This work is divided in two thematic parts. The first part shows a refurbishment of a Omicron low temperature STM set-up and its utilization for preparation of superconducting-magnetic interfaces. First, a cleaning procedure of suitable metallic substrates, specifically W(110) and Ir(111), is shown. It is followed by results of iron monolayer deposition on Ir(111) (Fe-Ir(111) interface). The last section deals with study of vanadium growth on pure Ir(111) substrate as well as on mentioned Fe-Ir(111) interface. The second thematic part deals with magnetism of cobalt atoms on a monolayer metal dichalcogenide WS2. It focuses primarily on studying their magnetic moment and magnetic anisotropy using X-ray magnetic circular dichroism (XMCD).

Im Rahmen dieser Arbeit wurden vier Phthalocyanine untersucht: Metallfreies-Phthalocyanin (H2Pc), Kupferphthalocyanin (CuPc) und Fluor-substituiertes Phthalocyanin (F4CuPc und F16CuPc). Das Ziel dieser Arbeit ist die Charakterisierung der elektronischen und chemischen Eigenschaften der Grenzflächen zwischen diesen Molekülen und Silizium. Die Moleküle wurden durch organische Molekularstrahldeposition (OMBD) im Ultrahochvakuum auf wasserstoffpassivierte Si(111)-Substrate aufgedampft. Oberflächensensitive Messmethoden wie Photoemissionsspektroskopie (PES), Bremsstrahlung Isochromaten Spektroskopie (BIS oder IPES - Inverse Photoemissionsspektroskopie) und Spektroskopie der Röntgen-Absorptions-Feinstruktur (NEXAFS – Near Edge X-Ray Absorption Fine Structure) wurden zur Charakterisierung eingesetzt. Um eine Zuordnung der verschiedenen Komponenten in PES und IPES zu ermöglichen, wurden Methoden der Dichtefunktionaltheorie zur theoretischen Berechnung eingesetzt. Die Energieniveauanpassung an der Grenzfläche zwischen der organischen Schicht und der H-Si-Grenzfläche, sowie die Transportbandlücke von H2Pc, CuPc, F4CuPc und F16CuPc wurden mit Hilfe von PES und IPES bestimmt. Die NEXAFS-Messungen ermöglichten eine genaue Bestimmung der Molekülorientierung relativ zum Substrat. Die Auswertung der Daten zeigte unterschiedliche Molekülorientierungen in dünnen und dicken Filmen. Diese Änderungen wurden mit dem bandverbiegungsähnlichen Verlauf der HOMO-und LUMO-Positionen in Verbindung gebracht. Zusätzlich zu diesem Verhalten wiesen die Grenzflächen auch einen Grenzflächendipol auf, welcher durch die unterschiedlichen Austrittsarbeiten der Kontaktmaterialien hervorgerufen wird. Der Einfluss des Grads der Flouridierung wird durch eine ähnlichen Zunahme der Elektronenaffinität (EA), der Austrittsarbeit (WF) und der Ionisierungsenergie (IE) bestätigt. Die elektronischen Eigenschaften von Metall/organische-Schicht-Grenzflächen und von organischen Schichten unter Sauerstoffeinfluss wurden mit Hilfe von PES und IPES untersucht. Die Ag/Pc Grenzflächen zeigten eine Mischung aus HOMO-LUMO-Verschiebungen und Grenzflächendipolbildung. An den Ag/H2Pc- und Ag/F16CuPc- Grenzflächen wurde ein Ladungstransferkomplex gebildet. Auf der CuPc-Schicht physisorbiert das Ag lediglich und im Fall von F4CuPc wird Ladung zu Ag transferiert, wobei eine andauernde n-Typ-Dotierung an der Grenzfläche erzeugt wird. In Analogie zum Fall der Pc/H-Si Grenzfläche wiesen die Dipole, die hier gefunden wurden, eine lineare Abhängigkeit von EA, WF und IE auf und können durch die Differenz zwischen den Austrittsarbeiten vorausgesagt werden. Das Verhalten der dicken organischen Schichten unter Sauerstoffeinfluss kann in zwei Gruppen eingeteilt werden. Eine Gruppe, bestehend aus H2Pc und F4CuPc, wies nur schwache Wechselwirkung auf und der Sauerstoff physisorbiert auf der Pc-Schicht. Die beiden anderen Moleküle, CuPc und F16CuPc konnten einer Gruppe starker Wechselwirkung zugeordnet werden. CuPc bildet einen Ladungstransferkomplex mit Sauerstoff und auf F16CuPc wird eine polarisierte Schicht gebildet. / In the context of this work four Phthalocyanine were studied: Metal-free Phthalocyanine (H2Pc), Copper Phthalocyanine (CuPc) and fluorine-substituted Phthalocyanine (F4CuPc and F16CuPc). The goal of this work is the electronic and chemical characteristics of the interfaces. The molecules were deposited by organic molecular beam deposition (OMBD) in the ultra high vacuum on hydrogen-passivated Si(111)-Substrate. Surface sensitive techniques such as photoemission spectroscopy (PES), bremsstrahlung isochromate spectroscopy (BIS or IPES - inverse photoemission spectroscopy) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) were used for characterisation. Theoretical computations by density functional theory methods were employed, in order to assign different components in PES and IPES. The energy level alignment at the organic/H-Si interface, as well as the transport gap of H2Pc, CuPc, F4CuPc and F16CuPc were determined by PES and IPES. The NEXAFS measurements determine the exact molecular orientation with respect to the substrate. The evaluation of the data showed different molecular orientation in the thin and thick films. This change was correlated with the band bending like behaviours that emerged at these interfaces. In addition to the band bending like behaviour, the interfaces show also an interface dipole which is driven by the work function difference between the contact materials. The influence of the degree of fluorination is confirmed in the similar increase of the EA, WF and IE. The electronic properties of metal/organic layer interfaces and of organic layer under oxygen influence were examined by PES and IPES. The Ag/Pc interfaces show a mixture of HOMO-LUMO shifts and interface dipole formation. A charge transfer complex is formed in the case of Ag/H2Pc and Ag/F16CuPc interfaces. Ag is physisorbed atop the CuPc. Charge transfers from F4CuPc to Ag creating a continuous n-type doping at the interface. Similar to the Pc/H-Si interfaces the interface dipoles found here show a linear dependence on the EA, WF and IE and can be predicted by the difference in the work functions. The data evaluation of oxygen exposed thick films determined two groups of behaviours. The weak interaction group is represented by H2Pc and F4CuPc, Pcs on which oxygen is physisorbed. The strong interaction group contains the other two molecules CuPc and F16CuPc. CuPc forms a charge transfer complex with oxygen and on top of F16CuPc a polarized layer is formed.

Plasma pretreatments are environmentally benign and energy efficient processes for modifying the surface chemistry of materials. In an effort to improve the strength of the titanium alloy/FM-5 polyimide adhesive joint for aerospace applications, oxygen plasma pretreatments and novel thin plasma polymerized (PP) films were investigated as adhesion promoters. Plasma treatments were carried out using custom-built, low pressure, radio frequency, inductively coupled plasma reactors. Ti-6Al-4V coupons were plasma treated and used to prepare miniature single lap shear (SLS) joints. The effects of plasma pretreatments on surface chemistry were studied using x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Fourier transform infrared analysis (FTIR), and contact angle measurements. Relationships between composition, mechanical properties, and adhesion of PP films on Ti-6Al-4V and silicon wafers were investigated. The nanomechanical properties (modulus, hardness and adhesion) were studied using atomic force microscopy (AFM) nanoindentation and nanoscratch testing. A design of experiments (DOE) three factorial model was used to optimize the parameters for oxygen plasma treatments. Oxygen plasma pretreatments enhanced joint strength by cleaning the titanium surface and creating an extended oxide layer. Nanoindentation of oxygen plasma treated substrates showed no change in the surface mechanical properties due to the oxygen plasma treatment. This suggested that the improved SLS strength of the oxygen plasma pretreated substrates was due to the cleaning of the substrate and the removal of carbonaceous contaminants, rather than any changes in the morphology of the oxide layer. PP acetylene films were predominantly carbon, with oxygen as the other main constituent (incorporated mostly as C-O and C=O). For all SLS specimens tested, the adhesion between PP acetylene and FM-5 adhesive was adequate. However, the strength of SLS joints was limited by the adhesion of the PP acetylene to the Ti-6Al-4V substrate. The effects of a large number of plasma parameters, such as substrate pretreatment, carrier gas, input power, flow rate and film thickness were investigated. All samples failed at the PP film/Ti-6Al-4V interface or within the PP acetylene film, and thicker PP films yielded lower SLS strengths. PP films deposited at lower power exhibited higher hardness and reduced modulus than films deposited at higher power. Overall, thinner films exhibited higher hardness and reduced Young's modulus than thicker films. PP films of higher hardness yielded higher critical loads at debond (thickness normalized) during the nanoscratch test. Thin films were developed via the vapor plasma polymerization of titanium(IV) isobutoxide (TiiB). XPS results suggested that titanium was incorporated into the film as TiO2 clusters dispersed in an organic matrix. No evidence for Ti-C was obtained from the XPS spectra. PP films of TiiB were much more compliant than PP acetylene films. This behavior was attributed to decreased fragmentation and lower crosslinking that occurred during PP TiiB film deposition. These PP films did not exhibit sol-gel-like qualities, and because of the way titanium was incorporated into the films, a more appropriate name for these films might be "titanium dioxide-doped plasma polymerized films." / Ph. D.

In this work the structural transitions of the rare earth oxides praseodymia and ceria grown on Si(111) are investigated. It is demonstrated that several of the rare earth intermediate phases can be stabilizied by post deposition annealing in ultra high vacuum. However, in most cases no single phased but coexisting species are observed. In addition, the surface structure and morphology of hex-Pr2O3(0001) as well as reduced ceria films are investigated.

No description available.

We have measured the optical properties of films of the organic semiconductors PTCDA (3,4:9,10-perylene-tetracarboxylic dianhydride) and HBC (peri-hexabenzocoronene), prepared by Organic Molecular Beam Expitaxy (OMBE), on different substrates by means of Differential Reflectance Spectroscopy (DRS). The optical setup enables us to directly follow the thickness dependent optical properties of the organic films, starting from submonolayer coverage up to thicker films on the order of 20 monolayers (ML) film thickness. Due to the different optical nature of the different substrates used, i.e., mica, glass, Au(111), and HOPG, the direct interpretation of the DRS signal is not feasible. Therefore, we have proposed a method by which the calculation of the optical constants n (index of refraction) and k (absorption index) of thin films on arbitrary substrates from just one spectral measurement (in our case the DRS) becomes possible. The results fulfill a priori a Kramers-Kronig consistency and no specific model is needed to express the spectral behavior of the optical constants. Based on our method, we have successfully calculated the optical constants, and therefore the absorption behavior, of films of different thickness of PTCDA on mica, glass, Au(111), and HOPG, as well as of HBC on mica, glass, and HOPG. Extrinsic effects due to island growth or the presence of a polarizable substrate (screening) have been accounted for. We have introduced a finite dipole model which considers the extended geometry and anisotropy of the organic molecules. The calculated absorption behavior is discussed in great detail in terms of spectral changes with varying film thickness, different growth modes, degree of ordering of the films, interactions with the substrates and oscillator strength. A direct observation of a monomer-dimer transition in solid films could be observed for the first time. Our results indicate an exciton delocalization over about 4 molecules for both molecules.

GaAs-based nanowires are attractive building blocks for the development of future (opto)electronic devices owing to their excellent intrinsic material properties, such as the direct band gap and high electron mobility. A pre-requisite for the implementation of novel functionalities on a single Si chip is the monolithic integration of the nanowires on the well-established Si complementary-metal-oxide-semiconductor (CMOS) platform with precise control of the nanowire growth process. The self-catalyzed (Ga-assisted) growth of GaAs nanowires on Si(111) substrates using molecular beam epitaxy has offered the possibility to obtain vertical nanowires with predominant zinc blende structure, while potential contamination by external catalysts like Au is eliminated. Although the growth mechanism is fairly well understood, control of the nucleation stage, the nanowire number density and the crystal structure has been proven rather challenging. Moreover, conventional growth processes are typically performed at relatively high substrate temperatures in the range of 560-630 °C, which limit their application to the industrial Si platform. This thesis provides two original methods in order to tackle the aforementioned challenges in the conventional growth processes. In the first part of this thesis, a simple surface modification procedure (SMP) for the in situ preparation of native-SiOx/Si(111) substrates has been developed. Using a pre-growth treatment of the substrates with Ga droplets and two annealing cycles, the SMP enables highly synchronized nucleation of all nanowires on their substrate and thus, the growth of exceptionally uniform GaAs nanowire ensembles with sub-Poissonian length distributions. Moreover, the nanowire number density can be tuned within three orders of magnitude and independent of the nanowire dimensions without prior ex situ patterning of the substrate. This work delivers a fundamental understanding of the nucleation kinetics of Ga droplets on native-SiOx and their interaction with SiOx, and confirms theoretical predictions about the so-called nucleation antibunching, the temporal anti-correlation of consecutive nucleation events. In the second part of this thesis, an alternative method called droplet-confined alternate-pulsed epitaxy (DCAPE) for the self-catalyzed growth of GaAs nanowires and GaAs/AlxGa1-xAs axial nanowire heterostructures has been developed. DCAPE enables nanowire growth at unconventional, low temperatures in the range of 450-550 °C and is compatible with the standard Si-CMOS platform. The novel growth approach allows one to precisely control the crystal structure of the nanowires and, thus, to produce defect-free pure zinc blende GaAs-based nanowires. The strength of DCAPE is further highlighted by the controlled growth of GaAs/AlxGa1-xAs axial quantum well nanowires with abrupt interfaces and tunable thickness and Al-content of the AlxGa1-xAs sections. The GaAs/AlxGa1-xAs axial nanowire heterostructures are interesting for applications as single photon emitters with tunable emission wavelength, when they are overgrown with thick lattice-mismatched InxAl1-xAs layers in a core-shell fashion. All results presented in this thesis contribute to paving the way for a successful monolithic integration of highly uniform GaAs-based nanowires with controlled number density, dimensions and crystal structure on the mature Si platform. / GaAs-basierte Nanodrähte sind attraktive Bausteine für die Entwicklung von zukünftigen (opto)elektronischen Bauelementen dank ihrer exzellenten intrinsischen Materialeigenschaften wie zum Beispiel die direkte Bandlücke und die hohe Elektronenbeweglichkeit. Eine Voraussetzung für die Realisierung neuer Funktionalitäten auf einem einzelnen Si Chip ist die monolithische Integration der Nanodrähte auf der etablierten Si-Metall-Oxid-Halbleiter-Plattform (CMOS) mit präziser Kontrolle des Wachstumsprozesses der Nanodrähte. Das selbstkatalytische (Ga-unterstützte) Wachstum von GaAs Nanodrähten auf Si(111)-Substrat mittels Molekularstrahlepitaxie bietet die Möglichkeit vertikale Nanodrähte mit vorwiegend Zinkblende-Struktur herzustellen, während die potentielle Verunreinigung der Nanodrähte und des Substrats durch externe Katalysatoren wie Au vermieden wird. Obwohl der Wachstumsmechanismus gut verstanden ist, erweist sich die Kontrolle der Nukleationsphase, Anzahldichte und Kristallstruktur der Nanodrähte als sehr schwierig. Darüber hinaus sind relativ hohe Temperaturen im Bereich von 560-630 °C in konventionellen Wachstumsprozessen notwendig, die deren Anwendung auf der industriellen Si Plattform begrenzen. Die vorliegende Arbeit liefert zwei originelle Methoden um die bestehenden Herausforderungen in konventionellen Wachstumsprozessen zu bewältigen. Im ersten Teil dieser Arbeit wurde eine einfache Prozedur, bezeichnet als surface modification procedure (SMP), für die in situ Vorbehandlung von nativem-SiOx/Si(111)-Substrat entwickelt. Die Substratvorbehandlung mit Ga-Tröpfchen und zwei Hochtemperaturschritten vor dem Wachstumsprozess ermöglicht eine synchronisierte Nukleation aller Nanodrähte auf ihrem Substrat und folglich das Wachstum von sehr gleichförmigen GaAs Nanodraht-Ensembles mit einer sub-Poisson Verteilung der Nanodrahtlängen. Des Weiteren kann die Anzahldichte der Nanodrähte unabhängig von deren Abmessungen und ohne ex situ Vorstrukturierung des Substrats über drei Größenordnungen eingestellt werden. Diese Arbeit liefert außerdem ein grundlegendes Verständnis zur Nukleationskinetik von Ga-Tröpfchen auf nativem-SiOx und deren Wechselwirkung mit SiOx und bestätigt theoretische Voraussagen zum sogenannten Nukleations-Antibunching, dem Auftreten einer zeitlichen Anti-Korrelation aufeinanderfolgender Nukleationsereignisse. Im zweiten Teil dieser Arbeit wurde eine alternative Methode, bezeichnet als droplet-confined alternate-pulsed epitaxy (DCAPE), für das selbstkatalytische Wachstum von GaAs Nanodrähten und GaAs/AlxGa1-xAs axialen Nanodraht-Heterostrukturen entwickelt. DCAPE ermöglicht das Nanodrahtwachstum bei unkonventionell geringeren Temperaturen im Bereich von 450-550 °C und ist vollständig kompatibel mit der Standard-Si-CMOS-Plattform. Der neue Wachstumsansatz erlaubt eine präzise Kontrolle der Kristallstruktur der Nanodrähte und folglich das Wachstum von defektfreien Nanodrähten mit phasenreiner Zinkblende-Struktur. Die Stärke der DCAPE Methode wird des Weiteren durch das kontrollierte Wachstum von GaAs/AlxGa1-xAs axialen Quantentopf-Nanodrähten mit abrupten Grenzflächen und einstellbarer Dicke und Al-Anteil der AlxGa1-xAs-Segmente aufgezeigt. Die GaAs/AlxGa1-xAs axialen Nanodraht-Heterostrukturen sind interessant für den Einsatz als Einzelphotonen-Emitter mit einstellbarer Emissionswellenlänge, wenn diese mit gitterfehlangepassten InxAl1-xAs-Schichten in einer Kern-Hülle-Konfiguration überwachsen werden. Alle Ergebnisse dieser Arbeit tragen dazu bei, den Weg für eine erfolgreiche monolithische Integration von sehr gleichförmigen GaAs-basierten Nanodrähten mit kontrollierbarer Anzahldichte, Abmessungen und Kristallstruktur auf der industriell etablierten Si-Plattform zu ebnen.

We have measured the optical properties of films of the organic semiconductors PTCDA (3,4:9,10-perylene-tetracarboxylic dianhydride) and HBC (peri-hexabenzocoronene), prepared by Organic Molecular Beam Expitaxy (OMBE), on different substrates by means of Differential Reflectance Spectroscopy (DRS). The optical setup enables us to directly follow the thickness dependent optical properties of the organic films, starting from submonolayer coverage up to thicker films on the order of 20 monolayers (ML) film thickness. Due to the different optical nature of the different substrates used, i.e., mica, glass, Au(111), and HOPG, the direct interpretation of the DRS signal is not feasible. Therefore, we have proposed a method by which the calculation of the optical constants n (index of refraction) and k (absorption index) of thin films on arbitrary substrates from just one spectral measurement (in our case the DRS) becomes possible. The results fulfill a priori a Kramers-Kronig consistency and no specific model is needed to express the spectral behavior of the optical constants. Based on our method, we have successfully calculated the optical constants, and therefore the absorption behavior, of films of different thickness of PTCDA on mica, glass, Au(111), and HOPG, as well as of HBC on mica, glass, and HOPG. Extrinsic effects due to island growth or the presence of a polarizable substrate (screening) have been accounted for. We have introduced a finite dipole model which considers the extended geometry and anisotropy of the organic molecules. The calculated absorption behavior is discussed in great detail in terms of spectral changes with varying film thickness, different growth modes, degree of ordering of the films, interactions with the substrates and oscillator strength. A direct observation of a monomer-dimer transition in solid films could be observed for the first time. Our results indicate an exciton delocalization over about 4 molecules for both molecules.

Die Dissertation liefert eine Neuinterpretation des theoretischen Hauptziels der Harmonischen Elemente des Aristoxenos, sofern in der späten Herausbildung seines Dynamis-Begriffs unstrittig die zentrale Konzeption eines Wissens von der Musik liegt. Im Unterschied zur vorherrschenden Lehrmeinung und den bisherigen, vornehmlich musikhistorisch und philosophiegeschichtlich argumentierenden Ansätzen, welche die Innovationen des Aristoxenos auf die Befolgung der Methodik seines Lehrers Aristoteles und einer wissenschaftlichen Ferne von den Pythagoreern zurückführen, kommt die vorliegende, hauptsächlich medientheoretisch vorgehende Untersuchung zu dem gegenteiligen Ergebnis, dass (i) die Dynamis des Aristoxenos der Metaphysik des Aristoteles eklatant widerspricht und (ii) allein aus einer weiter gefassten Ontohistorie der griechischen Mousa-Kultur und deren philosophischen Verarbeitung durch den späten, pythagoreisierenden Platon in ihrer musiktheoretischen Relevanz hinreichend erkannt und in ihrer epistemologischen Signifikanz ausreichend gewürdigt werden kann. Für den Ansatz gilt zum einen, ernst zu nehmen, wie die in ihrer Vehemenz und Absolutheit bislang unverstandene Kritik an der Musiknotation aus der erstmaligen Einbeziehung der Melodie in die Wissenschaft von der Harmonie resultiert und entsprechend die radikalen Konsequenzen zu verfolgen, wie durch diese Verzeitlichung die Theorie der Musik insgesamt zu einer logisch-technischen Betrachtung eines harmonischen Prozesses wird, der unweigerlich mit virtuellen Entitäten operieren muss. Zum anderen sieht sich die Arbeit gezwungen, weit auszuholen, um kulturtechnisch auf die epistemogenen Momente der Erfindung des Alphabets und der Entdeckung des Inkommensurablen einzugehen, sowie philologisch das Pythagoreerbild des Aristoteles zu korrigieren. Beides zusammen führt ferner auf die Notwendigkeit, einen ‚zeiteigenen Sinn der Geschichte‘ zu postulieren und methodisch eine ‚doppelt negative Medienarchäologie‘ zu entwickeln. / This dissertation provides a reinterpretation of the major goal of Aristoxenus’ Harmonic Elements, inasmuch as it is beyond dispute that his late notion of dynamis constitutes the pivotal conception for a scientific understanding of music. Up to now the prevailing doctrine and a primarily music-historical arguing underpinned by a common approach to the history of philosophy holds that the innovations of Aristoxenus were to be explained by reference to the methodology obtained from his teacher Aristotle and the scientific distance taken from the Pythagoreans. By contrast, the present, mainly media-theoretical investigation arrives at the converse conclusion that (i) Aristoxenus’ notion strikingly contradicts the metaphysics of Aristotle and that (ii) it is alone by attaining a deeper onto-historical insight into the Greek Mousa-Culture and its philosophical incorporation by the late Pythagorising Plato that the music-theoretical relevance of the dynamis of Aristoxenus becomes sufficiently identifiable and that its epistemological significance can adequately be assessed. On the one hand, regarding the approach, one has to seriously account for the fierceness and absoluteness of the hitherto not understood critique of musical notation resulting from the first-time inclusion of melody into harmonic science. Accordingly, the radical consequences are to be traced, namely how by this temporalisation the theory of music as a whole is turned into a logico-technical consideration of a harmonic process that inevitably has to operate with virtual entities. On the other hand, the study is forced to go far afield in order to elucidate the epistomogenic momentum accompanying the invention of the alphabet and the discovery of incommensurability, as well as to correct the image of the Pythagoreans drawn by Aristotle. Taken together, this led to the need of postulating a ‘time’s own sense of history’ and to methodologically develop a ‘double negative media archaeology’.

This dissertation focuses on the Liqoqo years in Swaziland and the extent to which King Sobhuza’s reign and the introduction of the 1973 Decree created the conditions that led to the crises that plagued the country after the monarch’s death in 1982. It argues that Sobhuza II’s brand of cultural nationalism, the removal of the Independence Constitution, the introduction of Tinkhundla governance and the transformation of the Liqoqo sowed the seeds for political crisis that engulfed the kingdom. This study refutes the traditionalist/modernist debate and proposes that King Sobhuza II, albeit unwittingly, was the architect of a scenario that almost destroyed the long reigning Swazi monarchy. While this dissertation focuses on events leading up to and during the Liqoqo era, the aftermath is equally fascinating witnessing unparalleled civic dissatisfaction and the emergence of more vocal and organised opposition groups during the final decade of the century. / History / M.A (History)