods by suitable sensors could allows patterns of human emotions based on
digitalization of signals by chemical sensors.
In this talk we review some chemical sensors and configurations for associate human odours with images of
emotional states, showing some promising results associates to our experiences: New Metal Oxide sensors based on
porous silicon membranes are used for the detection of low concentrations of amines ( NH3,DMA and TMA). Also for
detecting Volatiles, new masic sensors SAW and LOVE based ZnO seems attractive devices because their high
electromechanical coupling coefficient, and excellent bonding on various substrate materials, in particular silicon, silicon
dioxide and silicon nitride.
41
notes
42
WeM-IA.15
CHEMICAL SENSORS MADE OF POROUS SILICON
Vladimir Aroutiounian
Department of Physics of Semiconductors and Microelectronics,
Research Centre of Semiconductor Devices and Nanotechnology,
Yerevan State University, Yerevan 0025, Armenia
Porous silicon (PSi) is very promising material for many applications. It serves as a basis material in optoelectronics and
photonics, which follow from the very interesting and promising optical and luminescent properties of PSi. Last years
studies of its physical properties have shown that PSi is very sensitive to exposure to different gases, bio- and chemical
substances due to fine-grained nature of Si nano-crystallites and the ensuing large surface area. PSi is in the focus of
scientists working on drug delivery and in nanomedicine.
After a review of new applications of PSi, we will report about possibilities to improve stability and sensitivity of sensors
made of PSi by choose of different coatings and catalysts. Note also that noise properties of all type gas- and chemical
sensitive structures do not really investigated. Meanwhile, our measurements of low frequency noise spectra of PSi gas
sensors are shown that noise spectroscopy can serve as a powerful tool for studies of main characteristics of abovementioned sensors (including selectivity). Joint investigations of current-voltage characteristics and noise spectra of PS
semiconductor layers in different media can give detail information about the condition of the surface and parameters of
heterojunction PSi-single crystalline Si presented as a rule in all PSi sensors.
43