This thesis aims at investigating the feasibility of realizing antireflection (AR) and high-reflection (HR) to the semiconductor waveguide end facet using monolithically integratable deep-etching technology to replace the conventional thin film dielectric coating counterpart. Conventional AR coating and HR coatings are the building blocks of semiconductor optical amplifier and semiconductor lasers. In this thesis, the AR coating and HR coating are first studied systematically and comprehensively using two computational electromagnetics approaches: plane wave transmission matrix method (TMM) and finite difference time domain (FDTD) method. The comparison of the results from the two approaches are made and discussed. A few concepts are clarified based on the different treatment between the AR coatings for bulk optics and those for semiconductor waveguide laser structure. The second part uses the same two numerical tools and more importantly, the knowledge gained from the first part to analyze and design deep-etched waveguide gratings for the advantage of ease of monolithic integration. A variational correction to the TMM is provided in order to consider effect of the finite etching depth also in the plane wave model. Specially, a new idea of achieving AR using deep-etched waveguide gratings is proposed and analyzed comprehensively. A preliminary design is obtained by TMM optimization and FDTD verifications, which provides a minimum power reflectivity in the order of 10-5 and a bandwidth of 45nm for the power reflectivity less than 10-3. In order to eliminate the nonphysical reflections from the boundary, the perfectly matched layer (PML) absorbing condition is employed and pre-tested for antireflection analysis. The effects of etching depth and number of etching grooves are specifically analyzed for the performance of proposed structures. Numerical results obtained by FDTD method indicate a promising potential for this alternative technologies. / Thesis / Master of Engineering (ME)

>Magister Scientiae - MSc / Hydrogen has high energy density and it is regarded as the future energy carrier. Hydrogen can be stored as a gas in high-pressure cylinders, as a liquid in cryogenic tanks and as a solid in metal hydrides. The storage of hydrogen in gas and liquid form has many limitations. Light metal hydrides show high energy density and are a promising and more practical mode of hydrogen storage. In particular, titanium and its alloys are promising metal hydrides for hydrogen storage due to their high affinity to hydrogen. The aim of this study is to investigate the effect of thermal annealing on hydrogen storage capacity of Ti-Pd multilayer systems. Ti-Pd multilayer films were prepared on CP-Ti (commercial pure Ti) and Ti6Al4V substrates using an electron beam evaporator equipped with a thickness monitor. The sequential deposition of layers Pd(50nm)/Ti(25nm)/Pd(50nm) was done at a constant deposition rate of 0.6 Å/s. The first batch of samples were thermally annealed at 550 °C in vacuum for two hours, the second batch of samples were annealed at 550 oC under H2(15%)/Ar(85%) gas mixture for two hours and the third series of samples was annealed under pure H2 gas at 550 oC for one hour. SEM showed relatively homogeneous and smooth topography of surfaces in as-deposited samples, while a rough textured surface was observed in both samples annealed under vacuum and under H2/Ar gas mixture. The samples annealed under pure H2 gas did not show any sign of crystallites grow but instead a relatively smooth surface with sign of etching. XRD revealed structural transformation as evidenced by the presence of PdTi2 phase in samples annealed under vacuum; in samples annealed under the gas mixture Pd2Ti was noted in addition to TiH2 and TiO2. While the TiH2 phase is an indication of hydrogen absorption, the TiPd2 phase suggests intermixing of the deposited layers and the presence of TiO2 is evidence of oxidation. The samples annealed under pure H2 gas showed only TiH2 with no trace of structural transformation. RBS confirmed the intermixing of layers in the samples annealed under vacuum and H2(15%)/Ar(85%) gas mixture, while samples annealed under pure H2 gas did not show any intermixing of layers. ERDA revealed an average H content of ~ 3.5 at.% in CP-Ti and ~6.2 at.% in Ti6Al4V for samples annealed under H2(15%)/Ar(85%) gas mixture. We recorded an hydrogen content of ~19.5 at.% in CP-Ti annealed under pure H2 while ~25.5 at.% was found in Ti6Al4V annealed under the same conditions. When the thickness of the Pd catalyst layers was increased to 100 nm (i.e. Pd (100 nm)/Ti (25 nm)/Pd (100 nm)), only ~ 12.5 at.% and 11.2 at. % hydrogen content was recorded in samples prepared on CP-Ti and Ti6Al4V alloy respectively, both annealed under pure hydrogen for one hour as above.

Hard gold thin films and coatings are widely used in electronics as an effective material to reduce the friction and wear of relatively less expensive electrically conductive materials while simultaneously seeking to provide oxidation resistance and stable sliding electrical contact resistance (ECR). The main focus of this dissertation was to synthesize nanocrystalline Au films with grain structures capable of remaining stable during thermal exposure and under sliding electrical contact stress and the passing of electrical current. Here we have utilized a physical vapor deposition (PVD) technique, electron beam evaporation, to synthesize Au films modified by ion implantation and codeposited ZnO hardened Au nanocomposites. Simultaneous friction and ECR experiments of low fluence (< 1x10^17 cm^-2) He and Ar ion implanted Au films showed reduction in friction coefficients from ~1.5 to ~0.5 and specific wear rates from ~4x10^-3 to ~6x10^-5 mm^3/N·m versus as-deposited Au films without significant change in sliding ECR (~16 mΩ). Subsurface microstructural changes of He implanted films due to tribological stress were analyzed via site-specific cross-sectional transmission electron microscopy (TEM) and revealed the formation of nanocrystalline grains for low energy (22.5 keV) implantation conditions as well as the growth and redistribution of cavities. Nanoindentation hardness results revealed an increase from 0.84 GPa for as-deposited Au to ~1.77 GPa for Au uniformly implanted with 1 at% He. These strength increases are correlated with an Orowan hardening mechanism that increases proportionally to (He concentration)1/3. Au-ZnO nanocomposite films in the oxide dilute regime (< 5 vol% ZnO) were investigated for low temperature aging stability in friction and ECR. Annealing at 250 °C for 24 hours Au-(2 vol%)ZnO retained a friction coefficient comparable to commercial Ni hardened Au of ~ 0.3 and sliding ECR values of ~35 mΩ. Nanoindentation hardness increases of these films (~2.6 GPa for 5 vol% ZnO) are correlated to microstructure via high resolution TEM and scanning electron microscope cross-sections to both Hall-Petch and Orowan strengthening mechanisms. Also presented is a correlation between electrical resistivity and grain size in the oxide dilute range based on the Mayadas-Shatzkes (M-S) electron scattering model. Using the M-S model in combination with a model describing solute drag stabilized grain growth kinetics we present a new technique to probe grain boundary mobility and thermal stability from in-situ electrical resistivity measurements during annealing experiments.