I.1

Novel Materials Studied by Using Synchrotron Radiation Facilities

 

Asensio M.C.

Instituto de Ciencia de Materiales de Madrid (CSIC) Spain &

LURE, Centre Universitaire Paris Sud, Orsay Cedex, France

 

 

The most direct source of information on the electronic energy levels of atoms, molecules, and solids, is provided by different kind of spectroscopic techniques. Such information has played an important role in the development of the applied and basic physics of new materials. In material science the need of improved physical and chemical properties drives the evolution of new processing methods that lead to the production of artificial structures with enhanced attributes. The performance of these new structures strongly depends on the degree of control of their processing. This applies to a large majority of new developments based on existing techniques ranging from MBE to ion implantation to laser- and ion-assisted depositions. As is often the case, understanding of the formation mechanisms follows empirical preparation of new structures, to which it gives in turn new hints to the production of more sophisticated materials.

An important aspect of the new developments in material science is related to processes that occur at the surface. The centrality of the surface structure and electronics has been recognized many decades ago, but only from the late 60´s new experimental techniques for surface studies emerged as the result of the availability of ultra-high-vacuum (UHV) technologies, perfectioned electron spectroscopies and, starting from the seventies, large synchrotron radiation (SR) facilities. The availability of these intense sources of X-rays and the commissioning of new powerful facilities in Europe, Japan and the USA has stimulated a blooming of different X-ray techniques dedicated to the experimental determination of the properties of novel materials. The unique properties of SR, like intensity, polarization, time structure, tunability and collimation, make it ideally suited for new emerging techniques.

In general, the X-ray spectroscopies offer the advantages deriving from the weak interaction between the X-rays and matter and the good matching of the wavelength to the atomic scale. The high penetration of X-rays is extremely valuable. On the other hand, the weak coupling of X-rays with matter implies that the interaction with the surface or interface object of the study will be even unremarkable. This explains the vigorous drive that X-ray-based techniques received from the development of intense SR sources. A variety of X-ray techniques applies to the variety of situations that occur at surfaces, interfaces and bulk, altogether concurring in providing the information necessary to the build-up of a unified picture of each new type of novel material. Even if the diversity of the SR uses is quite wide, in this talk, the major areas of SR application in materials science will be reviewed with the aid of the latest highlight examples.

 

I.2

Caracterización de Heteroestructuras de Multicapas GaAs-Ge/GaAs por SEM, EDS y AES

 

Silva González Rutilo

Instituto de Física, Benemérita Universidad Autónoma de Puebla

 

Recientemente las estructuras de multicapas o multipelículas se han estado elaborando por diferentes técnicas de crecimiento: evaporación, erosión catódica  (sputtering), epitaxia por haz molecular, etc. debido a que se pueden fabricar con  propiedades que no están presentes en las aleaciones sencillas  de los elementos constituyentes. Además con las técnicas avanzadas de depósito existentes las estructuras de multipelículas se pueden diseñar para aplicaciones específicas.

El método ideal para explotar la no-linealidad de los semiconductores es lograr la inversión de dominio cristalino  de la cual depende la inversión de signo del coeficiente óptico no-lineal.  Tecnológicamente se ha ideado y logrado por MBE la inversión de las redes fcc que forman la estructura zincblenda de compuestos III-V como el GaAs, intercalando una película muy de átomos del grupo IV como el Si o Ge. Una heteroestructura de este tipo presenta entre otros problemas la contaminación o difusión transversal entre los 2 materiales.

Con el propósito de elucidar el papel que juegan la microestructura y la microquímica en este tipo de estructuras de multicapas se analizan por las técnicas de microscopía electrónica de barrido (SEM), espectroscopía de energía dispersiva de rayos-x (EDS) y espectroscopía de electrones Auger (AES)  un conjunto de heteroestructuras de GaAs-Ge/GaAs, en particular se hace énfasis en los efectos interfaciales de contaminación o difusión transversal.

 

I.3

Algunos Cambios Químicos y Físicos que Ocurren en el Almidón durante los Procesos de

Elaboración de las Tortillas de Maíz y Trigo

 

Ramírez-Wong, B., Campas-Baypoli, O.N., Ledesma-Osuna, A.I., Rosas-Burgos, E.C., y Torres, P.I.

Departamento de Investigación y Posgrado en Alimentos. Universidad de Sonora, Hermosillo, Sonora, México.

 

El maíz y el trigo son dos de los cereales mas importantes tanto a nivel mundial como nacional; ya que se utilizan para elaborar entre otros productos alimenticios.  El almidón es el principal componente químico y es la fuente primordial de energía almacenada de estos cereales. El contenido  de almidón varía en los cereales, pero generalmente se encuentra entre 60 y 75% del peso del grano y suministra el 70-80% de las calorías consumida por los seres humanos. Además del valor nutricional, el almidón de los cereales, también es importante debido a que afecta las propiedades físicas de muchos alimentos, entre los que se encuentran las tortillas de maíz y trigo. El propósito de esta presentación es la de describir algunos cambios químicos y físicos que ocurren en el almidón  en los procesos de la elaboración de ambos tipos de tortillas. Para la tortilla de maíz se describirán cambios químicos y físicos durante el proceso y almacenamiento medidos como  almidón resistente, entalpías y temperaturas de transición, microscopía , rayos X  y textura. Por otro lado,  para la tortilla de harina de trigo se describirán cambios en amilosa, textura,  frescura detectadas por el consumidor en tortillas almacenadas a diferentes temperaturas y digestibilidad in vitro.

 

e-mail: bramirez@guaymas.uson.mx.

I.4

The Science of Cu(In,Ga)Se2 for Photovoltaic Device Applications

 

Rockett Angus

Department of Msterials Science and Engineering

University of Illinois-Urbana Champaing

 

This talk will briefly review materials science of chalcopyrite Cu(In,Ga)Se2 and the major issues concerning the operation and  performance of solar cells made from this alloy. Issues include the microstructure and microchemistry of the Cu(In,Ga)Se2 absorber layer, particularly the point defect organization; the nature of the current collecting heterojunction and why it appears to collect current so well; the properties of majority and minority carriers in the material; methods for fabrication of the material; and properties of the back contact to the material. The presentation will draw together the large body of experimental data on the material with device models based on the AMPS computer code to show what are the limiting factors controlling performance of the devices.

 

I.5

Biomimetic Molecular Assemblies for Biosensing, High Throughput Drug Discovery and Proteomics

Gabriel P. Lopez
Department of Chemical and Nuclear Engineering and Department of Chemistry,
University of New Mexico, Albuquerque, New Mexico 87131


This talk will present recent developments at the University of New Mexico in the areas of microfluidics, chemical sensing, and instrumentation and molecular assemblies for high throughput drug discovery and proteomics. It will focus on the use of silica microspheres as versatile platforms for biomimetic molecular assemblies, tunable adsorbents, microcolumn packing matrices. Nanostructured mesoporous microspheres formed by a newly developed method based on evaporation-induced self-assembly of surfactant templates will be described. Affinity microcolumns formed by packing of surface modified microspheres are formed by soft lithography techniques and interrogated by steady state fluorescence and frequency fluorimetry techniques. Methods for high throughput flow cytometry will also be presented. Thus a comprehensive approach to bioanalytical systems based on microfluidics and nanomaterials will be described.

 

I.7

Recubrimientos Híbridos Cerámica-Polímero Para Aplicaciones Dentales

 

Rodríguez R., de la Isla A., Vargas S., Estévez M., Castaño V.

Física-Física Aplicada y Tecnología Avanzada, UNAM

 

Los recubrimientos híbridos cerámica-polímero reúnen, en un solo material, las propiedades de ambos tipos de materiales. En base a esto, se diseño un recubrimiento híbrido para ser usado en aplicaciones dentales. Este recubrimiento, aplicado sobre el esmalte dental, permite protegerlo contra procesos de tinción causados por diferentes tipos de substancias como: café, refrescos de cola y tabaco. La componente cerámica del recubrimiento proporciona a este una gran resistencia a la abrasión por cepillado. En este trabajo se reportan las pruebas de estabilidad en el color del esmalte dental y la resistencia a la abrasión usando espectroscopia micro-Raman

 

I.8

Metal Growth and Oxygen Etching of High-Index Si Surfaces

 

Baski Alison A.

Virginia Commonwealth University, Richmond, VA

 

Our group has extensively studied the growth behavior of Group IB metals such as Ag, Cu, and Au on the 1-D template provided by the high-index Si(5 5 12) surface. This surface is oriented approximately midway between the (001) and (111) planes and forms a single-domain, row-like reconstruction. Our scanning tunneling microscopy (STM) studies show that all three metals form a lower temperature phase (<500 °C) where the metal decorates the underlying (5 5 12) surface, as well as higher temperature phases (> 600 °C) where faceting occurs to nearby orientations. The lower temperature phase results in the formation of "nanowires" with a spacing equal to the 5.4 nm periodicity of the (5 5 12) surface. When the annealing temperature is increased, however, the (5 5 12) orientation is no longer stable to faceting. At higher metal coverages and annealing temperatures, the underlying Si structure is removed and other facet planes can be formed. In the case of Au, at least five nearby facet orientations have been observed that are composed of row arrays with periodicities ranging from 2.5 to 3.5 nm [1]. The occurrence of (113) planes has been seen for all three metals, indicating the inherent stability of this orientation. In addition to metal growth, we have also studied oxygen etching of the clean (5 5 12) surface and a few of the metal-induced facets [2]. For these examined surfaces, an amorphous oxide appears to grow at lower temperatures (< 650 °C), and etching occurs at higher temperatures (> 650 °C). In the case of etching, pyramidal or trapezoidal islands appear which incorporate (113) facets, again illustrating the stability of this plane. The density of these islands decreases with increasing temperature, indicating oxide nucleation effects. By manipulation of the oxide etching parameters, it is therefore possible to fabricate a variety of nanometer-sized islands on these high-index surfaces.

 

[1] A.A. Baski, K.M. Saoud, K.M. Jones, Appl. Surf. Sci. 182, 216 (2001).

[2] J.C. Moore, P.H. Woodworth, J.L. Skrobiszewski, A.A. Baski, Surf. Sci., in press.

 

I.10

Analysis of Optical Spectra in the Reciprocal Space: Application to Isotopically Pure Si

 

Lastras J. L.

Instituto de Investigación en Comunicación Óptica, UASLP

 

Reciprocal space analysis offers several advantages over the most common used direct space analysis, in the determination of optical properties of materials. One of the advantages is the separation of base line effects, information and noise in the low-, medium- and high-index Fourier coefficients. In the present work we discuss the basic ideas of the reciprocal space analysis, and as an example, we analyse ellipsometry spectra of isotopically pure Si using reciprocal space. We show clearly that the reciprocal space constitute a powerful tool in the analysis of optical spectra.

 

I.11

El Potencial Planar Continuo de Lindhard y sus Multiples Aplicaciones

 

Cruz Jiménez Salvador A.*

Departamento de Física,

Universidad Autónoma Metropolitana-Iztapalapa

 

Una de las áreas de investigación donde el potencial de superficie ha sido pieza clave es la de dispersión de átomos y moléculas por superficies a ángulos razantes, en el que el ángulo de dispersión y consecuente pérdida de energía dependen fuertemente del potencial de interacción con la superficie. En 1965, Jens Lindhard [1] propuso por primera vez la aproximación del potencial   contínuo, asociado con estudios de canalización de iones a través de orientaciones cristalográficas específicas en el material blanco. Posteriormente, Nicolás Cabrera y Frank Goodman [2] desarrollaron un modelo de interacción átomo-superficie, en el que consideran a la interacción en términos de la periodicidad de la red cristalina , obteniendo una representación para el potencial de superficie en términos de una expansión en términos de la red recíproca, en el que el término de orden más bajo corresponde al potencial de Lindhard y se interpreta como el promedio lateral de la interacción átomo-superficie, mientras que los términos de orden superior corresponden a potenciales difractivos.

En esta plática presentaré algunas de las aplicaciones del potencial de Lindhard para el estudio de interacción de átomos y moléculas con superficies; en particular el caso de dispersión de iones por superficies a ángulos razantes, la incorporación de hidrógeno atómico en superficies de a-Si:H , la interacción de fullereno (C60) con superficies de grafito y la fuerza de adhesión de  partículas asfalténicas con superficies de fierro. Se hará una comparación con información experimental y , en su caso, con otros cálculos teóricos.

 

[1] J. Lindhard, K. Dan. Videnskab. Selsk. Mat. Fys. Medd. 34 , No. 14 (1965).

[2] N. Cabrera and F. O. Goodman, J. Chem. Phys. 56 , 4899 (1972).

 

*Programa de Simulación Molecular, Instituto Mexicano del Petróleo

 

I.12

Photonic Crystals as Magic Material for Optoelectronics*

 

Katayama Yoshifumi **

Center for Taukuba Advanced Research Alliance (TARA),

University of Tsukuba, Tsukuba, Japan

 

It is well known that the motion of an electron in a solid is described as the electron wave motion in the energy-bands. Especially the modern technology made it possible to design the energy-bands arbitrarily in semiconductor structures. In analogy with electron motion, the motivation to control also light propagation in periodic structures can be traced back to late 70’s and the photonic crystal is now to be put into practical devices.

The first prediction of stop-bands for light wave propagating in periodic structures was made by Ohtaka for a array of dielectric balls.1 About ten years later, Yablonovitch demonstrated that if a three-dimensionally periodic dielectric has an electromagnetic band gap which overlaps the electronic band edge, then spontaneous emission can be rigorously forbidden.2  This brought a great shock to the field of optoelectronics, and since then a vast of experimental and theoretical works have been conducted over the world.3  

After a brief introduction to the concept of the photonic crystal and its research history above, some of our attempts to apply photonic crystal to novel optoelectonics devices are presented. Firstly, a trial to fabricate a wavelength-selective bent wave-guide using a two-dimensional photonic crystal of GaAs-AlGaAs 4 will be shown. This device structure was fabricated on an MBE grown GaAs-AlGaAs layer structure with the aid of electron-beam lithography and reactive ion etching. Device parameters therein were chosen based on the FDTD simulation of light propagation in a two-dimensional photonic crystal structure which contains a set of defect line to guide the incident light along the bent wave-guide.

 

1. K. Ohtaka, Phys. Rev. B 19, 5057 (1978).

2. E. Yablonovitch, Phys. Rev. Lett. 58, 2059 (1987).

3. Photonic & Sonic Band-Gap Bibliography at http://home.earthlink.net/~jpdowling/pbgbib.html

4. S. Yamada et al. J. Appl. Phys. 89, 855 (2001).

 

* In collaboration with S. Yamada (now with Graduate School of Integrated Science, Yokohama City

University) and J. B. Cole, Institute of Information Science, University of Tsukuba.

** Now with Tsukuba Industrial Liaison and Cooperative Research Center, University of Tsukuba


I.13

The Effect of Photon Energy, Average Power, and Repetition Rate on Nanotube

Synthesis Using a Free Electron Laser

 

Holloway B.C. 1, Smith M. W. 2, Adu C.K.W.3, Loper A.L. 3, Pradhan B.K. 3, Chen G. 3, Bhattacharyya S. 3, Eklund P.C. 3 and Fischer J.E. 4

1Dept. of Applied Science, College of Williams and Marry,Williamsburg, VA 23187

2NASA Langley Research Center, Hampton, VA 23681

3Dept. of Physics, The Pennsylvania State University, University Park, PA16802

4Department of Material Science and Engineering and Laboratory for Research

on the Structure of Matter, University of Pennsylvania

 

The free electron laser (FEL) located at Thomas Jefferson National Accelerator Facility (Jlab) was used to produce single-walled carbon nanotubes (SWNTs) by laser vaporization of several catalyzed carbon targets.  The Jlab FEL offers the advantage of a high power (~1000 Watts maximum average power), tunable (~2-7 micron), high repetition rate (MHz) photon source where parameters can be varied rather easily compared to tabletop systems.  Initial experiments with the FEL show that, under the appropriate conditions, large soot generation rates (grams per hour) with high SWNTs yield are also possible.  In addition thermal programmed oxidation (TPO), atomic force microscopy (AFM), Raman scattering and high-resolution transmission electron microscopy (HRTEM) of the FEL-produced material show novel properties such as long tube lengths, smaller bundle sizes, matching catalyst concentrations, and interesting variations with carbon target catalyst composition.  While the FEL operating conditions and synthesis system design have not yet been fully optimized, the potential for a large scale production and/or "diameter tuning" of SWNTs using an FEL will also be discussed.  Work supported by DARPA, ARO, NSF, and NASA.

 

I.14

Metodologías Fotoacústicas con Normalización para la Medición de Difusividad Térmica de Metales

 

Banderas López José Abraham

Unidad Profesional Interdisciplinaria de Biotecnología del IPN

 

Se analiza en detalle el modelo difusión térmica en una capa, con fuente de calor armónica y en el límite de absorción superficial. En base a la solución analítica se proponen diversas metodologías fotoacústicas, involucrando normalización de la señal para llevar a cabo medición de difusividad térmica en metales. El proceso de normalización involucra el cociente de señales fotoacústicas para las configuraciones trasera y delantera. Se demuestra la posibilidad de llevar a cabo dichas mediciones en los límites térmicamente fino y térmicamente grueso. La normalización de la señal, con la consecuente eliminación de la función de transferencia, permite el desarrollo de criterios para la selección de subconjuntos de datos experimentales sobre los cuales un análisis confiable es posible. Por último se presenta una nueva metodología fotoacústica por medio de la cual es posible determinar la difusividad térmica del material simplemente determinando las frecuencias de modulación para las cuales la función tangente de la diferencia de fases, para ambas configuraciones, es discontinua.

 

I.16

Development of New Devices Using Off Stoichiometry Silicon Oxide and Silicon

 

Aceves M. Mariano

Instituto Nacional de Astrofísica Óptica y Electrónica

Apdo. 51 Puebla, Pue. México 7000

 

The off stoichiometric silicon oxide, or Silicon Rich Oxide (SRO), is obtained by different techniques. The different kinds of Chemical Vapor Deposition (CVD) Low Pressure (LPCVD), Plasma Enhancement (PECVD), etc. are more frequently used. It is also obtained by implantation of silicon into thermal oxide. In this work, a short presentation of results obtained during the development of novel devices made of silicon and SRO is done. In our research, the Photo and cathodo–luminescence in CVD–SRO and in combination with Si implantation have been studied. The joint effects of characteristics of the SRO and the silicon have been studied in order to obtain SRO/Si devices. It has been found that depending on the silicon excess in the SRO and the silicon characteristics different behavior is obtained. Using these functions, two main devices have been proposed: a silicon surge suppresser was developed and characterized. It is ready to be transfer to massive production. The other device under study is intended to be used as a radiation sensor. Also, models to explain the physics involved are under development.

 

e-mail: maceves@ieee.org


I.17

Surface Analysis Measurement Issues Related to Characterization and Metrology Needs

in Semiconductor Processing

 

Brundle C. R.

Applied Materials,

3050 Bowers Ave., Santa Clara, CA 95150

 

For thin films the International Technology Roadmap for Semiconductors (ITRS) demands metrology in place now for sub 20A thick films on 12 inch wafers. The metrology required always includes thickness determination (to some very high precision, which is more important than absolute accuracy), but may also include composition, or even composition as a function of depth, depending on the nature of the film or film stack involved. The distinction between a metrology measurement and characterization is discussed, and the role of “traditional” surface analysis methods (eg XPS, Auger, SIMS) in both areas is examined. Surface analysis is relevant to both characterization and metrology for ultra thin films. Characterization of interface issues is already critical in developing viable ultra thin film processes, but the traditional surface analysis techniques also have a definite role to play in the metrology of these ultra thin films during actual wafer processing. Examples will be discussed.

 

I.19

Study of Iron Nanoparticles Deposited by Pulsed Laser Deposition

 

De La Cruz W., Contreras O., Song C.,* Poppa H.,* and Cota L.

Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México, Apartado Postal 2681 Ensenada, B.C., México

*National Center for Electron Microscopy , Lawrence Berkeley National Laboratory,  Berkeley CA 94720, USA

 

Nanosize particles of iron have been deposited by pulsed laser deposition (PLD) on the flat side of dimpled sapphire (0001) discs under ultra high vacuum. The substrate temperature was varied from room temperature up to 550C. Transmission Electron Microscopy was used to study the size distribution, shape and crystal structure of the deposited particles. In addition, the deposits were monitoring in-situ by Auger Electron Spectroscopy. It is shown that the substrate temperature, up to 550C, does not determine the size of the nanoparticles when these are produced by PLD. These nanoparticles are not directly related to spots in the transmission electron diffraction pattern of the samples, but there presence is confirmed by the Fe signals in the PEELS spectrum taken from the same samples in the TEM.

 

I.20

Recombination Processes in Semiconductor Structures

 

Gurevich Yu. G.

Departamento de Física, CINVESTAV, México

 

The new approach to investigate the transport phenomena in semiconductor structures is formulated. New expressions describing the recombination processes and spase charge under temperature inhomogeniuty are derived.

 

I.21

Recubrimientos en la Industria Petroquímica

 

Méndez Acevedo Juan Manuel

Surface Engineered Products-Westaim Corporation

 

El llamado coque catalítico no es otra cosa que una colección inmensa de nanotubos creada dentro de los reactores de reacción de etileno. Este proceso de formación de coque produce pérdidas de miles de millones de dólares anualmente en la industria petroquímica. Ciertos compuestos pueden ser aplicados al interior de los reactores para disminuir drásticamente la formación de estos nanotubos. En esta plática se revisarán aquellos métodos que utilizan erosión catódica en vacío capaces de recubrir tubos de hasta 6 metros de largo y 38 milímetros de diámetro interno, así como codos, distribuidores y conectores múltiples hechos de aceros de alta aleación y alta temperatura. Se revisará la eficiencia y velocidad de depósito, poniendo énfasis en los rangos en los que estos parámetros brindan una película de la calidad a un costo aceptable. Se revisará el perfil de presiones a lo largo de tubos con un gran razón de aspecto (longitud/sección transversal efectiva) y como corregir las desuniformidades en éste. Se darán resultados de los beneficios que estos recubrimientos traen a los productores de etileno en función de aumento de rendimiento y reducción de tiempo muerto.


I.22

Dielectrics in Multilayered Structures

 

McGuire G.E.

International Technology Center

 

The selection of interlevel dielectrics used in integrated circuit (IC) applications is undergoing rapid change. The speed and performance of ICs is now dependent on the delay of the interconnect metal resistance and dielectric capacitance (RC delay) rather than the transistor. As a result, there has been rapid development and introduction of Cu interconnections along with the introduction of low dielectric constant materials (low K). These low K materials include carbon-based materials and polymers with dielectric constants down to the range of 2. In addition, much effort has been devoted to aerogels which exhibit dielectric constants below 2. These materials show promise to push the performance of ICs to new levels. However, the selection of the best low K materials is challenging and the introduction into manufacturing has been slow. Some of the promising candidate low k materials will be reviewed and challenges associated with their introduction into IC manufacturing will be described.