Raman spectroscopy of nanostructures and single molecules

advertisement
Raman spectroscopy of nanostructures and single molecules
Alejandro Fainstein
Laboratorio de Propiedades Opticas
Centro Atómico Bariloche & Instituto Balseiro
Inelastic (Raman) scattering of light is a powerful technique for the
characterization of excitations in solids and molecules. In particular,
vibrational spectroscopy provides a very specific and sensitive tool
applicable to the study of fundamental phenomena and for sensing.
This technique can be used for the study of nanostructures and single
molecules, but in these cases amplification strategies are required. In
this talk I will present a tutorial on Raman scattering in solids and
molecules, and I will describe the different techniques used for the
enhancement of the Raman efficiency. These include the use of
electronic resonances (resonant Raman scattering, RRS), of plasmon
resonances in metallic nanostructures (surface enhanced Raman
scattering, SERS), and of photon confinement in microcavities (double
optical resonant Raman scattering). These techniques will be
illustrated with examples of current research on molecular and solid
nanostructures, and on single molecules, performed at our laboratory
and by other groups.
References:
M. Cardona, in Light Scattering in Solids II, edited by M. Cardona and
G. Güntherodt (Springer, Berlin, 1982).
B. Jusserand, and M. Cardona, in Light Scattering in Solids V, edited
by M. Cardona and G. Güntherodt, (Springer, Heidelberg, 1989).
A. Otto, in Light Scattering in Solids IV, edited by M. Cardona and G.
Güntherodt (Springer, Berlin, 1984).
A. Fainstein and B. Jusserand, in Light Scattering in Solids IX, edited
by M. Cardona and R. Merlin (Springer, Berlin, 2006).
Magnetic properties of the matter studied by X-rays magnetic circular
dichroism
Flavio García
Laboratorio Nacional de Luz Sincrotrón
Campinas, S. P., Brasil
Two fascinating subjects will be put together in theses lectures: the magnetism
of the matter and some of the X-rays absorption spectroscopy experimental
techniques available in synchrotrons radiation sources, namely the X-rays
magnetic circular dichroism (XMCD) spectroscopy. The first of these has
captured the imagination of humankind for 3000 years; while the XMCD is a
relatively new technique, which allows the quantitative measurement of
magnetic moments. The main strengths of this technique are the independent
determination of the spin and orbital magnetic moments and the elemental
specificity.
Since of Dispersive X-ray Absorption Spectroscopy (DXAS) beam line
opening for external users, in the first semester of 2003, it has been used for
scientists from several fields of chemical and physics disciplines, namely
magnetism, superconductivity, catalysis and electrical-chemistries. The great
advantage of this system, compared to the conventional XAS beamlines, is
that it allows measurements of a complete XAS spectrum without any
mechanical motion, in a few milliseconds. This is specially suited for in situ
XANES and XMCD studies, which require good accuracy and high stability.
Fast kinetics, like those occurring in a catalytic or electrochemical reaction,
can be tracked by in-situ experiments. The beamline opens the way to the
high-pressure community which are used to diamond anvil cells in their
studies.
The scope of these lectures will be a succinct presentation of the magnetism
properties of the magnetic materials and some interesting magnetic
phenomena; also, it will present the background of the XMCD as well as some
examples that will display the strength of XMCD method, and show that
XMCD spectroscopy is an extremely powerful tool in the analyzing complex
magnetic systems. Finally, it will present an overview of the research carried
at DXAS beamline, with especial attention to the high pressure opportunities.
My talks will be organized as followed: 1) Background of the magnetic
materials; 2) Some interesting magnetic systems; 3) Conventional
magnetometric techniques; 4) Background of the synchrotron radiation and
XAS; 5) introduction on the XMCD; 6) experimental details of the DXAS
beamline and others XMCD facilities at LNLS; 7) Some examples of the
XMCD experiments; 8) The others research possibilities at DXAS beamline
(kinetics XAS and in situ studies under hydrostatic pressure).
References
F. Garcia, PhD thesis, Centro Brasileiro de Pesquisas Físicas, 2000.
A.P.Guimarães, Magnetism and Magnetic Resonance in Solids, Wiley
Interscience Publication.
N. M Souza-Neto, Journal of Synchrotron Radiation 12, 168, 2005).
J. C. Cezar, PhD thesis, UNICAMP, 2002.
Métodos de Cristalografía y Difracción de Rayos X
Iris Torriani
Laboratorio Nacional de Luz Sincrotrón, Campinas, SP Brasil.
Laboratorio de Cristalografía Aplicada e Raios X, Instituto de Física,
Universidade Estadual de Campinas, SP, Brasil.
Objetivos
Dar una sólida base sobre los aspectos teóricos-experimentales de los métodos
de cristalografía y la difracción de rayos X y sus aplicaciones.
Las clases estarán orientadas a la difractometría de rayos X por las técnicas de
polvo y de bajo ángulo (SAXS), así como al refinamiento de estructuras
cristalinas. Se desarrollará el fundamento teórico de la difractometría de polvo
y de bajo ángulo.
Contenido
* Generación de rayos X. Aspectos históricos. Fuentes convencionales.
Radiación sincrotrón.
* Nociones de cristalografía. Celda unitaria, simetrías, sistemas cristalinos.
* Dispersión de rayos X. Dispersión a bajos ángulos (SAXS). Difracción por
materiales ordenados y cristalinos (DRX).
* Medidas difractométricas. Tratamiento de datos. Identificación de fases
cristalinas.
* Refinamiento de estructuras cristalinas. Método de Rietveld. Aplicación del
método en la obtención de parámetros estructurales.
* Aplicaciones en biología: Determinación de estructuras de macromoléculas.
Proteínas: estructura atómica y estructura en solución.
State-of-the-art of x-ray fluorescence with synchrotron radiation
Jorge Héctor Sánchez
Facultad de Matemática Astronomía y Física
Universidad Nacional de Córdoba
Ciudad Universitaria, Córdoba 5000, Argentina
It is well known that the use of synchrotron radiation in trace analysis by x-ray
fluorescence (SRXRF) allows to reduce detection limits and to improve
sensitivities1,2. The intrinsic characteristics of synchrotron radiation (high
intensity, polarization, natural collimation, etc.) and the construction of
dedicated sources of synchrotron light make possible to improve detection
limits for trace elements in several orders of magnitude. Besides, it permits to
implement spectrochemical analysis with spatial resolution on the micrometer
scale. As could be expected, this kind of experiment using conventional
sources is limited to detecting only major components (a few x-ray microbeam
systems working with capillaries and conventional excitation have reported
studies of trace elements). Grodzins3 compared intrinsic sensitivities of XRF
microprobes induced by electrons, protons and photons and concluded that the
photon microprobe presents better sensitivities for high-intensity emission
sources.
In general, the SRXRF technique is especially adequate for nondestructive trace analysis on the spatial range of 5 to 100 µm. Many situations
can be resolved efficiently with collimating systems, energy-dispersive setups
and white beam. The use of a monochromator and/or wavelength-dispersive
systems permits to optimize the irradiation conditions, to perform a selective
analysis and to extend the dynamic range of the technique, improving
sensitivities and detection limits for low-Z elements. Nevertheless, these
devices are expensive and produce an important loss of intensity.
In 1972 Yoneda and Horiuchi[4] proposed an innovative excitation
method for x-ray fluorescence (XRF) experiments based on external total
reflection of the incident x-ray beam (TXRF). In this condition the
background of the measured spectra can be drastically reduced and,
accordingly detection limits are improved reaching the ng/g level almost
without difficulty. During the mid-70s and the beginning of the 80s the first
applications of TXRF and the development of the first spectrometers using the
total reflection technique were reported[5-7]. Today it is a well-established
technique and several papers on the subject are published each year. The use
of synchrotron radiation in combination with total reflection permits to obtain
detection limits as low as 107 at/cm² and is the most accepted technique for
wafers analysis of micro and nano technologies.
In 1983 Becker et al.[8] demonstrated that XRF analysis can be attained
in grazing emission (GE) conditions. The Reciprocity Theorem of
Helmholtz[9] predicts that the GE setup reproduces the same conditions as
total reflection in grazing incidence (GI) and thus the same DL.
Experimentally, GE conditions are obtained in a different way than GI
conditions; hence the GEXRF technique represents an important progress in
the field for surface experiments with synchrotron radiation and total
reflection.
References
C. J. Sparks Jr. In Synchrotron Radiation Research, eds. H. Winick and S.
Doniach, Plenum, New York, 1980
B. M. Gordon, K.W. Jones, Nucl. Instrum. Methods B10/11, 293 (1985)
L. Grodzins, Neurotoxicol. 4, 23 (1983)
1. Y. Yoneda and T. Horiuchi, Rev. Sci. Instrum. 42, 1069 (1971)
2. H. Aiginger and P. Wobrauschek, Nucl. Instrum. Methods 114, 157 (1974)
3. P. Wobrauschek and H. Aiginger, Anal. Chem. 47, 852 (1975)
4. J. Knoth and H. Schwenke, Fresenius Z. Anal. Chem. 301, 7 (1980)
5. R. S. Becker, J. A. Golovchenko and J. R. Patel, Phys. Rev. Lett. 50, 153
(1983)
6. M. Born and E. Wolf, in “Principles of Optics”, Ch. 8 p. 381, Pergamon
Press, New York, (1980).
Introducción a la Física del Sólido
Oscar E. Piro
Departamento de Física, Facultad de Ciencias Exactas
Universidad Nacional de La Plata
PROGRAMA BÁSICO
1) Teoría de Drude de los metales.
2) Teoría de Sommerfeld de los metales.
3) Propiedades de estructuras periódicas. Redes directas y recíprocas.
Celdas de Bravais y de Wigner-Seitz.
4) Movimiento de electrones en potenciales periódicos. Teoría de bandas.
Teorema de Bloch. Zonas de Brillouin. Electrones en potenciales
periódicos débiles. Aproximación de ondas planas. Difracción de
electrones de valencia. Superficie de Fermi. Estructura de bandas de los
niveles electrónicos en sólidos; representación en esquemas reducido,
extendido y periódico. Clasificación de sólidos en conductores,
semiconductores y aisladores.
5) Método de ligadura fuerte (‘Tight binding’).
Bibliografía sugerida
1.
2.
3.
4.
5.
6.
N. W. Ashcroft & N. D. Mermin: “Solid State Physics”. Holt,
Rinehart & Winston, Philadelphia.
A. S. Davidov: “Teoría de Sólidos”. Mir, Moscú.
C. Kittel: “Introduction to Solid State Physics”. John Wiley, New
York, 4th Edition.
C. Kittel: “Quantum Theory of Solids”. John Wiley, New York.
J. M. Ziman: “Principles of the Theory of Solids”. Cambridge
University Press.
J. M. Ziman: “Electrons and Phonons”. Clarendon Press, Oxford.
LNLS: Infra-estrutura e Oportunidades para Pesquisa com Luz
Síncrotron
Gustavo Azevedo
Laboratorio Nacional de Luz Sincrotrón
Campinas, S. P., Brasil
O Laboratório Nacional de Luz Síncrotron (LNLS) localizado em
Campinas, na região sudeste do Brasil, possui diversas instalações abertas que
oferecem a cientistas do Brasil, e de toda a América Latina, condições de
realizar pesquisas com nível de competitividade mundial.
A principal instalação do LNLS é uma fonte de luz síncrotron de
terceira geração, que vem sendo utilizada desde 1997 por pesquisadores de
diversas áreas, incluindo físicos, químicos, biólogos, geólogos e engenheiros.
O anel de armazenamento do LNLS tem capacidade para acomodar 24 linhas
de luz. Atualmente, 12 linhas de luz encontram-se em operação e outras 4
encontram-se em fase final de projeto ou comissionamento. Estas linhas
disponibilizam luz síncrotron cobrindo desde a região visível do espectro
eletromagnético até a região dos raios x duros e são dedicadas a diversas
técnicas de caracterização, tais como XRD, SAXS, XPS, XAFS (XANES +
EXAFS) e cristalografia de proteínas.
Neste seminário, farei uma breve descrição da fonte de luz síncrotron
brasileira, ressaltando suas principais características.
Além disso
discutiremos as linhas disponíveis no LNLS e instrumentação associada. As
potencialidades de utilização dessas instalações na caracterização de materiais
serão discutidas.
Introdução à Espectroscopia de Estrutura Fina de Absorção de Raios-X
Gustavo Azevedo
Laboratorio Nacional de Luz Sincrotrón
Campinas, S. P., Brasil
Neste seminário, será apresentada uma introdução à Espectroscopia de
estrutura fina de absorção de raios-X - XAFS (X-ray Absorption Fine
Structure). Esta técnica explora a dependência do coeficiente de absorção de
raios-x de um material quando a energia dos fótons é suficiente para
remover um elétron de um nível interno de caroço de um átomo presente no
material. XAFS é sensível ao estado químico e à estrutura local em torno do
átomo ionizado (absorvedor). Em particular, XAFS é sensível às distâncias
interatômicas, números de coordenação e identidade química dos átomos nas
vizinhanças do absorvedor. Além disso, permite sondar a estrutura eletrônica
do sistema (densidade local de estados desocupados).
Abordaremos inicialmente a região de EXAFS (“Extended X-ray
Absorption Fine Structure”), que é a estrutura fina do espectro que se
manifesta na forma de oscilações do coeficiente de absorção entre 50 e 2000
eV acima da borda. Discutiremos os processos físicos que originam as
oscilações de EXAFS e como a análise da freqüência e amplitude das
oscilações permite obter informação sobre a ordem de curto alcance em torno
do átomo absorvedor. A seguir, abordaremos a região de XANES (“X-ray
Absorption Near Edge Structure”), que corresponde à estrutura fina do
espectro de absorção nos 200 eV em torno da borda de absorção. Como
veremos, esta região contém informação a respeito da estrutura eletrônica e da
simetria de coordenação em torno do átomo absorvedor. Discutiremos
brevemente alguns desenvolvimentos teóricos recentes que permitem a
modelagem ab-initio do espectro de XANES. Finalmente, algumas aplicações,
potencialidades e limitações da técnica XAS serão discutidas.
Vibrational spectroscopy in nanostructures
Volia Lemos Crivellenti
Departamento de Fisica
Universidade Federal do Ceará
Caixa Postal 6030, Fortaleza,CE, Brazil
The research field of nano structures has boomed in recent years due to the
increased demand from the portable electronic market, drug delivery, gas
sensors, rechargeable batteries, among others.1,2 One of the current techniques
for the characterization of particles with dimensions in the nanoscale domain
is Raman spectroscopy. A number of systems have been studied using this
technique, such as carbon nanotubes and fullerenes. Analysis of the carbon
nanotubes Raman spectrum allows determining the diameter of nanotubes,
chirality and resonance conditions. Functionalization or chemical
modifications are straightforwardly reveled using this spectroscopy. Alkalimetal dopants, for instance, leads to a shift of the Fermi level, 3-6 and to a
conductivity enhancement of the SWCNTs.7-10 Under pressure, the spectrum
gives information on the state of deformation of the isolated tube or the
bundle.11-15
The scope of this course is the study of carbon nanotubes physical and
vibrarional properties. It will be organized as follows: 1) Background of basic
definitions of lattice and other concepts needed to the understanding of the
subject. 2) The structure of single-wall carbon nanotubes, SWNTs. 3) The
electronic structure of grapheme and SWNTs. 4) The status of current research
in the field of Raman spectroscopy of SWNTs. 5) A review of pressure effects
in SWNTs: experiments and calculations.
References
1
M. S. Dresselhaus, G. G. Samsonidze, S. G. Chou, G. Dresselhaus, J. Jiang,
R. Saito, and A. Jori, Phys. E 29, 443 (2005). M. S. Dresselhaus, G.
Dresselhaus, A. Jorio, A. G. Souza, G. G. Samsonidze, and R. Saito, J.
NanoSci. Nanotech. 3, 19 (2003).
2
B. Vigolo, P. Poulin, M. Lucas, P. Launois, and P. Bernier, Appl. Phys. Lett.
81, 1210 (2002).
3
X. Liu, T. Pichler, M. Knupfer, et al., Phys. Rev. B 67, 125403 (2003).
4
S. Suzuki, C. Bower, Y. Watanabe, et al., Appl. Phys. Lett. 76, 4007 (2000).
5
S. Suzuki, F. Maeda, Y. Watanabe, et al., Phys. Rev. B 67, 115418 (2003).
6
H. Rauf, T. Pichler, M. Knupfer, et al., Phys. Rev. Lett. 93, 096805 (2004).
R.S. Lee, H.J. Kim, J.E. Fischer, et al., Nature 388, 255 (1997).
8
A. M. Rao, P. C. Eklund, S. Bandow, et al., Nature 388, 257 (1997).
9
N. Bendiab, L. Spina, A. Zahab, et al., Phys. Rev. B 63, 153407 (2001).
10
S. B. Fagan, S. Guerini, J. Mendes, et al., Microelectronics Journal 36, 499
(2005).
11
U. D. Venkateswaran, A. M. Rao, E. Richter, M. Menon, A. Rinzler, R. E.
Smalley, and P. C. Eklund, Phys. Rev. B 59, 10928 (1999).
12
U.D. Venkateswaran, E.A. Brandsen, U. Schlecht, A.M. Rao, E. Richter, I.
Loa, K. Syanssen, and P.C. Eklund, Phys. Stat. Solidi (b) 223, 225 (2001).
13
U. D. Venkateswaran, D. L. Masica, G. U. Sumanasekera, C. A. Furtado, U.
J. Kim, and P. C. Eklund, Phys. Rev. B 68, 241406 (2003).
14
M. J. Peters, L. E. McNeil, J. P. Lu, and D. Kahn, Phys. Rev. B 61, 5939
(2000).
15
P. V. Teredesai, A. K. Sood, D. V. S. Muthu, R. Sen, A. Govindaraj, and C.
N. R. Rao, Chem. Phys. Lett. 319, 296 (2000).
7
Infrared Spectroscopy
Néstor E. Massa
Laboratorio Nacional de Investigación y Servicios en Espectroscopía OpticaCEQUINOR
Universidad Nacional de La Plata
C.C. 962, 1900 La Plata, Argentina
In this tutorial we will review scientific topics involving a most important
analytical tool in which virtually any sample, crystals, liquids, solutions,
pastes, powders, films, fibres, gases and surfaces can be studied using current
easily available accessories. Infrared spectroscopy, spanning from 20 to
13000 cm-1, is a comprehensive tool for the quantitative study of vibrational
modes in terms of changes in electric dipoles associated with vibrations and
rotations. In addition, the electronic structure, as in highly correlated
materials from regular transition metal oxides to high Tc cuprates, may also
be probed through the interplay of external variables such as quasihydrostatic
pressure, temperature, and applied magnetic fields. This yields information
of instabilities of great interest to solid state research.
Infrared spectra are based on Fourier spectroscopy that is a powerful
technique applied to transmission as well as reflectivity measurements and
built on the Michelson Interferometer. An interferogram is created that it is
Fourier transform to obtain transmission (absorption) as function of frequency.
Then the optical properties are deduced by Kramers-Kronig integration or a
dielectric simulation (using damped oscillators and plasma) of the reflectivity
spectra. This allows the knowledge of the dielectric function real and
imaginary parts yielding a complete low energy characterization
We will also see more recent applications on biology where now the samples
of interest are biomolecules, very complex systems such as protein, nucleic
acid, carbohydrate, lipid, or biomembrane structure where spectroscopic IRmicroscopy helps bridging data from X-ray cristallography that otherwise
would be intractable.
Infrared Spectroscopy: Fundamentals and Applications B. Stuart 2004,
http://media.wiley.com/product_data/excerpt/86/04708542/0470854286.pdf#s
earch=%22introduction%20%2B%20%20infrared%22
M. S. Dresselhaus. Optical Properties of Solids
http://web.mit.edu/afs/athena/course/6/6.732/www/opt.pdf
F. Wooten, Optical Properties of Solids, Academic Press, 1972.
See for example, D. Nauman on Infrared Spectroscopy in Microbiology,
Encyclopedia of Analytical Chemistry, R. A. Meyers (Ed.) , John Wiley and
Sons Ltd , Chichester, (2000). Pp. 102-131.
L. Miller. Biomicrospectroscopy
file:///C:/Documents%20and%20Settings/Administrador/Configuraci%F3n%2
0local/Archivos%20temporales%20de%20Internet/Content.IE5/KRBV2K19/4
31,1,Diapositiva 1
Project for an infrared-beamline at the Swiss Light Source
http://www.solidphys.ethz.ch/spectro/DOC/SLS/slsreport.pdf#search=%22Pro
ject%20for%20an%20infraredbeamline%20at%20the%20Swiss%20Light%20Source%22
Download
Related flashcards
Salts

21 Cards

Dyes

45 Cards

Acids

25 Cards

Oxohalides

46 Cards

Create flashcards