Die vorliegende Arbeit beschreibt die Herstellung, Strukturierung und Modifizierung von poroesem Silizium. Es wird der Mechanismus der Lumineszenz in poroesem Silizium und der Einfluss von Herstellungsparametern und einer Dotierung mit Laserfarbstoffen auf die optischen Eigenschaften von poroesem Silizium untersucht. Fuer die optische Charakterisierung wurden Photolumineszenz-, Photolumineszenzanregungs- und Kathodolumineszenzspektren aufgenommen. Weiterhin werden Methoden zur Erzeugung von poroesen Mikrostrukturen mit Hilfe eines ECSTM sowie zum Schreiben von optischen Mustern in poroesem Silizium durch einen Elektronenstrahl vorgestellt. Strukturelle Untersuchungen wurden mit einem SEM und einem TEM durchgefuehrt.

Die Dissertation beschaeftigt sich mit der Analyse ballistischer Effekte, diein der Wechselwirkung niederenergetischer Ionen mit Oberflaechen kovalenter Festkoerper auftreten. Im Mittelpunkt stehen dabei Kohlenstoff- und Siliziumsysteme und Ionenenergien unter 100 eV. Das Eindringverhalten der hyperthermischen Atome unter die oberste Atomlage wird analysiert,woraus sich Schwellenergien fuer das Eindringen selbst sowie fuer die Erzeugung permanenter Gitterdefekte, die sogenannte Displacement-Energie, ergeben. Molekulardynamik-Simulationen (MD) bilden ein leistungsfaehiges Werkzeug fuer die Untersuchung dieser Prozesse. Die fuer die Berechnung der interatomaren Kreafte verwendete Dichtefunktional-Tight-Binding-Methode (DFTB)bietet bei vertretbarem rechentechnischen Aufwand eine hohe Genauigkeit bei der Beschreibung von Defekt-Topologien, Oberflaechenrekonstruktionen und amorphen Netzwerken.Die Displacement-Energien werden entsprechend ihrer Orientierungsabhaengigkeit fuer Diamant und Silizium diskutiert, wobei gleichzeitig die Umordnungsmechanismen und Defekte analysiert werden. Ein MD-Verfahren fuer die Bestimmung der ballistischen Eindringschwelle von Ionen in Oberflaechen wird vorgestellt, welches die Berechnung der Minimal-Ionenenergie fuer das Eindringen von Atomen unter die oberste Lage selbst komplizierter Oberflaechen erlaubt. Die Eindringschwelle sowie die Energieabhaengigkeit des Eindringquerschnittes fuer auf eine Si(100)-Oberflaeche auftreffende Siliziumatome werden diskutiert.Computersimulationen des Beschusses von amorphem Kohlenstoff mit Kohlenstoffatomen fuehren auf eine Spezifikation des Subplantationsmodells. Unter Beschuss wird die Ausbildung einer leerstellenreichen Oberflaechenschicht, einer Zwischenschicht mit einer hohen Zahl schwach gebundener Atome, sowie einer Schicht mit fortschreitender Anreicherung sp3-gebundener Atome beobachtet. Die Minimalenergie fuer die Ausbildung der Zwischenschicht wird mit 10 eV bestimmt.

Geprägt wird das Klima auf dem Indischen Subkontinent ganz erheblich durch den Einfluss des Monsuns, der ein Teilelement des gesamten asiatischen Monsunsystems ist. Der Monsun hat als wesentlicher Klimafaktor einen wichtigen Einfluss auf die geomorphologische Entwicklung der Flüsse und Flusstäler des Indischen Subkontinents in Verbindung mit den Überschwemmungen, die durch die Niederschläge des Monsuns verursacht werden.

Übungen zur Vorlesung Theoretische Physik II: Quantenmechanik im Sommersemester 2002 für den Studiengang Physik

In a previous publication [1] the author described the base rivalry in monotonous DNA sequences and their effect on the DNA repair mechanism. As described in the article, during the monotonous sequence replication, energies appear theoretically to increase with a progressive replication fork up to the quantum mechanical energy level n=2 because of the base rivalry, and these rivalry energies affect the bond strength between the complementary bases. If there is a tautomeric base pair in the replication position where the rivalry energy is large enough, then in this position an irreparable mutation will occur, since the DNA repair mechanism cannot repair that error because too much binding energy. Thus a mutation (caused by base rivalry) can occur only on condition that a transition of a base pair into its tautomeric form is happened. It is remarkable that this transition likewise can occur by the effect of base rivalry energy. The base rivalry - energy which has an effect on a normal base pair provokes a tunnel process in its hydrogen bond, and produces the tautomeric form. After whose replication a different, irreparable base pair develops from the tautomeric base pair, when the rivalry - energy leads into a very strong hydrogen bond. This happens, however, by chance and in the following we will compute the probabilities of such accidental events. The result of these calculations is the equation (32) which could be useful for the theory of evolution and besides for clearing up of virus mutations. It is remarkable that follows from these calculations that the length of DNA increases itself in the course of evolution (section 7).

Supersymmetry is an attractive extension of the Standard Model (SM) of particle physics. The minimal supersymmetric extension (MSSM) provides gauge coupling unification, a dark matter candidate particle and can explain the breaking of the electroweak symmetry dynamically. However, it suffers from the little hierarchy and the mu-problem. Non-minimal supersymmetric extensions of the SM with a larger particle content or a higher symmetry can evade the problems of the MSSM. Such models may be well-motivated by Grand Unified Theories (GUTs) and can provide a rich new phenomenology with an extended Higgs sector, exotic particles, additional interactions and a close connection to String Theory. Interesting examples are the Next-to Minimal Supersymmetric Standard Model (NMSSM), which is motivated by the mu-problem, and the Exceptional Supersymmetric Standard Model (E6SSM), which is inspired by E6 GUTs. For phenomenological investigations of supersymmetric (SUSY) models the pole mass spectrum must be calculated from the fundamental model parameters. This task, however, is non-trivial as the spectrum must be consistent with measured low-energy observables (fine-structure constant, Z boson pole mass, muon decay etc.) as well as electroweak symmetry breaking and potential universality conditions on the soft supersymmetry breaking parameters at the GUT scale. Programs, which calculate the SUSY mass spectrum consistent with constraints of this kind are called spectrum generators. In this thesis four different contributions to the prediction of mass spectra and model parameters in non-minimal SUSY models are presented. (i) One-loop matching corrections of the E6SSM gauge and Yukawa couplings to the SM are calculated to increase the precision of the mass spectrum prediction in the constrained E6SSM. (ii) The beta-functions of vacuum expectation values (VEVs) are calculated in a general and supersymmetric gauge theory at the one- and two-loop level. The results enable an accurate calculation of the renormalization group running of the VEVs in non-minimal SUSY models. (iii) An NMSSM extension of Softsusy, a spectrum generator for the MSSM, is implemented. It represents a precise alternative to the already existing spectrum generator NMSPEC. (iv) FlexibleSUSY is presented, a general framework which creates a fast, modular and precise spectrum generator for any user-defined SUSY model. It represents a generalization of the hand-written SUSY spectrum generators and allows the study of a large variety of new SUSY models easily with high precision.

It was the purpose of this thesis to contribute to a better understanding of spin caloritronic phenomena and thermoelectric effects as well as the anisotropy of magnetic thin films. Mostly this work was motivated by the recent discovery of the spin Seebeck effect (SSE) in Japan: a generation of a pure spin current across the interface between magnetic|nonmagnetic materials upon application of the temperature gradient along (transversal SSE) or across (longitudinal SSE) the interface. As the experimental configuration for the TSSE involves the heat flows, special care to spurious temperature gradients has to be taken. Semiconducting GaMnAs and insulating yttrium iron garnet (YIG) magnetic thin films were investigated. As nonmagnetic material platinum was chosen, providing also the opportunity to detect pure spin currents via the spin Hall effect (SPHE) in it. Starting with the measurement of in-plane voltages, transverse to the in-plane temperature gradient and measured along the platinum stripes, by sweeping the external magnetic field at different in-plane directions (TSSE geometry), symmetric and asymmetric contributions were observed in both, the GaAs/GaMnAs/Pt and GaAs/GaMnAs systems. The former was clearly attributed to the planar Nernst effect, arising from an in-plane temperature gradient along the sample, while the latter was shown to be result of the anomalous Nernst effect (ANE) caused by spurious out-of-plane temperature gradients. Using the ANE constant that was measured upon deliberately applying an out-of-plane temperature gradient, it was estimated that a rather small temperature drop of ΔT z ≈ 12 nK across the 200 nm magnetic film thickness can be responsible for the appearance of spurious ANE signals, leading to the asymmetry of the thermovoltages registered in the PNE/TSSE configuration. Thus, the TSSE if it exists at all in the GaMnAs sample, is very likely to be negligible. The transport measurements in the insulating YIG sample in TSSE/PNE configuration demonstrated no field dependencies, supporting the idea that the signals in the semiconducting GaMnAs film originated not from the TSSE, but rather from the conventional ANE. The voltages in ANE/LSSE configuration the characteristic LSSE signals were observed. This thesis is also devoted to the magnetic anisotropy investigation in GaMnAs thin film by applying wide-field Kerr microscopy simultaneously to galvanomagnetic measurements. Upon sweeping the magnetic field the development of magnetic domains was traced: at low temperatures (5 K) the sample exhibits a clear two-fold switching of magnetization, while at higher temperatures (above 20 K) only a one-step switching was detected, indicating a strong temperature dependence of the magnetic anisotropy. The same behavior was derived from the transport measurements in the PHE configuration. Rotating the field in the plane of the thin film and analyzing the resulting angle dependencies of the transversal voltage, we obtained the anisotropy constants K u and K c . The temperature dependence of the K u / K c -ratio showed a gradual substitution of the cubic anisotropy, prevailing at low temperatures, by a uniaxial one with rising temperature. For the purpose of the magneto-optical investigation and in-depth analysis of the magnetic anisotropy, within the frame of this thesis a new hardware and software realization for quantitative Kerr microscopy was developed. The principles of such a technique were formulated already years ago by Rave et al, but the experimental realization was limited to materials with in-plane surface magnetization and static domain imaging due to the manual adjustment of the microscope sensitivity. The realization of a separation of in-plane|out-of-plane magnetic contrast, suggested in this thesis, disposes those complications and improves the method, providing the opportunity for a simultaneous measurement of both components of magnetization in an automatic regime and, thus, allowing the quantitative analysis of the magnetization reorientation processes in magnetic media. This technique was successfully applied to the quantitative investigation of the magnetic domain structure in GaMnAs film, and was also demonstrated on a number of other materials, including a permalloy (Ni 81 Fe 19 ) patterned film element and the separation of the in-plane and out-of-plane components of magnetic contrast in sintered NdFeB polycrystals. In summary, this work contributes to a deeper understanding of the contribution of the conventional thermoelectric effects to the exploding field of spin caloritronic. It points out that thermoelectric phenomena have to be treated with care and that magnetic anisotropy and its temperature dependence have to be considered in any analysis of spin caloritronic phenomena. The thesis extends the existing methods of investigating magnetic anisotropy of magnetic films by introducing a novel technical realization of quantitative Kerr microscopy.:1 Introduction 1 2 Theoretical background 6 2.1 Thermoelectricity 6 2.2 The anomalous Hall and Nernst effects 8 2.3 Planar Hall and planar Nernst effects 9 2.4 Spin Hall and inverse spin Hall effects 11 2.5 Spin transfer torque and spin pumping 12 2.6 Spin caloritronics 15 2.7 Spin Seebeck effect 16 2.7.1 Experimental observation of the spin Seebeck effect 16 2.7.2 Theory of the spin Seebeck effect 23 2.8 Magnetic anisotropy of GaMnAs 26 2.9 Kerr microscopy 28 2.10 Quantitative Kerr microscopy 29 3 Experimental methods 33 3.1 Sample preparation 33 3.2 Measurement techniques 34 3.2.1 Vibrating Sample Magnetometry (VSM) 34 3.2.2 Transport measurement 35 3.2.3 Thermal conductivity measurements 38 3.2.4 Kerr Microscopy 39 4 Experimental results and discussion 43 4.1 Magnetization of GaMnAs (VSM data) 44 4.2 Thermal Properties of GaAs|GaMnAs heterostructure 46 4.3 Measurements in transversal spin Seebeck / planar Nernst effect configuration 48 4.4 Anomalous Nernst effect measurements 51 4.5 Planar Hall effect measurements and magnetic anisotropy 54 4.6 Domain studies by Kerr microscopy 60 4.7 Domain investigation in GaMnAs by quantitative Kerr microscopy 64 4.8 Measurements of YIG film in transversal spin Seebeck/planar Nernst effect configuration 67 5 Summary and conclusions 70 Appendices 73 A Selective sensitivity in Kerr microscopy 74 B Quantitative vector Kerr microscopy 81 Bibliography 87 Own publications 96

In the current contribution the application of bond valence method for the prediction (and diffraction-based techniques for the evalution) of ion diffusion pathways in different materials for electrochemical energy conversion and storage will be presented and discussed.

No description available.

No description available.