Organic transistors based on pentacene and dibenzothiophene derivatives

This thesis is concerned with the fabrication and characterisation of organic thin film transistors. Initially, pentacene thin films were investigated, with results comparable to those found in published literature. Initial studies of pentacene transistors revealed a poor hole mobility of 6.3 x 10(^-3) cm(^2)/V/s. Improvements in the fabrication process (using a more conductive silicon wafer as the gate, and treating the silicon oxide surface with a silanising agent) increased the mobility to around 0.1 cm(^2)/V/s. Better pentacene deposition conditions allowed a polycrystalline structure to form, with dendritic grains of the order of 2-3 pm in size. This increased the mobility of the transistor further, to 0.54 cm(^2)/V/s. Treatment of the silicon oxide surface prior to pentacene deposition was found to affect significantly the hysteresis in the transfer characteristics. Removal of photoresist with acetone and propan-2-ol prior to pentacene deposition resulted in fairly large threshold voltages, with an average shift between the off-on and on-off threshold voltages of 9.7 V. Application of an oxygen plasma prior to deposition resulted in decreased threshold voltages, and a reduced threshold voltage shift of 3.8 V. The hysteresis was attributed to charge trapping on the oxide surface due to organic contamination; the oxygen plasma served to reduce this. X-Ray Photoelectron Spectroscopy measurements confirmed this - following a plasma treatment, the carbon content on the surface was reduced significantly. Incorporation of a layer of gold nanoparticles between the oxide and pentacene was found to provide charge traps - this might be exploited in memory devices. Replacing the silicon oxide with PMMA produced favorable results. Negative threshold voltages with low hysteresis were observed for all the devices. Mobilities of up to 0.21 cm(^2)/V/s were recorded for devices with a 124 nm PMMA layer; a thinner (80 nm) layer of PMMA resulted in reduced mobility, as did a thicker (350 nm) layer. Replacing the silicon oxide with sputtered hafnium oxide produced devices with a large number of defects. Deposited pentacene did not form optimal crystal structures, and the output characteristics of a number of devices showed no significant variation with source-drain voltage. These output characteristics were therefore assumed to be the result of leakage through the oxide. The measured device that showed reasonable output characteristics was found to have a mobility of 0.59 cm(^2)/V/s demonstrating that hafnium oxide could have good potential as a dielectric, if deposited in a manner not resulting in a leaky oxide. Three dibenzothiophene-based molecules, synthesised in the University of Durham, were characterised and thin film transistors fabricated. 3,7-bis(dibenzothiophene-4-yl)-dibenzothiophene-5',S'-dioxide exhibited the characteristics of an air-stable n-type device, with a mobility of 3.5 x 10(^-6)cm(^2)/V/s. A related molecule, 3,7-bis(4-(ethylsulfonyl)phenyl)dibenzo[b,d]jthiophene, incorporating additional electron-deficient groups, did not exhibit any field-effect modified behaviour. A third molecule, that did not contain electron-deficient groups, exhibited p-type behaviour, and transistors showed good output characteristics, but only possessed a mobility of 3.7 x 10(^5) cm(^2)/V/s; the low mobility was attributed to the lack of long-range order in the structure of the deposited film

Mesh based Scene Evaluation Metrics for LOD and Simplification

I present seven metrics to quantify attributes of different meshes in a scene. Each metricrepresents a different geometrical or topological aspect of the mesh. Theresulting ratingvalues serve to convey the underlying complex data to the user. These allow the user toswiftly compare several features of multiple meshes. The metricsmay thus guide usersand programs during the process of mesh modification, i.e. optimization, simplification orsmoothing, and scene modification as a whole.I evaluate each metric individually by applying them to a sample scene. To examine thecorrectness and expressiveness of the metrics I compare the automatically calculated ratingsto the raw base data. I find two of the metrics to be immediately useful and four of theratings promising, but in need of adjustments. The remaining last metric, however, requiressignificant rework to generate useful data on par with the other six metrics.This thesis first introduces the subject with a motivating example. It then presents importantconcepts and research on related topics. Afterwards it details the concept of the programand the mathematical considerations it is based on. It also lists my approach to solving thechallenges which emerged during the implementation. Subsequently, the thesis focusses onthe visualized output of the program and challenges said ouput. Finally, it contrasts theexpectations and goals of each metric with the respective actual result

Constraining Modular Inflation in the MSSM from Giant Q-Ball Formation

We discuss constraints on which flat directions can have large vacuum expectation values (VEVs) after inflation. We show that only flat directions which are not charged under B-L and develop positive pressure due to renormalization group effects can have large VEVs of order \Mp. For example, within the MSSM only the $H_uH_d$ flat direction is found to be viable. This strongly constrains the embedding of a broad class of inflationary models in the MSSM or some other supersymmetric extension of the SM. For flat directions with negative pressure, the condensate fragments into very large Q-balls which we call Q-giants. We discuss the formation, evolution and reheating of these Q-giants and show that they decay too late. The analysis requires taking into account new phases of the flat directions, which have been overlooked in the formation and dynamics of the Q-balls. These constraints may be ameliorated by invoking a short period of thermal inflation. The latter, however, is viable in a very narrow window of parameter space and requires fine tuning.Comment: 40 pages, 3 figure

Preserving Conversations with Contemporary Holocaust Witnesses

Conversations with Holocaust survivors are an integral part of education at schools and universities as well as part of the German memory culture. The goal of interactive stereoscopic digital Holocaust testimonies is to preserve the effects of meeting and interacting with these contemporary witnesses as faithfully as possible. These virtual humans are non-synthetic. Instead, all their actions, such as answers and movements, are pre-recorded. We conducted a preliminary study to gauge how people perceive this first German-speaking digital interactive Holocaust testimony. The focus of our investigation is the ease-of-use, the accuracy and relevance of the answers given as well as the authenticity and emotiveness of the virtual contemporary witness, as perceived by the participants. We found that digital 3D testimonies can convey emotions and lead to enjoyable experiences, which correlates with the frequency of correctly matched answers

Dynamical horizons in binary black hole mergers

Marginally outer trapped surfaces (MOTSs) are the main tool in numerical relativity to infer properties of black holes in simulations of highly dynamical systems. On the one hand, the present work extends previous numerical methods in order to allow tracking of highly distorted horizons in axisymmetry. On the other hand, by applying the new method to a family of initial data as well as to simulations of head-on collisions of black holes, we discover three new phenomena: (i) the merger of MOTSs providing a connected history of the full merger in terms of marginal surfaces without any "jumps", (ii) the formation of self-intersecting MOTSs immediately after the merger, and (iii) a non-monotonicity result for the area of certain smoothly evolving MOTSs. The merger of MOTSs closes a gap in our understanding of binary-black-hole mergers in terms of the quasilocal horizon framework and provides the quasilocal analog of the famous "pair-of-pants" picture of the event horizon of two merging black holes. It allows tracking the evolution of properties such as the area through the highly dynamical regimes from the initially separate to the final common horizon. Through a detailed analysis of geometrical and dynamical properties, we uncover features of the horizons not often considered. In particular, we show why the area increase law for smoothly evolving MOTSs fails to hold in some of the cases analyzed here. Furthermore, we demonstrate a surprisingly direct correspondence of the decay behavior of multipoles and the shear on the outermost horizon with the quasinormal modes of a Schwarzschild black hole. An important role is played by the spectrum of the MOTS stability operator, for which we provide numerical examples of the connection between invertibility of the operator and the existence of a MOTS. Furthermore, we give a prospect of how the full spectrum can become useful for gaining more insight into the merger in absence of symmetries. Finally, a first working generalization of the new numerical algorithm to non-axisymmetric situations is shown, proving the general applicability of the method

Supersymmetric Baryogenesis from Exotic Quark Decays

In a simple extension of the minimal supersymmetric standard model, out-of-equilibrium decays of TeV scale exotic vector-like squarks may generate the baryon asymmetry of the universe. Baryon number and CP violation are present in the superpotential, so this mechanism does not rely on CP violation in supersymmetry breaking parameters. We discuss phenomenological constraints on the model as well as potential signals for the Large Hadron Collider and electronic dipole moment experiments. A variation on the TeV scale model allows the exotic squarks to be the messengers of gauge mediated supersymmetry breaking.Comment: 28 pages, 7 figures, 2 appendices, v2: typos corrected, results unchange

Evaluation of the Interaction with a Digital 3D Testimony

Conversations with Holocaust survivors are an integral part of education in German schools and universities as well as part of the German memory culture. The goal of interactive stereoscopic digital Holocaust testimonies is to preserve the effects of meeting and interacting with these contemporary witnesses as faithfully as possible. These virtual humans are non-synthetic, i.e., there exists no underlying system, which extrapolates from recorded data to synthesize and generate new answers. This means that immersion-breaking difficulties common to synthetic virtual humans, such as the audio-visual uncanny valley, can be prevented. Issues resulting from technical constraints, technological barriers to entry or errors, machine and human alike, during the design and creation of the application cannot, however, be ruled out. Therefore, I conducted a preliminary study to evaluate how people perceive this first German-speaking digital interactive 3D Holocaust testimony. I investigated how the study participants perceived the technical and semantic quality of recording and display, the difficulties in using and interacting, the accuracy and relevance of the answers given as well as the authenticity and emotiveness of the virtual contemporary witness. In this paper, I detail how the study was set up, the results of the survey, and my analysis of the data.Zeitzeugengespräche mit Holocaust-Überlebenden sind fester Bestandteil der Bildung an Schulen und Universitäten sowie Teil der deutschen Erinnerungskultur. Ziel interaktiver stereoskopischer digitaler Holocaustzeugnisse ist es, die Auswirkungen der Begegnung und Interaktion mit diesen Zeitzeug*innen so realitätstreu wie möglich zu bewahren. Diese virtuellen Menschen sind nicht-synthetisch, es gibt also kein zugrundeliegendes System, das aus aufgezeichneten Daten extrapoliert, um neue Antworten zu synthetisieren und zu generieren. Dadurch können einige immersionsbrechende Eigenschaften, wie das audiovisuelle Uncanny Valley, verhindert werden. Probleme, die sich aus technischen Beschränkungen, technologischen Eintrittsbarrieren oder menschlichen und technischen Fehlern während des Designs und der Erstellung der Anwendung ergeben, können jedoch nicht ausgeschlossen werden. Deshalb habe ich anhand des 3D-Zeugnisses des Holocaust-Überlebenden Abba Naor eine Vorstudie durchgeführt, um zu evaluieren, wie Menschen auf dieses erste deutschsprachige digitale interaktive 3D-Zeugnis reagieren. Ich untersuchte, wie die technische und semantische Qualität der Aufzeichnung und Darstellung, die Schwierigkeiten bei der Nutzung und Interaktion, die Genauigkeit und Relevanz der gegebenen Antworten sowie die Authentizität und Emotionalität des virtuellen Zeitzeugen wahrgenommen werden. In diesem Beitrag erläutere ich die Spezifikationen des Aufbaus, die Ergebnisse der Erhebung und meine Analyse der Ergebnisse