Electronic Structure Of Surface Supported Oxide Films And Scattering Dynamics Of Hydrogen Molecules

Films and molecules supported on surface can form various kinds of structures, which draw muchattention for their unique properties and potential applications in the field of spintronics, surfacemodification and surface treatment. In this dissertation, firstly we build our models for the surfacesupporting oxide and hydrogen. And then, we choose appropriate methods, for example, first principlecalculation, molecular dynamics simulations and reactive forcefield to obtain necessary information.Based on the information, we discuss the phenomena found in the surface supported systems, such asthe half-metallic property of the surface supporting oxide, the dissociation process of the molecule atthe surface, and the connection between the physical property and the surface structures. Someinteresting results are obtained. The outline is as follows:In chapter1, we review the development for the research about the surface supporting system. Thenwe give an introduction for its physical property and application prospect.In chapter2, the basic concepts of the density of functional theory (DFT) and the first principlecalculation program, VASP are introduced, with which we study the electronic structure transitionwhen MnO2is under tensile stress. We find that, under certain strain, MnO2will show half-metallicproperty. The formation of the ferromagnetic phase is caused by the variation of exchange integralbetween the Mn ions during the expansion. And the double exchange machanism leads to theoverlapping of the majority3d bands.In chapter3, the electronic structure and magnetic properties of CrO2films supported on TiO2(001)surface are studied via DFT calculation, in order to make clear the role the size effect and the epitaxialstrain play. The film’s thickness changes from one to six atomic slices. Some new phenomena can befound in these films, such as the insulator property in the1-3layer films, the AFM surface in the3-layer and thicker films, and the rebuilding of the half-metallic property in the4-layer and thickerfilms. With the help of crystal field theory and Heisonberg model, the physics behind thesephenomena are revealed.In chapter4, the molecular dynamic method，as well as the reactive forcefield used in oursimulation is discussed in detail. The function form, parameters fitting process, and the database usedin the forcefield are shown. Then we investigate the process when H2incident on clean Pd surface.The dynamic mechanism behind the phenomena found in the process, such as the nomonotonousvariation of the sticking coefficient with respect to the energy of the impinging molecule, the variation of the sticking coefficient with respect to the vibration quantum number, rotational quantum number,and surface temperature are revealed.Chapter5. Based on the molecular dynamics simulation and the reactive bond order forcefield, thesticking coefficient affected by the vacancy and step at the surface is investigated. We find that, bothof them lead to higher dissociative probability, while the dissociative mechanism in the low-energyregion is different. The vacancy will hinder the diffusion of H2molecules, while the step will trap themoleculars with bond counting mechanism.Chapter6is the summary of our dissertation. The latent works, which are worthy of furtherinvestigation are pointed out.