No description available.

Metallic bilayer samples of Mo(400 Å)/ Al(substrate) were characterized using Rutherford Backscattering Spectroscopy after first being irradiated with Xe ion beam having an energy of 1.8 MeV. The computer code RUMP was then used to simulate the RBS spectra. The interdiffusion at the interface was considered in terms of thermal spike induced atomic migration. It was found that the coupling of the chemical effect with spike is significant with regard to mixing of the bilayer samples. Furthermore, in addition to the initial contamination of carbon atoms on the surface and at the interface, more carbon atoms were found to be picked up by the surface, this carbon w.as from the vacuum pumps and tended to migrate into the surface once irradiation dose exceeded 11 x 10¹⁵cm². A semi-empirical model was developed for ion beam mixing taking into account collisional mixing and thermal spike effects, as well as the thermal spike shape. The collisional mixing part was accounted for by the Kinchin-Pease model, or, alternatively dynamic Monte Carlo simulation. For the thermal spike, the ion beam mixing parameter Dt/Φ was derived to be proportional to ( - F_D /ΔH_coh)^2+μ, where F_D is the damage energy deposited per unit path length, ΔH_coh is the cohesive energy of the target materials, and µ is a constant dependent on the spike shape and point defect density in the spike regions. The thermal spike introduces a nonlinear effect in the mixing process, distinguishing itself from the linear effect of ballistic mixing. The shape of the thermal spike that best fit the experimental results depends on the magnitude of the cascade density. For relatively high density collisional cascades, where thermal spikes start to be important, it was found that a spherical spike model was more consistent with experimental measurements at low temperatures. However, for extremely high density collisional cascade regions, a cylindrical shaped spike gave better results. The atomic migration energy in the spike regions is scaled by a factor of one out of 8.6 of cohesive energy. The migration mechanism was recognized to be interstitial-dominated one. / M.S.

The major objective of this thesis was to evaluate electrically the damage caused by a low energy (< 4keV) Ar⁺ bombardment on n-GaAs(100) surfaces. Electrical measurements were performed on Schottlky diodes formed on the virgin and the ion-etched surfaces. The l-V measurements show deterioration of diode parameters by ion etching. The ion etched diodes have a strong component of surface leakage current. The high frequency capacitance of ion-etched diodes is less than that of the virgin diodes. The low frequency capacitance of ion-etched diodes was found to be frequency dispersive. The extent of frequency dispersion diminishes at low temperatures and at low reverse biases. Virgin diode capacitance, on the other hand, was found to be independent of frequency. The electrical characteristics of ion-etched diodes are explained by means of an amorphous layer and a donor-like damaged layer formed as a result of ion etching. The depth of the top amorphous layer increases with etch energy. The damaged layer containing the ion induced traps superimposes over the amorphous layer and extends deep into the bulk semi-conductor. The density of such traps is very bias sensitive and also temperature dependent. A possible equivalent circuit model for the ion-etched material is proposed. Low temperature isochronal annealing (< 450°C, 10mins.) was not found effective in causing complete recovery of the ion-damaged surface. / Master of Science

No description available.

Lasers bombeados por diodo semicondutor emitindo em 1mm têm diversas aplicações. Para muitas destas aplicações é desejado um feixe laser com uma boa qualidade e alta potência. Um dos maiores problemas encontrado quando se utiliza altas potências de bombeamento é a forte lente térmica gerada no meio ativo. Neste trabalho estuda-se um laser de Nd:YVO4 bombeado transversalmente por diodo laser em regime contínuo. Este tipo de bombeamento possibilita aproveitar o alto coeficiente de absorção do cristal tornando possível a obtenção de altas eficiências. Duas configurações de ressonadores foram estudadas. A primeira com uma dobra em ângulo rasante na superfície de bombeamento do cristal e a segunda com duas dobras nesta mesma face. Um laser de 22 watts de potência de saída e eficiência angular de 74% foi obtido com a primeira configuração sob um bombeamento de 35 watts. A qualidade do modo era de M2 = 26 ´ 11, na horizontal e na vertical, respectivamente. Uma melhora significativa na qualidade do feixe foi demonstrada quando feita a segunda dobra dentro do cristal. Uma potência de 17 watts foi atingida com essa configuração com qualidade de feixe de M2 = 3,4 ´ 3,7, na horizontal e na vertical, respectivamente. / Within the existing variety of laser cavity geometries and gain materials there is one combination that is particularly interesting because of its reduced complexity and high efficiency: the edge-pumped slab-laser using grazing-incidence geometry and a gain media with a very high pump absorption cross-section. In this work we studied a diode side-pumped Nd:YVO4 cw laser. We describe a single and a multiple bounce laser configurations. We demonstrate 22 W of multimode output power for 35 watts of pump power with a single pass through the gain media. A high optical-to-optical conversion efficiency of 63% and a slope efficiency of 74% with a very compact and simple Nd:YVO4 cavity that uses joint stability zones was achieved. The beam quality was M2 = 26 ´ 11 in the horizontal and vertical direction, respectively. With a double pass configuration we achieved 17 watts with a better beam quality of M2 = 3,4 ´ 3,7, in the horizontal and vertical direction, respectively.

Lasers bombeados por diodo semicondutor emitindo em 1mm têm diversas aplicações. Para muitas destas aplicações é desejado um feixe laser com uma boa qualidade e alta potência. Um dos maiores problemas encontrado quando se utiliza altas potências de bombeamento é a forte lente térmica gerada no meio ativo. Neste trabalho estuda-se um laser de Nd:YVO4 bombeado transversalmente por diodo laser em regime contínuo. Este tipo de bombeamento possibilita aproveitar o alto coeficiente de absorção do cristal tornando possível a obtenção de altas eficiências. Duas configurações de ressonadores foram estudadas. A primeira com uma dobra em ângulo rasante na superfície de bombeamento do cristal e a segunda com duas dobras nesta mesma face. Um laser de 22 watts de potência de saída e eficiência angular de 74% foi obtido com a primeira configuração sob um bombeamento de 35 watts. A qualidade do modo era de M2 = 26 ´ 11, na horizontal e na vertical, respectivamente. Uma melhora significativa na qualidade do feixe foi demonstrada quando feita a segunda dobra dentro do cristal. Uma potência de 17 watts foi atingida com essa configuração com qualidade de feixe de M2 = 3,4 ´ 3,7, na horizontal e na vertical, respectivamente. / Within the existing variety of laser cavity geometries and gain materials there is one combination that is particularly interesting because of its reduced complexity and high efficiency: the edge-pumped slab-laser using grazing-incidence geometry and a gain media with a very high pump absorption cross-section. In this work we studied a diode side-pumped Nd:YVO4 cw laser. We describe a single and a multiple bounce laser configurations. We demonstrate 22 W of multimode output power for 35 watts of pump power with a single pass through the gain media. A high optical-to-optical conversion efficiency of 63% and a slope efficiency of 74% with a very compact and simple Nd:YVO4 cavity that uses joint stability zones was achieved. The beam quality was M2 = 26 ´ 11 in the horizontal and vertical direction, respectively. With a double pass configuration we achieved 17 watts with a better beam quality of M2 = 3,4 ´ 3,7, in the horizontal and vertical direction, respectively.

No description available.

No description available.

Despite the vast material that has been written about the Second World War, most literature mentions battleships in passing, giving little attention to a role that battleships filled- that of naval gunfire support for amphibious landings. The literature regarding the Navy’s older, obsolescent battleships such as the Texas is scarce. Using primary sources regarding the Texas and the evolution of naval gunfire doctrine from the pre-war and wartime periods, this study looks at the involvement of the Texas in the Second World War and how the Navy employed its oldest battleships. The amphibious landings of the war provided a role in which a ship’s speed and range became irrelevant when firing on fixed targets on an enemy beach. This work provides a look at a little discussed, though widely used aspect of the Second World War and helps further discussion regarding the evolution of the US navy.

The bombardment of surfaces by ions can lead to the spontaneous formation of nano-structures. Depending on the irradiation conditions, smoothening or roughening mechanisms can be the leading order in pattern formation which can result in the creation of dots, ripples or ultra-smoothening effects. Because ion bombardment is already ubiquitous in industrial settings, and is relatively inexpensive compared to other surface processing techniques, self-organized patterning by ion bombardment could enable a simple, economical means of inducing well-defined nanoscale structures in a variety of settings. Understanding the fundamental behavior of surfaces during ion bombardment is therefore a vital goal; however, a complete understanding of physical processes governing surface pattern formation has not been reached yet. In order to address this issue, my thesis research has utilized three primary approaches. First, I have done real-time non-coherent X-ray scattering experiments at Cornell High Energy Synchrotron Source (CHESS) for studying kinetics of structure formation of Silicon undergoing Ar⁺ bombardment over a range of wavenumbers 4-5 times larger than has previously been obtained. From our data, we were able to extract values of the angle-dependent thickness of the amorphous layer that forms under ion bombardment, the ion-enhanced fluidity within that film, the magnitude of the stress being generated by the ion beam, and the strength of prompt atomic displacement mechanisms. Second, to further deepen our knowledge of surface dynamics, I have performed coherent X-ray studies of Ar⁺ bombardment of SiO₂ at the Advanced Photon Source (APS) for investigating the dynamics more profoundly than can be done with traditional time-resolved experiments. When using a focused ion beam, an inhomogeneous ripple motion was generated, this phenomenon reflected as an oscillatory behavior in the two-time and corresponding g₂(t) correlation functions. By fitting the oscillations in the g₂(t) correlation function, we have determined the surface ripple velocity on SiO₂ driven by Ar⁺ sputter erosion. Finally, to support the results of coherent X-ray experiments, simulations of growth models such as linear Kuramoto-Sivashinsky (KS) and Kardar-Parisi-Zhang (KPZ) have been carried out in order to compare the simulated temporal correlation functions of the scattered intensity with those obtained from the coherent x-ray scattering experiments.