My PhD thesis consists in a multi-frequency approach to High Mass X-ray Binaries (HMXBs), using infrared and X-ray data. On one side, my research project aimed at the identification and characterization of IR counterparts to obscured HMXBs in the Scutum and Norma inner galactic arms. The identification of optical/IR counterparts to HMXBs is a necessary step to undertake detailed studies of these systems. With data limited to the high-energy range, the understanding of their complex structure and dynamics cannot be complete. In the last years, INTEGRAL has revealed the presence of an important population of heavily absorbed HMXBs in the Scutum and Norma regions, virtually unobservable below 4 keV. Optical counterparts to these obscured sources are hardly observable, due to the high interstellar extinction. I selected candidate counterparts by means of a photometric search for emission-line stars in the error boxes of the X-ray sources detected by INTEGRAL. With this objective, I built up (Brγ-K)-(H-K) and (HeI-K)-(H-K) IR color-color diagrams, in which emission-line stars are expected to show up below the absorption-line stars sequence. I applied this technique to search for counterparts to Be/XRBs, whose transient nature prevents the counterpart identification with follow-up X-ray observations with high spatial resolution. For each field, one to four candidate counterparts were identified. I also took spectra of proposed counterparts. The confirmation and spectral classifications of the systems led to unveil the nature of nine INTEGRAL objects. On the other hand, the work intended to provide for the first time a systematic study of four Be/XRBs during giant (type II) outbursts. I employed RXTE data, applying the three techniques of color-color/hardness-intensity diagrams (CD/HID), spectral fitting and Fourier power-spectral analysis, simultaneously, and using the retrieved results and correlations to try to define and characterize spectral states for this class of systems. In this way I followed both a model-independent (CD/HID) and model-dependent approach (spectral fits) to investigate the rapid aperiodic variability as a function of spectral sates in HMXBs. I obtained lightcurves, energy and power spectra for a total number of 320 observations. From X-ray colors, spectral and timing fitting, I clearly identified in all the four systems two different spectral states, i.e. the Diagonal Branch (DB) and Horizontal Branch (HB). The HB corresponds to a lower-flux state, with larger rms than the DB. Also, the power-law photon index decreases with flux in the HB, while stays constant or increases in the DB. The HB shows lower characteristic frequencies of the noise components than in the DB. The cyclotron resonant scattering features are generally associated with the DB, while absent or weaker during the DB. We showed how the transition between the two states may correspond to the transition from the standing shock emission to the thermal mound emission due to the turning point from super-Eddington luminosity regime (DB) to sub-Eddington luminosity regime (HB). From color, spectral and timing point of view, differences among systems easily distinguishes two subgroups, with the slower pulsars, KS 1947+300 and EXO2030+375, on one side, and the faster ones, 4U 0115+63 and V 0332+53, on the other. The first group is characterized by softer spectra in the HB compared with the other systems. Hysteresis is not observed in the slower pulsars, while it is evident in V 0332+53 and 4U 0115+63. Cyclotron resonant scattering features are crucial in the spectral shape of V 0332+53 and 4U 0115+63, where also a harmonic is observed in the 3-30 keV energy range. They are instead absent or very weak in the first group. According to timing features, a strong difference between the two groups is the presence of QPOs in the faster pulsars. / El trabajo de tesis consiste en un estudio multifrecuencia de Binarias de rayos X de Alta Masa (HMXBs), utilizando datos infrarrojos y en banda X. E n l o s úl t i m o s a ñ o s l a m i s i ó n I N T E G R A L d e l a A g e n c i a E s p a c i a l E u r o p e a h a r e v e l a d o l a p r e s e n c i a d e u n a i m p o r t a n t e p o b l a c i ó n d e H M X Bs e n l o s b r a z o s g a l ác t i c o s d e S c u t u m y N o r m a . E n e f e c t o , l a m a y o r í a d e l a s n u e v a s H M X Bs d e s c u b i e r t a s p o r INTEGRAL e s t án f u e r t e m e n t e a b s o r b i d a s , v i r t u a l m e n t e i n o b s e r v a b l e s a e n e r g ía s i n f e r i o r e s a l o s 4 k e V . E s o e x p l i c a c o m o n o f u e r o n d e t e c t a d a s p o r l a s m i s i o n e s d e r a y o s X a n t e r i o r e s a I N T E G R A L . L a s c o n t r a p a r t i d a s ó p t i c a s d e e s t a s f u e n t e s o s c u r e c i d a s s o n d i f í c i l m e n t e o b s e r v a b l e s a c a u s a d e l a e l e v a d a e x t i n c i ó n i n t e r e s t e l a r. Por un lado, el objetivo de este proyecto fue la i d e n t i f i c a c i ó n d e c o n t r a p a r t i d a s i n f r a r r o j a s a l a s f u e n t e s d e r a y o s g a m m a d e s c u b i e r t a s p o r I N T E G R A L . La identificación se llevó a cabo a partir de fotometría en las bandas H, K, Br y HeI, y espectroscopía de resolución intermedia en la banda K. Para cada campo de INTEGRAL analizado se identificaron de una a cuatro posibles contrapartidas; nueve objetos desconocidos fueron clasificados como HMXBs. Por otro lado, se llevó a cabo el primer estudio sistemático de cuatro HMXBs durante outbursts gigantes, con el objetivo de definir estados espectrales en esta clase de binarias de rayos X. Utilizando datos del satélite RXTE, se extrajeron curvas de luz, espectros de energía y espectros de potencia de 320 observaciones. A través de los tres diferentes tipos de análisis (colores en banda X, ajustes espectrales y temporales), se identificaron en todas las fuentes dos estados espectrales, denominados “Rama Horizontal” (HB) y “Rama Diagonal” (DB). Al mismo tiempo, las diferencias entre las fuentes analizadas permitieron definir dos subgrupos de sistemas, con características espectrales y temporales propias: por una lado los púlsares lentos, y por otro los más rápidos.

The interiors of the stars are among the most difficult parts of the Universe to observe. Essentially, asteroseismology tries to make use of the oscillations to prove the stellar interiors, which are not directly observable. The basic principles of asteroseismology are, to a certain extent, similar to those developed and employed by Earth seismologists. Asteroseismology relies on advanced mathematical descriptions of oscillations in a three-dimensional body and numerical modeling. It is therefore a prominent example of interdisciplinary science. The general aim of this work is the study of Be stars with the CoRoT space mission. Classical Be stars are B-type stars that exhibit line emission over the pho- tospheric spectrum. The excess is attributed to a circumstellar gaseous component that is commonly accepted to be in the form of an equatorial disk. The mechanisms responsible for the production and dynamics of the circumstellar gas are still not constrained. Observations of non-radial pulsation beating phenomena connected to outbursts point toward a relevance of pulsation, but this mechanism cannot be gene- ralized. In this regard, the observation of classical Be stars with the high-precision CoRoT satellite is providing important keys to understand the physics of these objects and the nature of the Be phenomenon. In order to study the light variations of the selected stars we use photometric and spectroscopic observations. These observations allow us to extract frequencies, amplitudes and phases of these variations. As we will show, these light variations can be connected with pulsations on the stellar surface. For carrying out the frequency analysis we have developed a new code based on standard Fourier analysis. The point is that this code, called pasper, allows the frequency analysis of large sets of light curves in an automatic mode. This Ph.D. thesis is arranged as follows: In the first three Chapters we describe the scientific framework of this project, giving a brief description on Asteroseismology, presenting the current status of Be stars, and describing the basics of the Fourier analysis and the rudiments of the time series analysis. At the early begin of this Ph.D. thesis, the CoRoT satellite was still on ground getting ready for the launch. In this context, we perform a search for shortperiod B and Be star variables in the low metallicity environment of the Magellanic Clouds. This study constitutes the Part I of this Ph.D. thesis. This Part has a double goal: i) to test the frequency analysis codes; and ii) to detect observationally β Cephei and SPB-like B-type pulsators in low metallicity environments, actually not predicted by the pulsational theory and models. This constitutes the Part I. Part II is devoted to the study of Be stars with the CoRoT space mission. Here we depict a complete review on the CoRoT mission. We also describe the results on the analysis of three Be stars from the CoRoT exoplanet field. Finally, we present the results on the frequency analysis of the late Be star HD 50 209, observed in the seismology field of the CoRoT satellite. The analysis of this Be star has revealed up to sixty frequencies, grouped in six different and separated sets, attributed to g-mode pulsations. Finally, we resume the main conclusions of the whole project, including prospects and future work to be done. An addendum with all the published results derived from this project has been added at the end of this Part II. Part III encloses the Appendixes, providing a brief summary of this work in Spanish, a complete description on basic equations of non-radial oscillation, the user guide of the PASPER code and the user guide of the KURTZ_BOS code. / El objetivo de la asterosismología es describir el interior de las estrellas a partir de las oscilaciones. El interior de las estrellas es, posiblemente, el lugar más difícil de estudiar de todo el Universo, ya que las condiciones especiales que allí se dan no pueden reproducirse en ningún laboratorio terrestre. Así, la importancia de esta ciencia en el estudio global de la física estelar es crucial. Los principios básicos de la asterosismología son, en esencia, similares a los que los geólogos usan en el estudio de terremotos terrestres. La asterosismología hace uso de descripciones matemáticas de las oscilaciones en cuerpos tridimensionales, creando para ello sofisticadas simulaciones numéricas. Es, por tanto, un claro ejemplo de ciencia multidisciplinar. El objetivo general de esta Tesis Doctoral es el estudio de las estrellas Be con las misión espacial CoRoT. Las estrellas Be son objetos de secuencia principal, con alta velocidad de rotación, que presentan un exceso infrarrojo y emisión en las líneas de Balmer, debido a la presencia de una envoltura circumestelar concentrada en el ecuador y generada por eyecciones discretas de materia originado por mecanismos que todavía no son bien conocidos. Los mecanismos propuestos para explicar la eyección de materia son hasta ahora, las pulsaciones no radiales combinadas con la alta velocidad de rotación característica de este tipo de estrellas. La observación de estrellas Be con el satélite de alta precisión CoRoT está aportando claves importantísimas para comprender la física de estos objetos y la naturaleza del fenómeno Be. Para la detección de señales periódicas en las estrellas seleccionadas utilizamos tanto observaciones fotométricas como espectroscópicas. A partir de las observaciones obtenemos las frecuencias, amplitudes y fases de las variaciones. Como se muestra en la tesis, las variaciones en las curvas de luz estudiadas podrían estar estrechamente relacionadas con los mecanismos de pulsación estelar. Para realizar el análisis de frecuencias hemos desarrollado un código basado en técnicas estándar de análisis de Fourier. Este código, llamado Pasper, nos permite analizar grandes conjuntos de datos de forma casi automática.

The work carried out during this Thesis is framed within the field of Numerical Cosmology and focused on several broad lines intimately related which deal with the theoretical and numerical study of galaxy clusters: (i) the halo-finding problem, (ii) new improvements in cosmological simulations, and (iii) the formation and evolution of galaxy clusters. In spite of the achievements reached by Computational Cosmology in the last years, present-day hydrodynamics/N-body simulations still present important discrepancies with the observations, especially in the inner regions of massive galaxy clusters. Among these discrepancies we can cite, for instance, the breaking up of the self-similar scaling relations or the cooling flow problem. These discrepancies have motivated the idea that, besides gravity and adiabatic gas dynamics, non-gravitational processes related with the baryonic component of the Universe need to be included in our simulations. Within this context, in a complementary way to the different non-gravitational processes being included in simulations, it is crucial to properly describe different gravitational processes inherent to the hierarchical formation of cosmic structures itself. In this sense, the objective of the present work is to describe, in a consistent way, some of the heating processes associated with the hierarchical evolution of galaxy clusters in a full cosmological context. To identify the different cosmological structures and analyse their evolutionary histories, an Eulerian cosmological code and a grid-based halo finder have been used. The cosmological code used during this Thesis, MASCLET (Quilis, 2004), is an Eulerian code based on an adaptive mesh refinement (AMR) scheme able to model the coupled evolution of the dark matter and the baryonic components of the Universe. To analyse the outputs of these complex simulations, a new halo finder based on the spherical overdensity method (SO) has been developed (ASOHF, Planelles & Quilis, 2010). This finder allows us to extract the dark matter haloes (numerical counterpart of galaxies and galaxy clusters) and analyse, in a precise way, their main physical properties. Making use of these numerical tools, MASCLET and ASOHF, the role played by galaxy cluster mergers, as well as by the cosmological shock waves developed during these events, as sources of heating of the intracluster medium (ICM) has been analysed in a full cosmological context. In order to do so, two simulations have been performed with the MASCLET code. In these simulations, the unique relevant feedback mechanism considered is the gravitational, that is, the inherent to the hierarchical evolution of the Universe. Analysing these simulations it has been demonstrated that galaxy cluster mergers and cosmological shock waves play a crucial role, not only on galaxy cluster properties, but on the thermalization of the ICM. In particular, it has been demonstrated that galaxy cluster mergers have a direct influence on the existence of cool cores in the centre of massive galaxy clusters as well as on the scatter observed in the self-similar scaling relations (Planelles & Quilis, 2009). On the other hand, shock waves are also crucial in galaxy cluster properties contributing very efficiently to the virialization of haloes and the thermalization of the Universe. Moreover, it has been observed that the strength of shocks within the virial radius of galaxy clusters shows some correlation with their virial masses, being directly related with their dynamical histories. / La presente Tesis se centra en varias líneas de investigación íntimamente relacionadas que tratan con el estudio teórico y numérico de los cúmulos de galaxias: (i) el problema de encontrar los halos de materia oscura, (ii) nuevas mejoras en simulaciones cosmológicas y, (iii) la formación y evolución de los cúmulos de galaxias. Las simulaciones hidrodinámicas/N-cuerpos actuales todavía presentan importantes discrepancias con las observaciones, especialmente en las regiones internas de los cúmulos de galaxias más masivos. Entre estas discrepancias podemos citar, por ejemplo, la ruptura de las relaciones de la escala auto-semejantes o el problema de los flujos de gas frío. Estas discrepancias han motivado la idea de que, además de gravedad y dinámica de gases adiabática, procesos no gravitacionales relacionados con la componente bariónica del Universo deben ser incluidos en las simulaciones. En este contexto, de forma complementaria a diferentes procesos no gravitacionales, es crucial describir de forma adecuada los distintos procesos gravitacionales inherentes a la propia formación jerárquica de la estructuras cósmicas. En este sentido, el objetivo del presente trabajo es describir, de forma auto-consistente, algunos de los procesos de calentamiento asociados a la propia evolución jerárquica de los cúmulos de galaxias en un contexto puramente cosmológico. Para ello, se ha hecho uso de un código cosmológico euleriano (MASCLET, Quilis, 2004) y un buscador de halos basado en el método de sobredensidad esférica (ASOHF, Planelles y Quilis, 2010). Haciendo uso de estos códigos, se ha analizado el papel que juegan las fusiones de cúmulos de galaxias y las ondas de choque generadas durante estos eventos como fuentes de calentamiento del medio intracúmulo en un contexto puramente cosmológico. En este sentido, se ha comprobado que las fusiones de cúmulos de galaxias influyen directamente en la existencia de núcleos fríos en el centro de los cúmulos más masivos, así como en la dispersión observada en las relaciones de escala auto-semejantes (Planelles y Quilis, 2009). Por otra parte, también se ha comprobado que las ondas de choque contribuyen eficientemente a la virialización de los halos y a la termalización del Universo.

In this thesis, we tackle several open problems in the study of large-scale structure through the clustering of galaxies. To this end, we analyse data from some of the latest surveys, and we also develop new statistical techniques needed for this analysis in specific cases. In the first part, we focus on small and intermediate scales, where the relation between galaxy properties and their clustering (known as segregation) is important. The work in this part is driven by the exploitation of data from the ongoing Advanced Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey, which is perfectly suited to study the evolution of segregation trough cosmic time. We developed a method for the recovery of the real-space clustering from photometric surveys with the characteristics of ALHAMBRA. This method is based on the use of the projected correlation function, and is adapted to data with typical photometric redshift errors Dz < 0.015(1+z). We tested the method using N-body simulations, and then applied it to the calculation of the correlation function for several samples drawn from the ALHAMBRA survey. We divided our sample in three redshift bins, and selected several galaxy samples in each of them based on B-band luminosity. In the range of scales studied, the correlation function for all samples was well fitted by a power law. We observed as well the effects of evolution, and of luminosity segregation. We also reviewed the basic tools available in the framework of the statistics of marked point processes to study galaxy segregation. We illustrated their application using a galaxy sample drawn from the 2dFGRS, characterised by a spectral classification parameter. We introduced the mark connection function, showing that it gives valuable information when analysing different galaxy populations defined by some set of galaxy characteristics. In the second part, we focus on the study of a large scale feature of the galaxy distribution, the baryon acoustic oscillations (BAO). We measured the two-point correlation function for several samples drawn from the largest surveys to date, 2dFGRS and SDSS. We obtained a peak corresponding to BAO at the expected scale in all cases, which shows the reliability of the detection of this feature. Finally, we developed a new method for the analysis of the BAO phenomenon. This method makes use of the possibilities of wavelets methods to look for the actual structures in configuration space which are responsible for the BAO. It is also based on the use of two complementary mass tracers, and we illustrated it using a catalogue formed by 'Main' and Luminous Red Galaxy samples from SDSS. In this way, we showed how we were able not only to detect BAO in the samples, but also to localise regions giving lower or higher BAO signal. This kind of information is completely lost when using the traditional two-point statistics methods. / En aquesta tesi, estudiem diferents problemes oberts en l'estudi de l'estructura a gran escala mitjançant l'agrupament de les galàxies. Per aquest fi, analitzem dades provinents de diversos cartografiats, i desenvolupem noves tècniques estadístiques necessàries per aquesta anàlisi en casos específics. En la primera part, ens centrem en escales petites i intermèdies. El treball en aquesta part està dirigit a l'explotació de les dades del cartografiat Advanced Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey, que és apropiat per l'estudi de l'evolució de la segregació amb el temps còsmic. Desenvolupem un mètode per la recuperació de la funció de correlació en l'espai real a partir de cartografiats fotomètrics com ALHAMBRA. Provem aquest mètode emprant simulacions, i posteriorment l'apliquem al càlcul de la funció de correlació per diferents mostres del cartografiat ALHAMBRA, seleccionades en funció del redshift i la lluminositat. Obtenim que la funció de correlació de les diferents mostres es comporta com una llei de potències, i s'observen els efectes de l'evolució i de la segregació per lluminositat. També examinem les eines bàsiques disponibles en el formalisme de l'estadística de marques per a l'estudi de la segregació de galàxies, i il•lustrem la seua aplicació emprant dades del cartografiat 2dFGRS. En la segona part, ens centrem en l'estudi d'una característica de la distribució de galàxies a gran escala, les oscil•lacions acústiques bariòniques (BAO). Mesurem la funció de correlació per diferents mostres dels cartografiats 2dFGRS i SDSS, obtenint un pic corresponent a les BAO a l'escala esperada en tots els casos, el que mostra la fiabilitat de la detecció. Finalment, desenvolupem un nou mètode per l'anàlisi de les BAO, basat en un mètode d'ondetes per cercar les estructures responsables per les BAO en l'espai de configuració. Il•lustrem el funcionament del mètode emprant una mostra del SDSS, i mostrem com no només podem detectar les BAO en la mostra, sinó també localitzar les regions que donen un menor o major senyal de les BAO.

Les matériaux semi-conducteurs à grand gap tels que le carbure de silicium (SiC) et le nitrure de gallium (GaN) sont utilisés pour fabriquer des composants semi-conducteurs de puissance, qui vont jouer un rôle très important dans le développement des futurs systèmes de conversion d'énergie. L'objectif est de réaliser des convertisseurs avec de meilleurs rendements énergétiques et fonctionnant à haute température. Pour atteindre cet objectif, il est donc nécessaire de bien connaître les caractéristiques de ces nouveaux composants afin de développer des modèles qui seront utilisés lors de la conception des convertisseurs. Cette thèse est donc dédiée à la caractérisation et la modélisation des composants à grand gap, mais également l'étude des dispositifs de mesure des courants des commutations des composants rapides. Afin de déterminer les caractéristiques statiques des composants semi-conducteurs, une méthode de mesure en mode pulsé est présentée. Dans le cadre de cette étude, une diode SiC et un JFET SiC "normally-off" sont caractérisés à l'aide de cette méthode. Afin de mesurer les capacités inter-électrodes de ces composants, une nouvelle méthode basée sur l'utilisation des pinces de courant est proposée. Des modèles comportementaux d'une diode Si et d'un JFET SiC sont proposés en utilisant les résultats de caractérisation. Le modèle de la diode obtenu est validé par des mesures des courants au blocage (recouvrement inverse) dans différentes conditions de commutation. Pour valider le modèle du JFET SiC, une méthode de mesure utilisant une pince de courant de surface est proposée. / Compared to traditional silicon (Si) semiconductor material, wide bandgap (WBG) materials like silicon carbide (SiC) and gallium nitride are gradually applied to fabricate power semiconductor devices, which are used in power converters to achieve high power efficiency, high operation temperature and high switching frequency. As those power devices are relatively new, their characterization and modeling are important to better understand their characteristics for better use. This dissertation is mainly focused on those WBG power semiconductor devices characterization, modeling and fast switching currents measurement. In order to measure their static characteristics, a single-pulse method is presented. A SiC diode and a "normally-off" SiC JFET is characterized by this method from ambient temperature to their maximal junction temperature with the maximal power dissipation around kilowatt. Afterwards, in order to determine power device inter-electrode capacitances, a measurement method based on the use of multiple current probes is proposed and validated by measuring inter-electrode capacitances of power devices of different technologies. Behavioral models of a Si diode and the SiC JFET are built by using the results of the above characterization methods, by which the evolution of the inter-electrode capacitances for different operating conditions are included in the models. Power diode models are validated with the measurements, in which the current is measured by a proposed current surface probe.

Les nanocristaux semi-conducteurs possèdent des tailles qui se situent entre celles des molécules et des matériaux cristallins. Leurs propriétés physiques sont donc dominées par des effets de confinement quantique et par des états électroniques discrets. Une étude approfondie de leur structure électronique et en particulier de la localisation des porteurs de charge s’avère nécessaire pour pouvoir à plus long terme faire de l’ingénierie de structure de bande des hétérostructures semi-conductrices. La microscopie à effet tunnel est l’outil idéal pour imager et sonder les propriétés électroniques de nanocristaux. Le système peut être comparé à une jonction tunnel à doublé barrière tunnel (chapitre 1). Pour caractériser les effets de Coulomb dans des objets quantiques par spectroscopie tunnel (technique détaillée au chapitre 2), mes travaux de recherche ont tout d’abord porté sur un système modèle : une liaison pendante silicium, dont l’état de charge a pu être modifié de manière contrôlée (chapitre 3). Des nanocristaux cœur-coquille (PbSe/CdSe) à symétrie sphérique ont ensuite été étudiés (chapitre 4). Contrairement aux nanocristaux sans coquille, les expériences révèlent que le transport est dominé par le même type de porteurs de charge à polarisation positive et négative de la jonction. Ces mesures donnent également accès à l’énergie de charge des nanocristaux. Un régime de transport similaire est obtenu pour des nanobâtonnets constitués d’un cœur sphérique CdSe enfermé dans un bâtonnet de CdS (chapitre 5), démontrant la reproductibilité des phénomènes observés par l’hétérostructures cœur-coquille. / Semiconductor colloidal nanocrystals are quite attractive, because of their physical properties, such as discrete energy levels. However, devices prepared from semiconductor nanocrystals are still facing limitations due to a high environmental sensitivity of their organic shell. In order to increase their optical properties, core-shell nanocrystals have thus been synthesized. Scanning tunneling microscopy is the appropriate tool to image and probe the electronic properties of individual nanostructures and. This system can be compared to a double barrier tunnel junction, where the transport properties are governed by the transmission probability across both potential barriers (chapter 1). In order to investigate the Coulomb effect in those quantum objects by tunneling spectroscopy (this technique being described in chapter 2), the thesis has first focussed on a prototypical model: an isolated silicon dangling bond, where its charge state has been changed in a controlled manner (chapter 3). Then, PbSe/CdSe core-shell nanocrystals have been studied and a general method is described to correctly identify the electrical nature of the charge carriers in the tunneling spectra (chapter 4). In contrast to the core nanocrystals the transport through core-shell structures reveals, for a majority of nanocrystals, that the same type of charge carrier tunnel on both sides of the apparent gap. Charging peaks are also observed and allow the measurements of the charging energy in these systems. A similar transport regime is obtained for CdSe/CdS dot in rod nanocrystals (chapter 5), demonstrating the reproducibility of the characterized transport phenomena of nanoheterostructure.

Dissertação apresentada para obtenção do grau de Doutor em Engenharia Civil, na Faculdade de Engenharia da Universidade do Porto

Le développement des nanotechnologies passe par la mise au point de nouveaux instruments adaptés à la caractérisation de la matière à l'échelle nanométrique. Le Nanoprobe acquis par l'IEMN au début de ma thèse répond à cet enjeu. Cet instrument constitué d'une plateforme de Microscopie à Effet Tunnel à Quatre-Pointes (4T-STM) et surmontée d'un Microscope Électronique à Balayage (MEB) a pour vocation d'effectuer des analyses, contrôles et tests de nanomatériaux et composants électroniques.Après une description détaillée du fonctionnement de cet appareil (chapitre 2), une première étude a été réalisée pour déterminer l'influence de l'irradiation électronique sur des nanostructures semi-conductrices, à savoir ici des nanofils d'InAs (chapitre 3). Sous irradiation, les fils deviennent quasi-métalliques. Grâce à des mesures originales du transport dans des nanofils semi-suspendus, ce changement des propriétés électriques est attribué à la formation de défauts chargés à la surface des fils. L'ionisation par impact est un phénomène responsable de la multiplication des porteurs dans les cellules photovoltaïques. Le quatrième chapitre démontre l'intérêt du Nanoprobe à caractériser ce phénomène sur un système modèle, une jonction p-n de silicium. Alors que deux pointes en contact polarisent la diode, une troisième injecte localement par effet tunnel des électrons possédant une énergie bien définie. La mesure de porteurs supplémentaires démontre le phénomène d'ionisation par impact avec une résolution inégalée jusqu'à présent. / The advent of nanotechnology involves the development of an instrumentation capable of investigating the matter at this scale. The Nanoprobe acquired by IEMN at the beginning of my thesis brings technical solutions to this issue. This instrument consisting of a Four-Tip Scanning Tunneling Microscopy platform (4T-STM) and topped with a Scanning Electron Microscope (SEM) is dedicated to perform analysis, inspections and tests on nanomaterials and electronic devices. After a detailed description of this instrument (Chapter 2), a first study was conducted to determine the influence of electron irradiation on semiconductor nanostructures, InAs nanowires are treated here. Under irradiation, the nanowires become quasi-metallic. Thanks to original transport measurements on freestanding nanowires, this change of the electrical properties is attributed to the formation of charged defects on the surface of nanowires. The impact ionization is a phenomenon responsible for carrier multiplication in solar cells. The fourth chapter shows the ability of the Nanoprobe to characterize this phenomenon in a typical model, a silicon p-n junction. While 2 tips in contact polarize the diode, a third one locally injects tunneling electrons that have a well defined energy. The measurement of supplementary carriers proves that impact ionization occurs and can be measured with a resolution never reached before.

Cette thèse aborde une approche originale de réalisation de composants organiques (transistors, mémoires volatiles et non volatiles) à base d’un semiconducteur de type N “PolyeraTM N2200”. Tout d’abord, des transistors à effet de champ ont été fabriqués et optimisés en améliorant notamment certains paramètres technologiques. Par la suite, ces transistors ont été simulés à l’aide du logiciel ISE TCAD®, un logiciel basé sur un modèle 2D à effet de champ et de dérive-diffusion. Les propriétés électriques de ces dispositifs organiques ont été étudiées en fonction de l’influence de la mobilité des porteurs, des densités des pièges, et de leur énergie… . Les effets des pièges d'interface ont également été pris en considération. Par ailleurs, on y incorporant une couche de nanoparticules d’or (NP’s Au), on a réussi à développer des composants appelés « NOMFET » qui miment le comportement d’une synapse biologique tout en reproduisant les effets dépressifs et facilitateurs avec une amplitude relative de 50% et une réponse dynamique de l’ordre de 4s. En étudiant la dynamique de chargement et de déchargement des NP’s d’or, on a mis en évidence une fonction d’apprentissage anti-Hebbienne, un des mécanismes fondamentaux de l’apprentissage non-supervisé d’une synapse inhibitrice dans un réseau de neurones biologiques. Finalement, des mémoires FLASH, ont été réalisées en combinant des NP’s d’or avec des monofeuillets d’oxyde de graphène réduit (rGO). Ces mémoires « FLASH » appelées aussi mémoires à double grille flottante montrent une large fenêtre de mémorisation (~68V), un temps de rétention élevé (>108s) et d’excellentes propriétés d’endurance (1000 cycles d’écriture/effacement). / The subject of this thesis adopt an original approach to realize new components (transistor, volatile and non-volatiles memory) based on N type organic semiconductor “PolyeraTM N2200”. First, we have fabricated and optimized organic field effect transistors by modifying some technological parameters related to fabrication. Then, we have analyzed their electrical properties with the help of two-dimensional drift-diffusion simulator using ISE-TCAD®. We studied the fixed surface charges and the effect of the organic semiconductor/oxide interface traps. The dependence of the threshold voltage on the density and energy level of the trap states has been also considered. , by incorporating gold nanoparticles in these devices, we have developed a new device called “NOMFETs” (nanoparticles organic memory field effect transistors), which mimic the behavior of biological synapse by reproducing a facilitating and a depressing drain current with a relative amplitude of about 50% and a dynamic response of about 4s. Studying the charging/discharging dynamics, we demonstrated a typical anti-Hebbien learning function, one of the fundamental mechanisms of the unsupervised learning in biological neural networks. Finally, we developed nonvolatile “FLASH” memory devices, by combining metallic gold nanoparticles and reduced graphene oxide (rGO) monolayer flakes. This double floating gate architecture provided us a good charge trapping ability which include a wide memory window (~68V), a long extrapolated retention time (> 108 s) and strong endurance properties (1000 write/erase cycles).

Avec la miniaturisation des composants optoélectroniques, contrôler la surface de leur constituants actifs devient prépondérant. C’est en particulier vrai pour les nanofils semi-conducteurs dont la géométrie favorise un rapport surface sur volume élevé. L’objectif de cette thèse consiste donc à mener une étude précise de la structure cristallographique et électronique de leur surface et à déterminer à quel point cette surface affecte leurs propriétés physiques globales. Ce travail commence par une description détaillée de la croissance des nanofils III-V en insistant sur l’intérêt de fabriquer des ensembles de nanofils uniformes, condition nécessaire pour assurer une grande reproductibilité des résultats. Il se poursuit par un éclairage sur une technique de choix pour analyser la surface des nanofils, la microscopie à effet tunnel, et une technique d’encapsulation des nanofils pour préserver leur surface de toute contamination. L’intérêt de ces deux techniques est démontré au travers de l’étude de la surface de nanofils GaAs et InAs pour expliquer comment la désorption d’une couche protectrice d’arsenic conduit à des morphologies de surface différentes. L’expertise ainsi acquise est alors mise à profit pour caractériser des nanofils GaAs cœur-coquille, dont la coquille est fabriquée à basse température. Au travers de l’identification des défauts rencontrés dans la coquille, cette dernière se révèle posséder des propriétés similaires à celles de films GaAs fabriqués à basse-température. La durée de vie limitée des porteurs de charge photoexcités est alors exploitée pour étudier les effets induits par les défauts sur les propriétés d’émission THz de nanofils à base de GaAs. / With the size reduction of optoelectronic devices, controlling the surface of semiconductor materials is becoming crucial to optimize their performances. This is particularly true for one-dimensional systems such as semiconductor nanowires that are subject to high surface-to-volume ratio. The aim of this thesis is therefore to perform a comprehensive study of the surface properties of III-V semiconductor nanowires and to determine to what extent they affect their overall properties. Starting with a description of the basic principles that govern their growth in order to obtain nanowire ensembles with a good uniformity, we then highlight a surface science tool, scanning tunneling microscopy, and a surface preparation technique, based on the use of a protective arsenic layer, that are key to further understand the structural and electronic properties of the surface of self-catalysed GaAs and InAs semiconductor nanowires. In the fourth part of this work, we apply these techniques to analyse the structural and electronic properties of GaAs core-shell nanowires consisting of a thin shell grown at low temperature. We show the similarity of the shell properties with low-temperature grown GaAs thin film through the identification of their point defects and finally compare the THz properties of these nanowires with GaAs nanowires. The importance of the shell in the dynamics of the free charge carriers is demonstrated from the analysis of the THz waveforms.