El rol estratégico de las opciones reales

OpenAIRE

Orellana Villeda, José Giovanni

2011-01-01

El análisis del Real Options Approach o ROA como también serán llamadas adelante, establece, una forma de cómo determinar el valor de la flexibilidad en las decisiones futuras. Está herramienta sofisticada constituye, un soporte al presupuesto de capital la cual no ha sido completamente explotada, por los gerentes, debido, a diversos aspectos pedagógicos. Las opciones reales permiten estructurar el pensamiento de manera estratégica. Y es precisamente, este argumento que ha motivado el desarro...

Desarrollo e implantación de modelos de evaluación de proyectos de investigación desarrollo e innovación

OpenAIRE

González de Rojas, Ramón

2016-01-01

Desarrollo de un nuevo modelo de evaluación de proyectos de I+D+i, en el cual se evalúa en primer lugar mediante el grado de factibilidad si ese proyecto en concreto tiene cabida en el contexto actual, posteriormente mediante un criterio llamado CIR, se establece cual es el mejor método de evaluación económica incluye diferentes métodos, el VAN, el VAN expandido, opciones reales, y la lógica borrosa (fuzzy-sets). Implementación del modelo anterior sobre una aplicación en el lenguaje de pro...

Ensayos sobre la sonrisa de volatilidad en mercados de opciones

OpenAIRE

Serna Calvo, Gregorio

2011-01-01

La tesis comienza analizando los determinantes de la "sonrisa de volatilidad" en el mercado de opciones sobre el indice IBEX-35,obteniendose evidencia de causalidad lineal en el sentido de Granger de los costes de transacción, representados por el diferencial "bid-ask" relativo, ala forma de la sonrisa. A continuación, se propone un modelo de Black-Scholes ampliando donde la volatilidad depende del precio de ejercicio y del diferencial "bid-ask" relativo, obteniendose que dicho modelo no mejo...

¿CUÁNTOS SIGNIFICADOS TIENE UN PRODUCTO?

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Jose Antonio Paris

2014-06-01

Full Text Available El marketing esencial se basa en la determinación de los significados en la mente del consumidor y de los códigos en la mente del mercado. Para poder sustentar esto se han creado metodologías como las técnicas de afloramiento de significado y las técnicas proyectivas entre otras. Pero, el nuevo problema que surge de esta conceptualización teórica es si vamos a poner al significado en la base del plan de marketing, la pregunta es ¿cuántos significados se deben determinar? Por lo que sabemos cada cultura tiene sus propias significaciones y los significados también cambian con el tiempo incluso lo hacen contextualmente. Lo cual hace aún más complejo el dilema presentado como título de este artículo. En se presentan los argumentos teóricos que sustentan uno de los descubrimientos más importantes del marketing esencial que sostenemos: en general para cada producto o servicio hay cuatro significados dominantes.

Reseña de: Caselli, Elisa, Antijudaïsme, pouvoir politique et administration de la justice. Juifs, chrétiens et converts dans l’ espace jurisdictionnel de la Chancillería de Valladolid (XVe-XVIe siècles.Villeneuve d’Ascq...

Directory of Open Access Journals (Sweden)

Enrique Cantera Montenegro

2017-05-01

Full Text Available Caselli, Elisa, Antijudaïsme, pouvoir politique et administration de la justice. Juifs, chrétiens et converts dans l’ espace jurisdictionnel de la Chancillería de Valladolid (XV^e-XVI^e siècles. Villeneuve d’Ascq Cedex. Atelier National de Reproduction des Thèses, 2016. 396 págs. isbn: 978-2-7295-8891-5.

El enfoque de las opciones estratégicas de los actores en el estudio de las relaciones laborales

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Carmen Marina López Pino

2003-06-01

Full Text Available El interés fundamental de este artículo es esclarecer la propuesta analítica desarrollada por el MIT (Massachussetts Institute of Technology, inspirada en el concepto de "opciones estratégicas" para el estudio de las relaciones laborales. De manera introductoria se plantea la problemática de las relaciones laborales actuales y los hallazgos fundamentales de las diferentes investigaciones del equipo del MIT. En segunda instancia se realiza una breve presentación del enfoque de sistemas de Dunlop que este equipo de investigadores busca superar. Seguidamente se exponen los principales conceptos y premisas del enfoque de las opciones estratégicas de los actores. Y, por último, se presentan brevemente algunas de las debilidades de dicha propuesta.

Da Chrétien de Troyes a Shakespeare («The tragedy of King Richard the Third», a. I, sc. 2

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Alfonso D'Agostino

2015-07-01

Full Text Available L’articolo si propone di considerare le somiglianze fra alcune vicende antico-francesi (l’Yvain di Chrétien de Troyes e il fabliau anonimo De celle que se fist foutre sur la fosse son mari con una scena del Riccardo III di Shakespeare. Anche se non si può dire che il dramma inglese dipenda dai testi narrativi oitanici, esso sviluppa lo stesso motivo della vedova consolata e una serie di motivi secondarî, di immagini (il sangue, il diavolo, la seduzione e di espressioni letterarie in modo sintomaticamente affine. The paper aims to evaluate similarities between some Old-French narratives (Chrétien de Troyes’ Yvain and the anonymous fabliau De celle que se fist foutre sur la fosse son mari and a scene from Shakespeare’s Richard III. Although we cannot affirm that Shakespeare’s play derives from the French narratives, it develops the same theme of “comforted widow” along with a series of secondary themes, of images (the blood, the devil, the seduction and literary expressions in a symptomatically, very similar way.

EL MÉTODO DE DIFERENCIAS FINITAS EN EVALUACIÓN DE OPCIONES REALES THE FINITE DIFFERENCE METHOD IN REAL OPTIONS VALUATION

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Sebastián Otero G

2008-06-01

Full Text Available Una respuesta a las falencias de los métodos tradicionales de evaluación de proyectos de inversión corresponde a la metodología de "Opciones Reales" que proviene del análisis de opciones sobre instrumentos financieros desarrollado en la década de los 70. Esta técnica, aplicada inicialmente a activos no financieros o reales, ha sido aplicada con singular éxito en la evaluación de proyectos de inversión y se presenta como una alternativa a los métodos de evaluación tradicionales, pues incluye tanto los aspectos estratégicos como de la teoría financiera. La variación fundamental que experimenta la evaluación de proyectos de inversión mediante opciones reales con respecto a la realizada mediante los métodos tradicionales es la incorporación de la incertidumbre y la flexibilidad como elementos que agregan valor al proyecto. En el presente este trabajo se realiza un recorrido del estado del arte en lo que respecta a la teoría de opciones reales para la evaluación de proyectos de inversión mediante diferencias finitas. Se describe la importancia de los componentes económicos y estratégicos a la hora de evaluar proyectos de inversión ante escenarios de incertidumbre, analizando las características de esta metodología, destacando sus virtudes y defectos e identificándose su aplicabilidad en la evaluación de proyectos de inversión. Finalmente se realiza una implementación del método de diferencias finitas implícitas (DFI para la evaluación de un caso real que cuenta con las opciones de esperar, abandonar, contraer, expandir y cambiar a mejor uso alternativo, evaluándose para todas las opciones y combinaciones de opciones posibles. Los resultados fueron comparados con la metodología tradicional (VAN y el árbol binomial con transformada logarítmica (ABTL. Ambas metodologías (DFI y ABTL entregan valores equivalentes, siendo ambos superiores a los obtenidos mediante la metodología tradicional (VAN, diferencia que

El Método de Elementos Finitos en la Valoración de Opciones

OpenAIRE

Sanz Herranz, Héctor

2016-01-01

En este trabajo se expone una introducción a los conceptos propios de la teoría de valoración de derivados financieros prestando especial atención a las opciones. Asimismo, se presenta el método de los elementos finitos para la resolución de ecuaciones en derivadas parciales justificando su uso desde el marco teórico. Finalmente, se muestran sendos algoritmos del método en algunos problemas de valoración de derivados financieros. Grado en Matemáticas

El uso de opciones reales para la valuación de proyectos innovadores

OpenAIRE

Grassetti, Virginia; García Fronti, Javier

2012-01-01

El análisis se divide en tres secciones, en la primera se abordan los métodos de valuación de proyectos de inversión propuestos por la Teoría Neoclasista, reflejando sus limitaciones para adaptarse al mercado de tecnologías innovadoras. Luego, se presenta un enfoque de las Opciones Reales como la alternativa que mejor se adapta a las características propias de este nuevo mercado. Por último, se plantea un modelo sencillo que permite analizar las cuestiones más fundamentales de estas metodolog...

Modelos de valorización de opciones europeas en tiempo continuo

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Villamil Jaime

2006-08-01

Full Text Available El clásico modelo de valoración de opciones europeas de Black y Scholes (1973 supone que los retornos logarítmicos de un activo financiero se distribuyen normalmente, no obstante varios estudios empíricos muestran, primero, que esta distribución puede ser asimétrica y tener “colas pesadas” y, segundo, que la varianza del precio del activo no es finita. Este artículo presenta la implementación numérica de tres modelos alternativos: elasticidad constante de la varianza (1976, jump-diffusion (1976 y volatilidad estocástica (1987.

Exhumation history of the western Kyrgyz Tien Shan: Implications for intramontane basin formation

Science.gov (United States)

Bande, Alejandro; Sobel, Edward R.; Mikolaichuk, Alexander; Schmidt, Alexander; Stockli, Daniel F.

2017-01-01

The dextral Talas-Fergana Fault separates the western from the central Tien Shan. Recent work has shed light on the Cenozoic evolution of the eastern and central Tien Shan; much less attention has been paid to the western Tien Shan. In this contribution we present new thermochronological ages for the Fergana and Alai ranges that, combined with the available data set, constrain the Cenozoic exhumation history of the western Tien Shan. Following a tectonically quiet early Cenozoic period, we suggest an onset of exhumation at 25 Ma. This early onset was followed by a period of slower exhumation and in some areas minor reheating. A final, strong late Miocene rapid cooling event is well represented in the western Tien Shan as in other sectors of the range. The early onset of uplift of the western Tien Shan dissected the previously continuous westernmost Parathethyan Sea, progressively isolating basins (e.g., Fergana, Tarim, and Alai basins) in the central Asian hinterland. Moreover, the coeval timing of late Miocene uplift along the length of entire Tien Shan implies that neither the Pamir nor Tarim can be the sole driver for exhumation of the entire range.

Options for rural electrification in Mexico; Opcion para la electrificacion de pequenas comunidades rurales en Mexico

Energy Technology Data Exchange (ETDEWEB)

Gutierrez Vera, Jorge [Luz y Fuerza del Centro, S. A., Mexico, D. F. (Mexico)

1994-12-31

The paper summarizes the results obtained in the study carried out in communities of the Hidalgo State, localized in remote and of difficult access sites. In the study 19 different options, which are technically and economically feasible, from the stand point of commercialization and electrification of the same. The performance of these systems was evaluated with respect to their capability to satisfy 12 technical goals and 5 social-economical, as well as their environmental impact. An hybrid system based on photovoltaic cells, diesel or gasoline generator and a wind-power generator, we think is the recommended option for this type of communities. [Espanol] Este trabajo sintetiza los resultados de un estudio llevado a cabo en comunidades del estado de Hidalgo, localizadas en lugares remotos y de dificil acceso. En el estudio se analizaron 19 diferentes opciones que son factibles tecnica y comercialmente hablando para la electrificacion de las mismas. El comportamiento de estos sistemas fue evaluado con respecto a su capacidad para satisfacer 12 objetivos tecnicos y 5 socioeconomicos, asi como su impacto ambiental. Un sistema hibrido a base de celdas fotovoltaicas, generador a diesel o gasolina y generador eolico, creemos que es la opcion recomendada para este tipo de comunidades.

Options for rural electrification in Mexico; Opcion para la electrificacion de pequenas comunidades rurales en Mexico

Energy Technology Data Exchange (ETDEWEB)

Gutierrez Vera, Jorge [Luz y Fuerza del Centro, S. A., Mexico, D. F. (Mexico)

1993-12-31

The paper summarizes the results obtained in the study carried out in communities of the Hidalgo State, localized in remote and of difficult access sites. In the study 19 different options, which are technically and economically feasible, from the stand point of commercialization and electrification of the same. The performance of these systems was evaluated with respect to their capability to satisfy 12 technical goals and 5 social-economical, as well as their environmental impact. An hybrid system based on photovoltaic cells, diesel or gasoline generator and a wind-power generator, we think is the recommended option for this type of communities. [Espanol] Este trabajo sintetiza los resultados de un estudio llevado a cabo en comunidades del estado de Hidalgo, localizadas en lugares remotos y de dificil acceso. En el estudio se analizaron 19 diferentes opciones que son factibles tecnica y comercialmente hablando para la electrificacion de las mismas. El comportamiento de estos sistemas fue evaluado con respecto a su capacidad para satisfacer 12 objetivos tecnicos y 5 socioeconomicos, asi como su impacto ambiental. Un sistema hibrido a base de celdas fotovoltaicas, generador a diesel o gasolina y generador eolico, creemos que es la opcion recomendada para este tipo de comunidades.

Calculo y comparacion de la prima de un reaseguro de salud usando el modelo de opciones de Black-Scholes y el modelo actuarial

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Luis Eduardo Giron

2015-12-01

Full Text Available La presente investigación pretende calcular y comparar la prima de un reaseguro  usando el modelo de opciones de Black-Scholes y el modelo clásico actuarial tradicional. El período de análisis va desde enero de 2011 hasta diciembre de 2012. Los resultados obtenidos muestran que el modelo de Black-Scholes, que se utiliza normalmente para valorar opciones financieras, puede ser también usado para la estimación de primas de reaseguros de salud; y que la prima neta estimada a partir de este modelo se aproxima a las establecidas por el método actuarial, excepto cuando el deducible del reaseguro es muy alto (por encima de $200.000.000.

El multinivel: como estrategía en la creación de empresa en Colombia

OpenAIRE

Sánchez Chavarro, Juan Gabriel

2010-01-01

Esta investigación evalúa las alternativas que tiene un empresario independiente de un multinivel para crear empresa y las opciones que tiene de generar ingresos adicionales en Colombia ejerciendo su respectiva profesión, conociendo y ofreciendo productos de excelente calidad y de biodegrabilidad. En el presente trabajo se pretende visualizar el multinivel como estrategia en la creación de empresa en el país, identificando a los empresarios independientes de los 7 multiniveles investigado...

Opciones socio técnicas en la formación de campus virtuales en universidades argentinas

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Luciana Guido

2010-09-01

Full Text Available Hoy en día, aproximadamente 65% de las universidades argentinas cuentan con un campus virtual. Este trabajoanaliza las estrategias desplegadas en los procesos de selección de diferentes opciones tecnológicas para la construcciónde campus virtuales en universidades nacionales argentinas. Se presenta la heterogeneidad de elementosoperantes a la hora de tomar decisiones acerca del tipo de plataforma utilizada (distribución “libre”, “propietaria” odesarrollo propio en función de los diferentes “modelos” de universidades y las definiciones sobre la innovación educativasustentada en la “virtualidad”. Se seleccionaron ocho casos de universidades nacionales basados en una muestrarepresentativa, en relación con el tipo de tecnología utilizada y con las características propias de cada universidad encuanto a sus proyectos fundacionales y sus propuestas “virtuales”. El estudio se centra en el análisis de fuentes deinformación secundaria (documentos institucionales de archivo, prensa nacional y local, resoluciones y normativa,sitios Web de las universidades y 30 entrevistas realizadas durante el periodo 2006-2008 a los gestores universitariosy empresas que prestan servicios a las iniciativas analizadas. La selección de las plataformas adoptadas muestra quelas opciones tecnológicas no se fundan solamente en cuestiones “estrictamente técnicas”, sino que también involucranaspectos organizacionales, cognitivos y culturales de las universidades analizadas.

Diferencias cualitativas entre experiencias tutoriales para opciones de aprendizaje universitario

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Ángel J. LÁZARO MARTÍNEZ

2008-01-01

Full Text Available Se analiza la tutoría como elemento básico de la excelencia educativa, resaltando su carácter nuclear en todo proceso formativo institucionalizado. Se constata la relación entre los procesos educativos, la orientación y la tutoría, desde el nuevo enfoque de la auténtica orientación. En el contexto universitario se debaten sus competencias, destacando que, desde sus orígenes, la tutoría ha constituido el sentido de la función y el quehacer de la finalidad y optimización de la formación universitaria, tanto en la búsqueda del saber como en la pretensión de aplicación social. Esta situación aboca en el análisis de las opciones de la acción tutorial en la Universidad, sus modalidades y sus posibilidades de intervención, y se plantean, de forma más concreta, recogiendo las experiencias destacables en el ámbito universitario, las estrategias organizativas y de desarrollo en aulas y situaciones individualizadas.

Source processes of strong earthquakes in the North Tien-Shan region

Science.gov (United States)

Kulikova, G.; Krueger, F.

2013-12-01

Tien-Shan region attracts attention of scientists worldwide due to its complexity and tectonic uniqueness. A series of very strong destructive earthquakes occurred in Tien-Shan at the turn of XIX and XX centuries. Such large intraplate earthquakes are rare in seismology, which increases the interest in the Tien-Shan region. The presented study focuses on the source processes of large earthquakes in Tien-Shan. The amount of seismic data is limited for those early times. In 1889, when a major earthquake has occurred in Tien-Shan, seismic instruments were installed in very few locations in the world and these analog records did not survive till nowadays. Although around a hundred seismic stations were operating at the beginning of XIX century worldwide, it is not always possible to get high quality analog seismograms. Digitizing seismograms is a very important step in the work with analog seismic records. While working with historical seismic records one has to take into account all the aspects and uncertainties of manual digitizing and the lack of accurate timing and instrument characteristics. In this study, we develop an easy-to-handle and fast digitization program on the basis of already existing software which allows to speed up digitizing process and to account for all the recoding system uncertainties. Owing to the lack of absolute timing for the historical earthquakes (due to the absence of a universal clock at that time), we used time differences between P and S phases to relocate the earthquakes in North Tien-Shan and the body-wave amplitudes to estimate their magnitudes. Combining our results with geological data, five earthquakes in North Tien-Shan were precisely relocated. The digitizing of records can introduce steps into the seismograms which makes restitution (removal of instrument response) undesirable. To avoid the restitution, we simulated historic seismograph recordings with given values for damping and free period of the respective instrument and

Glaciers and hydrological changes in the Tien Shan: simulation and prediction

International Nuclear Information System (INIS)

Aizen, V B; Aizen, E M; Kuzmichonok, V A

2007-01-01

In this study, we estimated the current glacier state and forecast the potential impact of global and regional climate change on the glaciers and glacier runoff in the Tien Shan. General (G) and detailed (D) simulations were developed based on assessment of the Tien Shan glacier recession between 1943 and 2003 using an iterative stepwise increase in the equilibrium line altitude of 20 m. The G simulation was developed for 2777 grids each of which covered over 1000 km 2 of glacier surface and D for the 15 953 Tien Shan glaciers. Both simulations employed glacier morphometric characteristics derived from Digital Elevation Model based on remote sensing data, high resolution maps and in situ GPS validation. Simulated changes in glacier area demonstrated that a possible increase in air temperature of 1 deg. C at E-barLA must be compensated by a 100 mm increase in precipitation at the same altitude if Tien Shan glaciers are to be maintained in their current state. An increase in mean air temperature of 4 deg. C and precipitation of 1.1 times the current level could increase E-barLA by 570 m during the 21st century. Under these conditions, the number of glaciers, glacier covered area, glacier volume, and glacier runoff are predicted to be 94%, 69%, 75%, and 75% of current values. The maximum glacier runoff may reach as much as 1.25 times current levels while the minimum will likely equal zero

Evaluación económica de proyectos de inversión basada en la teoría de opciones reales

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Ignacio Andres Garrido Concha

2003-07-01

Full Text Available En la presente investigación se analiza un nuevo enfoque, basado en la aplicación de la Teoría de Opciones Reales para realizar la evaluación económica de proyectos de inversión. El mismo, posee el potencial de entregar una aproximación del valor de la flexibilidad que posee un proyecto, permitiendo al evaluador capturar numéricamente el valor de la estrategia. El objetivo fundamental de la presente investigación fue proponer una “Metodología de Evaluación Económica de proyectos de inversión a partir de la Teoría de Opciones Reales”, con el fin de presentarla como una herramienta de evaluación alternativa a los métodos tradicionales. A modo de aplicación de esta metodología, basada en el Método Binomial con Transformada Logarítmica, se realizó la evaluación económica de distintos proyectos reales los cuales corresponden a distintas variaciones del proyecto “Implementación de un Sistema de Información Geográfica (SIG para controlar la cartografía de las plantaciones pertenecientes a Forestal Mininco S.A” estudiadas previamente por Julio Becker.  

Acciones para el desarrollo de competencias investigativas

OpenAIRE

Ruiz Domínguez, Benito

2012-01-01

La reforma integral de educación tiene su fundamento en los altos índices de deserción y en la desarticulación del nivel medio superior. Los retos principales que tiene la reforma son la ampliación de la cobertura de acceso a estudios del nivel medio, el mejoramiento de la calidad en los procesos de enseñanza-aprendizaje y la búsqueda de equidad. El marco de esta reforma permite articular los programas de distintas opciones educativas en la educación media en el país y comprende una serie de ...

Educación superior de calidad para el siglo XXI

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Alexander Vega Miranda

2001-01-01

Full Text Available Este artículo tiene como objetivo presentar de modo explícito la serie de opciones ideológicas y pedagógicas que, dentro del contexto costarricense, deben ser tenidas en cuenta por la persona encargada de tomar las decisiones, cuando intente mejorar la calidad de la educación para enfrentar los retos del siglo XXI

La gerencia del conflicto

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Nelsa Beatriz Rey de Astaiza

2015-05-01

Full Text Available RESUMEN Se hicieron investigaciones de estudios extensivos acerca de cómo la gente se comporta en situaciones de conflicto y han llegado a varias conclusiones. Algunos investigadores se refieren a diferentes estilos para gerenciar conflicto. Otros consideran que la forma como se responde al conflicto tiene que ver con las características de personalidad, entre otras opciones.

Valor en riesgo para un portafolio con opciones financieras Value at risk for a financial portfolio with options

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Carlos Alexánder Grajales Correa

2010-07-01

Full Text Available En este artículo se presentan y aplican diferentes formulaciones matemáticas, exactas y aproximadas, para el cálculo del valor en riesgo (VaR de algunos portafolios con activos financieros, haciendo especial énfasis en aquellos que contienen opciones financieras. El uso y pertinencia de tales formulaciones es analizado según las características e hipótesis que se tengan de los portafolios construidos, para lo cual se analizan en detalle la volatilidad y el percentil de la distribución de los cambios en el valor del portafolio, al igual que la volatilidad estocástica en un horizonte de tiempo dado. Para éste fin, se consideran los métodos de varianzas y covarianzas, simulación histórica y simulación Monte Carlo, desde una perspectiva formal y ampliada a portafolios que contienen opciones financieras, estableciendo algoritmos alternativos de cálculo y comparaciones entre los resultados.This article presents and applies different mathematical, exact and approximated formulations to estimate value at risk of some portfolios with financial assets, emphasizing on those which contain financial options. The use and appropriateness of such formulations is analyzed base don characteristics and hypothesis of constructed portfolios. With this purpose, volatility and distribution percentile of changes in the value of the portfolio are analyzed. Stochastic volatity at a given time is also analyzed. With this purpose, variances, and co-variance methods. Historic simulation and Monte Carlo simulation from a formal and extended perspective to portfolios containing financial options are taken into consideration, establishing alternative of calculation and comparison between the results.

Reciever Function Transect Across Tibet, Tarim and Tien Shan

Science.gov (United States)

Marshall, B.; Levin, V. L.; Huang, G.; Roecker, S. W.; Wang, H.

2010-12-01

We investigate the region of the ongoing collision between the India and Eurasia tectonic plates that results in widespread deformation of the continental lithosphere. Over the past decade, numerous regional studies were conducted between the Himalaya and the Tien Shan mountains, each illuminating a small part of the area. We combine the data from a number of portable and permanent networks to construct a ~1800 km long profile of lithospheric properties that cross three very different tectonic domains: the Tibetan plateau, the Tarim basin, and the Tien Shan mountains. We use data from 60 stations operated in the region by US, Chinese and French researchers. We use records of distant earthquakes to construct receiver function gathers for each station. The uniformity of processing ensures that our results are comparable along the transect. We examine receiver function gathers at each site, and rank their quality on the basis of number of records, noise levels, and directional stability of the wavefield. We select 27 sites with high-quality data. For these we construct average receiver function traces using data in the 60-85 degree range, and use them as a guide to the lithospheric layering beneath the region. On most receiver functions we constructed the most prominent feature is a positive phase likely associated with the crust-mantle transition. The timing of this phase varies significantly over the length of the profile. Beneath the Tibetan plateau delay times ~7-8 s are seen close to the Himalayas, and nearly 10 s delays are found further north. Delays of 6 to 8 s are seen beneath sites in the Tarim basin and the Tien Shan mountains, and nearly 10 s delays are seen at the border between them. In addition to the pulse associated with the crust-mantle transition we see other locally-consistent features, for example a negative phase with delay values between 3 and 5 s beneath much of the Tibetan plateau.

Retribución de directivos basada en opciones y comportamiento frente al riesgo =Option-based executive compensation and risk-taking behavior

OpenAIRE

Belda Ruiz, María

2015-01-01

La retribución de directivos basada en opciones, comúnmente conocidas como stock options, proporciona incentivos para modificar el perfil de riesgo de la empresa a través de la sensibilidad de la riqueza del directivo a las variaciones en el precio de las acciones de la empresa (delta) y a la volatilidad implícita negociada en el mercado (vega). El objetivo de esta Tesis Doctoral es analizar en detalle estos niveles de incentivos, delta y vega, a través de modelos de valoración que se adaptan...

Modelo para la selección de opciones estratégicas en el sector de textiles de uso técnico

OpenAIRE

Detrell Domingo, Ariadna

2007-01-01

El objeto de la tesis es establecer una sistemática para la detección de oportunidades estratégicas dentro del sector de textiles de uso técnico. Desde esta perspectiva, se analizan diversos modelos conceptuales para la selección de opciones estratégicas, para definir uno de nuevo adecuado a la idiosincrasia del sector industrial textil. El modelo conceptual a definir es ecléctico porqué utilizará algunas de las herramientas habitualmente empleadas para el análisis estratégico interno y exter...

Alcoholic fermentation: an option for renewable energy production from agricultural residues; Fermentacion alcoholica: una opcion para la produccion de energia renovable a partir de desechos agricolas

Energy Technology Data Exchange (ETDEWEB)

Vazquez, H. J [Universidad Autonoma Metropolitana (Mexico)]. E-mail: hjv@correo.azc.uam.mx; Dacosta, O [Oficina de Consejo, Desarrollo y Transferencia Tecnologica, Dijon (Francia)]. E-mail: statfor@yahoo.com

2007-10-15

Biotechnology offers several options for generating renewable energy. One of these technologies consists on producing bioethanol by fermentation. Bioethanol is mainly used to prepare fuel for motor vehicles. This paper presents a proposal to produce such as fuels with a hundred liters experimental fermentation pilot unit. Results derived from essays are similar, in terms of yield and productivity, to those presented by other systems, if we take into account that our unit works under non sterile conditions, which represents significant energy savings. This technology does not require specialized knowledge for its construction and it would accessible to groups of Mexican farmers. [Spanish] La biotecnologia ofrece diversas opciones para la generacion de energias renovables. Una de ellas es la produccion de bioetanol, el cual se obtiene mediante fermentacion. El bioetanol se usa en la preparacion de carburantes para vehiculos automotores. En este articulo se presenta una propuesta para la obtencion de este combustible mediante una unidad de fermentacion piloto experimental de 100 litros. Los resultados de nuestros ensayos, en rendimiento y productividad, son similares a los de otros laboratorios si se considera que esta unidad piloto funciona en condiciones no esteriles, lo que representa como ventaja un ahorro de energia no despreciable. Ademas, la tecnologia no requiere conocimientos especializados para su realizacion y estaria al alcance de grupos campesinos mexicanos.

Efecto del dopado con Si sobre la estructura de defectos en sistemas heteroepitaxiales GaN/AlN/Si(111

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Sánchez, A. M.

2000-08-01

Full Text Available The Si doping effect on the defect structure in GaN epilayers grown by molecular beam epitaxy on Si(111 substrates using AlN buffer layers has been studied. Transmission electron microscopy and related techniques have been used to carry out the structural characterization. The Si doping affects both the subgrain size and misorientation in GaN epilayer mosaic structure. The Si doping also leads to an increase of the planar defect density, as well as a decrease of the threading dislocation density. The enlargement of the subgrain tilt and the planar defect density explain the reduction of the dislocation density reaching the GaN free surface.

En el presente artículo se lleva a cabo el análisis del efecto que el dopado con Si tiene sobre la estructura de defectos en epicapas de GaN crecidas por epitaxia de haces moleculares sobre sustratos de Si (111 utilizando capas amortiguadoras de AlN. La caracterización estructural se llevó a cabo mediante microscopía electrónica de transmisión convencional y de alta resolución. El dopado con Si afecta a la desorientación y tamaño de los subgranos que constituyen la estructura mosaico de la epicapa de GaN. El dopado con Si provoca un aumento en la densidad de defectos planares, así como una disminución en la densidad de dislocaciones de propagación. El incremento en el grado de desorientación de inclinación, así como en la densidad de defectos planares que se produce conforme aumenta el dopado con Si explican la disminución en la densidad de dislocaciones que alcanzan la superficie libre de GaN.

Cualquier tiempo futuro tiene que ser mejor

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Paquita Armas Fonseca

2015-01-01

Full Text Available Cuba tiene un importante movimiento caricaturista, conocido y laureado en los diversos lugares del mundo. No es el caso de la historieta que, a pesar de contar con muy buenos dibujantes, el desarrollo dramatúrgico no está a la altura de la imagen por lo que se ha visto limitada en su desarrollo. El guión es el talón de Aquiles del cómic cubano que no ha evolucionado como se hermana la caricatura. Es con la animación que el cómic cubano ha trascendido sus fronteras. Se trata de un movimiento vivo que ha saltado los más increíbles obstáculos.

DUST LOADING OF THE ATMOSPHERE AND GLACIERS IN THE KUMTOR MINING AREA (AKSHYYRAK, TIEN SHAN)

OpenAIRE

V. A. Kuzmichenok

2012-01-01

Industrial development of the Kumtor Gold Mine in the nival-glacial zone of Tien Shan (altitude ranging from 4000 to 4500 m a.s.l.) is inevitably accompanied by the release of some additional amounts of dust in atmosphere. Sampling in 7 points and an analysis of the quantity (weight) of dust in the seasonal snow (September–April) on glaciers show that the dust pollution does not substantially exceed the natural level of dust in Tien Shan. An analysis of almost 3 000 daily measurements of dust...

La valoración de proyectos de energía eólica en Colombia bajo el enfoque de opciones reales.

OpenAIRE

Maya Ochoa, Cecilia; Hernández Betancur, Juan David; Gallego Múnera, Óscar Mauricio

2012-01-01

Este estudio explora diferentes metodologías de valoración de proyectos de generación de energía eólica en Colombia. Inicialmente se valora con base en flujos de caja descontados, luego se aplica el enfoque de opciones reales, estimando su valor extendido, incluida una opción real de expansión. Para estimar la volatilidad, parámetro fundamental de la valoración de la opción real, se simulan los procesos que siguen las variables con alta incidencia en ella, como el precio de la energía y los v...

¿Qué tienes en la cara, eso se quita?

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Jimmy Arévalo Romero

2013-10-01

Full Text Available El presente texto es un ensayo preparado por estudiantes de Medicina que tiene origen en su experiencia personal, ya que trata del padecimiento del acné en lo adolescencia, en él quieren concienciar a lo comunidad en general sobre las consecuencias psicológicas que genera el padecimiento del acné en el adolescente, y estimular a las personas a contribuir al desarrollo de estos jóvenes en la sociedad.

Asimetría y curtosis en el modelo binomial para valorar opciones reales: caso de aplicación para empresas de base tecnológica

OpenAIRE

Gastón Silverio Milanesi

2013-01-01

El trabajo propone un modelo de valoración de opciones reales con base en el modelo binomial utilizando la transformación de Edgeworth (Rubinstein, 1998) para incorporar momentos estocásticos de orden supe- rior, especialmente para ciertos tipos de organizaciones, como empresas de base tecnológica, donde no se dispone de cartera de activos financieros gemelos, comparables de mercado y procesos estocásticos no gaussianos. Primero, se presenta el desarrollo formal del modelo, luego su aplicació...

Heterogeneities of the shear wave attenuation field in the lithosphere of East Tien Shan and their relationship with seismicity

Science.gov (United States)

Kopnichev, Yu. F.; Sokolova, I. N.

2012-02-01

The shear wave attenuation field in the lithosphere of Eastern Tien Shan has been mapped. The method based on analysis of the ratio between amplitudes of Sn and Pn waves was used. On aggregate, about 120 seismograms made at the Makanchi station (MKAR), mainly in the period of 2003-2009, at epicentral distances of about 350-1200 km were analyzed. It was found that shear wave attenuation in the lithosphere of Eastern Tien Shan is weaker than that in the region of Central Tien Shan. This agrees with the fact that the rate of deformation of the Earth's crust in Eastern Tien Shan is lower (based on GPS data), as is the seismicity level, in comparison to Central Tien Shan. The zones of high attenuation, where strong earthquakes with M > 7.0 have not occurred for the last 200 years, have been identified: first of all, these are the area west of Urumqi and that of the Lop Nur test site. It is suggested that in the first zone, where an annular seismicity structure has formed over the last 30 years, a strong earthquake may be being prepared. The second zone is most probably related to the uplift of mantle fluids resulting from a long-term intensive technogenic effect, analogous to what has occurred in areas of other nuclear test sites (Nevada and Semipalatinsk).

Contabilización de Contratos de Futuros, Opciones, Forwards y Swaps (Accounting treatment for future, options, forwards and swap contracts

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Vernor Mesén Figueroa

2012-12-01

Full Text Available Un entorno cada vez más dinámico y evolutivo ha dado paso al surgimiento y, por ende, al uso cada vez más frecuente de instrumentos financieros cuya flexibilidad y capacidad de ajuste a las condiciones de mercado permitan a las personas y empresas lograr sus objetivos de operación, inversión y financiamiento. En el contexto antes descrito, los contratos de futuros, opciones, forwards y swaps representan mecanismos cuyas características operativas permiten a sus tenedores el logro de objetivos alternativos tales como la cobertura eficaz de diferentes tipos de riesgos o la obtención de ganancias o pérdidas derivadas de la especulación. El presente artículo pretende reseñar, en forma breve, los mecanismos de operación de los contratos de futuros, opciones, forwards y swaps, para luego enfatizar en los criterios de contabilización que toda entidad o intermediario financiero debe seguir para reconocer los efectos que dichos tipos de contratos tienen sobre su posición financiera, resultados de operación y flujos de efectivo.   ABSTRACT A rapidly changing and evolving environment has given rise and increased the use of financial tools whose flexibility and adjusting capabilities to variable market conditions allow individuals and companies to achieve their operating, investment and financial goals. Within this framework, contracts for futures, options, forwards and swaps provide mechanisms with operating characteristics that allow their tenants to achieve alternative objectives such as the effective coverage of different risks or the attaining of profits or losses as a result of speculation. This article attempts to resume the operating mechanisms of futures, options, forwards and swap contracts and then concentrates into the accounting criteria that must be followed by financial intermediaries or entities to recognize the effects such contracts have on their financial position, operational results and cash flow.

Salud Tiene Sabor: a model for healthier restaurants in a Latino community.

Science.gov (United States)

Nevarez, Carmen R; Lafleur, Mariah S; Schwarte, Liz U; Rodin, Beth; de Silva, Pri; Samuels, Sarah E

2013-03-01

The prevalence of overweight and obesity in children has risen nationally in recent decades, and is exceptionally high in low-income communities of color such as South Los Angeles CA. Independently owned restaurants participating in the Salud Tiene Sabor program at ethnic foods marketplace Mercado La Paloma in South Los Angeles are responding to the childhood obesity crisis by posting calories for menu items and providing nutrition information to patrons. To evaluate whether menu labeling and nutrition information at point of purchase have an influence on availability of healthy food options, patron awareness of calorie information, and restaurant owners' support of the program. A case-study design using mixed methods included restaurant owner and stakeholder interviews, patron surveys, and environmental assessments. Data were collected using originally designed tools, and analyzed in 2009-2011. Healthy eating options were available at the Mercado La Paloma; restaurant owners and the larger community supported the Salud Tiene Sabor program; 33% of patrons reported calorie information-influenced purchase decisions. Owners of independent restaurants have an important role in improving access to healthy foods in low-income, Latino communities. Copyright © 2013 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.

Identificación y análisis de las oportunidades de exportación de productos agrícolas y agro-industriales potenciales desde Colombia hacia Estados Unidos - periodo de estudio: 2003 a 2012

OpenAIRE

Cely Espinosa, Diana Lorena

2015-01-01

Una de las mayores brechas que tienen los empresarios colombianos es la falta de información sobre las opciones de exportación hacia otros países, especialmente con Estados Unidos siendo uno de los principales socios comerciales que tiene Colombia. Por esta razón el presente trabajo de investigación se propuso identificar y analizar las oportunidades de exportaciones de productos agrícolas y agro-industriales potenciales desde Colombia hacia Estados Unidos en el periodo de 2003 hasta 2012...

Medio ambiente, desarrollo sostenible y escalas de sustentabilidad

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ÁNGEL PANIAGUA

1998-01-01

Full Text Available El presente artículo tiene dos partes. En la primera se analiza la complejidad y las múltiples dimensiones de concepto de sustentabilidad. La perspectiva que se adopta se fundamenta en que no existe una opinión clara y universalmente admitida sobre el concepto y, en consecuencia, una de sus principales características es su vaguedad. En la segunda parte se estudian las diferentes opciones de desarrollo rural sustentable desde una perspectiva global y se proponen diferentes escalas de sustentabilidad rural.

El comercio internacional de productos agrícolas en los ochenta y las consecuencias para México

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Carlos Vidali

1989-09-01

Full Text Available El trabajo tiene como propósito analizar la evolución reciente y las tendencias del comercio agropecuario, las políticas de subsidios a la producción y exportación de los países desarrollados, el impacto de estas políticas en el tercer mundo y los planteamientos y negociaciones en el seno del GATT paza intentar el planteamiento de opciones productivas paza los países en desarrollo y en particular para México.

INFECCIONES POR BACTERIAS ANAEROBIAS: CRITERIOS DE MANEJO CLÍNICO Y PROCEDIMIENTOS MICROBIOLÓGICOS DE DIAGNÓSTICO

OpenAIRE

Luz Angélica Quintero B.

2009-01-01

El incremento de las infecciones por bacterias anaerobias, la resistencia de estos gérmenes a las limitadas opciones terapéuticas de uso empírico, el poco y reciente conocimiento que se tiene sobre estos gérmenes, conlleva a que el clínico no sospeche en la mayoría de los casos que se encuentra ante un posible cuadro infeccioso cuyo agente etiológico involucra un germen anaerobio, retardando el diagnostico oportuno y el inicio adecuado de la antibioticoterapia, explicando el súbito aumento en...

Security in the data link layer of the OSI model on LANs wired Cisco

OpenAIRE

María Genoveva Moreira Santos; Pedro Antonio Alcívar Marcillo

2018-01-01

Hay no hay tecnologías o protocolos completamente seguro en las infraestructuras de red, por esta razón, este documento tiene como objetivo demostrar la importancia de configurar opciones de seguridad en equipos de la red. En esta ocasión nos centraremos en la capa de enlace de datos del modelo OSI, que es donde los controles han comenzado a implementarse a nivel de protocolos. Las herramientas que se utilizan en la investigación facilitan la implementación de un laboratorio virtual, que cons...

Análisis de contenido del noticiario CNI Canal 40 (durante la tercera semana del mes de mayo referente a las campañas electorales para diputados federales

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Rafael Espinosa

2004-01-01

Full Text Available En las sociedades democráticas, cada persona tiene necesidad de conocer lo que sucede en su entorno para poder definir con libertad su voto. Esta libertad sólo se logra cuando los ciudadanos disponen de información que les permite elegir entre varias opciones. Basado en este principio, el autor realiza un monitoreo al noticiario principal de CNI Canal 40 con el fin de observar y analizar su participación dentro del proceso electoral federal del año 2003 en México.

Las flores del desierto. Opciones de vida en pueblos de la región central de Sonora

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Ma. Amalia Gracia

2014-01-01

Full Text Available Aunque la búsqueda de las localidades rurales por generar opciones de vida se observa en el esfuerzo de algunos pobladores, en México la política pública se restringe a ofrecer garantías sociales; le deja al mercado la creación de alternativas económicas, que no alcanzan para producir desarrollo local y regional. El presente artículo reflexiona sobre esto, a partir de una iniciativa de trabajo asociativo surgida hace más de seis años en pueblos de la región central del norte de Sonora, y muestra cómo se resuelven temporal y dinámicamente las tensiones entre prácticas de cooperación y reciprocidad y las de intercambio con el mercado utilizando postulados teóricos de distintas disciplinas, retomadas por las propuestas de economía solidaria. El caso ilustra las dificultades, riqueza y potencialidad de iniciativas como ésta, y la importancia del apoyo gubernamental en localidades a las que la baja capacidad económica y la generalización del narcotráfico las vuelve frágiles para contrarrestar procesos profundos de despoblamiento.

Empirical Relationship between particulate matter and Aerosol Optical Depth over Northern Tien-Shan, Central Asia

Science.gov (United States)

Measurements were obtained at two sites in northern Tien-Shan in Central Asia during a 1-year period beginning July 2008 to examine the statistical relationship between aerosol optical depth (AOD) and of fine [PM2.5, particles less than 2.5 μm aerodynamic diameter (AD)] and coars...

Are the cultural accounting values a relevant issue for the SMEs' financing options?

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Fabio Albuquerque

2017-01-01

Full Text Available El presente artículo tiene como objetivo examinar las opciones de financiamiento de los administradores y propietarios de las Pymes incorporando en el análisis los valores culturales relacionados con el conservadurismo y el secreto. Los datos fueron recogidos mediante un cuestionario realizado a los administradores y propietarios de una muestra de 1,629 pymes líderes en Portugal. También se analizó la información contable y financiera entre los ejercicios 2009 a 2011, habiendo obtenido 438 respuestas, lo que supone un 27%, que valida la misma. Basado en técnicas de regresión multivariante, los resultados muestran una correlación negativa entre el conservadurismo y el secreto, analizados en conjunto, y las opciones de financiamiento de las empresas relacionadas con un mayor riesgo, o sea, una financiamiento con costos. También se verifica una correlación entre la selección de las fuentes de financiamiento de las Pymes a la luz de la teoría de jerarquía de las preferencias de capital.

Los orígenes del grial en la literatura medieval: de Chrétien de Troyes a Robert de Boron

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Mario Martín Botero

2010-12-01

Full Text Available Este artículo muestra el origen literario del tema del Grial en la literatura medieval francesa, abordando dos textos esenciales para el surgimiento y consolidación de la “literatura del Grial”: Le Conte du Graal de Chrétien de Troyes y Le Roman de l’Estoire dou Graal de Robert de Boron. Los autores de estas obras establecen las bases para el desarrollo de toda una temática que gira alrededor del Grial a partir del siglo XII hasta nuestros días. El artículo muestra cómo de un objeto apenas sagrado en el texto de Chrétien de Troyes se pasa a una reliquia de la sangre de Cristo en la versión de Robert de Boron.This paper studies the literary origin of the Grail legend in medieval French literature, taking into account two important romances: Le Conte du Graal by Chrétien de Troyes and Le Roman de l’Estoire dou Graal by Robert de Boron. In these two texts the authors established the basis for the development of a new subject matter around the mysterious object called “Grail” from the Middle Ages to the present times. It will also be shown how an object, not totally sacred in Chrétien de Troyes, becomes a relic related with Jesus’s blood in Robert de Boron.

La alucinación verbal tiene la estructura de la holofrase

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Arturo de la Pava Ossa

2009-05-01

Full Text Available ¿En qué sentido la alucinaciónauditiva tiene la estructura dela holofrase? La holofrase es lainterjección, dice Lacan en 1958.En 1964, plantea que cuando enel primer par significante no hayintervalo, se solidifica, “se holofrasea”;a lo que añade que algo delmismo orden ocurre en la psicosis.Esta afirmación aporta elementospara pensar que la alucinación esuna holofrase y cómo a partir deella el psicótico construye su delirioparanoico.Palabras clave: holofrase, interjección,alucinación, discurso, funciónfálica.

Implicaciones metabólicas del consumo exesivo de fructosa

OpenAIRE

Esquivel-Solís, Viviana; Gómez-Salas, Georgina

2007-01-01

En los últimos años se ha dado un auge importante en la producción de alimentos endulzados con edulcorantes distintos a la sacarosa o azúcar de mesa, que por aportar menos calorías, son utilizados ya sea para perder peso o para mantener un peso saludable, o bien, para ofrecer opciones alimenticias a individuos que padecen de diabetes o intolerancia a la glucosa. Uno de los edulcorantes de mayor utilización es el jarabe de maíz alto en fructosa, el cual, en comparación con la sacarosa, tiene u...

VULNERACIONES DE LA DIGNIDAD HUMANA AL FINAL DE LA VIDA

OpenAIRE

ROBERTO GERMÁN ZURRIARÁIN

2017-01-01

La muerte es constitutiva a la naturaleza humana y por ello tiene que acontecer de forma natural. Pero hay dos realidades que, principalmente, la falsifican: la eutanasia y la obstinación terapéutica. Dos opciones erróneas que no aceptan la realidad humana de la muerte (la primera adelantándola y la otra retrasándola). Desde el punto de vista filosófico y ético ambas son rechazadas, porque atentan contra la dignidad humana al final de la vida. Aparte de estas, en este artículo también se rech...

Estudio Cinemático Comparativo de Tres Opciones de Tratamiento Conservador en el Manejo de los Trastornos de la Marcha de Niños con Equinismo Idiopático

OpenAIRE

Lerma Lara, Sergio

2016-01-01

Tesis Doctoral leída en la Universidad Rey Juan Carlos de Madrid en 2016. Directores de la Tesis: Carlos Goicoechea García y Tomás Epeldegui Torre El equinismo idiopático es una alteración de la marcha pediátrica caracterizada por la realización de una excesiva flexión plantar del tobillo durante la marcha. No hay consenso en la literatura acerca de la mejor oferta terapéutica, coexistiendo opciones conservadoras y quirúrgicas en la práctica clínica. El objetivo de este t...

Permian charnockites in the Pobeda area: Implications for Tarim mantle plume activity and HT metamorphism in the South Tien Shan range

Science.gov (United States)

Loury, Chloé; Rolland, Yann; Lanari, Pierre; Guillot, Stéphane; Bosch, Delphine; Ganino, Clément; Jourdon, Anthony; Petit, Carole; Gallet, Sylvain; Monié, Patrick; Riel, Nicolas

2018-04-01

The Permian history of the Central Asian Orogenic belt is marked by large-scale strike-slip faults that reactivate former Paleozoic structures, delineated by widespread alkaline magmatism. The genetic link between the syn-kinematic granitoids emplaced in the Tien Shan range and magmas emplaced within the Tarim Large Igneous Province, and the interaction between this plume and transcurrent tectonics, are still unsolved issues. We investigated the Pobeda massif, in the eastern Kyrgyz Tien Shan, located at the boundary between the Tien Shan range and the Tarim Craton, which exhibits a high-temperature unit. In this unit, Permian magmatism resulted in the emplacement of alkaline charnockites at mid-crustal levels. The primary mineralogical assemblage is nominally anhydrous and made of ortho- and clino-pyroxenes, fayalite, K-feldspar, plagioclase and quartz. These charnockites are associated with partially-molten paragneisses and marbles. Thermobarometry on these rocks indicates that the charnockites emplaced following the intrusion of a melt at a temperature > 1000 °C and pressure of around 6 kbar, corresponding to depth of 20 km. The resulting thermal anomaly triggered the partial melting of paragneisses. Bulk geochemistry including Sr, Nd, Pb and Hf isotopes suggests that charnockites fit into the Tarim Large Igneous Province magmatic series, with minor crustal assimilation. U-Pb ages on zircons of charnockites and surrounding paragneisses indicate that charnockites intruded and triggered partial melting of the gneisses at c. 287, 275 and 265 Ma. 40Ar/39Ar dating on amphibole gives a similar age as the U-Pb age at 276.2 ± 2.0 Ma. 40Ar/39Ar dating on biotite from the Charnockite unit marbles gives ages at ca. 256-265 Ma, which shows that exhumation onset directly follows the HT history, and is tentatively correlated to top-to-the-North thrusting of the Charnockite unit in a transpressive context. Additional 40Ar/39Ar dating on syn-kinematic white micas from an

Production of Al2O3–SiC nano-composites by spark plasma sintering; Producción de nano-composites – SiC–Al2O3 por spark plasma sinterizado

Energy Technology Data Exchange (ETDEWEB)

Mansour Razavi; Ali Reza Farajipour; Mohammad Zakeri; Mohammad Reza Rahimipour; Ali Reza Firouzbakht

2017-11-01

In this paper, Al2O3–SiC composites were produced by SPS at temperatures of 1600°C for 10min under vacuum atmosphere. For preparing samples, Al2O3 with the second phase including of micro and nano-sized SiC powder were milled for 5h. The milled powders were sintered in a SPS machine. After sintering process, phase studies, densification and mechanical properties of Al2O3–SiC composites were examined. Results showed that the specimens containing micro-sized SiC have an important effect on bulk density, hardness and strength. The highest relative density, hardness and strength were 99.7%, 324.6 HV and 2329MPa, respectively, in Al2O3–20wt% SiCmicro composite. Due to short time sintering, the growth was limited and grains still remained in nano-meter scale. [Spanish] En este trabajo se muestran compuestos de Al2O3-SiC producidos por SPS, en vacío, a 1.600 °C durante 10 min. Para la preparación de muestras, se molieron polvos de Al2O3 durante 5 h con la segunda fase de micro-y-nano polvo de SiC. Posteriormente, estos polvos molidos se sinterizaron mediante SPS. Después del proceso de sinterización, se realizaron estudios de fase, densificación y propiedades mecánicas de los compuestos de Al2O3-SiC obtenidos. Los resultados mostraron que micro-SiC en las muestras tiene un efecto importante en su densidad aparente, dureza y resistencia. La mayor densidad relativa, dureza y resistencia fueron respectivamente del 99,7%, 324,6 HV y 2.329 MPa para Al2O3 con un 20% en peso micro-SiC. Debido al corto tiempo de sinterización, el crecimiento los granos fue limitado y se mantuvieron en escala nanométrica.

P-type poly-Si prepared by low-temperature aluminum-induced crystallization and doping for solar cells

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, Yasuhiro; Yu, Zhenrui; Morales-Acevedo, Arturo [CINVESTAV-IPN, Mexico, D.F. (Mexico)

2000-07-01

P-type poly-Si thin films prepared by low temperature aluminum-induced crystallization and doping are reported. The starting material was boron-doped a-Si:H prepared by PECVD on glass substrates. Aluminum layers with different thickness were evaporated on a-Si:H surface and conventional thermal annealing was performed at temperatures ranging from 300 to 550 Celsius degrees. XRD, SIMS, and Hall effect measurements were carried out to characterize the annealed Al could be crystallized at temperature as low as 300 Celsius degrees in 60 minutes. This material has high carrier concentration as well as high Hall mobility and can be used as a p-layer of seed layer for thin film poly-Si solar cells. The technique reported here is compatible with PECVD process. [Spanish] Se informa sobre la preparacion de peliculas delgadas tipo P y Poli-Si mediante la cristalizacion inducida de aluminio a baja temperatura y el dopado. El material inicial era de boro dopado y a-Si:H preparado PECVD sobre substratos de vidrio. Se evaporaron capas de aluminio de diferente espesor sobre una superficie de a-Si:H y se llevo a cabo un destemplado termico convencional a temperaturas que varian entre 300 y 500 grados Celsius. Se llevaron a cabo mediciones de XRB, SIMS y del efecto Hall para caracterizar el aluminio destemplado para que pudiera ser cristalizado a temperaturas tan bajas como 300 grados Celsius en 60 minutos. Este material tiene una alta concentracion portadora asi como una alta movilidad Hall y puede usarse como una capa de semilla para celdas solares de pelicula delgada Poli-Si. La tecnica reportada aqui es compatible con el proceso PECVD.

DUST LOADING OF THE ATMOSPHERE AND GLACIERS IN THE KUMTOR MINING AREA (AKSHYYRAK, TIEN SHAN

Directory of Open Access Journals (Sweden)

V. A. Kuzmichenok

2012-01-01

Full Text Available Industrial development of the Kumtor Gold Mine in the nival-glacial zone of Tien Shan (altitude ranging from 4000 to 4500 m a.s.l. is inevitably accompanied by the release of some additional amounts of dust in atmosphere. Sampling in 7 points and an analysis of the quantity (weight of dust in the seasonal snow (September–April on glaciers show that the dust pollution does not substantially exceed the natural level of dust in Tien Shan. An analysis of almost 3 000 daily measurements of dust in the surface layer of air at 4 points around the gold mine has also shown that the economic activity has no significant impact on dust production. It is likely that the manmade component of overall dust in the immediate vicinity of the deposit and the gob pile does not exceed 20%. No increase in the content of dust and in its anthropogenic component with time has been found. Thus, we suggest that the principal amount of dust in the area is brought during the cold season from snow-free areas of Central Asia.

The origin and evolution of Iskanderkul Lake in the western Tien Shan and related geomorphic hazards

Czech Academy of Sciences Publication Activity Database

Emmer, Adam; Kalvoda, J.

2017-01-01

Roč. 99, č. 2 (2017), s. 139-154 ISSN 0435-3676 R&D Projects: GA MŠk(CZ) LO1415 Institutional support: RVO:86652079 Keywords : iskanderkul lake * rockslide dam * outburst flood * tien shan Subject RIV: EH - Ecology, Behaviour OBOR OECD: Environmental sciences (social aspects to be 5.7) Impact factor: 1.302, year: 2016

Energetic sustainability: Challenges and options in Mexico; Sustentabilidad energetica: Retos y opciones en Mexico

Energy Technology Data Exchange (ETDEWEB)

Rosas Flores, Dionicio; Sheinbaum Pardo, Claudia [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)

2000-07-01

In this report present a general overview of energy trends and objectives of policy for Mexico, in the context of sustainable development. The work is divided in two main parts: the first one presents trends in energy use and potential, energy sector reform, social and economics indicators and revision of efficiency and renewable energy. The second part discusses options and instruments of energy politics for the country in regard of the sustainable development. The energy is central to concerns of sustainable development, affecting economic; the local and global environment, and social problems as poverty, population, health and education. Mexico should promote political energy that permit the fulfillment the energy requirements while developing strategies that help to alleviate the social problems and productivity, based on lesser environmental impacts. [Spanish] Este reporte presenta una vision sobre las tendencias energeticas de Mexico y plantea prioridades y objetivos de politica para el pais, en el contexto de desarrollo sustentable. El trabajo muestra dos partes principales: la primera seccion presenta tendencias en el uso de energia, potenciales energeticos e indicadores economicos y sociales, ademas de una revision de eficiencias y politicas de energias renovables. La segunda parte discute opciones, instrumentos y restricciones en el contexto del desarrollo energetico sustentable en el pais. La energia es un elemento central en el desarrollo ya que esta relacionado con la economia, el ambiente local y global y aspectos sociales como pobreza, poblacion, salud y educacion. Esto obliga en Mexico a promover politicas que permitan la cobertura de los requerimientos energeticos, las cuales deben desarrollarse de manera conjunta con estrategias, para ayudar a disminuir los problemas, productivos y sociales con menores impactos ambientales.

Opciones reales como respuesta ante la valoración con flujo de caja libre en situaciones de incertidumbre: Caso de la compra de maquinaria en una empresa colombiana de consumo masivo

OpenAIRE

Donato Valdés, Nathalie; Forero Díaz, Nicolás

2017-01-01

El alto grado de incertidumbre de la economía actual impone retos y riesgos a las finanzas corporativas de cualquier compañía -- Encontrar alternativas que permitan la flexibilización de los modelos de evaluación de proyectos empresariales se constituye, en este sentido, en una de sus máximas tareas -- Una de estas alternativas es el método de valoración por Opciones Reales -- El presente estudio aplica dicho método a un proyecto de inversión en innovación tomando el caso de la compra de una ...

Miseria y violencia en El Coronel no tiene quien le escriba

Directory of Open Access Journals (Sweden)

Gloria Escobar Soriano

1999-02-01

Full Text Available El trabajo describe la marginación y la pobreza de un sector de la sociedad colombiana en El Coronel no tiene quien le escriba, la célebre novela de Gabriel García Márquez. Mientras el Coronel espera la llegada de la carta, su hijo Agustín, ha muerto por sus actividades revolucionarias. El y su mujer enferma viven en una casa hipotecada y comen de las migajas que le sobran al gallo. El grado de injusticia y violencia política que se respira en el ambiente aumentan la crisis económica del Coronel y generan en él una resistencia pasiva que recobra cuando se niega a vender el gallo y decide esperar la fecha de la pelea.

Aplicación de Opciones Reales a la Valuación de Proyectos en Empresas Pequeñas y Medianas y su Estructura de Capital-Edición Única

OpenAIRE

Sara Barajas Cortés

2006-01-01

En este trabajo de investigación se desarrolla la valuación de un proyecto de inversión de una Pyme mexicana, dicho proyecto consiste en el diseño, comercialización e implantación de soluciones especializadas de tecnología de información en el sector de seguridad pública. Para llevar a cabo la aplicación de la metodología de opciones reales en este caso real, sirvió de guía el método del caso, ya que la mayor parte de la investigación fue de campo. El proyecto fue evaluad...

Ordering at Si(111)/o-Si and Si(111)/SiO2 Interfaces

DEFF Research Database (Denmark)

Robinson, I. K.; Waskiewicz, W. K.; Tung, R. T.

1986-01-01

X-ray diffraction has been used to measure the intensity profile of the two-dimensional rods of scattering from a single interface buried inside a bulk material. In both Si(111)/a-Si and Si(111)/SiO2 examples there are features in the perpendicular-momentum-transfer dependence which are not expec...... are not expected from an ideal sharp interface. The diffraction profiles are explained by models with partially ordered layers extending into the amorphous region. In the Si(111)/a-Si case there is clear evidence of stacking faults which are attributed to residual 7×7 reconstruction....

A note on the Sumerian expression SI-ge4-de3/dam

Directory of Open Access Journals (Sweden)

Widell, Magnus

2002-12-01

Full Text Available The expression SI-ge4-dam/de3 appears in some of the loan documents of the Ur III period where it was used to establish the interest rate or the loan fee. In addition, it is sometimes preceded by ki-ba 'in its/this place/ground' or, in some cases, ma2 -a 'in the boat'. The regular verb SI.g was closely related, perhaps even synonymous with, the reduplication verb ḡar/ḡa2-ḡa2 'to put' or 'to place'. While it may be concluded that SI-ge4-dam/de3 had nothing to do with the verb si 'to fill' or gi4 'to return', the correct analysis of the expression remains somewhat uncertain. The article proposes that the SI should be read se and understood as a phonetic writing for the regular verb se3.g 'to put', 'to place'. The combination of the verb with the ki-ba may suggest that a more parochial form of keeping products existed side by side with the large centralized granaries and storehouses of the city.La expresión SI-ge4-dam/de3 aparece en algunos contratos de préstamo del período de Ur III, donde se empleaba para determinar el interés de dicho préstamo. Por otra parte, este término se hallaba a veces precedido de ki-ba 'en su/este lugar/suelo', y en algunos casos por ma2 -a 'en la barca'. El verbo regular SI.g está muy relacionado (quizás es incluso sinónimo con el verbo de la clase de la reduplicación ḡar/ḡa2-ḡa2 'poner' o 'colocar'. Mientras que puede concluirse que SI-ge4-dam/de3 no tiene nada que ver con el verbo si 'llenar', ni con gi4 'regresar, devolver', el análisis correcto de la expresión sigue siendo, de algún modo, incierto. En el artículo se propone que SI puede leerse como se , entendiéndolo como una escritura fonética del verbo regular se3.g 'poner', 'colocar'. La combinación del verbo con ki-ba podría indicar que, junto a los grandes graneros y almacenes centrales de la ciudad, había un modo distinto y más modesto de conservar los productos.

Study of Si/Si, Si/SiO2, and metal-oxide-semiconductor (MOS) using positrons

International Nuclear Information System (INIS)

Leung, To Chi.

1991-01-01

A variable-energy positron beam is used to study Si/Si, Si/SiO 2 , and metal-oxide-semiconductor (MOS) structures. The capability of depth resolution and the remarkable sensitivity to defects have made the positron annihilation technique a unique tool in detecting open-volume defects in the newly innovated low temperature (300C) molecular-beam-epitaxy (MBE) Si/Si. These two features of the positron beam have further shown its potential role in the study of the Si/SiO 2 . Distinct annihilation characteristics has been observed at the interface and has been studied as a function of the sample growth conditions, annealing (in vacuum), and hydrogen exposure. The MOS structure provides an effective way to study the electrical properties of the Si/SiO 2 interface as a function of applied bias voltage. The annihilation characteristics show a large change as the device condition is changed from accumulation to inversion. The effect of forming gas (FG) anneal is studied using positron annihilation and the result is compared with capacitance-voltage (C-V) measurements. The reduction in the number of interface states is found correlated with the changes in the positron spectra. The present study shows the importance of the positron annihilation technique as a non-contact, non-destructive, and depth-sensitive characterization tool to study the Si-related systems, in particular, the Si/SiO 2 interface which is of crucial importance in semiconductor technology, and fundamental understanding of the defects responsible for degradation of the electrical properties

Photoluminescence of Er-doped Si-SiO2 and Al-Si-SiO2 sputtered thin films

International Nuclear Information System (INIS)

Rozo, C.; Fonseca, L.F.; Jaque, D.; Sole, J.Garcia

2008-01-01

Er-doped Si-SiO 2 and Al-Si-SiO 2 films have been deposited by rf-sputtering being annealed afterwards. Annealing behavior of the Er 3+ : 4 I 13/2 → 4 I 15/2 emission of Er-doped Si-SiO 2 yields a maximum intensity for annealing at 700-800 deg. C. 4 I 13/2 → 4 I 15/2 peak emission for Er-doped Al-Si-SiO 2 at 1525 nm is shifted from that for Er-doped Si-SiO 2 at 1530 nm and the bandwidth increases from 29 to 42 nm. 4 I 13/2 → 4 I 15/2 emission decays present a fast decaying component related to Er ions coupled to Si nanoparticles, defects, or other ions, and a slow decaying component related to isolated Er ions. Excitation wavelength dependence and excitation power dependence for the 4 I 13/2 → 4 I 15/2 emission correspond with energy transfer from Si nanoparticles. Populating of the 4 I 11/2 level in Er-doped Si-SiO 2 involves branching and energy transfer upconversion involving two or more Er ions. Addition of Al reduces the populating of this level to an energy transfer upconversion involving two ions

Asimetría y curtosis en el modelo binomial para valorar opciones reales: caso de aplicación para empresas de base tecnológica

Directory of Open Access Journals (Sweden)

Gastón Silverio Milanesi

2013-01-01

Full Text Available El trabajo propone un modelo de valoración de opciones reales con base en el modelo binomial utilizando la transformación de Edgeworth (Rubinstein, 1998 para incorporar momentos estocásticos de orden superior, especialmente para ciertos tipos de organizaciones, como empresas de base tecnológica, donde no se dispone de cartera de activos financieros gemelos, comparables de mercado y procesos estocásticos no gaussianos. Primero, se presenta el desarrollo formal del modelo, luego su aplicación sobre la valuación de spin-off tecnológico universitario, sensibilizando asimetría-curtosis y exponiendo el impacto en el valor del proyecto. Finalmente, se concluye sobre limitaciones y ventajas de la propuesta de valoración que resume la simplicidad del modelo binomial e incorporando momentos de orden superior en subyacentes con procesos no normales.

Asimetría y curtosis en el modelo binomial para valorar opciones reales: caso de aplicación para empresas de base tecnológica

Directory of Open Access Journals (Sweden)

Gastón Silverio Milanesi

2013-07-01

Full Text Available El trabajo propone un modelo de valoración de opciones reales con base en el modelo binomial utilizando la transformación de Edgeworth (Rubinstein, 1998 para incorporar momentos estocásticos de orden supe- rior, especialmente para ciertos tipos de organizaciones, como empresas de base tecnológica, donde no se dispone de cartera de activos financieros gemelos, comparables de mercado y procesos estocásticos no gaussianos. Primero, se presenta el desarrollo formal del modelo, luego su aplicación sobre la valuación de spin-off tecnológico universitario, sensibilizando asimetría-curtosis y exponiendo el impacto en el valor del proyecto. Finalmente, se concluye sobre limitaciones y ventajas de la propuesta de valoración que resume la simplicidad del modelo binomial e incorporando momentos de orden superior en subyacentes con pro- cesos no normales.

Jeux et enjeux d’écriture chez Chrétien de Troyes: l’exemple de «Cligès»

Directory of Open Access Journals (Sweden)

Ida Lucia Machado

2011-10-01

Full Text Available Neste artigo, nos propomos descrever a estética da trama irônica presente na escritura de Chrétien de Troyes, tomando por base seu romance Cligès. A destacar algumas estratégias passíveis de criar o fenômeno irônico, estaremos também mostrando o poder de sedução que emana desta escritura.Nous nous proposons, dans cet artible, de décrire l’esthétique du jeu ironique chez Chrétien de Troyes, em puisant dans son roman Cligès. Enn dégageant qulques unes dês stratégies susceptibles de créer le phénomène ironique, nous montrerons, à la fois, le pouvoir de séduction qui emane de cette écriture.

Crustal block structure by GPS data using neural network in the Northern Tien Shan

Science.gov (United States)

Kostuk, A.; Carmenate, D.

2010-05-01

For over ten years regular GPS measurements have been carried out by Research Station RAS in the Central Asia. The results of these measurements have not only proved the conclusion that the Earth's crust meridional compression equals in total about 17 mm/year from the Tarim massif to the Kazakh shield, but have also allowed estimating deformation behavior in the region. As is known, deformation behavior of continental crust is an actively discussed issue. On the one hand, the Earth's crust is presented as a set of microplates (blocks) and deformation here is a result of shifting along the blocks boundaries, on the other hand, lithospheric deformation is distributed by volume and meets the rheological model of nonlinear viscous fluid. This work represents an attempt to detect the block structure of the surface of the Northern Tien Shan using GPS velocity fields. As a significant difference from analogous works, appears the vector field clustering with the help of neural network used as a classifier by many criteria that allows dividing input space into areas and using of all three components of GPS velocity. In this case, we use such a feature of neural networks as self-organization. Among the mechanisms of self-organization there are two main classes: self-organization based on the Hebb associative rule and the mechanism of neuronal competition based on the generalized Kohonen rule. In this case, we use an approach of self-organizing networks in which we take neuronal competition as an algorithm for their training. As a rule, these are single-layer networks where each neuron is connected to all components of m-dimensional input vector. GPS vectors of the Central Asian velocity field located within the territory of the Northern Tien Shan were used as input patterns. Measurements at GPS sites were fulfilled in 36 hour-long sessions by double-frequency receivers Trimble and Topcon. In so doing, measurement discreteness equaled 30 seconds; the data were processed by

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

International Nuclear Information System (INIS)

Jiang, Xiaofan; Ma, Zhongyuan; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

2014-01-01

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN x /SiN y multilayers with high on/off ratio of 10 9 . High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

Science.gov (United States)

Jiang, Xiaofan; Ma, Zhongyuan; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

2014-09-01

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiNx/SiNy multilayers with high on/off ratio of 109. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

CONOCEOS A VOSOTROS MISMOS. Un estudio sobre la relevancia democrática del fisgoneo, a partir de Plutarco

Directory of Open Access Journals (Sweden)

Alicia M.ª de Mingo Rodríguez

2012-01-01

Full Text Available El chismorreo puede parecer un comportamiento anecdótico en el contexto de una microsociología de la vida cotidiana. Sin embargo, cuando los medios de comunicación lo convierten en un tema masivo y rentable, cabe pensar que el conocimiento que ofrecen de la vida privada o íntima de los otros tiene relevancia ética y política en la imagen peculiar y ejemplarizante de la humanidad y de la propia comunidad, así como en las opciones axiológicas, con inevitables repercusiones en el prestigio de la democracia. Para indagar este tema, se parte del estudio sobre la actualidad o inactualidad del pensamiento de Plutarco sobre el fisgoneo.

Electronic states at Si-SiO2 interface introduced by implantation of Si in thermal SiO2

International Nuclear Information System (INIS)

Kalnitsky, A.; Poindexter, E.H.; Caplan, P.J.

1990-01-01

Interface traps due to excess Si introduced into the Si-SiO 2 system by ion implantation are investigated. Implanted oxides are shown to have interface traps at or slightly above the Si conduction band edge with densities proportional to the density of off-stoichiometric Si at the Si-SiO 2 interface. Diluted oxygen annealing is shown to result in physical separation of interface traps and equilibrium substrate electrons, demonstrating that ''interface'' states are located within a 0.5 nm thick layer of SiO 2 . Possible charge trapping mechanisms are discussed and the effect of these traps on MOS transistor characteristics is described using a sheet charge model. (author)

Nonvolatile field effect transistors based on protons and Si/SiO2Si structures

International Nuclear Information System (INIS)

Warren, W.L.; Vanheusden, K.; Fleetwood, D.M.; Schwank, J.R.; Winokur, P.S.; Knoll, M.G.; Devine, R.A.B.

1997-01-01

Recently, the authors have demonstrated that annealing Si/SiO 2 /Si structures in a hydrogen containing ambient introduces mobile H + ions into the buried SiO 2 layer. Changes in the H + spatial distribution within the SiO 2 layer were electrically monitored by current-voltage (I-V) measurements. The ability to directly probe reversible protonic motion in Si/SiO 2 /Si structures makes this an exemplar system to explore the physics and chemistry of hydrogen in the technologically relevant Si/SiO 2 structure. In this work, they illustrate that this effect can be used as the basis for a programmable nonvolatile field effect transistor (NVFET) memory that may compete with other Si-based memory devices. The power of this novel device is its simplicity; it is based upon standard Si/SiO 2 /Si technology and forming gas annealing, a common treatment used in integrated circuit processing. They also briefly discuss the effects of radiation on its retention properties

Sub-barrier fusion of Si+Si systems

Science.gov (United States)

Colucci, G.; Montagnoli, G.; Stefanini, A. M.; Bourgin, D.; Čolović, P.; Corradi, L.; Courtin, S.; Faggian, M.; Fioretto, E.; Galtarossa, F.; Goasduff, A.; Haas, F.; Mazzocco, M.; Scarlassara, F.; Stefanini, C.; Strano, E.; Urbani, M.; Szilner, S.; Zhang, G. L.

2017-11-01

The near- and sub-barrier fusion excitation function has been measured for the system 30Si+30Si at the Laboratori Nazionali di Legnaro of INFN, using the 30Si beam of the XTU Tandem accelerator in the energy range 47 - 90 MeV. A set-up based on a beam electrostatic deflector was used for detecting fusion evaporation residues. The measured cross sections have been compared to previous data on 28Si+28Si and Coupled Channels (CC) calculations have been performed using M3Y+repulsion and Woods-Saxon potentials, where the lowlying 2+ and 3- excitations have been included. A weak imaginary potential was found to be necessary to reproduce the low energy 28Si+28Si data. This probably simulates the effect of the oblate deformation of this nucleus. On the contrary, 30Si is a spherical nucleus, 30Si+30Si is nicely fit by CC calculations and no imaginary potential is needed. For this system, no maximum shows up for the astrophysical S-factor so that we have no evidence for hindrance, as confirmed by the comparison with CC calculations. The logarithmic derivative of the two symmetric systems highlights their different low energy trend. A difference can also be noted in the two barrier distributions, where the high-energy peak present in 28Si+28Si is not observed for 30Si+30Si, probably due to the weaker couplings in last case.

Sub-barrier fusion of Si+Si systems

Directory of Open Access Journals (Sweden)

Colucci G.

2017-01-01

Full Text Available The near- and sub-barrier fusion excitation function has been measured for the system 30Si+30Si at the Laboratori Nazionali di Legnaro of INFN, using the 30Si beam of the XTU Tandem accelerator in the energy range 47 - 90 MeV. A set-up based on a beam electrostatic deflector was used for detecting fusion evaporation residues. The measured cross sections have been compared to previous data on 28Si+28Si and Coupled Channels (CC calculations have been performed using M3Y+repulsion and Woods-Saxon potentials, where the lowlying 2+ and 3− excitations have been included. A weak imaginary potential was found to be necessary to reproduce the low energy 28Si+28Si data. This probably simulates the effect of the oblate deformation of this nucleus. On the contrary, 30Si is a spherical nucleus, 30Si+30Si is nicely fit by CC calculations and no imaginary potential is needed. For this system, no maximum shows up for the astrophysical S-factor so that we have no evidence for hindrance, as confirmed by the comparison with CC calculations. The logarithmic derivative of the two symmetric systems highlights their different low energy trend. A difference can also be noted in the two barrier distributions, where the high-energy peak present in 28Si+28Si is not observed for 30Si+30Si, probably due to the weaker couplings in last case.

Nitric acid oxidation of Si (NAOS) method for low temperature fabrication of SiO{sub 2}/Si and SiO{sub 2}/SiC structures

Energy Technology Data Exchange (ETDEWEB)

Kobayashi, H., E-mail: koba771@ybb.ne.jp [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Imamura, K.; Kim, W.-B.; Im, S.-S.; Asuha [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

2010-07-15

We have developed low temperature formation methods of SiO{sub 2}/Si and SiO{sub 2}/SiC structures by use of nitric acid, i.e., nitric acid oxidation of Si (or SiC) (NAOS) methods. By use of the azeotropic NAOS method (i.e., immersion in 68 wt% HNO{sub 3} aqueous solutions at 120 deg. C), an ultrathin (i.e., 1.3-1.4 nm) SiO{sub 2} layer with a low leakage current density can be formed on Si. The leakage current density can be further decreased by post-metallization anneal (PMA) at 200 deg. C in hydrogen atmosphere, and consequently the leakage current density at the gate bias voltage of 1 V becomes 1/4-1/20 of that of an ultrathin (i.e., 1.5 nm) thermal oxide layer usually formed at temperatures between 800 and 900 deg. C. The low leakage current density is attributable to (i) low interface state density, (ii) low SiO{sub 2} gap-state density, and (iii) high band discontinuity energy at the SiO{sub 2}/Si interface arising from the high atomic density of the NAOS SiO{sub 2} layer. For the formation of a relatively thick (i.e., {>=}10 nm) SiO{sub 2} layer, we have developed the two-step NAOS method in which the initial and subsequent oxidation is performed by immersion in {approx}40 wt% HNO{sub 3} and azeotropic HNO{sub 3} aqueous solutions, respectively. In this case, the SiO{sub 2} formation rate does not depend on the Si surface orientation. Using the two-step NAOS method, a uniform thickness SiO{sub 2} layer can be formed even on the rough surface of poly-crystalline Si thin films. The atomic density of the two-step NAOS SiO{sub 2} layer is slightly higher than that for thermal oxide. When PMA at 250 deg. C in hydrogen is performed on the two-step NAOS SiO{sub 2} layer, the current-voltage and capacitance-voltage characteristics become as good as those for thermal oxide formed at 900 deg. C. A relatively thick (i.e., {>=}10 nm) SiO{sub 2} layer can also be formed on SiC at 120 deg. C by use of the two-step NAOS method. With no treatment before the NAOS method

Joining of SiC ceramics and SiC/SiC composites

Energy Technology Data Exchange (ETDEWEB)

Rabin, B.H. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

1996-08-01

This project has successfully developed a practical and reliable method for fabricating SiC ceramic-ceramic joints. This joining method will permit the use of SiC-based ceramics in a variety of elevated temperature fossil energy applications. The technique is based on a reaction bonding approach that provides joint interlayers compatible with SiC, and excellent joint mechanical properties at temperatures exceeding 1000{degrees}C. Recent emphasis has been given to technology transfer activities, and several collaborative research efforts are in progress. Investigations are focusing on applying the joining method to sintered {alpha}-SiC and fiber-reinforced SiC/SiC composites for use in applications such as heat exchangers, radiant burners and gas turbine components.

Un représentant d'États européens dans l'arriète-pays ottoman. Le cas de Sponty à Serrès (fin XVIIIe-début XIXe siècle

Directory of Open Access Journals (Sweden)

Georges Koutzakiotis

2009-01-01

Full Text Available La domination des commerçants chrétiens orthodoxes, dans l'arrière-pays balkanique de l'Empire ottoman, et celle des Européens, dans les Échelles du Levant, pendant le XVIIIe siècle, sont aujourd'hui bien connues. Cependant, les Européens essayèrent, déjà depuis le même siècle, d'étendre leur rayon d'action à l'intérieur de l'Empire, en établissant des sujets non-ottomans comme agents commerciaux et consulaires et en écartant ainsi les intermédiaires autochtones. Un de ces premiers essais, plus exactement de la part de l'Autriche et de la France, eut lieu à Serrès, centre économique important des Balkans grâce au commerce du coton. Michel Sponty, protégé (beratlı de la France d'origine vénitienne, fut le seul de ces agents commerciaux et consulaires qui réussit finalement à s'enraciner dans la société de Serrès, en renonçant pourtant à son identité franco-levantine et en adoptant celle des commerçants dominants, c'est-à-dire l'identité du chrétien orthodoxe.

Microstructure and Mechanical Property of SiCf/SiC and Cf/SiC Composites

International Nuclear Information System (INIS)

Lee, S P; Cho, K S; Lee, H U; Lee, J K; Bae, D S; Byun, J H

2011-01-01

The mechanical properties of SiC based composites reinforced with different types of fabrics have been investigated, in conjunction with the detailed analyses of their microstructures. The thermal shock properties of SiC f /SiC composites were also examined. All composites showed a dense morphology in the matrix region. Carbon coated PW-SiC f /SiC composites had a good fracture energy, even if their strength was lower than that of PW-C f /SiC composites. SiC f /SiC composites represented a great reduction of flexural strength at the thermal shock temperature difference of 300 deg. C.

Magnetron-sputter epitaxy of β-FeSi2(220)/Si(111) and β-FeSi2(431)/Si(001) thin films at elevated temperatures

International Nuclear Information System (INIS)

Liu Hongfei; Tan Chengcheh; Chi Dongzhi

2012-01-01

β-FeSi 2 thin films have been grown on Si(111) and Si(001) substrates by magnetron-sputter epitaxy at 700 °C. On Si(111), the growth is consistent with the commonly observed orientation of [001]β-FeSi 2 (220)//[1-10]Si(111) having three variants, in-plane rotated 120° with respect to one another. However, on Si(001), under the same growth conditions, the growth is dominated by [-111]β-FeSi 2 (431)//[110]Si(001) with four variants, which is hitherto unknown for growing β-FeSi 2 . Photoelectron spectra reveal negligible differences in the valance-band and Fe2p core-level between β-FeSi 2 grown on Si(111) and Si(001) but an apparent increased Si-oxidization on the surface of β-FeSi 2 /Si(001). This phenomenon is discussed and attributed to the Si-surface termination effect, which also suggests that the Si/Fe ratio on the surface of β-FeSi 2 (431)/Si(001) is larger than that on the surface of β-FeSi 2 (220)/Si(111).

Study for obtaining a suppressor device of transients using the Al/SRO/Si structure; Estudio para la obtencion de un dispositivo supresor de transitorios utilizando la estructura Al/SRO/Si

Energy Technology Data Exchange (ETDEWEB)

Marin Ramos, Heriberto

1999-06-01

transitorios de voltaje. En este trabajo se presenta la estructura Aluminio/Oxido rico en Silicio/Silicio como otra opcion en el campo de los dispositivos supresores de transitorios. Algunos dispositivos utilizados en la supresion de transitorios de voltaje son: varistores de oxido de zinc, varistores de carburo de silicio, celdas de selenio, diodos zener, etcetera. La estructura AI/SRO/Si presenta propiedades conductoras debido a la presencia de exceso de silicio en la pelicula de SRO. Variando la razon de gases reaccionantes (Ro=N{sub 2}O/SiH{sub 4}) durante el crecimiento de la pelicula de Oxido Rico en Silicio (SRO, por sus siglas en ingles), se puede variar la conductividad del material. El SRO resulta de mucha importancia para el dispositivo supresor de transitorios que se pretende obtener en el presente trabajo debido a su comportamiento no-ohmico. El dispositivo AI/SRO/Si se comporta de varias maneras dependiendo de las caracteristicas del SRO y del sustrato de silicio. Se ha encontrado que uno de estos comportamientos es como un supresor de transitorios de voltaje. Verificando su comportamiento como supresor de transitorios, se estudiaron los efectos del espesor de la pelicula, del area y del exceso de silicio del dispositivo, para lo cual se obtuvo la caracteristica I-V, y la obtencion de algunos parametros en c.d. En el presente trabajo el SRO se obtuvo mediante LPCVD (Low Pressure Chemical Vapor Deposition), inicialmente se realizo una caracterizacion C-V para obtener parametros indicativos del exceso de silicio, tales como: permitividad de la pelicula de SRO. Tambien se obtuvo el indice de refraccion, el cual es un parametro indicativo de la presencia de exceso de silicio. Una vez teniendo la certeza de la presencia de exceso de silicio se procedio a obtener la caracteristica I-V de la estructura AI/SRO/Si como dispositivo. Se analizo el comportamiento de la estructura AI/SRO/Si con diferentes parametros, tales como: Ro, espesor de SOR, areas.

SiC Nanoparticles Toughened-SiC/MoSi2-SiC Multilayer Functionally Graded Oxidation Protective Coating for Carbon Materials at High Temperatures

Science.gov (United States)

Abdollahi, Alireza; Ehsani, Naser; Valefi, Zia; Khalifesoltani, Ali

2017-05-01

A SiC nanoparticle toughened-SiC/MoSi2-SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi2, α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi2-SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi2-SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10-2 g/cm3/h, respectively.

Reliability implications of defects in high temperature annealed Si/SiO2/Si structures

International Nuclear Information System (INIS)

Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S.; Devine, R.A.B.; Mathiot, D.; Wilson, I.H.; Xu, J.B.

1994-01-01

High-temperature post-oxidation annealing of poly-Si/SiO 2 /Si structures such as metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field effect transistors is known to result in enhanced radiation sensitivity, increased 1/f noise, and low field breakdown. The authors have studied the origins of these effects from a spectroscopic standpoint using electron paramagnetic resonance (EPR) and atomic force microscopy. One result of high temperature annealing is the generation of three types of paramagnetic defect centers, two of which are associated with the oxide close to the Si/SiO 2 interface (oxygen-vacancy centers) and the third with the bulk Si substrate (oxygen-related donors). In all three cases, the origin of the defects may be attributed to out-diffusion of O from the SiO 2 network into the Si substrate with associated reduction of the oxide. The authors present a straightforward model for the interfacial region which assumes the driving force for O out-diffusion is the chemical potential difference of the O in the two phases (SiO 2 and the Si substrate). Experimental evidence is provided to show that enhanced hole trapping and interface-trap and border-trap generation in irradiated high-temperature annealed Si/SiO 2 /Si systems are all related either directly, or indirectly, to the presence of oxygen vacancies

Fabrication and Mechanical Properties of SiCw(p/SiC-Si Composites by Liquid Si Infiltration using Pyrolysed Rice Husks and SiC Powders as Precursors

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Dan Zhu

2014-03-01

Full Text Available Dense silicon carbide (SiC matrix composites with SiC whiskers and particles as reinforcement were prepared by infiltrating molten Si at 1550 °C into porous preforms composed of pyrolysed rice husks (RHs and extra added SiC powder in different ratios. The Vickers hardness of the composites showed an increase from 18.6 to 21.3 GPa when the amount of SiC added in the preforms was 20% (w/w, and then decreased to 17.3 GPa with the increase of SiC added in the preforms up to 80% (w/w. The values of flexural strength of the composites initially decreased when 20% (w/w SiC was added in the preform and then increased to 587 MPa when the SiC concentration reached 80% (w/w. The refinement of SiC particle sizes and the improvement of the microstructure in particle distribution of the composites due to the addition of external SiC played an effective role in improving the mechanical properties of the composites.

Oscillations in the fusion of the Si + Si systems; Oscilaciones en la fusion de sistemas de Si + Si

Energy Technology Data Exchange (ETDEWEB)

Aguilera R, E F; Kolata, J J; DeYoung, P A; Vega, J J [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

1986-02-15

Excitation functions for the yields of all the residual nuclei from the {sup 28} Si + {sup 28,30} and {sup 30} Si + {sup 30} Si reactions have been measured via the {gamma}-ray technique for center of mass energies in the region within one and two times the Coulomb barrier.Thirteen elements were identified for the first reaction and ten for the other two. While no structure is shown by the data for the {sup 28} + {sup 28} Si reaction, we have found evidence for intermediate width structure in the 2{alpha} and the {alpha}pn channels in {sup 28} Si + {sup 30} Si and for broad structure in the total fusion cross sections for {sup 30} Si + {sup 30} Si. Calculations using a barrier penetration model with one free parameter reproduce the experimental results quite well. Evaporation model calculations indicate that the individual structure of the nuclei involved in the respective decay chains might have an important influence upon the deexcitation process at the energies relevant to our experiments. (Author)

Cladocera (Crustacea: Branchiopoda of Cat Tien National Park, South Vietnam

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Artem Y. Sinev

2013-08-01

Full Text Available Cladocera of Cat Tien National Park, South Vietnam, and the surrounding agricultural area, were surveyed during the spring of 2009 (onset of the wet season and autumn 2010 (end of the wet season. The studied water bodies included two large lakes (Bau Sau and Bau Chim, small lakes and ponds, temporary pools, rivers and streams, as well as rice fields and ponds in an agricultural area beyond the boundaries of the National Park. Fifty three species of Cladocera were found, 18 of them new for Vietnam. Distribution and taxonomical status of the species are discussed. Of the recorded species, 58.5% (31 were found only in the National Park, 34% (18 both in the National Park and the agricultural area, and only 7.5% (4 exclusively in the agricultural area. Of the 20 species new for Vietnam, only one was found both in the National Park and the agricultural area, all others were found in the National Park only. Such a difference can be directly attributed to the loss of natural habitats (forest ponds and streams in agricultural areas and to the pollution by pesticides. Our study shows the importance of surveys in pristine and protected areas, for the full evaluation of regional microcrustacean richness.

Analyses of the As doping of SiO{sub 2}/Si/SiO{sub 2} nanostructures

Energy Technology Data Exchange (ETDEWEB)

Ruffino, Francesco; Miritello, Maria [CNR-IMM MATIS, via S. Sofia 64, 95123 Catania (Italy); Tomasello, Mario Vincenzo [Scuola Superiore di Catania, via San Nullo 5/i, 95123 Catania (Italy); De Bastiani, Riccardo; Grimaldi, Maria Grazia [Dipartimento di Fisica ed Astronomia, Universita di Catania, via S. Sofia 64, 95123 Catania (Italy); CNR-IMM MATIS, via S. Sofia 64, 95123 Catania (Italy); Nicotra, Giuseppe; Spinella, Corrado [Consiglio Nazionale delle Ricerche-Istituto per la Microelettronica e Microsistemi (CNR-IMM), VIII Strada 5, 95121 Catania (Italy)

2011-03-15

We illustrate the behaviour of As when it is confined, by the implantation technique, in a SiO{sub 2}(70nm)/Si(30nm)/SiO{sub 2}(70nm) multilayer and its spatial redistribution when annealing processes are performed. By Rutherford backscattering spectrometry and Z-contrast transmission electron microscopy we found an As accumulation at the Si/SiO{sub 2} interfaces and at the Si grain boundaries with no segregation of the As in the Si layer. Such an effect is in agreement with a model that assumes a traps distribution in the Si in the first 2-3 nm above the SiO{sub 2}/Si interfaces and along the Si grain boundaries. The traps concentration at the Si/SiO{sub 2} interfaces was estimated in 10{sup 14} traps/cm{sup 2}. The outlined results can open perspectives on the doping properties of As in Si nanocrystals, whose applications in nanoelectronics and optoelectronics are widely investigated (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiN{sub x}/SiN{sub y} multilayers

Energy Technology Data Exchange (ETDEWEB)

Jiang, Xiaofan; Ma, Zhongyuan, E-mail: zyma@nju.edu.cn; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan [National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory of Photonic Electronic Materials Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China)

2014-09-28

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN{sub x}/SiN{sub y} multilayers with high on/off ratio of 10{sup 9}. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

DIÁLOGO DE LAS PERSPECTIVAS DE PERFIL CONCEPTUAL Y CONGLOMERADOS DE RELEVANCIA

Directory of Open Access Journals (Sweden)

Rosa I. Pedreros-M.

2013-12-01

Full Text Available El presente artículo forma parte del desarrollo de la investigación doctoral titulada “Perfil conceptual del calor en comunidades culturalmente diferenciadas” y tiene como intención socializar las perspectivas de perfil conceptual y conglomerados de relevancia como referentes teóricos y metodológicos que permitan proponer nuevas opciones para pensar la enseñanza-aprendizaje de las ciencias o la educación en ciencias, que observen los modos de pensar y hablar de los estudiantes y las relaciones entre la cultura local y el conocimiento escolar. Se exponen el origen, los referentes, las consideraciones sobre la enseñanza-aprendizaje de las ciencias y las razones para investigar desde estas perspectivas.

Strained Si/SiGe MOS transistor model

Directory of Open Access Journals (Sweden)

Tatjana Pešić-Brđanin

2009-06-01

Full Text Available In this paper we describe a new model of surfacechannel strained-Si/SiGe MOSFET based on the extension of non-quasi-static (NQS circuit model previously derived for bulk-Si devices. Basic equations of the NQS model have been modified to account for the new physical parameters of strained-Si and relaxed-SiGe layers. From the comparisons with measurements, it is shown that a modified NQS MOS including steady-state self heating can accurately predict DC characteristics of Strained Silicon MOSFETs.

Effect of hydrogen on passivation quality of SiNx/Si-rich SiNx stacked layers deposited by catalytic chemical vapor deposition on c-Si wafers

International Nuclear Information System (INIS)

Thi, Trinh Cham; Koyama, Koichi; Ohdaira, Keisuke; Matsumura, Hideki

2015-01-01

We investigate the role of hydrogen content and fixed charges of catalytic chemical vapor deposited (Cat-CVD) SiN x /Si-rich SiN x stacked layers on the quality of crystalline silicon (c-Si) surface passivation. Calculated density of fixed charges is on the order of 10 12 cm −2 , which is high enough for effective field effect passivation. Hydrogen content in the films is also found to contribute significantly to improvement in passivation quality of the stacked layers. Furthermore, Si-rich SiN x films deposited with H 2 dilution show better passivation quality of SiN x /Si-rich SiN x stacked layers than those prepared without H 2 dilution. Effective minority carrier lifetime (τ eff ) in c-Si passivated by SiN x /Si-rich SiN x stacked layers is as high as 5.1 ms when H 2 is added during Si-rich SiN x deposition, which is much higher than the case of using Si-rich SiN x films prepared without H 2 dilution showing τ eff of 3.3 ms. - Highlights: • Passivation mechanism of Si-rich SiN x /SiN x stacked layers is investigated. • H atoms play important role in passivation quality of the stacked layer. • Addition of H 2 gas during Si-rich SiN x film deposition greatly enhances effective minority carrier lifetime (τ eff ). • For a Si-rich SiN x film with refractive index of 2.92, τ eff improves from 3.3 to 5.1 ms by H 2 addition

U-Mo/Al-Si interaction: Influence of Si concentration

International Nuclear Information System (INIS)

Allenou, J.; Palancher, H.; Iltis, X.; Cornen, M.; Tougait, O.; Tucoulou, R.; Welcomme, E.; Martin, Ph.; Valot, C.; Charollais, F.; Anselmet, M.C.; Lemoine, P.

2010-01-01

Within the framework of the development of low enriched nuclear fuels for research reactors, U-Mo/Al is the most promising option that has however to be optimised. Indeed at the U-Mo/Al interfaces between U-Mo particles and the Al matrix, an interaction layer grows under irradiation inducing an unacceptable fuel swelling. Adding silicon in limited content into the Al matrix has clearly improved the in-pile fuel behaviour. This breakthrough is attributed to an U-Mo/Al-Si protective layer around U-Mo particles appeared during fuel manufacturing. In this work, the evolution of the microstructure and composition of this protective layer with increasing Si concentrations in the Al matrix has been investigated. Conclusions are based on the characterization at the micrometer scale (X-ray diffraction and energy dispersive spectroscopy) of U-Mo7/Al-Si diffusion couples obtained by thermal annealing at 450 deg. C. Two types of interaction layers have been evidenced depending on the Si content in the Al-Si alloy: the threshold value is found at about 5 wt.% but obviously evolves with temperature. It has been shown that for Si concentrations ranging from 2 to 10 wt.%, the U-Mo7/Al-Si interaction is bi-layered and the Si-rich part is located close to the Al-Si for low Si concentrations (below 5 wt.%) and close to the U-Mo for higher Si concentrations. For Si weight fraction in the Al alloy lower than 5 wt.%, the Si-rich sub-layer (close to Al-Si) consists of U(Al, Si) 3 + UMo 2 Al 20 , when the other sub-layer (close to U-Mo) is silicon free and made of UAl 3 and U 6 Mo 4 Al 43 . For Si weight concentrations above 5 wt.%, the Si-rich part becomes U 3 (Si, Al) 5 + U(Al, Si) 3 (close to U-Mo) and the other sub-layer (close to Al-Si) consists of U(Al, Si) 3 + UMo 2 Al 20 . On the basis of these results and of a literature survey, a scheme is proposed to explain the formation of different types of ILs between U-Mo and Al-Si alloys (i.e. different protective layers).

Porous SiC/SiC composites development for industrial application

International Nuclear Information System (INIS)

Maeta, S.; Hinoki, T.

2014-01-01

Silicon carbide (SiC) is promising structural materials in nuclear fields due to an excellent irradiation resistance and low activation characteristics. Conventional SiC fibers reinforced SiC matrix (SiC/SiC composites) fabricated by liquid phase sintering (LPS-SiC/SiC composites) have been required high cost and long processing time. And microstructure and mechanical property data of finally obtained LPS-SiC/SiC composites are easily scattered, because quality of the composites depend on personal skill. Thus, conventional LPS-SiC/SiC composites are inadequate for industrial use. In order to overcome these issues, the novel “porous SiC/SiC composites” have been developed by means of liquid phase sintering fabrication process. The composites consist of porous SiC matrix and SiC fibers without conventional carbon interfacial layer. The composites don’t have concerns of the degradation interfacial layer at the severe accident. Porous SiC/SiC composites preform was prepared with a thin sheet shape of SiC, sintering additives and carbon powder mixture by tape casting process which was adopted because of productive and high yielding rate fabrication process. The preform was stacked with SiC fibers and sintered in hot-press at the high temperature in argon environment. The sintered preform was decarburized obtain porous matrix structure by heat-treatment in air. Moreover, mechanical property data scattering of the obtained porous SiC/SiC composites decreased. In the flexural test, the porous SiC/SiC composites showed pseudo-ductile behavior with sufficient strength even after heat treatment at high temperature in air. From these conclusions, it was proven that porous SiC/SiC composites were reliable material at severe environment such as high temperature in air, by introducing tape casting fabrication process that could produce reproducible materials with low cost and simple way. Therefore development of porous SiC/SiC composites for industrial application was

Biomorphous SiSiC/Al-Si ceramic composites manufactured by squeeze casting: microstructure and mechanical properties

Energy Technology Data Exchange (ETDEWEB)

Zollfrank, C.; Travitzky, N.; Sieber, H.; Greil, P. [Department of Materials Science, Glass and Ceramics, University of Erlangen-Nuernberg (Germany); Selchert, T. [Advanced Ceramics Group, Technical University of Hamburg-Harburg (Germany)

2005-08-01

SiSiC/Al-Si composites were fabricated by pressure-assisted infiltration of an Al-Si alloy into porous biocarbon preforms derived from the rattan palm. Al-Si alloy was found in the pore channels of the biomorphous SiSiC preform, whereas SiC and carbon were present in the struts. The formation of a detrimental Al{sub 4}C{sub 3}-phase was not observed in the composites. A bending strength of 200 MPa was measured. The fractured surfaces showed pull-out of the Al-alloy. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

Reaction mechanisms at 4H-SiC/SiO2 interface during wet SiC oxidation

Science.gov (United States)

Akiyama, Toru; Hori, Shinsuke; Nakamura, Kohji; Ito, Tomonori; Kageshima, Hiroyuki; Uematsu, Masashi; Shiraishi, Kenji

2018-04-01

The reaction processes at the interface between SiC with 4H structure (4H-SiC) and SiO2 during wet oxidation are investigated by electronic structure calculations within the density functional theory. Our calculations for 4H-SiC/SiO2 interfaces with various orientations demonstrate characteristic features of the reaction depending on the crystal orientation of SiC: On the Si-face, the H2O molecule is stable in SiO2 and hardly reacts with the SiC substrate, while the O atom of H2O can form Si-O bonds at the C-face interface. Two OH groups are found to be at least necessary for forming new Si-O bonds at the Si-face interface, indicating that the oxidation rate on the Si-face is very low compared with that on the C-face. On the other hand, both the H2O molecule and the OH group are incorporated into the C-face interface, and the energy barrier for OH is similar to that for H2O. By comparing the calculated energy barriers for these reactants with the activation energies of oxide growth rate, we suggest the orientation-dependent rate-limiting processes during wet SiC oxidation.

Total Ionizing Dose Effects of Si Vertical Diffused MOSFET with SiO2 and Si3N4/SiO2 Gate Dielectrics

Directory of Open Access Journals (Sweden)

Jiongjiong Mo

2017-01-01

Full Text Available The total ionizing dose irradiation effects are investigated in Si vertical diffused MOSFETs (VDMOSs with different gate dielectrics including single SiO2 layer and double Si3N4/SiO2 layer. Radiation-induced holes trapping is greater for single SiO2 layer than for double Si3N4/SiO2 layer. Dielectric oxidation temperature dependent TID effects are also studied. Holes trapping induced negative threshold voltage shift is smaller for SiO2 at lower oxidation temperature. Gate bias during irradiation leads to different VTH shift for different gate dielectrics. Single SiO2 layer shows the worst negative VTH at VG=0 V, while double Si3N4/SiO2 shows negative VTH shift at VG=-5 V, positive VTH shift at VG=10 V, and negligible VTH shift at VG=0 V.

Nanocatalytic growth of Si nanowires from Ni silicate coated SiC nanoparticles on Si solar cell.

Science.gov (United States)

Parida, Bhaskar; Choi, Jaeho; Ji, Hyung Yong; Park, Seungil; Lim, Gyoungho; Kim, Keunjoo

2013-09-01

We investigated the nanocatalytic growth of Si nanowires on the microtextured surface of crystalline Si solar cell. 3C-SiC nanoparticles have been used as the base for formation of Ni silicate layer in a catalytic reaction with the Si melt under H2 atmosphere at an annealing temperature of 1100 degrees C. The 10-nm thick Ni film was deposited after the SiC nanoparticles were coated on the microtextured surface of the Si solar cell by electron-beam evaporation. SiC nanoparticles form a eutectic alloy surface of Ni silicate and provide the base for Si supersaturation as well as the Ni-Si alloy layer on Si substrate surface. This bottom reaction mode for the solid-liquid-solid growth mechanism using a SiC nanoparticle base provides more stable growth of nanowires than the top reaction mode growth mechanism in the absence of SiC nanoparticles. Thermally excited Ni nanoparticle forms the eutectic alloy and provides collectively excited electrons at the alloy surface, which reduces the activation energy of the nanocatalytic reaction for formation of nanowires.

Oxide Structure Dependence of SiO2/SiOx/3C-SiC/n-Type Si Nonvolatile Resistive Memory on Memory Operation Characteristics

Science.gov (United States)

Yamaguchi, Yuichiro; Shouji, Masatsugu; Suda, Yoshiyuki

2012-11-01

We have investigated the dependence of the oxide layer structure of our previously proposed metal/SiO2/SiOx/3C-SiC/n-Si/metal metal-insulator-semiconductor (MIS) resistive memory device on the memory operation characteristics. The current-voltage (I-V) measurement and X-ray photoemission spectroscopy results suggest that SiOx defect states mainly caused by the oxidation of 3C-SiC at temperatures below 1000 °C are related to the hysteresis memory behavior in the I-V curve. By restricting the SiOx interface region, the number of switching cycles and the on/off current ratio are more enhanced. Compared with a memory device formed by one-step or two-step oxidation of 3C-SiC, a memory device formed by one-step oxidation of Si/3C-SiC exhibits a more restrictive SiOx interface with a more definitive SiO2 layer and higher memory performances for both the endurance switching cycle and on/off current ratio.

Interfacial characterization of CVI-SiC/SiC composites

International Nuclear Information System (INIS)

Yang, W.; Kohyama, A.; Noda, T.; Katoh, Y.; Hinoki, T.; Araki, H.; Yu, J.

2002-01-01

The mechanical properties of the interfaces of two families of chemical vapor infiltration SiC/SiC composites, advanced Tyranno-SA and Hi-Nicalon fibers reinforced SiC/SiC composites with various carbon and SiC/C interlayers, were investigated by single fiber push-out/push-back tests. Interfacial debonding and fibers sliding mainly occurred adjacent to the first carbon layer on the fibers. The interfacial debonding strengths and frictional stresses for both Tyranno-SA/SiC and Hi-Nicalon/SiC composites were correlated with the first carbon layer thickness. Tyranno-SA/SiC composites exhibited much larger interfacial frictional stresses compared to Hi-Nicalon/SiC composites. This was assumed to be mainly contributed by the rather rough surface of the Tyranno-SA fiber

Research on a Micro-Nano Si/SiGe/Si Double Heterojunction Electro-Optic Modulation Structure

Directory of Open Access Journals (Sweden)

Song Feng

2018-01-01

Full Text Available The electro-optic modulator is a very important device in silicon photonics, which is responsible for the conversion of optical signals and electrical signals. For the electro-optic modulator, the carrier density of waveguide region is one of the key parameters. The traditional method of increasing carrier density is to increase the external modulation voltage, but this way will increase the modulation loss and also is not conducive to photonics integration. This paper presents a micro-nano Si/SiGe/Si double heterojunction electro-optic modulation structure. Based on the band theory of single heterojunction, the barrier heights are quantitatively calculated, and the carrier concentrations of heterojunction barrier are analyzed. The band and carrier injection characteristics of the double heterostructure structure are simulated, respectively, and the correctness of the theoretical analysis is demonstrated. The micro-nano Si/SiGe/Si double heterojunction electro-optic modulation is designed and tested, and comparison of testing results between the micro-nano Si/SiGe/Si double heterojunction micro-ring electro-optic modulation and the micro-nano Silicon-On-Insulator (SOI micro-ring electro-optic modulation, Free Spectrum Range, 3 dB Bandwidth, Q value, extinction ratio, and other parameters of the micro-nano Si/SiGe/Si double heterojunction micro-ring electro-optic modulation are better than others, and the modulation voltage and the modulation loss are lower.

Low dose irradiation performance of SiC interphase SiC/SiC composites

International Nuclear Information System (INIS)

Snead, L.L.; Lowden, R.A.; Strizak, J.; More, K.L.; Eatherly, W.S.; Bailey, J.; Williams, A.M.; Osborne, M.C.; Shinavski, R.J.

1998-01-01

Reduced oxygen Hi-Nicalon fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carbide (SiC) matrix and interphases of either 'porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1 x 10 25 n m -2 (E>0.1 MeV) in the temperature range of 260 to 1060 C. The unirradiated properties of these composites are superior to previously studied ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress was observed after irradiation for the multilayer SiC interphase material and a slight reduction in matrix microcracking stress was observed for the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest irradiation temperature. The ultimate fracture stress (in four point bending) following irradiation for the multilayer SiC and porous SiC interphase materials was reduced by 15% and 30%, respectively, which is an improvement over the 40% reduction suffered by irradiated ceramic grade Nicalon fiber materials fabricated in a similar fashion, though with a carbon interphase. The degradation of the mechanical properties of these composites is analyzed by comparison with the irradiation behavior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (CVD) SiC. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation of fiber and hence composite is reduced for the newer low-oxygen fiber. (orig.)

Análisis de la producción y comercialización de la soja orgánica de la provincia de Salta en el período 2008-2013

OpenAIRE

Nuñez, Ivanna Marisel

2017-01-01

106 p. il. Este trabajo tiene como objetivo principal demostrar si la provincia de Salta tiene la capacidad productiva de realizar soja orgánica y poder comercializarla tanto en el mercado nacional como internacional. Si se produjo en los años 2008-2013 soja orgánica en la provincia y si se exportó esa producción. Para ellos vamos analizar las estadísticas oficiales de la producción orgánica Argentina brindada por SENASA en diferentes períodos de año, y ver qué sucedió en la provincia d...

Carbon redistribution and precipitation in high temperature ion-implanted strained Si/SiGe/Si multi-layered structures

DEFF Research Database (Denmark)

Gaiduk, Peter; Hansen, John Lundsgaard; Nylandsted Larsen, Arne

2014-01-01

Graphical abstract Carbon depth profiles after high temperature implantation in strained Si/SiGe/Si multilayered system and induced structural defects.......Graphical abstract Carbon depth profiles after high temperature implantation in strained Si/SiGe/Si multilayered system and induced structural defects....

High-dose MeV electron irradiation of Si-SiO2 structures implanted with high doses Si+

Science.gov (United States)

Kaschieva, S.; Angelov, Ch; Dmitriev, S. N.

2018-03-01

The influence was studied of 22-MeV electron irradiation on Si-SiO2 structures implanted with high-fluence Si+ ions. Our earlier works demonstrated that Si redistribution is observed in Si+-ion-implanted Si-SiO2 structures (after MeV electron irradiation) only in the case when ion implantation is carried out with a higher fluence (1016 cm-2). We focused our attention on the interaction of high-dose MeV electron irradiation (6.0×1016 cm-2) with n-Si-SiO2 structures implanted with Si+ ions (fluence 5.4×1016 cm-2 of the same order magnitude). The redistribution of both oxygen and silicon atoms in the implanted Si-SiO2 samples after MeV electron irradiation was studied by Rutherford back-scattering (RBS) spectroscopy in combination with a channeling technique (RBS/C). Our results demonstrated that the redistribution of oxygen and silicon atoms in the implanted samples reaches saturation after these high doses of MeV electron irradiation. The transformation of amorphous SiO2 surface into crystalline Si nanostructures (after MeV electron irradiation) was evidenced by atomic force microscopy (AFM). Silicon nanocrystals are formed on the SiO2 surface after MeV electron irradiation. The shape and number of the Si nanocrystals on the SiO2 surface depend on the MeV electron irradiation, while their size increases with the dose. The mean Si nanocrystals height is 16-20 nm after irradiation with MeV electrons at the dose of 6.0×1016 cm-2.

Applications of Si/SiGe heterostructures to CMOS devices

International Nuclear Information System (INIS)

Sidek, R.M.

1999-03-01

For more than two decades, advances in MOSFETs used in CMOS VLSI applications have been made through scaling to ever smaller dimensions for higher packing density, faster circuit speed and lower power dissipation. As scaling now approaches nanometer regime, the challenge for further scaling becomes greater in terms of technology as well as device reliability. This work presents an alternative approach whereby non-selectively grown Si/SiGe heterostructure system is used to improve device performance or to relax the technological challenge. SiGe is considered to be of great potential because of its promising properties and its compatibility with Si, the present mainstream material in microelectronics. The advantages of introducing strained SiGe in CMOS technology are examined through two types of device structure. A novel structure has been fabricated in which strained SiGe is incorporated in the source/drain of P-MOSFETs. Several advantages of the Si/SiGe source/drain P-MOSFETs over Si devices are experimentally, demonstrated for the first time. These include reduction in off-state leakage and punchthrough susceptibility, degradation of parasitic bipolar transistor (PBT) action, suppression of CMOS latchup and suppression of PBT-induced breakdown. The improvements due to the Si/SiGe heterojunction are supported by numerical simulations. The second device structure makes use of Si/SiGe heterostructure as a buried channel to enhance the hole mobility of P-MOSFETs. The increase in the hole mobility will benefit the circuit speed and device packing density. Novel fabrication processes have been developed to integrate non-selective Si/SiGe MBE layers into self-aligned PMOS and CMOS processes based on Si substrate. Low temperature processes have been employed including the use of low-pressure chemical vapor deposition oxide and plasma anodic oxide. Low field mobilities, μ 0 are extracted from the transfer characteristics, Id-Vg of SiGe channel P-MOSFETs with various Ge

Irradiation effect on Nite-SiC/SiC composites

International Nuclear Information System (INIS)

Hinoki, T.; Choi, Y.B.; Kohyama, A.; Ozawa, K.

2007-01-01

Full text of publication follows: Silicon carbide (SiC) and SiC composites are significantly attractive materials for nuclear application in particular due to exceptional low radioactivity, excellent high temperature mechanical properties and chemical stability. Despite of the excellent potential of SiC/SiC composites, the prospect of industrialization has not been clear mainly due to the low productivity and the high material cost. Chemical vapor infiltration (CVI) method can produce the excellent SiC/SiC composites with highly crystalline and excellent mechanical properties. It has been reported that the high purity SiC/SiC composites reinforced with highly crystalline fibers and fabricated by CVI method is very stable to neutron irradiation. However the production cost is high and it is difficult to fabricate thick and dense composites by CVI method. The novel processing called Nano-powder Infiltration and Transient Eutectic Phase (NITE) Processing has been developed based on the liquid phase sintering (LPS) process modification. The NITE processing can achieve both the excellent material quality and the low processing cost. The productivity of the processing is also excellent, and various kinds of shape and size of SiC/SiC composites can be produced by the NITE processing. The NITE processing can form highly crystalline matrix, which is requirement for nuclear application. The objective of this work is to understand irradiation effect of the NITESiC/SiC composites. The SiC/SiC composites used were reinforced with high purity SiC fibers, Tyranno TM SA and fabricated by the NITE method. The NITE-SiC/SiC composite bars and reference monolithic SiC bars fabricated by CVI and NITE were irradiated at up to 1.0 dpa and 600-1000 deg. C at JMTR, Japan. Mechanical properties of non-irradiated and irradiated NITESiC/ SiC composites bars were evaluated by tensile tests. Monolithic SiC bars were evaluated by flexural tests. The fracture surface was examined by SEM. Ultimate

La formación para el trabajo en la educación media en Colombia

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Claudia Milena Díaz

2011-01-01

Full Text Available A partir de lo observado en las postulaciones del Premio Compartir al Maestro -versión 2009, en el área de formación para el trabajo-, intentamos reflexionar sobre las posibilidades y efectos de los programas de articulación de la educación media en el Sena con las iniciativas de formación en emprendimiento en este mismo nivel, los cuales se están constituyendo en esfuerzos principales para enfrentar la falta de oportunidades de formación postsecundaria y de trabajo de los jóvenes y las jóvenes de sectores populares. Revisamos en el artículo los efectos de la especialización temprana que pueden generar ambos programas, así como las reducidas opciones que la escuela tiene para desarrollar emprendimientos que superen la noción de unidades de supervivencia. Por último, contrastamos los alcances de los programas analizados con las funciones que tiene la media en la sociedad contemporánea en torno a la exploración, la orientación y el desarrollo del pensamiento científico técnico y creativo.

La formación para el trabajo en la educación media en Colombia

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Claudia Milena Diaz

2011-05-01

Full Text Available A partir de lo observado en las postulaciones del Premio Compartir al Maestro -versión 2009, en el área de formación para el trabajo-, intentamos reflexionar sobre las posibilidades y efectos de los programas de articulación de la educación media en el Sena con las iniciativas de formación en emprendimiento en este mismo nivel, los cuales se están constituyendo en esfuerzos principales para enfrentar la falta de oportunidades de formación postsecundaria y de trabajo de los jóvenes y las jóvenes de sectores populares. Revisamos en el artículo los efectos de la especialización temprana que pueden generar ambos programas, así como las reducidas opciones que la escuela tiene para desarrollar emprendimientos que superen la noción de unidades de supervivencia. Por último, contrastamos los alcances de los programas analizados con las funciones que tiene la media en la sociedad contemporánea en torno a la exploración, la orientación y el desarrollo del pensamiento científico-técnico y creativo.

ASESORIA y CAPACITACION: DOS FORMAS DE INSERCION

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María de los A. Carrillo

2012-11-01

Full Text Available El Instituto de Estudios Sociales en Población (lDESPO siempre ha comprendido que la Universidad Nacional tiene la responsabilidad de ofrecer opciones que puedan solucionar las necesidades concretas de la sociedad costarricense, pues es ahí donde nace la raíz de su razón de ser. Desde esta perspectiva, es que a partir de su fundación el Instituto ha planeado su quehacer. Por ejemplo, el programa que desarrolla en el área de extensión es un proyecto que se revitaliza constantemente, pues con su retroalimentación se generan nuevas actividades y otras opciones que contribuyan al progreso del país.El equipo interdisciplinario con que cuenta el IDESPO permite alcanzar metas institucionales, sin separar en áreas su trabajo. De los resultados de las investigaciones se pueden desprender aplicaciones que una vez puestas en práctica es conveniente asesorar, y a la vez, aunque administrativamente se ubique un proyecto en investigación, éste ha tenido su origen en algún contacto institucional realizado previamente por medio del trabajo extensivo. Este articulo ofrece información general sobre las principales características del quehacer del IDESPO en el área que se denomina "difusión cultural universitaria", con el fin de que pueda servir de modelo para futuras experiencias.

Stability analysis of SiO2/SiC multilayer coatings

International Nuclear Information System (INIS)

Fu Zhiqiang; Jean-Charles, R.

2006-01-01

The stability behaviours of SiC coatings and SiO 2 /SiC coatings in helium with little impurities are studied by HSC Chemistry 4.1, the software for analysis of Chemical reaction and equilibrium in multi-component complex system. It is found that in helium with a low partial pressure of oxidative impurities under different total pressure, the key influence factor controlling T cp of SiC depends is the partial pressure of oxidative impurities; T cp of SiC increases with the partial pressure of oxidative impurities. In helium with a low partial pressure of different impurities, the key influence factor of T cs of SiO 2 are both the partial pressure of impurities and the amount of impurities for l mol SiO 2 ; T cs of SiO 2 increases with the partial pressure of oxidative impurities at the same amount of the impurities for 1 mol SiO 2 while it decreases with the amount of the impurities for 1 mm SiO 2 at the same partial pressure of the impurities. The influence of other impurities on T cp of SiC in He-O 2 is studied and it is found that CO 2 , H 2 O and N-2 increase T cp of SiC in He-O 2 while H 2 , CO and CH 4 decrease T cp of SiC He-O 2 . When there exist both oxidative impurities and reductive impurities, their effect on T cs of SiO 2 can be suppressed by the other. In HTR-10 operation atmosphere, SiO 2 /SiC coatings can keep stable status at higher temperature than SiC coatings, so SiO 2 /SiC coatings is more suitable to improve the oxidation resistance of graphite in HTR-10 operation atmosphere compared with SiC coatings. (authors)

Si-O-Si bond-angle distribution in vitreous silica from first-principles 29Si NMR analysis

International Nuclear Information System (INIS)

Mauri, Francesco; Pasquarello, Alfredo; Pfrommer, Bernd G.; Yoon, Young-Gui; Louie, Steven G.

2000-01-01

The correlation between 29 Si chemical shifts and Si-O-Si bond angles in SiO 2 is determined within density-functional theory for the full range of angles present in vitreous silica. This relation closely reproduces measured shifts of crystalline polymorphs. The knowledge of the correlation allows us to reliably extract from the experimental NMR spectrum the mean (151 degree sign ) and the standard deviation (11 degree sign ) of the Si-O-Si angular distribution of vitreous silica. In particular, we show that the Mozzi-Warren Si-O-Si angular distribution is not consistent with the NMR data. This analysis illustrates the potential of our approach for structural determinations of silicate glasses. (c) 2000 The American Physical Society

Evaluación de un proyecto estratégico de administración de capacidad considerando flexibilidad operativa y opciones reales

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Camilo Andrés Micán-Rincón

2015-01-01

Full Text Available El desarrollo competitivo empresarial se basa en la satisfacción de las necesidades cambiantes de los clientes, por lo cual las empresas deben integrar la flexibilidad en la toma de decisiones para adaptar rápidamente su sistema productivo a dichos cambios. Las decisiones estratégicas de inversión en administración de la capacidad son de gran importancia en este proceso, debido a su carácter financiero y de largo plazo, por consiguiente, es necesario que estas sean evaluadas con precisión. Este documento plantea la evaluación de estas decisiones involucrando la valoración de la flexibilidad, tanto operativa como financiera, en una empresa del sector papel en el Valle del Cauca. En relación con esto, se caracterizaron las decisiones y los criterios a tener en cuenta al momento de evaluarlas usando como base la revisión de bibliografía especializada y el juicio de expertos. Por último, mediante un caso de estudio se ejemplificó el modelo propuesto. Siguiendo esta metodología se deben tener en cuenta tanto los criterios cuantitativos como los cualitativos para la evaluación de proyectos estratégicos de administración de la capacidad, siendo al análisis de opciones reales un elemento fundamental para evaluar la flexibilidad de la decisión.

Opciones vacunales contra los virus patógenos de porcinos PRRS y PCV2, un binomio frecuente

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Marcos Cajero-Juárez

2017-01-01

Full Text Available En la última década, el síndrome reproductivo y respiratorio porcino (PRRS, por sus siglas en inglés y las enfermedades asociadas al circovirus porcino tipo 2 (PCV2, por sus siglas en inglés, representan una gran preocupación para la industria porcícola, debido a la afectación de los índices productivos. En consecuencia, su presencia va acompañada de cuantiosas pérdidas económicas. Actualmente, en la mayoría de los centros de producción, se utilizan vacunas clásicas, es decir, elaboradas a partir del virus completo viable ó atenuado. En relación al PCV2, se dispone de pocas vacunas de nueva generación, referidas como aquellas obtenidas a través de la tecnología del ADN recombinante, mientras que, únicamente vacunas clásicas están disponibles contra el virus PRRSV. En este manuscrito, revisamos la naturaleza de los virus PRRSV y PCV2, así también, resaltamos la importancia económica, de acuerdo a los datos de prevalencia nacional e internacional. Además, se incluyen datos de nuevas opciones vacunales, en relación con las vacunas comerciales que, en algunos casos, se ha documentado una baja protección contra cepas heterólogas y cepas de reciente aparición. Por un lado, la investigación en vacunas de nueva generación, ha tenido buena aceptación, debido a la posibilidad de seleccionar la información genética del virus para estimular la respuesta inmune protectora del hospedero y, por otro, porque se acelera el desarrollo de vacunas, e incluso, es posible evitar las infecciones de las cuales es responsable el virus vacunal.

Interfacial microstructure of NiSi x/HfO2/SiO x/Si gate stacks

International Nuclear Information System (INIS)

Gribelyuk, M.A.; Cabral, C.; Gusev, E.P.; Narayanan, V.

2007-01-01

Integration of NiSi x based fully silicided metal gates with HfO 2 high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi x film. Ni content varies near the NiSi/HfO x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi x /HfO 2 interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi x /HfO x was found higher than that of poly-Si/HfO 2 , likely due to compositional non-uniformity of NiSi x . No intermixing between Hf, Ni and Si beyond interfacial roughness was observed

Luminescence properties of Si-capped β-FeSi{sub 2} nanodots epitaxially grown on Si(001) and (111) substrates

Energy Technology Data Exchange (ETDEWEB)

Amari, Shogo; Ichikawa, Masakazu [Department of Applied Physics, Graduate School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan); Nakamura, Yoshiaki, E-mail: nakamura@ee.es.osaka-u.ac.jp [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531 (Japan); PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)

2014-02-28

We studied the luminescence properties of Si-capped β-FeSi{sub 2} nanodots (NDs) epitaxially grown on Si substrates by using photoluminescence (PL) and electroluminescence (EL) spectroscopies. Codepositing Fe and Si on ultrathin SiO{sub 2} films induced the self-assembly of epitaxial β-FeSi{sub 2} NDs. The PL spectra of the Si/β-FeSi{sub 2} NDs/Si structure depended on the crystal orientation of the Si substrate. These structures exhibited a broad PL peak near 0.8 eV on both Si(001) and (111) substrates. The PL intensity depended on the shape of the β-FeSi{sub 2} NDs. For the flat NDs, which exhibited higher PL intensity, we also recorded EL spectra. We explained the luminescence properties of these structures by the presence of nanostructured Si offering radiative electronic states in the Si cap layers, generated by nano-stressors for upper Si layer: the strain-relaxed β-FeSi{sub 2} NDs.

Thermal shock properties of 2D-SiCf/SiC composites

International Nuclear Information System (INIS)

Lee, Sang Pill; Lee, Jin Kyung; Son, In Soo; Bae, Dong Su; Kohyama, Akira

2012-01-01

This paper dealt with the thermal shock properties of SiC f /SiC composites reinforced with two dimensional SiC fabrics. SiC f /SiC composites were fabricated by a liquid phase sintering process, using a commercial nano-size SiC powder and oxide additive materials. An Al 2 O 3 –Y 2 O 3 –SiO 2 powder mixture was used as a sintering additive for the consolidation of SiC matrix region. In this composite system, Tyranno SA SiC fabrics were also utilized as a reinforcing material. The thermal shock test for SiC f /SiC composites was carried out at the elevated temperature. Both mechanical strength and microstructure of SiC f /SiC composites were investigated by means of optical microscopy, SEM and three point bending test. SiC f /SiC composites represented a dense morphology with a porosity of about 8.2% and a flexural strength of about 160 MPs. The characterization of SiC f /SiC composites was greatly affected by the history of cyclic thermal shock. Especially, SiC f /SiC composites represented a reduction of flexural strength at the thermal shock temperature difference higher than 800 °C.

SiC/SiC Cladding Materials Properties Handbook

Energy Technology Data Exchange (ETDEWEB)

Snead, Mary A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koyanagi, Takaaki [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Singh, Gyanender P. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-08-01

When a new class of material is considered for a nuclear core structure, the in-pile performance is usually assessed based on multi-physics modeling in coordination with experiments. This report aims to provide data for the mechanical and physical properties and environmental resistance of silicon carbide (SiC) fiber–reinforced SiC matrix (SiC/SiC) composites for use in modeling for their application as accidenttolerant fuel cladding for light water reactors (LWRs). The properties are specific for tube geometry, although many properties can be predicted from planar specimen data. This report presents various properties, including mechanical properties, thermal properties, chemical stability under normal and offnormal operation conditions, hermeticity, and irradiation resistance. Table S.1 summarizes those properties mainly for nuclear-grade SiC/SiC composites fabricated via chemical vapor infiltration (CVI). While most of the important properties are available, this work found that data for the in-pile hydrothermal corrosion resistance of SiC materials and for thermal properties of tube materials are lacking for evaluation of SiC-based cladding for LWR applications.

¿El sentido del humor, tiene sentido en el aula? / Does Sense of the Humor Make Sense in the Classroom?

Directory of Open Access Journals (Sweden)

Freddy Antonio González Ynfante

2011-11-01

Full Text Available Recibido 09 de junio de 2011 • Aceptado 24 de octubre de 2011 • Corregido 27 de setiembre de 2011 Resumen. El presente ensayo tiene como finalidad reflexionar sobre la importancia del humor pedagógico como estrategia de enseñanza aprendizaje en el aula; esto, tomando en cuenta la problemática de desmotivación y aburrimiento que sucede normalmente en la clase. Para plantear si “el enseñar contento y el aprender con alegría” pueden aumentar la eficacia en el proceso de enseñanza-aprendizaje, se abordará cómo, a pesar de las múltiples ventajas que puede aportar el humor en las aulas, se omite su empleo por la existencia de ciertos prejuicios y temores. La idea no es que los docentes hagan el papel de comediantes o payasos, sino la de mediar y acercar la clase de manera pedagógica y didáctica a través del uso del humor, y sobre esto reflexionaba Platón (1992, cuando planteaba que muchas veces ayudaba una broma, en donde la seriedad oponía resistencia. Abstract. This paper studies the importance of humor as a teaching strategy in the classroom, considering the usual lack of motivation and boredom. To analyze whether the “happy teaching and happy learning” may increase effectiveness in the teaching-learning process, the author will discuss how, despite the many benefits it may bring, humor is not used in the classroom due to prejudices and fears. The idea is not for teachers to play the role of a comedian or a clown, but to intervene and get closer to the group with a teaching, didactic purpose through humor. Plato (1992 thought about this; he used to say that sometimes a joke may help, where seriousness put up resistance.

Exceptional cracking behavior in H-implanted Si/B-doped Si0.70Ge0.30/Si heterostructures

Science.gov (United States)

Chen, Da; Wang, Dadi; Chang, Yongwei; Li, Ya; Ding, Rui; Li, Jiurong; Chen, Xiao; Wang, Gang; Guo, Qinglei

2018-01-01

The cracking behavior in H-implanted Si/B-doped Si0.70Ge0.30/Si structures after thermal annealing was investigated. The crack formation position is found to closely correlate with the thickness of the buried Si0.70Ge0.30 layer. For H-implanted Si containing a buried 3-nm-thick B-doped Si0.70Ge0.30 layer, localized continuous cracking occurs at the interfaces on both sides of the Si0.70Ge0.30 interlayer. Once the thickness of the buried Si0.70Ge0.30 layer increases to 15 and 70 nm, however, a continuous sharp crack is individually observed along the interface between the Si substrate and the B-doped Si0.70Ge0.30 interlayer. We attribute this exceptional cracking behavior to the existence of shear stress on both sides of the buried Si0.70Ge0.30 layer and the subsequent trapping of hydrogen, which leads to a crack in a well-controlled manner. This work may pave the way for high-quality Si or SiGe membrane transfer in a feasible manner, thus expediting its potential applications to ultrathin silicon-on-insulator (SOI) or silicon-germanium-on-insulator (SGOI) production.

Opciones no protésicas en el tratamiento de la artrosis de tobillo

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DR. U. Giovanni Carcuro

2014-09-01

Full Text Available La artrosis de tobillo es una patología poco frecuente, tiene una incidencia nueve veces menor que la rodilla o la cadera a pesar de relación entre mayor carga y menor superficie de esta. La mayor parte son de causa secundaria, posterior a un trauma o a cambios en la biomecánica de la misma a diferencia de otras articulaciones como cadera o rodilla que su principal causa es idiopática o primaria. Causas menos frecuentes son las artropatías inflamatorias, hemocromatosis o artropatía neuropática. Es un problema creciente en la atención de salud en todo el mundo, con un 1% de prevalencia de artrosis sintomática en población adulta. El tobillo es la articulación que mayor carga recibe en cuanto a superficie se refiere, aproximadamente 500 N. La superficie articular mide 350 mm2 aproximadamente, mientras que la cadera 1100 mm2 y la rodilla 1120 mm2. Soporta hasta 5 veces el peso corporal durante la marcha. Cambios en la distribución de la carga durante la marcha podrían tener un efecto beneficioso en la lubricación y nutrición del cartílago. El cartílago articular es de 1a 1,7 mm comparado con el grosor de cartílago de la rodilla es de 1 a 6 mm. El tobillo con una gran congruencia articular presenta un cartílago más fino que es capaz de equilibrar mejor las cargas. Para el tratamiento de esta patología existen diferentes alternativas, tanto no quirúrgicas como quirúrgicas, y estas últimas se dividen en aquellas que preservan la articulación y las que no. Entre las alternativas no quirúrgicas esta la modificación de estilos de vida. Pacientes con IMC > 25 tienen un riesgo 1,5 veces mayor para el desarrollo de artrosis de pie y tobillo, siendo factor potencialmente mo-dificable, mejorando la eficacia de todas las otras opciones terapéuticas, conservadoras y quirúrgicas. Las actividades de la vida diaria que aumentan el estrés en la articulación del tobillo, así como los deportes de impacto, deben evitarse y

Du neuf dans les relations de l'Église orthodoxe avec les autres chrétiens

OpenAIRE

Famerée, Joseph

2015-01-01

Cette note évoque quatre réunions scientifiques (Athènes, Chambésy, Thessalonique, Iasi) qui, coup sur coup, de mai 2013 à mai 2014, ont permis à des Orthodoxes d’échanger avec d’autres chrétiens, catholiques notamment, sur des sujets théologiques et œcuméniques importants pour l’évolution des différentes Églises. Une nouvelle génération de théologiens orthodoxes se lève, osant parler librement à propos de leur Église et montrer l’écart entre l’Orthodoxie idéale et l’Orthodoxie réelle, spécia...

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process

Science.gov (United States)

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-01

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Electrical properties of Si/Si1-xGex/Si inverted modulation doped structures

International Nuclear Information System (INIS)

Sadeghzadeh, M.A.

1998-12-01

This thesis is a report of experimental investigations of growth strategy and electrical properties of Si/Si 1-x Ge x /Si inverted Modulation Doped (MD) structures grown by solid source Molecular Beam Epitaxy (MBE). If the grown Si layer is B-doped at some distance (as spacer) before or after the alloy layer, this remote doping induces the formation of a quasi Two Dimensional Hole Gas (2-DHG) near to the inverted (SiGe on Si) or normal (Si on SiGe) heterointerfaces of the Si/Si 1-x Ge x /Si quantum well, respectively. The latter arrangement is the well known 'normal' MD structure but the former one is the so-called 'inverted' MD structure which is of great interest for Field Effect Transistor (FET) applications. A reproducible growth strategy was employed by the use of a thick (400nm) Si cap for inverted MD structures with Ge composition in the range of 16-23%. Boron segregation and cap surface charges are significant in these inverted structures with small ( 20nm) spacer layers, respectively. It was demonstrated by secondary ion mass spectroscopy (SIMS) that boron segregation, which causes a reduction in the effective spacer dimension, can be suppressed by growth interruption after boron doping. The enhancement in hole sheet density with increasing Si cap layer thickness, is attributed to a reduction in the influence of positive surface charges in these structures. Top-gated devices were fabricated using these structures and the hole sheet density could be varied by applying a voltage to the metal-semiconductor gate, and the maximum Hall mobility of 5550 cm 2 V -1 s -1 with 4.2x10 11 cm -2 was measured (at 1.6K) in these structures. Comparison of measured Hall mobility (at 4.2K) as a function of hole sheet density in normal and inverted MD structures implies that both 2-DHG confined at normal and/or inverted structures are subjected to very similar interface charge, roughness, and alloy scattering potentials. Low temperatures magnetotransport measurements (down to

Abrupt GaP/Si hetero-interface using bistepped Si buffer

Energy Technology Data Exchange (ETDEWEB)

Ping Wang, Y., E-mail: yanping.wang@insa-rennes.fr; Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O. [UMR FOTON, CNRS, INSA Rennes, Rennes F-35708 (France); Stodolna, J.; Ponchet, A. [CEMES-CNRS, Université de Toulouse, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 04 (France); Bahri, M.; Largeau, L.; Patriarche, G. [Laboratoire de Photonique et Nanostructures, CNRS UPR 20, Route de Nozay, Marcoussis 91460 (France); Magen, C. [LMA, INA-ARAID, and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza (Spain)

2015-11-09

We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.

Abrupt GaP/Si hetero-interface using bistepped Si buffer

International Nuclear Information System (INIS)

Ping Wang, Y.; Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O.; Stodolna, J.; Ponchet, A.; Bahri, M.; Largeau, L.; Patriarche, G.; Magen, C.

2015-01-01

We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth

Synthesis and structural property of Si nanosheets connected to Si nanowires using MnCl{sub 2}/Si powder source

Energy Technology Data Exchange (ETDEWEB)

Meng, Erchao [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Ueki, Akiko [Toyota Central R& D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Meng, Xiang [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Suzuki, Hiroaki [Graduate School of Engineering, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Itahara, Hiroshi [Toyota Central R& D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Tatsuoka, Hirokazu, E-mail: tatsuoka.hirokazu@shizuoka.ac.jp [Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan)

2016-08-15

Graphical abstract: Si nanosheets connected to Si nanowires synthesized using a MnCl{sub 2}/Si powder source with an Au catalyst avoid the use of air-sensitive SiH{sub 4} or SiCl{sub 4}. It was evident from these structural features of the nanosheets (leaf blade) with nanowires (petiole) that the nanosheets were formed by the twin-plane reentrant-edge mechanism. The feature of the observed lattice fringes of the Si(111) nanosheets was clearly explained by the interference with the extra diffraction spots that arose due to the reciprocal lattice streaking effect. - Highlights: • New Si nanosheets connected to Si nanowires were synthesized using MnCl{sub 2}/Si powders. • The synthesis method has benefits in terms of avoiding air sensitive SiH{sub 4} or SiCl{sub 4}. • Structural property and electron diffraction of the Si nanosheets were clarified. • Odd lattice fringes of the Si nanosheets observed by HRTEM were clearly explained. - Abstract: Si nanosheets connected to Si nanowires were synthesized using a MnCl{sub 2}/Si powder source with an Au catalyst. The synthesis method has benefits in terms of avoiding conventionally used air-sensitive SiH{sub 4} or SiCl{sub 4}. The existence of the Si nanosheets connected to the Si<111> nanowires, like sprouts or leaves with petioles, was observed, and the surface of the nanosheets was Si{111}. The nanosheets were grown in the growth direction of <211> perpendicular to that of the Si nanowires. It was evident from these structural features of the nanosheets that the nanosheets were formed by the twin-plane reentrant-edge mechanism. The feature of the observed lattice fringes, which do not appear for Si bulk crystals, of the Si(111) nanosheets obtained by high resolution transmission electron microscopy was clearly explained due to the extra diffraction spots that arose by the reciprocal lattice streaking effect.

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process.

Science.gov (United States)

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-25

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Formation, structure, and phonon confinement effect of nanocrystalline Si1-xGex in SiO2-Si-Ge cosputtered films

International Nuclear Information System (INIS)

Yang, Y.M.; Wu, X.L.; Siu, G.G.; Huang, G.S.; Shen, J.C.; Hu, D.S.

2004-01-01

Using magnetron cosputtering of SiO 2 , Ge, and Si targets, Si-based SiO 2 :Ge:Si films were fabricated for exploring the influence of Si target proportion (P Si ) and annealing temperature (Ta) on formation, local structure, and phonon properties of nanocrystalline Si 1-x Ge x (nc-Si 1-x Ge x ). At low P Si and Ta higher than 800 deg. C, no nc-Si 1-x Ge x but a kind of composite nanocrystal consisting of a Ge core, GeSi shell, and amorphous Si outer shell is formed in the SiO 2 matrix. At moderate P Si , nc-Si 1-x Ge x begins to be formed at Ta=800 deg. C and coexists with nc-Ge at Ta=1100 deg. C. At high P Si , it was disclosed that both optical phonon frequency and lattice spacing of nc-Si 1-x Ge x increase with raising Ta. The possible origin of this phenomenon is discussed by considering three factors, the phonon confinement, strain effect, and composition variation of nc-Si 1-x Ge x . This work will be helpful in understanding the growth process of ternary GeSiO films and beneficial to further investigations on optical properties of nc-Ge 1-x Si x in the ternary matrix

Si/SiGe heterointerfaces in one-, two-, and three-dimensional nanostructures: their impact on SiGe light emission

Science.gov (United States)

Lockwood, David; Wu, Xiaohua; Baribeau, Jean-Marc; Mala, Selina; Wang, Xialou; Tsybeskov, Leonid

2016-03-01

Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide- semiconductor (CMOS) integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures, which can emit light at wavelengths within the important optical communication wavelength range of 1.3 - 1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1-xGex nanostructures have prevented the attainment of efficient light-emitting devices including the desired lasers. Thus, the engineering of Si/Si1-xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL) at energies in the range 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe nanostructures and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots), two dimensions (corresponding to quantum wires), and one dimension (corresponding to quantum wells). The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for nanostructure confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/Ge NW diameter in the range 50 - 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex nanostructures incorporated into a Si0.6Ge0.4 wavy

Experimental and thermodynamic assessments of substitutions in the AlFeSi, FeMnSi, FeSiZr and AlCaFeSi systems (65 wt % Si) - solidification simulation

International Nuclear Information System (INIS)

Gueneau, C.; Ansara, I.

1994-01-01

The substitutions of Al Si, Fe Mn and Fe Zr in some intermetallic compounds of the Al-Fe-Si, Fe-Mn-Si and Fe-Si-Zr systems are modelled in the Si-rich corner using a two sublattice model. The solidification paths of the studied alloys are determined at equilibrium. The ascalculated phase volume fractions of the alloys are compared to the experimental ones. Finally, a solidification simulation using the Gulliver-Scheil's model is performed in order to explain the formation of some precipitates experimentally observed. (authors). 14 figs., 19 refs

Ultrathin SiO{sub 2} layer formed by the nitric acid oxidation of Si (NAOS) method to improve the thermal-SiO{sub 2}/Si interface for crystalline Si solar cells

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, Taketoshi; Nakajima, Hiroki; Irishika, Daichi; Nonaka, Takaaki; Imamura, Kentaro; Kobayashi, Hikaru, E-mail: h.kobayashi@sanken.osaka-u.ac.jp

2017-02-15

Highlights: • The density of interface states at the SiO{sub 2}/Si interface is decreased by NAOS. • The minority carrier lifetime is increased by the NAOS treatment. • Great interfacial properties of the NAOS layer are kept after thermal oxidation. - Abstract: A combination of the nitric acid oxidation of Si (NAOS) method and post-thermal oxidation is found to efficiently passivate the SiO{sub 2}/n-Si(100) interface. Thermal oxidation at 925 °C and annealing at 450 °C in pure hydrogen atmosphere increases the minority carrier lifetime by three orders of magnitude, and it is attributed to elimination of Si dangling bond interface states. Fabrication of an ultrathin, i.e., 1.1 nm, NAOS SiO{sub 2} layer before thermal oxidation and H{sub 2} annealing further increases the minority carrier lifetime by 30% from 8.6 to 11.1 ms, and decreased the interface state density by 10% from 6.9 × 10{sup 9} to 6.3 × 10{sup 9}eV{sup −1} cm{sup −2}. After thermal oxidation at 800 °C, the SiO{sub 2} layer on the NAOS-SiO{sub 2}/Si(100) structure is 2.26 nm thick, i.e., 0.24 nm thicker than that on the Si(100) surface, while after thermal oxidation at 925 °C, it is 4.2 nm thick, i.e., 0.4 nm thinner than that on Si(100). The chemical stability results from the higher atomic density of a NAOS SiO{sub 2} layer than that of a thermal oxide layer as reported in Ref. [28] (Asuha et al., 2002). Higher minority carrier lifetime in the presence of the NAOS layer indicates that the NAOS-SiO{sub 2}/Si interface with a low interface state density is preserved after thermal oxidation, which supports out-diffusion oxidation mechanism, by which a thermal oxide layer is formed on the NAOS SiO{sub 2} layer.

Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

International Nuclear Information System (INIS)

Suvorova, N.A.; Lopez, C.M.; Irene, E.A.; Suvorova, A.A.; Saunders, M.

2004-01-01

(Ba,Sr)TiO 3 (BST) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO 2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO 2 on Si or 3.5 nm SiO 2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO 2 . Using the conductance method, capacitance-voltage measurements show a decrease in the interface trap density D it of an order of magnitude for oxidized Si substrates with a thicker SiO 2 underlayer. Further reduction of D it was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization

Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

Science.gov (United States)

Suvorova, N. A.; Lopez, C. M.; Irene, E. A.; Suvorova, A. A.; Saunders, M.

2004-03-01

(Ba,Sr)TiO3(BST) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO2 on Si or 3.5 nm SiO2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO2. Using the conductance method, capacitance-voltage measurements show a decrease in the interface trap density Dit of an order of magnitude for oxidized Si substrates with a thicker SiO2 underlayer. Further reduction of Dit was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization.

Mechanical behavior of SiCf/SiC composites with alternating PyC/SiC multilayer interphases

International Nuclear Information System (INIS)

Yu, Haijiao; Zhou, Xingui; Zhang, Wei; Peng, Huaxin; Zhang, Changrui

2013-01-01

Highlights: ► Superior combination of flexural strength and fracture toughness of the 3D SiC/SiC composite was achieved by interface tailoring. ► Resulted composite possesses a much higher flexural strength and fracture toughness than its counterparts in literatures. ► Mechanisms that PyC/SiC multilayer coatings improve the mechanical properties were illustrated. -- Abstract: In order to tailor the fiber–matrix interface of continuous silicon carbide fiber reinforced silicon carbide (SiC f /SiC) composites for improved fracture toughness, alternating pyrolytic carbon/silicon carbide (PyC/SiC) multilayer coatings were applied to the KD-I SiC fibers using chemical vapor deposition (CVD) method. Three dimensional (3D) KD-I SiC f /SiC composites reinforced by these coated fibers were fabricated using a precursor infiltration and pyrolysis (PIP) process. The interfacial characteristics were determined by the fiber push-out test and microstructural examination using scanning electron microscopy (SEM). The effect of interface coatings on composite mechanical properties was evaluated by single-edge notched beam (SENB) test and three-point bending test. The results indicate that the PyC/SiC multilayer coatings led to an optimum interfacial bonding between fibers and matrix and greatly improved the fracture toughness of the composites.

Oscillations in the fusion of the Si + Si systems

International Nuclear Information System (INIS)

Aguilera R, E.F.; Kolata, J.J.; DeYoung, P.A.; Vega, J.J.

1986-02-01

Excitation functions for the yields of all the residual nuclei from the 28 Si + 28,30 and 30 Si + 30 Si reactions have been measured via the γ-ray technique for center of mass energies in the region within one and two times the Coulomb barrier.Thirteen elements were identified for the first reaction and ten for the other two. While no structure is shown by the data for the 28 + 28 Si reaction, we have found evidence for intermediate width structure in the 2α and the αpn channels in 28 Si + 30 Si and for broad structure in the total fusion cross sections for 30 Si + 30 Si. Calculations using a barrier penetration model with one free parameter reproduce the experimental results quite well. Evaporation model calculations indicate that the individual structure of the nuclei involved in the respective decay chains might have an important influence upon the deexcitation process at the energies relevant to our experiments. (Author)

Structure of MnSi on SiC(0001)

Science.gov (United States)

Meynell, S. A.; Spitzig, A.; Edwards, B.; Robertson, M. D.; Kalliecharan, D.; Kreplak, L.; Monchesky, T. L.

2016-11-01

We report on the growth and magnetoresistance of MnSi films grown on SiC(0001) by molecular beam epitaxy. The growth resulted in a textured MnSi(111) film with a predominantly [1 1 ¯0 ] MnSi (111 )∥[11 2 ¯0 ] SiC(0001) epitaxial relationship, as demonstrated by transmission electron microscopy, reflection high energy electron diffraction, and atomic force microscopy. The 500 ∘C temperature required to crystallize the film leads to a dewetting of the MnSi layer. Although the sign of the lattice mismatch suggested the films would be under compressive stress, the films acquire an in-plane tensile strain likely driven by the difference in thermal expansion coefficients between the film and substrate during annealing. As a result, the magnetoresistive response demonstrates that the films possess a hard-axis out-of-plane magnetocrystalline anisotropy.

Laser-controlled stress of Si nanocrystals in a free-standing Si /SiO2 superlattice

Science.gov (United States)

Khriachtchev, Leonid; Räsänen, Markku; Novikov, Sergei

2006-01-01

We report laser manipulations with stress at the nanoscale level. The continuous-wave Ar+ laser radiation melts Si nanocrystals in a free-standing Si /SiO2 superlattice. Silicon crystallization from the liquid phase leads to a compressive stress, which can be accurately tuned in the 3GPa range using laser annealing below the Si melting temperature and then recovered by laser annealing above the melting temperature. This allows investigations of various phenomena as a function of stress and makes a case of Si-nanocrystal memory with very long retention time, which can be written, erased, and read by optical means.

Laser-controlled stress of Si nanocrystals in a free-standing Si/SiO2 superlattice

International Nuclear Information System (INIS)

Khriachtchev, Leonid; Raesaenen, Markku; Novikov, Sergei

2006-01-01

We report laser manipulations with stress at the nanoscale level. The continuous-wave Ar + laser radiation melts Si nanocrystals in a free-standing Si/SiO 2 superlattice. Silicon crystallization from the liquid phase leads to a compressive stress, which can be accurately tuned in the 3 GPa range using laser annealing below the Si melting temperature and then recovered by laser annealing above the melting temperature. This allows investigations of various phenomena as a function of stress and makes a case of Si-nanocrystal memory with very long retention time, which can be written, erased, and read by optical means

Isotopic effects in sub-barrier fusion of Si + Si systems

Science.gov (United States)

Colucci, G.; Montagnoli, G.; Stefanini, A. M.; Esbensen, H.; Bourgin, D.; Čolović, P.; Corradi, L.; Faggian, M.; Fioretto, E.; Galtarossa, F.; Goasduff, A.; Grebosz, J.; Haas, F.; Mazzocco, M.; Scarlassara, F.; Stefanini, C.; Strano, E.; Szilner, S.; Urbani, M.; Zhang, G. L.

2018-04-01

Background: Recent measurements of fusion cross sections for the 28Si+28Si system revealed a rather unsystematic behavior; i.e., they drop faster near the barrier than at lower energies. This was tentatively attributed to the large oblate deformation of 28Si because coupled-channels (CC) calculations largely underestimate the 28Si+28Si cross sections at low energies, unless a weak imaginary potential is applied, probably simulating the deformation. 30Si has no permanent deformation and its low-energy excitations are of a vibrational nature. Previous measurements of this system reached only 4 mb, which is not sufficient to obtain information on effects that should show up at lower energies. Purpose: The aim of the present experiment was twofold: (i) to clarify the underlying fusion dynamics by measuring the symmetric case 30Si+30Si in an energy range from around the Coulomb barrier to deep sub-barrier energies, and (ii) to compare the results with the behavior of 28Si+28Si involving two deformed nuclei. Methods: 30Si beams from the XTU tandem accelerator of the Laboratori Nazionali di Legnaro of the Istituto Nazionale di Fisica Nucleare were used, bombarding thin metallic 30Si targets (50 μ g /cm2) enriched to 99.64 % in mass 30. An electrostatic beam deflector allowed the detection of fusion evaporation residues (ERs) at very forward angles, and angular distributions of ERs were measured. Results: The excitation function of 30Si+30Si was measured down to the level of a few microbarns. It has a regular shape, at variance with the unusual trend of 28Si+28Si . The extracted logarithmic derivative does not reach the LCS limit at low energies, so that no maximum of the S factor shows up. CC calculations were performed including the low-lying 2+ and 3- excitations. Conclusions: Using a Woods-Saxon potential the experimental cross sections at low energies are overpredicted, and this is a clear sign of hindrance, while the calculations performed with a M3Y + repulsion

Self-aligned indium–gallium–zinc oxide thin-film transistors with SiNx/SiO2/SiNx/SiO2 passivation layers

International Nuclear Information System (INIS)

Chen, Rongsheng; Zhou, Wei; Zhang, Meng; Kwok, Hoi-Sing

2014-01-01

Self-aligned top-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with SiN x /SiO 2 /SiN x /SiO 2 passivation layers are developed in this paper. The resulting a-IGZO TFT exhibits high reliability against bias stress and good electrical performance including field-effect mobility of 5 cm 2 /Vs, threshold voltage of 2.5 V, subthreshold swing of 0.63 V/decade, and on/off current ratio of 5 × 10 6 . With scaling down of the channel length, good characteristics are also obtained with a small shift of the threshold voltage and no degradation of subthreshold swing. The proposed a-IGZO TFTs in this paper can act as driving devices in the next generation flat panel displays. - Highlights: • Self-aligned top-gate indium–gallium–zinc oxide thin-film transistor is proposed. • SiN x /SiO 2 /SiN x /SiO 2 passivation layers are developed. • The source/drain areas are hydrogen-doped by CHF3 plasma. • The devices show good electrical performance and high reliability against bias stress

Synthesis and characterization of laminated Si/SiC composites

Science.gov (United States)

Naga, Salma M.; Kenawy, Sayed H.; Awaad, Mohamed; Abd El-Wahab, Hamada S.; Greil, Peter; Abadir, Magdi F.

2012-01-01

Laminated Si/SiC ceramics were synthesized from porous preforms of biogenous carbon impregnated with Si slurry at a temperature of 1500 °C for 2 h. Due to the capillarity infiltration with Si, both intrinsic micro- and macrostructure in the carbon preform were retained within the final ceramics. The SEM micrographs indicate that the final material exhibits a distinguished laminar structure with successive Si/SiC layers. The produced composites show weight gain of ≈5% after heat treatment in air at 1300 °C for 50 h. The produced bodies could be used as high temperature gas filters as indicated from the permeability results. PMID:25685404

Synthesis and characterization of laminated Si/SiC composites

Directory of Open Access Journals (Sweden)

Salma M. Naga

2013-01-01

Full Text Available Laminated Si/SiC ceramics were synthesized from porous preforms of biogenous carbon impregnated with Si slurry at a temperature of 1500 °C for 2 h. Due to the capillarity infiltration with Si, both intrinsic micro- and macrostructure in the carbon preform were retained within the final ceramics. The SEM micrographs indicate that the final material exhibits a distinguished laminar structure with successive Si/SiC layers. The produced composites show weight gain of ≈5% after heat treatment in air at 1300 °C for 50 h. The produced bodies could be used as high temperature gas filters as indicated from the permeability results.

Propagation of misfit dislocations from buffer/Si interface into Si

Science.gov (United States)

Liliental-Weber, Zuzanna [El Sobrante, CA; Maltez, Rogerio Luis [Porto Alegre, BR; Morkoc, Hadis [Richmond, VA; Xie, Jinqiao [Raleigh, VA

2011-08-30

Misfit dislocations are redirected from the buffer/Si interface and propagated to the Si substrate due to the formation of bubbles in the substrate. The buffer layer growth process is generally a thermal process that also accomplishes annealing of the Si substrate so that bubbles of the implanted ion species are formed in the Si at an appropriate distance from the buffer/Si interface so that the bubbles will not migrate to the Si surface during annealing, but are close enough to the interface so that a strain field around the bubbles will be sensed by dislocations at the buffer/Si interface and dislocations are attracted by the strain field caused by the bubbles and move into the Si substrate instead of into the buffer epi-layer. Fabrication of improved integrated devices based on GaN and Si, such as continuous wave (CW) lasers and light emitting diodes, at reduced cost is thereby enabled.

Tailoring of SiC nanoprecipitates formed in Si

Energy Technology Data Exchange (ETDEWEB)

Velisa, G., E-mail: gihan.velisa@cea.fr [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Magurele (Romania); Trocellier, P. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Thomé, L. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, UMR8609, Bât. 108, 91405 Orsay (France); Vaubaillon, S. [CEA, INSTN, UEPTN, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Miro, S.; Serruys, Y.; Bordas, É. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Meslin, E. [CEA, DEN, Service de Recherches de Métallurgie Physique, F-91191 Gif-sur-Yvette (France); Mylonas, S. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, UMR8609, Bât. 108, 91405 Orsay (France); Coulon, P.E. [Ecole Polytechnique, Laboratoire des Solides Irradiés, CEA/DSM/IRAMIS-CNRS, 91128 Palaiseau Cedex (France); Leprêtre, F.; Pilz, A.; Beck, L. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France)

2013-07-15

The SiC synthesis through single-beam of C{sup +}, and simultaneous-dual-beam of C{sup +} and Si{sup +} ion implantations into a Si substrate heated at 550 °C has been studied by means of three complementary analytical techniques: nuclear reaction analysis (NRA), Raman, and transmission electron microscopy (TEM). It is shown that a broad distribution of SiC nanoprecipitates is directly formed after simultaneous-dual-beam (520-keV C{sup +} and 890-keV Si{sup +}) and single-beam (520-keV C{sup +}) ion implantations. Their shape appear as spherical (average size ∼4–5 nm) and they are in epitaxial relationship with the silicon matrix.

Uniform Si nano-dot fabrication using reconstructed structure of Si(110)

Science.gov (United States)

Yano, Masahiro; Uozumi, Yuki; Yasuda, Satoshi; Asaoka, Hidehito

2018-06-01

Si nano-dot (ND) formation on Si(110) is observed by means of a scanning tunneling microscope (STM). The initial Si-NDs are Si crystals that are continuous from the substrate and grow during the oxide layer desorption. The NDs fabricated on the flat surface of Si(110)-1 × 1 are surrounded by four types of facets with almost identical appearance probabilities. An increase in the size of the NDs increases the variety of its morphology. In contrast, most Si-NDs fabricated on straight-stepped surface of Si(110)-16 × 2 reconstructed structure are surrounded by only a single type of facet, namely the \\text{Si}(17,15,1)-2 × 1 plane. An appearance probability of the facet in which the base line is along the step of Si(110)-16 × 2 exceeds 75%. This finding provides a fabrication technique of uniformed structural Si-NDs by using the reconstructed structure of Si(110).

Neutron tolerance of advanced SiC-fiber/CVI-SiC composites

International Nuclear Information System (INIS)

Katoh, Y.; Kohyama, A.; Snead, L.L.; Hinoki, T.; Hasegawa, A.

2003-01-01

Fusion blankets employing a silicon carbide (SiC) fiber-reinforced SiC matrix composite (SiC/SiC composite) as the structural material provide attractive features represented by high cycle efficiency and extremely low induced radioactivity. Recent advancement in processing and utilization techniques and application studies in ceramic gas turbine and advanced transportation systems, SiC/SiC composites are steadily getting matured as industrial materials. Reference SiC/SiC composites for fusion structural applications have been produced by a forced-flow chemical vapor infiltration (FCVI) method using conventional and advanced near-stoichiometric SiC fibers and extensively evaluated primarily in Japan-US collaborative JUPITER program. In this work, effect of neutron irradiation at elevated temperatures on mechanical property of these composites is characterized. Unlike in conventional SiC/SiC composites, practically no property degradation was identified in advanced composites with a thin carbon interphase by a neutron fluence level of approximately 8dpa at 800C. (author)

High thermal conductivity SiC/SiC composites for fusion applications -- 2

International Nuclear Information System (INIS)

Kowbel, W.; Tsou, K.T.; Withers, J.C.; Youngblood, G.E.

1998-01-01

This report covers material presented at the IEA/Jupiter Joint International Workshop on SiC/SiC Composites for Fusion Structural Applications held in conjunction with ICFRM-8, Sendai, Japan, Oct. 23--24, 1997. An unirradiated SiC/SiC composite made with MER-developed CVR SiC fiber and a hybrid PIP/CVI SiC matrix exhibited room temperature transverse thermal conductivity of 45 W/mK. An unirradiated SiC/SiC composite made from C/C composite totally CVR-converted to a SiC/SiC composite exhibited transverse thermal conductivity values of 75 and 35 W/mK at 25 and 1000 C, respectively. Both types of SiC/SiC composites exhibited non-brittle failure in flexure testing

Passivation of defect states in Si and Si/SiO2 interface states by cyanide treatment: improvement of characteristics of pin-junction amorphous Si and crystalline Si-based metal-oxide-semiconductor junction solar cells

International Nuclear Information System (INIS)

Fujiwara, N.; Fujinaga, T.; Niinobe, D.; Maida, O.; Takahashi, M.; Kobayashi, H.

2003-01-01

Defect states in Si can be passivated by cyanide treatment which simply involves immersion of Si materials in KCN solutions, followed by rinse. When the cyanide treatment is applied to pin-junction amorphous Si [a-Si] solar cells, the initial conversion efficiency increases. When the crown-ether cyanide treatment using a KCN solution of xylene containing 18-crown-6 is performed on i-a-Si films, decreases in the photo- and dark current densities with the irradiation time are prevented. The cyanide treatment can also passivate interface states present at Si/SiO 2 interfaces, leading to an increase in the conversion efficiency of 2 / Si (100)> solar cells.. Si-CN bonds formed by the reaction of defect states with cyanide ions have a high bond energy of about 4.5 eV and hence heat treatment at 800 0 C does not rupture the bonds, making thermal stability of the cyanide treatment.. When the cyanide treatment is applied to ultrathin SiO 2 /Si structure, the leakage current density is markedly decreased (Authors)

Ora et labora. Paradigmes du modèle monacal médiéval chez Chrétien de Troyes / Ora et labora. Paradigms of the Medieval Monastic Model in Chrétien de Troyes’s Work

Directory of Open Access Journals (Sweden)

Diana Gradu

2015-05-01

Full Text Available The medieval monachal model is marked out by the faith, by the power, by the morality. It is also shared between confidence and fear with regard to the power on the earth, but, certainly, all the clerks and the monks of the Middle Age know and assume the rule Redde Caesari quae sunt Cesaris and quae sunt Dei Deo. The medieval literature, the unfaithful mirror, is reflected in an incomplete and sometimes idealized way, the example of the hermit, but it constitutes in the essential source of its paradigm. I shall stop to Chrétien of Troyes and to its novels, they are the most glorious proof of the Renaissance of the 12th century.

Enfoque de opciones reales para la valoración financiera de marcas Real Options Approach to Financial Valuation of Brands

Directory of Open Access Journals (Sweden)

Yessica González Londoño

2012-12-01

Full Text Available Los activos intangibles, especialmente las marcas, son parte fundamental del valor de mercado de las compañías, pues representan su ventaja competitiva; sin embargo, la Contabilidad y las Finanzas se enfrentan ante un reto difícil al momento de valorarlos. Los métodos de medición de intangibles en la literatura revisada se caracterizan por ser limitados y subjetivos, e incluso presentan algunos errores conceptuales, encontrándose su utilidad principal en el campo de la gestión. Este artículo propone una metodología para la valoración financiera de marcas a partir de una extensión de la aplicación de opciones reales compuestas de las patentes, aprovechando las similitudes en su construcción. Su aplicación se ilustra mediante la valoración de la marca de una compañía aseguradora.Intangible assets are an important component of the market value of a company, particularly in brands which represent the competitive advantage of the company; however, both Accounting and Finance face a great challenge when trying to value them. The methods which have been proposed by the literature appear to be subjective, limited, and based on some theoretical errors. Their use is mainly circumscribed to the management of intangibles. This paper proposes a methodology for the financial valuation of brands based on the application of a compound real option model to a patent valuation, acknowledging the similarities in their construction. Later, an application to an insurance company is presented.

The dependence of the interface and shape on the constrained growth of nc-Si in a-SiN sub x /a-Si:H/a-SiN sub x structures

CERN Document Server

Zhang Li; Wang Li; Li Wei; Xu Jun; Huang Xin Fan; Chen Kun Ji

2002-01-01

Size-controlled nanocrystalline silicon (nc-Si) has been prepared from a-SiN sub x /a-Si:H/a-SiN sub x ('a' standing for amorphous) structures by thermal annealing. Transmission electron microscope analyses show that the lateral size of the nc-Si is controlled by the annealing conditions and the a-Si sublayer thickness. The deviation of the nc-Si grain size distribution decreases with the a-Si sublayer thickness, so thinner a-Si sublayers are favourable for obtaining uniform nc-Si grains. In the a-Si:H (10 nm) sample annealed at 1000 deg. C for 30 min, an obvious bi-modal size distribution of nc-Si grains appears, but no obvious bi-modal size distribution is found in other samples with thinner a-Si:H sublayers. On the basis of the experimental results, we discuss the process of transition from the sphere-like shape to the disc-like shape in the growth model of the nc-Si crystallization. The critical thickness of the a-Si sublayer for the constrained crystallization can be determined by the present model. More...

Gas leak tightness of SiC/SiC composites at elevated temperature

Energy Technology Data Exchange (ETDEWEB)

Hayasaka, Daisuke, E-mail: hayasaka@oasis.muroran-it.ac.jp [OASIS, Muroran Institute of Technology, Muroran, Hokkaido (Japan); Graduate School of Engineering, Muroran Institute of Technology, Muroran, Hokkaido (Japan); Park, Joon-Soo. [OASIS, Muroran Institute of Technology, Muroran, Hokkaido (Japan); Kishimoto, Hirotatsu [OASIS, Muroran Institute of Technology, Muroran, Hokkaido (Japan); Graduate School of Engineering, Muroran Institute of Technology, Muroran, Hokkaido (Japan); Kohyama, Akira [OASIS, Muroran Institute of Technology, Muroran, Hokkaido (Japan)

2016-11-01

Highlights: • NITE-SiC/SiC has extremely densified microstructure compared with other SiC/SiC composite like CVI. • Excellent helium and hydrogen gas-leak tightness of SiC/SiC composites by DEMO-NITE method from prototype industrialization production line was presented. • The excellence against stainless steel and Zircaloy at elevated temperature, together with generic excellent properties of SiC will be inevitable for innovative blanket and divertors for DEMO- and power- fusion reactors. - Abstract: SiC/SiC composite materials are attractive candidates for high heat flux components and blanket of fusion reactor, mainly due to their high temperature properties, radiation damage tolerance and low induced radioactivity. One of the challenges for SiC/SiC application in fusion reactors is to satisfy sufficient gas leak tightness of hydrogen and helium isotopes. Although many efforts have been carried-out, SiC/SiC composites by conventional processes have not been successful to satisfy the requirements, except SiC/SiC composites by NITE-methods. Toward the early realization of SiC/SiC components into fusion reactor systems process development of NITE-process has been continued. Followed to the brief introduction of recently developed DEMO-NITE process, baseline properties and hydrogen and helium gas leak tightness is presented. SiC/SiC claddings with 10 mm in diameter and 1 mm in wall thickness are tested by gas leak tightness system developed. The leak tightness measurements are done room temperature to 400 °C. Excellent gas leak tightness equivalent or superior to Zircaloy claddings for light water fission reactors is confirmed. The excellent gas leak tightness suggests nearly perfect suppression of large gas leak path in DEMO-NITE SiC/SiC.

Advanced Optoelectronic Devices based on Si Quantum Dots/Si Nanowires Hetero-structures

International Nuclear Information System (INIS)

Xu, J; Zhai, Y Y; Cao, Y Q; Chen, K J

2017-01-01

Si quantum dots are currently extensively studied since they can be used to develop many kinds of optoelectronic devices. In this report, we review the fabrication of Si quantum dots (Si QD) /Si nanowires (Si NWs) hetero-structures by deposition of Si QDs/SiO 2 or Si QDs/SiC multilayers on Si NWs arrays. The electroluminescence and photovoltaic devices based on the formed hetero-structures have been prepared and the improved performance is confirmed. It is also found that the surface recombination via the surface defects states on the Si NWs, especially the ones obtained by the long-time etching, may deteriorate the device properties though they exhibit the better anti-reflection characteristics. The possible surface passivation approaches are briefly discussed. (paper)

Low-temperature magnetotransport in Si/SiGe heterostructures on 300 mm Si wafers

Science.gov (United States)

Scappucci, Giordano; Yeoh, L.; Sabbagh, D.; Sammak, A.; Boter, J.; Droulers, G.; Kalhor, N.; Brousse, D.; Veldhorst, M.; Vandersypen, L. M. K.; Thomas, N.; Roberts, J.; Pillarisetty, R.; Amin, P.; George, H. C.; Singh, K. J.; Clarke, J. S.

Undoped Si/SiGe heterostructures are a promising material stack for the development of spin qubits in silicon. To deploy a qubit into high volume manufacturing in a quantum computer requires stringent control over substrate uniformity and quality. Electron mobility and valley splitting are two key electrical metrics of substrate quality relevant for qubits. Here we present low-temperature magnetotransport measurements of strained Si quantum wells with mobilities in excess of 100000 cm2/Vs fabricated on 300 mm wafers within the framework of advanced semiconductor manufacturing. These results are benchmarked against the results obtained in Si quantum wells deposited on 100 mm Si wafers in an academic research environment. To ensure rapid progress in quantum wells quality we have implemented fast feedback loops from materials growth, to heterostructure FET fabrication, and low temperature characterisation. On this topic we will present recent progress in developing a cryogenic platform for high-throughput magnetotransport measurements.

Si-to-Si wafer bonding using evaporated glass

DEFF Research Database (Denmark)

Reus, Roger De; Lindahl, M.

1997-01-01

Anodic bonding of Si to Si four inch wafers using evaporated glass was performed in air at temperatures ranging from 300°C to 450°C. Although annealing of Si/glass structures around 340°C for 15 minutes eliminates stress, the bonded wafer pairs exhibit compressive stress. Pull testing revealed...

Centrifugally cast Zn-27Al-xMg-ySi alloys and their in situ (Mg2Si + Si)/ZA27 composites

International Nuclear Information System (INIS)

Wang Qudong; Chen Yongjun; Chen Wenzhou; Wei Yinhong; Zhai Chunquan; Ding Wenjiang

2005-01-01

Effects of composition, mold temperature, rotating rate and modification on microstructure of centrifugally cast Zn-27Al-xMg-ySi alloys have been investigated. In situ composites of Zn-27Al-6.3Mg-3.7Si and Zn-27Al-9.8Mg-5.2Si alloys were fabricated by centrifugal casting using heated permanent mold. These composites consist of three layers: inner layer segregates lots of blocky primary Mg 2 Si and a litter blocky primary Si, middle layer contains without primary Mg 2 Si and primary Si, outer layer contains primary Mg 2 Si and primary Si. The position, quantity and distribution of primary Mg 2 Si and primary Si in the composites are determined jointly by alloy composition, solidification velocity under the effect of centrifugal force and their floating velocity inward. Na salt modifier can refine grain and primary Mg 2 Si and make primary Mg 2 Si distribute more evenly and make primary Si nodular. For centrifugally cast Zn-27Al-3.2Mg-1.8Si alloy, the microstructures of inner layer, middle layer and outer layer are almost similar, single layer materials without primary Mg 2 Si and primary Si are obtained, and their grain sizes increased with the mold temperature increasing

siRNAmod: A database of experimentally validated chemically modified siRNAs.

Science.gov (United States)

Dar, Showkat Ahmad; Thakur, Anamika; Qureshi, Abid; Kumar, Manoj

2016-01-28

Small interfering RNA (siRNA) technology has vast potential for functional genomics and development of therapeutics. However, it faces many obstacles predominantly instability of siRNAs due to nuclease digestion and subsequently biologically short half-life. Chemical modifications in siRNAs provide means to overcome these shortcomings and improve their stability and potency. Despite enormous utility bioinformatics resource of these chemically modified siRNAs (cm-siRNAs) is lacking. Therefore, we have developed siRNAmod, a specialized databank for chemically modified siRNAs. Currently, our repository contains a total of 4894 chemically modified-siRNA sequences, comprising 128 unique chemical modifications on different positions with various permutations and combinations. It incorporates important information on siRNA sequence, chemical modification, their number and respective position, structure, simplified molecular input line entry system canonical (SMILES), efficacy of modified siRNA, target gene, cell line, experimental methods, reference etc. It is developed and hosted using Linux Apache MySQL PHP (LAMP) software bundle. Standard user-friendly browse, search facility and analysis tools are also integrated. It would assist in understanding the effect of chemical modifications and further development of stable and efficacious siRNAs for research as well as therapeutics. siRNAmod is freely available at: http://crdd.osdd.net/servers/sirnamod.

Development of SiC/SiC composite for fusion application

International Nuclear Information System (INIS)

Kohyama, A.; Katoh, Y.; Snead, L.L.; Jones, R.H.

2001-01-01

The recent efforts to develop SiC/SiC composite materials for fusion application under the collaboration with Japan and the USA are provided, where material performance with and without radiation damage has been greatly improved. One of the accomplishments is development of the high performance reaction sintering process. Mechanical and thermal conductivity are improved extensively by process modification and optimization with inexpensive fabrication process. The major efforts to make SiC matrix by CVI, PIP and RS methods are introduced together with the representing baseline properties. The resent results on mechanical properties of SiC/SiC under neutron irradiation are quite positive. The composites with new SiC fibers, Hi-Nicalon Type-S, did not exhibit mechanical property degradation up to 10 dpa. Based on the materials data recently obtained, a very preliminary design window is provided and the future prospects of SiC/SiC technology integration is provided. (author)

Growth of CoSi2 on Si(001) by reactive deposition epitaxy

International Nuclear Information System (INIS)

Lim, C.W.; Shin, C.-S.; Gall, D.; Zuo, J.M.; Petrov, I.; Greene, J.E.

2005-01-01

CaF 2 -structure CoSi 2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi 2 layers obtained by conventional solid phase growth (SPG). In both sets of experiments, Co was deposited by ultrahigh-vacuum magnetron sputtering and CoSi 2 formed at 600 deg. C. However, in the case of RDE, CoSi 2 formation occurred during Co deposition while for SPG, Co was deposited at 25 deg. C and silicidation took place during subsequent annealing. X-ray diffraction pole figures and transmission electron microscopy results demonstrate that RDE CoSi 2 layers are epitaxial with a cube-on-cube relationship (001) CoSi 2 parallel (001) Si and [100] CoSi 2 parallel[100] Si . In contrast, SPG films are polycrystalline with an average grain size of ≅1000 A and a mixed 111/002/022/112 orientation. We attribute the striking difference to rapid Co diffusion into the Si(001) substrate during RDE for which the high Co/Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. In contrast, sequential nucleation and transformation among increasingly Si-rich phases--from orthorhombic Co 2 Si to cubic CoSi to CoSi 2 --during SPG results in polycrystalline layers with a complex texture

Microscopic and macroscopic characterization of the charging effects in SiC/Si nanocrystals/SiC sandwiched structures

International Nuclear Information System (INIS)

Xu, Jie; Xu, Jun; Wang, Yuefei; Cao, Yunqing; Li, Wei; Yu, Linwei; Chen, Kunji

2014-01-01

Microscopic charge injection into the SiC/Si nanocrystals/SiC sandwiched structures through a biased conductive AFM tip is subsequently characterized by both electrostatic force microscopy and Kelvin probe force microscopy (KPFM). The charge injection and retention characteristics are found to be affected by not only the band offset at the Si nanocrystals/SiC interface but also the doping type of the Si substrate. On the other hand, capacitance–voltage (C–V) measurements investigate the macroscopic charging effect of the sandwiched structures with a thicker SiC capping layer, where the charges are injected from the Si substrates. The calculated macroscopic charging density is 3–4 times that of the microscopic one, and the possible reason is the underestimation of the microscopic charging density caused by the averaging effect and detection delay in the KPFM measurements. (paper)

Comparative study of SiC- and Si-based photovoltaic inverters

Science.gov (United States)

Ando, Yuji; Oku, Takeo; Yasuda, Masashi; Shirahata, Yasuhiro; Ushijima, Kazufumi; Murozono, Mikio

2017-01-01

This article reports comparative study of 150-300 W class photovoltaic inverters (Si inverter, SiC inverter 1, and SiC inverter 2). In these sub-kW class inverters, the ON-resistance was considered to have little influence on the efficiency. The developed SiC inverters, however, have exhibited an approximately 3% higher direct current (DC)-alternating current (AC) conversion efficiency as compared to the Si inverter. Power loss analysis indicated a reduction in the switching and reverse recovery losses of SiC metal-oxide-semiconductor field-effect transistors used for the DC-AC converter is responsible for this improvement. In the SiC inverter 2, an increase of the switching frequency up to 100 kHz achieved a state-of-the-art combination of the weight (1.25 kg) and the volume (1260 cm3) as a 150-250 W class inverter. Even though the increased switching frequency should cause the increase of the switching losses, the SiC inverter 2 exhibited an efficiency comparable to the SiC inverter 1 with a switching frequency of 20 kHz. The power loss analysis also indicated a decreased loss of the DC-DC converter built with SiC Schottky barrier diodes led to the high efficiency for its increased switching frequency. These results clearly indicated feasibility of SiC devices even for sub-kW photovoltaic inverters, which will be available for the applications where compactness and efficiency are of tremendous importance.

Influence of SiC coating thickness on mechanical properties of SiCf/SiC composite

Science.gov (United States)

Yu, Haijiao; Zhou, Xingui; Zhang, Wei; Peng, Huaxin; Zhang, Changrui

2013-11-01

Silicon carbide (SiC) coatings with varying thickness (ranging from 0.14 μm to 2.67 μm) were deposited onto the surfaces of Type KD-I SiC fibres with native carbonaceous surface using chemical vapour deposition (CVD) process. Then, two dimensional SiC fibre reinforced SiC matrix (2D SiCf/SiC) composites were fabricated using polymer infiltration and pyrolysis (PIP) process. Influences of the fibre coating thickness on mechanical properties of SiC fibre and SiCf/SiC composite were investigated using single-filament test and three-point bending test. The results indicated that flexural strength of the composites initially increased with the increasing CVD SiC coating thickness and reached a peak value of 363 MPa at the coating thickness of 0.34 μm. Further increase in the coating thickness led to a rapid decrease in the flexural strength of the composites. The bending modulus of composites showed a monotonic increase with increasing coating thickness. A chemical attack of hydrogen or other ions (e.g. a C-H group) on the surface of SiC fibres during the coating process, owing to the formation of volatile hydrogen, lead to an increment of the surface defects of the fibres. This was confirmed by Wang et al. [35] in their work on the SiC coating of the carbon fibre. In the present study, the existing ˜30 nm carbon on the surface of KD-I fibre [36] made the fibre easy to be attacked. Deposition of non-stoichiometric SiC, causing a decrease in strength. During the CVD process, a small amount of free silicon or carbon always existed [35]. The existence of free silicon, either disordered the structure of SiC and formed a new source of cracks or attacked the carbon on fibre surface resulting in properties degeneration of the KD-I fibre. The effect of residual stress. The different thermal expansion coefficient between KD-I SiC fibre and CVD SiC coating, which are 3 × 10-6 K-1 (RT ˜ 1000 °C) and 4.6 × 10-6 K-1 (RT ˜ 1000 °C), respectively, could cause residual stress

Conversion of wood flour/SiO2/phenolic composite to porous SiC ceramic containing SiC whiskers

Directory of Open Access Journals (Sweden)

Li Zhong

2013-01-01

Full Text Available A novel wood flour/SiO2/phenolic composite was chosen to be converted into porous SiC ceramic containing SiC whiskers via carbothermal reduction. At 1550°C the composite is converted into porous SiC ceramic with pore diameters of 10~40μm, and consisting of β-SiC located at the position of former wood cell walls. β-SiC wire-like whiskers of less than 50 nm in diameter and several tens to over 100 μm in length form within the pores. The surface of the resulting ceramic is coated with β-SiC necklace-like whiskers with diameters of 1~2μm.

Tunable Synthesis of SiC/SiO2 Heterojunctions via Temperature Modulation

Directory of Open Access Journals (Sweden)

Wei Li

2018-05-01

Full Text Available A large-scale production of necklace-like SiC/SiO2 heterojunctions was obtained by a molten salt-mediated chemical vapor reaction technique without a metallic catalyst or flowing gas. The effect of the firing temperature on the evolution of the phase composition, microstructure, and morphology of the SiC/SiO2 heterojunctions was studied. The necklace-like SiC/SiO2 nanochains, several centimeters in length, were composed of SiC/SiO2 core-shell chains and amorphous SiO2 beans. The morphologies of the as-prepared products could be tuned by adjusting the firing temperature. In fact, the diameter of the SiO2 beans decreased, whereas the diameter of the SiC fibers and the thickness of the SiO2 shell increased as the temperature increased. The growth mechanism of the necklace-like structure was controlled by the vapor-solid growth procedure and the modulation procedure via a molten salt-mediated chemical vapor reaction process.

(113) Facets of Si-Ge/Si Islands; Atomic Scale Simulation

Science.gov (United States)

Kassem, Hassan

We have studied, by computer simulation, some static and vibrationnal proprieties of SiGe/Si islands. We have used a Valence Force Field combined to Monte Carlo technique to study the growth of Ge and SiGe on (001)Si substrates. We have focalised on the case of large pyramidal islands presenting (113) facets on the free (001)Si surface with various non uniform composition inside the islands. The deformation inside the islands and Raman spectroscopy are discussed.

La promoción de la belleza. Narración y argumentación en la publicidad impresa en revistas femeninas

OpenAIRE

Jiménez Bonilla, Ana Lucía

2011-01-01

El análisis que se presenta a continuación, hace parte de una investigación que estudia la narración y la argumentación en la publicidad impresa de productos de belleza. Como narración, la publicidad focaliza la belleza y la convierte en un valor deseable que, si se tiene, se quiere conservar y, si no se tiene, se puede lograr mediante un proceso de mejoramiento. La publicidad hace énfasis en el producto y discursivamente, aumenta sus cualidades recurriendo a técnicas argumentativas que bu...

Photoemission study on electrical dipole at SiO_2/Si and HfO_2/SiO_2 interfaces

International Nuclear Information System (INIS)

Fujimura, Nobuyuki; Ohta, Akio; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

2017-01-01

Electrical dipole at SiO_2/Si and HfO_2/SiO_2 interfaces have been investigated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. From the analysis of the cut-off energy for secondary photoelectrons measured at each thinning step of a dielectric layer by wet-chemical etching, an abrupt potential change caused by electrical dipole at SiO_2/Si and HfO_2/SiO_2 interfaces has been clearly detected. Al-gate MOS capacitors with thermally-grown SiO_2 and a HfO_2/SiO_2 dielectric stack were fabricated to evaluate the Al work function from the flat band voltage shift of capacitance-voltage (C-V) characteristics. Comparing the results of XPS and C-V measurements, we have verified that electrical dipole formed at the interface can be directly measured by photoemission measurements. (author)

Compositional and optical properties of SiO x films and (SiO x /SiO y ) junctions deposited by HFCVD

Science.gov (United States)

2014-01-01

In this work, non-stoichiometric silicon oxide (SiO x ) films and (SiO x /SiO y ) junctions, as-grown and after further annealing, are characterized by different techniques. The SiO x films and (SiO x /SiO y ) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900°C to 1,150°C. Transmittance spectra of the SiO x films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiO x /SiO y ) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiO x matrix. For the case of the as-grown SiO x films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiO x /SiO y ) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiO x matrix is present. After thermal annealing, a phase separation into Si and SiO2 occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices. PACS 61.05.-a; 68.37.Og; 61.05.cp; 78.55.-m; 68.37.Ps; 81.15.Gh PMID:25342935

Thermal Stability of siRNA Modulates Aptamer- conjugated siRNA Inhibition

Directory of Open Access Journals (Sweden)

Alexey Berezhnoy

2012-01-01

Full Text Available Oligonucleotide aptamer-mediated in vivo cell targeting of small interfering RNAs (siRNAs is emerging as a useful approach to enhance the efficacy and reduce the adverse effects resulting from siRNA-mediated genetic interference. A current main impediment in aptamer-mediated siRNA targeting is that the activity of the siRNA is often compromised when conjugated to an aptamer, often requiring labor intensive and time consuming design and testing of multiple configurations to identify a conjugate in which the siRNA activity has not been significantly reduced. Here, we show that the thermal stability of the siRNA is an important parameter of siRNA activity in its conjugated form, and that siRNAs with lower melting temperature (Tm are not or are minimally affected when conjugated to the 3′ end of 2′F-pyrimidine-modified aptamers. In addition, the configuration of the aptamer-siRNA conjugate retains activity comparable with the free siRNA duplex when the passenger strand is co-transcribed with the aptamer and 3′ overhangs on the passenger strand are removed. The approach described in this paper significantly reduces the time and effort necessary to screening siRNA sequences that retain biological activity upon aptamer conjugation, facilitating the process of identifying candidate aptamer-siRNA conjugates suitable for in vivo testing.

An Isotope Study of Hydrogenation of poly-Si/SiOx Passivated Contacts for Si Solar Cells: Preprint

Energy Technology Data Exchange (ETDEWEB)

Schnabel, Manuel; Nemeth, William; van de Loo, Bas, W.H.; Macco, Bart; Kessels, Wilhelmus, M.M.; Stradins, Paul; Young, David, L.

2017-06-26

For many years, the record Si solar cell efficiency stood at 25.0%. Only recently have several companies and institutes managed to produce more efficient cells, using passivated contacts of made doped poly-Si or a-Si:H and a passivating intrinsic interlayer in all cases. Common to these designs is the need to passivate the layer stack with hydrogen. In this contribution, we perform a systematic study of passivated contact passivation by hydrogen, using poly-Si/SiOx passivated contacts on n-Cz-Si, and ALD Al2O3 followed by a forming gas anneal (FGA) as the hydrogen source. We study p-type and n-type passivated contacts with implied Voc exceeding 690 and 720 mV, respectively, and perform either the ALD step or the FGA with deuterium instead of hydrogen in order to separate the two processes via SIMS. By examining the deuterium concentration at the SiOx in both types of samples, we demonstrate that the FGA supplies negligible hydrogen species to the SiOx, regardless of whether the FGA is hydrogenated or deuterated. Instead, it supplies the thermal energy needed for hydrogen species in the Al2O3 to diffuse there. Furthermore, the concentration of hydrogen species at the SiOx can saturate while implied Voc continues to increase, showing that the energy from the FGA is also required for hydrogen species already at the SiOx to find recombination-active defects to passivate.

Pseudomorphic GeSiSn, SiSn and Ge layers in strained heterostructures

Science.gov (United States)

Timofeev, V. A.; Nikiforov, A. I.; Tuktamyshev, A. R.; Mashanov, V. I.; Loshkarev, I. D.; Bloshkin, A. A.; Gutakovskii, A. K.

2018-04-01

The GeSiSn, SiSn layer growth mechanisms on Si(100) were investigated and the kinetic diagrams of the morphological GeSiSn, SiSn film states in the temperature range of 150 °C-450 °C at the tin content from 0% to 35% were built. The phase diagram of the superstructural change on the surface of Sn grown on Si(100) in the annealing temperature range of 0 °C-850 °C was established. The specular beam oscillations were first obtained during the SiSn film growth from 150 °C to 300 °C at the Sn content up to 35%. The transmission electron microscopy and x-ray diffractometry data confirm the crystal perfection and the pseudomorphic GeSiSn, SiSn film state, and also the presence of smooth heterointerfaces between GeSiSn or SiSn and Si. The photoluminescence for the multilayer periodic GeSiSn/Si structures in the range of 0.6-0.8 eV was detected. The blue shift with the excitation power increase is observed suggesting the presence of a type II heterostructure. The creation of tensile strained Ge films, which are pseudomorphic to the underlying GeSn layer, is confirmed by the results of the formation and analysis of the reciprocal space map in the x-ray diffractometry. The tensile strain in the Ge films reached the value in the range of 0.86%-1.5%. The GeSn buffer layer growth in the Sn content range from 8% to 12% was studied. The band structure of heterosystems based on pseudomorphic GeSiSn, SiSn and Ge layers was calculated and the valence and conduction band subband position dependences on the Sn content were built. Based on the calculation, the Sn content range in the GeSiSn, SiSn, and GeSn layers, which corresponds to the direct bandgap GeSiSn, SiSn, and Ge material, was obtained.

Density-functional theory molecular dynamics simulations of a-HfO2/a-SiO2/SiGe and a-HfO2/a-SiO2/Ge with a-SiO2 and a-SiO suboxide interfacial layers

Science.gov (United States)

Chagarov, Evgueni A.; Kavrik, Mahmut S.; Fang, Ziwei; Tsai, Wilman; Kummel, Andrew C.

2018-06-01

Comprehensive Density-Functional Theory (DFT) Molecular Dynamics (MD) simulations were performed to investigate interfaces between a-HfO2 and SiGe or Ge semiconductors with fully-stoichiometric a-SiO2 or sub-oxide SiO interlayers. The electronic structure of the selected stacks was calculated with a HSE06 hybrid functional. Simulations were performed before and after hydrogen passivation of residual interlayer defects. For the SiGe substrate with Ge termination prior to H passivation, the stacks with a-SiO suboxide interlayer (a-HfO2/a-SiO/SiGe) demonstrate superior electronic properties and wider band-gaps than the stacks with fully coordinated a-SiO2 interlayers (a-HfO2/a-SiO2/SiGe). After H passivation, most of the a-HfO2/a-SiO2/SiGe defects are passivated. To investigate effect of random placement of Si and Ge atoms additional simulations with a randomized SiGe slab were performed demonstrating improvement of electronic structure. For Ge substrates, before H passivation, the stacks with a SiO suboxide interlayer (a-HfO2/a-SiO/Ge) also demonstrate wider band-gaps than the stacks with fully coordinated a-SiO2 interlayers (a-HfO2/a-SiO2/Ge). However, even for a-HfO2/a-SiO/Ge, the Fermi level is shifted close to the conduction band edge (CBM) consistent with Fermi level pinning. Again, after H passivation, most of the a-HfO2/a-SiO2/Ge defects are passivated. The stacks with fully coordinated a-SiO2 interlayers have much stronger deformation and irregularity in the semiconductor (SiGe or Ge) upper layers leading to multiple under-coordinated atoms which create band-edge states and decrease the band-gap prior to H passivation.

Gd-Ni-Si system

International Nuclear Information System (INIS)

Bodak, O.I.; Shvets, A.F.

1983-01-01

By X-ray phase analysis method isothermal cross section of phase diagram of the Gd-Ni-Si system at 870 K is studied. The existence of nine previously known compounds (GdNisub(6.72)Sisub(6.28), GdNi 10 Si 2 , GdNi 5 Si 3 , GdNi 4 Si, GdNi 2 Si 2 , GdNiSi 3 , GdNiSi 2 , Gd 3 Ni 6 Si 2 and GdNiSi) is confirmed and three new compounds (GdNisub(0.2)Sisub(1.8), Gdsub(2)Nisub(1-0.8)Sisub(1-1.2), Gd 5 NiSi 4 ) are found. On the base of Gd 2 Si 3 compound up to 0.15 at. Ni fractions, an interstitial solid solution is formed up to 0.25 at Ni fractions dissolution continues of substitution type. The Gd-Ni-Si system is similar to the Y-Ni-Si system

Comparative study on stress in AlGaN/GaN HEMT structures grown on 6H-SiC, Si and on composite substrates of the 6H-SiC/poly-SiC and Si/poly-SiC

International Nuclear Information System (INIS)

Guziewicz, M; Kaminska, E; Piotrowska, A; Golaszewska, K; Domagala, J Z; Poisson, M-A; Lahreche, H; Langer, R; Bove, P

2008-01-01

The stresses in GaN-based HEMT structures grown on both single crystal 6H SiC(0001) and Si(111) have been compared to these in the HEMT structures grown on new composite substrates engendered as a thin monocrystalline film attached to polycrystalline 3C-SiC substrate. By using HRXRD technique and wafer curvature method we show that stress of monocrystalline layer in composite substrates of the type mono-Si/poly-SiC is lower than 100 MPa and residual stress of epitaxial GaN buffer grown on the composite substrate does not exceed 0.31 GPa, but in the cases of single crystal SiC or Si substrates the GaN buffer stress is compressive in the range of -0.5 to -0.75 GPa. The total stress of the HEMT structure calculated from strains is consistent with the averaged stress of the multilayers stack measured by wafer curvature method. The averaged stress of HEMT structure grown on single crystals is higher than those in structures grown on composites substrates

3C-SiC nanocrystal growth on 10° miscut Si(001) surface

Energy Technology Data Exchange (ETDEWEB)

Deokar, Geetanjali, E-mail: gitudeo@gmail.com [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); D' Angelo, Marie; Demaille, Dominique [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); Cavellin, Catherine Deville [INSP, UPMC, CNRS UMR 7588, 4 place Jussieu, Paris F-75005 (France); Faculté des Sciences et Technologie UPEC, 61 av. De Gaulle, Créteil F-94010 (France)

2014-04-01

The growth of 3C-SiC nano-crystal (NC) on 10° miscut Si(001) substrate by CO{sub 2} thermal treatment is investigated by scanning and high resolution transmission electron microscopies. The vicinal Si(001) surface was thermally oxidized prior to the annealing at 1100 °C under CO{sub 2} atmosphere. The influence of the atomic steps at the vicinal SiO{sub 2}/Si interface on the SiC NC growth is studied by comparison with the results obtained for fundamental Si(001) substrates in the same conditions. For Si miscut substrate, a substantial enhancement in the density of the SiC NCs and a tendency of preferential alignment of them along the atomic step edges is observed. The SiC/Si interface is abrupt, without any steps and epitaxial growth with full relaxation of 3C-SiC occurs by domain matching epitaxy. The CO{sub 2} pressure and annealing time effect on NC growth is analyzed. The as-prepared SiC NCs can be engineered further for potential application in optoelectronic devices and/or as a seed for homoepitaxial SiC or heteroepitaxial GaN film growth. - Highlights: • Synthesis of 3C-SiC nanocrystals epitaxied on miscut-Si using a simple technique • Evidence of domain matching epitaxy at the SiC/Si interface • SiC growth proceeds along the (001) plane of host Si. • Substantial enhancement of the SiC nanocrystal density due to the miscut • Effect of the process parameters (CO{sub 2} pressure and annealing duration)

SiGe layer thickness effect on the structural and optical properties of well-organized SiGe/SiO2 multilayers

Science.gov (United States)

Vieira, E. M. F.; Toudert, J.; Rolo, A. G.; Parisini, A.; Leitão, J. P.; Correia, M. R.; Franco, N.; Alves, E.; Chahboun, A.; Martín-Sánchez, J.; Serna, R.; Gomes, M. J. M.

2017-08-01

In this work, we report on the production of regular (SiGe/SiO2)20 multilayer structures by conventional RF-magnetron sputtering, at 350 °C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 °C leads to the formation of SiGe nanocrystals between SiO2 thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (t SiGe) from 3.5-2 nm results in a transition from continuous SiGe crystalline layer (t SiGe ˜ 3.5 nm) to layers consisting of isolated nanocrystals (t SiGe ˜ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals ˜3-8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe thickness. A clear blue-shift in the optical absorption is observed for t SiGe ˜ 2 nm multilayer, as a consequence of the presence of isolated nanocrystals. Furthermore, the observed near infrared values of n = 2.8 and k = 1.5 are lower than those of bulk SiGe compounds, suggesting the presence of electronic confinement effects in the nanocrystals. The low temperature (70 K) photoluminescence measurements performed on annealed SiGe/SiO2 nanostructures show an emission band located between 0.7-0.9 eV associated with the development of interface states between the formed nanocrystals and surrounding amorphous matrix.

Modification effect of Ni-38 wt.%Si on Al-12 wt.%Si alloy

International Nuclear Information System (INIS)

Wu Yuying; Liu Xiangfa; Jiang Binggang; Huang Chuanzhen

2009-01-01

Modification effect of Ni-38 wt.%Si on the Al-12 wt.%Si alloy has been studied by differential scanning calorimeter, torsional oscillation viscometer and liquid X-ray diffraction experiments. It is found that there is a modification effect of Ni-38 wt.%Si on Al-12 wt.%Si alloy, i.e. primary Si can precipitate in the microstructure of Al-12 wt.%Si alloy when Ni and Si added in the form of Ni-38 wt.%Si, but not separately. Ni-38 wt.%Si alloy brings 'genetic materials' into the Al-Si melt, which makes the melt to form more ordering structure, promotes the primary Si precipitated. Moreover, the addition of Ni-38 wt.%Si, which decreases the solidification supercooling degree of Al-12 wt.%Si alloy, is identical to the effect of heterogeneous nuclei.

Modification effect of Ni-38 wt.%Si on Al-12 wt.%Si alloy

Energy Technology Data Exchange (ETDEWEB)

Wu Yuying [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Ji' nan 250061 (China)], E-mail: wyy532001@163.com; Liu Xiangfa [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Ji' nan 250061 (China); Shandong Binzhou Bohai Piston Co., Ltd., Binzhou 256602, Shandong (China); Jiang Binggang [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Ji' nan 250061 (China); Huang Chuanzhen [School of Mechanical Engineering, Shandong University, Jinan 250061 (China)

2009-05-27

Modification effect of Ni-38 wt.%Si on the Al-12 wt.%Si alloy has been studied by differential scanning calorimeter, torsional oscillation viscometer and liquid X-ray diffraction experiments. It is found that there is a modification effect of Ni-38 wt.%Si on Al-12 wt.%Si alloy, i.e. primary Si can precipitate in the microstructure of Al-12 wt.%Si alloy when Ni and Si added in the form of Ni-38 wt.%Si, but not separately. Ni-38 wt.%Si alloy brings 'genetic materials' into the Al-Si melt, which makes the melt to form more ordering structure, promotes the primary Si precipitated. Moreover, the addition of Ni-38 wt.%Si, which decreases the solidification supercooling degree of Al-12 wt.%Si alloy, is identical to the effect of heterogeneous nuclei.

Effect of irradiation on thermal expansion of SiCf/SiC composites

International Nuclear Information System (INIS)

Senor, D.J.; Trimble, D.J.; Woods, J.J.

1996-06-01

Linear thermal expansion was measured on five different SiC-fiber-reinforced/SiC-matrix (SiC f /SiC) composite types in the unirradiated and irradiated conditions. Two matrices were studied in combination with Nicalon CG reinforcement and a 150 nm PyC fiber/matrix interface: chemical vapor infiltrated (CVI) SiC and liquid-phase polymer impregnated precursor (PIP) SiC. Composites of PIP SiC with Tyranno and HPZ fiber reinforcement and a 150 nm PyC interface were also tested, as were PIP SiC composites with Nicalon CG reinforcement and a 150 nm BN fiber/matrix interface. The irradiation was conducted in the Experimental Breeder Reactor-II at a nominal temperature of 1,000 C to doses of either 33 or 43 dpa-SiC. Irradiation caused complete fiber/matrix debonding in the CVI SiC composites due to a dimensional stability mismatch between fiber and matrix, while the PIP SiC composites partially retained their fiber/matrix interface after irradiation. However, the thermal expansion of all the materials tested was found to be primarily dependent on the matrix and independent of either the fiber or the fiber/matrix interface. Further, irradiation had no significant effect on thermal expansion for either the CVI SiC or PIP SiC composites. In general, the thermal expansion of the CVI SiC composites exceeded that of the PIP SiC composites, particularly at elevated temperatures, but the expansion of both matrix types was less than chemical vapor deposited (CVD) β-SiC at all temperatures

Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers

International Nuclear Information System (INIS)

Liua, S.; Lia, Y.; Chena, P.; Lia, W.; Gaoa, S.; Zhang, B.; Yeb, F.

2017-01-01

The effect of residual stresses on the strength, toughness and work of fracture of Si3N4/SiC multilayered composites with different SiC layers has been investigated. It may be an effective way to design and optimize the mechanical properties of Si3N4/SiC multilayered composites by controlling the properties of SiC layers. Si3N4/SiC multilayered composites with different SiC layers were fabricated by aqueous tape casting and pressureless sintering. Residual stresses were calculated by using ANSYS simulation, the maximum values of tensile and compressive stresses were 553.2MPa and −552.1MPa, respectively. Step-like fracture was observed from the fracture surfaces. Fraction of delamination layers increased with the residual stress, which can improve the reliability of the materials. Tensile residual stress was benefit to improving toughness and work of fracture, but the strength of the composites decreased. [es

Effect of germanium concentrations on tunnelling current calculation of Si/Si1-xGex/Si heterojunction bipolar transistor

Science.gov (United States)

Hasanah, L.; Suhendi, E.; Khairrurijal

2018-05-01

Tunelling current calculation on Si/Si1-xGex/Si heterojunction bipolar transistor was carried out by including the coupling between transversal and longitudinal components of electron motion. The calculation results indicated that the coupling between kinetic energy in parallel and perpendicular to S1-xGex barrier surface affected tunneling current significantly when electron velocity was faster than 1x105 m/s. This analytical tunneling current model was then used to study how the germanium concentration in base to Si/Si1-xGex/Si heterojunction bipolar transistor influenced the tunneling current. It is obtained that tunneling current increased as the germanium concentration given in base decreased.

Thermochemical instability effects in SiC-based fibers and SiC{sub f}/SiC composites

Energy Technology Data Exchange (ETDEWEB)

Youngblood, G.E.; Henager, C.H.; Jones, R.H. [Pacific Northwest National Laboratory, Richland, WA (United States)

1997-08-01

Thermochemical instability in irradiated SiC-based fibers with an amorphous silicon oxycarbide phase leads to shrinkage and mass loss. SiC{sub f}/SiC composites made with these fibers also exhibit mass loss as well as severe mechanical property degradation when irradiated at 800{degrees}C, a temperature much below the generally accepted 1100{degrees}C threshold for thermomechanical degradation alone. The mass loss is due to an internal oxidation mechanism within these fibers which likely degrades the carbon interphase as well as the fibers in SiC{sub f}/SiC composites even in so-called {open_quotes}inert{close_quotes} gas environments. Furthermore, the mechanism must be accelerated by the irradiation environment.

Determination of optimum Si excess concentration in Er-doped Si-rich SiO2 for optical amplification at 1.54 μm

International Nuclear Information System (INIS)

Savchyn, Oleksandr; Coffey, Kevin R.; Kik, Pieter G.

2010-01-01

The presence of indirect Er 3+ excitation in Si-rich SiO 2 is demonstrated for Si-excess concentrations in the range of 2.5-37 at. %. The Si excess concentration providing the highest density of sensitized Er 3+ ions is demonstrated to be relatively insensitive to the presence of Si nanocrystals and is found to be ∼14.5 at. % for samples without Si nanocrystals (annealed at 600 deg. C) and ∼11.5 at. % for samples with Si nanocrystals (annealed at 1100 deg. C). The observed optimum is attributed to an increase in the density of Si-related sensitizers as the Si concentration is increased, with subsequent deactivation and removal of these sensitizers at high Si concentrations. The optimized Si excess concentration is predicted to generate maximum Er-related gain at 1.54 μm in devices based on Er-doped Si-rich SiO 2 .

Oxidation protection of multilayer CVD SiC/B/SiC coatings for 3D C/SiC composite

International Nuclear Information System (INIS)

Liu Yongsheng; Cheng Laifei; Zhang Litong; Wu Shoujun; Li Duo; Xu Yongdong

2007-01-01

A CVD boron coating was introduced between two CVD SiC coating layers. EDS and XRD results showed that the CVD B coating was a boron crystal without other impurity elements. SEM results indicated that the CVD B coating was a flake-like or column-like crystal with a compact cross-section. The crack width in the CVD SiC coating deposited on CVD B is smaller than that in a CVD SiC coating deposited on CVD SiC coating. After oxidation at 700 deg. C and 1000 deg. C, XRD results indicated that the coating was covered by product B 2 O 3 or B 2 O 3 .xSiO 2 film. The cracks were sealed as observed by SEM. There was a large amount of flake-like material on hybrid coating surface after oxidation at 1300 deg. C. Oxidation weight loss and residual flexural strength results showed that hybrid SiC/B/SiC multilayer coating provided better oxidation protection for C/SiC composite than a three layer CVD SiC coating at temperatures from 700 deg. C to 1000 deg. C for 600 min, but worse oxidation protection above 1000 deg. C due to the large amount of volatilization of B 2 O 3 or B 2 O 3 .xSiO 2

Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers; Las tensiones residuales y las propiedades mecánicas de compuestos multicapa de Si3N4/SiC con diferentes capas de SiC

Energy Technology Data Exchange (ETDEWEB)

Liua, S.; Lia, Y.; Chena, P.; Lia, W.; Gaoa, S.; Zhang, B.; Yeb, F.

2017-11-01

The effect of residual stresses on the strength, toughness and work of fracture of Si3N4/SiC multilayered composites with different SiC layers has been investigated. It may be an effective way to design and optimize the mechanical properties of Si3N4/SiC multilayered composites by controlling the properties of SiC layers. Si3N4/SiC multilayered composites with different SiC layers were fabricated by aqueous tape casting and pressureless sintering. Residual stresses were calculated by using ANSYS simulation, the maximum values of tensile and compressive stresses were 553.2MPa and −552.1MPa, respectively. Step-like fracture was observed from the fracture surfaces. Fraction of delamination layers increased with the residual stress, which can improve the reliability of the materials. Tensile residual stress was benefit to improving toughness and work of fracture, but the strength of the composites decreased. [Spanish] Se ha investigado el efecto de las tensiones residuales en la resistencia, dureza y trabajo de fractura de los compuestos multicapa de Si3N4/SiC con diferentes capas de SiC. Puede ser una manera eficaz de diseñar y optimizar las propiedades mecánicas de los compuestos multicapa de Si3N4/SiC mediante el control de las propiedades de las capas de SiC. Los compuestos multicapa de Si3N4/SiC con diferentes capas de SiC se fabricaron por medio de colado en cinta en medio acuoso y sinterización sin presión. Las tensiones residuales se calcularon mediante el uso de la simulación ANSYS, los valores máximos de las fuerzas de tracción y compresión fueron 553,2 MPa y −552,1 MPa, respectivamente. Se observó una fractura escalonada a partir de las superficies de fractura. La fracción de capas de deslaminación aumenta con la tensión residual, lo que puede mejorar la fiabilidad de los materiales. La fuerza de tracción residual era beneficiosa para la mejora de la dureza y el trabajo de fractura, pero la resistencia de los compuestos disminuyó.

Circumferential tensile test method for mechanical property evaluation of SiC/SiC tube

Energy Technology Data Exchange (ETDEWEB)

Yu, Ju-Hyeon, E-mail: 15096018@mmm.muroran-it.ac.jp [Graduate School, Muroran Institute of Technology, 27-1, Muroran, Hokkaido (Japan); Kishimoto, Hirotatsu [Graduate School, Muroran Institute of Technology, 27-1, Muroran, Hokkaido (Japan); OASIS, Muroran Institute of Technology, 27-1, Muroran, Hokkaido (Japan); Park, Joon-soo [OASIS, Muroran Institute of Technology, 27-1, Muroran, Hokkaido (Japan); Nakazato, Naofumi [Graduate School, Muroran Institute of Technology, 27-1, Muroran, Hokkaido (Japan); Kohyama, Akira [OASIS, Muroran Institute of Technology, 27-1, Muroran, Hokkaido (Japan)

2016-11-01

Highlights: • NITE SiC/SiC cooling channel system to be a candidate of divertor system in future. • Hoop strength is one of the important factors for a tube. • This research studies the relationship between deformation and strain of SiC/SiC tube. - Abstract: SiC fiber reinforced/SiC matrix (SiC/SiC) composite is expected to be a candidate material for the first-wall, components in the blanket and divertor of fusion reactors in future. In such components, SiC/SiC composites need to be formed to be various shapes. SiC/SiC tubes has been expected to be employed for blanket and divertor after DEMO reactor, but there is not established mechanical investigation technique. Recent progress of SiC/SiC processing techniques is likely to realize strong, having gas tightness SiC/SiC tubes which will contribute for the development of fusion reactors. This research studies the relationship between deformation and strain of SiC/SiC tube using a circumferential tensile test method to establish a mechanical property investigation method of SiC/SiC tubes.

Dielectric Properties of SiCf/PyC/SiC Composites After Oxidation

Institute of Scientific and Technical Information of China (English)

SONG Huihui; ZHOU Wancheng; LUO Fa; QING Yuchang; CHEN Malin; LI Zhimin

2016-01-01

In this paper, the SiC fiber-reinforced SiC matrix composites with a 0.15mm thick pyrocarbon interphase (notedas SiCf/PyC/SiC) were prepared by chemical vapor infiltration (CVI). The SiCf/PyC/SiC were oxidized in air at 950℃ for 50h. The dielectric properties after this high temperature oxidation were investigated in X-band from room temperature (RT) to 700℃. Results suggested that:e' of the SiCf/PyC/SiC after oxidation increased at first then de-creased with temperature elevating;e" increased with temperature raising in the temperature range studied.

Photoelectric Properties of Si Doping Superlattice Structure on 6H-SiC(0001).

Science.gov (United States)

Li, Lianbi; Zang, Yuan; Hu, Jichao; Lin, Shenghuang; Chen, Zhiming

2017-05-25

The energy-band structure and visible photoelectric properties of a p/n-Si doping superlattice structure (DSL) on 6H-SiC were simulated by Silvaco-TCAD. The,n the Si-DSL structures with 40 nm-p-Si/50 nm-n-Si multilayers were successfully prepared on 6H-SiC(0001) Si-face by chemical vapor deposition. TEM characterizations of the p/n-Si DSL confirmed the epitaxial growth of the Si films with preferred orientation and the misfit dislocations with a Burgers vector of 1/3 at the p-Si/n-Si interface. The device had an obvious rectifying behavior, and the turn-on voltage was about 1.2 V. Under the visible illumination of 0.6 W/cm², the device demonstrated a significant photoelectric response with a photocurrent density of 2.1 mA/cm². Visible light operation of the Si-DSL/6H-SiC heterostructure was realized for the first time.

Photoelectric Properties of Si Doping Superlattice Structure on 6H-SiC(0001

Directory of Open Access Journals (Sweden)

Lianbi Li

2017-05-01

Full Text Available The energy-band structure and visible photoelectric properties of a p/n-Si doping superlattice structure (DSL on 6H-SiC were simulated by Silvaco-TCAD. The,n the Si-DSL structures with 40 nm-p-Si/50 nm-n-Si multilayers were successfully prepared on 6H-SiC(0001 Si-face by chemical vapor deposition. TEM characterizations of the p/n-Si DSL confirmed the epitaxial growth of the Si films with preferred orientation and the misfit dislocations with a Burgers vector of 1/3 <21-1> at the p-Si/n-Si interface. The device had an obvious rectifying behavior, and the turn-on voltage was about 1.2 V. Under the visible illumination of 0.6 W/cm2, the device demonstrated a significant photoelectric response with a photocurrent density of 2.1 mA/cm2. Visible light operation of the Si-DSL/6H-SiC heterostructure was realized for the first time.

Development of Petrov glacial-lake system (Tien Shan and outburst risk assessment

Directory of Open Access Journals (Sweden)

I. A. Torgoev

2013-01-01

Full Text Available Global climate warming causes an intensive melting and retreat of glaciers in the Tien Shan mountains. Melting water of glaciers causes overfilling of high mountain lakes. The increase of the surface and volume of the Petrov Lake accompanied with the decrease of stability of the dam represents an extremely dangerous situation that can produce a natural disaster. Failure can happen due to erosion, a buildup of water pressure, an earthquake or if a large enough portion of a glacier breaks off and massively displaces the waters in a glacial lake at its base. In case of the lake dam rupture, flooding of a disposal site of highly toxic tailing from the gold mine Kumtor is a threat. If this happens, the toxic waste containing cyanides would contaminate a large area in the Naryn (Syrdarya river basin. Even if the flooding of the disposal site does not occur, the damage after lake dam fracture will be immense due to the glacial lake outburst flood may be a devastating mudslide. In order to prevent or reduce the risk of this event we recommend performing engineering surveys for the development and implementation of the project for the controlled reduction of water level in the Blue Bay of the Petrov Lake to a safe volume.

C-H and C-C activation of n -butane with zirconium hydrides supported on SBA15 containing N-donor ligands: [(≡SiNH-)(≡SiX-)ZrH2], [(≡SiNH-)(≡SiX-)2ZrH], and[(≡SiN=)(≡SiX-)ZrH] (X = -NH-, -O-). A DFT study

KAUST Repository

Pasha, Farhan Ahmad; Bendjeriou-Sedjerari, Anissa; Huang, Kuo-Wei; Basset, Jean-Marie

2014-01-01

: [(≡SiNH-)(≡SiO-)ZrH2] (A), [(≡SiNH-)2ZrH2] (B), [(≡SiNH-)(≡SiO-) 2ZrH] (C), [(≡SiNH-)2(≡SiO-)ZrH] (D), [(≡SiN=)(≡Si-O-)ZrH] (E), and [(≡SiN=)(≡SiNH-)ZrH] (F). The roles of these hydrides have been investigated in C-H/C-C bond activation and cleavage

Role of the SiO2 buffer layer thickness in the formation of Si/SiO2/nc-Ge/SiO2 structures by dry oxidation

International Nuclear Information System (INIS)

Kling, A.; Ortiz, M.I.; Prieto, A.C.; Rodriguez, A.; Rodriguez, T.; Jimenez, J.; Ballesteros, C.; Soares, J.C.

2006-01-01

Nanomemories, containing Ge-nanoparticles in a SiO 2 matrix, can be produced by dry thermal oxidation of a SiGe layer deposited onto a Si-wafer with a barrier SiO 2 layer on its top. Rutherford backscattering spectrometry has been used to characterize the kinetics of the oxidation process, the composition profile of the growing oxide, the Ge-segregation and its diffusion into the barrier oxide in samples with thin and thick barrier oxide layers. The Ge segregated during the oxidation of the SiGe layer diffuses into the barrier oxide. In the first case the diffusion through the thin oxide is enhanced by the proximity of the substrate that acts as a sink for the Ge, resulting in the formation of a low Ge concentration SiGe layer in the surface of the Si-wafer. In the second case, the Ge-diffusion progresses as slowly as in bulk SiO 2 . Since barrier oxide layers as thin as possible are favoured for device fabrication, the structures should be oxidized at lower temperatures and the initial SiGe layer thickness reduced to minimize the Ge-diffusion

Microstructure and properties of MoSi2-MoB and MoSi2-Mo5Si3 molybdenum silicides

International Nuclear Information System (INIS)

Schneibel, J.H.; Sekhar, J.A.

2003-01-01

MoSi 2 -based intermetallics containing different volume fractions of MoB or Mo 5 Si 3 were fabricated by hot-pressing MoSi 2 , MoB, and Mo 5 Si 3 powders in vacuum. Both classes of alloys contained approximately 5 vol.% of dispersed silica phase. Additions of MoB or Mo 5 Si 3 caused the average grain size to decrease. The decrease in the grain size was typically accompanied by an increase in flexure strength, a decrease in the room temperature fracture toughness, and a decrease in the hot strength (compressive creep strength) measured around 1200 deg. C, except when the Mo 5 Si 3 effectively became the major phase. Oxidation measurements on the two classes of alloys were carried out in air. Both classes of alloys were protected from oxidation by an in-situ adherent scale that formed on exposure to high temperature. The scale, although not analyzed in detail, is commonly recognized in MoSi 2 containing materials as consisting mostly of SiO 2 . The MoB containing materials showed an increase in the scale thickness and the cyclic oxidation rate at 1400 deg. C when compared with pure MoSi 2 . However, in contrast with the pure MoSi 2 material, oxidation at 1400 deg. C began with a weight loss followed by a weight gain and the formation of the protective silica layer. The Mo 5 Si 3 containing materials experienced substantial initial weight losses followed by regions of small weight changes. Overall, the MoB and Mo 5 Si 3 additions to MoSi 2 tended to be detrimental for the mechanical and oxidative properties

Evolution of a novel Si-18Mn-16Ti-11P alloy in Al-Si melt and its influence on microstructure and properties of high-Si Al-Si alloy

Directory of Open Access Journals (Sweden)

Xiao-Lu Zhou

Full Text Available A novel Si-18Mn-16Ti-11P master alloy has been developed to refine primary Si to 14.7 ± 1.3 μm, distributed uniformly in Al-27Si alloy. Comparing with traditional Cu-14P and Al-3P, Si-18Mn-16Ti-11P provided a much better refining effect, with in-situ highly active AlP. The refined Al-27Si alloy exhibited a CTE of 16.25 × 10−6/K which is slightly higher than that of Sip/Al composites fabricated by spray deposition. The UTS and elongation of refined Al-27Si alloy were increased by 106% and 235% comparing with those of unrefined alloy. It indicates that the novel Si-18Mn-16Ti-11P alloy is more suitable for high-Si Al-Si alloys and may be a candidate for refining hypereutectic Al-Si alloy for electronic packaging applications. Moreover, studies showed that TiP is the only P-containing phase in Si-18Mn-16Ti-11P master alloy. A core-shell reaction model was established to reveal mechanism of the transformation of TiP to AlP in Al-Si melts. The transformation is a liquid-solid diffusion reaction driven by chemical potential difference and the reaction rate is controlled by diffusion. It means sufficient holding time is necessary for Si-18Mn-16Ti-11P master alloy to achieve better refining effect. Keywords: Hypereutectic Al-Si alloy, Primary Si, Refinement, AlP, Thermal expansion behavior, Si-18Mn-16Ti-11P master alloy

Oblique roughness replication in strained SiGe/Si multilayers

NARCIS (Netherlands)

Holy, V.; Darhuber, A.A.; Stangl, J.; Bauer, G.; Nützel, J.-F.; Abstreiter, G.

1998-01-01

The replication of the interface roughness in SiGe/Si multilayers grown on miscut Si(001) substrates has been studied by means of x-ray reflectivity reciprocal space mapping. The interface profiles were found to be highly correlated and the direction of the maximal replication was inclined with

Transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1-xCx nanocomposites mixed with Si nanoparticles and C atoms

International Nuclear Information System (INIS)

Shin, J.W.; Oh, D.H.; Kim, T.W.; Cho, W.J.

2009-01-01

Bright-field transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and fast-Fourier transformed electron-diffraction patterns showed that n-butyl terminated Si nanoparticles were aggregated. The formation of Si 1-x C x nanocomposites was mixed with Si nanoparticles and C atoms embedded in a SiO 2 layer due to the diffusion of C atoms from n-butyl termination shells into aggregated Si nanoparticles. Atomic force microscopy (AFM) images showed that the Si 1-x C x nanocomposites mixed with Si nanoparticles and C atoms existed in almost all regions of the SiO 2 layer. The formation mechanism of Si nanoparticles and the transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si 1-x C x nanocomposites mixed with Si nanoparticles and C atoms are described on the basis of the TEM, HRTEM, and AFM results. These results can help to improve the understanding of the formation mechanism of Si nanoparticles.

Positron annihilation at the Si/SiO2 interface

International Nuclear Information System (INIS)

Leung, T.C.; Weinberg, Z.A.; Asoka-Kumar, P.; Nielsen, B.; Rubloff, G.W.; Lynn, K.G.

1992-01-01

Variable-energy positron annihilation depth-profiling has been applied to the study of the Si/SiO 2 interface in Al-gate metal-oxide-semiconductor (MOS) structures. For both n- and p-type silicon under conditions of negative gate bias, the positron annihilation S-factor characteristic of the interface (S int ) is substantially modified. Temperature and annealing behavior, combined with known MOS physics, suggest strongly that S int depends directly on holes at interface states or traps at the Si/SiO 2 interface

La falta de financiacion publica hipoteca el futuro del acelerador de protones valenciano. La Universidad de Valencia tiene avanzado el diseno de este dispositivo de alta tecnologia

CERN Multimedia

Jatvia, J M

2002-01-01

"La Universidad de Valencia tiene avanzado el diseno de un acelerador lineal de protones, cuya culminacion depende del compromiso del Consell en sufragar la plantilla que necesitaria el centro para estar operativo" (1 page).

La Concha Shell

Directory of Open Access Journals (Sweden)

Levy, Matthys P.

1961-01-01

Full Text Available La estructura de hormigón armado que cubre el club en el hotel La Concha, de San Juan de Puerto Rico, tiene forma de concha ondulada elipsoidal. Se ha situado en un estanque poco profundo, del que emerge como si hubiese venido del océano que tiene delante.

Pressureless sintering of dense Si3N4 and Si3N4/SiC composites with nitrate additives

International Nuclear Information System (INIS)

Kim, J.Y.; Iseki, Takayoshi; Yano, Toyohiko

1996-01-01

The effect of aluminum and yttrium nitrate additives on the densification of monolithic Si 3 N 4 and a Si 3 N 4 /SiC composite by pressureless sintering was compared with that of oxide additives. The surfaces of Si 3 N 4 particles milled with aluminum and yttrium nitrates, which were added as methanol solutions, were coated with a different layer containing Al and Y from that of Si 3 N 4 particles milled with oxide additives. Monolithic Si 3 N 4 could be sintered to 94% of theoretical density (TD) at 1,500 C with nitrate additives. The sintering temperature was about 100 C lower than the case with oxide additives. After pressureless sintering at 1,750 C for 2 h in N 2 , the bulk density of a Si 3 N 4 /20 wt% SiC composite reached 95% TD with nitrate additives

Chemical vapor deposition of Si/SiC nano-multilayer thin films

International Nuclear Information System (INIS)

Weber, A.; Remfort, R.; Woehrl, N.; Assenmacher, W.; Schulz, S.

2015-01-01

Stoichiometric SiC films were deposited with the commercially available single source precursor Et_3SiH by classical thermal chemical vapor deposition (CVD) as well as plasma-enhanced CVD at low temperatures in the absence of any other reactive gases. Temperature-variable deposition studies revealed that polycrystalline films containing different SiC polytypes with a Si to carbon ratio of close to 1:1 are formed at 1000 °C in thermal CVD process and below 100 °C in the plasma-enhanced CVD process. The plasma enhanced CVD process enables the reduction of residual stress in the deposited films and offers the deposition on temperature sensitive substrates in the future. In both deposition processes the film thickness can be controlled by variation of the process parameters such as the substrate temperature and the deposition time. The resulting material films were characterized with respect to their chemical composition and their crystallinity using scanning electron microscope, energy dispersive X-ray spectroscopy (XRD), atomic force microscopy, X-ray diffraction, grazing incidence X-ray diffraction, secondary ion mass spectrometry and Raman spectroscopy. Finally, Si/SiC multilayers of up to 10 individual layers of equal thickness (about 450 nm) were deposited at 1000 °C using Et_3SiH and SiH_4. The resulting multilayers features amorphous SiC films alternating with Si films, which feature larger crystals up to 300 nm size as measured by transmission electron microscopy as well as by XRD. XRD features three distinct peaks for Si(111), Si(220) and Si(311). - Highlights: • Stoichiometric silicon carbide films were deposited from a single source precursor. • Thermal as well as plasma-enhanced chemical vapor deposition was used. • Films morphology, crystallinity and chemical composition were characterized. • Silicon/silicon carbide multilayers of up to 10 individual nano-layers were deposited.

Formation of metallic Si and SiC nanoparticles from SiO2 particles by plasma-induced cathodic discharge electrolysis in chloride melt

International Nuclear Information System (INIS)

Tokushige, M.; Tsujimura, H.; Nishikiori, T.; Ito, Y.

2013-01-01

Silicon nanoparticles are formed from SiO 2 particles by conducting plasma-induced cathodic discharge electrolysis. In a LiCl–KCl melt in which SiO 2 particles were suspended at 450 °C, we obtained Si nanoparticles with diameters around 20 nm. During the electrolysis period, SiO 2 particles are directly reduced by discharge electrons on the surface of the melt just under the discharge, and the deposited Si atom clusters form Si nanoparticles, which leave the surface of the original SiO 2 particle due to free spaces caused by a molar volume difference between SiO 2 and Si. We also found that SiC nanoparticles can be obtained using carbon anode. Based on Faraday's law, the current efficiency for the formation of Si nanoparticles is 70%

Formation of Si/Ge/Si heterostructures with quantum dots

International Nuclear Information System (INIS)

Zinov'ev, V.A.; Dvurechenskij, A.V.; Novikov, P.L.

2003-01-01

It is present the Monte Carlo simulation of epitaxial embedding of faceted three-dimensional Ge islands (quantum dots) in a Si matrix. Under a Si flux these islands expand and undergo a shape change (from pyramidal to drop-like shape). The main expansion occurs at initial stage of embedding in Si (deposition of 1-2 monolayers). This change is controlled by surface diffusion. The shape of island can be preserved when one uses the higher Si fluxes. The reason of island conservation lies in blocking of Ge surface diffusion [ru

Metallization of ion beam synthesized Si/3C-SiC/Si layer systems by high-dose implantation of transition metal ions

International Nuclear Information System (INIS)

Lindner, J.K.N.; Wenzel, S.; Stritzker, B.

2001-01-01

The formation of metal silicide layers contacting an ion beam synthesized buried 3C-SiC layer in silicon by means of high-dose titanium and molybdenum implantations is reported. Two different strategies to form such contact layers are explored. The titanium implantation aims to convert the Si top layer of an epitaxial Si/SiC/Si layer sequence into TiSi 2 , while Mo implantations were performed directly into the SiC layer after selectively etching off all capping layers. Textured and high-temperature stable C54-TiSi 2 layers with small additions of more metal-rich silicides are obtained in the case of the Ti implantations. Mo implantations result in the formation of the high-temperature phase β-MoSi 2 , which also grows textured on the substrate. The formation of cavities in the silicon substrate at the lower SiC/Si interface due to the Si consumption by the growing silicide phase is observed in both cases. It probably constitutes a problem, occurring whenever thin SiC films on silicon have to be contacted by silicide forming metals independent of the deposition technique used. It is shown that this problem can be solved with ion beam synthesized contact layers by proper adjustment of the metal ion dose

Effects of atomic hydrogen on the selective area growth of Si and Si1-xGex thin films on Si and SiO2 surfaces: Inhibition, nucleation, and growth

International Nuclear Information System (INIS)

Schroeder, T.W.; Lam, A.M.; Ma, P.F.; Engstrom, J.R.

2004-01-01

Supersonic molecular beam techniques have been used to study the nucleation of Si and Si 1-x Ge x thin films on Si and SiO 2 surfaces, where Si 2 H 6 and GeH 4 have been used as sources. A particular emphasis of this study has been an examination of the effects of a coincident flux of atomic hydrogen. The time associated with formation of stable islands of Si or Si 1-x Ge x on SiO 2 surfaces--the incubation time--has been found to depend strongly on the kinetic energy of the incident molecular precursors (Si 2 H 6 and GeH 4 ) and the substrate temperature. After coalescence, thin film morphology has been found to depend primarily on substrate temperature, with smoother films being grown at substrate temperatures below 600 deg. C. Introduction of a coincident flux of atomic hydrogen has a large effect on the nucleation and growth process. First, the incubation time in the presence of atomic hydrogen has been found to increase, especially at substrate temperatures below 630 deg. C, suggesting that hydrogen atoms adsorbed on Si-like sites on SiO 2 can effectively block nucleation of Si. Unfortunately, in terms of promoting selective area growth, coincident atomic hydrogen also decreases the rate of epitaxial growth rate, essentially offsetting any increase in the incubation time for growth on SiO 2 . Concerning Si 1-x Ge x growth, the introduction of GeH 4 produces substantial changes in both thin film morphology and the rate nucleation of poly-Si 1-x Ge x on SiO 2 . Briefly, the addition of Ge increases the incubation time, while it lessens the effect of coincident hydrogen on the incubation time. Finally, a comparison of the maximum island density, the time to reach this density, and the steady-state polycrystalline growth rate strongly suggests that all thin films [Si, Si 1-x Ge x , both with and without H(g)] nucleate at special sites on the SiO 2 surface, and grow primarily via direct deposition of adatoms on pre-existing islands

Anomalous defect processes in Si implanted amorphous SiO2, II

International Nuclear Information System (INIS)

Fujita, Tetsuo; Fukui, Minoru; Okada, Syunji; Shimizu-Iwayama, Tsutomu; Hioki, Tatsumi; Itoh, Noriaki

1994-01-01

Aanomalous features of the defects in Si implanted amorphous SiO 2 are reported. The numbers of E 1 prime centers and B 2 centers are found to increase monotonically with implanted Si dose, in contrast to the saturating feature of these numbers in Ar implanted samples. Moreover, when H ions are implanted in amorphous SiO 2 predamaged by Si implantation, both of the density and the number of E 1 prime centers increase and they reach a constant value at a small H dose. We point out that these anomalies can be explained in terms of the difference in the cross-section for defect annihilation in the specimens implanted with Si ions and other ions, in accordance with the homogeneous model proposed by Devine and Golanski. We consider that the main mechanism of defect annihilation is the recombination of an E 1 prime center and an interstitial O, which is stabilized by an implanted Si, reducing the cross-section in Si-implanted specimens. ((orig.))

Une catastrophe glorieuse : le martyre des premiers chrétiens du Japon, Nagasaki, 1597

Directory of Open Access Journals (Sweden)

Clotilde Jacquelard

2011-11-01

Full Text Available Le naufrage du galion San Felipe dans le port de Urado (Shikoku, Japon en octobre 1596 fut le déclencheur d’un désastre missionnaire : le martyre de vingt-six chrétiens, franciscains espagnols et chrétiens japonais, à Nagasaki, le 5 février 1597. Cet article s’attache à examiner la relation dialectique entre les deux événements par l’étude de deux discours missionnaires franciscains hagiographiques. Il s’agit tout d’abord de rappeler la lecture providentialiste du temps à travers la perception de présages matériels et spirituels de la part des acteurs, puis de montrer que ces évènements paroxystiques révèlent en même temps qu’ils résolvent – temporairement – des tensions et des crises latentes, résultat de la confrontation entre plusieurs communautés culturelles comme la japonaise, l’espagnole et la portugaise, autour de prétentions géopolitiques, commerciales et religieuses dans cette zone de frontière de l’antiméridien du Pacifique nord.El naufragio del galeón San Felipe en el puerto de Urado (Shikoku, Japón en octubre de 1596 desembocó en un desastre misionero : el martirio de veintiséis cristianos, franciscanos españoles y cristianos japoneses, en Nagasaki, el 5 de febrero de 1597. Este artículo quiere examinar la relación dialéctica entre ambos acontecimientos, mediante el estudio de dos discursos misioneros franciscanos hagiográficos. Se trata de recordar primero la lectura providencialista de la época a través de la percepción de presagios tanto materiales como espirituales por parte de los actores, y mostrar luego que estos acontecimientos paroxísticos revelan, al mismo tiempo que resuelven –temporalmente– tensiones y crisis latentes, resultados de la confrontación de varias comunidades culturales como la japonesa, la española y la portuguesa, en torno a pretensiones geopolíticas, comerciales y religiosas en la zona fronteriza del antimeridiano del Pacífico norte.

Structural and electrical evaluation for strained Si/SiGe on insulator

International Nuclear Information System (INIS)

Wang Dong; Ii, Seiichiro; Ikeda, Ken-ichi; Nakashima, Hideharu; Ninomiya, Masaharu; Nakamae, Masahiko; Nakashima, Hiroshi

2006-01-01

Three strained Si/SiGe on insulator wafers having different Ge fractions were evaluated using dual-metal-oxide-semiconductor (dual-MOS) deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM) methods. The interface of SiGe/buried oxide (BOX) shows roughness less than 1 nm by high resolution TEM observation. The interface states densities (D it ) of SiGe/BOX are approximately 1 x 10 12 cm -2 eV -1 , which is approximately one order of magnitude higher than that of Si/BOX in a Si on insulator wafer measured as reference by the same method of dual-MOS DLTS. The high D it of SiGe/BOX is not due to interface roughness but due to Ge atoms. The threading dislocations were also clearly observed by TEM and were analyzed

Escolhas Associadas ao Automóvel por Homens e por Mulheres: confluência ou divergência? Choices associated with automobiles for Men and Women: convergence or divergence? Opciones relacionadas con el Automóvil por Hombres y por Mujeres: ¿convergencia o divergencia?

Directory of Open Access Journals (Sweden)

LICHT, René Henrique Götz

2009-03-01

revealed there are more similarities than differences between choices associated to the automobile by men and choices associated to the automobile by women. The similarity between the choices suggests that the representations, the meanings and values assigned to the car by men and women are similar and thus the strategy of product differentiation does not apply to the automotive industry.RESUMENEl aumento del poder de compra de las mujeres llevó a las empresas a adoptar estrategias de diferenciación de los productos y a producir productos específicos para el público femenino. La industria automovilística no es inmune a este fenómeno, pues las mujeres concentran aproximadamente la mitad de las ventas de automóviles en el país. Considerando las diferencias de consumo e de comportamiento entre mujeres y hombres se plantea la siguiente cuestión: ¿hay diferencias en las opciones relacionadas con el automóvil entre hombres y mujeres? Se presentaron ante los participantes algunos ítems que forman parte de la vida diaria de las personas y que ellas valorizan; se solicitó a los participantes que escogiesen y asociasen estos ítems al automóvil. El análisis de los resultados reveló que había más similitudes que diferencias entre las opciones relacionadas con el automóvil por parte de los hombres y las opciones relacionadas al automóvil por parte de las mujeres. La similitud entre las opciones indica que las representaciones, los significados y valores atribuidos al automóvil por hombres y mujeres son similares y por lo tanto, la estrategia de diferenciación de productos no se aplica a la industria automovilística.

Effect of Ti and Si interlayer materials on the joining of SiC ceramics

Energy Technology Data Exchange (ETDEWEB)

Jung, Yang Il; Park, Jung Hwan; Kim, Hyun Gil; Park, Dong Jun; Park, Jeong Yong; Kim, Weon Ju [LWR Fuel Technology Division, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-08-15

SiC-based ceramic composites are currently being considered for use in fuel cladding tubes in light-water reactors. The joining of SiC ceramics in a hermetic seal is required for the development of ceramic-based fuel cladding tubes. In this study, SiC monoliths were diffusion bonded using a Ti foil interlayer and additional Si powder. In the joining process, a very low uniaxial pressure of ∼0.1 MPa was applied, so the process is applicable for joining thin-walled long tubes. The joining strength depended strongly on the type of SiC material. Reaction-bonded SiC (RB-SiC) showed a higher joining strength than sintered SiC because the diffusion reaction of Si was promoted in the former. The joining strength of sintered SiC was increased by the addition of Si at the Ti interlayer to play the role of the free Si in RB-SiC. The maximum joint strength obtained under torsional stress was ∼100 MPa. The joint interface consisted of TiSi{sub 2}, Ti{sub 3}SiC{sub 2}, and SiC phases formed by a diffusion reaction of Ti and Si.

On the line intensity ratios of prominent Si II, Si III, and Si IV multiplets

International Nuclear Information System (INIS)

Djenize, S.; Sreckovic, A.; Bukvic, S.

2010-01-01

Line intensities of singly, doubly and triply ionized silicon (Si II, Si III, and Si IV, respectively) belonging to the prominent higher multiplets, are of interest in laboratory and astrophysical plasma diagnostics. We measured these line intensities in the emission spectra of pulsed helium discharge. The Si II line intensity ratios in the 3s3p 22 D-3s 2 4p 2 P o , 3s 2 3d 2 D-3s 2 4f 2 F o , and 3s 2 4p 2 P o -3s 2 4d 2 D transitions, the Si III line intensity ratios in the 3s3d 3 D-3s4p 3 P o , 3s4p 3 P o -3s4d 3 D, 3s4p 3 P o -3s5s 3 S, 3s4s 3 S-3s4p 3 P o , and 3s4f 3 F o -3s5g 3 G transitions, and the Si IV line intensity ratios in the 4p 2 P o -4d 2 D and 4p 2 P o -5s 2 S transitions were obtained in a helium plasma at an electron temperature of about 17,000 ± 2000 K. Line shapes were recorded using a spectrograph and an ICCD camera as a highly-sensitive detection system. The silicon atoms were evaporated from a Pyrex discharge tube designed for the purpose. They represent impurities in the optically thin helium plasma at the silicon ionic wavelengths investigated. The line intensity ratios obtained were compared with those available in the literature, and with values calculated on the basis of available transition probabilities. The experimental data corresponded well with line intensity ratios calculated using the transition probabilities obtained from a Multi Configuration Hartree-Fock approximation for Si III and Si IV spectra. We recommend corrections of some Si II transition probabilities.

Mushroom-free selective epitaxial growth of Si, SiGe and SiGe:B raised sources and drains

Science.gov (United States)

Hartmann, J. M.; Benevent, V.; Barnes, J. P.; Veillerot, M.; Lafond, D.; Damlencourt, J. F.; Morvan, S.; Prévitali, B.; Andrieu, F.; Loubet, N.; Dutartre, D.

2013-05-01

We have evaluated various Cyclic Selective Epitaxial Growth/Etch (CSEGE) processes in order to grow "mushroom-free" Si and SiGe:B Raised Sources and Drains (RSDs) on each side of ultra-short gate length Extra-Thin Silicon-On-Insulator (ET-SOI) transistors. The 750 °C, 20 Torr Si CSEGE process we have developed (5 chlorinated growth steps with four HCl etch steps in-between) yielded excellent crystalline quality, typically 18 nm thick Si RSDs. Growth was conformal along the Si3N4 sidewall spacers, without any poly-Si mushrooms on top of unprotected gates. We have then evaluated on blanket 300 mm Si(001) wafers the feasibility of a 650 °C, 20 Torr SiGe:B CSEGE process (5 chlorinated growth steps with four HCl etch steps in-between, as for Si). As expected, the deposited thickness decreased as the total HCl etch time increased. This came hands in hands with unforeseen (i) decrease of the mean Ge concentration (from 30% down to 26%) and (ii) increase of the substitutional B concentration (from 2 × 1020 cm-3 up to 3 × 1020 cm-3). They were due to fluctuations of the Ge concentration and of the atomic B concentration [B] in such layers (drop of the Ge% and increase of [B] at etch step locations). Such blanket layers were a bit rougher than layers grown using a single epitaxy step, but nevertheless of excellent crystalline quality. Transposition of our CSEGE process on patterned ET-SOI wafers did not yield the expected results. HCl etch steps indeed helped in partly or totally removing the poly-SiGe:B mushrooms on top of the gates. This was however at the expense of the crystalline quality and 2D nature of the ˜45 nm thick Si0.7Ge0.3:B recessed sources and drains selectively grown on each side of the imperfectly protected poly-Si gates. The only solution we have so far identified that yields a lesser amount of mushrooms while preserving the quality of the S/D is to increase the HCl flow during growth steps.

Unipersonalidad societaria: a propósito de un debate actual en el derecho colombiano.

Directory of Open Access Journals (Sweden)

Fabio Andrés Bonilla Sanabria

2008-07-01

Full Text Available Con ocasión de la reforma introducida en el ordenamiento jurídico Colombiano por la ley 1014 de 2006, y en concreto la norma contenida en el artículo 22, así como con ocasión de un reciente pronunciamiento de nuestra Corte Constitucional, la doctrina ha vuelto a discutir sobre si necesariamente se tiene que hablar de pluralidad de individuos en las sociedades mercantiles Colombianas. Por lo anterior, el artículo tiene dos objetivos: De un lado, determinar si existe una contradicción entre los conceptos de sociedad y la unipersonalidad aplicada a las mismas, y de otro lado, establecer si con ocasión del pronunciamiento constitucional referido, la sociedad unipersonal se encuentra vigente en Colombia.

Ni-Si oxide as an inducing crystallization source for making poly-Si

Energy Technology Data Exchange (ETDEWEB)

Meng, Zhiguo; Liu, Zhaojun; Li, Juan; Wu, Chunya; Xiong, Shaozhen [Institute of Photo-electronics, Nankai University, Tianjin (China); Zhao, Shuyun; Wong, Man; Kwok, Hoi Sing [Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong (China)

2010-04-15

Nickel silicon oxide mixture was sputtered on a-Si with Ni-Si alloy target with Ni:Si weight ratio of 1:9 and used as a new inducing source for metal induced lateral crystallization (MILC). The characteristics of the resulted poly-Si materials induced by Ni-Si oxide with different thickness were nearly the same. This means the metal induced crystallization with this new inducing source has wide processing tolerance to make MILC poly-Si. Besides, it reduced the residual Ni content in the resulted poly-Si film. The transfer characteristic curve of poly-Si TFT and a TFT-OLED display demo made with this kind of new inducing source were also presented in this paper. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Alpha-particle irradiation induced defects in SiO2 films of Si-SiO2 structures

International Nuclear Information System (INIS)

Koman, B.P.; Gal'chynskyy, O.V.; Kovalyuk, R.O.; Shkol'nyy, A.K.

1996-01-01

The aim of the work was to investigate alpha-particle irradiation induced defects in Si-SiO 2 structures by means of the thermostimulated discharge currents (TSDC) analysis. The object of investigation were (p-Si)-SiO 2 structures formed by a combined oxidation of the industrial p-Si wafers in dry and wet oxygen at temperature of 1150 C. The TSD currents were investigated in the temperature range between 90 and 500 K under linear heating rate. Pu 238 isotopes were the source of alpha-particles with an energy of 4-5 MeV and a density of 5.10 7 s -1 cm -2 . The TSD current curves show two peculiar maxima at about 370 and 480 K. Alpha-particle irradiation doesn't affect the general shape of the TSDC curves but leads to a shift of the maximum at 370 K and reduces the total electret charge which is accumulated in the Si-SiO 2 structures during polarization. The energy distribution function of the defects which are involved in SiO 2 polarization has been calculated. It showes that defects with activation energies of about 0.8 and 1.0 eV take part in forming the electret state, and these activation energies have certain energy distributions. It has been found that the TSDC maximum at 370 K has space charge nature and is caused by migration of hydrogen ions. In irradiated samples hydrogen and natrium ions localize on deeper trapping centres induced by alpha-particle irradiation. (orig.)

Interfacial stability of CoSi2/Si structures grown by molecular beam epitaxy

Science.gov (United States)

George, T.; Fathauer, R. W.

1992-01-01

The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.

Hybrid Integrated Si/SiN Platforms for Wideband Optical Processing

Science.gov (United States)

2017-05-08

annealing process, makes the process prone to dopant redistribution, that hinderers the SiN deposition after full Si device fabrication. To resolve...with 220 nm of crystalline Si. In parallel, a Si die goes through a wet oxidation process to grow 5 μm of thermal oxide. In the next step, 400 nm of... annealing methods. As a figure of merit in hydrophilic bonding, we monitored the surface roughness and bonding strength of a thin oxide layer to

Formation mechanism of SiC in C-Si system by ion irradiation

International Nuclear Information System (INIS)

Hishita, Shunichi; Aizawa, Takashi; Suehara, Shigeru; Haneda, Hajime

2003-01-01

The irradiation effects of 2 MeV He + , Ne + , and Ar + ions on the film structure of the C-Si system were investigated with RHEED and XPS. The ion dose dependence of the SiC formation was kinetically analyzed. The SiC formation at moderate temperature was achieved by 2 MeV ion irradiation when the thickness of the initial carbon films was appropriate. The evolution process of the SiC film thickness consisted of the 3 stages. The first stage was the steep increase of the SiC, and was governed by the inelastic collision. The second was the gentle increase of the SiC, and was governed by the diffusion. The last was the decrease of the SiC, and was caused by the sputtering. The formation mechanism of the SiC was discussed. (author)

Silicon Effects on Properties of Melt Infiltrated SiC/SiC Composites

Science.gov (United States)

Bhatt, Ramakrishna T.; Gyekenyesi, John Z.; Hurst, Janet B.

2000-01-01

Silicon effects on tensile and creep properties, and thermal conductivity of Hi-Nicalon SiC/SiC composites have been investigated. The composites consist of 8 layers of 5HS 2-D woven preforms of BN/SiC coated Hi-Nicalon fiber mats and a silicon matrix, or a mixture of silicon matrix and SiC particles. The Hi-Nicalon SiC/silicon and Hi-Nicalon SiC/SiC composites contained about 24 and 13 vol% silicon, respectively. Results indicate residual silicon up to 24 vol% has no significant effect on creep and thermal conductivity, but does decrease the primary elastic modulus and stress corresponding to deviation from linear stress-strain behavior.

Simulation of electron transmittance and tunnel current in n{sup +} Poly-Si/HfSiO{sub x}N/Trap/SiO{sub 2}/Si(100) capacitors using analytical and numerical approaches

Energy Technology Data Exchange (ETDEWEB)

Noor, Fatimah A., E-mail: fatimah@fi.itb.ac.id; Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal [Physics of Electronic Materials Research Division Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Jalan Ganesa 10, Bandung 40132 (Indonesia)

2015-04-16

In this paper, we discuss the electron transmittance and tunneling current in high-k-based-MOS capacitors with trapping charge by including the off-diagonal effective-mass tensor elements and the effect of coupling between transverse and longitudinal energies represented by an electron velocity in the gate. The HfSiO{sub x}N/SiO{sub 2} dual ultrathin layer is used as the gate oxide in an n{sup +} poly- Si/oxide/Si capacitor to replace SiO{sub 2}. The main problem of using HfSiO{sub x}N is the charge trapping formed at the HfSiO{sub x}N/SiO{sub 2} interface that can influence the performance of the device. Therefore, it is important to develop a model taking into account the presence of electron traps at the HfSiO{sub x}N/SiO{sub 2} interface in the electron transmittance and tunneling current. The transmittance and tunneling current in n{sup +} poly- Si/HfSiO{sub x}N/trap/SiO2/Si(100) capacitors are calculated by using Airy wavefunctions and a transfer matrix method (TMM) as analytical and numerical approaches, respectively. The transmittance and tunneling current obtained from the Airy wavefunction are compared to those computed by the TMM. The effects of the electron velocity on the transmittance and tunneling current are also discussed.

Switching Performance Evaluation of Commercial SiC Power Devices (SiC JFET and SiC MOSFET) in Relation to the Gate Driver Complexity

DEFF Research Database (Denmark)

Pittini, Riccardo; Zhang, Zhe; Andersen, Michael A. E.

2013-01-01

and JFETs. The recent introduction of SiC MOSFET has proved that it is possible to have highly performing SiC devices with a minimum gate driver complexity; this made SiC power devices even more attractive despite their device cost. This paper presents an analysis based on experimental results...... of the switching losses of various commercially available Si and SiC power devices rated at 1200 V (Si IGBTs, SiC JFETs and SiC MOSFETs). The comparison evaluates the reduction of the switching losses which is achievable with the introduction of SiC power devices; this includes analysis and considerations...

Effect of PECVD SiNx/SiOy Nx –Si interface property on surface passivation of silicon wafer

International Nuclear Information System (INIS)

Jia Xiao-Jie; Zhou Chun-Lan; Zhou Su; Wang Wen-Jing; Zhu Jun-Jie

2016-01-01

It is studied in this paper that the electrical characteristics of the interface between SiO y N x /SiN x stack and silicon wafer affect silicon surface passivation. The effects of precursor flow ratio and deposition temperature of the SiO y N x layer on interface parameters, such as interface state density Di t and fixed charge Q f , and the surface passivation quality of silicon are observed. Capacitance–voltage measurements reveal that inserting a thin SiO y N x layer between the SiN x and the silicon wafer can suppress Q f in the film and D it at the interface. The positive Q f and D it and a high surface recombination velocity in stacks are observed to increase with the introduced oxygen and minimal hydrogen in the SiO y N x film increasing. Prepared by deposition at a low temperature and a low ratio of N 2 O/SiH 4 flow rate, the SiO y N x /SiN x stacks result in a low effective surface recombination velocity (S eff ) of 6 cm/s on a p-type 1 Ω·cm–5 Ω·cm FZ silicon wafer. The positive relationship between S eff and D it suggests that the saturation of the interface defect is the main passivation mechanism although the field-effect passivation provided by the fixed charges also make a contribution to it. (paper)

Preparation and Characterization of SiO2/SiCN Core-shell Ceramic Microspheres

Directory of Open Access Journals (Sweden)

ZHANG Hai-yuan

2017-05-01

Full Text Available The SiO2/PSN core-shell microspheres were prepared via an emulsion reaction combined with the polymer-derived ceramics (PDCs method using polysilazane (PSN in situ polymerization on the surface of SiO2 modified by silane coupling agents MPS, followed by pyrolysis process to obtain SiO2/SiCN core-shell ceramic microspheres. The effects of raw mass ratio, curing time and pyrolysis temperature on the formation and the morphology of core-shell microspheres were studied. The morphology, chemical composition and phase transformation were characterized by SEM, EDS, TEM, FT-IR and XRD. The results show that after reaction for 4h at 200℃, SiO2 completely coated PSN forms a core-shell microsphere with rough surface when the mass ratio of SiO2 and PSN is 1:4; when pyrolysis temperature is at 800-1200℃, amorphous SiO2/SiCN core-shell ceramic microspheres are prepared; at 1400℃, the amorphous phase partially crystallizes to produce SiO2, SiC and Si3N4 phase.

The Effect of Si Morphology on Machinability of Al-Si Alloys

Directory of Open Access Journals (Sweden)

Muhammet Uludağ

2015-12-01

Full Text Available Many of the cast parts require some sort of machining like milling, drilling to be used as a finished product. In order to improve the wear properties of Al alloys, Si is added. The solubility of Si in Al is quite low and it has a crystallite type structure. It behaves as particulate metal matrix composite which makes it an attractive element. Thus, the wear and machinability properties of these type of alloys depend on the morphology of Si in the matrix. In this work, Sr was added to alter the morphology of Si in Al-7Si and Al-12Si. Cylindrical shaped samples were cast and machinability characteristics of Sr addition was studied. The relationship between microstructure and machinability was evaluated.

Diámetro del conducto cístico y coledocolitiasis secundaria Hospital Nacional Arzobispo Loayza 2015

OpenAIRE

Oré de la Cruz, Ronald Arnaldo

2015-01-01

Introducción: en pacientes con sospecha de colédocolitiasis secundaria entre otras opciones se puede plantear la realización de colangiografía intraoperatoria transcístico para hacer el diagnóstico. Algunos cirujanos optan por no hacer efectivo este procedimiento si consideran que el conducto cístico no está dilatado Objetivo: Conocer la relación entre el diámetro del conducto cístico y la colédocolitiasis secundaria en los pacientes intervenidos quirúrgicamente en el hospital nacional Arz...

Comparative study of anisotropic superconductivity in CaAlSi and CaGaSi

International Nuclear Information System (INIS)

Tamegai, T.; Uozato, K.; Kasahara, S.; Nakagawa, T.; Tokunaga, M.

2005-01-01

In order to get some insight into the origin of the anomalous angular dependence of H c2 in a layered intermetallic compound CaAlSi, electronic, superconducting, and structural properties are compared between CaAlSi and CaGaSi. The angular dependence of H c2 in CaGaSi is well described by the anisotropic GL model. Parallel to this finding, the pronounced lattice modulation accompanying the superstructure along the c-axis in CaAlSi is absent in CaGaSi. A relatively large specific heat jump at the superconducting transition in CaAlSi compared with CaGaSi indicates the presence of strong electron-phonon coupling in CaAlSi, which may cause the superstructure and the anomalous angular dependence of H c2

Si/Fe flux ratio influence on growth and physical properties of polycrystalline β-FeSi2 thin films on Si(100) surface

Science.gov (United States)

Tarasov, I. A.; Visotin, M. A.; Aleksandrovsky, A. S.; Kosyrev, N. N.; Yakovlev, I. A.; Molokeev, M. S.; Lukyanenko, A. V.; Krylov, A. S.; Fedorov, A. S.; Varnakov, S. N.; Ovchinnikov, S. G.

2017-10-01

This work investigates the Si/Fe flux ratio (2 and 0.34) influence on the growth of β-FeSi2 polycrystalline thin films on Si(100) substrate at 630 °C. Lattice deformations for the films obtained are confirmed by X-ray diffraction analysis (XRD). The volume unit cell deviation from that of β-FeSi2 single crystal are 1.99% and 1.1% for Si/Fe =2 and Si/Fe =0.34, respectively. Absorption measurements show that the indirect transition ( 0.704 eV) of the Si/Fe =0.34 sample changes to the direct transition with a bandgap value of 0.816 eV for the sample prepared at Si/Fe =2. The absorption spectrum of the Si/Fe =0.34 sample exhibits an additional peak located below the bandgap energy value with the absorption maximum of 0.36 eV. Surface magneto-optic Kerr effect (SMOKE) measurements detect the ferromagnetic behavior of the β-FeSi2 polycrystalline films grown at Si/Fe =0.34 at T=10 K, but no ferromagnetism was observed in the samples grown at Si/Fe =2. Theoretical calculations refute that the cell deformation can cause the emergence of magnetization and argue that the origin of the ferromagnetism, as well as the lower absorption peak, is β-FeSi2 stoichiometry deviations. Raman spectroscopy measurements evidence that the film obtained at Si/Fe flux ratio equal to 0.34 has the better crystallinity than the Si/Fe =2 sample.

Improved thermal stability and hole mobilities in a strained-Si/strained-Si1-yGe y/strained-Si heterostructure grown on a relaxed Si1-xGe x buffer

International Nuclear Information System (INIS)

Gupta, Saurabh; Lee, Minjoo L.; Isaacson, David M.; Fitzgerald, Eugene A.

2005-01-01

A dual channel heterostructure consisting of strained-Si/strained-Si 1-y Ge y on relaxed Si 1-x Ge x (y > x), provides a platform for fabricating metal-oxide-semiconductor field-effect transistors (MOSFETs) with high hole mobilities (μ eff ) which depend directly on Ge concentration and strain in the strained-Si 1-y Ge y layer. Ge out-diffuses from the strained-Si 1-y Ge y layer into relaxed Si 1-x Ge x during high temperature processing, reducing peak Ge concentration and strain in the strained-Si 1-y Ge y layer and degrades hole μ eff in these dual channel heterostructures. A heterostructure consisting of strained-Si/strained-Si 1-y Ge y /strained-Si, referred to as a trilayer heterostructure, grown on relaxed Si 1-x Ge x has much reduced Ge out-flux from the strained-Si 1-y Ge y layer and retains higher μ eff after thermal processing. Improved hole μ eff over similar dual channel heterostructures is also observed in this heterostructure. This could be a result of preventing the hole wavefunction tunneling into the low μ eff relaxed Si 1-x Ge x layer due to the additional valence band offset provided by the underlying strained-Si layer. A diffusion coefficient has been formulated and implemented in a finite difference scheme for predicting the thermal budget of the strained SiGe heterostructures. It shows that the trilayer heterostructures have superior thermal budgets at higher Ge concentrations. Ring-shaped MOSFETs were fabricated on both platforms and subjected to various processing temperatures in order to compare the extent of μ eff reduction with thermal budget. Hole μ eff enhancements are retained to a much higher extent in a trilayer heterostructure after high temperature processing as compared to a dual channel heterostructure. The improved thermal stability and hole μ eff of a trilayer heterostructure makes it an ideal platform for fabricating high μ eff MOSFETs that can be processed over higher temperatures without significant losses in hole �

Rod-like β-FeSi2 phase grown on Si (111) substrate

International Nuclear Information System (INIS)

Han Ming; Tanaka, Miyoko; Takeguchi, Masaki; Furuya, Kazuo

2004-01-01

Pure Fe with coverage of 0.5-2.0 nm was deposited on Si (111) 7x7 surfaces by reactive deposition epitaxy (RDE) in an integrated ultrahigh vacuum (UHV) system. Transmission electron microscopy (TEM) confirmed that the as-deposited epitaxial phase exhibits rod-like and equilateral triangular morphology. The as-deposited phase was identified as c-FeSi 2 by electron diffraction and high-resolution transmission electron microscopy. It was found that there exists lattice distortion in epitaxial c-FeSi 2 phase. Upon annealing at 1073 K, the metastable c-FeSi 2 transforms into equilibrium β-FeSi 2 phase, the latter inherits completely the morphology of c-FeSi 2 phase. Based on RDE and subsequent annealing, a new fabrication technique to grow rod-like semiconducting β-FeSi 2 on a Si substrate has been proposed in the present work

En Defensa del Fin de Lucro en Salud.

Directory of Open Access Journals (Sweden)

Ramón Abel Castaño Yepes

2007-06-01

La quinta premisa se deriva de la cuarta y de la segunda, es decir, que si el diseño del sistema de salud introducido por la Ley 100 tiene como elemento distintivo el fin de lucro, entonces el resultado de dicho diseño tiene que ser indeseable, puesto que el fin de lucro es indeseable...

Passivation of surface-nanostructured f-SiC and porous SiC

DEFF Research Database (Denmark)

Ou, Haiyan; Lu, Weifang; Ou, Yiyu

The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper.......The further enhancement of photoluminescence from nanostructured fluorescent silicon carbide (f-SiC) and porous SiC by using atomic layer deposited (ALD) Al2O3 is studied in this paper....

Reduced Pressure-Chemical Vapour Deposition of Si/SiGe heterostructures for nanoelectronics

International Nuclear Information System (INIS)

Hartmann, J.M.; Andrieu, F.; Lafond, D.; Ernst, T.; Bogumilowicz, Y.; Delaye, V.; Weber, O.; Rouchon, D.; Papon, A.M.; Cherkashin, N.

2008-01-01

We have first of all quantified the impact of pressure on Si and SiGe growth kinetics. Definite growth rate and Ge concentration increases with the pressure have been evidenced at low temperatures (650-750 deg. C). By contrast, the high temperature (950-1050 deg. C) Si growth rate either increases or decreases with pressure (gaseous precursor depending). We have then described the selective epitaxial growth process we use to form Si or Si 0.7 Ge 0.3 :B raised sources and drains on ultra-thin patterned Silicon-On-Insulator (SOI) substrates. We have afterwards presented the specifics of SiGe virtual substrates and of the tensile-strained Si layers grown on top (used as templates for the elaboration of tensily strained-SOI wafers). The tensile strain, which can be tailored from 1.3 up to 3 GPa, leads to an electron mobility gain by a factor of 2 in n-Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) built on top. High Ge content SiGe virtual substrates can also be used for the elaboration of compressively strained Ge channels, with impressive hole mobility gains (x9) compared to bulk Si. After that, we have described the main structural features of thick Ge layers grown directly on Si (that can be used as donor wafers for the elaboration of GeOI wafers or as the active medium of near infrared photo-detectors). Finally, we have shown how Si/SiGe multilayers can be used for the formation of high performance 3D devices such as multi-bridge channel or nano-beam gate-all-around FETs, the SiGe sacrificial layers being removed thanks to plasma dry etching, wet etching or in situ gaseous HCl etching

¿Le han hecho pruebas de detección de cáncer colorrectal? - (Have You Been Tested for Colorectal Cancer?)

Centers for Disease Control (CDC) Podcasts

2013-11-05

Este podcast se basa en la edición de noviembre del 2013 del informe Signos Vitales de los CDC. Las pruebas de detección de cáncer colorrectal salvan vidas, pero solo si usted se las hace. Si tiene entre 50 y 75 años, hable con su médico acerca de cuál prueba es mejor para usted. Si tiene enfermedad inflamatoria intestinal o antecedentes de cáncer colorrectal o pólipos en su familia, pregúntele al médico si debería empezar a hacerse las pruebas de detección antes de cumplir los 50 años.  Created: 11/5/2013 by Centers for Disease Control and Prevention (CDC).   Date Released: 11/5/2013.

Si/SiC heterojunction optically controlled transistor with charge compensation layer

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Pu Hongbin

2016-01-01

Full Text Available A novel n-SiC/p-Si/n-Si optically controlled transistor with charge compensation layer has been studied in the paper. The performance of the device is simulated using Silvaco Atlas tools, which indicates excellent performances of the device in both blocking state and conducting state. The device also has a good switching characteristic with 0.54μs as rising time and 0.66μs as falling time. With the charge compensation layer, the breakdown voltage and the spectral response intensity of the device are improved by 90V and 33A/W respectively. Compared with optically controlled transistor without charge compensation layer, the n-SiC/p-Si/n-Si optically controlled transistor with charge compensation layer has a better performance.

Characterization of SiC–SiC composites for accident tolerant fuel cladding

Energy Technology Data Exchange (ETDEWEB)

Deck, C.P., E-mail: Christian.Deck@ga.com; Jacobsen, G.M.; Sheeder, J.; Gutierrez, O.; Zhang, J.; Stone, J.; Khalifa, H.E.; Back, C.A.

2015-11-15

Silicon carbide (SiC) is being investigated for accident tolerant fuel cladding applications due to its high temperature strength, exceptional stability under irradiation, and reduced oxidation compared to Zircaloy under accident conditions. An engineered cladding design combining monolithic SiC and SiC–SiC composite layers could offer a tough, hermetic structure to provide improved performance and safety, with a failure rate comparable to current Zircaloy cladding. Modeling and design efforts require a thorough understanding of the properties and structure of SiC-based cladding. Furthermore, both fabrication and characterization of long, thin-walled SiC–SiC tubes to meet application requirements are challenging. In this work, mechanical and thermal properties of unirradiated, as-fabricated SiC-based cladding structures were measured, and permeability and dimensional control were assessed. In order to account for the tubular geometry of the cladding designs, development and modification of several characterization methods were required.

EFFECT OF THE Si POWDER ADDITIONS ON THE PROPERTIES OF SiC COMPOSITES

Directory of Open Access Journals (Sweden)

GUOGANG XU

2012-09-01

Full Text Available By means of transient plastic phase process, the SiC silicon carbide kiln furniture materials were produced through adding Si powder to SiC materials. At the condition of the same additions of SiO2 powder, the effect of the Si powder additions on properties of silicon carbide materials after sintered at 1450°C for 3 h in air atmosphere was studied by means of SEM and other analysis methods. The results showed that silicon powder contributes to both sintering by liquid state and plastic phase combination to improve the strength of samples. When the Si powder additions is lower than 3.5 %, the density and strength of samples increase and porosity decrease with increasing Si powder additions. However when the Si powder additions is higher than 3.5 %, the density and strength of samples decrease and porosity increase with increasing Si powder additions. With increasing of Si additions, the residual strength of sample after thermal shocked increased and linear change rate decreased, and get to boundary value when Si additions is 4.5 %. The results also indicated that at the same sintering temperature, the sample with 3.5 % silicon powder has maximum strength.

Irradiation project of SiC/SiC fuel pin 'INSPIRE': Status and future plan

International Nuclear Information System (INIS)

Kohyama, Akira; Kishimoto, Hirotatsu

2015-01-01

After the March 11 Disaster in East-Japan, Research and Development towards Ensuring Nuclear Safety Enhancement for LWR becomes a top priority R and D in nuclear energy policy of Japan. The role of high temperature non-metallic materials, such as SiC/SiC, is becoming important for the advanced nuclear reactor systems. SiC fibre reinforced SiC composite has been recognised to be the most attractive option for the future, now, METI fund based project, INSPIRE, has been launched as 5-year termed project at OASIS in Muroran Institute of Technology aiming at early realisation of this system. INSPIRE is the irradiation project of SiC/SiC fuel pins aiming to accumulate material, thermal, irradiation effect data of NITE-SiC/SiC in BWR environment. Nuclear fuel inserted SiC/SiC fuel pins are planned to be installed in the Halden reactor. The project includes preparing the NITE-SiC/SiC tubes, joining of end caps, preparation of rigs to control the irradiation environment to BWR condition and the instruments to measure the condition of rigs and pins in operation. Also, basic neutron irradiation data will be accumulated by SiC/SiC coupon samples currently under irradiation in BR2. The output from this project may present the potentiality of NITE-SiC/SiC fuel cladding with the first stage fuel-cladding interaction. (authors)

Reliability study of ultra-thin gate oxides on strained-Si/SiGe MOS structures

International Nuclear Information System (INIS)

Varzgar, John B.; Kanoun, Mehdi; Uppal, Suresh; Chattopadhyay, Sanatan; Tsang, Yuk Lun; Escobedo-Cousins, Enrique; Olsen, Sarah H.; O'Neill, Anthony; Hellstroem, Per-Erik; Edholm, Jonas; Ostling, Mikael; Lyutovich, Klara; Oehme, Michael; Kasper, Erich

2006-01-01

The reliability of gate oxides on bulk Si and strained Si (s-Si) has been evaluated using constant voltage stressing (CVS) to investigate their breakdown characteristics. The s-Si architectures exhibit a shorter life time compared to that of bulk Si, which is attributed to higher bulk oxide charges (Q ox ) and increased surface roughness in the s-Si structures. The gate oxide in the s-Si structure exhibits a hard breakdown (HBD) at 1.9 x 10 4 s, whereas HBD is not observed in bulk Si up to a measurement period of 1.44 x 10 5 s. The shorter lifetime of the s-Si gate oxide is attributed to a larger injected charge (Q inj ) compared to Q inj in bulk Si. Current-voltage (I-V) measurements for bulk Si samples at different stress intervals show an increase in stress induced leakage current (SILC) of two orders in the low voltage regime from zero stress time to up to 5 x 10 4 s. In contrast, superior performance enhancements in terms of drain current, maximum transconductance and effective channel mobility are observed in s-Si MOSFET devices compared to bulk Si. The results from this study indicate that further improvement in gate oxide reliability is needed to exploit the sustained performance enhancement of s-Si devices over bulk Si

Electrochemical characteristics of nc-Si/SiC composite for anode electrode of lithium ion batteries

International Nuclear Information System (INIS)

Jeon, Bup Ju; Lee, Joong Kee

2014-01-01

Graphical abstract: Cycling performances and coulombic efficiencies of the nc-Si/SiC composite anodes at different CH 4 /SiH 4 mole ratios. -- Highlights: • Our work has focused on irreversible discharge capacity and capacity retention of nc-Si/SiC composite particles. • Particles comprised a mixed construction of nc-Si/SiC structure with dual phases. • The SiC phase acted as retarding media, leading to enhanced cycle stability. -- Abstract: nc-Si/SiC composite particles were prepared as an anode material for lithium ion batteries using a plasma jet with DC arc discharge. The composition of the nc-Si/SiC composite particles was controlled by setting the mole ratio of CH 4 and SiH 4 precursor gases. X-ray diffraction, TEM images, and Raman shift analyses revealed that the synthesized nc-Si/SiC composite particles comprised a construction of nano-nocaled structure with crystalline phases of active silicon, highly disordered amorphous carbon of graphite and crystalline phases of β-SiC. In the experimental range examined, the nc-Si/SiC composite particles showed good coulombic efficiency in comparison with particles high Si–Si bonding content due to the interplay of particles with a small proportion of carbon and the buffering effect against volume expansion by structural stabilization, and played a role as retarding media for the rapid electrochemical reactions of the SiC crystal against lithium

Electrochemical characteristics of nc-Si/SiC composite for anode electrode of lithium ion batteries

Energy Technology Data Exchange (ETDEWEB)

Jeon, Bup Ju [Department of Energy Resources, Shinhan University, 233-1, Sangpae-dong, Dongducheon, Gyeonggi-do, 483-777 (Korea, Republic of); Lee, Joong Kee, E-mail: leejk@kist.re.kr [Advanced Energy Materials Processing Laboratory, Center for Energy Convergence Research, Green City Technology Institute, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791 (Korea, Republic of)

2014-03-25

Graphical abstract: Cycling performances and coulombic efficiencies of the nc-Si/SiC composite anodes at different CH{sub 4}/SiH{sub 4} mole ratios. -- Highlights: • Our work has focused on irreversible discharge capacity and capacity retention of nc-Si/SiC composite particles. • Particles comprised a mixed construction of nc-Si/SiC structure with dual phases. • The SiC phase acted as retarding media, leading to enhanced cycle stability. -- Abstract: nc-Si/SiC composite particles were prepared as an anode material for lithium ion batteries using a plasma jet with DC arc discharge. The composition of the nc-Si/SiC composite particles was controlled by setting the mole ratio of CH{sub 4} and SiH{sub 4} precursor gases. X-ray diffraction, TEM images, and Raman shift analyses revealed that the synthesized nc-Si/SiC composite particles comprised a construction of nano-nocaled structure with crystalline phases of active silicon, highly disordered amorphous carbon of graphite and crystalline phases of β-SiC. In the experimental range examined, the nc-Si/SiC composite particles showed good coulombic efficiency in comparison with particles high Si–Si bonding content due to the interplay of particles with a small proportion of carbon and the buffering effect against volume expansion by structural stabilization, and played a role as retarding media for the rapid electrochemical reactions of the SiC crystal against lithium.

Synthesis of SiC decorated carbonaceous nanorods and its hierarchical composites Si@SiC@C for high-performance lithium ion batteries

Energy Technology Data Exchange (ETDEWEB)

Wang, Chundong [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China); Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Li, Yi, E-mail: liyi@suda.edu.cn [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou (China); Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China); Ostrikov, Kostya [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland 4000 (Australia); Plasma Nanoscience, Industrial Innovation Program, CSIRO Manufacturing Flagship, Lindfield, New South Wales 2070 (Australia); Yang, Yonggang [College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou (China); Zhang, Wenjun, E-mail: apwjzh@cityu.edu.hk [Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China)

2015-10-15

SiC- based nanomaterials possess superior electric, thermal and mechanical properties. However, due to the tricky synthesis process, which needs to be carried out under high temperature with multi-step reaction procedures, the further application is dramatically limited. Herein, a simple as well as a controllable approach is proposed for synthesis of SiC- based nanostructures under low temperature. Phenyl-bridged polysilsesquioxane was chosen as the starting material to react with magnesium at 650 °C, following which SiC@C nanocomposites were finally obtained, and it maintains the original bent rod-like architecture of polysilsesquioxanes. The possible formation process for the nanocomposites can proposed as well. The electrochemical behaviour of nanocomposites was accessed, verifying that the synthesized SiC@C nanocomposites deliver good electrochemical performance. Moreover, SiC@C also shows to be a promising scaffold in supporting Si thin film electrode in achieving stable cycling performance in lithium ion batteries. - Highlights: • SiC@C bent nanorods were synthesized with a magnesium reaction approach. • Carbon nanorod spines studded with ultrafine β-SiC nanocrystallines was realized. • The synthesized SiC@C keeps the original rod-like structure of polysilsesquioxanes. • The possible formation process for the nanocomposites was analysed and proposed. • Si@SiC@C nanocomposites reveal good electrochemical performance in LIBs.

Progress in blanket designs using SiCf/SiC composites

International Nuclear Information System (INIS)

Giancarli, L.; Golfier, H.; Nishio, S.; Raffray, R.; Wong, C.; Yamada, R.

2002-01-01

This paper summarizes the most recent design activities concerning the use of SiC f /SiC composite as structural material for fusion power reactor breeding blanket. Several studies have been performed in the past. The most recent proposals are the TAURO blanket concept in the European Union, the ARIES-AT concept in the US, and DREAM concept in Japan. The first two concepts are self-cooled lithium-lead blankets, while DREAM is an helium-cooled beryllium/ceramic blanket. Both TAURO and ARIES-AT blankets are essentially formed by a SiC f /SiC box acting as a container for the lithium-lead which has the simultaneous functions of coolant, tritium breeder, neutron multiplier and, finally, tritium carrier. The DREAM blanket is characterized by small modules using pebble beds of Be as neutron multiplier material, of Li 2 O (or other lithium ceramics) as breeder material and of SiC as shielding material. The He coolant path includes a flow through the pebble beds and a porous partition wall. For each blanket, this paper describes the main design features and performances, the most recent design improvements, and the proposed manufacturing routes in order to identify specific issues and requirements for the future R and D on SiC f /SiC

Gas-source molecular beam epitaxy of Si(111) on Si(110) substrates by insertion of 3C-SiC(111) interlayer for hybrid orientation technology

Energy Technology Data Exchange (ETDEWEB)

Bantaculo, Rolando, E-mail: rolandobantaculo@yahoo.com; Saitoh, Eiji; Miyamoto, Yu; Handa, Hiroyuki; Suemitsu, Maki

2011-11-01

A method to realize a novel hybrid orientations of Si surfaces, Si(111) on Si(110), has been developed by use of a Si(111)/3C-SiC(111)/Si(110) trilayer structure. This technology allows us to use the Si(111) portion for the n-type and the Si(110) portion for the p-type channels, providing a solution to the current drive imbalance between the two channels confronted in Si(100)-based complementary metal oxide semiconductor (CMOS) technology. The central idea is to use a rotated heteroepitaxy of 3C-SiC(111) on Si(110) substrate, which occurs when a 3C-SiC film is grown under certain growth conditions. Monomethylsilane (SiH{sub 3}-CH{sub 3}) gas-source molecular beam epitaxy (GSMBE) is used for this 3C-SiC interlayer formation while disilane (Si{sub 2}H{sub 6}) is used for the top Si(111) layer formation. Though the film quality of the Si epilayer leaves a lot of room for betterment, the present results may suffice to prove its potential as a new technology to be used in the next generation CMOS devices.

Magnetic ordering of YPd{sub 2}Si-type HoNi{sub 2}Si and ErNi{sub 2}Si compounds

Energy Technology Data Exchange (ETDEWEB)

Morozkin, A.V., E-mail: morozkin@tech.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow, 119992 (Russian Federation); Isnard, O. [CNRS, Insitut. Néel, 25 Rue Des Martyrs BP166 x, F-38042 Grenoble (France); Université Grenoble Alpes, Inst. Néel, F-38042 Grenoble (France); Nirmala, R. [Indian Institute of Technology Madras, Chennai 600 036 (India); Quezado, S.; Malik, S.K. [Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Natal 59082-970 (Brazil)

2016-12-01

Magnetic properties of YPd{sub 2}Si-type HoNi{sub 2}Si and ErNi{sub 2}Si were investigated via neutron diffraction and magnetisation measurements. HoNi{sub 2}Si and ErNi{sub 2}Si show ferromagnetic-like ordering at T{sub C} of 9 K and 7 K, respectively. The paramagnetic Weiss temperatures are 9 K and 11 K and the effective magnetic moments are 10.76 μ{sub B}/fu and 9.79 μ{sub B}/fu for HoNi{sub 2}Si and ErNi{sub 2}Si compounds, respectively. The HoNi{sub 2}Si and ErNi{sub 2}Si are soft ferromagnets with saturation magnetization of 8.1 μ{sub B}/fu and 7.5 μ{sub B}/fu, respectively at 2 K and in field of 140 kOe. The isothermal magnetic entropy change, ΔS{sub m}, has a maximum value of −15.6 J/kg·K at 10 K for HoNi{sub 2}Si and −13.9 J/kg·K at 6 K for ErNi{sub 2}Si for a field change of 50 kOe. Neutron diffraction study in zero applied field shows mixed ferromagnetic-antiferromagnetic ordering of HoNi{sub 2}Si at ~9 K and its magnetic structure is a sum of a-axis ferromagnetic F{sub a}, b-axis antiferromagnetic AF{sub b} and c-axis antiferrromagnetic AF{sub c} components of Pn′a2{sub 1}′={1, m_x′/[1/2, 1/2, 1/2], 2_y′/[0, 1/2, 0], m_z/[1/2, 0, 1/2]} magnetic space group and propagation vector K{sub 0}=[0, 0, 0]. The holmium magnetic moment reaches a value of 9.23(9) μ{sub B} at 1.5 K and the unit cell of HoNi{sub 2}Si undergoes isotropic contraction around the temperature of magnetic transition. - Graphical abstract: HoNi{sub 2}Si: mixed ferro-antiferromagnet (F{sub a}+AF{sub b}+AF{sub c}){sup K0} with Pn′a2{sub 1}′ magnetic space group and K{sub 0}=[0, 0, 0] propagation vector below 10 K. - Highlights: • Ferro-antiferromagnetic ordering is observed in HoNi{sub 2}Si at 9 K and in ErNi{sub 2}Si at 7 K. • HoNi{sub 2}Si is soft ferromagnet with ΔS{sub m} of −15.6 J/kg·K at 10 K in field of 0–50 kOe. • ErNi{sub 2}Si is soft ferromagnet with ΔS{sub m} of −13.9 J/kg·K at 6 K in field of 0–50 kOe. • HoNi{sub 2}Si shows mixed F�

Compósitos SiCf /SiC utilizados em sistemas de proteção térmica SiCf /SiC composites for thermal protection systems

Directory of Open Access Journals (Sweden)

M. Florian

2005-09-01

Full Text Available Compósitos de carbeto de silício (SiC reforçado com fibras de carbeto de silício (SiCf são materiais candidatos em potencial para utilização em sistemas de proteção térmica em altas temperaturas devido principalmente à boa condutividade térmica na direção da fibra e muito baixa condutividade térmica na direção transversal à fibra, alta dureza, estabilidade térmica e à corrosão por oxidação. O compósito SiCf/SiC possui uma matriz de SiC reforçada com fibras contínuas policristalinas de SiC e é obtido por reações de conversão em altas temperaturas e atmosfera controlada, utilizando o compósito carbono/carbono como precursor. O processo de Reação Química em Vapor (CVR foi utilizado para a fabricação de compósitos SiCf/SiC com alta pureza na fase de SiC-beta. O compósito precursor de carbono/carbono foi fabricado com fibra de carbono não estabilizada e matriz carbonosa derivada da resina fenólica na forma de carbono isotrópico. O compósito convertido exibiu uma densidade de 1,75 g/cm³, com 40% de porosidade aberta e resistência à flexão de 80 MPa medida por ensaio flexão em 4 pontos. A área especifica medida pela técnica de BET é dependente da temperatura de conversão e das condições inicias do precursor de carbono, podendo chegar a 18 m²/g.Composites based on silicon carbide are potential candidate materials for thermal protection systems mainly due to its good thermal conductivity in fiber direction and very low transversal thermal conductivity, high hardness, corrosion and thermal resistance. SiCf/SiC composite presents a SiC matrix reinforced with SiC polycrystalline continuous fibers. The composite was obtained by conversion reactions at high temperature and controlled atmosphere from a carbon/carbon composite precursor. The CVR process was used to fabricate SiC /SiC composite with crystalline high-purity beta-SiC from a carbon-carbon precursor fabricated with non-stabilized carbon fiber and

The Leakage Current Improvement of a Ni-Silicided SiGe/Si Junction Using a Si Cap Layer and the PAI Technique

International Nuclear Information System (INIS)

Chang Jian-Guang; Wu Chun-Bo; Ji Xiao-Li; Ma Hao-Wen; Yan Feng; Shi Yi; Zhang Rong

2012-01-01

We investigate the leakage current of ultra-shallow Ni-silicided SiGe/Si junctions for 45 nm CMOS technology using a Si cap layer and the pre-amorphization implantation (PAI) process. It is found that with the conventional Ni silicide method, the leakage current of a p + (SiGe)—n(Si) junction is large and attributed to band-to-band tunneling and the generation-recombination process. The two leakage contributors can be suppressed quite effectively when a Si cap layer is added in the Ni silicide method. The leakage reduction is about one order of magnitude and could be associated with the suppression of the agglomeration of the Ni germano-silicide film. In addition, the PAI process after the application of a Si cap layer has little effect on improving the junction leakage but reduces the sheet resistance of the silicide film. As a result, the novel Ni silicide method using a Si cap combined with PAI is a promising choice for SiGe junctions in advanced technology. (cross-disciplinary physics and related areas of science and technology)

Narrow photoluminescence peak from Ge(Si) islands embedded between tensile-strained Si layers

Energy Technology Data Exchange (ETDEWEB)

Shaleev, Mikhail; Novikov, Alexey; Baydakova, Nataliya; Yablonskiy, Artem; Drozdov, Yuriy; Lobanov, Dmitriy; Krasilnik, Zakhary [Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod (Russian Federation); Kuznetsov, Oleg [Physical-Technical Research Institute, Nizhny Novgorod State University, pr. Gagarina 23, 603950 Nizhny Novgorod (Russian Federation)

2011-03-15

The influence of thickness of the strained Si layers, measurement temperature and optical pumping power on width of the photoluminescence line from Ge(Si) self-assembled nanoislands grown on relaxed SiGe/Si(001) buffer layers and embedded between tensile-stained Si layers was studied. This line appears due to the II-type optical transition between the holes localized in islands and the electrons confined in tensile-strained Si layers under and above the islands. The possibility of tuning the photoluminescence line width by changing the strained Si layer thicknesses under and above the islands is showed. The decrease of the photoluminescence line width from Ge(Si) islands down to values comparable with width of the PL line from InAs/GaAs quantum dots was achieved due to the quantum confinement of electrons in thin strained Si layers and taking into account of the higher diffusion-induced smearing of strained Si layer above the islands. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

The structure modification of Si-SiO2 irradiated by Fe+ ion

International Nuclear Information System (INIS)

Jin Tao; Ma Zhongquan; Guo Qi

1992-01-01

The effect of the iron ion implantation on the oxide surface and SiO 2 -Si interface of MOS structure was studied by X-ray photo-electron spectroscopy (XPS), and the chemical states of compounds formed were examined. The results obtained show that in the surface layers of SiO 2 the pure Si micro-regions are formed under the implantation and the interface layers of SiO 2 the pure Si micro-regions are formed under the implantation and the interface thickness is almost doubled that leads to failure of MOS capacitors. The physical and chemical mechanisms of MOS structure change by Fe + ion implantation are also discussed and analyzed

Electroplating chromium on CVD SiC and SiCf-SiC advanced cladding via PyC compatibility coating

Science.gov (United States)

Ang, Caen; Kemery, Craig; Katoh, Yutai

2018-05-01

Electroplating Cr on SiC using a pyrolytic carbon (PyC) bond coat is demonstrated as an innovative concept for coating of advanced fuel cladding. The quantification of coating stress, SEM morphology, XRD phase analysis, and debonding test of the coating on CVD SiC and SiCf-SiC is shown. The residual tensile stress (by ASTM B975) of electroplated Cr is > 1 GPa prior to stress relaxation by microcracking. The stress can remove the PyC/Cr layer from SiC. Surface etching of ∼20 μm and roughening to Ra > 2 μm (by SEM observation) was necessary for successful adhesion. The debonding strength (by ASTM D4541) of the coating on SiC slightly improved from 3.6 ± 1.4 MPa to 5.9 ± 0.8 MPa after surface etching or machining. However, this improvement is limited due to the absence of an interphase, and integrated CVI processing may be required for further advancement.

High-performance a -Si/c-Si heterojunction photoelectrodes for photoelectrochemical oxygen and hydrogen evolution

KAUST Repository

Wang, Hsin Ping; Sun, Ke; Noh, Sun Young; Kargar, Alireza; Tsai, Meng Lin; Huang, Ming Yi; Wang, Deli; He, Jr-Hau

2015-01-01

Amorphous Si (a-Si)/crystalline Si (c-Si) heterojunction (SiHJ) can serve as highly efficient and robust photoelectrodes for solar fuel generation. Low carrier recombination in the photoelectrodes leads to high photocurrents and photovoltages

Luminescence of solar cells with a-Si:H/c-Si heterojunctions

Science.gov (United States)

Zhigunov, D. M.; Il'in, A. S.; Forsh, P. A.; Bobyl', A. V.; Verbitskii, V. N.; Terukov, E. I.; Kashkarov, P. K.

2017-05-01

We have studied the electroluminescence (EL) and photoluminescence (PL) of solar cells containing a-Si:H/c-Si heterojunctions. It is established that both the EL and PL properties of these cells are determined by the radiative recombination of nonequilibrium carriers in crystalline silicon (c-Si). The external EL energy yield (efficiency) of solar cells with a-Si:H/c-Si heterojunctions at room temperature amounts to 2.1% and exceeds the value reached in silicon diode structures. This large EL efficiency can be explained by good passivation of the surface of crystalline silicon and the corresponding increase in lifetime of minority carrier s in these solar cells.

Thermogravimetric and microscopic analysis of SiC/SiC materials with advanced interfaces

Energy Technology Data Exchange (ETDEWEB)

Windisch, C.F. Jr.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States); Snead, L.L. [Oak Ridge National Lab., TN (United States)

1997-04-01

The chemical stability of SiC/SiC composites with fiber/matrix interfaces consisting of multilayers of SiC/SiC and porous SiC have been evaluated using a thermal gravimetric analyzer (TGA). Previous evaluations of SiC/SiC composites with carbon interfacial layers demonstrated the layers are not chemically stable at goal use temperatures of 800-1100{degrees}C and O{sub 2} concentrations greater than about 1 ppm. No measureable mass change was observed for multilayer and porous SiC interfaces at 800-1100{degrees}C and O{sub 2} concentrations of 100 ppm to air; however, the total amount of oxidizable carbon is on the order of the sensitivity of the TGA. Further studies are in progress to evaluate the stability of these materials.

Fermi surfaces of YRu2Si2 and LaRu2Si2

International Nuclear Information System (INIS)

Settai, R.; Ikezawa, H.; Toshima, H.; Takashita, M.; Ebihara, T.; Sugawara, H.; Kimura, T.; Motoki, K.; Onuki, Y.

1995-01-01

We have measured the de Haas-van Alphen effect of YRu 2 Si 2 and LaRu 2 Si 2 to clarify the Fermi surfaces and cyclotron masses. Main hole-Fermi surfaces of both compounds with a distorted ellipsoid shape are similar, occupying about half of the Brillouin zone. The small hole-Fermi surfaces with the shape of a rugby ball are three in number for LaRu 2 Si 2 , and one for YRu 2 Si 2 . An electron-Fermi surface consists of a doughnut like shape for LaRu 2 Si 2 , while a cylinder along the [001] direction and a multiply-connected shape exist for YRu 2 Si 2 . The cyclotron masses of YRu 2 Si 2 are a little larger than those of LaRu 2 Si 2 . ((orig.))

Thickness dependent formation and properties of GdSi2/Si(100) interfaces

International Nuclear Information System (INIS)

Peto, G.; Molnar, G.; Dozsa, L.; Horvath, Z.E.; Horvath, Zs.J.; Zsoldos, E.; Dimitriadis, C.A.; Papadimitriou, L.

2005-01-01

Epitaxial and polycrystalline orthorhombic GdSi 2 films were grown on Si(100) substrates by solid phase reaction between Si and Gd films at different thicknesses of the Gd film. The most important property of these GdSi 2 /Si interfaces was defect formation. This was investigated by studying the properties of the Schottky barriers by means of current voltage and capacitance-voltage characteristics, deep level transient spectroscopy by double crystal X-ray diffractometry, and transmission electron microscopy. Epitaxial growth of the silicide layer ensured a relatively low interface defect density (about 10 10 cm -2 ), while the non-epitaxial growth induced defects of a much higher density (about 10 12 cm -2 ). The defects generated during the silicide formation are located within a depth of about 10 nm from the GdSi 2 /Si interface. (orig.)

On formation of silicon nanocrystals under annealing SiO2 layers implanted with Si ions

International Nuclear Information System (INIS)

Kachurin, G.A.; Yanovskaya, S.G.; Volodin, V.A.; Kesler, V.G.; Lejer, A.F.; Ruault, M.-O.

2002-01-01

Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence have been used to study the formation of silicon nanocrystals in SiO 2 implanted with Si ions. Si clusters have been formed at once in the postimplanted layers, providing the excessive Si concentration more ∼ 3 at. %. Si segregation with Si-Si 4 bonds formation is enhanced as following annealing temperature increase, however, the Raman scattering by Si clusters diminishes. The effect is explained by a transformation of the chain-like Si clusters into compact phase nondimensional structures. Segregation of Si nanoprecipitates had ended about 1000 deg C, but the strong photoluminescence typical for Si nanocrystals manifested itself only after 1100 deg C [ru

Implantation of P ions in SiO2 layers with embedded Si nanocrystals

International Nuclear Information System (INIS)

Kachurin, G.A.; Cherkova, S.G.; Volodin, V.A.; Kesler, V.G.; Gutakovsky, A.K.; Cherkov, A.G.; Bublikov, A.V.; Tetelbaum, D.I.

2004-01-01

The effect of 10 13 -10 16 cm -2 P ions implantation and of subsequent annealing on Si nanocrystals (Si-ncs), formed preliminarily in SiO 2 layers by the ion-beam synthesis, has been studied. Photoluminescence (PL), Raman spectroscopy, high resolution electron microscopy (HREM), X-Ray Photoelectron Spectroscopy (XPS) and optical absorption were used for characterizations. The low fluence implantations have shown even individual displacements in Si-ncs quench their PL. Restoration of PL from partly damaged Si-ncs proceeds at annealing less than 1000 deg. C. In the low fluence implanted and annealed samples an increased Si-ncs PL has been found and ascribed to the radiation-induced shock crystallization of stressed Si nanoprecipitates. Annealing at temperatures under 1000 deg. C are inefficient when P ion fluences exceed 10 14 cm -2 , thus becoming capable to amorphize Si-ncs. High crystallization temperature of the amorphized Si-ncs is attributed to a counteraction of their shell layers. After implantation of the highest P fluences an enhanced recovery of PL was found from P concentration over 0.1 at.%. Raman spectroscopy and HREM showed an increased Si-ncs number in such layers. The effect resembles the impurity-enhanced crystallization, known for heavily doped bulk Si. This effect, along with the data obtained by XPS, is considered as an indication P atoms are really present inside the Si-ncs. However, no evidence of free electrons appearance has been observed. The fact is explained by an increased interaction of electrons with the donor nuclei in Si-ncs

Investigation into solubility and diffusion in SiC-NbC, SiC-TiC, SiC-ZrC systems

International Nuclear Information System (INIS)

Safaraliev, G.K.; Tairov, Yu.M.; Tsvetkov, V.F.; Shabanov, Sh.Sh.

1991-01-01

An investigation is carried out which demonstrates solid-phase interaction between SiC and NbC, TiC and ZrC monocrystals. The monocrystals are subjected to hot pressing in SiC powder with dispersity of 5x10 -6 m. The pressing temperature is 2270-2570 K and pressure is varied in the range of 20-40 MPa. Element composition and the distribution profile in a thin layer near the boundary of SiC-NbC, SiC-TiC and SiC-ZrC are investigated by the Anger spectroscopy method. The obtained results permit to make the conclusion in the possibility of solid solution formation in investigated systems

Materials and devices for quantum information processing in Si/SiGe

Energy Technology Data Exchange (ETDEWEB)

Sailer, Juergen

2010-12-15

In this thesis, we cover and discuss the complete way from material science, the fabrication of two-dimensional electron systems (2DES) in Si/SiGe heterostructures in molecular beam epitaxy (MBE), to quantum effects in few-electron devices based on these samples. We applied and compared two different approaches for the creation of pseudo-substrates that are as smooth, relaxed and defect free as possible. In the 'graded buffer' concept, starting from pure Si, the Ge content of the SiGe alloy is slowly and linearly increased until the desired Ge content is reached. In contrast, in the so-called 'low-temperature Si' concept, the SiGe alloy is deposited directly with the final Ge content, but onto a layer of highly defective Si. In terms of crystal defects, the 'graded buffer' turned out to be superior in comparison to the 'low-temperature Si' concept at the expense of a significantly higher material consumption. By continued optimization of the growth process, aiming at reducing the influence of the impurity, it nevertheless became possible to improve the charge carrier mobility from a mere 2000 cm{sup 2}/(Vs) to a record mobility exceeding 100 000 cm{sup 2}/(Vs). Within this work, we extended our MBE system with an electron beam evaporator for nuclear spin free {sup 28}Si. Together with the already existing effusion cell for {sup 70}Ge we were able to realize first 2DES in a nuclear spin free environment after successfully putting it to operation. The highest mobility 2DES in a nuclear spin free environment which have been realized in this thesis exhibited electron mobilities of up to 55 000 cm{sup 2}/(Vs). Quantum effects in Si/SiGe have been investigated in two- and zero-dimensional nanostructures. A remarkable phenomenon in the regime of the integer quantum Hall effect in Si/SiGe 2DES has been discovered and researched. For applications in quantum information processing and for the creation of qubits it is mandatory to

Structure and chemistry of passivated SiC/SiO{sub 2} interfaces

Energy Technology Data Exchange (ETDEWEB)

Houston Dycus, J.; Xu, Weizong; LeBeau, James M. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907 (United States); Lichtenwalner, Daniel J.; Hull, Brett; Palmour, John W. [Power Devices R& D, Wolfspeed, A Cree Company, Research Triangle Park, North Carolina 27709 (United States)

2016-05-16

Here, we report on the chemistry and structure of 4H-SiC/SiO{sub 2} interfaces passivated either by nitric oxide annealing or Ba deposition. Using aberration corrected scanning transmission electron microscopy and spectroscopy, we find that Ba and N remain localized at SiC/SiO{sub 2} interface after processing. Further, we find that the passivating species can introduce significant changes to the near-interface atomic structure of SiC. Specifically, we quantify significant strain for nitric oxide annealed sample where Si dangling bonds are capped by N. In contrast, strain is not observed at the interface of the Ba treated samples. Finally, we place these results in the context of field effect mobility.

Self-aligned indium–gallium–zinc oxide thin-film transistors with SiN{sub x}/SiO{sub 2}/SiN{sub x}/SiO{sub 2} passivation layers

Energy Technology Data Exchange (ETDEWEB)

Chen, Rongsheng, E-mail: rschen@ust.hk; Zhou, Wei; Zhang, Meng; Kwok, Hoi-Sing

2014-08-01

Self-aligned top-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with SiN{sub x}/SiO{sub 2}/SiN{sub x}/SiO{sub 2} passivation layers are developed in this paper. The resulting a-IGZO TFT exhibits high reliability against bias stress and good electrical performance including field-effect mobility of 5 cm{sup 2}/Vs, threshold voltage of 2.5 V, subthreshold swing of 0.63 V/decade, and on/off current ratio of 5 × 10{sup 6}. With scaling down of the channel length, good characteristics are also obtained with a small shift of the threshold voltage and no degradation of subthreshold swing. The proposed a-IGZO TFTs in this paper can act as driving devices in the next generation flat panel displays. - Highlights: • Self-aligned top-gate indium–gallium–zinc oxide thin-film transistor is proposed. • SiN{sub x}/SiO{sub 2}/SiN{sub x}/SiO{sub 2} passivation layers are developed. • The source/drain areas are hydrogen-doped by CHF3 plasma. • The devices show good electrical performance and high reliability against bias stress.

Chemical compatibility issues associated with use of SiC/SiC in advanced reactor concepts

Energy Technology Data Exchange (ETDEWEB)

Wilson, Dane F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2015-09-01

Silicon carbide/silicon carbide (SiC/SiC) composites are of interest for components that will experience high radiation fields in the High Temperature Gas Cooled Reactor (HTGR), the Very High Temperature Reactor (VHTR), the Sodium Fast Reactor (SFR), or the Fluoride-cooled High-temperature Reactor (FHR). In all of the reactor systems considered, reactions of SiC/SiC composites with the constituents of the coolant determine suitability of materials of construction. The material of interest is nuclear grade SiC/SiC composites, which consist of a SiC matrix [high-purity, chemical vapor deposition (CVD) SiC or liquid phase-sintered SiC that is crystalline beta-phase SiC containing small amounts of alumina-yttria impurity], a pyrolytic carbon interphase, and somewhat impure yet crystalline beta-phase SiC fibers. The interphase and fiber components may or may not be exposed, at least initially, to the reactor coolant. The chemical compatibility of SiC/SiC composites in the three reactor environments is highly dependent on thermodynamic stability with the pure coolant, and on reactions with impurities present in the environment including any ingress of oxygen and moisture. In general, there is a dearth of information on the performance of SiC in these environments. While there is little to no excess Si present in the new SiC/SiC composites, the reaction of Si with O₂ cannot be ignored, especially for the FHR, in which environment the product, SiO₂, can be readily removed by the fluoride salt. In all systems, reaction of the carbon interphase layer with oxygen is possible especially under abnormal conditions such as loss of coolant (resulting in increased temperature), and air and/ or steam ingress. A global outline of an approach to resolving SiC/SiC chemical compatibility concerns with the environments of the three reactors is presented along with ideas to quickly determine the baseline compatibility performance of SiC/SiC.

Heteroepitaxial growth of SiC films by carbonization of polyimide Langmuir-Blodgett films on Si

Directory of Open Access Journals (Sweden)

Goloudina S.I.

2017-01-01

Full Text Available High quality single crystal SiC films were prepared by carbonization of polyimide Langmuir-Blodgett films on Si substrate. The films formed after annealing of the polyimide films at 1000°C, 1100°C, 1200°C were studied by Fourier transform-infrared (FTIR spectroscopy, X-ray diffraction (XRD, Raman spectroscopy, transmission electon microscopy (TEM, transmission electron diffraction (TED, and scanning electron microscopy (SEM. XRD study and HRTEM cross-section revealed that the crystalline SiC film begins to grow on Si (111 substrate at 1000°C. According to the HRTEM cross-section image five planes in 3C-SiC (111 film are aligned with four Si(111 planes at the SiC/Si interface. It was shown the SiC films (35 nm grown on Si(111 at 1200°C have mainly cubic 3C-SiC structure with a little presence of hexagonal polytypes. Only 3C-SiC films (30 nm were formed on Si (100 substrate at the same temperature. It was shown the SiC films (30-35 nm are able to cover the voids in Si substrate with size up to 10 μm.

Purity and radioactive decay behaviour of industrial 2D-reinforced SiCf/SiC composites

International Nuclear Information System (INIS)

Scholz, H.W.; Zucchetti, M.; Casteleyn, K.; Adelhelm, C.

1994-01-01

Ceramic matrix composites based on SiC with continuous fibres (SiC f /SiC) are considered promising structural materials for future fusion devices. It was still to clarify, whether impurities in industrial SiC f /SiC could jeopardise radiological advantages. Experimental impurity analyses revealed a two-dimensionally reinforced SiC f /SiC with the matrix produced by CVI as very pure. Chemo-spectrometric methods were combined with radioactivation methods (CPAA, NAA). A quantification of the main constituents Si, C and O was added. Calculations with the FISPACT-2.4 code and EAF-2 library identified elements detrimental for different low-activation criteria. For the neutron exposure, EEF reactor-study first wall and blanket conditions were simulated. The calculated SiC f /SiC included 48 trace elements. Even under conservative assumptions, all low-activation limits of European interest are fulfilled. Exclusively the hands-on recycling limit for the First Wall can intrinsically not be satisfied with SiC. The theoretical goal of a SiC f /SiC depleted of 28 Si (isotopic tailoring) is critically discussed. ((orig.))

Transformation of sludge Si to nano-Si/SiOx structure by oxygen inward diffusion as precursor for high performance anodes in lithium ion batteries

Science.gov (United States)

Hua, Qiqi; Dai, Dongyang; Zhang, Chengzhi; Han, Fei; Lv, Tiezheng; Li, Xiaoshan; Wang, Shijie; Zhu, Rui; Liao, Haojie; Zhang, Shiguo

2018-05-01

Although several Si/C composite structures have been proposed for high-performance lithium-ion batteries (LIBs), they have still suffered from expensive and complex processes of nano-Si production. Herein, a simple, controllable oxygen inward diffusion was utilized to transform Si sludge obtained from the photovoltaic (PV) industry into the nano-Si/SiOx structure as a result of the high diffusion efficiency of O inside Si and high surface area of the sludge. After further process, a yolk/shell Si/C structure was obtained as an anode material for LIBs. This composite demonstrated an excellent cycling stability, with a high reversible capacity (˜ 1250 mAh/g for 500 cycles), by void space originally left by the SiOx accommodate inner Si expansion. We believe this is a rather simple way to convert the waste Si into a valuable nano-Si for LIB applications.

Carrier recombination in tailored multilayer Si/Si{sub 1−x}Ge{sub x} nanostructures

Energy Technology Data Exchange (ETDEWEB)

Mala, S.A. [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Tsybeskov, L., E-mail: tsybesko@njit.edu [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Lockwood, D.J.; Wu, X.; Baribeau, J.-M. [National Research Council, Ottawa, ON, Canada KIA 0R6 (Canada)

2014-11-15

Photoluminescence (PL) measurements were performed in Si/Si{sub 1−x}Ge{sub x} nanostructures with a single Si{sub 0.92}Ge{sub 0.08} nanometer-thick layer incorporated into Si/Si{sub 0.6}Ge{sub 0.4} cluster multilayers. Under pulsed laser excitation, the PL decay associated with the Si{sub 0.92}Ge{sub 0.08} nano-layer is found to be nearly a 1000 times faster compared to that in Si/Si{sub 0.6}Ge{sub 0.4} cluster multilayers. A model considering Si/SiGe hetero-interface composition and explaining the fast and slow time-dependent recombination rates is proposed.

Structural and photoluminescence properties of Si-based nanosheet bundles rooted on Si substrates

Science.gov (United States)

Yuan, Peiling; Tamaki, Ryo; Kusazaki, Shinya; Atsumi, Nanae; Saito, Yuya; Kumazawa, Yuki; Ahsan, Nazmul; Okada, Yoshitaka; Ishida, Akihiro; Tatsuoka, Hirokazu

2018-04-01

Si-based nanosheet bundles were synthesized by the extraction of Ca atoms from CaSi2 microwalls grown on Si substrates by inositol hexakisphosphate solution or thermal treatment in FeCl2 vapor. The structural and photoluminescence properties of the Si-based nanosheet bundles were examined. The photoluminescence emissions in the visible region were clearly observed, and the temperature and excitation intensity dependences of the emissions were characterized. The observed Si-based nanosheets consist of thin Si layers, and a superlattice-like layered structural model is proposed to describe the Si-based nanosheet bundle structures and their photoluminescence property. The photoluminescence property of the nanosheets significantly depends on their treatment process. The luminescence mechanism of the nanosheets was discussed.

An optically controlled SiC lateral power transistor based on SiC/SiCGe super junction structure

International Nuclear Information System (INIS)

Pu Hongbin; Cao Lin; Ren Jie; Chen Zhiming; Nan Yagong

2010-01-01

An optically controlled SiC/SiCGe lateral power transistor based on superjunction structure has been proposed, in which n-SiCGe/p-SiC superjunction structure is employed to improve device figure of merit. Performance of the novel optically controlled power transistor was simulated using Silvaco Atlas tools, which has shown that the device has a very good response to the visible light and the near infrared light. The optoelectronic responsivities of the device at 0.5 μm and 0.7 μm are 330 mA/W and 76.2 mA/W at 2 V based voltage, respectively. (semiconductor devices)

An optically controlled SiC lateral power transistor based on SiC/SiCGe super junction structure

Energy Technology Data Exchange (ETDEWEB)

Pu Hongbin; Cao Lin; Ren Jie; Chen Zhiming; Nan Yagong, E-mail: puhongbin@xaut.edu.c [Xi' an University of Technology, Xi' an 710048 (China)

2010-04-15

An optically controlled SiC/SiCGe lateral power transistor based on superjunction structure has been proposed, in which n-SiCGe/p-SiC superjunction structure is employed to improve device figure of merit. Performance of the novel optically controlled power transistor was simulated using Silvaco Atlas tools, which has shown that the device has a very good response to the visible light and the near infrared light. The optoelectronic responsivities of the device at 0.5 {mu}m and 0.7 {mu}m are 330 mA/W and 76.2 mA/W at 2 V based voltage, respectively. (semiconductor devices)

Si/C and H coadsorption at 4H-SiC{0001} surfaces

Energy Technology Data Exchange (ETDEWEB)

Wachowicz, E., E-mail: elwira@ifd.uni.wroc.pl [Institute of Experimental Physics, University of Wrocław, Plac M. Borna 9, PL-50-204 Wrocław (Poland); Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, Pawińskiego 5a, PL-02-106 Warsaw (Poland)

2016-06-15

Highlights: • Si on C-terminated and C on Si-terminated surface adsorb in the H{sub 3} hollow site. • The preferred adsorption site is in contrary to the stacking order of bulk crystal. • The presence of hydrogen increases the adsorption energy of Si/C. • Hydrogen weakens the bonds between the adsorbed Si or C and the surface. • Carbon adsorbs on top of the surface carbon on the C-terminated surface. • With both C and H on Si-terminated surface the surface state vanishes. - Abstract: Density functional theory (DFT) study of adsorption of 0.25 monolayer of either Si or C on 4H-SiC{0001} surfaces is presented. The adsorption in high-symmetry sites on both Si- and C-terminated surfaces was examined and the influence of the preadsorbed 0.25 ML of hydrogen on the Si/C adsorption was considered. It was found out that for Si on C-terminated surface and C on Si-terminated the most favourable is threefolded adsorption site on both clean and H-precovered surface. This is contrary to the bulk crystal stacking order which would require adsorption on top of the topmost surface atom. In those cases, the presence of hydrogen weakens the bonding of the adsorbate. Carbon on the C-terminated surface, only binds on-top of the surface atom. The C−C bond-length is almost the same for the clean surface and for one with H and equals to ∼1.33 Å which is shorter by ∼0.2 than in diamond. The analysis of the electronic structure changes under adsorption is also presented.

Fluorocarbon based atomic layer etching of Si_3N_4 and etching selectivity of SiO_2 over Si_3N_4

International Nuclear Information System (INIS)

Li, Chen; Metzler, Dominik; Oehrlein, Gottlieb S.; Lai, Chiukin Steven; Hudson, Eric A.

2016-01-01

Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO_2 ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar"+ ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO_2 from the surface. In the present article, the authors describe controlled etching of Si_3N_4 and SiO_2 layers of one to several Angstroms using this cyclic ALE approach. Si_3N_4 etching and etching selectivity of SiO_2 over Si_3N_4 were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si_3N_4 were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si_3N_4 has a lower physical sputtering energy threshold than SiO_2, Si_3N_4 physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si_3N_4 to SiO_2 ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO_2 to Si_3N_4 etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si_3N_4 surfaces. This highly selective etching is explained by a lower carbon consumption of Si_3N_4 as compared to SiO_2. The comparison of C_4F_8 and CHF_3 only showed a difference in etching selectivity for FC depleted conditions. For FC accumulation conditions

Electrical properties of SiO{sub 2}/SiC interfaces on 2°-off axis 4H-SiC epilayers

Energy Technology Data Exchange (ETDEWEB)

Vivona, M., E-mail: marilena.vivona@imm.cnr.it [CNR-IMM, Strada VIII, n. 5 – Zona Industriale, I-95121 Catania (Italy); Fiorenza, P. [CNR-IMM, Strada VIII, n. 5 – Zona Industriale, I-95121 Catania (Italy); Sledziewski, T.; Krieger, M. [Friedrich-Alexander-University (FAU) Erlangen-Nuremberg, Department of Physics, Staudtstrasse 7/Bld. A3, D-91058 Erlangen (Germany); Chassagne, T.; Zielinski, M. [NOVASiC, Savoie Technolac, BP267, F-73375 Le Bourget-du-Lac Cedex (France); Roccaforte, F. [CNR-IMM, Strada VIII, n. 5 – Zona Industriale, I-95121 Catania (Italy)

2016-02-28

Graphical abstract: - Highlights: • Processing and electrical characterization of MOS capacitors fabricated on 4H-SiC epilayers grown on 2°-off axis heavily doped substrates. • Excellent characteristics of the SiO{sub 2}/4H-SiC interface in terms of flatness, interface state density and oxide reliability. • Electrical behavior of the MOS devices comparable with that obtained for the state-of-the-art of 4°-off axis 4H-SiC material. • Demonstration of the maturity of the 2°-off axis material for application in 4H-SiC MOSFET device technology. - Abstract: In this paper, the electrical properties of the SiO{sub 2}/SiC interface on silicon carbide (4H-SiC) epilayers grown on 2°-off axis substrates were studied. After epilayer growth, chemical mechanical polishing (CMP) allowed to obtain an atomically flat surface with a roughness of 0.14 nm. Metal-oxide-semiconductor (MOS) capacitors, fabricated on this surface, showed an interface state density of ∼1 × 10{sup 12} eV{sup −1} cm{sup −2} below the conduction band, a value which is comparable to the standard 4°-off-axis material commonly used for 4H-SiC MOS-based device fabrication. Moreover, the Fowler–Nordheim and time-zero-dielectric breakdown analyses confirmed an almost ideal behavior of the interface. The results demonstrate the maturity of the 2°-off axis material for 4H-SiC MOSFET device fabrication.

Unraveling the role of SiC or Si substrates in water vapor incorporation in SiO 2 films thermally grown using ion beam analyses

Science.gov (United States)

Corrêa, S. A.; Soares, G. V.; Radtke, C.; Stedile, F. C.

2012-02-01

The incorporation of water vapor in SiO 2 films thermally grown on 6H-SiC(0 0 0 1) and on Si (0 0 1) was investigated using nuclear reaction analyses. Water isotopically enriched in deuterium ( 2H or D) and in 18O was used. The dependence of incorporated D with the water annealing temperature and initial oxide thickness were inspected. The D amount in SiO 2/SiC structures increases continuously with temperature and with initial oxide thickness, being incorporated in the surface, bulk, and interface regions of SiO 2 films. However, in SiO 2/Si, D is observed mostly in near-surface regions of the oxide and no remarkable dependence with temperature or initial oxide thickness was observed. At any annealing temperature, oxygen from water vapor was incorporated in all depths of the oxide films grown on SiC, in contrast with the SiO 2/Si.

Search for EAS radio-emission at the Tien-Shan shower installation at a height of 3340 m above sea level

Science.gov (United States)

Beisenova, A.; Boos, E.; Haungs, A.; Sadykov, T.; Salihov, N.; Shepetov, A.; Tautayev, Y.; Vildanova, L.; Zhukov, V.

2017-06-01

The complex EAS installation of the Tien Shan mountain cosmic ray station which is situated at a height of 3340 m above sea level includes the scintillation and Cherenkov detectors of charged shower particles, an ionization calorimeter and a set of neutron detectors for registering the hadronic component of the shower, and a number of underground detectors of the penetrative EAS component. Now it is intended to expand this installation with a promising method for detecting the radio-emission generated by the particles of the developing shower. The facility for radio-emission detection consists of a three crossed dipole antennae, one being set vertically, and another two - mutually perpendicularly in a horizontal plane, all of them being connected to a three-channel radio-frequency amplifier of German production. By the passage of an extensive air shower, which is defined by a scintillation shower detector system, the output signal of antenna amplifier is digitized by a fast multichannel DT5720 ADC of Italian production, and kept within computer memory. The further analysis of the detected signal anticipates its operation according to a special algorithm and a search for the pulse of radio-emission from the shower. A functional test of the radio-installation is made with artificial signals which imitate those of the shower, and with the use of a N1996A type wave analyzer of Agilent Technologies production. We present preliminary results on the registration of extensive air shower emission at the Tien Shan installation which were collected during test measurements held in Summer 2016.

Sensing performance of plasma-enhanced chemical vapor deposition SiC-SiO2-SiC horizontal slot waveguides

NARCIS (Netherlands)

Pandraud, G.; Margallo-Balbas, E.; Sarro, P.M.

2012-01-01

We have studied, for the first time, the sensing capabilities of plasma-enhanced chemical vapor deposition (PECVD) SiC-SiO2-SiC horizontal slot waveguides. Optical propagation losses were measured to be 23.9 dB?cm for the quasi-transverse magnetic mode. To assess the potential of this device as a

High resolution investigation of the 30Si(þ, þ)30Si reaction

NARCIS (Netherlands)

Walinga, J.; Rinsvelt, H.A. van; Endt, P.M.

The differential cross section for elastic scattering of protons on 30Si was measured with surface barrier counters at four angles. Thirty-six 30Si(þ, γ)31P resonances are known in the Ep=1–2MeV region. Fifteen of these were also observed in the 30Si(þ, þ)30Si reaction, with natural widths varying

Construction and characterization of spherical Si solar cells combined with SiC electric power inverter

Science.gov (United States)

Oku, Takeo; Matsumoto, Taisuke; Hiramatsu, Kouichi; Yasuda, Masashi; Shimono, Akio; Takeda, Yoshikazu; Murozono, Mikio

2015-02-01

Spherical silicon (Si) photovoltaic solar cell systems combined with an electric power inverter using silicon carbide (SiC) field-effect transistor (FET) were constructed and characterized, which were compared with an ordinary Si-based converter. The SiC-FET devices were introduced in the direct current-alternating current (DC-AC) converter, which was connected with the solar panels. The spherical Si solar cells were used as the power sources, and the spherical Si panels are lighter and more flexible compared with the ordinary flat Si solar panels. Conversion efficiencies of the spherical Si solar cells were improved by using the SiC-FET.

El regreso del andrógino

Directory of Open Access Journals (Sweden)

Juan Manuel Rodríguez

2014-12-01

Full Text Available Refiriéndose al chip, señala que hoy este es tan indispensable como el oxígeno, este minicomponente tiene ventajas múltiples: portátil, memoria extraordinaria, liviano, con múltiples opciones de diversión y placer, sin consumo de energía y fácil de remplazarlo. El mundo moderno exige estar enchufados. La memoria humana ya no reside en la razón histórica, sino en la del circuito integrado, la conciencia tiende a desaparecer y se ha remplazado por el chip. La capacidad de recibir información esta limitada por la incapacidad humana de captarla y entenderla, quizá por eso seamos bastante pobres en varios de los procesos de manejo de información. Se afirma que la persona es un lamentable sistema de información; las máquinas en esto tienen su ventajas.

La relación de voluntad y entendimiento en la modernidad temprana: una clave antropológica para la teoría y la praxis

Directory of Open Access Journals (Sweden)

Espinosa, Luciano

2015-12-01

Full Text Available The paper inquires into two philosophical positions, the first one emphasizes the importance of the will and the second one prefers the understanding. These anthropological options are decisive in order to explain other questions (God, knowledge, ethics, nature and history, and have many practical consequences too. After a genealogical exposition, we study the cases of Leibniz and Spinoza because they unify both dimensions but in a different way.El artículo indaga en dos tradiciones filosóficas, la primera enfatiza la importancia de la voluntad y la segunda prefiere el entendimiento. Estas opciones antropológicas son decisivas para explicar otras cuestiones (Dios, conocimiento, ética, naturaleza e historia, y tiene también muchas consecuencias prácticas. Después de una exposición genealógica, estudiamos los casos de Leibniz y Spinoza porque unifican ambas dimensiones pero de manera distinta.

Sistema de Información Geográfico para el control y operación de las Redes Eléctricas de Sancti Spíritus.

Directory of Open Access Journals (Sweden)

Alfredo Castro López

2008-07-01

Este sistema resulta muy útil a los operadores de la Red Eléctrica del Despacho Provincial, brindándoles la posibilidad no solo de acceder a la información eléctrica de los elementos sino además a la información física de los mismos, o sea que cuentan en el mapa con los datos necesarios para un mejor control y operación del Sistema Eléctrico. Ello facilita la toma de decisiones en un momento dado, conocer el lugar de una avería y los sitios donde tiene mayor posibilidad de ocurrir un fallo de la red, entre otras opciones. Todo esto incide de manera importante en la gestión de la empresa en cuanto a la atención de las interrupciones y la mejor operación de la Red.

Removal of C and SiC from Si and FeSi during ladle refining and solidification

Energy Technology Data Exchange (ETDEWEB)

Klevan, Ole Svein

1997-12-31

The utilization of solar energy by means of solar cells requires the Si to be very pure. The purity of Si is important for other applications as well. This thesis mainly studies the total removal of carbon from silicon and ferrosilicon. The decarburization includes removal of SiC particles by stirring and during casting in addition to reduction of dissolved carbon by gas purging. It was found that for three commercial qualities of FeSi75, Refined, Gransil, and Standard lumpy, the refined quality is lowest in carbon, followed by Gransil and Standard. A decarburization model was developed that shows the carbon removal by oxidation of dissolved carbon to be a slow process at atmospheric pressure. Gas stirring experiments have shown that silicon carbide particles are removed by transfer to the ladle wall. The casting method of ferrosilicon has a strong influence on the final total carbon content in the commercial alloy. Shipped refined FeSi contains about 100 ppm total carbon, while the molten alloy contains roughly 200 ppm. The total carbon out of the FeSi-furnace is about 1000 ppm. It is suggested that low values of carbon could be obtained on an industrial scale by injection of silica combined with the use of vacuum. Also, the casting system could be designed to give low carbon in part of the product. 122 refs., 50 figs., 24 tabs.

Positron annihilation spectroscopy of the interface between nanocrystalline Si and SiO2

International Nuclear Information System (INIS)

Pi, X.D.; Coleman, P.G.; Harding, R.; Davies, G.; Gwilliam, R.M.; Sealy, B.J.

2003-01-01

Positron annihilation spectroscopy has been employed to study changes in the interface region between nanocrystalline Si and SiO 2 , following annealing between 400 deg. C and 900 deg. C in nitrogen or oxygen. With the support of photoluminescence spectroscopy we find that nitrogen and oxygen are trapped in voids at the interface at low temperatures. At temperatures above 700 deg. C both nitrogen and oxygen react with Si nanocrystals, and the resulting volume increase introduces stress in the SiO 2 matrix which is relaxed by the shrinkage of its intrinsic open volume. Oxygen appears to enhance Si diffusion in SiO 2 so that the agglomeration of Si nanocrystals occurs more readily during annealing in oxygen than in nitrogen

Heteroepitaxy of zinc-blende SiC nano-dots on Si substrate by organometallic ion beam

International Nuclear Information System (INIS)

Matsumoto, T.; Kiuchi, M.; Sugimoto, S.; Goto, S.

2006-01-01

The self-assembled SiC nano-dots were fabricated on Si(111) substrate at low-temperatures using the organometallic ion beam deposition technique. The single precursor of methylsilicenium ions (SiCH 3 + ) with the energy of 100 eV was deposited on Si(111) substrate at 500, 550 and 600 deg. C. The characteristics of the self-assembled SiC nano-dots were analyzed by reflection high-energy electron diffraction (RHEED), Raman spectroscopy and atomic force microscope (AFM). The RHEED patterns showed that the crystal structure of the SiC nano-dots formed on Si(111) substrate was zinc-blende SiC (3C-SiC) and it was heteroepitaxy. The self-assembled SiC nano-dots were like a dome in shape, and their sizes were the length of 200-300 nm and the height of 10-15 nm. Despite the low-temperature of 500 deg. C as SiC crystallization the heteroepitaxial SiC nano-dots were fabricated on Si(111) substrate using the organometallic ion beam

Electrical resistivity and thermal conductivity of SiC/Si ecoceramics prepared from sapele wood biocarbon

Science.gov (United States)

Parfen'eva, L. S.; Orlova, T. S.; Smirnov, B. I.; Smirnov, I. A.; Misiorek, H.; Mucha, J.; Jezowski, A.; Gutierrez-Pardo, A.; Ramirez-Rico, J.

2012-10-01

Samples of β-SiC/Si ecoceramics with a silicon concentration of ˜21 vol % have been prepared using a series of consecutive procedures (carbonization of sapele wood biocarbon, synthesis of high-porosity biocarbon with channel-type pores, infiltration of molten silicon into empty channels of the biocarbon, formation of β-SiC, and retention of residual silicon in channels of β-SiC). The electrical resistivity ρ and thermal conductivity κ of the β-SiC/Si ecoceramic samples have been measured in the temperature range 5-300 K. The values of ρ{Si/chan}( T) and κ{Si/chan}( T) have been determined for silicon Sichan located in β-SiC channels of the synthesized β-SiC/Si ecoceramics. Based on the performed analysis of the obtained results, the concentration of charge carriers (holes) in Sichan has been estimated as p ˜ 1019 cm-3. The factors that can be responsible for such a high value of p have been discussed. The prospects for practical application of β-SiC/Si ecoceramics have been considered.

Ordered GeSi nanorings grown on patterned Si (001 substrates

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Ma Yingjie

2011-01-01

Full Text Available Abstract An easy approach to fabricate ordered pattern using nanosphere lithography and reactive iron etching technology was demonstrated. Long-range ordered GeSi nanorings with 430 nm period were grown on patterned Si (001 substrates by molecular beam epitaxy. The size and shape of rings were closely associated with the size of capped GeSi quantum dots and the Si capping processes. Statistical analysis on the lateral size distribution shows that the high growth temperature and the long-term annealing can improve the uniformity of nanorings. PACS code1·PACS code2·more Mathematics Subject Classification (2000 MSC code1·MSC code2·more

White photoluminescence from Si/SiO{sub 2} nanostructured film

Energy Technology Data Exchange (ETDEWEB)

Duong, P.H.; Ngan, N.T.T.; Tuan, C.A. [Institute of Materials Science, Vietnamese Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi (Viet Nam); Huy, P.T. [International Training Institute of Materials Science, Hanoi University of Technology, 1 Dai Co Viet, Hanoi (Viet Nam); Itoh, T. [Graduate School of Engineering Science, Osaka University, Toyonaka (Japan)

2008-12-15

We present in this work the results of PL measurement of Si-NC embedded in Si/SiO{sub 2} multilayer system. A very intense broad luminescence band was observed in the sample under illumination in vacuum by UV laser line. The PL intensity enhancement and quenching effect observed in different ambients can be attributed to the energy exchange from NC to MO. The storage of the annealed sample in vacuum for a long time drastically changed the PL properties of Si-NC. The origin of these phenomena will be discussed. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Status and prospects for SiC-SiC composite materials development for fusion applications

International Nuclear Information System (INIS)

Sharafat, S.; Jones, R.H.; Kohyama, A.; Fenici, P.

1995-01-01

Silicon carbide (SiC) composites are very attractive for fusion applications because of their low afterheat and low activation characteristics coupled with excellent high temperature properties. These composites are relatively new materials that will require material development as well as evaluation of hermiticity, thermal conductivity, radiation stability, high temperature strength, fatigue, thermal shock, and joining techniques. The radiation stability of SiC-SiC composites is a critical aspect of their application as fusion components and recent results will be reported. Many of the non-fusion specific issues are under evaluation by other ceramic composite development programs, such as the US national continuous fiber ceramic composites.The current development status of various SiC-SiC composites research and development efforts is given. Effect of neutron irradiation on the properties of SiC-SiC composite between 500 and 1200 C are reported. Novel high temperature properties specific to ceramic matrix composite (CMC) materials are discussed. The chemical stability of SiC is reviewed briefly. Ongoing research and development efforts for joining CMC materials including SiC-SiC composites are described. In conclusion, ongoing research and development efforts show extremely promising properties and behavior for SiC-SiC composites for fusion applications. (orig.)

Si K-edge XANES study of SiOxCyHz amorphous polymeric materials

International Nuclear Information System (INIS)

Chaboy, J.; Barranco, A.; Yanguas-Gil, A.; Yubero, F.; Gonzalez-Elipe, A. R.

2007-01-01

This work reports on x-ray absorption spectroscopy study at the Si K edge of several amorphous SiO x C y H z polymers prepared by plasma-enhanced chemical-vapor deposition with different C/O ratios. SiO 2 and SiC have been used as reference materials. The comparison of the experimental Si K-edge x-ray absorption near-edge structure spectra with theoretical computations based on multiple scattering theory has allowed us to monitor the modification of the local coordination around Si as a function of the overall C/O ratio in this kind of materials

High-performance a -Si/c-Si heterojunction photoelectrodes for photoelectrochemical oxygen and hydrogen evolution

KAUST Repository

Wang, Hsin Ping

2015-05-13

Amorphous Si (a-Si)/crystalline Si (c-Si) heterojunction (SiHJ) can serve as highly efficient and robust photoelectrodes for solar fuel generation. Low carrier recombination in the photoelectrodes leads to high photocurrents and photovoltages. The SiHJ was designed and fabricated into both photoanode and photocathode with high oxygen and hydrogen evolution efficiency, respectively, by simply coating of a thin layer of catalytic materials. The SiHJ photoanode with sol-gel NiOx as the catalyst shows a current density of 21.48 mA/cm2 at the equilibrium water oxidation potential. The SiHJ photocathode with 2 nm sputter-coated Pt catalyst displays excellent hydrogen evolution performance with an onset potential of 0.640 V and a solar to hydrogen conversion efficiency of 13.26%, which is the highest ever reported for Si-based photocathodes. © 2015 American Chemical Society.

Microstructural optimization of high temperature SiC/SiC composites by nite process

International Nuclear Information System (INIS)

Shimoda, K.; Park, J.S.; Hinoki, T.; Kohyama, A.

2007-01-01

Full text of publication follows: SiC/SiC composites are one of the promising structural materials for future fusion reactor because of the excellent potentiality in thermal and mechanical properties under very severe environment including high temperature and high energy neutron bombardment. For fusion-grade SiC/SiC composites, high-crystallinity and near-stoichiometric characteristic are required to keep excellent stability against neutron irradiation. The realization of the reactor will be strongly depend on optimization of SiC/SiC composites microstructure, particularly in regard to the materials and processes used for the fiber, interphase and matrix constituents. One of the important accomplishments is the new process, called nano-particle infiltration and transient eutectic phase (NITE) process developed in our group. The microstructure of NITE-SiC/SiC composites, such as fiber volume fraction, porosity and type of pores, can be controlled precisely by the selection of sintering temperature/applied stress history. The objective of this study is to investigate thermal stability and mechanical properties of NITE-SiC/SiC composites at high-temperature. Two kinds of highly-densified SiC/SiC composites with the difference of fiber volume fraction were prepared, and were subjected to exposure tests from 1000 deg. C to 1500 deg. C in an argon-oxygen gas mixture with an oxygen partial pressure of 0.1 Pa. The thermal stability of the composites was characterized through mass change and TEM/SEM observation. The in-situ tensile tests at 1300 deg. C and 1500 deg. C were carried out in the same atmosphere. Most of SiC/SiC composites, even for the advanced CVI-SiC/SiC composites with multi-layered SiC/C inter-phases, underwent reduction in the maximum strength by about 20% at 1300 deg. C. In particular, this reduction was attributed to a slight burnout of the carbon interphase due to oxygen impurities in test atmosphere. However, there was no significant degradation for

Microstructural optimization of high temperature SiC/SiC composites by nite process

Energy Technology Data Exchange (ETDEWEB)

Shimoda, K. [Kyoto Univ., Graduate School of Energy Science (Japan); Park, J.S. [Kyoto Univ., Institute of Advanced Energy (Japan); Hinoki, T.; Kohyama, A. [Kyoto Univ., lnstitute of Advanced Energy, Gokasho, Uji (Japan)

2007-07-01

Full text of publication follows: SiC/SiC composites are one of the promising structural materials for future fusion reactor because of the excellent potentiality in thermal and mechanical properties under very severe environment including high temperature and high energy neutron bombardment. For fusion-grade SiC/SiC composites, high-crystallinity and near-stoichiometric characteristic are required to keep excellent stability against neutron irradiation. The realization of the reactor will be strongly depend on optimization of SiC/SiC composites microstructure, particularly in regard to the materials and processes used for the fiber, interphase and matrix constituents. One of the important accomplishments is the new process, called nano-particle infiltration and transient eutectic phase (NITE) process developed in our group. The microstructure of NITE-SiC/SiC composites, such as fiber volume fraction, porosity and type of pores, can be controlled precisely by the selection of sintering temperature/applied stress history. The objective of this study is to investigate thermal stability and mechanical properties of NITE-SiC/SiC composites at high-temperature. Two kinds of highly-densified SiC/SiC composites with the difference of fiber volume fraction were prepared, and were subjected to exposure tests from 1000 deg. C to 1500 deg. C in an argon-oxygen gas mixture with an oxygen partial pressure of 0.1 Pa. The thermal stability of the composites was characterized through mass change and TEM/SEM observation. The in-situ tensile tests at 1300 deg. C and 1500 deg. C were carried out in the same atmosphere. Most of SiC/SiC composites, even for the advanced CVI-SiC/SiC composites with multi-layered SiC/C inter-phases, underwent reduction in the maximum strength by about 20% at 1300 deg. C. In particular, this reduction was attributed to a slight burnout of the carbon interphase due to oxygen impurities in test atmosphere. However, there was no significant degradation for

Growth of CNTs on Fe-Si catalyst prepared on Si and Al coated Si substrates

International Nuclear Information System (INIS)

Teng, F-Y; Ting, J-M; Sharma, Sahendra P; Liao, Kun-Hou

2008-01-01

In this paper we report the effect of Al interlayers on the growth characteristics of carbon nanotubes (CNTs) using as-deposited and plasma etched Fe-Si catalyst films as the catalysts. Al interlayers having various thicknesses ranging from 2 to 42 nm were deposited on Si substrates prior to the deposition of Fe-Si catalysts. It was found that the Al interlayer diffuses into the Fe-Si catalyst during the plasma etching prior to the CNT growth, leading to the swelling and amorphization of the catalyst. This allows enhanced carbon diffusion in the catalyst and therefore a faster growth rate of the resulting CNTs. It was also found that use of an Al interlayer having a thickness of ∼3 ± 1 nm is most effective. Due to the effectiveness of this, the normally required catalyst etching is no longer needed for the growth of CNTs

Growth of CNTs on Fe-Si catalyst prepared on Si and Al coated Si substrates.

Science.gov (United States)

Teng, F-Y; Ting, Jyh-Ming; Sharma, Sahendra P; Liao, Kun-Hou

2008-03-05

In this paper we report the effect of Al interlayers on the growth characteristics of carbon nanotubes (CNTs) using as-deposited and plasma etched Fe-Si catalyst films as the catalysts. Al interlayers having various thicknesses ranging from 2 to 42 nm were deposited on Si substrates prior to the deposition of Fe-Si catalysts. It was found that the Al interlayer diffuses into the Fe-Si catalyst during the plasma etching prior to the CNT growth, leading to the swelling and amorphization of the catalyst. This allows enhanced carbon diffusion in the catalyst and therefore a faster growth rate of the resulting CNTs. It was also found that use of an Al interlayer having a thickness of ∼3 ± 1 nm is most effective. Due to the effectiveness of this, the normally required catalyst etching is no longer needed for the growth of CNTs.

Wafer-scale high-throughput ordered arrays of Si and coaxial Si/Si(1-x)Ge(x) wires: fabrication, characterization, and photovoltaic application.

Science.gov (United States)

Pan, Caofeng; Luo, Zhixiang; Xu, Chen; Luo, Jun; Liang, Renrong; Zhu, Guang; Wu, Wenzhuo; Guo, Wenxi; Yan, Xingxu; Xu, Jun; Wang, Zhong Lin; Zhu, Jing

2011-08-23

We have developed a method combining lithography and catalytic etching to fabricate large-area (uniform coverage over an entire 5-in. wafer) arrays of vertically aligned single-crystal Si nanowires with high throughput. Coaxial n-Si/p-SiGe wire arrays are also fabricated by further coating single-crystal epitaxial SiGe layers on the Si wires using ultrahigh vacuum chemical vapor deposition (UHVCVD). This method allows precise control over the diameter, length, density, spacing, orientation, shape, pattern and location of the Si and Si/SiGe nanowire arrays, making it possible to fabricate an array of devices based on rationally designed nanowire arrays. A proposed fabrication mechanism of the etching process is presented. Inspired by the excellent antireflection properties of the Si/SiGe wire arrays, we built solar cells based on the arrays of these wires containing radial junctions, an example of which exhibits an open circuit voltage (V(oc)) of 650 mV, a short-circuit current density (J(sc)) of 8.38 mA/cm(2), a fill factor of 0.60, and an energy conversion efficiency (η) of 3.26%. Such a p-n radial structure will have a great potential application for cost-efficient photovoltaic (PV) solar energy conversion. © 2011 American Chemical Society

Uso de los símbolos algebraicos en las fórmulas matemáticas de los artículos científicos médicos

Directory of Open Access Journals (Sweden)

Beyda González Camacho

2015-10-01

Full Text Available Si la medicina es un arte o una ciencia no es tema para tratar en este artículo, aunque no hay dudas que tiene de ambas partes; sin embargo, lo que sí es un hecho es que tiene la misión de «curar a veces, aliviar a menudo y consolar siempre». Esta frase, atribuida a Hipocrates por unos y a los médicos franceses Bérard y Gubler, por otros; no puede hacerse realidad si en los artículos científicos médicos se cometen errores en los símbolos y fórmulas matemáticas.

Reduction in interface defect density in p-BaSi2/n-Si heterojunction solar cells by a modified pretreatment of the Si substrate

Science.gov (United States)

Yamashita, Yudai; Yachi, Suguru; Takabe, Ryota; Sato, Takuma; Emha Bayu, Miftahullatif; Toko, Kaoru; Suemasu, Takashi

2018-02-01

We have investigated defects that occurred at the interface of p-BaSi2/n-Si heterojunction solar cells that were fabricated by molecular beam epitaxy. X-ray diffraction measurements indicated that BaSi2 (a-axis-oriented) was subjected to in-plane compressive strain, which relaxed when the thickness of the p-BaSi2 layer exceeded 50 nm. Additionally, transmission electron microscopy revealed defects in the Si layer near steps that were present on the Si(111) substrate. Deep level transient spectroscopy revealed two different electron traps in the n-Si layer that were located at 0.33 eV (E1) and 0.19 eV (E2) below the conduction band edge. The densities of E1 and E2 levels in the region close to the heterointerface were approximately 1014 cm-3. The density of these electron traps decreased below the limits of detection following Si pretreatment to remove the oxide layers from the n-Si substrate, which involved heating the substrate to 800 °C for 30 min under ultrahigh vacuum while depositing a layer of Si (1 nm). The remaining traps in the n-Si layer were hole traps located at 0.65 eV (H1) and 0.38 eV (H2) above the valence band edge. Their densities were as low as 1010 cm-3. Following pretreatment, the current versus voltage characteristics of the p-BaSi2/n-Si solar cells under AM1.5 illumination were reproducible with conversion efficiencies beyond 5% when using a p-BaSi2 layer thickness of 100 nm. The origin of the H2 level is discussed.

Ukraine’s Multi-Vectorial Foreign Policy: Looking West while not Overlooking its Eastern Neighbour

Directory of Open Access Journals (Sweden)

María Raquel Freire

2009-05-01

Full Text Available La Ucrania post-soviética ha perseguido un curso independiente en su política exterior desde que lograse la independencia en 1991. Sin embargo su posición geográfica condicionó mucho el contorno de su política exterior. De hecho, mientras que un acercamiento al Oeste ha sido valorado grandemente, las relaciones con Rusia han seguido siendo el pilar central de Ucrania, intentándose por tanto, mirar hacia el Oeste sin perder de vista a su vecino oriental. En tal contexto, ¿cómo podrían conciliar las autoridades ucranianas los diferentes vectores de la política exterior de su país?¿En qué medida podrían pervivir los principios de la Revolución Naranja entre un contexto interior tan difícil y un contexto exterior complejo?¿En qué medida pueden afectar a las opciones en política exterior de Kiev la influencia occidental y las interferencias rusas? Intentando encontrar respuestas a tales preguntas, este artículo tiene como objetivo la deconstrucción de los varios círculos en la política exterior multi-vectorial de Kiev que se encargan de atender a la política exterior de una manera integrada y donde las formulaciones interiores se ven condicionadas por las opciones externas, echando luz de esta manera sobre cómo las interrelaciones e interconexiones se desarrollan en el proceso de toma de decisiones y en el curso elegido.

Formation of AlFeSi phase in AlSi12 alloy with Ce addition

Directory of Open Access Journals (Sweden)

S. Kores

2012-04-01

Full Text Available The influence of cerium addition on the solidification sequence and microstructure constituents of the Al-Si alloys with 12,6 mass % Si was examined. The solidification was analyzed by a simple thermal analysis. The microstructures were examined with conventional light and scanning electron microscopy. Ternary AlSiCe phase was formed in the Al-Si alloys with added cerium during the solidification process. AlSiCe and β-AlFeSi phases solidified together in the region that solidified the last. Cerium addition influenced on the morphology of the α-AlFeSi phase solidification.

Crystallization behavior of Li2O-SiO2, Na2O-SiO2 and Na2O-CaO-SiO2 glasses; Li2O-SiO2, Na2O-SiO2, Na2O-CaO-SiO2 kei glass no kessho sekishutsu kyodo

Energy Technology Data Exchange (ETDEWEB)

Tsutsumi, K.; Otake, J.; Nagasaka, T.; Hino, M. [Tohoku University, Sendai (Japan)

1998-06-01

It has been known that crystallization of mold powder is effective on the disturbance of heat transfer between mold and solidified shell in production of middle carbon steel slabs in continuous casting process. But it has not yet been made clear which composition of mold powder is the most suitable for crystallization. The crystallization behavior of Li2O-SiO2, Na2O-SiO2 and Na2O-CaO-SiO2 glasses was observed by differential thermal analysis (DTA) and hot-thermocouple methods with DTA in the present work. As a result, addition of alkaline metal and alkaline earth metal oxides to SiO2 increased the critical cooling rate for glass formation in binary system of Li2O-SiO2 and Na2O-SiO2 and Li2O-SiO2 system crystallized easier than Na2O-SiO2 system. In ternary system of Na2O-CaO-SiO2, addition of Na2O hurried the critical cooling rate at CaO/SiO2=0.93 mass ratio, but the rate was almost constant in the composition range of more than 15 mass% Na2O. The slag of CaO/SiO2=0.93 made the rate faster than the slag of CaO/SiO2=0.47 at constant content of 10mass% Na2O. 17 refs., 10 figs., 3 tabs.

Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

Directory of Open Access Journals (Sweden)

Wei-Ting eLai

2016-02-01

Full Text Available We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5−90 nm, the SiO2 thickness (3−4 nm, and as well the SiGe-shell thickness (2−15 nm has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5 in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge MOS nanoelectronic and nanophotonic applications.

Virtual instrumentation of a laboratory synchronous generator with LabVIEW; Instrumentacion virtual de un generador sincrono de laboratorio con LabVIEW

Energy Technology Data Exchange (ETDEWEB)

Uribe Fernandez, Uriel

2003-07-01

On this work measurement algorithms for variables from a synchronous generator are developed and implemented, in open architecture by means of virtual instrument in real time with the Laboratory Virtual Instrument Engineering Workbench (LabBIEW) that it is a development atmosphere based on the graphic programming. The main program menu of the virtual instrumentation has three options of measurement: The first option is a program that carries out the three phase measurement of: tension RMS, current RMS, magnitude, phase angle, power factor, apparent, active and reactive power and the graphic of these signals. The second option is a program that carries out the measurement of load angle from the synchronous generator. This measurement is made through the Fast Fourier Transformed (FFT), obtaining the voltage terminal, magnitude and phase angle with respect to the rotor position reference. This measurement varies from synchronous generator, operation conditions. The speed angle measurement is obtained from the load angle changes. These measurements are presented in graphic form in the time, with a virtual instrument type needle and in digital form. The range of load angle is +/- 180 degrees. The third option is a program that carries out the measurement of the load angle against active power (curve d-W), from the synchronous machine. [Spanish] En este trabajo se desarrollan e implementan algoritmos de medicion para variables de un generador sincrono, en arquitectura abierta, por medio de la instrumentacion virtual en tiempo real con el uso del Laboratory Virtual Instrument Engineering Workbench (LabVIEW) que es un ambiente de desarrollo basado en la programacion grafica. El programa principal menu de la instrumentacion virtual tiene tres opciones de medicion: La primera opcion es un programa que realiza la medicion trifasica de tension RMS, corriente RMS, magnitud, angulo de fase, factor de potencia, potencia aparente, activa y reactiva, y la graficacion de estas

Thermally induced formation of SiC nanoparticles from Si/C/Si multilayers deposited by ultra-high-vacuum ion beam sputtering

International Nuclear Information System (INIS)

Chung, C-K; Wu, B-H

2006-01-01

A novel approach for the formation of SiC nanoparticles (np-SiC) is reported. Deposition of Si/C/Si multilayers on Si(100) wafers by ultra-high-vacuum ion beam sputtering was followed by thermal annealing in vacuum for conversion into SiC nanoparticles. The annealing temperature significantly affected the size, density, and distribution of np-SiC. No nanoparticles were formed for multilayers annealed at 500 0 C, while a few particles started to appear when the annealing temperature was increased to 700 0 C. At an annealing temperature of 900 0 C, many small SiC nanoparticles, of several tens of nanometres, surrounding larger submicron ones appeared with a particle density approximately 16 times higher than that observed at 700 0 C. The higher the annealing temperature was, the larger the nanoparticle size, and the higher the density. The higher superheating at 900 0 C increased the amount of stable nuclei, and resulted in a higher particle density compared to that at 700 0 C. These particles grew larger at 900 0 C to reduce the total surface energy of smaller particles due to the higher atomic mobility and growth rate. The increased free energy of stacking defects during particle growth will limit the size of large particles, leaving many smaller particles surrounding the large ones. A mechanism for the np-SiC formation is proposed in this paper

Modulating the Surface State of SiC to Control Carrier Transport in Graphene/SiC.

Science.gov (United States)

Jia, Yuping; Sun, Xiaojuan; Shi, Zhiming; Jiang, Ke; Liu, Henan; Ben, Jianwei; Li, Dabing

2018-05-28

Silicon carbide (SiC) with epitaxial graphene (EG/SiC) shows a great potential in the applications of electronic and photoelectric devices. The performance of devices is primarily dependent on the interfacial heterojunction between graphene and SiC. Here, the band structure of the EG/SiC heterojunction is experimentally investigated by Kelvin probe force microscopy. The dependence of the barrier height at the EG/SiC heterojunction to the initial surface state of SiC is revealed. Both the barrier height and band bending tendency of the heterojunction can be modulated by controlling the surface state of SiC, leading to the tuned carrier transport behavior at the EG/SiC interface. The barrier height at the EG/SiC(000-1) interface is almost ten times that of the EG/SiC(0001) interface. As a result, the amount of carrier transport at the EG/SiC(000-1) interface is about ten times that of the EG/SiC(0001) interface. These results offer insights into the carrier transport behavior at the EG/SiC heterojunction by controlling the initial surface state of SiC, and this strategy can be extended in all devices with graphene as the top layer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

NIMROD Simulations of the HIT-SI and HIT-SI3 Devices

Science.gov (United States)

Morgan, Kyle; Jarboe, Tom; Hossack, Aaron; Chandra, Rian; Everson, Chris

2017-10-01

The Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI) experiment uses a set of inductively driven helicity injectors to apply non-axisymmetric current drive on the edge of the plasma, driving an axisymmetric spheromak equilibrium in a central confinement volume. Significant improvements have been made to extended MHD modeling of HIT-SI, with both the resolution of disagreement at high injector frequencies in HIT-SI in addition to successes with the new upgraded HIT-SI3 device. Previous numerical studies of HIT-SI, using a zero-beta eMHD model, focused on operations with a drive frequency of 14.5 kHz, and found reduced agreement with both the magnetic profile and current amplification at higher frequencies (30-70 kHz). HIT-SI3 has three helicity injectors which are able to operate with different mode structures of perturbations through the different relative temporal phasing of the injectors. Simulations that allow for pressure gradients have been performed in the parameter regimes of both devices using the NIMROD code and show improved agreement with experimental results, most notably capturing the observed Shafranov-shift due to increased beta observed at higher finj in HIT-SI and the variety of toroidal perturbation spectra available in HIT-SI3. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under Award Number DE-FG02- 96ER54361.

Non-switching to switching transferring mechanism investigation for Ag/SiO x /p-Si structure with SiO x deposited by HWCVD

Science.gov (United States)

Liu, Yanhong; Wang, Ruoying; Li, Zhongyue; Wang, Song; Huang, Yang; Peng, Wei

2018-04-01

We proposed and fabricated an Ag/SiO x /p-Si sandwich structure, in which amorphous SiO x films were deposited through hot wire chemical vapor deposition (HWCVD) using tetraethylorthosilicate (TEOS) as Si and O precursor. Experimental results indicate that the I–V properties of this structure transfer from non-switching to switching operation as the SiO x deposition temperature increased. The device with SiO x deposited at high deposition temperature exhibits typical bipolar switching properties, which can be potentially used in resistive switching random accessible memory (RRAM). The transferring mechanism from non-switching to switching can be ascribed to the change of structural and electronic properties of SiO x active layer deposited at different temperatures, as evidenced by analyzing FTIR spectrum and fitting its I–V characteristics curves. This work demonstrates a safe and practicable low-temperature device-grade SiO x film deposition technology by conducting HWCVD from TEOS.

SI Notes.

Science.gov (United States)

Nelson, Robert A.

1983-01-01

Discusses legislation related to SI (International Systems of Units) in the United States. Indicates that although SI metric units have been officially recognized by law in the United States, U.S. Customary Units have never received a statutory basis. (JN)

Polarized luminescence of nc-Si-SiO x nanostructures on silicon substrates with patterned surface

Science.gov (United States)

Michailovska, Katerina; Mynko, Viktor; Indutnyi, Ivan; Shepeliavyi, Petro

2018-05-01

Polarization characteristics and spectra of photoluminescence (PL) of nc-Si-SiO x structures formed on the patterned and plane c-Si substrates are studied. The interference lithography with vacuum chalcogenide photoresist and anisotropic wet etching are used to form a periodic relief (diffraction grating) on the surface of the substrates. The studied nc-Si-SiO x structures were produced by oblique-angle deposition of Si monoxide in vacuum and the subsequent high-temperature annealing. The linear polarization memory (PM) effect in PL of studied structure on plane substrate is manifested only after the treatment of the structures in HF and is explained by the presence of elongated Si nanoparticles in the SiO x nanocolumns. But the PL output from the nc-Si-SiO x structure on the patterned substrate depends on how this radiation is polarized with respect to the grating grooves and is much less dependent on the polarization of the exciting light. The measured reflection spectra of nc-Si-SiO x structure on the patterned c-Si substrate confirmed the influence of pattern on the extraction of polarized PL.

The Degradation Behavior of SiCf/SiO2 Composites in High-Temperature Environment

Science.gov (United States)

Yang, Xiang; Cao, Feng; Qing, Wang; Peng, Zhi-hang; Wang, Yi

2018-04-01

SiCf/SiO2 composites had been fabricated efficiently by Sol-Gel method. The oxidation behavior, thermal shock property and ablation behavior of SiCf/SiO2 composites was investigated. SiCf/SiO2 composites showed higher oxidation resistance in oxidation atmosphere, the flexural strength retention ratio was larger than 90.00%. After 1300 °C thermal shock, the mass retention ratio was 97.00%, and the flexural strength retention ratio was 92.60%, while after 1500 °C thermal shock, the mass retention ratio was 95.37%, and the flexural strength retention ratio was 83.34%. After 15 s ablation, the mass loss rate was 0.049 g/s and recession loss rate was 0.067 mm/s. The SiO2 matrix was melted in priority and becomes loosen and porous. With the ablation going on, the oxides were washed away by the shearing action of the oxyacetylene flame. The evaporation of SiO2 took away large amount of heat, which is also beneficial to the protection for SiCf/SiO2 composites.

Effect of Si implantation on the microstructure of silicon nanocrystals and surrounding SiO2 layer

International Nuclear Information System (INIS)

Ross, G.G.; Smirani, R.; Levitcharsky, V.; Wang, Y.Q.; Veilleux, G.; Saint-Jacques, R.G.

2005-01-01

Si nanocrystals (Si-nc) embedded in a SiO 2 layer have been characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For local Si concentration in excess 8 x 10 21 Si + /cm 3 , the size of the Si-nc was found to be ∼3 nm and comparatively homogeneous throughout the whole implanted layer. For local Si concentration in excess of ∼2.4 x 10 22 Si + /cm 3 , the Si-nc diameter ranges from ∼2 to ∼12 nm in the sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface and the bottom of the layer. Also, Si-nc are visible deeper than the implanted depth. Characterization by XPS shows that a large quantity of oxygen was depleted from the first ∼25 nm in this sample (also visible on TEM image) and most of the SiO 2 bonds have been replaced by Si-O bonds. Experimental and simulation results suggest that a local Si concentration in excess of ∼3 x 10 21 Si/cm 3 is required for the production of Si-nc

Chemically activated graphene/porous Si@SiO{sub x} composite as anode for lithium ion batteries

Energy Technology Data Exchange (ETDEWEB)

Tao, Hua-Chao [College of Materials and Chemical Engineering, China Three Gorges University, 8 Daxue Road, Yichang, Hubei 443002 (China); Collaborative Innovation Center for Microgrid of New Energy, Hubei Province (China); Yang, Xue-Lin, E-mail: xlyang@ctgu.edu.cn [College of Materials and Chemical Engineering, China Three Gorges University, 8 Daxue Road, Yichang, Hubei 443002 (China); Collaborative Innovation Center for Microgrid of New Energy, Hubei Province (China); Zhang, Lu-Lu; Ni, Shi-Bing [College of Materials and Chemical Engineering, China Three Gorges University, 8 Daxue Road, Yichang, Hubei 443002 (China); Collaborative Innovation Center for Microgrid of New Energy, Hubei Province (China)

2014-10-15

Chemically activated graphene/porous Si@SiO{sub x} (CAG/Si@SiO{sub x}) composite has been synthesized via magnesiothemic reduction of mesoporous SiO{sub 2} (MCM-48) to porous Si@SiO{sub x} and dispersing in the suspension of chemically activated graphene oxide (CAGO) followed by thermal reduction. The porous Si@SiO{sub x} particles are well encapsulated in chemically activated graphene (CAG) matrix. The resulting CAG/Si@SiO{sub x} composite exhibits a high reversible capacity and excellent cycling stability up to 763 mAh g{sup −1} at a current density of 100 mA g{sup −1} after 50 cycles. The porous structure of CAG layer and Si@SiO{sub x} is beneficial to accommodate volume expansion of Si during discharge and charge process and the interconnected CAG improves the electronic conductivity of composite. - Highlights: • Chemically activated graphene encapsulated porous Si composite was prepared. • The graphene offers a continuous electrically conductive network. • The porous structure can accommodate volume expansion of Si-based materials. • The composite exhibits excellent lithium storage performance.

Preparation and Oxidation Resistance of Mo-Si-B Coating on Nb-Si Based Alloy Surface

Directory of Open Access Journals (Sweden)

PANG Jie

2018-02-01

Full Text Available Mo-Si-B coating was prepared on Nb-Si alloys to improve the high-temperature oxidation. The influence of the halide activators (NaF and AlF3 on Si-B co-depositing to obtain Mo-Si-B coating on Nb-Si alloys was analyzed by thermochemical calculations. The results show that NaF proves to be more suitable than AlF3 to co-deposit Si and B. Then Mo-Si-B can be coated on Nb-Si based alloys using detonation gun spraying of Mo followed by Si and B co-deposition. The fabricated coatings consist of outer MoSi2 layer with fine boride phase and inner unreacted Mo layer. The mass gain of the Mo-Si-B coating is 1.52mg/cm2 after oxidation at 1250℃ for 100h. The good oxidation resistance results in a protective borosilicate scale formed on the coating.

The effect of SiC particle size on the properties of Cu–SiC composites

International Nuclear Information System (INIS)

Celebi Efe, G.; Zeytin, S.; Bindal, C.

2012-01-01

Graphical abstract: The relative densities of Cu–SiC composites sintered at 700 °C for 2 h are ranged from 97.3% to 91.8% for SiC with 1 μm particle size and 97.5% to 95.2% for SiC with 5 μm particle size, microhardness of composites ranged from 143 to 167 HV for SiC having 1 μm particle size and 156–182 HVN for SiC having 5 μm particle size and the electrical conductivity of composites changed between 85.9% IACS and 55.7% IACS for SiC with 1 μm particle size, 87.9% IACS and 65.2%IACS for SiC with 5 μm particle size. It was found that electrical conductivity of composites containing SiC with 5 μm particle size is better than that of Cu–SiC composites containing SiC with particle size of 1 μm. Highlights: ► In this research, the effect of SiC particle size on some properties of Cu–SiC composites were investigated. ► The mechanical properties were improved. ► The electrical properties were obtained at desirable level. -- Abstract: SiC particulate-reinforced copper composites were prepared by powder metallurgy (PM) method and conventional atmospheric sintering. Scanning electron microscope (SEM), X-ray diffraction (XRD) techniques were used to characterize the sintered composites. The effect of SiC content and particle size on the relative density, hardness and electrical conductivity of composites were investigated. The relative densities of Cu–SiC composites sintered at 700 °C for 2 h are ranged from 97.3% to 91.8% for SiC with 1 μm particle size and from 97.5% to 95.2% for SiC with 5 μm particle size. Microhardness of composites ranged from 143 to 167 HV for SiC having 1 μm particle size and from 156 to 182 HV for SiC having 5 μm particle size. The electrical conductivity of composites changed between 85.9% IACS and 55.7% IACS for SiC with 1 μm particle size, between 87.9% IACS and 65.2% IACS for SiC with 5 μm particle size.

Structural and electronic properties of Si/SiO2 MOS structures with aligned 3C-SiC nanocrystals in the oxide

International Nuclear Information System (INIS)

Pongracz, A.; Battistig, G.; Duecso, Cs.; Josepovits, K.V.; Deak, P.

2007-01-01

Our group previously proved that a simple reactive annealing in CO containing gas produces 3C-SiC nanocrystals, which are epitaxially and void-free aligned in the Si substrate. By a further thermal oxidation step, these nanocrystals can be lifted from the Si and incorporated into the SiO 2 matrix, thereby creating a promising structure for charge storage. In this work the structural and electrical properties of such systems with nanocrystalline SiC will be presented. Prototype MOS structures with 3C-SiC nanocrystals were produced for current-voltage and capacitance-voltage measurements. The results indicate that the high-temperature annealing did not damage the MOS structure, despite the fact that the CO annealing changed the electrical properties of the system. There was a positive charge accumulation and a reversible carrier injection observed in the structure. We assume that the positive charges originated from oxygen vacancies and the charge injection is related to the presence of SiC nanocrystals

Amorphization threshold in Si-implanted strained SiGe alloy layers

International Nuclear Information System (INIS)

Simpson, T.W.; Love, D.; Endisch, E.; Goldberg, R.D.; Mitchell, I.V.; Haynes, T.E.; Baribeau, J.M.

1994-12-01

The authors have examined the damage produced by Si-ion implantation into strained Si 1-x Ge x epilayers. Damage accumulation in the implanted layers was monitored in situ by time-resolved reflectivity and measured by ion channeling techniques to determine the amorphization threshold in strained Si 1-x Ge x (x = 0.16 and 0.29) over the temperature range 30--110 C. The results are compared with previously reported measurements on unstrained Si 1-x Ge x , and with the simple model used to describe those results. They report here data which lend support to this model and which indicate that pre-existing strain does not enhance damage accumulation in the alloy layer

Elevated Temperature Properties of Commercially Available NITE-SiC/SiC Composites

International Nuclear Information System (INIS)

Choi, Y.B.; Hinoki, T.; Kohyama, A.

2007-01-01

Full text of publication follows: Continuous fiber-reinforced ceramic matrix composites (CMCs) have been expected as a new type of material having high fracture resistance up to a high temperature. In recent years, there have been extensive efforts in our research group to develop high performance SiC/SiC composites for energy applications, where improvements in mechanical properties and damage resistance by innovative new fabrication process with emphasis on interface improvement have been greatly accomplished. One of the most outstanding accomplishments is the Nano-powder Infiltration and Transient Eutectic (NITE) process using PyC coated Tyranno-SA fibers. For making SiC/SiC composites more attractive and competitive for high temperature structural components and for other industrial applications, one of the key issues is to demonstrate its reliability and safety under severe environments. Also to demonstrate the potential to produce SiC/SiC by NITE process from large scale production line at industries is very important. This paper provides fundamental database of mechanical properties and microstructure of Cera-NITE, the trade name of NITE-SiC/SiC composites. The mechanical properties were evaluated by uni-axial tensile test from room temperature to high temperatures. The tensile properties, including elastic modulus, PLS and ultimate tensile strength, are superior to those of other conventional SiC/SiC composites. The macroscopic observation of Cera-NITE indicated high density as planned with almost no-porosity and cracks. Furthermore, Cera-NITE showed outstanding microstructural uniformity. The characteristic variation coming from the sampling location was hardly observed.. Further information about database of properties and microstructure at evaluated temperature will be provided. (authors)

Mechanics of patterned helical Si springs on Si substrate.

Science.gov (United States)

Liu, D L; Ye, D X; Khan, F; Tang, F; Lim, B K; Picu, R C; Wang, G C; Lu, T M

2003-12-01

The elastic response, including the spring constant, of individual Si helical-shape submicron springs, was measured using a tip-cantilever assembly attached to a conventional atomic force microscope. The isolated, four-turn Si springs were fabricated using oblique angle deposition with substrate rotation, also known as the glancing angle deposition, on a templated Si substrate. The response of the structures was modeled using finite elements, and it was shown that the conventional formulae for the spring constant required modifications before they could be used for the loading scheme used in the present experiment.

Mobility-limiting mechanisms in single and dual channel strained Si/SiGe MOSFETs

International Nuclear Information System (INIS)

Olsen, S.H.; Dobrosz, P.; Escobedo-Cousin, E.; Bull, S.J.; O'Neill, A.G.

2005-01-01

Dual channel strained Si/SiGe CMOS architectures currently receive great attention due to maximum performance benefits being predicted for both n- and p-channel MOSFETs. Epitaxial growth of a compressively strained SiGe layer followed by tensile strained Si can create a high mobility buried hole channel and a high mobility surface electron channel on a single relaxed SiGe virtual substrate. However, dual channel n-MOSFETs fabricated using a high thermal budget exhibit compromised mobility enhancements compared with single channel devices, in which both electron and hole channels form in strained Si. This paper investigates the mobility-limiting mechanisms of dual channel structures. The first evidence of increased interface roughness due to the introduction of compressively strained SiGe below the tensile strained Si channel is presented. Interface corrugations degrade electron mobility in the strained Si. Roughness measurements have been carried out using AFM and TEM. Filtering AFM images allowed roughness at wavelengths pertinent to carrier transport to be studied and the results are in agreement with electrical data. Furthermore, the first comparison of strain measurements in the surface channels of single and dual channel architectures is presented. Raman spectroscopy has been used to study channel strain both before and after processing and indicates that there is no impact of the buried SiGe layer on surface macrostrain. The results provide further evidence that the improved performance of the single channel devices fabricated using a high thermal budget arises from improved surface roughness and reduced Ge diffusion into the Si channel

Implantation of P ions in SiO{sub 2} layers with embedded Si nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Kachurin, G.A. E-mail: kachurin@isp.nsc.ru; Cherkova, S.G.; Volodin, V.A.; Kesler, V.G.; Gutakovsky, A.K.; Cherkov, A.G.; Bublikov, A.V.; Tetelbaum, D.I

2004-08-01

The effect of 10{sup 13}-10{sup 16} cm{sup -2} P ions implantation and of subsequent annealing on Si nanocrystals (Si-ncs), formed preliminarily in SiO{sub 2} layers by the ion-beam synthesis, has been studied. Photoluminescence (PL), Raman spectroscopy, high resolution electron microscopy (HREM), X-Ray Photoelectron Spectroscopy (XPS) and optical absorption were used for characterizations. The low fluence implantations have shown even individual displacements in Si-ncs quench their PL. Restoration of PL from partly damaged Si-ncs proceeds at annealing less than 1000 deg. C. In the low fluence implanted and annealed samples an increased Si-ncs PL has been found and ascribed to the radiation-induced shock crystallization of stressed Si nanoprecipitates. Annealing at temperatures under 1000 deg. C are inefficient when P ion fluences exceed 10{sup 14} cm{sup -2}, thus becoming capable to amorphize Si-ncs. High crystallization temperature of the amorphized Si-ncs is attributed to a counteraction of their shell layers. After implantation of the highest P fluences an enhanced recovery of PL was found from P concentration over 0.1 at.%. Raman spectroscopy and HREM showed an increased Si-ncs number in such layers. The effect resembles the impurity-enhanced crystallization, known for heavily doped bulk Si. This effect, along with the data obtained by XPS, is considered as an indication P atoms are really present inside the Si-ncs. However, no evidence of free electrons appearance has been observed. The fact is explained by an increased interaction of electrons with the donor nuclei in Si-ncs.

Formation of Si/SiC multilayers by low-energy ion implantation and thermal annealing

NARCIS (Netherlands)

Dobrovolskiy, S.; Yakshin, Andrey; Tichelaar, F.D.; Verhoeven, J.; Louis, Eric; Bijkerk, Frederik

2010-01-01

Si/SiC multilayer systems for XUV reflection optics with a periodicity of 10–20 nm were produced by sequential deposition of Si and implantation of 1 keV View the MathML source ions. Only about 3% of the implanted carbon was transferred into the SiC, with a thin, 0.5–1 nm, buried SiC layer being

Effects of MeV Si ions bombardment on the thermoelectric generator from SiO{sub 2}/SiO{sub 2} + Cu and SiO{sub 2}/SiO{sub 2} + Au nanolayered multilayer films

Energy Technology Data Exchange (ETDEWEB)

Budak, S., E-mail: satilmis.budak@aamu.edu [Department of Electrical Engineering, Alabama A and M University, Normal, AL (United States); Chacha, J., E-mail: chacha_john79@hotmail.com [Department of Electrical Engineering, Alabama A and M University, Normal, AL (United States); Smith, C., E-mail: cydale@cim.aamu.edu [Center for Irradiation of Materials, Alabama A and M University, Normal, AL (United States); Department of Physics, Alabama A and M University, Normal, AL (United States); Pugh, M., E-mail: marcuspughp@yahoo.com [Department of Electrical Engineering, Alabama A and M University, Normal, AL (United States); Colon, T. [Department of Mechanical Engineering, Alabama A and M University, Normal, AL (United States); Heidary, K., E-mail: kaveh.heidary@aamu.edu [Department of Electrical Engineering, Alabama A and M University, Normal, AL (United States); Johnson, R.B., E-mail: barry@w4wb.com [Department of Physics, Alabama A and M University, Normal, AL (United States); Ila, D., E-mail: ila@cim.aamu.edu [Center for Irradiation of Materials, Alabama A and M University, Normal, AL (United States); Department of Physics, Alabama A and M University, Normal, AL (United States)

2011-12-15

The defects and disorder in the thin films caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We prepared the thermoelectric generator devices from 100 alternating layers of SiO{sub 2}/SiO{sub 2} + Cu multi-nano layered superlattice films at the total thickness of 382 nm and 50 alternating layers of SiO{sub 2}/SiO{sub 2} + Au multi-nano layered superlattice films at the total thickness of 147 nm using the physical vapor deposition (PVD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation have been used to determine the stoichiometry of the elements of SiO{sub 2}, Cu and Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardments have been performed using the AAMU-Center for Irradiation of Materials (CIM) Pelletron ion beam accelerator to make quantum (nano) dots and/or quantum (quantum) clusters in the multilayered superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured Seebeck coefficient, cross-plane electrical conductivity, and thermal conductivity in the cross-plane geometry for different fluences.

Antioxidant migration resistance of SiOx layer in SiOx/PLA coated film.

Science.gov (United States)

Huang, Chongxing; Zhao, Yuan; Su, Hongxia; Bei, Ronghua

2018-02-01

As novel materials for food contact packaging, inorganic silicon oxide (SiO x ) films are high barrier property materials that have been developed rapidly and have attracted the attention of many manufacturers. For the safe use of SiO x films for food packaging it is vital to study the interaction between SiO x layers and food contaminants, as well as the function of a SiO x barrier layer in antioxidant migration resistance. In this study, we deposited a SiO x layer on polylactic acid (PLA)-based films to prepare SiO x /PLA coated films by plasma-enhanced chemical vapour deposition. Additionally, we compared PLA-based films and SiO x /PLA coated films in terms of the migration of different antioxidants (e.g. t-butylhydroquinone [TBHQ], butylated hydroxyanisole [BHA], and butylated hydroxytoluene [BHT]) via specific migration experiments and then investigated the effects of a SiO x layer on antioxidant migration under different conditions. The results indicate that antioxidant migration from SiO x /PLA coated films is similar to that for PLA-based films: with increase of temperature, decrease of food simulant polarity, and increase of single-sided contact time, the antioxidant migration rate and amount in SiO x /PLA coated films increase. The SiO x barrier layer significantly reduced the amount of migration of antioxidants with small and similar molecular weights and similar physical and chemical properties, while the degree of migration blocking was not significantly different among the studied antioxidants. However, the migration was affected by temperature and food simulant. Depending on the food simulants considered, the migration amount in SiO x /PLA coated films was reduced compared with that in PLA-based films by 42-46%, 44-47%, and 44-46% for TBHQ, BHA, and BHT, respectively.

C-V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

International Nuclear Information System (INIS)

Onojima, Norio; Kasamatsu, Akihumi; Hirose, Nobumitsu; Mimura, Takashi; Matsui, Toshiaki

2008-01-01

Electrical properties of Schottky- and metal-insulator-semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance-voltage (C-V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance (g m ) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f T compared with that of the Schottky-gate device. In this study, C-V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel

C-V characterization of Schottky- and MIS-gate SiGe/Si HEMT structures

Energy Technology Data Exchange (ETDEWEB)

Onojima, Norio [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan)], E-mail: nonojima@nict.go.jp; Kasamatsu, Akihumi; Hirose, Nobumitsu [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan); Mimura, Takashi [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan); Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197 (Japan); Matsui, Toshiaki [National Institute of Information and Communications Technology (NICT), Koganei, Tokyo 184-8795 (Japan)

2008-07-30

Electrical properties of Schottky- and metal-insulator-semiconductor (MIS)-gate SiGe/Si high electron mobility transistors (HEMTs) were investigated with capacitance-voltage (C-V) measurements. The MIS-gate HEMT structure was fabricated using a SiN gate insulator formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN thin film (5 nm) was found to be an effective gate insulator with good gate controllability and dielectric properties. We previously investigated device characteristics of sub-100-nm-gate-length Schottky- and MIS-gate HEMTs, and reported that the MIS-gate device had larger maximum drain current density and transconductance (g{sub m}) than the Schottky-gate device. The radio frequency (RF) measurement of the MIS-gate device, however, showed a relatively lower current gain cutoff frequency f{sub T} compared with that of the Schottky-gate device. In this study, C-V characterization of the MIS-gate HEMT structure demonstrated that two electron transport channels existed, one at the SiGe/Si buried channel and the other at the SiN/Si surface channel.

Energetic prediction on the stability of A2Mg12Si7, A2Mg4Si3, and AMgSi in the A2Si–Mg2Si system (A = Ca, Sr and Ba) and their calculated electronic structures

International Nuclear Information System (INIS)

Imai, Yoji; Mori, Yoshihisa; Nakamura, Shigeyuki; Takarabe, Ken-ichi

2014-01-01

Highlights: • Formation energies of A 2 Mg 4 Si 3 , A 2 Mg 12 Si 7 , and AMgSi (A = Ca,Sr,Ba) were calculated. • All AMgSi are quite stable compared to mixture of A 2 Si and Mg 2 Si. • Ba 2 Mg 4 Si 3 and Sr 2 Mg 4 Si 3 are predicted to be stable, but Ca 2 Mg 4 Si 3 is not. • Ca 2 Mg 12 Si 7 and Sr 2 Mg 12 Si 7 are energetically unstable. • Stability of Ba 2 Mg 12 Si 7 is a tender subject. -- Abstract: In order to evaluate the relative stability of A 2 Mg 4 Si 3 , A 2 Mg 12 Si 7 , and AMgSi (A = Ca, Sr, and Ba) in the A 2 Si–Mg 2 Si system, electronic energy changes in the formation of these compounds were calculated using a density-functional theory with the Perdew–Wang generalized gradient approximations. It was found that (1) AMgSi’s are quite stable compared to equi-molar mixture of A 2 Si and Mg 2 Si, (2) Ba 2 Mg 4 Si 3 and Sr 2 Mg 4 Si 3 are also stable, (3) Ca 2 Mg 4 Si 3 and Ca 2 Mg 12 Si 7 are less stable than the mixture of CaMgSi and Mg 2 Si, and (4) Stability of Ba 2 Mg 12 Si 7 is a tender subject and Sr 2 Mg 12 Si 7 is energetically unstable compared to the mixture of Sr 2 Mg 4 Si 3 (or, SrMgSi) and Mg 2 Si. The presence of Sr 2 Mg 12 Si 7 may be due to the vibrational and/or configurational entropy, which are not treated in the present study. From the calculated electronic densities of state, complex compounds of SrMgSi and Mg 2 Si have both p-type and n-type character, depending on the ratio of SrMgSi and Mg 2 Si in that compound

Palladium transport in SiC

International Nuclear Information System (INIS)

Olivier, E.J.; Neethling, J.H.

2012-01-01

Highlights: ► We investigate the reaction of Pd with SiC at typical HTGR operating temperatures. ► The high temperature mobility of palladium silicides within polycrystalline SiC was studied. ► Corrosion of SiC by Pd was seen in all cases. ► The preferential corrosion and penetration of Pd along grain boundaries in SiC was found. ► The penetration and transport of palladium silicides in SiC along grain boundaries was found. - Abstract: This paper reports on a transmission electron microscopy (TEM) and scanning electron microscopy (SEM) study of Pd corroded SiC. The reaction of Pd with different types of SiC at typical HTGR operating temperatures was examined. In addition the high temperature mobility of palladium silicides within polycrystalline SiC was investigated. The results indicated corrosion of the SiC by Pd in all cases studied. The corrosion leads to the formation of palladium silicides within the SiC, with the predominant phase found being Pd 2 Si. Evidence for the preferential corrosion and penetration of Pd along grain boundaries in polycrystalline SiC was found. The penetration and transport, without significant corrosion, of palladium silicides into polycrystalline SiC along grain boundaries was also observed. Implications of the findings with reference to the use of Tri Isotropic particles in HTGRs will be discussed.

Marker experiments in growth studies of Ni2Si, Pd2Si, and CrSi2 formed both by thermal annealing and by ion mixing

International Nuclear Information System (INIS)

Hung, L.S.; Mayer, J.W.; Pai, C.S.; Lau, S.S.

1985-01-01

Inert markers (evaporated tungsten and silver) were used in growth studies of silicides formed both by thermal annealing and by ion mixing in the Ni/Si, Pd/Si, and Cr/Si systems. The markers were initially imbedded inside silicides and backscattering spectrometry was used to determine the marker displacement after different processing conditions. The results obtained in thermal annealing are quite consistent with that found in previous investigations. Ni is the dominant diffusing species in Ni 2 Si, while Si is the diffusing species in CrSi 2 . In Pd 2 Si, both Pd and Si are moving species with Pd the faster of the two. In contrast, in growth of silicides by ion irradiation Si is the faster diffusing species in all three systems

Marbled texture of sputtered Al/Si alloy thin film on Si

Energy Technology Data Exchange (ETDEWEB)

Gentile, M.G. [Physics Department and NIS Interdepartmental Center, University of Torino, via P. Giuria 1, 10125 Torino (Italy); Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Muñoz-Tabares, J.A.; Chiodoni, A. [Istituto Italiano di Tecnologia, Center for Space Human Robotics, Corso Trento 21, 10129 Torino (Italy); Sgorlon, C. [Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Para, I. [Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Carta, R.; Richieri, G. [Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Bejtka, K. [Istituto Italiano di Tecnologia, Center for Space Human Robotics, Corso Trento 21, 10129 Torino (Italy); Merlin, L. [Vishay Intertechnology, Diodes Division, Via Liguria 49, 10071 Borgaro Torinese, Turin (Italy); Vittone, E. [Physics Department and NIS Interdepartmental Center, University of Torino, via P. Giuria 1, 10125 Torino (Italy)

2016-08-01

DC magnetron sputtering is a commonly used technique for the fabrication of silicon based electronic devices, since it provides high deposition rates and uniform large area metallization. However, in addition to the thickness uniformity, coating optical uniformity is a crucial need for semiconductor industrial processes, due to the wide use of optical recognition tools. In the silicon-based technology, aluminum is one of the most used materials for the metal contact. Both the pre-deposition substrate cleaning and the sputtering conditions determine the quality and the crystalline properties of the final Al deposited film. In this paper is shown that not all the mentioned conditions lead to good quality and uniform Al films. In particular, it is shown that under certain standard process conditions, Al/Si alloy (1% Si) metallization on a [100] Si presents a non-uniform reflectivity, with a marbled texture caused by flakes with milky appearance. This optical inhomogeneity is found to be caused by the coexistence of randomly orient Al/Si crystal, with heteroepitaxial Al/Si crystals, both grown on Si substrate. Based on the microstructural analysis, some strategies to mitigate or suppress this marbled texture of the Al thin film are proposed and discussed. - Highlights: • Sputtered Al/Si layers deposited on Si present evident optical non-uniformity • It could be an issue for optical recognition tools used in semiconductor industries • Optical non-uniformity is due to randomly oriented growth of Al grains. • Substrate misorientation and process temperature can mitigate the problem.

Analysis of Si/SiGe Heterostructure Solar Cell

Directory of Open Access Journals (Sweden)

Ashish Kumar Singh

2014-01-01

Full Text Available Sunlight is the largest source of carbon-neutral energy. Large amount of energy, about 4.3 × 1020 J/hr (Lewis, 2005, is radiated because of nuclear fusion reaction by sun, but it is unfortunate that it is not exploited to its maximum level. Various photovoltaic researches are ongoing to find low cost, and highly efficient solar cell to fulfil looming energy crisis around the globe. Thin film solar cell along with enhanced absorption property will be the best, so combination of SiGe alloy is considered. The paper presented here consists of a numerical model of Si/Si1-xGex heterostructure solar cell. The research has investigated characteristics such as short circuit current density (Jsc, generation rate (G, absorption coefficient (α, and open circuit voltage (Voc with optimal Ge concentration. The addition of Ge content to Si layer will affect the property of material and can be calculated with the use of Vegard’s law. Due to this, short circuit current density increases.

C-H and C-C activation of n -butane with zirconium hydrides supported on SBA15 containing N-donor ligands: [(≡SiNH-)(≡SiX-)ZrH2], [(≡SiNH-)(≡SiX-)2ZrH], and[(≡SiN=)(≡SiX-)ZrH] (X = -NH-, -O-). A DFT study

KAUST Repository

Pasha, Farhan Ahmad

2014-07-01

Density functional theory (DFT) was used to elucidate the mechanism of n-butane hydrogenolysis (into propane, ethane, and methane) on well-defined zirconium hydrides supported on SBA15 coordinated to the surface via N-donor surface pincer ligands: [(≡SiNH-)(≡SiO-)ZrH2] (A), [(≡SiNH-)2ZrH2] (B), [(≡SiNH-)(≡SiO-) 2ZrH] (C), [(≡SiNH-)2(≡SiO-)ZrH] (D), [(≡SiN=)(≡Si-O-)ZrH] (E), and [(≡SiN=)(≡SiNH-)ZrH] (F). The roles of these hydrides have been investigated in C-H/C-C bond activation and cleavage. The dihydride A linked via a chelating [N,O] surface ligand was found to be more active than B, linked to the chelating [N,N] surface ligand. Moreover, the dihydride zirconium complexes are also more active than their corresponding monohydrides C-F. The C-C cleavage step occurs preferentially via β-alkyl transfer, which is the rate-limiting step in the alkane hydrogenolysis. The energetics of the comparative pathways over the potential energy surface diagram (PES) reveals the hydrogenolysis of n-butane into propane and ethane. © 2014 American Chemical Society.

Sr-Al-Si co-segregated regions in eutectic Si phase of Sr-modified Al-10Si alloy.

Science.gov (United States)

Timpel, M; Wanderka, N; Schlesiger, R; Yamamoto, T; Isheim, D; Schmitz, G; Matsumura, S; Banhart, J

2013-09-01

The addition of 200 ppm strontium to an Al-10 wt% Si casting alloy changes the morphology of the eutectic silicon phase from coarse plate-like to fine fibrous networks. In order to clarify this modification mechanism the location of Sr within the eutectic Si phase has been investigated by a combination of high-resolution methods. Whereas three-dimensional atom probe tomography allows us to visualise the distribution of Sr on the atomic scale and to analyse its local enrichment, transmission electron microscopy yields information about the crystallographic nature of segregated regions. Segregations with two kinds of morphologies were found at the intersections of Si twin lamellae: Sr-Al-Si co-segregations of rod-like morphology and Al-rich regions of spherical morphology. Both are responsible for the formation of a high density of multiple twins and promote the anisotropic growth of the eutectic Si phase in specific crystallographic directions during solidification. The experimental findings are related to the previously postulated mechanism of "impurity induced twinning". Copyright © 2012 Elsevier B.V. All rights reserved.

Desprendimiento seroso macular asociado a foseta papilar congénita y coloboma de papila: ¿Qué opciones terapéuticas tenemos?

Directory of Open Access Journals (Sweden)

Caridad Chiang Rodríguez

Full Text Available La foseta papilar es una rara anomalía congénita que forma parte del espectro de las anormalidades congénitas del disco óptico. Se trata de invaginaciones intrapapilares que suelen localizarse en el margen del disco óptico. La mayoría se localiza a nivel temporal; en torno al 20 % son de localización central seguidas por las fosetas superiores, inferiores o nasales. La bilateralidad se estima en un 10-15 % y su incidencia se ha establecido en torno al 0,19 %. Suelen ser asintomáticas, aunque en aproximadamente el 50 % de los casos se produce afectación macular por el paso de fluido procedente desde la foseta papilar hacia las diferentes capas retinianas, lo que afecta secundariamente la agudeza visual y es, por tanto, el motivo de consulta. Hasta el momento se han descrito múltiples alternativas terapéuticas para el tratamiento de los desprendimientos de retina serosos asociados a foseta de papila, pero ninguna de estas alternativas se ha impuesto sobre el resto. El tratamiento de esta enfermedad consiste en cerrar la comunicación entre la foseta y el espacio subretiniano con diversas opciones terapéuticas como: la fotocoagulación láser, la neumoretinopexia, la indentación escleral posterior, la fenestración del nervio óptico, la vitrectomía o alguna combinación de las anteriores. La actual revisión bibliográfica se propone profundizar en el tema, sobre la base de pacientes en consulta con dicha afección retiniana.

Dolarización, caja de conversión o tipo de cambio flexible. ¿Opciones para América Latina hoy?

Directory of Open Access Journals (Sweden)

Esmeralda Villegas

2002-01-01

Full Text Available El objetivo del presente artículo es el de describir las diferentes opciones de regímenes cambiarios para los mercados emergentes de América Latina; que van desde el tipo de cambio fijo, al flexible; con sus variantes como son la Caja de Conversión y la dolarización de la economía, en el contexto actual caracterizado por situaciones de persistente volatilidad de capital y crisis cambiaria. Se concluye que existen hoy más argumentos en contra de establecer durante mucho tiempo regímenes de tipo de cambio fijo, no solamente debido a las distorsiones y costos de la sobrevaluación de la moneda nacional, sino también por los costos que entraña su abandono, asimismo habría que sopesar los argumentos en contra de una excesiva flexibilidad que devendría en volatilidad del tipo de cambio; para ello cabe dar un espacio a que la autoridad pública intervenga, dando con su intervención una señal del tipo de cambio real que se considera conveniente, y reafirmar la importancia de desalentar los flujos de capitales externos especulativos. Se destaca con respecto a la proposición de la Caja de Conversión o de la Dolarización que son alternativas que privilegian la estabilidad monetaria, sacrificando otros objetivos macroeconómicos como el de la producción, el comercio, el empleo. Por lo cual es necesario actuar sobre determinantes fundamentales como son la disciplina fiscal, el avance en las reformas económicas; impulsando el progreso tecnológico que consiste en hacer más eficiente los procesos productivos a través de la inversión en tecnologías de punta.

SHS synthesis of Si-SiC composite powders using Mg and reactants from industrial waste

Science.gov (United States)

Chanadee, Tawat

2017-11-01

Si-SiC composite powders were synthesized by self-propagating high-temperature synthesis (SHS) using reactants of fly ash-based silica, sawdust-based activated carbon, and magnesium. Fly ash-based silica and sawdust-based activated carbon were prepared from coal mining fly ash and Para rubber-wood sawdust, respectively. The work investigated the effects of the synthesis atmosphere (air and Ar) on the phase and morphology of the SHS products. The SHS product was leached by a two-step acid leaching processes, to obtain the Si-SiC composite powder. The SHS product and SHS product after leaching were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectrometry. The results indicated that the SHS product synthesized in air consisted of Si, SiC, MgO, and intermediate phases (SiO2, Mg, Mg2SiO4, Mg2Si), whereas the SHS product synthesized in Ar consisted of Si, SiC, MgO and a little Mg2SiO4. The SiC content in the leached-SHS product was higher when Ar was used as the synthesis atmosphere. As well as affecting the purity, the synthesis atmospheres also affected the average crystalline sizes of the products. The crystalline size of the product synthesized in Ar was smaller than that of the product synthesized in air. All of the results showed that fly ash and sawdust could be effective waste-material reactants for the synthesis of Si-SiC composite powders.

First-principles calculations of orientation dependence of Si thermal oxidation based on Si emission model

Science.gov (United States)

Nagura, Takuya; Kawachi, Shingo; Chokawa, Kenta; Shirakawa, Hiroki; Araidai, Masaaki; Kageshima, Hiroyuki; Endoh, Tetsuo; Shiraishi, Kenji

2018-04-01

It is expected that the off-state leakage current of MOSFETs can be reduced by employing vertical body channel MOSFETs (V-MOSFETs). However, in fabricating these devices, the structure of the Si pillars sometimes cannot be maintained during oxidation, since Si atoms sometimes disappear from the Si/oxide interface (Si missing). Thus, in this study, we used first-principles calculations based on the density functional theory, and investigated the Si emission behavior at the various interfaces on the basis of the Si emission model including its atomistic structure and dependence on Si crystal orientation. The results show that the order in which Si atoms are more likely to be emitted during thermal oxidation is (111) > (110) > (310) > (100). Moreover, the emission of Si atoms is enhanced as the compressive strain increases. Therefore, the emission of Si atoms occurs more easily in V-MOSFETs than in planar MOSFETs. To reduce Si missing in V-MOSFETs, oxidation processes that induce less strain, such as wet or pyrogenic oxidation, are necessary.

Solid-state 27Al and 29Si NMR investigations on Si-substituted hydrogarnets

International Nuclear Information System (INIS)

Rivas Mercury, J.M.; Pena, P.; Aza, A.H. de; Turrillas, X.; Sobrados, I.; Sanz, J.

2007-01-01

Partially deuterated Ca 3 Al 2 (SiO 4 ) 3-x (OH) 4x hydrates prepared by a reaction in the presence of D 2 O of synthetic tricalcium aluminate with different amounts of amorphous silica were characterized by 29 Si and 27 Al magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. The 29 Si NMR spectroscopy was used for quantifying the non-reacted silica and the resulting hydrated products. The incorporation of Si into Ca 3 Al 2 (SiO 4 ) 3-x (OH) 4x was followed by 27 Al NMR spectroscopy: Si:OH ratios were determined quantitatively from octahedral Al signals ascribed to Al(OH) 6 and Al(OSi)(OH) 5 environments. The NMR data obtained were consistent with the concentrations of the Al and Si species deduced from transmission electron microscopy energy-dispersive spectrometry and Rietveld analysis of both X-ray and neutron diffraction data

Mechanical properties of MeV ion-irradiated SiC/SiC composites characterized by indentation technique

International Nuclear Information System (INIS)

Park, J.Y.; Park, K.H.; Kim, W.; Kishimoto, H.; Kohyama, A.

2007-01-01

Full text of publication follows: SiC/SiC composites have been considered as a structural material for advanced fusion concepts. In the core of fusion reactor, those SiC/SiC composites are experienced the complex attacks such as strong neutron, high temperature and transmuted gases. One of the vital data for designing the SiC/SiC composites to the fusion reactor is mechanical properties under the severe neutron irradiation. In this work, various SiC/SiC composites were prepared by the different fabrication processes like CVI (chemical vapor infiltration), WA-CVI (SiC whisker assisted CVI) and hot-pressed method. The expected neutron irradiation was simulated by a silicon self-ion irradiation at a DuET facility; Dual-beam for Energy Technologies, Kyoto University. The irradiation temperature were 600 deg. C and 1200 deg. C, and the irradiation does were 5 dpa and 20 dpa, respectively. The 5.1 MeV Si ions were irradiated to the intrinsic CVI-SiC, SiC whisker reinforced SiC and SiC composites produced by hot-press method. The mechanical properties like hardness, elastic modulus and fracture toughness were characterized by an indentation technique. The ion irradiation caused the increase of the hardness and fracture toughness, which was dependent on the irradiation temperature. SiC whisker reinforcement in the SiC matrix accelerated the increase of the fracture toughness by the ion irradiation. For SiC/SiC composites after the ion irradiation, this work will provide the additional data for the mechanical properties as well as the effect of SiC whisker reinforcement. (authors)

Silicon electrodeposition from chloride-fluoride melts containing K2SiF6 and SiO2

Directory of Open Access Journals (Sweden)

Zhuk Sergey I.

2017-01-01

Full Text Available Silicon electrodeposition on glassy carbon from the KF-KCl-K2SiF6, KF-KCl-K2SiF6-KOH and KF-KCl-K2SiF6-SiO2 melts was studied by the cyclic voltammetry. Тhe electroreduction of Si(IV to metallic Si was observed as a single 4-electron wave under all considered conditions. The reactions of cathode reduction of silicon from fluoride and oxyfluoride complexes were suggested. It was shown that the process can be controlled by the preliminary transformation of SiO44- to SiF62- and SiOxFyz-. The influence of the current density on structure and morphology of silicon deposits obtained during galvanostatic electrolysis of the KF-KCl-K2SiF6-SiO2 melt was studied.

Formation of permeation barriers on ceramic SiC/SiC composites

International Nuclear Information System (INIS)

Racault, C.; Fenici, P.

1996-01-01

The effectiveness as permeation barriers of the following CVD and PVD (sputtering) coatings has been investigated: TiC+Al 2 O 3 (CVD), SiC(CVD), SiO 2 (CVD), TiN(CVD), TiN(CVD)+TiN(PVD) and SiC(CVD)+Al 2 O 3 (PVD). The substrate material was a SiC/SiC composite, proposed as low activation structural material for fusion applications. Permeation measurements were performed in the temperature range 300-750 K using deuterium at pressures in the range 0.5-150 kPa. A linear dependence of permeation rate on pressure was measured. The efficiency of the coatings as deuterium permeation barriers is discussed in terms of coating microstructure. The best result was obtained with a bilayer of TiN(CVD) (15 μm) +TiN(PVD) (8 μm). (orig.)

Physical studies of strained Si/SiGe heterostructures. From virtual substrates to nanodevices

Energy Technology Data Exchange (ETDEWEB)

Minamisawa, Renato Amaral

2011-10-21

During the past two decades, the decrease in intrinsic delay of MOSFETs has been driven by the scaling of the device dimensions. The performance improvement has relied mostly in the increase of source velocity with gate scaling, while the transport properties of the channel have remained constant, i.e., those of conventional Si. Starting at the 90 nm node, uniaxial strain has been introduced in the transistor channel in order to further increase the source velocity. Beyond the 32 nm node, novel channel materials, with superior carrier velocities, and novel device architectures are required in order to continue the performance enhancement of MOSFETs while preserving the electrostatic control. In this Thesis, different physical aspects of strained Si and SiGe materials are investigated as a mean to increase carrier velocity in MOSFET channels. Novel approaches for the fabrication of strained Si based on ion implantation and anneal induced relaxation of virtual substrates are developed. The strain relaxation of SiGe layers is improved using a buried thin Si:C layer in the Si(100) substrate. Further, a Si{sup +} ion implantation and annealing method is investigated for relaxing virtual substrates using lower implantation dose. Finally, the uniaxial relaxation of {l_brace}110{r_brace} surface oriented substrates is demonstrated using a He ion implantation and anneal technique. Apart of channel material studies, the fundamental and technological challenges involved in the integration of strained Si and SiGe into MOSFETs are assessed. The impact of source and drain formation on the elastic strain and electrical properties of strained Si layers and nanowires is examined. Also, the formation of ultra-shallow junction in strained Si/strained Si{sub 0.5}Ge{sub 0.5}/SSOI heterostructures is investigated using different types of ion implanted specie and annealing. The results show that BF{sup +}{sub 2} implantation and low temperature annealing are suitable approaches for

A TEM study of strained SiGe/Si and related heteroepitaxial structures

International Nuclear Information System (INIS)

Benedetti, Alessandro

2002-01-01

The role of SiGe/Si heterostructures and related materials has become increasingly important within the last few decades. In order to increase the scale of integration, however, devices with active elements not larger than few tens of nanometer have been recently introduced. There is, therefore, a strong need for an analytical technique capable of giving information about submicron-sized components. An investigation on a nanometre scale can be performed by the combination of a fully equipped Transmission Electron Microscope (TEM) with a Field Emission Gun (PEG) electron source, which enables one to use a wide range of analytical techniques with an electron probe as small as 0.5 nm. In this work, two different types of SiGe/Si-based devices were investigated. Strained-Si n-channel MOSFETs. The use of Strained-Si n-channel grown on SiGe should improve both carrier mobility and transconductance with respect to conventional MOSFETs. Materials analysed in this work showed an extremely high transconductance but a rather low mobility. In order to relate their microstructural properties to their electrical performance, as well as to improve the device design, a full quantitative and qualitative structural characterisation was performed. SiGe Multiple Quantum Wells (MQW) IR detectors Light detection is achieved by collecting the photogenerated carriers, injected from the SiGe QWs layers into the Si substrate. A key factor is the Ge profile across a single QW, since it governs the band structure and therefore the device performances. Four different TEM techniques were used to determine the Ge distribution across a single well, showing an overall good agreement among the results. The Ge profiles broadening, consistent with data available in literature, was successfully explained and theoretically predicted by the combined effect of Ge segregation and gas dwell times within the reactor. (author)

MeV Si ion modifications on the thermoelectric generators from Si/Si + Ge superlattice nano-layered films

Science.gov (United States)

Budak, S.; Heidary, K.; Johnson, R. B.; Colon, T.; Muntele, C.; Ila, D.

2014-08-01

The performance of thermoelectric materials and devices is characterized by a dimensionless figure of merit, ZT = S2σT/K, where, S and σ denote, respectively, the Seebeck coefficient and electrical conductivity, T is the absolute temperature in Kelvin and K represents the thermal conductivity. The figure of merit may be improved by means of raising either S or σ or by lowering K. In our laboratory, we have fabricated and characterized the performance of a large variety of thermoelectric generators (TEG). Two TEG groups comprised of 50 and 100 alternating layers of Si/Si + Ge multi-nanolayered superlattice films have been fabricated and thoroughly characterized. Ion beam assisted deposition (IBAD) was utilized to assemble the alternating sandwiched layers, resulting in total thickness of 300 nm and 317 nm for 50 and 100 layer devices, respectively. Rutherford Backscattering Spectroscopy (RBS) was employed in order to monitor the precise quantity of Si and Ge utilized in the construction of specific multilayer thin films. The material layers were subsequently impregnated with quantum dots and/or quantum clusters, in order to concurrently reduce the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and raise the cross plane electrical conductivity. The quantum dots/clusters were implanted via the 5 MeV Si ion bombardment which was performed using a Pelletron high energy ion beam accelerator. We have achieved remarkable results for the thermoelectric and optical properties of the Si/Si + Ge multilayer thin film TEG systems. We have demonstrated that with optimal setting of the 5 MeV Si ion beam bombardment fluences, one can fabricate TEG systems with figures of merits substantially higher than the values previously reported.

MeV Si ion modifications on the thermoelectric generators from Si/Si + Ge superlattice nano-layered films

Energy Technology Data Exchange (ETDEWEB)

Budak, S., E-mail: satilmis.budak@aamu.edu [Department of Electrical Engineering and Computer Science, Alabama A and M University, Huntsville, AL (United States); Heidary, K. [Department of Electrical Engineering and Computer Science, Alabama A and M University, Huntsville, AL (United States); Johnson, R.B.; Colon, T. [Department of Physics, Alabama A and M University, Huntsville, AL (United States); Muntele, C. [Cygnus Scientific Services, Huntsville, AL (United States); Ila, D. [Department of Physics, Fayetteville St. University, Fayetteville, NC (United States)

2014-08-15

The performance of thermoelectric materials and devices is characterized by a dimensionless figure of merit, ZT = S{sup 2}σT/K, where, S and σ denote, respectively, the Seebeck coefficient and electrical conductivity, T is the absolute temperature in Kelvin and K represents the thermal conductivity. The figure of merit may be improved by means of raising either S or σ or by lowering K. In our laboratory, we have fabricated and characterized the performance of a large variety of thermoelectric generators (TEG). Two TEG groups comprised of 50 and 100 alternating layers of Si/Si + Ge multi-nanolayered superlattice films have been fabricated and thoroughly characterized. Ion beam assisted deposition (IBAD) was utilized to assemble the alternating sandwiched layers, resulting in total thickness of 300 nm and 317 nm for 50 and 100 layer devices, respectively. Rutherford Backscattering Spectroscopy (RBS) was employed in order to monitor the precise quantity of Si and Ge utilized in the construction of specific multilayer thin films. The material layers were subsequently impregnated with quantum dots and/or quantum clusters, in order to concurrently reduce the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and raise the cross plane electrical conductivity. The quantum dots/clusters were implanted via the 5 MeV Si ion bombardment which was performed using a Pelletron high energy ion beam accelerator. We have achieved remarkable results for the thermoelectric and optical properties of the Si/Si + Ge multilayer thin film TEG systems. We have demonstrated that with optimal setting of the 5 MeV Si ion beam bombardment fluences, one can fabricate TEG systems with figures of merits substantially higher than the values previously reported.

Mass Spectrometric Investigation of Silicon Extremely Enriched in (28)Si: From (28)SiF4 (Gas Phase IRMS) to (28)Si Crystals (MC-ICP-MS).

Science.gov (United States)

Pramann, Axel; Rienitz, Olaf

2016-06-07

A new generation of silicon crystals even further enriched in (28)Si (x((28)Si) > 0.999 98 mol/mol), recently produced by companies and institutes in Russia within the framework of a project initiated by PTB, were investigated with respect to their isotopic composition and molar mass M(Si). A modified isotope dilution mass spectrometric (IDMS) method treating the silicon as the matrix containing a so-called virtual element (VE) existing of the isotopes (29)Si and (30)Si solely and high resolution multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) were applied in combination. This method succeeds also when examining the new materials holding merely trace amounts of (29)Si (x((29)Si) ≈ 5 × 10(-6) mol/mol) and (30)Si (x((30)Si) ≈ 7 × 10(-7) mol/mol) extremely difficult to detect with lowest uncertainty. However, there is a need for validating the enrichment in (28)Si already in the precursor material of the final crystals, silicon tetrafluoride (SiF4) gas prior to crystal production. For that purpose, the isotopic composition of selected SiF4 samples was determined using a multicollector magnetic sector field gas-phase isotope ratio mass spectrometer. Contaminations of SiF4 by natural silicon due to storing and during the isotope ratio mass spectrometry (IRMS) measurements were observed and quantified. The respective MC-ICP-MS measurements of the corresponding crystal samples show-in contrast-several advantages compared to gas phase IRMS. M(Si) of the new crystals were determined to some extent with uncertainties urel(M) < 1 × 10(-9). This study presents a clear dependence of the uncertainty urel(M(Si)) on the degree of enrichment in (28)Si. This leads to a reduction of urel(M(Si)) during the past decade by almost 3 orders of magnitude and thus further reduces the uncertainty of the Avogadro constant NA which is one of the preconditions for the redefinition of the SI unit kilogram.

Positron annihilation in SiO 2-Si studied by a pulsed slow positron beam

Science.gov (United States)

Suzuki, R.; Ohdaira, T.; Uedono, A.; Kobayashi, Y.

2002-06-01

Positron and positronium (Ps) behavior in SiO 2-Si have been studied by means of positron annihilation lifetime spectroscopy (PALS) and age-momentum correlation (AMOC) spectroscopy with a pulsed slow positron beam. The PALS study of SiO 2-Si samples, which were prepared by a dry-oxygen thermal process, revealed that the positrons implanted in the Si substrate and diffused back to the interface do not contribute to the ortho-Ps long-lived component, and the lifetime spectrum of the interface has at least two components. From the AMOC study, the momentum distribution of the ortho-Ps pick-off annihilation in SiO 2, which shows broader momentum distribution than that of crystalline Si, was found to be almost the same as that of free positron annihilation in SiO 2. A varied interface model was proposed to interpret the results of the metal-oxide-semiconductor (MOS) experiments. The narrow momentum distribution found in the n-type MOS with a negative gate bias voltage could be attributed to Ps formation and rapid spin exchange in the SiO 2-Si interface. We have developed a two-dimensional positron lifetime technique, which measures annihilation time and pulse height of the scintillation gamma-ray detector for each event. Using this technique, the positronium behavior in a porous SiO 2 film, grown by a sputtering method, has been studied.

SiC/SiC composite fabricated with carbon nanotube interface layer and a novel precursor LPVCS

Energy Technology Data Exchange (ETDEWEB)

Zhao, Shuang, E-mail: zhsh6007@126.com [Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073 (China); School of Mechanical, Aerospace, and Civil Engineering, University of Manchester, Manchester M13 9PL (United Kingdom); Zhou, Xingui; Yu, Jinshan [Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073 (China); Mummery, Paul [School of Mechanical, Aerospace, and Civil Engineering, University of Manchester, Manchester M13 9PL (United Kingdom)

2014-02-15

Highlights: • The CNTs were distributed uniformly on the SiC fibers in the fabric by CVD process. • The microstructural evolution of the CNTs interface coating was studied. • The closed porosity was investigated by X-ray tomography. • The liquid precursor LPVCS exhibited high densification efficiency. - Abstract: Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied as promising candidate materials for nuclear applications. Three-dimensional SiC/SiC composite was fabricated via polymer impregnation and pyrolysis (PIP) process using carbon nanotubes (CNTs) as the interface layer and LPVCS as the polymer precursor. The microstructural evolution of the fiber/matrix interface was studied. The porosity, mechanical properties, thermal and electrical conductivities of the SiC/SiC composite were investigated. The results indicated that the high densification efficiency of the liquid precursor LPVCS resulted in a low porosity of the SiC/SiC composite. The SiC/SiC composite exhibited non-brittle fracture behavior, however, bending strength and fracture toughness of the composite were relatively low because of the absence of CNTs as the interface layer. The thermal and electrical conductivities of the SiC/SiC composite were low enough to meet the requirements desired for flow channel insert (FCI) applications.

Influence of air exposure duration and a-Si capping layer thickness on the performance of p-BaSi2/n-Si heterojunction solar cells

Directory of Open Access Journals (Sweden)

Ryota Takabe

2016-08-01

Full Text Available Fabrication of p-BaSi2(20nm/n-Si heterojunction solar cells was performed with different a-Si capping layer thicknesses (da-Si and varying air exposure durations (tair prior to the formation of a 70-nm-thick indium-tin-oxide electrode. The conversion efficiencies (η reached approximately 4.7% regardless of tair (varying from 12–150 h for solar cells with da-Si = 5 nm. In contrast, η increased from 5.3 to 6.6% with increasing tair for those with da-Si = 2 nm, in contrast to our prediction. For this sample, the reverse saturation current density (J0 and diode ideality factor decreased with tair, resulting in the enhancement of η. The effects of the variation of da-Si (0.7, 2, 3, and 5 nm upon the solar cell performance were examined while keeping tair = 150 h. The η reached a maximum of 9.0% when da-Si was 3 nm, wherein the open-circuit voltage and fill factor also reached a maximum. The series resistance, shunt resistance, and J0 exhibited a tendency to decrease as da-Si increased. These results demonstrate that a moderate oxidation of BaSi2 is a very effective means to enhance the η of BaSi2 solar cells.

Palladium transport in SiC

Energy Technology Data Exchange (ETDEWEB)

Olivier, E.J., E-mail: jolivier@nmmu.ac.za [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Neethling, J.H. [Centre for High Resolution Transmission Electron Microscopy, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa)

2012-03-15

Highlights: Black-Right-Pointing-Pointer We investigate the reaction of Pd with SiC at typical HTGR operating temperatures. Black-Right-Pointing-Pointer The high temperature mobility of palladium silicides within polycrystalline SiC was studied. Black-Right-Pointing-Pointer Corrosion of SiC by Pd was seen in all cases. Black-Right-Pointing-Pointer The preferential corrosion and penetration of Pd along grain boundaries in SiC was found. Black-Right-Pointing-Pointer The penetration and transport of palladium silicides in SiC along grain boundaries was found. - Abstract: This paper reports on a transmission electron microscopy (TEM) and scanning electron microscopy (SEM) study of Pd corroded SiC. The reaction of Pd with different types of SiC at typical HTGR operating temperatures was examined. In addition the high temperature mobility of palladium silicides within polycrystalline SiC was investigated. The results indicated corrosion of the SiC by Pd in all cases studied. The corrosion leads to the formation of palladium silicides within the SiC, with the predominant phase found being Pd{sub 2}Si. Evidence for the preferential corrosion and penetration of Pd along grain boundaries in polycrystalline SiC was found. The penetration and transport, without significant corrosion, of palladium silicides into polycrystalline SiC along grain boundaries was also observed. Implications of the findings with reference to the use of Tri Isotropic particles in HTGRs will be discussed.

ESTUDIO COMPARATIVO DEL EFECTO DE ZHONGJI (RM3) MOXADO MAS PUNTOS REGULARES VS PUNTOS REGULARES EN PACIENTES CON NEUROPATIA DIABETICA -NO TIENE CARATULA-

OpenAIRE

LERMA GARCIA, HECTOR ALFONSO

2010-01-01

ANTECEDENTES: DESDE LA ANTIGUEDAD SE HA COMPROBADO LA EFECTIVIDAD DE LA ACUPUNTURA PARA EL TRATAMIENTO DEL DOLOR Y PARA LA DIABETES EN EL SER HUMANO. OBJETIVO: EL PRESENTE ESTUDIO TIENE COMO OBJETIVO ANALIZAR EL EFECTO DEL TRATAMIENTO DEL DOLOR Y ALTERACIONES SENSITIVAS EN PACIENTES CON NEUROPATIA DIABETICA. METODO: SE ESTUDIARON TREINTA PACIENTES CON UN DIAGNOSTICO DE NEUROPATIA DIABETICA LOS CUALES SE DIVIDIERON EN TRES GRUPOS A LOS CUALES SE LES APLICO EN EL GRUPO 1 ZHONG...

Moessbauer and channeling experiments on TeSi and SmSi

International Nuclear Information System (INIS)

Kemerink, G.J.; Boerma, D.O.; Waard, H. de; Wit, J.C. de; Drentje, S.A.

1980-01-01

Considerable effort is made to obtain an insight in the structural and electronic properties of ion implanted elemental semiconductors. This research is strongly stimulated by the many applications of semi-conductor devices. We report here on Moessbauer studies of 129 TeSi and 153 SmSi, using the 27.8 keV transition in 129 I and the 103.2 keV transition in 153 Eu, respectively, and on channeling experiments on 128 TeSi and 152 SmSi with a 2 MeV α-beam from the Groningen Van de Graaff generator. In the Moessbauer experiments we used Cu 129 I and EuF 3 .1/2H 2 O as absorber materials. Source and absorber were held at 4.2 K. The implantations were generally done at room temperature with an implantation energy of 100-115 keV. For the Moessbauer and channeling measurements we applied similar Si single crystals and the same implantation and annealing conditions. Crystals with low doses could only be investigated with the Moessbauer effect

Light emissions from LiNbO sub 3 /SiO sub 2 /Si structures

CERN Document Server

Wu, X L; Tang, N; Deng, S S; Bao, X M

2003-01-01

LiNbO sub 3 (LN) films with a high degree of (006) texture were deposited on Si-based dense SiO sub 2 layers by pulsed laser deposition. After annealing, the LN/SiO sub 2 /Si structures were revealed to have ultraviolet-, green-, and red-emitting properties related to self-trapped excitons and E' defect pairs in the SiO sub 2 surface, which are induced by the photorefractive effect of the LN films. The emission wavelength can be tuned by introducing different dopants into the LN films. Waveguiding properties of the structures were demonstrated. The results obtained indicate that the LN/SiO sub 2 /Si structures could be expected to have important applications in modern optoelectronic integration. (letter to the editor)

Surface acoustic wave devices on AlN/3C–SiC/Si multilayer structures

International Nuclear Information System (INIS)

Lin, Chih-Ming; Lien, Wei-Cheng; Riekkinen, Tommi; Senesky, Debbie G; Pisano, Albert P; Chen, Yung-Yu; Felmetsger, Valery V

2013-01-01

Surface acoustic wave (SAW) propagation characteristics in a multilayer structure including a piezoelectric aluminum nitride (AlN) thin film and an epitaxial cubic silicon carbide (3C–SiC) layer on a silicon (Si) substrate are investigated by theoretical calculation in this work. Alternating current (ac) reactive magnetron sputtering was used to deposit highly c-axis-oriented AlN thin films, showing the full width at half maximum (FWHM) of the rocking curve of 1.36° on epitaxial 3C–SiC layers on Si substrates. In addition, conventional two-port SAW devices were fabricated on the AlN/3C–SiC/Si multilayer structure and SAW propagation properties in the multilayer structure were experimentally investigated. The surface wave in the AlN/3C–SiC/Si multilayer structure exhibits a phase velocity of 5528 m s −1 and an electromechanical coupling coefficient of 0.42%. The results demonstrate the potential of AlN thin films grown on epitaxial 3C–SiC layers to create layered SAW devices with higher phase velocities and larger electromechanical coupling coefficients than SAW devices on an AlN/Si multilayer structure. Moreover, the FWHM values of rocking curves of the AlN thin film and 3C–SiC layer remained constant after annealing for 500 h at 540 °C in air atmosphere. Accordingly, the layered SAW devices based on AlN thin films and 3C–SiC layers are applicable to timing and sensing applications in harsh environments. (paper)

β-FeSi2 films prepared on 6H-SiC substrates by magnetron sputtering

Science.gov (United States)

Hong, Li; Hongbin, Pu; Chunlei, Zheng; Zhiming, Chen

2015-06-01

β-FeSi2 thin films have been successfully prepared by magnetron sputtering and post rapid thermal annealing method on 6H-SiC (0001) substrates using a FeSi2 target and a Si target. X-ray diffraction (XRD) and Raman spectroscopy are applied to analyze the formation of β-FeSi2 films. XRD spectra reveal that the amorphous FeSi2 films are transformed to β-FeSi2 phase as the annealing temperature is increased from 500 to 900 °C for 5 min and the optimal annealing temperature is 900 °C. The formation of β-FeSi2 is also confirmed by Raman spectroscopy. Scanning electron microscope (SEM) observations indicate that the film is flat, relatively compact and the interface between β-FeSi2 and 6H-SiC is clear. Atomic force microscope (AFM) measurements demonstrate that the surface roughness confirmed by the root mean square (RMS) of the β-FeSi2 film is 0.87 nm. Near-infrared spectrophotometer observation shows that the absorption coefficient is of the order of 105 cm-1 and the optical band-gap of the β-FeSi2 film is 0.88 eV. The β-FeSi2 film with high crystal quality is fabricated by co-sputtering a FeSi2 target and a Si target for 60 min and annealing at 900 °C for 5 min. Project supported by the National Natural Science Foundation of China (No. 51177134) and the Natural Science Basic Research Plan in Shaanxi Province of China (No. 2015JM6286).

Specimen size effect considerations for irradiation studies of SiC/SiC

Energy Technology Data Exchange (ETDEWEB)

Youngblood, G.E.; Henager, C.H. Jr.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)

1996-10-01

For characterization of the irradiation performance of SiC/SiC, limited available irradiation volume generally dictates that tests be conducted on a small number of relatively small specimens. Flexure testing of two groups of bars with different sizes cut from the same SiC/SiC plate suggested the following lower limits for flexure specimen number and size: Six samples at a minimum for each condition and a minimum bar size of 30 x 6.0 x 2.0 mm{sup 3}.

Analysis on the sequence of formation of Ti{sub 3}SiC{sub 2} and Ti{sub 3}SiC{sub 2}/SiC composites

Energy Technology Data Exchange (ETDEWEB)

Radhakrishnan, R.; Bhaduri, S.B. [Idaho Univ., Moscow, ID (United States). Dept. of Mining and Metallurgy; Henager, C.H. Jr. [Pacific Northwest Lab., Richland, WA (United States)

1995-05-01

Ti{sub 3}SiC{sub 2}, a compound in the ternary Ti-Si-C system, is reported to be ductile. This paper reports the sequence of formation of Ti{sub 3}SiC{sub 2} and Ti{sub 3}SiC{sub 2}/SiC composites involving either combustion synthesis or by displacement reaction, respectively. Onset of exothermic reaction temperatures were determined using Differential Thermal Analysis (DTA). Phases present after the exothermic temperatures were analyzed by X-Ray diffraction. Based on these observations, a route to formation of Ti{sub 3}SiC{sub 2} and Ti{sub 3}SiC{sub 2}/SiC composites is proposed for the two`s thesis methods.

X-ray absorption spectroscopy study on SiC-side interface structure of SiO2–SiC formed by thermal oxidation in dry oxygen

Science.gov (United States)

Isomura, Noritake; Kosaka, Satoru; Kataoka, Keita; Watanabe, Yukihiko; Kimoto, Yasuji

2018-06-01

Extended X-ray absorption fine structure (EXAFS) spectroscopy is demonstrated to measure the fine atomic structure of SiO2–SiC interfaces. The SiC-side of the interface can be measured by fabricating thin SiO2 films and using SiC-selective EXAFS measurements. Fourier transforms of the oscillations of the EXAFS spectra correspond to radial-structure functions and reveal a new peak of the first nearest neighbor of Si for m-face SiC, which does not appear in measurements of the Si-face. This finding suggests that the m-face interface could include a structure with shorter Si–C distances. Numerical calculations provide additional support for this finding.

Investigation on fabrication of SiC/SiC composite as a candidate material for fuel sub-assembly

International Nuclear Information System (INIS)

Lee, Jae-Kwang; Naganuma, Masayuki; Park, Joon-Soo; Kohyama, Akira

2005-01-01

The possibility of SiC/SiC (Silicon carbide fiber reinforced Silicon carbide) composites application for fuel sub-assembly of Fast Breeder Reactor was investigated. To select a raw material of SiC/SiC composites, a few kinds of SiC nano powder was estimated by SEM observation and XRD analysis. Furthermore, SiC monolithic was sintered from them and estimated by flexural test. SiC nano-powder which showed good sinterability, it was used for fabrication of SiC/SiC composites by Hot Pressing method. From the sintering condition of 1800, 1820degC temperature and 15, 20 MPa pressure, SiC/SiC composite was fabricated and then estimated by tensile test. SiC/SiC composite, which made by 1820degC and 20 MPa condition, showed the highest mechanical strength by the monotonic tensile test. SiC/SiC composite, which made by 1800degC and 15 MPa condition, showed a stable fracture behavior at the monotonic and cyclic tensile test. And then, the hoop stress of ideal model of SiC/SiC composites was discussed. It was confirmed that applicability of SiC/SiC composites by Hot Pressing method for fuel sub-assembly structural material. To make it real attractive one, to maintain the reliability and safety as a high temperature structural material, the design and process study on SiC/Sic composites material will be continued. (author)

Phenomenological inelastic constitutive equations for SiC and SiC fibers under irradiation

International Nuclear Information System (INIS)

El-Azab, A.; Ghoniem, N.M.

1994-01-01

Experimental data on irradiation-induced dimensional changes and creep in β-SiC and SiC fibers is analyzed, with the objective of studying the constitutive behavior of these materials under high-temperature irradiation. The data analysis includes empirical representation of irradiation-induced dimensional changes in SiC matrix and SiC fibers as function of time and irradiation temperature. The analysis also includes formulation of simple scaling laws to extrapolate the existing data to fusion conditions on the basis of the physical mechanisms of radiation effects on crystalline solids. Inelastic constitutive equations are then developed for SCS-6 SiC fibers, Nicalon fibers and CVD SiC. The effects of applied stress, temperature, and irradiation fields on the deformation behavior of this class of materials are simultaneously represented. Numerical results are presented for the relevant creep functions under the conditions of the fusion reactor (ARIES IV) first wall. The developed equations can be used in estimating the macro mechanical properties of SiC-SiC composite systems as well as in performing time-dependent micro mechanical analysis that is relevant to slow crack growth and fiber pull-out under fusion conditions

Si cycling in a forest biogeosystem - the importance of transient state biogenic Si pools

Science.gov (United States)

Sommer, M.; Jochheim, H.; Höhn, A.; Breuer, J.; Zagorski, Z.; Busse, J.; Barkusky, D.; Meier, K.; Puppe, D.; Wanner, M.; Kaczorek, D.

2013-07-01

The relevance of biological Si cycling for dissolved silica (DSi) export from terrestrial biogeosystems is still in debate. Even in systems showing a high content of weatherable minerals, like Cambisols on volcanic tuff, biogenic Si (BSi) might contribute > 50% to DSi (Gerard et al., 2008). However, the number of biogeosystem studies is rather limited for generalized conclusions. To cover one end of controlling factors on DSi, i.e., weatherable minerals content, we studied a forested site with absolute quartz dominance (> 95%). Here we hypothesise minimal effects of chemical weathering of silicates on DSi. During a four year observation period (05/2007-04/2011), we quantified (i) internal and external Si fluxes of a temperate-humid biogeosystem (beech, 120 yr) by BIOME-BGC (version ZALF), (ii) related Si budgets, and (iii) Si pools in soil and beech, chemically as well as by SEM-EDX. For the first time two compartments of biogenic Si in soils were analysed, i.e., phytogenic and zoogenic Si pool (testate amoebae). We quantified an average Si plant uptake of 35 kg Si ha-1 yr-1 - most of which is recycled to the soil by litterfall - and calculated an annual biosilicification from idiosomic testate amoebae of 17 kg Si ha-1. The comparatively high DSi concentrations (6 mg L-1) and DSi exports (12 kg Si ha-1 yr-1) could not be explained by chemical weathering of feldspars or quartz dissolution. Instead, dissolution of a relictic, phytogenic Si pool seems to be the main process for the DSi observed. We identified canopy closure accompanied by a disappearance of grasses as well as the selective extraction of pine trees 30 yr ago as the most probable control for the phenomena observed. From our results we concluded the biogeosystem to be in a transient state in terms of Si cycling.

Low thermal budget surface preparation of Si and SiGe

International Nuclear Information System (INIS)

Abbadie, A.; Hartmann, J.M.; Holliger, P.; Semeria, M.N.; Besson, P.; Gentile, P.

2004-01-01

Using a two-step cleaning, we have investigated the low thermal budget surface preparation of Si and Si 1-x Ge x (x=0.2-0.33). It consists of an ex situ 'HF-last' wet-cleaning and an in situ low thermal budget H 2 bake in a reduced pressure-chemical vapor deposition reactor. Using secondary ion mass spectrometry, we have evaluated the effects of different H 2 bake temperatures (in between 750 and 850 deg. C for 2 min) on the removal efficiency of C, O and F atoms still present on the surface of Si and SiGe virtual substrates after the 'HF-last' wet-cleaning. We have then examined the impact of the (wet-cleaning+H 2 bake) combination on the surface cross-hatch of SiGe as-grown virtual substrates, focusing on the analysis, notably by atomic force microscopy, of the surface topography before and after the miscellaneous thermal treatments. In situ hydrogen baking steps in between 775 and 850 deg. C do not modify the surface morphology and roughness. An easy and rapid optical characterization method, i.e. the optical interferometry, is presented as well to monitor in line the morphological changes induced by such processing steps as chemical mechanical polishing, wet-cleaning, H 2 bake, etc. Despite the lower resolution of the optical profilometer, the surface roughness values coming from it have been correctly correlated with those obtained from AFM. An optimized 'HF-last' wet-cleaning using a diluted chemistry in conjunction with a H 2 bake at 800 deg. C for 2 min (775 deg. C, 2') is a good compromise for SiGe (Si) surface preparation

Bladder Control Problems

Science.gov (United States)

... la vejiga, la uretra y los músculos del suelo pélvico; por problemas de la próstata en los hombres; cambios físicos que ... si tiene incontinencia urinaria, incluso si siente vergüenza de hacerlo. Los tratamientos pueden incluir cambios en la cantidad y el ...

Formation of ferromagnetic interface between β-FeSi2 and Si(111) substrate

International Nuclear Information System (INIS)

Hattori, Azusa N.; Hattori, Ken; Kodama, Kenji; Hosoito, Nobuyoshi; Daimon, Hiroshi

2007-01-01

Epitaxial β-FeSi 2 thin films were grown on Si(111)7x7 clean surfaces by solid phase epitaxy in ultrahigh vacuum: iron deposition at low temperature and subsequent annealing. We found that a ferromagnetic interface layer of iron-rich silicides forms between a β-FeSi 2 surface layer and a Si(111) substrate spontaneously from transmission electron microscopy observations and magnetization measurements

Tunable graphene doping by modulating the nanopore geometry on a SiO2/Si substrate

KAUST Repository

Lim, Namsoo

2018-02-28

A tunable graphene doping method utilizing a SiO2/Si substrate with nanopores (NP) was introduced. Laser interference lithography (LIL) using a He–Cd laser (λ = 325 nm) was used to prepare pore size- and pitch-controllable NP SiO2/Si substrates. Then, bottom-contact graphene field effect transistors (G-FETs) were fabricated on the NP SiO2/Si substrate to measure the transfer curves. The graphene transferred onto the NP SiO2/Si substrate showed relatively n-doped behavior compared to the graphene transferred onto a flat SiO2/Si substrate, as evidenced by the blue-shift of the 2D peak position (∼2700 cm−1) in the Raman spectra due to contact doping. As the porosity increased within the substrate, the Dirac voltage shifted to a more positive or negative value, depending on the initial doping type (p- or n-type, respectively) of the contact doping. The Dirac voltage shifts with porosity were ascribed mainly to the compensation for the reduced capacitance owing to the SiO2–air hetero-structured dielectric layer within the periodically aligned nanopores capped by the suspended graphene (electrostatic doping). The hysteresis (Dirac voltage difference during the forward and backward scans) was reduced when utilizing an NP SiO2/Si substrate with smaller pores and/or a low porosity because fewer H2O or O2 molecules could be trapped inside the smaller pores.

Metastability of a-SiO{sub x}:H thin films for c-Si surface passivation

Energy Technology Data Exchange (ETDEWEB)

Serenelli, L., E-mail: luca.serenelli@enea.it [ENEA Research centre “Casaccia”, via Anguillarese 301, 00123 Rome (Italy); DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Martini, L. [DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Imbimbo, L. [ENEA Research centre “Casaccia”, via Anguillarese 301, 00123 Rome (Italy); DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Asquini, R. [DIET University of Rome “Sapienza”, via Eudossiana 18, 00184 Rome (Italy); Menchini, F.; Izzi, M.; Tucci, M. [ENEA Research centre “Casaccia”, via Anguillarese 301, 00123 Rome (Italy)

2017-01-15

Highlights: • a-SiO{sub x}:H film deposition by RF-PECVD is optimized from SiH{sub 4}, CO{sub 2} and H{sub 2} gas mixture. • Metastability of a-SiO{sub x}:H/c-Si passivation is investigated under thermal annealing and UV exposure. • A correlation between passivation metastability and Si−H bonds is found by FTIR spectra. • A metastability model is proposed. - Abstract: The adoption of a-SiO{sub x}:H films obtained by PECVD in heterojunction solar cells is a key to further increase their efficiency, because of its transparency in the UV with respect to the commonly used a-Si:H. At the same time this layer must guarantee high surface passivation of the c-Si to be suitable in high efficiency solar cell manufacturing. On the other hand the application of amorphous materials like a-Si:H and SiN{sub x} on the cell frontside expose them to the mostly energetic part of the sun spectrum, leading to a metastability of their passivation properties. Moreover as for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In this work we explored the reliability of a-SiO{sub x}:H thin film layers surface passivation on c-Si substrates under UV exposition, in combination with thermal annealing steps. Both p- and n-type doped c-Si substrates were considered. To understand the effect of UV light soaking we monitored the minority carriers lifetime and Si−H and Si−O bonding, by FTIR spectra, after different exposure times to light coming from a deuterium lamp, filtered to UV-A region, and focused on the sample to obtain a power density of 50 μW/cm{sup 2}. We found a certain lifetime decrease after UV light soaking in both p- and n-type c-Si passivated wafers according to a a-SiO{sub x}:H/c-Si/a-SiO{sub x}:H structure. The role of a thermal annealing, which usually enhances the as-deposited SiO{sub x} passivation properties, was furthermore considered. In

Control of the graphene growth rate on capped SiC surface under strong Si confinement

International Nuclear Information System (INIS)

Çelebi, C.; Yanık, C.; Demirkol, A.G.; Kaya, İsmet İ.

2013-01-01

Highlights: ► Graphene is grown on capped SiC surface with well defined cavity size. ► Graphene growth rate linearly increases with the cavity height. ► Graphene uniformity is reduced with thickness. - Abstract: The effect of the degree of Si confinement on the thickness and morphology of UHV grown epitaxial graphene on (0 0 0 −1) SiC is investigated by using atomic force microscopy and Raman spectroscopy measurements. Prior to the graphene growth process, the C-face surface of a SiC substrate is capped by another SiC comprising three cavities on its Si-rich surface with depths varying from 0.5 to 2 microns. The Si atoms, thermally decomposed from the sample surface during high temperature annealing of the SiC cap /SiC sample stack, are separately trapped inside these individual cavities at the sample/cap interface. Our analyses show that the growth rate linearly increases with the cavity height. It was also found that stronger Si confinement yields more uniform graphene layers.

C/SiC/MoSi2-Si multilayer coatings for carbon/carbon composites for protection against oxidation

International Nuclear Information System (INIS)

Zhang Yulei; Li Hejun; Qiang Xinfa; Li Kezhi; Zhang Shouyang

2011-01-01

Highlights: → A C/SiC/MoSi 2 -Si multilayer coating was prepared on C/C by slurry and pack cementation. → Multilayer coating can protect C/C for 300 h at 1873 K or 103 h at 1873 K in air. → The penetration cracks in the coating result in the weight loss of the coated C/C. → The fracture of the coated C/C in wind tunnel result from the excessive local stress. - Abstract: To improve the oxidation resistance of carbon/carbon (C/C) composites, a C/SiC/MoSi 2 -Si multilayer oxidation protective coating was prepared by slurry and pack cementation. The microstructure of the as-prepared coating was characterized by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The isothermal oxidation and erosion resistance of the coating was investigated in electrical furnace and high temperature wind tunnel. The results showed that the multilayer coating could effectively protect C/C composites from oxidation in air for 300 h at 1773 K and 103 h at 1873 K, and the coated samples was fractured after erosion for 27 h at 1873 K h in wind tunnel. The weight loss of the coated specimens was considered to be caused by the formation of penetration cracks in the coating. The fracture of the coated C/C composites might result from the excessive local stress in the coating.

À propos du lexique juridique en ancien français avant le 13e siècle : la Règle de saint Benoît et le Perceval de Chrétien de Troyes

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Schauwecker Yela

2012-07-01

Full Text Available La plus ancienne traduction de la {em Règle} de saint Benoît en franc{c}ais, rédigée en dialecte picard-wallon, date de la première moitié ou du milieu du {sc xii}$^{m e}$~siècle. On veut montrer que son auteur, pour qui le changement de langue, n'est pas le premier objectif s'efforce de transférer le texte de son milieu originel de l'Antiquité tardive dans le monde chevaleresque-féodal du {sc xii}$^{m e}$~siècle. Même sans nécessité apparente, quand il a eu à sa disposition l'équivalent du mot employé dans la {em Regula}, il substitue aux mots latins des termes juridiques et féodaux franc{c}ais. par Son texte, en tant que document de droit pour les moines, devient ainsi une source de vocabulaire juridique franc{c}ais avant le {sc xiii}$^{m e}$~siècle, c'est-à-dire dans un temps où les documents juridiques en langue vulgaire sont extrêmement rares. Cela est dû au fait que la justice, dans le Nord, fondée sur des coutumes, utilisait la langue vernaculaire à l'oral. La terminologie juridique franc{c}aise est bien enracinée dans la langue courante de l'époque~: leur insertion dans les Lais et les Chansons de geste en fait preuve. Mais cette terminologie est souvent méconnue par la lexicographie traditionnelle de l'ancien franc{c}ais, en raison des contextes littéraires et figurés. par

Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting.

Science.gov (United States)

Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

2016-02-07

We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ∼20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

Paleo-Climate and Glaciological Reconstruction in Central Asia through the Collection and Analysis of Ice Cores and Instrumental Data from the Tien Shan

International Nuclear Information System (INIS)

Vladimir Aizen; Donald Bren; Karl Kreutz; Cameron Wake

2001-01-01

While the majority of ice core investigations have been undertaken in the polar regions, a few ice cores recovered from carefully selected high altitude/mid-to-low latitude glaciers have also provided valuable records of climate variability in these regions. A regional array of high resolution, multi-parameter ice core records developed from temperate and tropical regions of the globe can be used to document regional climate and environmental change in the latitudes which are home to the vase majority of the Earth's human population. In addition, these records can be directly compared with ice core records available from the polar regions and can therefore expand our understanding of inter-hemispheric dynamics of past climate changes. The main objectives of our paleoclimate research in the Tien Shan mountains of middle Asia combine the development of detailed paleoenvironmental records via the physical and chemical analysis of ice cores with the analysis of modern meteorological and hydrological data. The first step in this research was the collection of ice cores from the accumulation zone of the Inylchek Glacier and the collection of meteorological data from a variety of stations throughout the Tien Shan. The research effort described in this report was part of a collaborative effort with the United State Geological Survey's (USGS) Global Environmental Research Program which began studying radionuclide deposition in mid-latitude glaciers in 1995

Paleo-Climate and Glaciological Reconstruction in Central Asia through the Collection and Analysis of Ice Cores and Instrumental Data from the Tien Shan

Energy Technology Data Exchange (ETDEWEB)

Vladimir Aizen; Donald Bren; Karl Kreutz; Cameron Wake

2001-05-30

While the majority of ice core investigations have been undertaken in the polar regions, a few ice cores recovered from carefully selected high altitude/mid-to-low latitude glaciers have also provided valuable records of climate variability in these regions. A regional array of high resolution, multi-parameter ice core records developed from temperate and tropical regions of the globe can be used to document regional climate and environmental change in the latitudes which are home to the vase majority of the Earth's human population. In addition, these records can be directly compared with ice core records available from the polar regions and can therefore expand our understanding of inter-hemispheric dynamics of past climate changes. The main objectives of our paleoclimate research in the Tien Shan mountains of middle Asia combine the development of detailed paleoenvironmental records via the physical and chemical analysis of ice cores with the analysis of modern meteorological and hydrological data. The first step in this research was the collection of ice cores from the accumulation zone of the Inylchek Glacier and the collection of meteorological data from a variety of stations throughout the Tien Shan. The research effort described in this report was part of a collaborative effort with the United State Geological Survey's (USGS) Global Environmental Research Program which began studying radionuclide deposition in mid-latitude glaciers in 1995.

Precipitation kinetics of Al-1.12 Mg{sub 2}Si-0.35 Si and Al-1.07 Mg{sub 2}Si-0.33 Cu alloys

Energy Technology Data Exchange (ETDEWEB)

Gaber, A. [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt); Gaffar, M.A. [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt)]. E-mail: mgaafar@aucegypt.edu; Mostafa, M.S. [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt); Zeid, E.F. Abo [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt)

2007-02-21

The kinetics of hardening precipitates of Al-1.12 wt.% Mg{sub 2}Si-0.35 wt.% Si (excess Si) and Al-1.07 wt.% Mg{sub 2}Si-0.33 wt.% Cu (balanced + Cu) alloys have been investigated by means of differential scanning calorimetry and hardness measurements. The excess Si enhances the precipitation kinetics and improves the strength of the material. On the other hand, however addition of Cu assist formation of the Q' phase which positively changed the alloy strength. The high binding energy between vacancies and solute atoms (Si and Mg) enhances the combination of Si, Mg and vacancies to form Si-Mg-vacancy clusters. These clusters act as nucleation sites for GP-zones. The coexistence of the {beta}'- and Q'-precipitates in the balanced + Cu alloy results in a higher peak age hardening compared to the alloy with Si in excess.

Self-assembled epitaxial NiSi2 nanowires on Si(001) by reactive deposition epitaxy

International Nuclear Information System (INIS)

Chen, S.Y.; Chen, L.J.

2006-01-01

Self-assembled epitaxial NiSi 2 nanowires have been fabricated on Si(001) by reactive deposition epitaxy (RDE). The RDE method promoted nanowire growth since it provides deposited atoms sufficient kinetic energy for movement on the Si surface during the growth of silicide islands. The twin-related interface between NiSi 2 and Si is directly related to the nanowire formation since it breaks the symmetry of the surface and leads to the asymmetric growth. The temperature of RDE was found to greatly influence the formation of nanowires. By RDE at 750 deg. C, a high density of NiSi 2 nanowires was formed with an average aspect ratio of 30

Influence of substrate treatment on the growth of advanced core–shell alloys and compounds of FeSi@SiO2 and SiO2 nanowires

CSIR Research Space (South Africa)

Thabethe, S

2014-12-01

Full Text Available Advanced core–shell FeSi@SiO(subx) nanowires are observed when FeCl(sub3) vapour is made to flow over a SiO(sub2)/Si substrate at 1100 degress C. The thickness of the SiO(subx) sheath (d0) is found to depend inversely as the period of time of HF...

Surface Chemistry Involved in Epitaxy of Graphene on 3C-SiC(111/Si(111

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Abe Shunsuke

2010-01-01

Full Text Available Abstract Surface chemistry involved in the epitaxy of graphene by sublimating Si atoms from the surface of epitaxial 3C-SiC(111 thin films on Si(111 has been studied. The change in the surface composition during graphene epitaxy is monitored by in situ temperature-programmed desorption spectroscopy using deuterium as a probe (D2-TPD and complementarily by ex situ Raman and C1s core-level spectroscopies. The surface of the 3C-SiC(111/Si(111 is Si-terminated before the graphitization, and it becomes C-terminated via the formation of C-rich (6√3 × 6√3R30° reconstruction as the graphitization proceeds, in a similar manner as the epitaxy of graphene on Si-terminated 6H-SiC(0001 proceeds.

New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics.

Science.gov (United States)

Graczyk-Zajac, Magdalena; Reinold, Lukas Mirko; Kaspar, Jan; Sasikumar, Pradeep Vallachira Warriam; Soraru, Gian-Domenico; Riedel, Ralf

2015-02-24

Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics

Directory of Open Access Journals (Sweden)

Magdalena Graczyk-Zajac

2015-02-01

Full Text Available Within this work we define structural properties of the silicon carbonitride (SiCN and silicon oxycarbide (SiOC ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

Joining of SiCf/SiC composites for thermonuclear fusion reactors

International Nuclear Information System (INIS)

Ferraris, M.; Badini, C.; Montorsi, M.; Appendino, P.; Scholz, H.W.

1994-01-01

Due to their favourable radiological behaviour, SiC f /SiC composites are promising structural materials for future use in fusion reactors. A problem to cope with is the joining of the ceramic composite material (CMC) to itself for more complex structures. Maintenance concepts for a reactor made of SiC f /SiC will demand a method of joining. The joining agents should comply with the low-activation approach of the base material. With the acceptable elements Si and Mg, sandwich structures of composite/metal/composite were prepared in Ar atmosphere at temperatures just above the melting points of the metals. Another promising route is the use of joining agents of boro-silicate glasses: their composition can be tailored to obtain softening temperatures of interest for fusion applications. The glassy joint can be easily ceramised to improve thermomechanical properties. The joining interfaces were investigated by SEM-EDS, XRD and mechanical tests. ((orig.))

On the interplay between Si(110) epilayer atomic roughness and subsequent 3C-SiC growth direction

Science.gov (United States)

Khazaka, Rami; Michaud, Jean-François; Vennéguès, Philippe; Nguyen, Luan; Alquier, Daniel; Portail, Marc

2016-11-01

In this contribution, we performed the growth of a 3C-SiC/Si/3C-SiC layer stack on a Si(001) substrate by means of chemical vapor deposition. We show that, by tuning the growth conditions, the 3C-SiC epilayer can be grown along either the [111] direction or the [110] direction. The key parameter for the growth of the desired 3C-SiC orientation on the Si(110)/3C-SiC(001)/Si(001) heterostructure is highlighted and is linked to the Si epilayer surface morphology. The epitaxial relation between the layers has been identified using X-ray diffraction and transmission electron microscopy (TEM). We showed that, regardless of the top 3C-SiC epilayer orientation, domains rotated by 90° around the growth direction are present in the epilayer. Furthermore, the difference between the two 3C-SiC orientations was investigated by means of high magnification TEM. The results indicate that the faceted Si(110) epilayer surface morphology results in a (110)-oriented 3C-SiC epilayer, whereas a flat hetero-interface has been observed between 3C-SiC(111) and Si(110). The control of the top 3C-SiC growth direction can be advantageous for the development of new micro-electro-mechanical systems.