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Electron energy-loss spectroscopy of V2O5 nanofibers synthesized by electro-spinning

MARTHA TERESITA OCHOA LARA FRANCISCO ESPINOSA MAGAÑA (2013)

The dielectric properties of V2O5 nanofibers, synthesized by the electrospinning method, are studied by analyzing the low-loss region of the electron energy loss spectroscopy (EELS) in a transmission electron microscope. A comparison of experimental EELS spectra and ab initio density-functional theory calcula-tions (WIEN2k code) within the Generalized Gradient Approximation (GGA) is presented, having found an excellent agreement between them. Although the experimental EELS has been acquired for the nanopar-ticles composing the fibers, and numerical calculations were carried out for bulk material, agreement between experimental and calculated results shows that no difference exists between the electronic structure in calculated bulk material and the nanoparticles. Furthermore, our results from EELS confirm that we accomplished the expected crystalline phase. The origins of interband transitions are identified in the electronic band structure by calculating the partial imaginary part of the dielectric function and the partial density of states.

Article

EELS Dielectric function CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA OTRAS ESPECIALIDADES FÍSICAS OTRAS

Optical matrix elements in tight-binding approach of hydrogenated Si nanowires

JOSE ALEJANDRO DIAZ MENDEZ MIGUEL CRUZ IRISSON (2009)

The dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes: intra-atomic and interatomic optical matrix elements are applied and compared. The optical spectra of Si nanowires are studied by means of a semi-empirical sp3s* tight-binding supercell model. The surface dangling bonds are passivated by hydrogen atoms. The results show that although the intra-atomic matrix elements are small in magnitude, the interference between these terms and the interatomic matrix elements contributes with nearly 25% of the total absorption. Thus, a quantitative treatment of nanostructures may not be possible without the inclusion of intra-atomic matrix elements.

Article

Silicon nanowires Tight-binding approach Dielectric function CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

AUTOMATED PROGRAM FOR THE CALCULATION OF THE QUASIPARTICLE ENERGIES WITH THE GW APPROXIMATION

Crisitian Camilo Montes Vargas (2019)

"This thesis presents a general description of a program that automatizes the calculation of the quasiparticle energies of crystalline systems, by using the GW approximation. In this context, G is a Green’s function that describes the dynamic of an electron. W is the dynamical screen interaction between electrons in a homogeneous and polarizable medium. The automation of the program consists in computing important functions that are needed to calculate the quasiparticle energies. These functions are the charge density, wave functions, the polarizability and theself-energy. All these functions can be computed by the software Abinit. However, the computation of those functions are not automatized by Abinit. The program developed in this thesis allows one to compute the eigen-energies of the system by using Density Functional Theory, and the Local Density Approximation for exchange-correlation potential Vxc. The program calculates quasiparticle energies and the optical band of semiconductors. The program also calculates the quasiparticle energies, Fermi energy and spectral function of metals. We calculated the linear dielectric function with the quasiparticle energies, by using the Random Phase Approximation for polarizability. The results show that the linear dielectric function computed with the quasiparticle energies is in agreement with experiments for semiconductors. The results also show that the optical bandgap computed with GW approximation is more precise respect to experiments, in comparison with the optical bandgap predicted by the Density Functional theory."

Master thesis

Quasiparticle GW Dielectric function Self-energy Band structure Absorption CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA PROPIEDADES ÓPTICAS DE LOS SÓLIDOS PROPIEDADES ÓPTICAS DE LOS SÓLIDOS

Sensor de anisotropía dieléctrica usando resonadores acoplados

Hector Noel Morales Lovera (2019)

Today, 5G telecommunications networks, beyond improving the data rate, this technology is expected to provide an environment where everything is connected, known as the Internet of Things (IoT). These communication systems have the ideology of connecting not only users to internet, but also all everyday objects can connect to the network, allowing its management and identification by other devices, as well as a human being does it. For the development of a communication system of this magnitude, it is required that the circuits and communications channels be designed with higher requirements in terms of speed of operation, bandwidth, energy consumption, etc. With the increase in the speed of operation of the telecommunication systems, effects caused by characteristics of the material with which they are manufactured begin to be increasingly evident. For this reason, an continue improvement in the models and methods of characterization of material in the microwave range is required. In this work, a sensor and the methodology for the measurements of the uniaxial dielectric constant of anisotropic materials is presented. The sensor is based on microstrip resonators, which allows by non-destructive and non-invasive testing of samples under test (SUT). The method results a low cost and fast method, since with a single sensor it is possible to characterize several samples. The sensor is used for the successful dielectric characterization of different commercial substrates (Arlon Diclad 880, RO 4350B, FR4 y RO 3010). Obtaining a difference lower than 0.8% compared to that reported in previous works.

Hoy en día, las redes de telecomunicaciones 5G, más allá de mejorar la velocidad de transferencia de datos, se espera que esta tecnología propicie un ambiente donde todo está conectado, conocido como Internet de las Cosas (IoT). Este sistema de comunicaciones tiene la ideología de conectar no solo a los usuarios a internet, sino que todos los objetos de uso cotidianos puedan conectarse a la red, permitiendo su gestión e identificación por otros dispositivos, al igual que lo hace un ser humano. Para el desarrollo de un sistema de comunicaciones de tal magnitud, se requiere que los circuitos y canales de comunicación se diseñen con mayores exigencias en cuanto la velocidad de operación, ancho de banda, consumo energético, etc. Con el aumento en la velocidad de operación de los sistemas de telecomunicaciones, los efectos provocados por las características de los materiales con los que están fabricados comienzan a ser cada vez más evidentes. Por tal motivo, se requiere una mejora en los modelos y métodos de caracterización de los materiales en el rango de las microondas. En este trabajo se presenta un sensor y metodología para la medición de la constante dieléctrica uniaxial de materiales dieléctricos anisótropos. El sensor está basado en resonadores de microcinta, lo que permite realizar pruebas no destructivas y no invasivas de muestras sometidas a prueba (SUT). El método resulta de bajo costo y rápido, pues con un solo sensor es posible caracterizar muchas muestras. El sensor es utilizado para la exitosa caracterización dieléctrica de diferentes sustratos comerciales (Arlon Diclad 880, RO 4350B, FR4 y RO 3010). Obteniendo una diferencia menor al 0.8% respecto a lo reportado en trabajos previos.

Master thesis

Dielectric Anisotropy PCB CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

Límites indeterminados mediante el uso de tablas de valores y gráficas.

VICTOR IGNACIO ESPIRITU MONTIEL CATALINA NAVARRO SANDOVAL (2014)

This document proposes an alternative for calculating indeterminate limits through using tables of values and graphs, to pre-university students (aged between 17 and 18 years). For this, we have been given the task of analyzing research considering the historicalepistemological aspects, didactic and cognitive. Furthermore, was elaborated a questionnaire preliminary with the objective of exploring the procedures used by students to solve indeterminate limits, once applied and analyzed the results, we identified various problematic and according to these was designed a didactic proposal covering in particular the calculation of indeterminate limits, also presented in this paper, the results of the staging.

Article

Limit Indeterminate Function table of values graph HUMANIDADES Y CIENCIAS DE LA CONDUCTA PEDAGOGÍA OTRAS ESPECIALIDADES PEDAGÓGICAS

Causal modeling and characterization of printed circuit board interconnects considering high-order effects in the microwave frequency range

Erika Yazmin Teran Bahena (2019)

The operation frequency and the data transfer rate of the modern electronic systems have a constant increase. Therefore, nowadays is very common to talk about gigabits per second data information transfer rates. In this case, the contribution of the components that communicate these systems, such as the interconnects, cannot be considered insignificant. In fact, the interconnects are the main responsible to cause reflection, delay and distortion of the signal that travels between the integrated circuits and other elements. Therefore, the accurate analyze, characterization and modeling of the interconnects are necessary. These procedures allow to develop tools that help to predict the behavior of the interconnects to optimum their design in order to improve the performance of the electronic systems implemented in printed circuit board technology (PCB).

All interconnect model must to accomplish two requirements: the model must to have a good model-experiment correlation in the frequency domain and to have a causal response in the time domain. However, even though many interconnect characterization and model methods in the current literature accomplish with to have a good model-experiment correlation in the frequency domain, not always these methods provide a causal response in the time domain. This is a consequence of simplify the description of the phenomena that have influence in the signals propagation. Therefore, this thesis work is focused in analyzed the physical phenomena that significant contribute in the development of a causal model. In order to validate the proposals presented in this work, many PCB prototypes were fabricated and measured. In this way, a comparison between the obtained results from the application of the proposals and the experimental data was performed in the frequency and time domains. It was observed that the obtained results present a good model-experiment correlation in both domains. Therefore, it was demonstrated that the proposals presented in this work allow the development and the implementation of causal models for interconnects fabricated on printed circuit boards in the gigabit per second range.

La velocidad de operación y tasa de transferencia de los sistemas electrónicos modernos presentan un incremento constante. De este modo, en la actualidad es común hablar de tasas de transmisión de información de gigabits por segundo. En este caso, la contribución de los componentes que comunican estos sistemas, como lo son las interconexiones, ya no puede ser considerada insignificante. De hecho, son las principales responsables de ocasionar reflexión, retraso y distorsión de la señal que viaja entre circuitos integrados y otros elementos. Por tal motivo, el análisis, la caracterización y el modelado preciso de las interconexiones son necesarios. Esto permite el desarrollo de herramientas que ayudan a predecir su comportamiento y diseñarlas de forma óptima con el fin de mejorar el rendimiento de los sistemas electrónicos implementados en tecnologías de tarjeta de circuito impreso (PCB, por sus siglas en inglés).

Todo modelo de interconexión debe de cumplir con dos requisitos: tener una buena correlación modelo-experimento en el dominio de la frecuencia y presentar una respuesta causal en el dominio del tiempo. Sin embargo, aunque la mayoría de los métodos de caracterización y modelado de interconexiones presentes en la literatura actual cumplen con tener una buena correlación modelo-experimento en el dominio de la frecuencia, no siempre presentan una respuesta causal en el dominio del tiempo. Esto como consecuencia de simplificar la descripción de los fenómenos físicos que influyen en la propagación de las señales. Por tal motivo, este trabajo de tesis está enfocado en analizar qué fenómenos físicos influyen de forma significativa en la generación de un modelo causal.

Con el fin de validar las propuestas presentadas en este trabajo, se fabricaron y midieron diversos prototipos de interconexiones en PCB. Es así como, se realizó una comparación entre los resultados obtenidos mediante la aplicación de las propuestas y los datos experimentales tanto en el dominio de la frecuencia como en el domino del tiempo. Se observó que los resultados obtenidos tienen una buena correlación modelo-experimento en ambos dominios. De esta forma, se comprobó que las propuestas presentadas permiten la generación e implementación de modelos causales precisos para interconexiones fabricadas en tarjetas de circuito impreso en el rango de los gigabits por segundo.

Doctoral thesis

Dielectric permittivity Transmission lines Modeling Characterization CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA ELECTRÓNICA

Reactance and resistance: main properties to follow the cell differentiation process in Bacillus thuringiensis by dielectric spectroscopy in real time

JABEL DINORIN TELLEZ GIRON (2015)

During growth, Bacillus thuringiensis presents three phases: exponential phase (EP), transition state (TS),

and sporulation phase (SP). In order to form a dormant spore and to synthesize delta-endotoxins during SP, bacteria must undergo a cellular differentiation process initiated during the TS. Dielectric spectroscopy is a technique that can be utilized for continuous and in situ monitoring of the cellular state. In order to study on-line cell behavior in B. thuringiensis cultures, we conducted a number of batch cultures under different conditions, by scanning 200 frequencies from42Hz to 5MHz and applying fixed current and voltage of 20 mA and 5 V DC,

respectively. The resulting signals included Impedance (Z), Angle phase (Deg), Voltage (V), Current (I), Conductance (G), Reactance (X), and Resistance (R). Individual raw data relating to observed dielectric property profiles were correlated with the different growth phases established using data from cellular growth, cry1Ac gene expression, and free spores obtained with conventional techniques and fermentation parameters. Based on these correlations, frequencies of 0.1, 0.5, and 1.225 MHz were selected for the purpose of measuring dielectric properties in independent batch cultures, at a fixed frequency. X and R manifest more propitious behavior in relation to EP, TS, SP, and spore release, due to particular changes in their signals. Interestingly, these profiles underwent pronounced changes during EP and TS that were not noticed when using conventional methods, but were indicative of the beginning of the B. thuringiensis cell differentiation

process.

Article

CIENCIAS AGROPECUARIAS Y BIOTECNOLOGÍA Cell differentiation Dielectric spectroscopy Bacillus thuringiensis On-linemeasuring Resistance (R) Reactance (X)

Luminescent Devices Based on Silicon-Rich Dielectric Materials

LILIANA PALACIOS HUERTA MARIANO ACEVES MIJARES LILIANA LICEA JIMENEZ (2016)

Luminescent silicon‐rich dielectric materials have been under intensive research due to

their potential applications in optoelectronic devices. Silicon‐rich nitride (SRN) and silicon‐

rich oxide (SRO) films have been mostly studied because of their high luminescence

and compatibility with the silicon-based technology. In this chapter, the luminescent

characteristics of SRN and SRO films deposited by low‐pressure chemical vapor deposition

are reviewed and discussed. SRN and SRO films, which exhibit the strongest photoluminescence

(PL), were chosen to analyze their electrical and electroluminescent (EL)

properties, including SRN/SRO bilayers. Light emitting capacitors (LECs) were fabricated

with the SRN, SRO, and SRN/SRO films as the dielectric layer. SRN‐LECs emit broad EL

spectra where the maximum emission peak blueshifts when the polarity is changed. On

the other hand, SRO‐LECs with low silicon content (~39 at.%) exhibit a resistive switching

(RS) behavior from a high conduction state to a low conduction state, which produce

a long spectrum blueshift (~227 nm) between the EL and PL emission. When the silicon

content increases, red emission is observed at both EL and PL spectra. The RS behavior

is also observed in all SRN/SRO‐LECs enhancing an intense ultraviolet EL. The carrier

transport in all LECs is analyzed to understand their EL mechanism.

Book part

Dielectric Materials CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA OTRAS ESPECIALIDADES FÍSICAS OTRAS

Relationship between Polymer Dielectric Constant and Percolation Threshold in Conductive Poly(styrene)-Type Polymer and Carbon Black Composites

MARIANA CASTRO MARTINEZ SUSANA HERNANDEZ LOPEZ ENRIQUE VIGUERAS SANTIAGO (2015)

Se presenta un criterio fenomenológico para determinar el umbral de percolación en compuestos poliméricos polímero - negro de carbono, en términos de la constante dieléctrica del polímero

SIEA

Article

dielectric constant percolation polymer composite BIOLOGÍA Y QUÍMICA

Análisis del desempeño de interconexiones fabricadas en substratos dieléctricos anisotrópicos

FRANCISCO JAVIER OLGUIN TELLEZ (2012)

This thesis presents a research about the microscale effects occurring in PCB interconnections associated with the anisotropy of the substrate. Two effects are considered: i) resonances originated by the fiber weave effect, and b) the impact of the anisotropy in the dielectric losses. For the case of the resonances, a model was developed using a 3D simulator, whereas the impact of the substrate anisotropy on the variation of the dielectric properties with the line position and orientation is analyzed through measurements. For the latter case, three pairs of microstrip lines were fabricated at 0°, 7°, and 15° with respect of the substrate weave in order to carry out the corresponding analysis. The frequency range of our interest covers from 50 MHz to 50 GHz since this range is required for communication channels transmitting signals up to approximately 30 Gbps.

The attenuation constant was experimentally obtained for the fabricated lines. Subsequently, the dielectric and conductor losses were separated from the experimental attenuation. It is important to mention that the dielectric losses presented an unexpected behavior (i.e. non linear variation with frequency). This behavior is originated by the microscale effects as explained in this document.

The results obtained in this thesis will allow PCB designers to select the appropriate layout for a particular application operating under specific frequency ranges while reducing the undesired microscale effects occurring on high-speed interconnects.

En esta tesis se presenta un estudio acerca de los efectos debidos al substrato en las interconexiones en las PCBs. Se consideran los siguientes dos efectos: resonancias originadas por el efecto de fibra de vidrio y el impacto que tiene la anisotropía en las pérdidas por dieléctrico. Para el caso de las resonancias, se realizó un modelo, en HFSS, para obtener la frecuencia de resonancia. En el caso de la anisotropía del substrato, se realizaron mediciones experimentales en 3 pares de líneas, que se encuentran a 0º, 7º y 15º con respecto al tejido horizontal de la tarjeta de prueba. El rango de frecuencias medido fue hasta los 50 GHz. Y los pares de líneas son microstrip depositados en dos tipos de substrato.

A partir de estas mediciones se obtuvo la constante de atenuación, la cual posteriormente es separada en sus contribuciones debidas al conductor y al dieléctrico. Es importante mencionar que las pérdidas por dieléctrico presentaron un comportamiento no esperado (y que no ha sido reportado en el estado del arte), por lo que se buscaron los posibles motivos del origen de esta discrepancia. Sin embargo, las posibles causas no satisficieron completamente este comportamiento, por lo que se reportan para posibles trabajos futuros.

Describir correctamente este comportamiento permitiría plantear modelos que representen estas pérdidas en función del ángulo de la línea de transmisión y las características geométricas de las líneas. En este sentido, habría grandes beneficios para el diseño de la circuitería de los PCBs. Encontrado este efecto hasta los 10 GHz ayudaría a disminuir las pérdidas y mejorar la integridad de las señales transmitidas, en especial aquéllas de alta frecuencia.

Master thesis

Transmission lines PCB Anisotropic media Dielectric losses Wave propagation Microstrip lines CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA