Exploring the physical and chemical properties on the novel 2D structures in electronic and atomic details

by Shih-Yu Wu

Institution: NSYSU
Department: Physics
Degree: PhD
Year: 2015
Keywords: GaN; 2D structure; Indium; Quantized unoccupied states; Graphene; Scanning tunneling microscopy; H2O
Record ID: 1388024
Full text PDF: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0302115-170630


The progress of the surface science is driven by the new tools and also the novel condense materials. The aim of this thesis relative to both of them especially in atomic details. For the first part of the thesis, STM/STS was used to probed the quantized unoccupied states above the vacuum level. By using the Bohr-Sommerfeld quantization, the quantized unoccupied Ï states in epitaxial graphene layers were quantitatively identified. These quantized unoccupied states are strongly layer dependent and can be used to identify the absolute number of graphene layers with sub-nanometered resolution. Second part of the thesis is the study of novel 2D structure: â7Ãâ3 In on Si(111)-α-â3-Au. α-â3-Au overlayer on Si(111) is one of the famous two-dimensional electron gas system. Here, an ordered In surface structure with 0.8 ML In coverage was found to be stable on Si(111)-α-â3-Au. Detailed atomic model of this In surface structure was studied by STM/STS, LEED and further comparing with that proposed by the density functional theory. The last work is the atomic structure of H2O molecules on cleaved GaN(1-100) surface. From the theoretical calculations, the H2O molecules was expected to dissociated spontaneously simply by the thermal energy on the non-polar GaN(1-100) surface. Here, the structure and the chemical information of H2O molecules on the cleaved GaN(1-100) surface is studied by STM/STS, LEED and time-dependent XPS. Detailed atomic model was built and compared with that from the calculations.