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Silicon is widely used in optoelectronic devices, including solar cells. In recent years new forms of silicon have become available, including amorphous, microcrystalline and nano-crystalline material. These new forms have great promise for low cost, thin film solar cells and the purpose of this work is to investigate their preparation and properties with a view to their future use in solar cells. A Hot Wire-Deposition Chemical Vapour Deposition CVD (HW-CVD) system was constructed to create a multi-chamber high vacuum system in combination with an existing Plasma Enhanced Chemical Vapour Deposition (PECVD) system; to study the amorphous to crystalline transition in silicon thin films. As the two chambers were linked by a common airlock, it was essential to construct a transfer mechanism to allow the transfer of the sample holder between the two systems. This was accomplished by the incorporation of two gate valves between the two chambers and the common airlock as well as a rail system and a magnetic drive that were designed to support the weight of, and to guide the sample holder through the system. The effect of different deposition conditions on the properties and structure of the material deposited in the combined HW-CVD:PECVD system were investigated. The conditions needed to obtain a range of materials, including amorphous, nano- and microcrystalline silicon films were determined and then successfully replicated. The structure of each material was analysed using Transmission Electron Microscopy (TEM). The presence of crystallites in the material was confirmed and the structure of the material detected by TEM was compared to the results obtained by Raman spectroscopy. The Raman spectrum of each sample was decoupled into three components representing the amorphous, intermediate and crystalline phases. The Raman analysis revealed that the amorphous silicon thin film had a dominant amorphous phase with smaller contribution from the intermediate and crystalline phase. This result supported the findings of the TEM studies which showed some medium range order. Analysis of the Raman spectrum for samples deposited at increasing filament temperatures showed that the degree of order within the samples increased, with the evolution of the crystalline phase and decline of the amorphous phase. The Selected Area Diffraction (SAD) patterns obtained from the TEM were analysed to gain qualitative information regarding the change in crystallite size. These findings have been confirmed by the TEM micrograph measurements. The deposition regime where the transition from amorphous to microcrystalline silicon took place was examined by varying the deposition parameters of filament temperature, total pressure in the chamber, gas flow rate, deposition time and substrate temperature. The IR absorption spectrum for ƒÝc-Si showed the typical peaks at 2100cm-1 and 626cm-1, of the stretching and wagging modes, respectively. The increase in the crystallinity of the thin films was consistent with the evolution of the 2100cm-1 band in IR, and the decreasing hydrogen content, as well as the shift of the wagging mode to lower wavenumber. IR spectroscopy has proven to be a sensitive technique for detecting the crystalline phase in the deposited material. Several devices were also constructed by depositing the ƒÝc-Si thin films as the intrinsic layer in a solar cell, to obtain information on their characteristics. The p- layer (amorphous silicon) was deposited in the PECVD chamber, and the sample was then transferred under vacuum using the transport system to the HW-CVD chamber where the i-layer (microcrystalline silicon) was deposited. The sample holder was transferred back to the PECVD chamber where the n-layer (amorphous silicon) was deposited. The research presented in this thesis represents a preliminary investigation of the properties of ƒÝc-Si thin films. Once the properties and optimum deposition characteristics for thin films are established, this research can form the basis for the optimization of a solar cell consisting of the most efficient combination of amorphous, nano- and microcrystalline materials.

Understanding mechanisms at the molecular level is essential for interpreting and predicting the outcome of processes in all fields of chemistry. Insight into gas-surface reaction dynamics can be gained through molecular beam scattering experiments combined with classical trajectory simulations. In particular, energy exchange and thermal accommodation in the initial collision, the first step in most chemical reactions, can be probed with these experimental and computational tools. There are many questions regarding the dynamic details that occur during the interaction time between gas molecules and organic surfaces. For example, how does interfacial structure and density affect energy transfer? What roles do intramonolayer forces and chemical identity play in the dynamics? We have approached these questions by scattering high-energy, rare gas atoms from functionalized self-assembled monolayers. We used classical trajectory simulations to investigate the atomic-level details of the scattering dynamics. We find that approximately six to ten carbon atoms are involved in impulsive collision events, which is dependent on the packing density of the alkyl chains. Moreover, the higher the packing density of the alkyl chains, the less energy is transferred to the surface on average and the less often the incident atoms come into thermal equilibrium with the surface. In addition to the purely hydrocarbon monolayers, organic surfaces with lateral hydrogen-bonding networks create more rigid collision partners than surfaces with smaller inter-chain forces, such as van der Waals forces. Finally, we find some interesting properties for organic surfaces that possess fluorinated groups. For argon scattering, energy transfer decreases with an increasing amount of surface fluorination, whereas krypton and xenon scattering transfer most energy to monolayers terminated in CF₃ groups, followed by purely hydrocarbon surfaces, and then perfluorinated surfaces. / Ph. D.

GaAsBi is a relatively unexplored alloy with interesting features such as a large bandgap reduction for a given lattice mismatch with GaAs substrates and good photoluminescence which make it promising for long wavelength light detection and emission applications. In this research, the molecular beam epitaxy (MBE) method was used to grow epi-layers and hetero-structures. A Vertical-external-cavity surface-emitting-laser (VECSEL) was grown as a part of collaboration with Tampere University in Finland. The process of laser growth promoted the writer’s skills in the growth of hetero-structures and led into an investigation of the effect of growth conditions on GaAsBi optical properties with important results. For instance, when the substrate temperature during growth was reduced from 400°C to 300°C and all other growth conditions were fixed, the Bi concentration in the deposited films increased from 1% to 5% and the photoluminescence (PL) intensity decreased by more than a factor of 1000. This is an indication of the importance of growth temperature in GaAsBi crystal quality. n+/p junctions were grown for the deep level transient spectroscopy (DLTS) experiments in collaboration with Simon Fraser University. The DLTS measurements showed that lowering the GaAsBi growth temperature increases the deep level density by a factor of 10. These deep levels are the source of non-radiative recombination and decrease the PL intensity. The structural properties of GaAsBi were investigated by high resolution x-ray diffraction and polarized PL and revealed long distance atomic arrangement (Cu-Pt ordering) in GaAsBi. The measurements showed that the ordering is more probable at high growth temperature. This can be due to the larger mobility of the atoms on the surface at high growth temperatures that allows them to find the ordered low energy sites. / Graduate

The hydrogenation of β-ketoesters over chirally modified Ni catalysts is a celebrated and thoroughly researched example of an enantioselective heterogeneous catalytic reaction. Enantioselective heterogeneous processes, although extremely attractive in terms of fewer complications in the separation of products from the catalyst, are hindered in their viability as industrial applications due to the lack of detailed knowledge on how chirality is conferred to the metal surface. Surface science techniques have afforded substantial progress into determining mechanisms between modifier, reactant and catalyst to explain the source of enantioselectivity of the system. In this study, a combination of solution and ultra-high vacuum (UHV)-based experiments allow a more realistic interpretation of the surface chemistry underpinning the catalytic reaction as the key step in achieving enantioselective performance is the adsorption of chiral modifiers from solution. The behaviour of (S)-aspartic acid and (S)-lysine on Ni{111} and their interaction with the prochiral β-ketoester methylacetoacetate is investigated in this study to understand their potential as chiral modifiers for the system. In UHV, scanning tunnelling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), and temperature programmed desorption (TPD) are used to analyse the conformation and order of the amino acids on the metal, and their thermal stability. Additionally, liquid-solid interface RAIRS and X-ray photoelectron spectroscopy (XPS) are used to examine the modified Ni surface, prepared under aqueous conditions, to give an accurate representation of the catalytic studies. It has been found highly likely that, for (S)-aspartic acid modified Ni{111}, enantioselective sites exist at step or step/kink defects, formed by corrosive leaching of the Ni substrate. Conversely, lysine appears to bind with a high sticking probability to Ni, in the form of lysine islands, and does not appear to etch the Ni chirally. Finally, similar experiments have been carried out on Au{111}, where lysine was found to chiral restructure the surface and form nanofingers, and 2D Ni clusters grown on Au{111} in order to investigate the formation of possible metal-organic frameworks.

Nos últimos 30 anos o crescimento paralelo das Ciências de Superfície tradicionais, em ambiente de ultra-alto vácuo (UHV), com a Eletroquímica levou ao nascimento de um novo campo interdisciplinar: Física de Superfície e Eletroquímica. Técnicas de ambas as áreas dão informações complementares e assim, quando realizadas em conjunto podem fornecer muitas respostas em nível atômico, estrutural e eletrônico quando o eletrodo está em contato com a solução eletrolítica. A intenção primordial dessa Dissertação foi o estudo fundamental das fases ricas em oxigênio presentes na superfície de Ru(0001) através de caracterizações eletroquímicas e morfológicas utilizando um sistema que permitiu o acoplamento de uma célula eletroquímica miniatura de fluxo a câmaras de UHV. Inicialmente exibi-se a modificação e a construção de equipamentos necessários para a preparação do sistema binário Au-Pt(111) e do óxido monocristalino Ru2O(110). Imagens de STM em escala morfológica mostraram o crescimento anisotrópico do filme de RuO2(110) sobre um substrato monocristalino de Ru(0001). Resultados obtidos através da técnica de Voltametria Cíclica na eletrooxidação de CO em RuO2(110) corroboraram cálculos teóricos sobre a estrutura da superfície quando esta em ambiente úmido. Superfícies modelos baseadas em ouro, crescido epitaxialmente sobre um substrato de Pt(111), foram preparadas no sistema de UHV. Dados eletroquímicos foram correlacionados às composições superficiais destas, mostrando o efeito do substrato prevalecendo sobre o efeito eletrônico. / In the last 30 years the parallel growth of the traditional Surface Science, under UHV environment, and Electrochemistry gave rise to a new interdisciplinary field: Surface Science and Electrochemistry. Techniques from both sciences give complementary information. Thus, in tandem, they are able to elucidate many atomic, structural and electronic phenomena, of an electrode in contact with a solution. The main goal of this Dissertation was the fundamental study of the Oxygen-rich Ru(0001) surface through electrochemical and morphologic characterizations using a coupled system which allowed the attachment of a miniature flow cell to UVH-chambers. Initially it is shown the construction and modifications of required equipments for the preparation of the binary system Au-Pt(111) and single crystal RuO2(110) oxide. Attainable morphological STM images demonstrated the anisotropic growth of the RuO2(110) over a Ru(0001) substrate. Results of the electrooxidation of CO on RuO2(110), obtained by means of Cyclic Voltammetry, corroborated theoretical calculations concerning the oxide superficial structure in a humid environment. Model surfaces based on Au, epitaxialy grown on a Pt(111) substrate, were prepared under UHV conditions. Electrochemical data and superficial composition were correlated, confirming that the substrate effect overcomes electronic strain effects.

The design and construction of a state-of-the-art ultra-high vacuum spectrometer for the performance of angle-resolved inverse photoemission spectroscopy is presented. Detailed descriptions of its most important components are included, especially the Geiger-Muller ultraviolet photodetectors. By building on recent developments in the literature, we expect our spectrometer to achieve resolution comparable or superior to that of other prominent groups, and in general be one of the foremost apparatus for studying the momentum dependence of the unoccupied states in strongly correlated materials. Summaries of the theory of angle-resolved inverse photoemission spectroscopy and the basics of ultra-high vacuum science are also included.

The design and construction of a state-of-the-art ultra-high vacuum spectrometer for the performance of angle-resolved inverse photoemission spectroscopy is presented. Detailed descriptions of its most important components are included, especially the Geiger-Muller ultraviolet photodetectors. By building on recent developments in the literature, we expect our spectrometer to achieve resolution comparable or superior to that of other prominent groups, and in general be one of the foremost apparatus for studying the momentum dependence of the unoccupied states in strongly correlated materials. Summaries of the theory of angle-resolved inverse photoemission spectroscopy and the basics of ultra-high vacuum science are also included.

This dissertation provides a brief introduction into scanning tunneling microscopy, and then Chapter III reports on the design and operation of a cryogenic ultra-high vacuum scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Other performance characteristics such as thermal drift analysis and a cool-down analysis are reported. Scanning tunneling spectroscopy (STS) measurements based on the lock-in technique were also carried out and showed no detectable presence of noise from the CCC. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic-scale. A study of electron transport in single-walled carbon nanotubes (SWCNTs) was also conducted. In Chapter IV, STS is used to study the quantum-confined electronic states in SWCNTs deposited on the Au(111) surface. The STS spectra show the vibrational overtones which suggest rippling distortion and dimerization of carbon atoms on the SWCNT surface. This study experimentally connects the properties of well-defined localized electronic states to the properties of their associated vibronic states. In Chapter V, a study of PbS nanocrystals was conducted to study the effect of localized sub-bandgap states associated with surface imperfections. A correlation between their properties and the atomic-scale structure of chemical imperfections responsible for their appearance was established to understand the nature of such surface states. This dissertation includes both previously published/unpublished and co-authored material.