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.

Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2002. / Vita. Includes bibliographical references.