Electronic processes, such as electronic breakdown and electron emission, in gases and liquids have implications in microplasmas, laser applications, water purification, biomedical applications, geographical mapping, and radiation detection. Electron emission and breakdown mechanisms are heavily researched and characterized in gases. Much of the current research into these mechanisms is focused on unifying breakdown and emission mechanisms. For electron emission, these mechanisms include field emission (FE), space-charge-limited emission (SCLE), thermionic emission (TE), and photoemission (PE), while gas breakdown emission mechanisms include Paschen’s law (PL) and Townsend breakdown (TB)with ion-enhanced FE becoming important at microscale. This research first unified SCLE and FE in vacuum and has been extended to include SCLE with collisions (for a gas at non-vacuum) and TE. This thesis extends this approach in electron emission unification, referred to as “nexus” theory, in two directions. First, we will apply this theory to liquids to examine the transition from FE to SCLE and hypothesize about the implications should there be a phase change. Second, we will incorporate PE, which becomes important with increasing interest in ultrafast laser phenomena at nanoscale and development of solar cells, with SCLE, TE, and FE.<div><br></div><div>Initial nexus theory studies included gas at non-vacuum pressures by including electron mobility in the electron force law. In principle, this behavior should be the same whether the medium is air or liquid. Electron emission and breakdown, which can arise from field emission, are increasingly important in plasma water treatment, pulsed power systems, radiation detection, and even understanding the physics of high electric fields applied to liquid helium for the Spallation Neutron Source. To demonstrate the applicability of nexus theory to liquids, we fit experimental data for electron emission in hydrocarbons to the full theory unifying FE to SCLE with and without collisions. The measured current followed Fowler-Nordheim scaling for FE at lower voltages with space charge beginning to contribute at higher voltages; none of the hydrocarbons study fully transitioned to Mott-Gurney (SCLE with collisions) scaling within the experimentally studied parameter range. Considering a higher mobility representative of a vapor in the theory demonstrates the feasibility of achieving Child-Langmuir (SCLE in vacuum)scaling for the gaps of the size considered experimentally. Thus, this approach may ultimately be applied to model electron emission during both phases changes and transitions between the mechanisms.<br></div><div><br></div><div>We next extended the gas nexus theory to analyze the transitions between PE and the other emission mechanisms. We modified the previous theory that used the generalized thermal-field emission (GTF) theory for electron current to instead use the generalized thermal-field photoemission (GTFP) theory. Using this, we obtained exact solutions for current as a function of applied voltage and demonstrated the asymptotic behavior with regard to the modified Fowler DuBridge (MFD) equation, which models PE. We combined the MFD equation with the other asymptotic solutions to develop state diagrams unifying the various emission mechanisms to provide guidance to the mechanisms and transitions relevant under various conditions of mobility, gap distance, temperature, and laser energy/wavelength/frequency. These diagrams provide guidance on which asymptotic solution or more detailed theory would be necessary to accurately relate current and voltage under various operating conditions.<br></div>

Ce travail porte sur une étude des propriétés électroniques des boîtes quantiques InAs/InP, qui est un système très prometteur pour les télécommunications. Ces nanoparticules sont étudiées pour différentes tailles, densité et dopage. Dans le premier chapitre, nous décrivons l’intérêt du système InAs/InP pour les applications optoélectroniques. Nous présentons la technique de croissance et quelques exemples d’applications de ces boîtes quantiques. Nous donnons une description générale complète des processus d’émission susceptible d’exister dans ces structures. Dans le deuxième chapitre, nous présentons les méthodologies de caractérisation électrique mises en jeu, en insistant sur la complémentarité de deux techniques d’analyse : la spectroscopie transitoire des défauts profonds et la mesure C(V). Dans le troisième chapitre, nous étudions ces boîtes quantiques avec la technique C(V) pour aboutir à une analyse qualitative et quantitative des profils N(W) des échantillons. Une étude de ce profil en fonction de la température nous permet de déterminer les types d’émission qui dominent dans nos structures. L’effet du fort dopage de la couche matrice, ainsi que la densité de boîtes est discuté. Dans le quatrième chapitre, une étude DLTS menée sur l’ensemble des échantillons disponibles montre plusieurs défauts reliés au contrôle de la croissance et de la qualité des interfaces. En outre, une étude plus approfondie nous permet d’extraire la réponse électrique des boîtes quantiques ainsi que leurs états électroniques s et p existants. / This work deals with a study of the electronic properties of InAs / InP quantum dots, which is a very promising material system for telecommunications. These nanoparticles are studied for different sizes, density and doping. In the first chapter, we describe the interest of the InAs / InP system for optoelectronic applications. As a result we present the growth technique and some examples of applications of these quantum dots. In addition, we present a description of the emission process may exist in these structures. In the second chapter, we present the electrical characterization methodologies: the Deep Level Transient Spectroscopy (DLTS) and the C (V) measurement. In the third chapter, we study the quantum dots to achieve a qualitative and quantitative analysis of profiles N (W) samples. A study of the profile as a function of temperature gives an overview of the types of emission that dominate in our structures. The effect of heavy doping of the matrix layer and of density of dots is discussed. In the fourth chapter, a DLTS study of all samples shows several defects related to growth and interface quality. In addition, further study allows us to extract the s and p electronical state response of quantum dot.

<div>Developments in modern electronics drive device design to smaller scale and higher electric fields and currents. Device size reductions to microscale and smaller have invalidated the assumption of avalanche formation for the traditional Paschen’s law for predicting gas breakdown. Under these conditions, the stronger electric fields induce field emission driven microscale gas breakdown; however, these theories often rely upon semi-empirical models to account for surface effects and the dependence of gas ionization on electric field, making them difficult to use for predicting device behavior a priori.</div><div>This dissertation hypothesizes that one may predict a priori how to tune emission physics and breakdown conditions for various electrode conditions (sharpness and surface roughness), gap size, and pressure. Specifically, it focuses on experiments to demonstrate the implications of surface roughness and emitter shape on gas breakdown for microscale and nanoscale devices at atmospheric pressure and simulations to extend traditional semi-empirical representations of the ionization coefficient to the relevant electric fields for these operating conditions.</div><div>First, this dissertation reports the effect of multiple discharges for 1 μm, 5 μm, and 10 μm gaps at atmospheric pressure. Multiple breakdown events create circular craters to 40 μm deep with crater depth more pronounced for smaller gap sizes and greater cathode surface roughness. Theoretical models of microscale breakdown using this modified effective gap distance agree well with the experimental results.</div><div>We next investigated the implications of gap distance and protrusion sharpness for nanoscale devices made of gold and titanium layered onto silicon wafers electrically isolated with SiO2 for gas breakdown and electron emission at atmospheric pressure. At lower voltages, the emitted current followed the Fowler-Nordheim (FN) law for field emission (FE). For either a 28 nm or 450 nm gap, gas breakdown occurred directly from FE, as observed for microscale gaps. For a 125 nm gap, emission current begins to transition toward the Mott-Gurney law for space-charge limited emission (SCLE) with collisions prior to undergoing breakdown. Thus, depending upon the conditions, gas breakdown may directly transition from either SCLE or FE for submicroscale gaps.</div><div>Applying microscale gas breakdown theories to predict this experimental behavior requires appropriately accounting for all physical parameters in the model. One critical parameter in these theories is the ionization coefficient, which has been determined semi-empirically with fitting parameters tabulated in the literature. Because these models fail at the strong electric fields relevant to the experiments reported above, we performed particle-in-cell simulations to calculate the ionization coefficient for argon and helium at various gap distances, pressures, and applied voltages to derive more comprehensive semi-empirical relationships to incorporate into breakdown theories.</div><div>In summary, this dissertation provides the first comprehensive assessment of the implications of surface roughness on microscale gas breakdown, the transition in gas breakdown and electron emission mechanisms at nanoscale, and the extension of semi-empirical laws for ionization coefficient. These results will be valuable in developing theories to predict electron emission and gas breakdown conditions for guiding nanoscale device design.</div>

<p dir="ltr">Calculating space-charge limited current (SCLC) is a critical problem in plasma physics and intense particle beams. Accurate calculations are important for validation and verification of particle-in-cell (PIC) simulations. The theoretical assessment of SCLC is complicated by the nonlinearity of the Poisson equation when combined with the energy balance and continuity equations. This dissertation provides several theoretical tools to convert the nonlinear Poisson equation into a corresponding linear differential equation, which is then solved for numerous geometries of practical interest.</p><p dir="ltr">The first and second chapters briefly summarize the application of variational calculus (VC) to solve for one-dimensional (1D) SCLC in cylindrical and spherical diode geometries by extremizing the current in the gap. Next, conformal mapping (CM) is presented to convert the concentric cylindrical diode geometry into a planar geometry to obtain the same SCLC solution as VC. In the next chapter, SCLC is determined for several geometries with curvilinear electron flow that cannot be solved using VC because the Poisson equation cannot be written easily. We then map a hyperboloid tip onto a plane to form a non-Euclidean disk (Poincaré disk). These mappings on to Poincaré disk are utilized to solve for SCLC in tip-to-tip and tip-to-plane geometries. Lie symmetries are then introduced to solve for SCLC with nonzero monoenergetic injection velocity, recovering the solutions for concentric cylinders, concentric spheres, tip-to-plane, and tip-to-tip for zero injection velocity. We then extend the SCLC calculations to account for any geometry in multiple dimensions by using VC and vacuum capacitance. First, we derive a relationship between the space-charge limited (SCL) potential and vacuum potential that holds for any geometry. This relationship is utilized to obtain exact closed-form solutions for SCLC in two-dimensional (2D) and three-dimensional (3D) planar geometries considering emission from the full surface of the cathode. PIC simulations using VSim were performed that agreed with the SCLC in 2D diode with a maximum error of 13%. In the final chapters, we extend these multidimensional SCLC calculations to nonzero monoenergetic emission. The SCLC in any orthogonal diode in any number of dimensions is obtained by relating it to the vacuum capacitance. The current in the bifurcation regime is also derived from first-principles from vacuum capacitance. The simulations performed in VSim agreed with the theory with a maximum error of 7%.</p><p dir="ltr">These mathematical techniques form a set of powerful tools that extend prior studies by yielding exact and approximate SCLC in numerous nonplanar and multidimensional diode geometries, thereby not requiring expensive and time-consuming PIC simulations. While more experiments are required to benchmark the validity of these calculations, these results may ultimately prove useful by providing a rapid first-principles approach to determine SCLC for many geometries that can be used to assess the validity of PIC simulations and facilitate multiphysics simulations.</p>

Les particules en suspension dans l’air (notées « PM » pour « Particulate matter ») sont aujourd’hui au cœur des préoccupations sociétales en raison de leur impact majeur sur la santé publique et leur forte participation au changement climatique. La matière organique (MO) représente généralement la première composante en masse des PM mais reste encore très mal appréhendée, en particulier la fraction organique d’origine biogénique primaire (PBOA). Des sucres primaires sont proposés comme des traceurs moléculaires pour étudier les processus de transport atmosphérique ainsi que pour estimer la contribution des PBOAs à la masse totale des PM. Cependant, les connaissances sont encore très limitées sur leurs distributions spatiales et temporelles (i.e., cycles journaliers, saisonniers et annuels), leurs principales sources d’émissions, ou encore les facteurs environnementaux qui déterminent leurs concentrations atmosphériques. Par ailleurs, si la comprehension du potentiel oxydant (PO) —proxy de l’effet sanitaire des PM— inhérent à la composante chimique des aérosols a relativement bien avancé ces dernières années, la contribution de cette fraction PBOA est encore est très mal connue. Ces différents aspects constituent les objectifs de ce travail de thèse. D’un point de vue méthodologique, nos questions ont été abordées par une approche interdisciplinaire, qui a impliquée l’exploitation statistique d’une large base de données et le couplage de campagnes de terrain spécifiques avec la mise en œuvre d’une stratégie expérimentale novatrice développée pour l’étude simultanée des caractéristiques chimiques et microbiologiques des échantillons prélevés.Dans un premier travail basé sur l’exploitation d’une large base de données, nous avons montré que les PBOAs constituent une fraction très importante des PM en France, independamment de la typologie de l’environnement, contribuant en moyenne annuelle à 13 ± 4 % de la MO dans les PM10. On met en évidence une similitude entre les évolutions temporelles de concentrations et de ratios entre sucres primaires pour des sites localisés dans une même région géographique (jusqu’à une distance inter-sites d’environ 200 km). Ces observations indiquent que la source PBOA est très homogène spatialement sur des distances cohérentes avec celle de grands types d'écosystèmes. Cette observation a ensuite été validée par une expérimentation basée sur deux échantillonnages annuels de terrain qui nous a permis de démontrer (i) que les évolutions journalières des concentrations atmosphériques en sucres primaires sont déterminées par seulement quelques taxons microbiens atmosphériques, variables d’un point de vue regionale ; et (ii) que ces taxons proviennent respectivement de la flore locale et régionale pour les sites d’étude qui sont directement influencés et non par les activités agricoles. Enfin, dans le cadre d’étude de PO, nos résultats ont permis de démontrer (i) que tous les bioaérosols modèles testés possèdent un PO intrinsèque significatif, comparable pour certaines espèces à celui de composants chimiques atmosphériques modèles connus pour leur forte reactivité redox ; et (ii) qu’ils sont capables d’influencer significativement le PO des PM chimiques modèles ou collectées en condition réelle.Ces travaux apportent un nouveau regard sur l’importance massique des PBOAs et des nouvelles connaissances sur les sources et processus dominants conduisant à leur introduction dans l’atmosphère, ainsi que l’influence des facteurs environnementaux sur ces processus. L’ensemble des résultats de ce travail plaide pour une prise en compte systematique des PBOAs dans les modèles de chimie atmosphérique pour une meilleure prédiction de la qualité de l’air. / Airborne particles (called « PM » for Particulate matter") are nowadays at the core of societal concerns because of their major impact on public health and their strong participation in climate change. Organic matter (OM) generally represents the first mass component of PM but it is still poorly understood, in particular the organic fraction from primary biogenic origin (PBOA). Some specific primary sugars are proposed as molecular tracers to study the atmospheric transport processes as well as to estimate the contribution of PBOAs to the total mass of PM. However, knowledge is still very limited about their spatial and temporal distributions (i.e., daily, seasonal and annual cycles), their main emission sources, or the environmental factors that drive their atmospheric concentrations. Moreover, although the understanding of the oxidative potential (OP) —a proxy of the health effect of PM— inherent in the chemical component of aerosols has progressed quite well in recent years, the contribution of this PBOA fraction is still very poorly understood. These aspects constitute the main objectives of this thesis work. From a methodological point of view, our questions were addressed by an interdisciplinary approach, which involved the statistical exploitation of a large database and the coupling of specific field campaigns with the implementation of an innovative experimental strategy developed for the simultaneous study of the chemical and microbiological characteristics of the samples collected.In a first work based on the exploitation of a large database, we showed that PBOAs constitute a very important fraction of PM in France, regardless of the typology of the environment, contributing on average to 13 ± 4% of the annual MO in PM10. We observed a synchronous temporal trends in both concentrations and ratios between primary sugars species for sites located in the same geographical region (up to an inter-site distance of about 200 km). These observations indicate that the PBOA source is very spatially homogeneous over distances consistent with those of large ecosystem types. This observation was then validated by an experimental approach based on two annual field sampling studies that allowed us to demonstrate (i) that daily changes in atmospheric concentrations of primary sugars are drived by only a few regionally variable atmospheric microbial taxa; and (ii) that these taxa come from local and regional flora for study sites that are directly influenced and not by agricultural activities, respectively. Finally, in the framework of the OP study, our results demonstrated (i) that all the tested model bioaerosols have a significant intrinsic OP, which is comparable for some species to the model atmospheric chemical components known for their high redox reactivity; and (ii) that they can significantly influence the OP of chemical PM models or sampled under real ambient conditions.This work provides a different look into the mass importance of PBOAs and new insights into the dominant sources and processes leading to their introduction into the atmosphere, as well as the influence of environmental factors on these processes. Alltogether these results argue for a systematic consideration of PBOAs in atmospheric chemistry models for better prediction of air quality.