BACKGROUND.One group of theories aiming at providing a framework explaining the etiology, maintenance and phenomenology of anxiety disorders is classified as cognitive models of anxiety. These approaches assume that distortions in specific levels of information processing are relevant for the onset and maintenance of the disorder. A detailed knowledge about the nature of these distortions would have important implications for the therapy of anxiety, as the implementation of confrontative or cognitive elements precisely fitting the distortions might enhance efficacy. Still, these models and related empirical evidence provide conflicting assumptions about the nature of disorder-linked processing distortions. Many cognitive models of anxiety (e.g., Fox, Russo, & Dutton, 2002; Mathews & Mackintosh, 1998; Williams, Watts, MacLeod, & Mathews, 1997) postulate that anxiety-linked biases of attention imply hypervigilance to threat and distractibility from other stimuli in the presence of feared materials. This is convincingly confirmed by various experimentalclinical studies assessing attention for threat in anxious participants compared to non-anxious controls (for a review, seeMathews &MacLeod, 2005). In contrast, assumptions concerning anxiety-linked biased memory for threat are less convincing; based on the shared tendency for avoidance of deeper elaboration in anxiety disorders, some models predict memory biases only for implicit memory tasks (Williams et al., 1997) or even disclaim the relevance of memory in anxiety at all (e.g., Mogg, Bradley, Miles, & Dixon, 2004). Other theories restrict the possibility of measuring disorder-specific memory biases to tasks that require merely perceptual encoding of the materials instead of verbal-conceptual memory (e.g., Fox et al., 2002; Mathews &Mackintosh, 1998). On the one hand, none of these models has integrated all the inconsistencies in empirical data on the topic. On the other hand, the numerous empirical studies on memory in anxiety that have been conducted with varying materials, anxiety disorders, encoding and retrieval conditions do not allow final conclusions about the prerequisites for finding memory biases (for a review, see MacLeod & Mathews, 2004). A more detailed investigation of the complete spectrum of memory for threat utilizing carefully controlled variations of depth of encoding and materials is needed. In view of these inconsistencies, it is all the more surprising that one important part of this spectrum has so far remained completely uninvestigated: visual working memory (VWM). No study has ever differentially addressed VWM for threat in anxious vs. nonanxious participants and none of the cognitive models of anxiety provides any predictions concerning this stage of information processing. Research on cognitive biases in anxiety has thus far only addressed the two extremes of the processing continuum: attention and longer-term memory. In between, a gap remains, the bridging of which might bring us closer to defining the prerequisites of memory biases in anxiety. As empirical research has provided substantial and coherent knowledge concerning attention in anxiety, and as attention and VWM are so closely linked (see, for instance, Cowan, 1995), the thorough investigation of VWM may provide important clues for models of anxiety. Is anxiety related to VWM biases favoring the processing of threatening information, or does the avoidance presumed by cognitive models of anxiety already begin at this stage? RESEARCH AIMS. To investigate the relevance of biased VWM in anxiety, the present research focused in eight experiments on the following main research questions: (1) Is threat preferably stored in VWM in anxious individuals? (2) Does threat preference occur at the cost of the storage of other items, or is extra storage capacity provided? (3) Would the appearance of threat interrupt ongoing encoding of non-threatening items? (4) Does prioritized encoding of threat in anxiety occur strategically or automatically? (5) Are disorder-specific VWM biases also materials-specific? (6) Are VWM biases in anxiety modifiable through cognitive-behavioral therapy? METHODS. In Experiments 1-4, a spatial-sequential cueing paradigm was used. A subset of real-object display items was successively cued on each trial by a sudden change of the picture background for 150 ms each. After the cueing, one of the display pictures was hidden and probed for a memory test. On most trials, a cued item was tested, and memory accuracy was determined depending on the item’s position within the cue string and depending on its valence. In some cases, memory for an uncued item was tested. Experiment 1 and 2 were directed at discovering whether spider fearfuls and non-anxious controls would differ with respect to the accuracy in memorizing cued spiders and uncued spiders and, thus, reveal disorder-specific biases of VWM. In addition, the question whether the presence of a spider image is related to costs for the memorization of other images was tested. Experiment 3 addressed whether any disorder-specific VWM biases found earlier were specific to the feared spiders. Therefore, the critical stimuli here were a snake and a spider. Participants were spider fearfuls and non-anxious controls, both without snake anxiety. In Experiment 4, it was tested whether disorder-specific biases found in Experiment 1 and 2 were modifiable through cognitive-behavioral treatment. The critical stimulus was a spider image. Spider fearfuls were tested three times. Half of them received a cognitive-behavioral intervention after the first test, the other half only after the second test. In two additional experiments, VWM was assessed with a change-detection paradigm. The main aim was to clarify whether disorder-specific effects found in the previous experiments were associated with automatic or with strategic selective encoding of threatening materials, and whether any group differences in spider change detection were materials-specific to spiders, but not to snakes. In Experiment 5, several images were presented simultaneously in a study display for either 100 or 500 milliseconds. After a short interruption, a test display was presented including either the same items as the first one or one changed item. Participants’ accuracy in determining whether displays were the same or different was measured depending on the valence of the changed item, set size, and presentation time of the display. There were trials with and without spiders. If a change was made, it could involve either a non-spider or a spider item. Of specific interest was the condition in which a spider image was presented initially, but not in the test phase, as noticing this specific change would require storage of that image in VWM. Would group differences be particularly pronounced in the shorter encoding condition suggesting automatic encoding of threat, or would they occur in the longer encoding condition, suggesting strategic encoding of spiders? In Experiment 6, change detection accuracy for spiders vs. snakes was tested. The participants in both experiments were spider fearfuls vs. controls, but those of Experiment 6 were additionally required to lack snake anxiety. Moreover, a temporal VWM paradigm - an attentional blink task - was applied to assess whether a biased encoding of spider images in spider fearfuls would occur at the expense of non-threatening items undergoing concurrent processing, and whether this effect was specific to spiders, but not to snakes. Series of real-object pictures were presented at rates of 80 ms at the display center. The observer’s task was to identify and report the two target pictures indicated by a brighter background. In Experiment 7, the first target always depicted a neutral item. The valence of the second target was varied - either negative depicting a spider, positive, or neutral. Participants varied with respect to their spider anxiety. In Experiment 8, spider fearfuls and non-anxious controls, both without snake anxiety, were tested. The experiment was nearly the same as the previous one, but two negative target types were tested: disorder-relevant spiders and negative but not feared snakes. Of specific interest was whether the appearance of a threatening target would reduce the report probability of the earlier attended target, indicating the interruption of its VWM encoding in favor of the threat item. RESULTS. (1) Both anxious and non-anxious controls, showed VWM advantages for negative materials such as spider or snake images. (2) In addition, there were disorderspecific VWM biases: some effects were larger in spider fearfuls than in non-anxious controls and some effects occurred exclusively in spider fearfuls. (3) Group differences and, thus, disorder-specificity were particularly pronounced under competitive circumstances, that is, under the condition of numerous stimuli competing for processing resources: when only little orientation time was allowed, when only little time was provided for selecting and encoding items from a crowd, and when VWMfor the critical item required reflexive instead of voluntary attention. (4) Pronounced memory for task-relevant, voluntarily attended spiders was related to difficulties in disengaging attention from these items in the fearful group, reflected in reduced memory accuracy for the item following it. (5) Disorder-specific VWM biases seem to be based on attentional biases to threatening materials resulting in a very quick, automatic memory consolidation. However, this preferential encoding was not at the cost of neutral materials currently undergoing encoding processes. (6) All disorder-specific VWM biases occured only with fear-related materials, not with other negative materials. (7) Automatic and highly disorder-specific fear-related VWM biases – but not strategic VWM biases occuring in both groups - were modifiable through cognitive-behavioral intervention. CONCLUSIONS. This work provides additional information about informationprocessing distortions related to specific anxiety. With the experimental investigation of biased VWM, this work has been performed to fill a gap within research on cognitive biases in anxiety. Moreover, this dissertation contributes to cognitive theories of anxiety by proposing several recommendations for refinements of current theoretical approaches. Most important, it was suggested to extend existing models by a more detailed consideration of attention and memory. In view of numerous previous empirical studies on the topic and the conclusions of this dissertation, a differentiation of the attentional engagement and disengagement component appears inevitable. Even more important, in view of the data presented here predictions concerning VWM for threatening materials need to be taken into account. In addition, suggestions are provided for the differential consideration of biases occuring from prepotent threat value of negative stimuli vs. individual threat value. A proposal for a cognitive model of anxiety extended by all these aspects is provided to serve as an invitation of further research in the investigation of the nature of memory biases in anxiety disorders. REFERENCES: Cowan, N. (1995). Attention and Memory. An integrated framework.New York: Oxford University Press. Fox, E., Russo, R., & Dutton, K. (2002). Attentional bias for threat: Evidence for delayed disengagement from emotional faces. Cognition and Emotion, 16, 355-379. MacLeod, C., & Mathews, A. (2004). Selective memory effects in anxiety disorders: An overview of research findings and their implications. In D. Reisberg & P. Hertel (eds.), Memory and Emotion. Oxford: Oxford University Press. Mathews, A., & Mackintosh, B. (1998). A cognitive model of selective processing in anxiety. Cognitive Therapy and Research, 22 (6), 539-560. Mathews, A., & MacLeod, C. (2005). Cognitive vulnerability to emotional disorders. Annual Review of Clinical Psychology, 1, 167-195.Mathews, Mogg, May, & Eysenck (1989). Mogg, K., Bradley, B.P., Miles, F., & Dixon, R. (2004). Time course of attentional bias for threat scenes: Testing the vigilance avoidance hypothesis. Cognition and Emotion, 18(5), 689-700. Williams, J.M.G., Watts, F.N., MacLeod, C., & Mathews, A. (1997). Cognitive psychology and emotional disorders. Chichester: John Wiley.

Metal acetylacetonates of the general formula [M(acac)3] (MIII=Cr, Mn, Fe, Co) are among the best investigated coordination compounds. Many of these first-row transition metal complexes are known to have unique electronic properties. Independently, photophysical research with different β-diketonate ligands pointed towards the possibility of a special effect of the 2,4,6-trimethylphenyl substituted acetylacetonate (mesacac) on the electron distribution between ligand and metal (MLCT). We therefore synthesized and fully characterized the previously unknown octahedral title complex. Its solid-state structure shows a Jahn-Teller elongation with two Mn−O bonds of 2.12/2.15 Å and four Mn−O bonds of 1.93 Å. Thermogravimetric data show a thermal stability up to 270 °C. High-resolution mass spectroscopy helped to identify the decomposition pathways. The electronic state and spin configuration of manganese were characterized with a focus on its magnetic properties by measurement of the magnetic susceptibility and triple-zeta density functional theory (DFT) calculations. The high-spin state of manganese was confirmed by the determination of an effective magnetic moment of 4.85 μB for the manganese center.

Beeinflusst unsere Variabilität, wie wir über andere denken? Betrifft die Veränderung unserer Persönlichkeitszustände mehr als uns selbst? Wie beeinflussen andere unsere Persönlichkeitsentwicklung? Wie wirkt sich Selbstbezug auf das Denken über andere aus? In dieser Arbeit werden die vielfältigen Beziehungen zwischen unserer Persönlichkeit und der Beziehung zu und Interaktion mit anderen Menschen in verschiedenen Bereichen der Persönlichkeitspsychologie untersucht. Neben der Zusammenfassung der vier Veröffentlichungen, wird der theoriegeleitete Ansatz erläutert und in Persönlichkeitsdynamik und -prozesse eingeführt. Zentral sind die Konzepte der Persönlichkeitsmerkmale, der innerpersonellen Variabilität, der Persönlichkeitsentwicklung, des Selbstfokus, des Egozentrismus und der egozentrischen Verzerrung–im Rahmen ihrer Bedeutung für die Theory of Mind (ToM). Publikation 1 schlägt ein zweistufiges Model vor, wie die innerpersonelle Variabilität die ToM durch Erweiterung und Relativierung des Egozentrismus einer Person erleichtern kann. Publikation 2 fürht die Terminologie und die statistischen Werkzeuge der dynamischen Systemtheorie für die Untersuchung von Persönlichkeitszuständen ein und diskutiert Anwendungsfälle. Publikation 3 stellt ein Klassifizierungssystem vor, mit dem systematisch zwischen persönlichen und kollektiven Lebensereignissen unterschieden werden kann, wobei die unterschiedlichen Mechanismen berücksichtigt werden, durch die beide Arten von Lebensereignissen die Persönlichkeitsentwicklung beeinflussen können. Publikation 4 präsentiert Belege für eine kleine, aber robuste positive Beziehung zwischen achtsamer Selbstfokussierung und ToM. Nach der Reflektion der Beiträge zum Fachgebiet werden drei Forschungsansätze aus dem Risikomanagement, der Persönlichkeitspsychologie und den Neurowissenschaften diskutiert, die auf die Forschung zu innerpersönlicher Variabilität und Persönlichkeitsentwicklung sowie zu Egozentrismus und ToM einzahlen könnten. / Does our own variability affect how we think about others? Do personality states changes involve more than ourselves? How do others affect our personality development? How does focusing on oneself affect thinking about others? This dissertation explores the many relationships between an individual’s personality and ther relation to and interaction with other people across multiple areas of personality psychological research. Before summarizing four publications of this cumulative project, I explain my theory-driven approach and introduce the field of personality dynamics and processes. In particular, I focus on the concepts of personality traits, within-person variability, personality development, self-focus, egocentrism, egocentric bias–often in light of their relevant for Theory of Mind. The first publication proposes a two-tier framework of how within-person variability can facilitate Theory of Mind by broadening and relativizing a person’s egocentrism. The second publication introduces the terminology and statistical tools of dynamic systems theory to the investigation of personality state levels and presents possible use cases. The third publication introduces a classification system to differentiate between personal and collective live events in a systematic way that is sensitive to the different mechanisms by which both kinds of life events can affect personality development. The fourth publication presents evidence for a small but robust positive relationship between mindful self-focus and Theory of Mind. Finally, I reflect on the publications’ contributions to the field and suggest three lines of research stemming from risk management, personality psychology, and neuroscience that could inform research on within-person variability and personality development as well as on egocentrism and Theory of Mind further in the future.

Die vorliegende Arbeit beschaeftigt sich mit dem strukturellen Aufbau von (1-100) M-plane GaN, das mit plasmaunterstuetzter Molekularstrahlepitaxie auf gamma-LiAlO2(100) Substraten gewachsen wurde. Die heteroepitaktische Ausrichtung einerseits, sowie die Mikrostruktur und die Erzeugungsmechanismen der Defekte andererseits, wurde mit der Transmissionselektronenemikroskopie (TEM) systematisch untersucht. Das gamma-LiAlO2 Substrat reagiert heftig im Mikroskop unter Bestrahlung mit hochenergetischen Elektronen. Waehrend dieser Strahlenschaedigung verliert das Material seine urspruengliche kristalline Struktur und vollzieht eine Phasentransformation, die anhand einer Serie von Feinbereichsbeugungsdiagrammen nachgewiesen werden konnte. Die atomare Grenzflaechenstruktur zwischen epitaktisch gewachsenem alpha-GaN(1-100) und tetragonalem gamma-LiAlO2 Substrat ist mittels HRTEM untersucht worden. Die neuartige Epitaxiebeziehung ist mit Elektronenbeugung bestaetigt worden und lautet folgendermassen: (1-100)GaN liegt parallel zu (100)gamma-LiAlO2 und [11-20]GaN ist parallel zu [001]gamma-LiAlO2. Die Realstruktur der M-plane GaN Schichten, die auf (100)gamma-LiAlO2 gewachsen werden, unterscheidet sich erheblich von der in C-plane Orientierung hergestellten Epischichten. Ausfuehrliche TEM Untersuchungen zeigen, dass die M-plane Schichten vor allem intrinsische (I1 und I2) und extrinsische (E) Stapelfehler in der Basalebene enthalten. Der vorherrschende I2 Stapelfehler besitzt keine Komponente des Verschiebungsvektors senkrecht zur Ebene und ist damit nicht geeignet, epitaktische Dehnung entlang der [11-20] Richtung abzubauen. Darueberhinaus ist eine komplexe Grenze in der (10-10) Prismen- flaeche entdeckt worden, die zur Grenzflaeche geneigt verlaeuft. Die Defekte in den M-plane GaN Epischichten werden waehrend der anfaenglichen Keimbildungsphase erzeugt. Atomare Stufen entlang der [001] Richtung auf dem LiAlO2 Substrat fuehren zur Bildung von Stapelfehlern vom Typ I2. / In this work the structure of (1-100)M-plane GaN epitaxially grown on gamma-LiAlO2(100) by using plasmaassisted molecular beam epitaxy (PAMBE) is studied. The heteroepitaxial alignment and the microstructure of M-plane GaN as well as the defect formation in the layer are systematically investigated by using transmission electron microscopy (TEM). The gamma-LiALO2 substrate reacts under irradiation of high-energy electrons in the TEM (200-300 keV).The material looses its original crystalline structure during this process undergoing irradiation damage followed by a phase transformation as it is verified by a series of selected area diffraction patterns taken under constant electron dose. The result is a structural phase transformation from the tetragonal gamma to the trigonal alpha phase. The atomic interface structure of epitaxially grown hexagonal alpha-GaN(1-100) layers on tetragonal gamma-LiAlO2 (100) substrates is investigated by means of HRTEM. The novel epitaxial orientation relationship verified by electron diffraction is given by (1-100)GaN parallel to (100)gamma-LiAlO2 and [11-20]GaN parallel to [001]gamma-LiAlO2. The defect structure of M-plane GaN epilayers grown on gamma-LiAlO2(100) substrates is different to that of C-plane GaN. Our detailed TEM studies reveal that the M-plane layers mainly contain intrinsic I1 and I2 and extrinsic E basal plane stacking faults. The dominant I2 stacking fault has no out-of-plane displacement vector component and is thus not qualified for epitaxial strain relief along the [11-20] axis. Beyond this, a complex type of planar defect is detected in the (10-10) prism plane which is inclined with respect to the interface. The study of nucleation samples shows that the surface morphology is directly correlated to the generation of the dominant planar defects. Atomic steps along the [001] direction in the gamma-LiAlO2 substrate result in the formation of basal plane stacking faults I2.

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Die fortschreitenden Entwicklungen in der Mikro- und Nanotechnologie erfordern eine solide Unterstützung durch Simulationen. Numerische Bauelementesimulationen waren und sind dabei unerlässliche Werkzeuge, die jedoch zunehmend an ihre Grenzen kommen. So basieren sie auf Parametern, die für beliebige Atomanordnungen nicht verfügbar sind, und scheitern für stark verkleinerte Strukturen infolge zunehmender Relevanz von Quanteneffekten. Diese Arbeit behandelt den Transport in Siliziumnanodrähten sowie durch NiSi2-Si-Grenzflächen. Dichtefunktionaltheorie wird dabei verwendet, um die stabile Atomanordnung und alle für den elektronischen Transport relevanten quantenmechanischen Effekte zu beschreiben. Bei der Untersuchung der Nanodrähte liegt das Hauptaugenmerk auf der radialen Abhängigkeit der elektronischen Struktur sowie deren Änderung bei Variation des Durchmessers. Dabei zeigt sich, dass der Kern der Nanodrähte für den Ladungstransport bestimmend ist. Weiterhin kann ein Durchmesser von ungefähr 5 nm identifiziert werden, oberhalb dessen die Zustandsdichte im Nanodraht große Ähnlichkeiten mit jener des Silizium-Volumenkristalls aufweist und der Draht somit zunehmend mit Näherungen für den perfekt periodischen Kristall beschrieben werden kann. Der Fokus bei der Untersuchung der NiSi2-Si-Grenzflächen liegt auf der Symmetrie von Elektron- und Lochströmen im Tunnelregime, welche für die Entwicklung von rekonfigurierbaren Feldeffekttransistoren besondere Relevanz hat. Verschiedene NiSi2-Si-Grenzflächen und Verzerrungszustände werden dabei systematisch untersucht. Je nach Grenzfläche ist die Symmetrie dabei sehr unterschiedlich und zeigt auch ein sehr unterschiedliches Verhalten bei externer Verzerrung. Weiterhin werden grundlegende physikalische Größen mit Bezug zu NiSi2-Si-Grenzflächen betrachtet. So wird beispielsweise die Stabilität anhand von Grenzflächen-Energien ermittelt. Am stabilsten sind {111}-Grenzflächen, was deren bevorzugtes Auftreten in Experimenten erklärt. Weitere wichtige Größen, deren Verzerrungsabhängigkeit untersucht wird, sind die Schottky-Barrierenhöhe, die effektive Masse der Ladungsträger sowie die Austrittsarbeiten von NiSi2- und Si-Oberflächen. Ein Beitrag zur Modellentwicklung numerischer Bauelementesimulationen wird durch einen Vergleich zwischen den Ergebnissen von Dichtefunktionaltheorie-basierten Transportrechnungen und denen eines vereinfachten Models basierend auf der Wentzel-Kramers-Brillouin-Näherung geliefert. Diese Näherung ist Teil vieler numerischer Bauelementesimulatoren und erlaubt die Berechnung des Tunnelstroms basierend auf grundlegenden physikalischen Größen. Der Vergleich ermöglicht eine Evaluierung des vereinfachten Models, welches anschließend genutzt wird, um den Einfluss der grundlegenden physikalischen Größen auf den Tunneltransport zu untersuchen.:Index of Abbreviations 1. Introduction 2. Silicon Based Devices and Silicon Nanowires 2.1. Introduction 2.2. The Reconfigurable Field-effect Transistor 2.2.1. Design and Functionality 2.2.2. Fabrication 2.3. Overview Over Silicon Nanowires 2.3.1. Geometric Structure 2.3.2. Fabrication Techniques 2.3.3. Electronic Properties 3. Simulation Tools 3.1. Introduction 3.2. Electronic Structure Calculations 3.2.1. Introduction and Basis Functions 3.2.2. Density Functional Theory 3.2.3. Description of Exchange and Correlation Effects 3.2.4. Practical Aspects of Density Functional Theory 3.3. Electron Transport 3.3.1. Introduction 3.3.2. Scattering Theory 3.3.3. Wentzel-Kramers-Brillouin Approximation for a Triangular Barrier 3.3.4. Non-equilibrium Green’s Function Formalism A. Radially Resolved Electronic Structure and Charge Carrier Transport in Silicon Nanowires A.1. Introduction A.2. Model System A.3. Results and Discussion A.4. Summary and Conclusions A.5. Appendix A: Computational Details A.6. Appendix B: Supplementary Material A.6.1. Comparison of the Band Gap Between Relaxed and Unrelaxed SiNWs A.6.2. Band Structures for Some of the Calculated SiNWs A.6.3. Radially Resolved Density of States for Some of the Calculated SiNWs B. Electron Transport Through NiSi2-Si Contacts and Their Role in Reconfigurable Field-effect Transistors B.1. Introduction B.2. Model for Reconfigurable Field-effect Transistors B.2.1. Atomistic Quantum Transport Model to Describe Transport Across the Contact Interface B.2.2. Simplified Compact Model to Calculate the Device Characteristics B.3. Results and Discussion B.3.1. Characteristics of a Reconfigurable Field-effect Transistor B.3.2. Variation of the Crystal Orientations and Influence of the Schottky Barrier B.3.3. Comparison to Fabricated Reconfigurable Field-effect Transistors B.4. Summary and Conclusions B.5. Appendix: Supplementary Material B.5.1. Band Structure and Density of States of the Contact Metal B.5.2. Relaxation Procedure B.5.3. Total Transmission Through Multiple Barriers C. Formation and Crystallographic Orientation of NiSi2-Si Interfaces C.1. Introduction C.2. Fabrication and characterization methods C.3. Model System and Simulation Details C.4. Results and discussion C.4.1. Atomic structure of the interface C.4.2. Discussion of ways to modify the interface orientation C.5. Summary C.6. Appendix: Supplementary Material D. NiSi2-Si Interfaces Under Strain: From Bulk and Interface Properties to Tunneling Transport D.1. Introduction D.2. Model System and Simulation Approach D.3. Computational Details D.3.1. Electronic Structure Calculations (Geometry Relaxations) D.3.2. Electronic Structure Calculations (Electronic Structure) D.3.3. Device Calculations D.4. Tunneling Transport From First-principles Calculations D.4.1. Evaluation of the Current D.4.2. Isotropic Strain D.4.3. Anisotropic Strain D.5. Transport Related Properties and Effective Modeling Schemes D.5.1. Schottky Barrier Height D.5.2. Simplified Transport Model D.5.3. Models for the Schottky Barrier Height D.6. Summary and Conclusions D.7. Appendix: Supplementary Material D.7.1. Schottky Barriers of the {110} Interface Under Anisotropic Strain D.7.2. Silicon Band Structure, Electric Field, and Number of Transmission Channels D.7.3. k∥-resolved Material Properties D.7.4. Evaluation of the Work Functions and Electron Affinities D.7.5. Verification of the Work Function Calculation 4. Discussion 5. Ongoing Work and Possible Extensions 6. Summary Bibliography List of Figures List of Tables Acknowledgements Selbstständigkeitserklärung Curriculum Vitae Scientific Contributions / The ongoing developments in micro- and nanotechnologies require a profound support from simulations. Numerical device simulations were and still are essential tools to support the device development. However, they gradually reach their limits as they rely on parameters, which are not always available, and neglect quantum effects for small structures. This work addresses the transport in silicon nanowires and through NiSi2-Si interfaces. By using density functional theory, the atomic structure is considered, and all electron transport related quantum effects are taken into account. Silicon nanowires are investigated with special attention to their radially resolved electronic structure and the corresponding modifications when the silicon diameter is reduced. The charge transport occurs mostly in the nanowire core. A diameter of around 5 nm can be identified, above which the nanowire core exhibits a similar density of states as bulk silicon. Thus, bulk approximations become increasingly valid above this diameter. NiSi2-Si interfaces are studied with focus on the symmetry between electron and hole currents in the tunneling regime. The symmetry is especially relevant for the development of reconfigurable field-effect transistors. Different NiSi2-Si interfaces and strain states are studied systematically. The symmetry is found to be different between the interfaces. Changes of the symmetry upon external strain are also very interface dependent. Furthermore, fundamental physical properties related to NiSi2-Si interfaces are evaluated. The stability of the different interfaces is compared in terms of interface energies. {111} interfaces are most stable, which explains their preferred occurrence in experiments. Other properties, whose strain dependence is studied, include the Schottky barrier height, the effective mass of the carriers, and work functions. A contribution to the development of numerical device simulators will be given by comparing the results from density functional theory based transport calculations and a model based on the Wentzel-Kramers-Brillouin approximation. This approximation, which is often employed in numerical device simulators, offers a relation between interface properties and the tunneling transport. The comparison allows an evaluation of the simplified model, which is then used to investigate the relation between the fundamental physical properties and the tunneling transport.:Index of Abbreviations 1. Introduction 2. Silicon Based Devices and Silicon Nanowires 2.1. Introduction 2.2. The Reconfigurable Field-effect Transistor 2.2.1. Design and Functionality 2.2.2. Fabrication 2.3. Overview Over Silicon Nanowires 2.3.1. Geometric Structure 2.3.2. Fabrication Techniques 2.3.3. Electronic Properties 3. Simulation Tools 3.1. Introduction 3.2. Electronic Structure Calculations 3.2.1. Introduction and Basis Functions 3.2.2. Density Functional Theory 3.2.3. Description of Exchange and Correlation Effects 3.2.4. Practical Aspects of Density Functional Theory 3.3. Electron Transport 3.3.1. Introduction 3.3.2. Scattering Theory 3.3.3. Wentzel-Kramers-Brillouin Approximation for a Triangular Barrier 3.3.4. Non-equilibrium Green’s Function Formalism A. Radially Resolved Electronic Structure and Charge Carrier Transport in Silicon Nanowires A.1. Introduction A.2. Model System A.3. Results and Discussion A.4. Summary and Conclusions A.5. Appendix A: Computational Details A.6. Appendix B: Supplementary Material A.6.1. Comparison of the Band Gap Between Relaxed and Unrelaxed SiNWs A.6.2. Band Structures for Some of the Calculated SiNWs A.6.3. Radially Resolved Density of States for Some of the Calculated SiNWs B. Electron Transport Through NiSi2-Si Contacts and Their Role in Reconfigurable Field-effect Transistors B.1. Introduction B.2. Model for Reconfigurable Field-effect Transistors B.2.1. Atomistic Quantum Transport Model to Describe Transport Across the Contact Interface B.2.2. Simplified Compact Model to Calculate the Device Characteristics B.3. Results and Discussion B.3.1. Characteristics of a Reconfigurable Field-effect Transistor B.3.2. Variation of the Crystal Orientations and Influence of the Schottky Barrier B.3.3. Comparison to Fabricated Reconfigurable Field-effect Transistors B.4. Summary and Conclusions B.5. Appendix: Supplementary Material B.5.1. Band Structure and Density of States of the Contact Metal B.5.2. Relaxation Procedure B.5.3. Total Transmission Through Multiple Barriers C. Formation and Crystallographic Orientation of NiSi2-Si Interfaces C.1. Introduction C.2. Fabrication and characterization methods C.3. Model System and Simulation Details C.4. Results and discussion C.4.1. Atomic structure of the interface C.4.2. Discussion of ways to modify the interface orientation C.5. Summary C.6. Appendix: Supplementary Material D. NiSi2-Si Interfaces Under Strain: From Bulk and Interface Properties to Tunneling Transport D.1. Introduction D.2. Model System and Simulation Approach D.3. Computational Details D.3.1. Electronic Structure Calculations (Geometry Relaxations) D.3.2. Electronic Structure Calculations (Electronic Structure) D.3.3. Device Calculations D.4. Tunneling Transport From First-principles Calculations D.4.1. Evaluation of the Current D.4.2. Isotropic Strain D.4.3. Anisotropic Strain D.5. Transport Related Properties and Effective Modeling Schemes D.5.1. Schottky Barrier Height D.5.2. Simplified Transport Model D.5.3. Models for the Schottky Barrier Height D.6. Summary and Conclusions D.7. Appendix: Supplementary Material D.7.1. Schottky Barriers of the {110} Interface Under Anisotropic Strain D.7.2. Silicon Band Structure, Electric Field, and Number of Transmission Channels D.7.3. k∥-resolved Material Properties D.7.4. Evaluation of the Work Functions and Electron Affinities D.7.5. Verification of the Work Function Calculation 4. Discussion 5. Ongoing Work and Possible Extensions 6. Summary Bibliography List of Figures List of Tables Acknowledgements Selbstständigkeitserklärung Curriculum Vitae Scientific Contributions