No description available.

No description available.

No description available.

The orientation relationship and interfaces of Ni3Sn4 and Ni3Sn2 with the Ni (001) and (111) surfaces have been studied with transmission electron microscopy. Ni was evaporated onto the NaCl (001) and (111) surfaces to form epitaxial Ni thin films and Sn was evaporated onto the Ni film and heat treated to form Ni3Sn4 and Ni3Sn2. No orientation relationship between Ni3Sn4 and Ni was found. Two types of orientation relationships between £b-Ni3Sn2 and Ni were found: (1) (0002) £b-Ni3Sn2//(220)Ni and (01 0) £b-Ni3Sn2//(2 0)Ni on the (2 0) £b-Ni3Sn2/(001)Ni interface¡Fand (2) (0002) £b-Ni3Sn2 //(2 0)Ni and (01 0) £b-Ni3Sn2//(22 )Ni on the (2 0) £b-Ni3Sn2/(001)Ni interface.

No description available.

The objective of this research is to achieve high-efficiency, low-cost, commercial-ready, screen-printed Silicon (Si) solar cells by reducing material costs and raising cell efficiencies. Two specific solutions to material cost reduction are implemented in this thesis. The first one is low to medium concentrator (2-20 suns) Si solar cells. By using some optics to concentrate sunlight, the same amount of output power can be achieved with cell area reduced by a factor equal to the concentration ratio. Since the cost of optics is less than the semiconductor material, electricity price from the concentrator photovoltaics (PV) system is therefore reduced. The second solution is the use of epitaxially grown Si (epi-Si) wafers. This epi-Si technology bypasses three costly process steps (the need for polycrystalline silicon feedstock, ingot growth, and wafer slicing) compared to the traditional Si wafer technology and therefore reduces the material cost by up to 50% in a finished PV module. In addition, high efficiency Si solar cells with reduced metal contact recombination are studied and modeled by implementation of passivated contacts composed of tunnel oxide, n+ polycrystalline Si and metal on top of n-type Si absorber to reduce the cost ($/Wp) of PV module.

The elusive 2D carbon poly-type was argued more than 70 years ago. Meanwhile, the recent discovery of graphene has proved that such materials can indeed be obtained and are thermodynamically stable. Graphene has demonstrated the unique properties that lead to many innovations in laboratory conditions. However, the current approaches available for the industrial fabrication yield the low graphene quality against the theoretical predictions. Furthermore, any graphene combination with the supporting units causes a newly-induced quality for adaptation to the other condensed matters. Therefore, the unusual ability for sensitive alteration in the external world has turned into a regulation for intended graphene engineering. The submitted investigation has been undertaken to elaborate a novel methodology for the goal-directed control of epitaxial graphene fabrication by using interaction design. This is the most perspective pathway to scale-up production of intended quality subjected to the manufacturing of novel carbide derived carbon (CDC) patterns via interaction with specific substrates under hydrogen halides impact. The graphene layers and structural arrangement of the composite systems, as well as their electronic properties depend on the particular substrate, coherent commensuration of the adjacent units, interaction between them and the physical environment of fabrication. It is crucial to understand the interaction processes leading to stable construction. Density Functional Theory (DFT) implemented in the CASTEP system has been employed in this research in order to develop this knowledge and also to determine how to tune and engineer the band gaps of such composite assemblies. The substrate alternating reconstructions, polarity of surface terminations, commensuration and number of layers, their stacking order and distances between constituting units are taken into consideration for intended simulation. The (3x3) and (√3x√3) reconstructions of 4H-SiC poly-type are the starting points for epitaxial growth (EG) on the Si-face and C-face unit cells. The results of the substrate induced interaction are interpreted via the versatility of band states gradually traced from the dehydrogenated SiC framework to CDC bi-layer. The distinctive feature resulted from the substrate influence is kept as the transitional band for different arrangements and locations in vicinity of the Fermi level. The first buffering C-plane reinforces substrate distinctions between the initial configurations and polarities. The n-type of gap state is the characteristic of the Si-face termination, whereas, the p-type is found for the C-face case. Both structures are devoid of the freestanding graphene signs. The appropriate indications of dominant graphene identity are found for the (0001) - (√3x√3) substrate only, at a close distance between two upper C-planes acceptable for covalent bonds. As for graphene EG the chemical conversion by using fluorination is employed to avoid the possible damage inspired by initial substrate roughness. The few layered CDC assemblage on the (0001) - (√3x√3) support is trailed via gradual Si – F interaction and SiFx groups penetrating through the bulk. Regular control over potential energy surfaces, minimal energy pathways, transition states and activation barriers enable the indicative indexes for reaction credibility and progress. By means of the Arrhenius equation using the activation energy values the average temperature of 1500 - 2000 C are predicted for the real conversion events. Under these conditions the wet surface etching for the topmost Si-atoms and release of oxidised CDC are accompanied with a complementary promotion mechanism which resulted in a highly ordered graphene structure.

The work presented in this thesis may be considered in two main parts; firstly a description of the design and operation of a display type photoelectron spectrometer. Secondly a series of experiments investigating the electronic properties of thin epitaxial films (1-5 atomic layers) of cobalt grown on a clean single crystal copper (001) substrate. Conventional angle resolved photoelectron spectrometers of the deflection type are only capable of observing one point in the (E,θ,φ) space at a time. This is often perfectly acceptable if one is concerned with optimal resolution in order to perform accurate band mapping experiments. However certain experiments are essentially impossible, for instance the observation of the emitted photocurrent over all θ,φ at the fermi energy. This is partly because of the time limitations imposed by the necessity to keep the sample atomically clean in the U.H.V. environment. Several previous workers have tackled this problem by designing spectrometers that observe large sections of θ,φ space simultaneously, for a given energy. The first part of this work concerns the design and implementation of a display type spectrometer which embodies some new and quite novel features. Thin epitaxial films of ferromagnetic materials grown on non-magnetic substrates have long been of interest. Partly as a prototypical surface for the investigation of surface magnetism, and partly for the investigation of the changes induced in the magnetic properties as the dimensionality is reduced or as the lattice size is changed. The second part of this thesis concerns experiments using three different spectroscopies on a system of this type, specifically Co on Cu(001). Firstly, a photoemission study using the display spectrometer is presented, observations of the spin-split bands as a function of wavevector parallel to the surface are shown. Secondly an Auger electron study of the growth mode of the epitaxial film, together with a LEED I/V study of the changing lattice strain as a function of film thickness are presented. Although none of these measurements directly probe the magnetism of the films, they provide very necessary information in order to understand their behaviour.

No description available.

No description available.