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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Surface studies on α–sapphire for potential use in GaN epitaxial growth

Agnarsson, Björn January 2009 (has links)
<p>This Licentiate thesis summarizes the work carried out by the author the years 2004 to 2008 at the University of Iceland and the Royal Institute of Technology (KTH) in Sweden. The aim of the project was to investigate the structure of sapphire (alpha-Al2O3) surfaces, both for pure scientific reasons and also for potential use as substrate for GaN-growth by molecular beam epitaxy.</p><p>More generally the thesis describes some surface science methods used for investigating the substrates; the general physical back ground, the experi- mental implementation and what information they can give. The described techniques are used for surface analysis on sapphire substrates which have been treated variously in order to optimize them for use as templates for epi- taxial growth of GaN or related III-V compounds.</p><p>The thesis is based on three published papers.</p><p>The first paper focuses on the formation a thin AlN layer on sapphire, which may act as a buffer layer for potential epitaxial growth of GaN or any related III-V materials. Two types of sapphire substrates (reconstructed and non- reconstructed) were exposed to ammonia resulting in the formation of AlN on the surface. The efficiency of the AlN formation (nitridation efficiency) for the two surfaces was then compared as a function of substrate temperature through photoelectron spectroscopy and low electron energy diffraction. The reconstructed surface showed a much higher nitridation efficiency than the non-reconstructed surface.</p><p>In the second paper, the affect of different annealing processes on the sapphire morphology, and thus its capability to act as a template for GaN growth, was studied. Atomic force microscopy, X-ray diffraction analysis together with ellipsometry measurements showed that annealing in H2 ambient and subse- quent annealing at 1300 °C in O2 for 11 hours resulted in high quality and atomically flat sapphire surface suitable for III-V epitaxial growth.</p><p>The third paper describes the effect of argon sputtering on cleaning GaN surfaces and the possibility of using indium as surfactant for establishing a clean and stoichiometric GaN surface, after such sputtering. Soft sputtering, followed by deposition of 2 ML of indium and subsequent annealing at around 500 °C resulted in a well ordered and clean GaN surface while hard sputtering introduced defects and incorporated both metallic gallium and indium in the surface.</p>
142

Studies of ultra-thin epitaxial Fe/Cu(100) films

Arnott, Michael January 1991 (has links)
No description available.
143

Analytic energy derivatives and their application to small and medium-sized molecules

Rice, J. E. January 1985 (has links)
No description available.
144

Surface plasmon effects in planar metal-oxide-metal tunnel junctions

Soole, Julian B. D. January 1987 (has links)
This thesis gives an account of experiments which investigate the detection of light by, and the emission of light from, planar metal-oxide-metal (M-O-M) tunnel junctions. The particular focus of attention is the mediation of these processes by surface plasmons, or surface electromagnetic waves bound to metal-dielectric interfaces, in the two processes. It describes how the coupling of incident bulk radiation to a surface plasmon supported by the junction structure may enhance the response of the device when used as a photodetector. This idea is then extended to cover other electromagnetic resonances supported by the junction system in different operating configurations. There is a brief departure from M-O-M devices to consider how a metal-semiconductor Schottky barrier diode may also have its photoresponse enhanced in a similar manner by coupling to a surface plasma wave localised at the metal-vacuum interface before returning to M-O-M devices to show that, in addition to their use as discrete detectors, they may also be used as integrated detectors of guided radiation. Attention is then turned onto the reverse process of light emission from M-O-M tunnel junctions. When these devices are 'rough' or are corrugated in some manner and pass a current they emit broadband light with an upper frequency cut-off determined by the applied bias, hv= e<SUP>V<SUB>bias</SUB></SUP>. This light emission process is mediated by the surface plasmons of the structure, of which there are three in the energy range considered. Experimental results on the light emission from residually rough and deliberately roughened junctions are reported. In particular, the results of an experiment are presented which show that the majority of the radiation outcoupled from statistically rough devices is derived from the 'fast' surface plasmon localised at the outer metal surface.
145

Positron annihilation studies of electronic and defect structures in metallic systems

Fretwell, H. M. January 1993 (has links)
No description available.
146

Studies on the uptake, translocation and metabolism of three nonionic ethoxylate surfactants following foliar application

Silcox, D. January 1988 (has links)
No description available.
147

Computations on static and dynamic models of solid surfaces

Williams, M. P. January 1986 (has links)
No description available.
148

Characterization of the surface acidity of passivated iron particles by flow microcalorimetry

Andrews, Marilyn Mockus, 1958- January 1987 (has links)
The characteristics of passivated iron particles have been examined with flow microcalorimetry to determine the acidic nature of the surface sites. The molar heat of adsorption of pyridine from hexane was measured with a FMC and a differential refractive index detector, at 23 and 40°C. The adsorption data were found to obey the assumptions of the Freundlich isotherm. The adsorption densities at different temperatures were used to calculate the isosteric heat of adsorption. The molar heat of adsorption of triethylamine from hexane was also measured and combined with the data for pyridine in order to calculate the Drago constants for the iron particles. A static adsorption method was used for the adsorption of pyridine from hexane onto the iron particles, for comparison with the dynamic method. The heat of wetting for the iron particles, with hexane, has also been measured. The iron particles were examined with X-ray diffraction. Mossbauer spectroscopy, XPS, SEM, TEM, and electrophoresis to characterize the surface layer. These techniques have revealed that the iron particles are coated with ferric oxide and this surface is amphoteric in aqueous solutions.
149

The effect of aggregate properties on the aggregate/bitumen adhesive bond

Russell, Tracey Edith Isobel January 1997 (has links)
No description available.
150

Environmentally-assisted crack growth in deaerator storage vessel steels

Wedgbury, Melanie Kim January 1990 (has links)
No description available.

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