Call number: LD2668 .T4 1985 S25 / Master of Science

Hydrogen desorption mechanisms on hydrogenated silicon surface such as H/Si(1 00)-1x1, H/Si(l00)-2xl and H/Si(100)-3x1 surfaces have been explored by theoretical calculations with slab models. Similar desorption mechanisms have been identified for three hydrogenated surfaces and the calculated barriers were in agreement with experimental values. More interestingly, a common bridge structure has been identified as an intermediate. Its unique electronic structure is analyzed in detail. The identification of such a structure provides an alternative account for previous experimental results on STM tip-induced desorption. / Metal atom clusters are nanoscale intermediates between metal atoms and the bulk metal. Al13- can be regarded as a cluster model for Al(111) due to its special electronic and geometric structures. The reaction between Al13- and O2 was explored by various DFT methods such as BLYP, PW91, PBE, B3LYP and BHHLYP and post-HF methods such as CCSD and QCISD(T). The calculation results demonstrated that the reaction was exothermic and thermodynamically quite favorable, and the reason for the stability of Al13- towards oxygen exposure was kinetic, due to the presence of a reaction barrier. True to the expectation of Al13- as a molecular model for the Al surface, the identification of this barrier resolved a long standing puzzle in the initial chemisorption of O2 on Al(111): a barrier was identified in experiment but not in any theoretical calculations on the ground state potential surface. / Reactions on solid surfaces play a crucial role in many technologically important areas such as corrosion, adhesion, synthesis of new materials and heterogeneous catalysis. Theoretical studies on chemical reactions at surfaces can provide much useful information to understand and control these chemical processes. The present project is devoted to explore chemical reactions occurred on the aluminum cluster of Al13- and on the Si(100) surface by first principle calculations, using Gaussian 03 and Vienna Ab Initio Simulation Package (VASP). / The Al13-+HX reactions, with HX being either HCl or HI, are explored by first principle calculations and two importance dynamic factors are identified. Firstly, there was a barrier to the dissociative adsorption of FIX on the surface of an Al13- cluster, which involved charge transfer from Al13-. Secondly, the H atom could be bonded to the cluster in multiple ways, similar to the top, bridge and hollow adsorption sites on Al(111) surface. With a large amount of energy (>40 kcal/mol) deposited during the formation of Al13 -HX-, the H atom could easily migrate among these sites, similar to the diffusion of H on metal surfaces. The two dynamic factors were therefore important considerations in the formation and dissociation of Al 13-HX- And moreover, these dynamic factors make Al13- a fascinating model to probe the dynamic aspect of surface reactions, which should be an important consideration in the reactivity of other metal clusters. / Yuan, Qinghong. / "October 2009." / Source: Dissertation Abstracts International, Volume: 72-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

A surface pretreatment for aluminum and titanium involving the reaction of phosphonic acid (RPO(OH)2), R=butyl or vinyl for aluminum and R=vinyl for titanium, has been investigated. The durability of phosphonic acid-pretreated samples was compared with that for P2-etched (ferric sulfate-sulfuric acid) adherends. Samples were bonded with LaRC-IA adhesive in a wedge test geometry. Environmental testing consisted of static and cyclical exposure for 240 hours in three atmospheres: 1) 170°C, 2 torr; 2) -20°C; 3) 60°C, 70% relative humidity. Crack propagation arrested within 48 hours. The order of durability in static environmental tests for aluminum was vinyl phosphonic acid > P2 > butyl phosphonic acid. The durability performance was reversed for cyclic testing. The durability of specimens using P2-etched titanium was superior to that for vinyl phosphonic acid-treated titanium in all environmental tests. / Master of Science

Surface roughness exists at many length scales-from atomic dimensions to meters. At sub-micron scale, the distribution of roughness is largely dependent on the process that generates the surface through the mechanisms of material removal/addition involved and the process parameters. The focus of the research is to quantitatively characterize the evolution of sub-micron scale surface roughness in the mechanical, chemical and electrochemical material removal techniques and study the influence of roughness on the mechanical behavior of surfaces. High purity aluminum surfaces are subjected to surface dissolution techniques such as electropolishing, chemical etching and anodization. Owing to the lack of sufficient lateral resolution in conventional roughness measurement techniques and appropriate scale independent roughness characterization techniques, the effect sub-micron scale electrochemical inhomogeneities present on the surfaces have on the roughness evolution at various length scales has not been understood. In this work, the power spectral density method of roughness characterization is used to quantitatively evaluate the roughness length scales affected in the surface generation processes as a function of time. Results indicate that in the case of electropolishing, roughness is not uniformly reduced at all length scales. Further, cut-off frequencies are suggested to optimize the electropolishing process. In chemical etching, the nature of roughness produced is found to be dependent on the nature of the starting surface. The nature of surface and sub-surface structures produced in the initial stage of the anodization process, and the transition from a disordered to an ordered structure are studied. In order to study the mechanical behavior of surfaces as a function of surface roughness, a single asperity indentation is modeled using nanoindentation of micropillar produced by focused ion beam machining of aluminum surfaces. Load-displacement curves are constructed to show the transition from a single asperity deformation to bulk deformation as function of indentation depth. Additionally, indentation responses of polymer coated surfaces with varying degree of roughness that were produced by the aforementioned surface generation processes are studied. it is shown how high interface roughness gives rise to high scatter both in loading and unloading portions of the load-displacement curves. Finally, porous alumina surface generated by the anodization process discussed above is indented to simulate a multi-asperity interaction.