Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 8 uppsatser.

Thesis (Ph.D.) Dept. of Physics, University of Adelaide, 1982. / Typescript (photocopy).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 301-309).

In this study, we have investigated the photo-response of gallium antimonide (GaSb) by measuring the spectral, injection level, as well as the temperature dependence of the steady-state photoconductivity of epitaxial films. By combining the various photo-response measurements with-galvanometric measurements, the effective excess carrier lifetimes could be calculated and described in terms of the various experimental variables considered. From a comparison of the measured and theoretical carrier lifetimes, a clear discrepancy was found for the injection dependent results. This inconsistency between the expected and measured behaviours was resolved using a two-layer model to describe the photo-conductive response of the thin film. In this model, the generation/recombination processes are considered for the bulk as well as for a depleted near-surface region. By combining these two contributions when calculating the total excess photocurrent, the various experimental results could be successfully described. The photo-response measurements revealed that the main contribution to the photocurrent came from the near-surface region, where the bandto- band and Auger recombination transitions are reduced. From the simulation of the injection level dependence of the excess carrier lifetime, some of the near-surface characteristics, such as the position of the surface Fermi-level and the surface recombination velocity, could be determined. In the case of p-type GaSb, the room temperature surface Fermi-level was found to be pinned (290±20) meV above the valence band maximum, whereas the n-type material had a pinning position of (150±20) meV above the valence band maximum. These pinning positions were shown to be independent of the doping density and relatively insensitive to the surface treatments considered. The presence of a near-surface depletion region, as well as the position of the surface Fermi-level, was corroborated by Raman spectroscopy. From a comparison of the phonon mode and the phonon-hole plasmon coupled mode, a surface Fermi-level position of (300 ± 30) meV was deduced for p-type GaSb. Finally, the effect various surface treatments have on the photo-response, and related surface properties, were investigated. Removal of the native oxide (HCl:H2O) followed by sulphur passivation (Na2S:9H2O) results in a slight decrease in the surface Fermi-level position. Aging studies however revealed that the surface characteristics reverted back to the untreated values following a few days in air. Coating the GaSb surfaces with a thin ZnS layer was found to have little effect on the surface potential, resulting only in a slight increase in the near-surface donor density. The sensitivity of the measured photocurrent to surface treatments and changes in the ambient with cooling, further validate the importance of considering the surface potential and the related space-charge when describing the photoconductive response of GaSb thin films.

This thesis details the use of x-ray photoelectron spectroscopy to monitor in-situ surface processing of solid surfaces in real-time. The processing methods investigated were annealing, deposition of thin organic films and exposure to oxygen and hydrogen produced by in-situ microwave plasmas. Three solid surfaces were investigated; metals, diamond and zinc oxide. Clean copper and gold were annealed up to 1000 K while monitoring with real-time XPS. A temperature-dependent shift of the Cu 2p3/2 and Au 4f7/2 core-level to lower binding energy was measured, -1.29 ± 0.04 meV/10 K and -2.36 ± 0.01 meV/10 K respectively. The shift was identified as being due to a thermal expansion of the lattice. The removal of argon ion induced damage to the copper surface was monitored in real-time and a critical temperature of 680 ± 20 K for the removal of the damage was measured. The formation of an interface between aluminium and copper phthalocyanine was monitored in real-time. Hydrogen and oxygen terminated (111) natural diamond surfaces were prepared in-situ and surface reconstruction by annealing up to 1200 K was monitored in real-time. Large reversible shifts to core-level binding energies were attributed to a surface photovoltage that was persistent at high temperature on the hydrogen and oxygen terminated surfaces. A model of the surface photovoltage is given where the bulk resistance of the diamond is identified as sustaining the photovoltage at elevated temperature. The zinc oxide (0001) surface was found to have a temperature-dependent core-level binding energy shift that was fully reversible up to 900 K and symmetric with cooling. The shift was attributed to a diffusion of oxygen vacancies from the bulk into the sub-surface. The zinc oxide (0001) surface was found to exhibit different temperature dependence to the (0001) surface that was fully reversible up to 700K but not symmetric with cooling. The shift was attributed to an additional disruption to stabilizing charge transfer between the polar surfaces. The formation of interfaces between the (0001) surface with copper phthalocyanine and C60 were monitored in real-time.

The carbon is photoelectron spectrum of CO��� has been measured with very high photon energy resolution. The natural lifetime of the carbon is hole state has been determined from a series of spectra taken at photon energies of 308, 320, and 330 eV. The measured values of the lifetimes show a dependence on photon energy; this is attributed to failure of the theory of post-collision interaction to predict correctly the observed electron spectrum near threshold. The lifetime widths reported here are critically compared with those values from the literature that are based on other spectroscopic techniques. The oxygen 1s photoelectron spectrum for CO��� has been calculated using ab initio electronic structure theory, a localized hole simulated by the equivalent-cores approximation, and the harmonic oscillator approximation. There is good agreement between the calculated spectrum and a recently reported experimental spectrum. / Graduation date: 1999

Thesis (B.S.)--Rochester Institute of Technology, 1983. / Typescript. Includes bibliographical references (leaf 17).

The study of semiconductor materials and more recently, artificially struc¬tured materials, is important for both scientific and industrial purposes. Many techniques have been developed to characterize the electronic properties of these materials. Optical characterization is a popular approach to this field of study, as the absorption or reflection of incident photons is directly related to the band structure of a semiconductor material. When measuring the absolute reflectivity or absorptivity, the resulting spec¬trum is often rather featureless, making it difficult to observe band structure features. This led to the invention of modulation spectroscopy techniques where the derivative of the absorptivity or reflectivity of a semiconductor ma¬terial with respect to some experimental parameter, is evaluated. Weak fea¬tures in the absolute spectrum are thus enhanced, making the identification of band structure features easier. This study describes the technique of photo reflection spectroscopy (com¬monly known as photoreflectance spectroscopy) where modulation is achiev¬ed optically. The theory behind photoreflectance spectroscopy is discussed in detail, whereafter the practical implementation is described. This is followed by measurements done on GaAs to do a basic comparison with published re¬sults. Finally, three different doping superlattices were investigated with this technique; including the influence that a-particle irradiation and consequent annealing have on the measured photoreflectance spectra. / Dissertation (MSc (Physics))--University of Pretoria, 2006. / Physics / unrestricted

The surface-specific analytical technique of X-ray photoelectron spectroscopy (XPS) is described, and was used to study various geochemical materials and organic compounds. Variation of surface pyrite density with coal particle size (53-250/µm) in a typical Canadian coal (Minto) provided some interesting data- it is very likely that as coal is crushed, one eventually reaches a particle size where the surface pyrite/carbon ratio maximizes. It is this parameter that is examined here, and correlations were found between (i) surface pyrite concentration,(ii) surface pyrite/sulfate ratio, and (iii) oxidized and non-oxidized sulfur with particle size. This is information which should find useful application in coal cleaning technology. For non-oxidized coal, we find the area of exposed pyrite on the coal surface is approximately inversely proportional to coal particle radius. However, for oxidized coal the appearance of curves depends on the oxidation times, but there is a particle size which exhibits maximum surface pyrite relative to 1/radius, corresponding to the intercept point of the two linear segments (low and higher values of 1/R) for the non-oxidized coal (fig. 3.9), and which is evidently that we will call the "characteristic" size of constituent pyrite. XPS 2p₃/₂ sulfur peaks from major sulfur constituents other than sulfate in sediment recovered from Mahoney Lake (south-central British Columbia, Canada) show a surprisingly periodic variation in sulfur 2p₃/₂ binding energy (BE), and hence molecular structure, with sediment age. The pattern ceases at a core depth of about 3.2 meters, where a major deposit of fine sandy sediment occurs just below ash deposition (2.6m) from a major eruption of Mount Mazama, Oregon, approximately 6500 year ago, which led to the formation of Crater Lake. Sedimental sulfur exists mainly as sulfate; however, there is a pronounced increase in amount of the lower BE sulfur species relative to sulfate toward lower depths. The "reduced" species also shows a trend towards slightly higher oxidation level at lower depths. We are able to suggest the probable chemical forms in which the sulfur species exist, which is of interest to biologists working on sulfur transformation studies in lakes. BE' s for nitrogen Is and sulfur 2p₃/₂ in the metal chelates of dibenzyldithiocarbamic acid M(DBDTC)n for n=2, M=Cu(II) and Zn(II), and for n=3, M=Bi(III), have been measured. The nature of the spectral peaks and core BE's indicates that the nitrogen atom in the DBDTC is not intramolecularly bound with the metal as had been previously suggested. The relatively high BE's for the nitrogen Is orbitals indicate planar geometry for the coordinated ligands, and the form [formula omitted] to reasonably represent their structure, which agrees with previous infrared studies. / Science, Faculty of / Chemistry, Department of / Graduate

Chiral molecules are composed of the same constituent atoms, but are inherently different due to being mirror images of each other. The physical properties of such molecules are nearly identical, but the biochemical interactions can differ wildly, which has extreme implications in the pharmaceutical industry. It is for this reason that it is important to be able to characterize and study individual enantiomers, and develop physical methods to do so. Optical techniques have evolved over the past two decades of scientific work which have been shown to be able to distinguish one enantiomer from another. These techniques tend to involve the use of circularly polarized light to induce a forward/backward asymmetry along the axis of light's propagation. The resulting sensitivity difference between enantiomers is typically on the order of a few percent. Recently, a novel optical pulse scheme has been developed whose electric field is fully three-dimensional and inherently chiral. This field was computationally used to demonstrate that the signal difference between enantiomers can reach upwards of 100\% sensitivity through the generation of high harmonics. Presented in this thesis are the results of an experimental measurement performed using just such a novel pulse scheme. A cold target recoil ion momentum spectroscopy machine is used to detect the photoelectron spectra from the ionization of each enantiomer of propylene oxide. A comprehensive discussion on the practical realization of the novel pulse scheme is presented, and the circular dichroism due to the novel field is shown. Also discussed are fragmentation of propylene oxide, three dimensional chiral signals found in the data, and a new measure to define the magnitude of chirality in a photoelectron distribution. Finally, measurements pertaining to the ionic yield of each enantiomer under varying handedness of light are shown. These results are the first experimental realization of optical measurements using synthetically designed chirality.