In modern low pressure plasma discharges, the electron mean free path often exceeds the device dimensions. Under such conditions the electron velocity distribution function may significantly deviate from Maxwellian, which strongly affects the discharge properties. The description of such plasmas has to be kinetic and often requires the use of numerical methods. This thesis presents the study of kinetic effects in inductively coupled plasmas and Hall thrusters carried out by means of particle-in-cell simulations. The important result and the essential part of the research is the development of particle-in-cell codes. <p>An advective electromagnetic 1d3v particle-in-cell code is developed for modelling the inductively coupled plasmas. An electrostatic direct implicit 1d3v particle-in-cell code EDIPIC is developed for plane geometry simulations of Hall thruster plasmas. The EDIPIC code includes several physical effects important for Hall thrusters: collisions with neutral atoms, turbulence, and secondary electron emission. In addition, the narrow sheath regions crucial for plasma-wall interaction are resolved in simulations. The code is parallelized to achieve fast run times. <p>Inductively coupled plasmas sustained by the external RF electromagnetic field are widely used in material processing reactors and electrodeless lighting sources. In a low pressure inductive discharge, the collisionless electron motion strongly affects the absorption of the external electromagnetic waves and, via the ponderomotive force, the density profile. The linear theory of the anomalous skin effect based on the linear electron trajectories predicts a strong decrease of the ponderomotive force for warm plasmas. Particle-in-cell simulations show that the nonlinear modification of electron trajectories by the RF magnetic field partially compensates the effects of electron thermal motion. As a result, the ponderomotive force in warm collisionless plasmas is stronger than predicted by linear kinetic theory. <p>Hall thrusters, where plasma is maintained by the DC electric field crossed with the stationary magnetic field, are efficient low-thrust devices for spacecraft propulsion. The energy exchange between the plasma and the wall in Hall thrusters is enhanced by the secondary electron emission, which strongly affects electron temperature and, subsequently, thruster operation. Particle-in-cell simulations show that the effect of secondary electron emission on electron cooling in Hall thrusters is quite different from predictions of previous fluid studies. Collisionless electron motion results in a strongly anisotropic, nonmonotonic electron velocity distribution function, which is depleted in the loss cone, subsequently reducing the electron wall losses compared to Maxwellian plasmas. Secondary electrons form two beams propagating between the walls of a thruster channel in opposite radial directions. The secondary electron beams acquire additional energy in the crossed external electric and magnetic fields. The energy increment depends on both the field magnitudes and the electron flight time between the walls. <p>A new model of secondary electron emission in a bounded plasma slab, allowing for emission due to the counter-propagating secondary electron beams, is developed. It is shown that in bounded plasmas the average energy of plasma bulk electrons is far less important for the space charge saturation of the sheath than it is in purely Maxwellian plasmas. A new regime with relaxation oscillations of the sheath has been identified in simulations. Recent experimental studies of Hall thrusters indirectly support the simulation results with respect to the electron temperature saturation and the channel width effect on the thruster discharge.

In modern low pressure plasma discharges, the electron mean free path often exceeds the device dimensions. Under such conditions the electron velocity distribution function may significantly deviate from Maxwellian, which strongly affects the discharge properties. The description of such plasmas has to be kinetic and often requires the use of numerical methods. This thesis presents the study of kinetic effects in inductively coupled plasmas and Hall thrusters carried out by means of particle-in-cell simulations. The important result and the essential part of the research is the development of particle-in-cell codes. <p>An advective electromagnetic 1d3v particle-in-cell code is developed for modelling the inductively coupled plasmas. An electrostatic direct implicit 1d3v particle-in-cell code EDIPIC is developed for plane geometry simulations of Hall thruster plasmas. The EDIPIC code includes several physical effects important for Hall thrusters: collisions with neutral atoms, turbulence, and secondary electron emission. In addition, the narrow sheath regions crucial for plasma-wall interaction are resolved in simulations. The code is parallelized to achieve fast run times. <p>Inductively coupled plasmas sustained by the external RF electromagnetic field are widely used in material processing reactors and electrodeless lighting sources. In a low pressure inductive discharge, the collisionless electron motion strongly affects the absorption of the external electromagnetic waves and, via the ponderomotive force, the density profile. The linear theory of the anomalous skin effect based on the linear electron trajectories predicts a strong decrease of the ponderomotive force for warm plasmas. Particle-in-cell simulations show that the nonlinear modification of electron trajectories by the RF magnetic field partially compensates the effects of electron thermal motion. As a result, the ponderomotive force in warm collisionless plasmas is stronger than predicted by linear kinetic theory. <p>Hall thrusters, where plasma is maintained by the DC electric field crossed with the stationary magnetic field, are efficient low-thrust devices for spacecraft propulsion. The energy exchange between the plasma and the wall in Hall thrusters is enhanced by the secondary electron emission, which strongly affects electron temperature and, subsequently, thruster operation. Particle-in-cell simulations show that the effect of secondary electron emission on electron cooling in Hall thrusters is quite different from predictions of previous fluid studies. Collisionless electron motion results in a strongly anisotropic, nonmonotonic electron velocity distribution function, which is depleted in the loss cone, subsequently reducing the electron wall losses compared to Maxwellian plasmas. Secondary electrons form two beams propagating between the walls of a thruster channel in opposite radial directions. The secondary electron beams acquire additional energy in the crossed external electric and magnetic fields. The energy increment depends on both the field magnitudes and the electron flight time between the walls. <p>A new model of secondary electron emission in a bounded plasma slab, allowing for emission due to the counter-propagating secondary electron beams, is developed. It is shown that in bounded plasmas the average energy of plasma bulk electrons is far less important for the space charge saturation of the sheath than it is in purely Maxwellian plasmas. A new regime with relaxation oscillations of the sheath has been identified in simulations. Recent experimental studies of Hall thrusters indirectly support the simulation results with respect to the electron temperature saturation and the channel width effect on the thruster discharge.

The field of hybrid electronics of molecules and traditional semiconductors is deemed to be a realistic route towards possible use of molecular electronics. Such hybrid electronics finds its potential technological applications in nuclear detectors, near-infrared detectors, organic thin film transistors and gas sensors. Specifically Metal / organic / n-Silicon structures in this regard are mostly reported to have two regimes of charge transport at lower and higher applied voltages in such two terminal devices. The fact is mostly attributed to the change in conduction mechanism while moving from lower to higher applied voltages. These reports describe interactions between the semiconductors and molecules in terms of both transport and electrostatics but finding the exact potential distribution between the two components still require numerical calculations. The challenge in this regard is to give the exact relations and the transport models, towards practical quantification of charge transport properties of metal / organic / inorganic semiconductor devices. Some of the most exiting questions in this regard are; whether the existing models are sufficient to describe the device performances of the hybrid devices or some new models are needed? What type of charge carriers are responsible for conduction at lower and higher applied voltages? What is the source of such charge carriers in the sandwiched organic layer between the metal and inorganic semiconductors? How the transition applied voltage for the change in conduction mechanism is determined? What is the role of dopants in the organic layer semiconductors? What are the possible explanations for observed temperature effects in such devices? In present work the charge transport properties of metal / metal-phthalocyanine / n-Si structures with low (ND = 4×1014 cm-3), medium (ND = 1×1016 cm-3) and high (ND = 2×1019 cm-3) doped n-Si as injecting electrode and the effect of air exposure of the vacuum evaporated metal-phthalocyanine film in these structures is investigated. The results obtained through temperature dependent electrical characterizations of the structures suggest that in terms of dominant conduction mechanism in these devices Schottky-type conduction mechanism dominates the charge transport in low-bias region of these devices up to 0.8 V, 0.302 V and 0.15 V in case of low, medium and high doped n-Silicon devices. For higher voltages, in each case of devices, the space-charge-limited conduction, controlled by exponential trap distribution, is found to dominate the charge transport properties of the devices. The interface density of states at the CuPc / n-Si interface of the devices are found to be lower in case of lower work function difference at the CuPc / n-Si interface of the devices. The results also suggest that the work function difference at the CuPc / n-Si interface of these devices causes charge transfer at the interface and these phenomena results in formation of interface dipole. The width of the Schottky depletion region at the CuPc / n-Si interface of these devices is found to be higher with higher work function difference at the interface. The investigation of charge transport properties of Al / ZnPc / medium n-Si and Au / ZnPc / medium n-Si devices suggest that the Schottky depletion region formed at the ZnPc / n-Si interface of these devices determines the charge transport in the low-bias region of both the devices. Therefore, the Schottky-type (injection limited) and the space-charge-limited (bulk limited) conduction are observed in the low and the high bias regions of these devices, respectively. The determined width of the Schottky depletion region at the ZnPc / n-Si interface of these devices is found to be similar for both the devices, therefore, the higher work function difference at the metal / ZnPc interface of the devices has no influence on the Schottky depletion region formed at the ZnPc / n-Si interface of the devices. The similar diode ideality factor, barrier height and the width of the Schottky depletion region, determined for both of these devices, demonstrates that these device characteristics originate from ZnPc / n-Si interface of these devices. Therefore, the work function difference at the metal / ZnPc interface of these devices has no noticeable influence on the device properties originating from ZnPc / n-Si interface in these devices. The investigation of charge transport properties of Al / CuPc / low n-Si devices with and without air exposure of the CuPc film, before depositing metal contact demonstrate that Schottky-type conduction mechanism dominates the charge transport in these devices up to bias of 0.45 V in case devices with the air exposure, and up to 0.8 V in case devices without the air exposure. This decrease in the threshold voltage, for the change in conduction mechanism in the devices, is attributed to wider Schottky depletion width determined at the CuPc / n-Si interface of the devices without the air exposure of CuPc film. For higher voltage the space-charge-limited conduction controlled by exponential trap distribution, is found to dominate the charge transport properties of the devices without the air exposure of CuPc, and in case of devices with the air exposure of CuPc film, the SCLC is controlled by single dominating trap level probably introduced by oxygen impurities.

L'électroluminescence (EL) de isolants polymères est étudiée car elle peut permettre d'approcher les phénomènes de vieillissement électrique en fournissant la signature optique d'espèces excitées sous champ électrique. Le vieillissement et la rupture diélectrique dans les isolants polymères est d'un intérêt fondamental pour les chercheurs, concepteurs et fabricants de dispositif du génie électrique. À cet égard, les décharges partielles (DPs) sont un des principaux processus conduisant au vieillissement et à la défaillance des isolants. Cependant, avec le développement des matériaux et procédés, les DPs sont évitées dans certaines situations, par exemple, les câbles haute tension, les condensateurs, etc. Par conséquent, le besoin reste prégnant pour la compréhension des mécanismes de dégradation électrique sous forte contrainte électrique, qui peut être initiée par des porteurs énergétiques. Dans ce travail, l'EL, la cathodoluminescence (CL) excitée sous faisceau d'électrons, ainsi que d'autres techniques de luminescence ont été appliquées à la caractérisation de polyoléfines et d'autres polymères isolants. Afin de comprendre la formation d'excitons dans des films minces de Polypropylène (PP) et Polyéthylène (PE), la dépendance en champ de l'EL et du courant sous contrainte continue, et de l'EL et de sa résolution selon la phase sous contrainte AC, sont étudiées. Les spectres d'EL du PP et du PE ont le même pic principal à environ 570 nm, ce qui implique des structures et des défauts chimiques similaires pour les deux matériaux, et le même processus de dégradation. Le pic principal peut être complété par une émission à environ 750 nm dominante à faible champ. L'impact de la nature des électrodes a été étudiée sur du PEN pour comprendre l'origine de l'émission dans le rouge. A travers la dépendance en champ de l'EL et sa résolution selon la phase avec des métallisations or et ITO, on montre que l'émission dans le rouge est liée à la nature des électrodes et correspond à l'excitation de plasmons de surface ou d'états d'interface. Une étude plus approfondie est effectuée sur la cathodoluminescence d'isolants polymères. Des couches minces de PP, PE, ainsi que de Polyethylene Naphthalate (PEN) et de Polyether Ether Ketone (PEEK) ont été irradiés par faisceau d'électrons jusqu'à 5 keV. Nous avons pu reconstruire les spectres de CL et d'EL du PE et du PP à partir de quatre composants élémentaires: fluorescence, chimiluminescence, luminescence induite par recombinaison, et composante principale du spectre d'EL à 570nm décrite plus haut et considérée comme signature du vieillissement. Pour la première fois, la nature de l'EL et de la CL de polyoléfines est décomposée en quatre composantes de base avec des contributions relatives différentes. L'identification de ces composantes spectrales est utile pour interpréter la luminescence de polyoléfines et autres isolants polymères, et établir les liens entre distribution de charge d'espace et vieillissement diélectrique. A travers ces recherches sur l'EL et la CL dans plusieurs isolants polymères, i.e. polyoléfines ou polyesters, la formation d'excitons et les processus de relaxation d'énergie sous contrainte électrique et électrons énergétiques sont mis en évidence. Surtout, l'analyse en composantes spectrales et la reconstruction des spectres donne accès aux mécanismes d'excitation de la luminescence et à une corrélation avec le vieillissement électrique. A l'avenir, les mesures de luminescence peuvent devenir une méthode standard pour sonder et analyser les isolants polymères. / Electroluminescence (EL) of insulating polymers is a subject of great interest because it is associated with electrical ageing and could provide the signature of excited species under electric field. Electrical ageing and breakdown in insulating polymers is of fundamental interest to the researchers, the design engineers, the manufacturers and the customers of electrical apparatus. In this respect, Partial Discharge (PD) is a harmful process leading to ageing and failure of insulating polymers. However, with the development of the materials and apparatus, PDs can be weakened or avoided in some situations, e.g. extra high voltage cables, capacitors, etc. Therefore, there is urgent demand for understanding electrical degradation mechanisms under high electric field, which can be triggered by energetic charge carriers. In this work, Electroluminescence, EL, and cathodoluminescence, CL, excited under electron beam, along with other luminescence-family techniques are carried out for probing polyolefins and other insulating polymers. In order to uncover the excitons formation in Polypropylene (PP) and Polyethylene (PE) thin films, the field dependence of EL and current under DC stress and field dependence of EL and phase-resolved EL under AC stress, are investigated. The EL spectra of both PP and PE have the same main peak at approximately 570 nm, pointing towards similar chemical structures and defects in both polyolefins, and same route to degradation. This main peak can be complemented by an emission at approximately 750 nm dominating at low field. Electrode effect on the EL of Polyethylene Naphthalte (PEN) was investigated to understand the origin of the red emission at 750 nm. Through field dependence of EL and phase-resolved EL of Au or ITO electrodes, we proved the red component is due to the nature of electrode, more precisely Surface Plasmons and/or interface states. Further thorough study was carried out on cathodoluminescence of insulating polymers. Thin films of PP, PE, along with Polyethylene Naphthalate (PEN) and Polyether Ether Ketone (PEEK) were irradiated under electron beam up to 5 keV to be excited. We could reconstruct EL and CL spectra of both PE and PP using four elementary components: i.e. Fluorescence, Chemiluminescence, Recombination-induced Luminescence, and main component of the EL spectrum at 570 nm reported above and constituting an ageing marker. For the first time the nature of both EL and CL in polyolefins is uncovered, containing four basic components with different relative contributions. Identification of these spectral components is helpful to interpret the nature of light emission from polyolefins and other insulating polymers and to bridge the gap between space charge distribution and electrical ageing or breakdown. Through researches on EL and CL in several insulating polymers, i.e. polyolefins and a polyester, excitons formation and relaxation processes under electric stress and kinetic electrons are evidenced. More importantly, the spectral components analyses and reconstruction uncovers the nature of luminescence and its correlation to electrical ageing. In the future, luminescence measurement can be developed to be a standard method to probe and analyze insulating polymers.

La thèse porte sur les mesures de courants transitoires limités par la charge d'espace dans des films minces organiques (épaisseur < 500 nm). Ce type de films est souvent utilisé dans des applications dans le domaine de l'électronique organique comme couches actives semi-conductrices. Le transport électrique dans ces films dépend en premier lieu du transport des porteurs de charge dans le milieu massif et de leur piégeage, mais aussi de l'efficacité de l'injection des porteurs de charges à partir des électrodes métalliques. L'ensemble est de plus conditionné par le taux de désordre inhérent aux matériaux organiques. L'approche qui consiste à utiliser la mesure de courants transitoires est extrêmement attractive car elle permet en principe de fournir une information sur tous ces aspects à l'issue d'un seul type de mesure. Dans ce cadre, trois contributions principales peuvent être dégagées de la thèse. 1) Tout d'abord, nous avons validé un montage expérimental qui utilise un amplificateur à transfert d'impédance pour la mesure des courants transitoires limités par la charge d'espace. Ce type de montage s'avère supérieur au circuit de pont électrique le plus largement utilisé jusqu'à maintenant car il présente une meilleure sensibilité en courant, une meilleure bande passante, et ne nécessite aucun réglage ni de la symétrie du pont ni de l'ajustement de la taille de l'échantillon. On a pu démontrer que le pic de courant de déplacement initial, qui sature l'amplificateur au tout début de la mesure n'introduit pas d'erreur dans la mesure de la mobilité. 2) Ensuite concernant l'étude plus spécifique du transport dans un dendrimère à base de tri-arylamine, les réponse en courant obtenues expérimentalement se sont avérées en bon accord avec le modèle de déplacement-diffusion. Cependant, la troisième leçon que nous avons apprise est que l'obtention d'un tel accord a nécessité que soient très bien définies les conditions initiales tant de l'expérience que de la simulation et qu'un modèle théorique le plus complet possible de l'échantillon soit considéré. Pour le dendrimère ce modèle a dû prendre en compte l'effet de la barrière au contact et les effets de piégeage. Un accord encore meilleur a été obtenu en intégrant de surcroit les effets de désordre. 3) La complète impossibilité d'obtenir un bon accord sans un modèle physique complet de l'échantillon indique que les paramètres liés au piégeage, à la barrière au contact et à la mobilité peuvent véritablement être ajustés sans aucune ambigüité. Ainsi, une caractérisation électrique complète en cohérence avec la simulation a pu être obtenue à l'issue d'un seul type de mesures. Les résultats obtenus, alliant à la fois amélioration technique et support numérique, témoignent de la grande utilité de cette technique de mesure de courant transitoire limité par la charge d'espace pour caractériser en détails le transport dans les films minces organiques. / The thesis concerns space-charge-limited transient current measurements in thin (le500 nm) organic films. Such films find important applications in organic electronics, where they are referred to as organic semiconductor layers. Electrical transport in such films depends on bulk charge carrier transport and trapping, as well efficiency of charge carrier injection from electrodes. These, are all in turn depend on disorder inherent to organic materials. The transient measurement approach is very attractive, as it can, in principle, deliver information on all these aspects in one single measurement. In the thesis, three main contributions are presented. 1) A transimpedance amplifier based setup for space-charge-limited current transient measurement is validated. This type of setup is superior to the widely used bridge circuit, notably because of better current sensitivity, bandwidth, no need for bridge symmetry and no need for per sample adjustment. It is demonstrated that initial displacement current spike, which saturates the amplifier at the beginning of measurement, does not introduce error in the measurement of mobility. 2) A dendrimer molecule has been investigated. Experimental current responses are shown to be in agreement with the drift-diffusion model. However, obtaining agreement requires well defined initial conditions in experiment as well as in simulation, and also complete theoretical model of the sample. In the case of dendrimer, this model had to take into account both contact barrier and trapping effects. Furthermore, better agreement was obtained when taking disorder effects into account. 3) The impossibility of obtaining any agreement without complete physical model of the sample indicates that trapping, contact barrier and mobility parameters could be fitted without ambiguity. Therefore, complete electrical characterization consistent with simulation can be obtained using the transient technique. The results obtained further increase well known usefulness of transient space-charge-limited current characterization of thin organic films.

Neste trabalho estudamos o movimento de cargas espaciais livres em sólidos dielétricos isolantes ou condutores, sub¬metidos à uma d.d.p. conhecida, admitindo uma distribuição qualquer de cargas que toca inicialmente um dos eletródios.Usando o método das características, reduzimos o problema à solução de uma equação diferencial de la. ordem. Como aplicações, resolvemos os casos de uma densidade linear, quadrática e exponencial, em sólidos com condutividade nula sob a condição de curto-circuito. Observamos que as distribuições tendem rapidamente para distribuições uniformes e, em certos casos, pode ocorrer inversão de corrente, dependendo do tipo de distribuição inicial / Free space charge motion is studied in solid dielectrics, insulators or conductors, under a given voltage. We assume an arbitrary charge distribution contact which is initially in contact with one of the electrodes. Using the \"Method of Characteristics\" we can reduce the problem to the resolution of a first order differential equation. Results are applied for linear, quadratic and exponential charge distributions in solids with zero conductivity under short¬circuit conditions. We saw that the charge profiles fall rapidly to uniform distributions and for cases dependent on initial distributions, current inversions are observed

Neste trabalho descreve-se a implementação da técnica do pulso eletroacústico (PEA) para a determinação de perfis de carga espacial em dielétricos. O método é baseado no sinal acústico gerado pela aplicação de um pulso de tensão elétrica de curta duração na amostra. O sinal acústico gerado é detectado usando-se um transdutor piezoelétrico acoplado à amostra. São discutidos os detalhes experimentais do sistema e os procedimentos matemáticos para o tratamento do sinal elétrico medido. O tratamento matemático do sinal é baseado na técnica de desconvolução que permite determinar a função de transferência do sistema. A função de transferência permite eliminar do sinal medido as distorções introduzidas pelo circuito de medida, pelas reflexões espúrias do sinal acústico, etc.. Mostra-se também os procedimentos matemáticos para se corrigir a atenuação e dispersão do sinal acústico durante a propagação através da amostra. A técnica PEA foi utilizada para o estudo dos perfis de carga espacial injetada em amostras de polietileno sintetizados com diferentes catalisadores: Ziegler-Natta e Metallocene. O campo elétrico aplicado para polarizar as amostras e injetar cargas elétricas nas amostras foi variado de 0,05 MV/cm a 0,9 MV/cm. Nas amostras de polietileno sem aditivos a injeção de cargas elétricas na amostra é bem menor que em amostras com aditivos anti-oxidantes Mostra-se também que o campo elétrico de ruptura depende da carga injetada na amostra, sendo ele maior quando a polaridade da tensão de teste de ruptura é a mesma da tensão aplicada que provocou a injeção de cargas elétricas na amostra. / It is described the implementation of the electroacustic pulse technique, PEA, for the determination of space charge profiles in dielectrics. The method is based on the acoustic signal generated by the application of a voltage pulse with short duration on the sample. The acoustic signal generated by pulse is detected by using a piezoelectric transducer coupled to the sample. Details of the experimental system and of the mathematical procedure for the treatment of the measured electric signals are discussed. The mathematical treatment is based on the deconvolution technique which enables us to obtain the transference function of the system. The use of a transference function eliminates distortions caused by reflections that are introduced by the measurement circuit. Mathematical procedures for the correction of attenuation and dispersion of the acoustic signal during the propagation throughout the sample are also discussed. The PEA technique was used to measure the profiles of injected space charge in polyethylene synthesized using different catalysts: Ziegler-Natta and Metallocene. The electric field applied to polarize and to inject electric charges in the sample was varied form 0.05MV/cm to 0.9MV/cm. In samples of polyethylene without additives it was observed that the injection of charges is less intense than in samples containing anti oxidant additives. It is also shown that the critical electric field for the breakdown depends on the injected charge on the sample being; larger if the rupture tests were performed using the same polarity of the voltage used to pole the samples. Breakdown measurements were also performed with ozone treated samples.

Dans le cadre de l'Approche Elargie pour la Fusion conclue entre le Japon et l'Europe, le projet IFMIF (International Fusion Materials Irradiation Facility) a été lancé pour l'étude des futurs matériaux pour la fusion qui devront résister à d'intenses flux de neutrons. Un composant majeur en est son ensemble de deux accélérateurs à très haute puissance (2×5 MW) qui produit le flux de neutrons en bombardant une cible de Lithium avec un faisceau de Deutérium à une énergie de 40 MeV. Vues ces spécifications ambitieuses, une première phase appelée EVEDA (Engineering Validation and Engineering Design Activity) prévoit l'étude et la réalisation d'un accélérateur prototype à l'échelle un jusqu'à 9 MeV au Japon. Le travail de cette thèse concerne le domaine de la Physique des Accélérateurs. Il consiste en des études de dynamique faisceau pour l'accélérateur prototype LIPAc, caractérisé par une intensité et une puissance jamais encore réalisées, exigeant de ce fait des qualités de faisceau exceptionnelles. Les caractéristiques de cet accélérateur, font qu'il requiert de nombreuses études et simulations pour toutes les étapes de sa mise en service. En parallèle, des études de fond sur les interactions coeur-halo et les effets de la charge d'espace dans les accélérateurs intenses, seront aussi menées. En particulier une nouvelle définition du halo d'un faisceau de particules, adaptée à l'étude de ces accélérateurs sera proposée et appliquée. / As part of the Broader Approach to Fusion concluded between Japan and Europe, the IFMIF (International Fusion Materials Irradiation Facility) project was launched for the study of future fusion materials resisting intense neutron fluxes. A major component of it is the couple of twin high power accelerators (2 × 5 MW) which will produce the neutron flux by bombarding a Lithium target with a deuterium beam at an energy of 40 MeV. Considering these ambitious specifications, a first phase called EVEDA (Engineering Validation and Engineering Design Activity) is ongoing to provide the design and construction of an up to scale prototype accelerator to an energy of 9 MeV in Japan. The work of this thesis belongs to the field of Accelerators Physics. It consists of beam dynamics studies for the prototype accelerator LIPAc, characterized by unprecedented current and power, thereby requiring outstanding beam quality. The characteristics of this accelerator, makes many studies and simulations for all stages of its commissioning required. Concurrently, background studies on core-halo interactions and on the effects of space charge on high current beams will also be conducted. In particular a new definition of the halo of a particle beam, adapted to the study of these accelerators will be proposed and implemented.

The field of hybrid electronics of molecules and traditional semiconductors is deemed to be a realistic route towards possible use of molecular electronics. Such hybrid electronics finds its potential technological applications in nuclear detectors, near-infrared detectors, organic thin film transistors and gas sensors. Specifically Metal / organic / n-Silicon structures in this regard are mostly reported to have two regimes of charge transport at lower and higher applied voltages in such two terminal devices. The fact is mostly attributed to the change in conduction mechanism while moving from lower to higher applied voltages. These reports describe interactions between the semiconductors and molecules in terms of both transport and electrostatics but finding the exact potential distribution between the two components still require numerical calculations. The challenge in this regard is to give the exact relations and the transport models, towards practical quantification of charge transport properties of metal / organic / inorganic semiconductor devices. Some of the most exiting questions in this regard are; whether the existing models are sufficient to describe the device performances of the hybrid devices or some new models are needed? What type of charge carriers are responsible for conduction at lower and higher applied voltages? What is the source of such charge carriers in the sandwiched organic layer between the metal and inorganic semiconductors? How the transition applied voltage for the change in conduction mechanism is determined? What is the role of dopants in the organic layer semiconductors? What are the possible explanations for observed temperature effects in such devices? In present work the charge transport properties of metal / metal-phthalocyanine / n-Si structures with low (ND = 4×1014 cm-3), medium (ND = 1×1016 cm-3) and high (ND = 2×1019 cm-3) doped n-Si as injecting electrode and the effect of air exposure of the vacuum evaporated metal-phthalocyanine film in these structures is investigated. The results obtained through temperature dependent electrical characterizations of the structures suggest that in terms of dominant conduction mechanism in these devices Schottky-type conduction mechanism dominates the charge transport in low-bias region of these devices up to 0.8 V, 0.302 V and 0.15 V in case of low, medium and high doped n-Silicon devices. For higher voltages, in each case of devices, the space-charge-limited conduction, controlled by exponential trap distribution, is found to dominate the charge transport properties of the devices. The interface density of states at the CuPc / n-Si interface of the devices are found to be lower in case of lower work function difference at the CuPc / n-Si interface of the devices. The results also suggest that the work function difference at the CuPc / n-Si interface of these devices causes charge transfer at the interface and these phenomena results in formation of interface dipole. The width of the Schottky depletion region at the CuPc / n-Si interface of these devices is found to be higher with higher work function difference at the interface. The investigation of charge transport properties of Al / ZnPc / medium n-Si and Au / ZnPc / medium n-Si devices suggest that the Schottky depletion region formed at the ZnPc / n-Si interface of these devices determines the charge transport in the low-bias region of both the devices. Therefore, the Schottky-type (injection limited) and the space-charge-limited (bulk limited) conduction are observed in the low and the high bias regions of these devices, respectively. The determined width of the Schottky depletion region at the ZnPc / n-Si interface of these devices is found to be similar for both the devices, therefore, the higher work function difference at the metal / ZnPc interface of the devices has no influence on the Schottky depletion region formed at the ZnPc / n-Si interface of the devices. The similar diode ideality factor, barrier height and the width of the Schottky depletion region, determined for both of these devices, demonstrates that these device characteristics originate from ZnPc / n-Si interface of these devices. Therefore, the work function difference at the metal / ZnPc interface of these devices has no noticeable influence on the device properties originating from ZnPc / n-Si interface in these devices. The investigation of charge transport properties of Al / CuPc / low n-Si devices with and without air exposure of the CuPc film, before depositing metal contact demonstrate that Schottky-type conduction mechanism dominates the charge transport in these devices up to bias of 0.45 V in case devices with the air exposure, and up to 0.8 V in case devices without the air exposure. This decrease in the threshold voltage, for the change in conduction mechanism in the devices, is attributed to wider Schottky depletion width determined at the CuPc / n-Si interface of the devices without the air exposure of CuPc film. For higher voltage the space-charge-limited conduction controlled by exponential trap distribution, is found to dominate the charge transport properties of the devices without the air exposure of CuPc, and in case of devices with the air exposure of CuPc film, the SCLC is controlled by single dominating trap level probably introduced by oxygen impurities.:1 INTRODUCTION 3 1.1 Organic / Inorganic Semiconductor Interfaces 5 1.2 Organic / Metal Interfaces 6 1.3 Organic Material / Semiconductor Interfaces 6 1.4 Interface Dipoles at Organic / Inorganic Interfaces 7 1.5 Objectives of the Study 9 1.6 Research Methodology 10 1.7 References 12 2 BASIC CONCEPTS OF ORGANIC ELECTRONICS 16 2.1 Localized and Delocalized Orbital in Organic Semiconductors 16 2.2 Operating principle of some basic organic / inorganic devices 19 2.3 Electronic Structure of an Organic Solid 20 2.4 Validity Limits of band model and the tunneling model 21 2.5 Dark Electric Conduction 23 2.6 Injection of Carriers from Electrodes 24 2.7 References 26 3 MATERIALS AND DEVICE FABRICATION 27 3.1 Assembly of the hybrid organic / inorganic structures 27 3.2 The Vacuum Systems for Device Fabrication 27 3.3 The n-Si substrates 29 3.4 The Organic semiconductors; CuPc and ZnPc 30 3.5 Sample Fabrication Procedures 32 3.5.1 Experimental Details of Samples Prepared at PCRET labs 32 3.5.2 Experimental details of samples Prepared at TU Chemnitz labs 33 3.6 References 34 4 METHODS FOR DATA ANALYSIS 35 4.1 The Dominant Conduction Mechanisms in the Devices 35 4.1.1 Schottky-type Conduction 35 4.1.1.1 The Standard Characterization Technique 38 4.1.1.2 The R. J. Bennett Technique 39 4.1.1.3 The Cheung and Cheung Technique 42 4.1.1.4 The H. Norde Technique 42 4.1.2 Space Charge Limited Conduction (SCLC) 43 4.1.3 The MIM Models to Determine Dominant Conduction Mechanism 44 4.2 Interface State Energy Distribution 46 4.3 References 48 5 CHARGE TRANSPORT PROPERTIES OF Al / CuPc / n-Si DEVICES IN DARK 50 5.1 Charge Transport Properties of Al / CuPc / low-doped n-Si Devices 51 5.1.1 Interface State Energy Distribution 65 5.2 Charge Transport Properties of Al / CuPc / medium-doped n-Si Devices 67 5.3 Charge Transport Properties of Al / CuPc / High-doped n-Si Devices 75 5.3.1 Charge Transport Properties of Al / CuPc / High-doped n-Si Devices as Metal-Insulator-Metal Structures 82 5.4 Summary 85 5.5 Final Remarks 87 5.6 References 88 6 INFLUENCE OF TOP METAL CONTACT ON CHARGE TRANSPORT PROPERTIES META / ZnPc / n-Si DEVICES IN DARK 89 6.1 Charge Transport Properties of Metal / ZnPc / Medium-doped n-Si Devices 89 6.2 Interface State Energy Distribution 99 6.3 Summary 100 6.4 Final Remarks 101 6.5 References 103 7 INFLUENCE AIR EXPOSURE ON THE CHARGE TRANSPORT PROPERTIES OF Al / CuPc / n-Si DEVICES 104 7.1 Charge Transport Properties of Al / CuPc / low n-Si Devices With (or) without air exposure of CuPc film 104 7.2 Summary 115 7.3 Final Remarks 116 7.4 References 117 8 CONCLUSIONS 118 8.1 Scope of Future Work 120 Index of Figures 121 Curriculum Vitae and List of Publications 125

Cumulative Dissertation on models in nonlinear condensed-matter optics. In chapter 2, the coupled-wave theory first introduced by Kogelnik is reviewed and extended with emphasis on out-of-phase mixed holographic gratings. This class of gratings becomes increasingly important due to novel methods of hologram recording and new classes of materials and metamaterials like holographic polymer dispersed liquid crystals. Additionally, advances in laser technology suggest a stronger spectro- scopic view on holography. The model presented in this thesis accounts for both of these demands and provides a closed analytical solution. Chapter 3 contributes to the field of space-charge waves (SCW), which provides powerful tools for material analysis, especially in semiconductor technology. Although the underlying theory is generally understood, recent improvements of the ex- perimental techniques required extensions of the model and the interpretation of new effects. In this thesis, the existing formalism is adapted to a new method of excitation, which not only simplifies the experimental setup, allowing for easier adoption into industrial environments, but also provides insight into the direction of carrier motion. Furthermore, the model is extended to describe the influence of an external magnetic field, adding the possibility to examine the Hall mobility of carriers. Eventually, chapter 4 studies the dynamics of light induced absorption in pho- tochromic [Ru(bpy)2 (OSO)]+ . Compared to other photofunctional compounds, this molecule is nontoxic and exhibits exceptional photochromic reactions. These properties make it a promising candidate for important industrial and technological applications, ranging from data storage to non-electronic computation. For a profound analysis, the models used for the description of photofunctional molecules have been completely revised to account for the pronounced absortion changes in the material. Furthermore, a setup with orthogonal pump and probe beams is modeled and exper- imentally tested. This novel geometry is introduced to resemble common industrial setups.