Thèses sur le sujet « Drift current »

Space-charge effects play a dominant role in many areas of physics. In high-power microwave devices using high-current, relativistic electron beams, it places a limit on the amount of radiation a device can produce. Because the beam's space-charge can actually reflect a portion of the beam, the ability to accurately predict the amount of current a device can carry is needed. This current value is known as the space-charge limited current. Because of the mathematical difficulties, this limit is typically estimated from a one-dimensional theory. This work presents a two-dimensional theory for calculating an upper-bound for the space-charge limited current of relativistic electron beams propagating in grounded coaxial drift tubes. Applicable to annular beams of arbitrary radius and thickness, the theory includes the effect introduced by a finite-length drift tube of circular cross-section. Using Green's second identity, the need to solve Poisson's equation is transferred to solving a Sturm-Liouville eigenvalue problem, which is easily solved by elementary methods. In general, the resulting eigenvalue, which is required to estimate the limiting current, must be numerically determined. However, analytic expressions can be found for frequently encountered limiting cases. Space-charge effects also produce the fundamental collective behavior found in plasmas, especially in plasma sheaths. A plasma sheath is the transition region between a bulk plasma and an adjacent plasma-facing surface. The sheath controls the loss of particles from the plasma in order to maintain neutrality. Using a fully kinetic theory, the problem of a planar sheath with a single-minimum electric potential profile is investigated. Appropriate for single charge-state ions of arbitrary temperature, the theory includes the emission of warm electrons from the surface as well as a net current through the sheath and is compared to particle-in-cell simulations. Approximate expressions are developed for estimating the sheath potential as well as the transition to space-charge saturation. The case of a space-charge limited sheath is discussed and compared to the familiar Child-Langmuir law.

The patterns of surface drift of eighty-nine undrogued RAFOS floats in the California Current System have been studied. The floats were launched in the California Undercurrent during 19922010 and were tracked by the ARGOS system when they surfaced at the end of their subsurface mission. The surface drift of these floats was typically equatorward in the California Current. However, some floats moved poleward into the Subpolar Gyre, and others drifted westward into the North Equatorial Current. The duration of surface trajectories varied from as short as 11 days to as long as 280 days. Observations of surface currents typically use drifters which are coupled to the surface layer by drogues which are located at 15 m depth. While drogued observations are useful for studies of circulation of the upper layer of the ocean, a more typical operational problem involves trying to find flotsam that has fallen off the deck of a ship or to predict the path of a floating mine. To better understand the behavior of these surface drifting objects, observations of the surface drift of RAFOS floats in the California Current system were used to compare their motion to wind induced drift and evaluate the drift prediction by three ocean models, Ocean Surface Current Simulator (OSCURS), Global Navy Coastal Model (gNCOM) and Hybrid Coordinate Ocean Model (HYCOM). The results indicate that summer and fall months provided the best correlation between float drift speed and wind speed. Evaluation of the drift prediction by three ocean models was conducted by comparing observed drifter trajectories with model simulated trajectories at 7-day timescales. The model-simulated trajectories were initially collocated with RAFOS positions and restarted every 15 days. These results showed that OSCURS was able to give better short-term prediction of surface drift than gNCOM and HYCOM when OSCURS model parameters were chosen as to minimize separation between modeled and observed trajectories.

In this work Random Discrete Dopant induced on-current variations have been studied using the Glasgow 3D atomistic drift/diffusion simulator and Monte Carlo simulations. A methodology for incorporating quantum corrections into self-consistent atomistic Monte Carlo simulations via the density gradient effective potential is presented. Quantum corrections based on the density gradient formalism are used to simultaneously capture quantum confinement effects. The quantum corrections not only capture charge confinement effects, but accurately represent the electron impurity interaction used in previous \textit{ab initio} atomistic MC simulations, showing agreement with bulk mobility simulation. The effect of quantum corrected transport variation in statistical atomistic MC simulation is then investigated using a series of realistic scaled devices nMOSFETs transistors with channel lengths 35 nm, 25 nm, 18nm, 13 nm and 9 nm. Such simulations result in an increased drain current variability when compared with drift diffusion simulation. The comprehensive statistical analysis of drain current variations is presented separately for each scaled transistor. The investigation has shown increased current variation compared with quantum corrected drift diffusion simulation and with previous classical MC results. Furthermore, it has been studied consistently the impact of transport variability due to scattering from random discrete dopants on the on-current variability in realistic nano CMOS transistors. For the first time, a hierarchic simulation strategy to accurately transfer the increased on-current variability obtained from the ‘ab initio’ MC simulations to DD simulations is subsequently presented. The MC corrected DD simulations are used to produce target $I_D-V_G$ characteristics from which statistical compact models are extracted for use in preliminary design kits at the early stage of new technology development. The impact of transport variability on the accuracy of delay simulation are investigated in detail. Accurate compact models extraction methodology transferring results from accurate physical variability simulation into statistical compact models suitable for statistical circuit simulation is presented. In order to examine te size of this effect on circuits Monte Carlo SPICE simulations of inverter were carried out for 100 samples.

A proper understanding of the effects of turbulence on the diffusion and drift of cosmic-rays in the heliosphere is imperative for a better understanding of cosmic-ray modulation. This study presents an ab initio model for cosmic-ray modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. The latter model is solved for solar minimum heliospheric conditions, utilizing boundary values chosen in such a way that the results of this model are in fair to good agreement with spacecraft observations of turbulence quantities, not only in the ecliptic plane, but also along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for modelled slab and 2D turbulence energy spectra, which in turn are used as inputs for parallel mean free paths based on those derived from quasi-linear theory, and perpendicularmean free paths from extended nonlinear guiding center theory. The modelled 2D spectrum is chosen based on physical considerations, with a drop-off at the very lowest wavenumbers commencing at the 2D outerscale. There currently exist no models or observations for this quantity, and it is the only free parameter in this study. The use of such a spectrum yields a non-divergent 2D ultrascale, which is used as an input for the reduction terms proposed to model the effects of turbulence on cosmic-ray drifts. The resulting diffusion and drift coefficients are applied to the study of galactic cosmic-ray protons, electrons, antiprotons, and positrons using a three-dimensional, steady-state numerical cosmic-ray modulation code. The magnitude and spatial dependence of the 2D outerscale is demonstrated to have a significant effect on computed cosmic-ray intensities. A form for the 2D outerscale was found that resulted in computed cosmic-ray intensities, for all species considered, in reasonable agreement with multiple spacecraft observations. Computed galactic electron intensities are shown to be particularly sensitive to choices of parameters pertaining to the dissipation range of the slab turbulence spectrum, and certain models for the onset wavenumber of the dissipation range could be eliminated in this study.
Thesis (PhD (Physics))--North-West University, Potchefstroom Campus, 2013

Atlantic Meridional Overturning Circulation (AMOC) is a vital process that transfers heat and nutrients throughout the world's oceans, helping to regulate global climate and support marine ecosystems. The timing and nature of the shift to modern AMOC, and especially to deep-water formation in the North Atlantic, has been a topic of ongoing study, with the Eocene-Oligocene Transition (EOT, ~34 Ma) as a potential focal point of this shift. However, the role played by abrupt EOT cooling and Antarctic glaciation in North Atlantic circulation remains unclear. Improved constraints on Paleogene circulation will provide insight into the sensitivity of AMOC to perturbations in global climate, which is particularly relevant in light of contemporary climate change. To examine deep North Atlantic circulation response to the EOT we obtained grain-size data from the terrigenous fraction of the mud-dominated sediments of the Southeast Newfoundland Ridge contourite drift complex at IODP Site U1411, which is interpreted to have formed under the influence of the Deep Western Boundary Current. We analyzed 195 samples that span 150 m of stratigraphy from 36-26 Ma. The main objective was to use the 'sortable silt' fraction (10-63 µm) to generate a record of relative change in bottom-current intensity. These data are complemented with a record of the abundance and size of lithogenic sand (>63 µm). Here we present the first physical proxy record of abyssal current intensity in the North Atlantic, from late Eocene to mid Oligocene. Invigoration of North Atlantic deep circulation occurred gradually (over Myr timescales), with no significant changes linked temporally to the EOT. We infer that deep circulation in the North Atlantic was not sensitive to the abrupt global cooling and Antarctic glaciation associated with the EOT. Rather, our data suggest that changes in North Atlantic circulation were likely governed by longer-term processes related to the opening of key tectonic gateways, such as the Greenland-Scotland Ridge in the North Atlantic, and the Drake and Tasman Passages in the Southern Ocean. Additionally, we identify a significant mid-Oligocene invigoration of North Atlantic abyssal circulation, which climaxes around 27.9 Ma, and is coeval with a decrease in atmospheric CO2.
Master of Science

Jádrem této disertační práce bylo studovat optické a elektrické charakteristiky tenkovrstvých elektroluminiscenčních součástek řízených střídavým proudem (ACTFEL) a zejména vliv procesu stárnutí luminiforů na jejich optické a elektrické vlastnosti. Cílem této studie měl být příspěvek ke zvýšení celkové účinnosti luminoforů, vyjádřené pomocí jasu, účinnosti a stability. Vzhledem k tomu, že současnou dominantní technologií plochých obrazovek je LCD, musí se další alternativní technologie plošných displejů porovnávat s LCD. Výhodou ACTFEL displejů proti LCD je lepší rozlišení, větší teplotní rozsah činnosti, větší čtecí úhel, či možnost čtení při mnohem vyšší intenzitě pozadí. Na druhou stranu je jejich nevýhodou vyšší energetická náročnost, problém s odpovídající barevností tří základních barev a podstatně vyšší napětí nutné pro činnost displeje. K dosažení tohoto cíle jsme provedli optická, elektrická a optoelektrická měření ACTFEL struktur a ZnS:Mn luminoforů. Navíc jsme studovali vliv dotování vrstvy pomocí KCl na chování mikrostruktury a na elektroluminiscenční vlastnosti (zejména na jas a světelnou účinnost) ZnS:Mn luminoforů. Provedli jsme i některá, ne zcela obvyklá, měření ACTFEL součástek. Vypočítali jsme i rozptylový poměr nabitých barevných center a simulovali transportní charakteristiky v ACTFEL součástkách. Studovali jsme vliv stárnutí dvou typů ZnS:Mn luminoforů (s vrstvou napařenou či získanou pomocí epitaxe atomových vrstev) monitorováním závislostí svítivost-napětí (L-V), velikost vnitřního náboje - elektrické pole luminoforu (Q-Fp) a kapacitance-napětí (C-V) ve zvolených časových intervalech v průběhu stárnutí. Provedli jsme krátkodobá i dlouhodobá měření a pokusili jsme se i o vizualizaci struktury luminoforu se subvlnovým rozlišením pomocí optického rastrovacího mikroskopu pracujícího v blízkém poli (SNOM). Na praktickém případu zeleného Zn2GeO4:Mn (2% Mn) ACTFEL displeje, pracujícího při 50 Hz, jsme také studovali stabilitu svítivosti pomocí měření závislosti svítivosti na napětí (L-V) a světelné účinnosti na napětí (eta-V). Přitom byl zhodnocen význam těchto charakteristik. Nezanedbatelnou a neoddělitelnou součástí této práce je i její pedagogický aspekt. Předložený text by mohl být využit i jako učebnice pro studenty na mé univerzitě v Lybii.

Les matériaux à changement de phase montrent la combinaison exceptionnelle d'un contraste énorme dans leurs propriétés physiques entre la phase amorphe et cristalline allié à une cinétique de changement de phase extrêmement rapide. La grande différence en résistivité permet leur application dans les mémoires numériques. De plus, cette classe de matériaux montre dans leur état vitreux des phénomènes de transport électronique caractéristiques. Le seuil de commutation dénote la chute de la résistivité dans l'état amorphe au delà d'un champ électrique critique. Le phénomène de seuil de commutation permet la transition de phase en appliquant des tensions relativement faibles. Au-dessous de cette valeur critique l'état désordonné montre une conductivité d'obscurité activée en température ainsi qu'une résistance - dans les cellules mémoires et les couches minces également - qui augmente avec le temps. Cette évolution de la résistivité amorphe entrave le stockage à plusieurs niveaux, qui offrirait la possibilité d'accroître la capacité ou la densité de stockage considérablement. Comprendre les origines physiques de ces deux phénomènes est crucial pour développer de meilleures mémoires à changement de phase. Bien que ces deux phénomènes soient généralement attribués aux défauts localisés, la connaissance de la distribution de défauts dans les matériaux amorphes à changement de phase est assez limitée. Cette thèse se concentre sur la densité des défauts mesurée dans différents verres chalcogénures présentant l'effet de seuil de commutation. Sur la base d'expériences de photo courant modulé (MPC) et de spectroscopie par déviation photothermique, un modèle sophistiqué des défauts a été développé pour GeTe amorphe (a-GeTe) mettant en évidence les états de la bande de valence et plusieurs défauts. Cette étude sur a-GeTe montre que l'analyse des données MPC peut être grandement améliorée en prenant en compte la variation de la bande de l'énergie interdite avec la température. Afin de mieux appréhender l'évolution de la résistivité amorphe, la présente étude porte sur l'évolution avec les recuits et le vieillissement de la résistivité, de l'énergie d'activation du courant d'obscurité, de la densité des défauts, du stress mécanique, de l'environnement atomique et de l'énergie de la bande interdite mesurée par des méthodes optiques sur les couches minces de a-GeTe. Le recuit d'un échantillon entraîne un élargissement de la bande interdite et de l'énergie d'activation du courant d'obscurité. De plus, la technique MPC a révélé une diminution des défauts profonds dans les couches minces de a-GeTe vieillies. Ces résultats illustrent l'impact de l'annihilation des défauts et de l'élargissement de la bande interdite sur l'évolution de la résistivité des matériaux à changement de phase amorphe. Cette thèse présente également une étude sur les alliages à changement de phase GeSnTe. En augmentant la concentration d'étain, on observe une décroissance systématique de la résistivité amorphe, de l'énergie d'activation du courant d'obscurité, de la largeur de bande interdite et de la densité des défauts, qui conduisent à une résistivité amorphe plus stables dans les compositions riches en étain comme a-Ge2Sn2Te4. L'étude sur les alliages GeSnTe montre que les matériaux à changement de phase ayant une résistivité amorphe plus stable présentent une faible énergie d'activation du courant d'obscurité. À l'exemple du Ge2Sn2Te4 et GeTe la présente étude montre un lien étroit entre l'évolution de la résistivité et la relaxation du stress mécanique. L'étude sur les verres chalcogénures montrent que les matériaux ayant un grand champ d'électrique de seuil, bien connu d'après la littérature, présentent aussi une grande densité de défauts. Ce résultat implique que l'origine du phénomène de seuil de commutation se trouve dans un mécanisme de génération à travers la bande interdite et de recombinaison dans les défauts profonds comme proposé par D. Adler.

Le magnétisme induit par la lumière décrit l'effet par lequel un matériau est magnétisé par une impulsion optique. Dans les matériaux transparents, la magnétisation induite optiquement peut être réalisée directement par la lumière polarisée circulairement. Parfois, dans les matériaux métalliques, ce type de magnétisation existe également en raison du trajet solénoïdal microscopique des électrons entraînés par la lumière polarisée circulairement. Dans certains cas, la lumière crée des courants de dérive continus circulants macroscopiques, qui induisent également une magnétisation continue dans le métal. De manière générale, ces magnétismes induits par la lumière sont connus sous le nom d'effet Faraday inverse. Dans le projet de doctorat, j'ai étudié les courants de dérive induits par la lumière dans plusieurs nanoantennes en or. Nous avons réalisé des champs magnétiques stationnaires amplifiés plasmoniquement grâce à ces courants de dérive. L'étude est basée sur la méthode des différences finies dans le domaine temporel (FDTD) et les théories correspondantes du magnétisme induit par la lumière. Dans différents sujets de recherche, nous avons réalisé : 1) un champ magnétique stationnaire ultra-rapide, confiné et fort dans une nanoantenne en forme d'œil de taureau. 2) Un champ magnétique stationnaire à travers une polarisation linéaire dans un nanorod. 3) Un skyrmion de type Neel construit par un champ magnétique stationnaire dans un nanoring. Dans ces études, nous avons examiné les propriétés optiques de différentes nanoantennes et expliqué l'origine physique des courants de dérive induits par la lumière et des champs magnétiques stationnaires. Nous avons démontré la méthode pour obtenir des effets Faraday inverses amplifiés plasmoniquement et exploré la possibilité de réaliser une magnétisation par la lumière incidente polarisée linéairement. Enfin, nous avons étendu l'effet Faraday inverse à d'autres domaines de recherche physique, tels que la construction de skyrmions par des champs magnétiques stationnaires à travers l'effet Faraday inverse. L'effet magnétique de la lumière reste un domaine de recherche riche. Mes études pourraient trouver des applications dans de nombreux domaines, y compris les matériaux et dispositifs magnéto-optiques, le stockage de données optiques, les applications biomédicales, la spintronique, l'informatique quantique, la recherche fondamentale en électromagnétisme et la recherche sur les matériaux avancés
Light-induced magnetism describes the effect where a material is magnetized by an optical pulse. In transparent materials, optically-induced magnetization can be realized directly by circularly polarized light. Sometimes, in metallic materials, this type of magnetization also exists due to the microscopic solenoidal path of electrons driven by circularly polarized light. In some cases, the light creates macroscopic circulating DC drift currents, which also induce DC magnetization in metal. In a broad sense, these light-induced magnetisms are known as the inverse Faraday effect.In the PhD project, I studied light-induced drift currents in multiple gold nanoantennas. We realized plasmonically enhanced stationary magnetic fields through these drift currents. The study is based on the Finite-Difference Time-Domain (FDTD) method and the corresponding light-induced magnetism theories. In different research topics, we have realized: 1) an ultrafast, confined, and strong stationary magnetic field in a bull-eye nanoantenna. 2) A stationary magnetic field through linear polarization in a nanorod. 3) A Neel-type skyrmion constructed by a stationary magnetic field in a nanoring. In these studies, we examined the optical properties of different nanoantennas and explained the physical origin of light-induced drift currents and stationary magnetic fields. We demonstrated the method to achieve plasmonically enhanced inverse Faraday effects and explored the possibility of realizing magnetization through linearly polarized incident light. Finally, we extended the inverse Faraday effect to more physical research areas, such as constructing skyrmions by stationary magnetic fields through the inverse Faraday effect.The magnetic effect of light remains a rich area of research. My studies might find applications in many areas, including magneto-optical materials and devices, optical data storage, biomedical applications, spintronics, quantum computing, fundamental research in electromagnetism, and advanced materials research

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2005.
F. Michael Saunders, Ph.D., Committee Member ; Kevin Haas, Ph.D., Committee Member ; Paul A. Work, Ph.D., Committee Chair. Includes bibliographical references.

A contourite drift complex on the J-Anomaly Ridge (JAR) and Southeast Newfoundland Ridge (SENR), offshore eastern Canada, records an extensive archive of North Atlantic circulatory and sedimentary dynamics formed under the influence of the Deep Western Boundary Current (DWBC). Seismic-reflection profiles constrained by drill sites from IODP Expedition 342 are used to map the spatial and temporal distribution of contourite sedimentation and to evaluate the Cenozoic history of the DWBC within a preexisting climatic framework. This study indicates three phases of sedimentation termed here Pre-Contourite-Drift Phase (~115-50 Ma), Active-Contourite-Drift Phase (~50-2.6 Ma), and Post-Contourite-Drift Phase (~2.6-0 Ma). Bottom current controlled sedimentation began at the boundary between Pre-Contourite-Drift Phase and Active-Contourite-Drift Phase (~50 Ma), and correlates to a long-term global cooling trend that initiated at the end of the Early Eocene Climatic Optimum. Within the Active-Contourite-Drift Phase at ~30 Ma depocenters shifted deeper and current energy and focus is interpreted to have increased in association with global oceanographic change at the Eocene-Oligocene transition. The beginning of Post-Contourite-Drift Phase sedimentation (~2.6 Ma) marks a shift in bottom current path towards shallower water depths, and corresponds with the onset of Northern Hemisphere ice sheets. These events of circulatory reorganization correlate with other North Atlantic seismic stratigraphic studies, suggesting that these events occurred throughout the North Atlantic. An improved understanding of long-term (>1000000 yr) dynamics of North Atlantic circulation in response to significant reorganization of Cenozoic climate provides important context towards refining models and prediction of oceanic response to contemporary climate change.
Master of Science

Les principaux objectifs de cette thèse sont :* analyser les mécanismes déterminant l’équilibre rétention / fuite pour l’Azote et le Néon dans le régime de plasma détaché du divertor;* comparer l’efficacité du piégeage relatif aux fuites pour l’Azote et le Néon ainsi que pour les divertors des tokamaks ASDEX-Upgrade et ITER.Pour ce faire, le package de modélisation de code SOLPS-ITER a été développé et utilisé. Dans un premier temps, la précision de la modélisation des impuretés dans SOLPS-ITER a été augmentée en introduisant des formulations analytiques plus précises du frottement et des termes de force thermique. Les principales conclusions de ce travail de modélisation sont :* Le transport des impuretés le long des lignes de champ, de la région du divertor vers la région amont, à proximité du volume de confinement, est différent pour l’Azote et le Néon aussi bien dans ASDEX-U que dans ITER. On observe que la rétention de l’Azote dans le volume divertor est supérieure à celle du Néon dans les simulations pour les deux tokamaks.* Si les mécanismes de rétention et de migration des impuretés dans le divertor donnent des résultats comparables pour ASDEX-Upgrade et pour ITER, la situation est assez différente du point de vue de la distribution spatiale du rayonnement. Cette différence permet de penser que le Néon sera efficace dans les scénarios pour ITER.L’ensemble des résultats de simulation et leurs interprétations a été présenté à la conférence internationale "Plasma Surface Interaction" en 2018 et publié en 2019
The main goals of the present thesis are to:* investigate the differences between retention and leakage mechanisms of nitrogen and neon impurities in the context of the detachment formation;* compare the retention and leakage mechanisms of the nitrogen and neon impurities for the ASDEX Upgrade and ITER.To do this, the SOLPS-ITER code modeling package was further developed and then used. Modeling of ITER and ASDEX Upgrade scenarios with Ne and N impurity seeding was performed. The same ratio of radiated to input power ratio was maintained for all four modeling cases to make further comparisons possible. On the basis of the modeling, the following conclusions are made:* impurity transport from the divertor region upstream is found to be different for the neon and nitrogen impurities in both ITER and ASDEX Upgrade. Nitrogen is found to be better retained in the divertor volume than neon for both devices. * even though the retention and leakage of nitrogen and neon has the same mechanism in ITER and ASDEX Upgrade (nitrogen is better retained), in terms of the radiation distribution point of view thetwo machines behave differently. This difference suggests that neon impurity seeding seem to be an appropriate radiator for the ITER, even though for ASDEX Upgrade it results in an unacceptable radiation pattern

A Neogene contourite depositional system was identified and mapped along the DeSoto Slope in the northeastern Gulf of Mexico, U.S.A. A series of drift deposits comprising the larger contourite depositional system were interpreted from a 2-D industry seismic data set. The now subsurface drift deposits are adjacent to the anomalous seabed feature, the DeSoto Canyon, and these data suggest contourite deposition and ocean currents are in integral part of the canyon’s depositional history. The contourite depositional system is underlain by an extensive, middle Miocene aged, erosional unconformity formed by ocean currents. The timing of this erosional surface is in alignment with the widely accepted premise that the Miocene represented a transitional period in Gulf of Mexico basin circulation. The discovery of this contourite depositional system adds to an established list of Miocene-aged features pointing to the onset of enhanced Loop Current circulation in the Neogene Gulf of Mexico.

For over a period of over sixty years, South Africa has applied the provisions of the MSA enacted in 1951 to matters relating to shipowner’s right to limit liability. Since then, Parliament has made several attempts at amending the MSA with no success. However, determining whether South Africa should implement the proposed amendments in terms of the MSA Draft Bill, is an inquiry that should not only include a comparison of the old order with the newly proposed order, but, it should also require reasons as to why the reform should be achieved in a particular manner. This is important because knowing what the discrepancies of the current dispensation are, will enable us to evaluate whether the newly proposed amendments will address them.

Effective prediction of objects drifting on the water surface is essential to successful maritime search and rescue (SAR) services, since a more accurate prediction of the object’s likely location results in a greater probability for the success of a SAR operation. SAR drift models, based on Lagrangian stochastic particle trajectory models, are frequently utilised for this task. More recently, metocean (meteorological and oceanographic) forecast data has been used as input to these models to provide the environmental forcing (due to winds and ocean currents) that the object may be subject to. Further, the slip of a drifting object across the water surface due to the ambient wind and waves (irrespective of currents) is described by its leeway drift coefficients, which are also required by the SAR drift model to calculate the potential drift of the object. This study examined several ways to improve the prediction of an objects drift on the water surface, with the primary focus being the improvement of SAR forecasting. To achieve this, many simulations were undertaken, comparing the trajectories of actual drifters deployed in the ocean, and the corresponding model simulations of drift, using the commercially available SARMAP (Search and Rescue Mapping and Analysis Program) SAR drift model. Each drifter trajectory was simulated independently using a different ocean model to provide ocean current forcing. The ocean models tested included BLUElink, FOAM (Forecasting Ocean Assimilation Model), HYCOM (Hybrid Coordinate Ocean Model) and NCOM (Navy Coastal Ocean Model).
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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Le Canal de Corse est un bassin confiné asymétrique localisé entre l’Île de Corse et l’Archipel de la Toscane, dont le flanc ouest est dominé par des processus turbiditiques et hémipélagiques et le flanc est par des mouvements en masse et des processus contouritiques. Le présent projet de doctorat a pour objectif de comprendre plus précisément les mécanismes contrôlant la formation des glissements sous-marins dans les contourites vaseuses (dépôts sédimentaires formés par les courants) pendant la période Plio-Quaternaire. Le vaste jeu de données disponible pour ce projet de doctorat inclut : la bathymétrie multifaisceaux, la sismique réflexion, les mesures géotechniques in situ, les mesures de vitesse de courant et les résultats d’un modèle hydrodynamique.Les contourites du Canal de Corse sont principalement composées de vase avec la présence de couches de sable formées par de forts courants de fond pendant les périodes de baisse du niveau marin. La croissance des dépôts contouritiques dépend de la disponibilité de sédiment fourni par le système turbiditique. Ainsi, cette croissance est lente pendant les périodes interglaciaires de haut niveau marin et rapide pendant les bas niveaux marins. Les courants contrôlent la morphologie du fond et génèrent les plastered drifts de forme convexe avec des pentes plus raides dans la partie avale, limités par une incision créée par les courants (moat). Le Pianosa Slump a été initié dans cette partie basse du plastered drift. Les moats pourraient être érodés préférentiellement pendant les périodes froides passées déclenchant ainsi certains glissements observés. Un autre facteur prédisposant l’instabilité de pente sur la Ride de Pianosa est la faiblesse d’une couche dont le comportement mécanique se caractérise par du radoucissement (perte de résistance avec le cisaillement). Cette propriété particulière est due à la présence de zéolites (produit de l’altération des roches volcaniques). Cette couche a formé la surface basale de rupture du Pianosa Slump. En conclusion, les deux principaux facteurs prédisposant la formation de glissements sous-marins sur la Ride de Pianosa sont : la morphologie du plastered drift avec une pente plus raide en aval et la couche faible composée de sédiment vaseux riche en zéolites. Le principal facteur déclenchant semble être l’érosion basale
The Corsica Trough is an asymmetric confined basin located between the Corsica Island and the Tuscan Ar-chipelago, with the western flank dominated by turbiditic and hemipelagic processes and the eastern flank by mass transport and contouritic processes. The present PhD project aims to develop our understanding of the mechanisms that control the formation of submarine landslides within muddy contourites (sediment deposits related to bottom currents) during the Plio-Quaternary. The broad data set available for this PhD project includes: multibeam bathymetry, seismic reflection data, sediment cores, in situ geotechnical measurements, current ADCP measurements and results of a hydrodynamic model.The contourites of the Corsica Trough are mainly composed of mud with sandy layers formed by enhanced bottom currents during periods of sea level fall. The contourite drifts grow slowly during sea level high-stands and rapidly during sea level low-stands due to the high sediment availability provided by an active turbidite sys¬tem. Bottom currents control the seafloor morphology and generate plastered drifts on the slope. This is a con¬vex-shaped contourite with steep slope gradients in the lower part limited by a moat (incision created by bottom currents). The Pianosa Slump was initiated in this lower part of the plastered drift. The occurrence of continuous erosive processes during cold periods could undercut the slope and trigger submarine landslides. Another predis¬posing factor for slope instability identified is the presence of a potential weak layer with a post-peak strain soften¬ing behaviour (strength loss with increasing strain). This particular property is caused by the presence of zeolites (product of the alteration of volcanic rocks). This layer originated the basal failure surface of the Pianosa Slump.In summary, the two main factors predispose the formation of submarine landslides in the Pianosa Ridge are: the morphology of the plastered drift with steep slopes in the lower part and a potential weak layer composed of zeolitic muddy sediment. The main triggering factor seems to be undercutting by bottom currents

The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when they experience the same transport processes. These particles spend more time in the heliosphere, and also lose more energy, in the drift cycle where they drift towards Earth mainly along the heliospheric current sheet. The propagation times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric tilt angles and it is found that current sheet drift becomes less effective with increasing solar activity. Comparing calculated propagation times of Jovian electrons with observations, the transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton to anti-proton ratio at Earth and comparing the results to recent PAMELA observations. A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using this model, it is shown that cosmic ray modulation persists beyond the heliopause. The level of modulation in this region is found to exhibit solar cycle related changes and, more importantly, is independent of the magnitude of the individual diffusion coefficients, but is rather determined by the ratio of parallel to perpendicular diffusion.
PhD (Space Physics), North-West University, Potchefstroom Campus, 2013

Organic semiconductors are a new key technology for large-area and flexible thin-film electronics. They are deposited as thin films (sub-nanometer to micrometer) on large-area substrates. The technologically most advanced applications are organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). For the improvement of performance and efficiency, correct modeling of the electronic processes in the devices is essential. Reliable characterization and validation of the electronic properties of the materials is simultaneously required for the successful optimization of devices. Furthermore, understanding the relations between material structures and their key characteristics opens the path for innovative material and device design. In this thesis, two material characterization methods are developed, respectively refined and applied: a novel technique for measuring the charge carrier mobility μ and a way to determine the ionization energy IE or the electron affinity EA of an organic semiconductor. For the mobility measurements, a new evaluation approach for space-charge limited current (SCLC) measurements in single carrier devices is developed. It is based on a layer thickness variation of the material under investigation. In the \"potential mapping\" (POEM) approach, the voltage as a function of the device thickness V(d) at a given current density is shown to coincide with the spatial distribution of the electric potential V(x) in the thickest device. On this basis, the mobility is directly obtained as function of the electric field F and the charge carrier density n. The evaluation is model-free, i.e. a model for μ(F, n) to fit the measurement data is not required, and the measurement is independent of a possible injection barrier or potential drop at non-optimal contacts. The obtained μ(F, n) function describes the effective average mobility of free and trapped charge carriers. This approach realistically describes charge transport in energetically disordered materials, where a clear differentiation between trapped and free charges is impossible or arbitrary. The measurement of IE and EA is performed by characterizing solar cells at varying temperature T. In suitably designed devices based on a bulk heterojunction (BHJ), the open-circuit voltage Voc is a linear function of T with negative slope in the whole measured range down to 180K. The extrapolation to temperature zero V0 = Voc(T → 0K) is confirmed to equal the effective gap Egeff, i.e. the difference between the EA of the acceptor and the IE of the donor. The successive variation of different components of the devices and testing their influence on V0 verifies the relation V0 = Egeff. On this basis, the IE or EA of a material can be determined in a BHJ with a material where the complementary value is known. The measurement is applied to a number of material combinations, confirming, refining, and complementing previously reported values from ultraviolet photo electron spectroscopy (UPS) and inverse photo electron spectroscopy (IPES). These measurements are applied to small molecule organic semiconductors, including mixed layers. In blends of zinc-phthalocyanine (ZnPc) and C60, the hole mobility is found to be thermally and field activated, as well as increasing with charge density. Varying the mixing ratio, the hole mobility is found to increase with increasing ZnPc content, while the effective gap stays unchanged. A number of further materials and material blends are characterized with respect to hole and electron mobility and the effective gap, including highly diluted donor blends, which have been little investigated before. In all materials, a pronounced field activation of the mobility is observed. The results enable an improved detailed description of the working principle of organic solar cells and support the future design of highly efficient and optimized devices
Organische Halbleiter sind eine neue Schlüsseltechnologie für großflächige und flexible Dünnschichtelektronik. Sie werden als dünne Materialschichten (Sub-Nanometer bis Mikrometer) auf großflächige Substrate aufgebracht. Die technologisch am weitesten fortgeschrittenen Anwendungen sind organische Leuchtdioden (OLEDs) und organische Photovoltaik (OPV). Zur weiteren Steigerung von Leistungsfähigkeit und Effizienz ist die genaue Modellierung elektronischer Prozesse in den Bauteilen von grundlegender Bedeutung. Für die erfolgreiche Optimierung von Bauteilen ist eine zuverlässige Charakterisierung und Validierung der elektronischen Materialeigenschaften gleichermaßen erforderlich. Außerdem eröffnet das Verständnis der Zusammenhänge zwischen Materialstruktur und -eigenschaften einen Weg für innovative Material- und Bauteilentwicklung. Im Rahmen dieser Dissertation werden zwei Methoden für die Materialcharakterisierung entwickelt, verfeinert und angewandt: eine neuartige Methode zur Messung der Ladungsträgerbeweglichkeit μ und eine Möglichkeit zur Bestimmung der Ionisierungsenergie IE oder der Elektronenaffinität EA eines organischen Halbleiters. Für die Beweglichkeitsmessungen wird eine neue Auswertungsmethode für raumladungsbegrenzte Ströme (SCLC) in unipolaren Bauteilen entwickelt. Sie basiert auf einer Schichtdickenvariation des zu charakterisierenden Materials. In einem Ansatz zur räumlichen Abbildung des elektrischen Potentials (\"potential mapping\", POEM) wird gezeigt, dass das elektrische Potential als Funktion der Schichtdicke V(d) bei einer gegebenen Stromdichte dem räumlichen Verlauf des elektrischen Potentials V(x) im dicksten Bauteil entspricht. Daraus kann die Beweglichkeit als Funktion des elektrischen Felds F und der Ladungsträgerdichte n berechnet werden. Die Auswertung ist modellfrei, d.h. ein Modell zum Angleichen der Messdaten ist für die Berechnung von μ(F, n) nicht erforderlich. Die Messung ist außerdem unabhängig von einer möglichen Injektionsbarriere oder einer Potentialstufe an nicht-idealen Kontakten. Die gemessene Funktion μ(F, n) beschreibt die effektive durchschnittliche Beweglichkeit aller freien und in Fallenzuständen gefangenen Ladungsträger. Dieser Zugang beschreibt den Ladungstransport in energetisch ungeordneten Materialien realistisch, wo eine klare Unterscheidung zwischen freien und Fallenzuständen nicht möglich oder willkürlich ist. Die Messung von IE und EA wird mithilfe temperaturabhängiger Messungen an Solarzellen durchgeführt. In geeigneten Bauteilen mit einem Mischschicht-Heteroübergang (\"bulk heterojunction\" BHJ) ist die Leerlaufspannung Voc im gesamten Messbereich oberhalb 180K eine linear fallende Funktion der Temperatur T. Es kann bestätigt werden, dass die Extrapolation zum Temperaturnullpunkt V0 = Voc(T → 0K) mit der effektiven Energielücke Egeff , d.h. der Differenz zwischen EA des Akzeptor-Materials und IE des Donator-Materials, übereinstimmt. Die systematische schrittweise Variation einzelner Bestandteile der Solarzellen und die Überprüfung des Einflusses auf V0 bestätigen die Beziehung V0 = Egeff. Damit kann die IE oder EA eines Materials bestimmt werden, indem man es in einem BHJ mit einem Material kombiniert, dessen komplementärer Wert bekannt ist. Messungen per Ultraviolett-Photoelektronenspektroskopie (UPS) und inverser Photoelektronenspektroskopie (IPES) werden damit bestätigt, präzisiert und ergänzt. Die beiden entwickelten Messmethoden werden auf organische Halbleiter aus kleinen Molekülen einschließlich Mischschichten angewandt. In Mischschichten aus Zink-Phthalocyanin (ZnPc) und C60 wird eine Löcherbeweglichkeit gemessen, die sowohl thermisch als auch feld- und ladungsträgerdichteaktiviert ist. Wenn das Mischverhältnis variiert wird, steigt die Löcherbeweglichkeit mit zunehmendem ZnPc-Anteil, während die effektive Energielücke unverändert bleibt. Verschiedene weitere Materialien und Materialmischungen werden hinsichtlich Löcher- und Elektronenbeweglichkeit sowie ihrer Energielücke charakterisiert, einschließlich bisher wenig untersuchter hochverdünnter Donator-Systeme. In allen Materialien wird eine deutliche Feldaktivierung der Beweglichkeit beobachtet. Die Ergebnisse ermöglichen eine verbesserte Beschreibung der detaillierten Funktionsweise organischer Solarzellen und unterstützen die künftige Entwicklung hocheffizienter und optimierter Bauteile

碩士
國立成功大學
水利及海洋工程學系碩博士班
94
With the increasing of population and the improvement of industrial and/or commercial activities, coastal zone’s usage has been put on more emphasis in Taiwan. Due to the limit territory and ocean surrounding environment, it is necessary to ensure the efficient usage of space and avoid the negative affections caused by human over-developed in coastal zone. So, nearshore current survey and marine data collections such as wind, wave, and depth were indispensable on the characters studing of coastal zone. The relative low price free drift float which is based on GPS positioning and Radio transmission technique carried out the measuring operation instead of using the precious bottom assembled ADCP/current meter to describe the marine flow field characters. Operation risk so, could be reduced by using several free drift floats and few of precious equipment to pick up the current data in marine environment. Theoretically, similar measuring results (false in reality) should be obtained with Eulerian type measuring (ADCP/current meter) and Lagrangian type (free drift float) procedure under the stationary assumption. These studies focus on the wind effect research of interfering the drift tracking and to evaluate the positioning accuracy of this custom-built free drift float. The coastal zone in between southern(Ching Shuei) and northern(Gong Guan) coast of Lan Yang River in YiLan has been selected as the test environment. According to the test results, the free drift float can response the nearshore current field character in 3m/s less of wind velocity and begin gradually the interfering in 1.5m/s up of wind velocity. The average longshore current velocity estimated by both Sato and Eagleson(1965) formula provided a verification datum of current measuring by the free drift float and being identical in speed and, the deviation of 28% in speed has been found which could be affected by wind. Through the measuring data corrected by environmental interfere factors, the free drift float can be applied in field measuring operation and offer the accurate current data as references on coastal engineering planning, designing, evaluating and managing.

abstract: A general continuum model for simulating the flow of ions in the salt baths that surround and fill excitable neurons is developed and presented. The ion densities and electric potential are computed using the drift-diffusion equations. In addition, a detailed model is given for handling the electrical dynamics on interior membrane boundaries, including a model for ion channels in the membranes that facilitate the transfer of ions in and out of cells. The model is applied to the triad synapse found in the outer plexiform layer of the retina in most species. Experimental evidence suggests the existence of a negative feedback pathway between horizontal cells and cone photoreceptors that modulates the flow of calcium ions into the synaptic terminals of cones. However, the underlying mechanism for this feedback is controversial and there are currently three competing hypotheses: the ephaptic hypothesis, the pH hypothesis and the GABA hypothesis. The goal of this work is to test some features of the ephaptic hypothesis using detailed simulations that employ rigorous numerical methods. The model is first applied in a simple rectangular geometry to demonstrate the effects of feedback for different extracellular gap widths. The model is then applied to a more complex and realistic geometry to demonstrate the existence of strictly electrical feedback, as predicted by the ephaptic hypothesis. Lastly, the effects of electrical feedback in regards to the behavior of the bipolar cell membrane potential is explored. Figures for the ion densities and electric potential are presented to verify key features of the model. The computed steady state IV curves for several cases are presented, which can be compared to experimental data. The results provide convincing evidence in favor of the ephaptic hypothesis since the existence of feedback that is strictly electrical in nature is shown, without any dependence on pH effects or chemical transmitters.
Dissertation/Thesis
Ph.D. Applied Mathematics 2013

A medição de correntes em tempo quasi-real pelos sistemas de deteção remota assume grande relevo para as atividades desenvolvidas no mar, tanto militares como civis. Os dados obtidos através dos radares de alta frequência (HF), no caso específico de Portugal os CODAR SeaSonde, são também fundamentais nas operações de busca e salvamento e de recolha de objetos à deriva, visto que permite um cálculo da deriva mais próximo da realidade. O presente trabalho focou-se na análise da deriva estimada através dos dados obtidos pelo sistema de radares HF de Lisboa, e na sua comparação com a deriva real de cinco objetos. Os objetos foram lançados à água durante o exercício DERIVEX, inserido no exercício GUARDEX 13, tendo sido os seus percursos monitorizados através de derivantes equipados com localizadores GPS (Global Positioning System). Pela comparação das derivas estimadas, considerando apenas os dados das correntes obtidas pelos radares HF, com as derivas reais dos cinco objetos, foi possível perceber que dois dos objetos apresentaram um percurso mais semelhante ao estimado. Estes dois objetos, ao contrário do que se poderia esperar, entre os cinco, são os que têm uma maior área vélica. Este facto pode dever-se à superficialidade das correntes que são determinadas pelos radares HF. Torna-se, por isso, necessário a continuação de estudos associados aos radares HF para se poder tirar o melhor proveito possível dos dados que fornecem.
The measurement of currents in almost real time by the remote sensing systems takes great importance for the activities developed at sea, both military and civil. The data obtained through the high-frequency (HF) radars, in the specific case of Portugal, the CODAR SeaSonde, are also fundamental in the search and rescue operations and the collection of drifting objects, since it allows a calculation of the drift closest to the reality. The present work focused on the analysis of the estimated drift through the data obtained by the Lisbon HF radar system, and in its comparison with the real drift of five objects. The objects were thrown into the water during the DERIVEX exercise, inserted in the GUARDEX 13 exercise, and their tracks were monitored through drifts equipped with GPS locators. By comparing the estimated drifts, considering only the data of the currents obtained by the HF radars, with the real drifts of the five objects, it was possible to notice that two of the objects presented a path similar to the one estimated. These two objects, contrary to what could be expected, among the five, are those that have a greater wing area. This may be due to the superficiality of the currents that are determined by the HF radar. It is therefore necessary to continue studies associated with HF radars in order to make the best use of the data they provide.

Until recently, numerical modulation models for the solar modulation of cosmic rays have been based primarily on finite difference approaches; however, models based on the solution of an appropriate set of stochastic differential equations have become increasingly popular. This study utilises such a spatially three-dimensional and time-stationary model, based on that of Strauss et al. (2011b). The remarkable numerical stability and powerful illustrative capabilities of this model are utilised extensively and in a distinctly comparative fashion to enable new insights into the processes of modulation. The model is refined to provide for both the Smith-Bieber (Smith and Bieber, 1991) and Jokipii-Kota (Jokipii and Kota, 1989) modifcations to the Parker heliospheric magnetic field (Parker, 1958) and the implications for modulation are investigated. During this investigation it is conclusively illustrated that the Parker field is most conducive to drift dominated modulation, while the Jokipii-Kota and Smith-Bieber modifcations are seen to induce successively larger contributions from diffusive processes. A further refinement to the model is the incorporation of a different profile for the heliospheric current sheet. This profile is defined by its latitudinal extent given by Kota and Jokipii (1983), as opposed to the profile given by Jokipii and Thomas (1981). An extensive investigation into current sheet related matters is launched, illustrating the difference between these current sheet geometries, the associated drift velocity fields and the effect on modulation. At high levels of solar activity, such that the current sheet enters deep enough into the polar regions, the profile of Kota and Jokipii (1983) is found to significantly reduce the effective inward (outward) drifts of positively (negatively) charged particles during A > 0 polarity cycles. The analogous effect is true for A < 0 polarity cycles and the overall effect is of such an extent that the A > 0 and A < 0 solutions are found to coincide at the highest levels of solar activity to form a closed loop. This is a result that has never before been achieved without having to scale down the drift coefficient to zero at solar maximum, as was done by e.g. Ndiitwani et al. (2005). Furthermore, it is found that the drift velocity fields associated with these two current sheet profiles lead to significant differences in modulation even at such low levels of solar activity where no difference in the geometries of these profiles are yet in evidence. The model is finally applied to reproduce four observed galactic proton spectra, selected from PAMELA measurements (Adriani et al., 2013) during the atypical solar minimum of 2006 to 2009; a new proton local interstellar spectrum was employed. The results are found to be in accordance with that found by other authors and in particular Vos (2011), i.e. the diffusion was required to consistently increase from 2006 to 2009 and, in addition, the rigidity dependence below ~ 3 GV was required to change over this time so that the spectra became increasingly softer.
MSc (Space Physics), North-West University, Potchefstroom Campus, 2015

Organic semiconductors are a new key technology for large-area and flexible thin-film electronics. They are deposited as thin films (sub-nanometer to micrometer) on large-area substrates. The technologically most advanced applications are organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). For the improvement of performance and efficiency, correct modeling of the electronic processes in the devices is essential. Reliable characterization and validation of the electronic properties of the materials is simultaneously required for the successful optimization of devices. Furthermore, understanding the relations between material structures and their key characteristics opens the path for innovative material and device design. In this thesis, two material characterization methods are developed, respectively refined and applied: a novel technique for measuring the charge carrier mobility μ and a way to determine the ionization energy IE or the electron affinity EA of an organic semiconductor. For the mobility measurements, a new evaluation approach for space-charge limited current (SCLC) measurements in single carrier devices is developed. It is based on a layer thickness variation of the material under investigation. In the \"potential mapping\" (POEM) approach, the voltage as a function of the device thickness V(d) at a given current density is shown to coincide with the spatial distribution of the electric potential V(x) in the thickest device. On this basis, the mobility is directly obtained as function of the electric field F and the charge carrier density n. The evaluation is model-free, i.e. a model for μ(F, n) to fit the measurement data is not required, and the measurement is independent of a possible injection barrier or potential drop at non-optimal contacts. The obtained μ(F, n) function describes the effective average mobility of free and trapped charge carriers. This approach realistically describes charge transport in energetically disordered materials, where a clear differentiation between trapped and free charges is impossible or arbitrary. The measurement of IE and EA is performed by characterizing solar cells at varying temperature T. In suitably designed devices based on a bulk heterojunction (BHJ), the open-circuit voltage Voc is a linear function of T with negative slope in the whole measured range down to 180K. The extrapolation to temperature zero V0 = Voc(T → 0K) is confirmed to equal the effective gap Egeff, i.e. the difference between the EA of the acceptor and the IE of the donor. The successive variation of different components of the devices and testing their influence on V0 verifies the relation V0 = Egeff. On this basis, the IE or EA of a material can be determined in a BHJ with a material where the complementary value is known. The measurement is applied to a number of material combinations, confirming, refining, and complementing previously reported values from ultraviolet photo electron spectroscopy (UPS) and inverse photo electron spectroscopy (IPES). These measurements are applied to small molecule organic semiconductors, including mixed layers. In blends of zinc-phthalocyanine (ZnPc) and C60, the hole mobility is found to be thermally and field activated, as well as increasing with charge density. Varying the mixing ratio, the hole mobility is found to increase with increasing ZnPc content, while the effective gap stays unchanged. A number of further materials and material blends are characterized with respect to hole and electron mobility and the effective gap, including highly diluted donor blends, which have been little investigated before. In all materials, a pronounced field activation of the mobility is observed. The results enable an improved detailed description of the working principle of organic solar cells and support the future design of highly efficient and optimized devices.:1. Introduction 2. Organic semiconductors and devices 2.1. Organic semiconductors 2.1.1. Conjugated π system 2.1.2. Small molecules and polymers 2.1.3. Disorder in amorphous materials 2.1.4. Polarons 2.1.5. Polaron hopping 2.1.6. Fermi-Dirac distribution and Fermi level 2.1.7. Quasi-Fermi levels 2.1.8. Trap states 2.1.9. Doping 2.1.10. Excitons 2.2. Interfaces and blend layers 2.2.1. Interface dipoles 2.2.2. Energy level bending 2.2.3. Injection from metal into semiconductor, and extraction 2.2.4. Excitons at interfaces 2.3. Charge transport and recombination in organic semiconductors 2.3.1. Drift transport 2.3.2. Charge carrier mobility 2.3.3. Thermally activated transport 2.3.4. Diffusion transport 2.3.5. Drift-diffusion transport 2.3.6. Space-charge limited current 2.3.7. Recombination 2.4. Mobility measurement 2.4.1. SCLC and TCLC 2.4.2. Time of flight 2.4.3. Organic field effect transistors 2.4.4. CELIV 2.5. Organic solar cells 2.5.1. Exciton diffusion towards the interface 2.5.2. Dissociation of CT states 2.5.3. CT recombination 2.5.4. Flat and bulk heterojunction 2.5.5. Transport layers 2.5.6. Thin film optics 2.5.7. Current-voltage characteristics and equivalent circuit 2.5.8. Solar cell efficiency 2.5.9. Limits of efficiency 2.5.10. Correct solar cell characterization 2.5.11. The \"O-Factor\" 3. Materials and experimental methods 3.1. Materials 3.2. Device fabrication and layout 3.2.1. Layer deposition 3.2.2. Encapsulation 3.2.3. Homogeneity of layer thickness on a wafer 3.2.4. Device layout 3.3. Characterization 3.3.1. Electrical characterization 3.3.2. Sample illumination 3.3.3. Temperature dependent characterization 3.3.4. UPS 4. Simulations 5.1. Design of single carrier devices 5.1.1. General design requirements 5.1.2. Single carrier devices for space-charge limited current 5.1.3. Ohmic regime 5.1.4. Design of injection and extraction layers 5.2. Advanced evaluation of SCLC – potential mapping 5.2.1. Potential mapping by thickness variation 5.2.2. Further evaluation of the transport profile 5.2.3. Injection into and extraction from single carrier devices 5.2.4. Majority carrier approximation 5.3. Proof of principle: POEM on simulated data 5.3.1. Constant mobility 5.3.2. Field dependent mobility 5.3.3. Field and charge density activated mobility 5.3.4. Conclusion 5.4. Application: Transport characterization in organic semiconductors 5.4.1. Hole transport in ZnPc:C60 5.4.2. Hole transport in ZnPc:C60 – temperature variation 5.4.3. Hole transport in ZnPc:C60 – blend ratio variation 5.4.4. Hole transport in ZnPc:C70 5.4.5. Hole transport in neat ZnPc 5.4.6. Hole transport in F4-ZnPc:C60 5.4.7. Hole transport in DCV-5T-Me33:C60 5.4.8. Electron transport in ZnPc:C60 5.4.9. Electron transport in neat Bis-HFl-NTCDI 5.5. Summary and discussion of the results 5.5.1. Phthalocyanine:C60 blends 5.5.2. DCV-5T-Me33:C60 5.5.3. Conclusion 6. Organic solar cell characteristics: the influence of temperature 6.1. ZnPc:C60 solar cells 6.1.1. Temperature variation 6.1.2. Illumination intensity variation 6.2. Voc in flat and bulk heterojunction organic solar cells 6.2.1. Qualitative difference in Voc(I, T) 6.2.2. Interpretation of Voc(I, T) 6.3. BHJ stoichiometry variation 6.3.1. Voc upon variation of stoichiometry and contact layer 6.3.2. V0 upon stoichiometry variation 6.3.3. Low donor content stoichiometry 6.3.4. Conclusion from stoichiometry variation 6.4. Transport material variation 6.4.1. HTM variation 6.4.2. ETM variation 6.5. Donor:acceptor material variation 6.5.1. Donor variation 6.5.2. Acceptor variation 6.6. Conclusion 7. Summary and outlook 7.1. Summary 7.2. Outlook A. Appendix A.1. Energy pay-back of this thesis A.2. Tables and registers
Organische Halbleiter sind eine neue Schlüsseltechnologie für großflächige und flexible Dünnschichtelektronik. Sie werden als dünne Materialschichten (Sub-Nanometer bis Mikrometer) auf großflächige Substrate aufgebracht. Die technologisch am weitesten fortgeschrittenen Anwendungen sind organische Leuchtdioden (OLEDs) und organische Photovoltaik (OPV). Zur weiteren Steigerung von Leistungsfähigkeit und Effizienz ist die genaue Modellierung elektronischer Prozesse in den Bauteilen von grundlegender Bedeutung. Für die erfolgreiche Optimierung von Bauteilen ist eine zuverlässige Charakterisierung und Validierung der elektronischen Materialeigenschaften gleichermaßen erforderlich. Außerdem eröffnet das Verständnis der Zusammenhänge zwischen Materialstruktur und -eigenschaften einen Weg für innovative Material- und Bauteilentwicklung. Im Rahmen dieser Dissertation werden zwei Methoden für die Materialcharakterisierung entwickelt, verfeinert und angewandt: eine neuartige Methode zur Messung der Ladungsträgerbeweglichkeit μ und eine Möglichkeit zur Bestimmung der Ionisierungsenergie IE oder der Elektronenaffinität EA eines organischen Halbleiters. Für die Beweglichkeitsmessungen wird eine neue Auswertungsmethode für raumladungsbegrenzte Ströme (SCLC) in unipolaren Bauteilen entwickelt. Sie basiert auf einer Schichtdickenvariation des zu charakterisierenden Materials. In einem Ansatz zur räumlichen Abbildung des elektrischen Potentials (\"potential mapping\", POEM) wird gezeigt, dass das elektrische Potential als Funktion der Schichtdicke V(d) bei einer gegebenen Stromdichte dem räumlichen Verlauf des elektrischen Potentials V(x) im dicksten Bauteil entspricht. Daraus kann die Beweglichkeit als Funktion des elektrischen Felds F und der Ladungsträgerdichte n berechnet werden. Die Auswertung ist modellfrei, d.h. ein Modell zum Angleichen der Messdaten ist für die Berechnung von μ(F, n) nicht erforderlich. Die Messung ist außerdem unabhängig von einer möglichen Injektionsbarriere oder einer Potentialstufe an nicht-idealen Kontakten. Die gemessene Funktion μ(F, n) beschreibt die effektive durchschnittliche Beweglichkeit aller freien und in Fallenzuständen gefangenen Ladungsträger. Dieser Zugang beschreibt den Ladungstransport in energetisch ungeordneten Materialien realistisch, wo eine klare Unterscheidung zwischen freien und Fallenzuständen nicht möglich oder willkürlich ist. Die Messung von IE und EA wird mithilfe temperaturabhängiger Messungen an Solarzellen durchgeführt. In geeigneten Bauteilen mit einem Mischschicht-Heteroübergang (\"bulk heterojunction\" BHJ) ist die Leerlaufspannung Voc im gesamten Messbereich oberhalb 180K eine linear fallende Funktion der Temperatur T. Es kann bestätigt werden, dass die Extrapolation zum Temperaturnullpunkt V0 = Voc(T → 0K) mit der effektiven Energielücke Egeff , d.h. der Differenz zwischen EA des Akzeptor-Materials und IE des Donator-Materials, übereinstimmt. Die systematische schrittweise Variation einzelner Bestandteile der Solarzellen und die Überprüfung des Einflusses auf V0 bestätigen die Beziehung V0 = Egeff. Damit kann die IE oder EA eines Materials bestimmt werden, indem man es in einem BHJ mit einem Material kombiniert, dessen komplementärer Wert bekannt ist. Messungen per Ultraviolett-Photoelektronenspektroskopie (UPS) und inverser Photoelektronenspektroskopie (IPES) werden damit bestätigt, präzisiert und ergänzt. Die beiden entwickelten Messmethoden werden auf organische Halbleiter aus kleinen Molekülen einschließlich Mischschichten angewandt. In Mischschichten aus Zink-Phthalocyanin (ZnPc) und C60 wird eine Löcherbeweglichkeit gemessen, die sowohl thermisch als auch feld- und ladungsträgerdichteaktiviert ist. Wenn das Mischverhältnis variiert wird, steigt die Löcherbeweglichkeit mit zunehmendem ZnPc-Anteil, während die effektive Energielücke unverändert bleibt. Verschiedene weitere Materialien und Materialmischungen werden hinsichtlich Löcher- und Elektronenbeweglichkeit sowie ihrer Energielücke charakterisiert, einschließlich bisher wenig untersuchter hochverdünnter Donator-Systeme. In allen Materialien wird eine deutliche Feldaktivierung der Beweglichkeit beobachtet. Die Ergebnisse ermöglichen eine verbesserte Beschreibung der detaillierten Funktionsweise organischer Solarzellen und unterstützen die künftige Entwicklung hocheffizienter und optimierter Bauteile.:1. Introduction 2. Organic semiconductors and devices 2.1. Organic semiconductors 2.1.1. Conjugated π system 2.1.2. Small molecules and polymers 2.1.3. Disorder in amorphous materials 2.1.4. Polarons 2.1.5. Polaron hopping 2.1.6. Fermi-Dirac distribution and Fermi level 2.1.7. Quasi-Fermi levels 2.1.8. Trap states 2.1.9. Doping 2.1.10. Excitons 2.2. Interfaces and blend layers 2.2.1. Interface dipoles 2.2.2. Energy level bending 2.2.3. Injection from metal into semiconductor, and extraction 2.2.4. Excitons at interfaces 2.3. Charge transport and recombination in organic semiconductors 2.3.1. Drift transport 2.3.2. Charge carrier mobility 2.3.3. Thermally activated transport 2.3.4. Diffusion transport 2.3.5. Drift-diffusion transport 2.3.6. Space-charge limited current 2.3.7. Recombination 2.4. Mobility measurement 2.4.1. SCLC and TCLC 2.4.2. Time of flight 2.4.3. Organic field effect transistors 2.4.4. CELIV 2.5. Organic solar cells 2.5.1. Exciton diffusion towards the interface 2.5.2. Dissociation of CT states 2.5.3. CT recombination 2.5.4. Flat and bulk heterojunction 2.5.5. Transport layers 2.5.6. Thin film optics 2.5.7. Current-voltage characteristics and equivalent circuit 2.5.8. Solar cell efficiency 2.5.9. Limits of efficiency 2.5.10. Correct solar cell characterization 2.5.11. The \"O-Factor\" 3. Materials and experimental methods 3.1. Materials 3.2. Device fabrication and layout 3.2.1. Layer deposition 3.2.2. Encapsulation 3.2.3. Homogeneity of layer thickness on a wafer 3.2.4. Device layout 3.3. Characterization 3.3.1. Electrical characterization 3.3.2. Sample illumination 3.3.3. Temperature dependent characterization 3.3.4. UPS 4. Simulations 5.1. Design of single carrier devices 5.1.1. General design requirements 5.1.2. Single carrier devices for space-charge limited current 5.1.3. Ohmic regime 5.1.4. Design of injection and extraction layers 5.2. Advanced evaluation of SCLC – potential mapping 5.2.1. Potential mapping by thickness variation 5.2.2. Further evaluation of the transport profile 5.2.3. Injection into and extraction from single carrier devices 5.2.4. Majority carrier approximation 5.3. Proof of principle: POEM on simulated data 5.3.1. Constant mobility 5.3.2. Field dependent mobility 5.3.3. Field and charge density activated mobility 5.3.4. Conclusion 5.4. Application: Transport characterization in organic semiconductors 5.4.1. Hole transport in ZnPc:C60 5.4.2. Hole transport in ZnPc:C60 – temperature variation 5.4.3. Hole transport in ZnPc:C60 – blend ratio variation 5.4.4. Hole transport in ZnPc:C70 5.4.5. Hole transport in neat ZnPc 5.4.6. Hole transport in F4-ZnPc:C60 5.4.7. Hole transport in DCV-5T-Me33:C60 5.4.8. Electron transport in ZnPc:C60 5.4.9. Electron transport in neat Bis-HFl-NTCDI 5.5. Summary and discussion of the results 5.5.1. Phthalocyanine:C60 blends 5.5.2. DCV-5T-Me33:C60 5.5.3. Conclusion 6. Organic solar cell characteristics: the influence of temperature 6.1. ZnPc:C60 solar cells 6.1.1. Temperature variation 6.1.2. Illumination intensity variation 6.2. Voc in flat and bulk heterojunction organic solar cells 6.2.1. Qualitative difference in Voc(I, T) 6.2.2. Interpretation of Voc(I, T) 6.3. BHJ stoichiometry variation 6.3.1. Voc upon variation of stoichiometry and contact layer 6.3.2. V0 upon stoichiometry variation 6.3.3. Low donor content stoichiometry 6.3.4. Conclusion from stoichiometry variation 6.4. Transport material variation 6.4.1. HTM variation 6.4.2. ETM variation 6.5. Donor:acceptor material variation 6.5.1. Donor variation 6.5.2. Acceptor variation 6.6. Conclusion 7. Summary and outlook 7.1. Summary 7.2. Outlook A. Appendix A.1. Energy pay-back of this thesis A.2. Tables and registers