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Title: Nanomesh on SIC surface: Structure, reactions and template effects
Authors: CHEN SHI
Keywords: Silicon carbide, surface reconstruction, nanomesh, molecule template, intercalation, reaction
Issue Date: 28-Sep-2010
Citation: CHEN SHI (2010-09-28). Nanomesh on SIC surface: Structure, reactions and template effects. ScholarBank@NUS Repository.
Abstract: In this thesis, the nanomesh structure on the 6H-SiC(0001) surface, also known as the 6v3 × 6v3 R30º reconstruction, is experimentally studied. Several surface analytical methods including synchrotron based X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning tunneling microscopy (STM) and other complementary methods are used in this investigation. The XPS study reveals a variable elemental composition in this structure depending on the duration of annealing, suggesting that this structure is thermodynamically metastable. Substantial surface disorders at short and intermediate length scales are observed by STM, implying that the surface comprises of self-organized local structures instead of a global surface reconstruction. Due to the richness of carbon in the nanomesh structure, most studies focus on the carbon atoms. In this thesis, the silicon atoms in the nanomesh are studied by XAS method at the Si K-edge using both surface sensitive and bulk sensitive yields. Using the bulk sensitive yield, silicon vacancies are identified, revealing that the silicon desorption process not only happens at surface but also from the bulk beneath the surface. Using the surface sensitive yield, Si-Si bonds are observed, suggesting that the SiC nanomesh surface also contains silicon clusters. The existence of surface silicon is also supported by the oxidation of the SiC nanomesh at elevated temperature, in which surface silicon oxide formation is observed. The reaction of the SiC nanomesh is also observed even when it is covered by an epitaxial graphene (EG) overlayer. Both oxygen molecules and iron atoms are able to penetrate the topmost EG layer and react with the SiC nanomesh, giving rise to the formation of silicon dioxide and iron silicide at the interface, respectively. Intercalation at the EG/SiC nanomesh interface provides a possible route to modify the EG-substrate interface without external transfer of the EG film. Having a honeycomb-like corrugation in long range, the SiC nanomesh has a potential application as a nanotemplate. In this work, the template effect of this surface is probed by three organic molecules: fullerene, copper phthalocyanine (CuPc) and pentacene. Spherical fullerene molecules are not affected by the surface corrugations, packing closely together. CuPc molecules, on the other hand, are confined by the cells of the SiC nanomesh, forming single molecular arrays. Pentacene molecules are also confined by the cells, and form a quasi-amorphous layer due to random adsorption at three equivalent absorption sites. As no significant molecule-substrate interaction is present, the different behaviors of three molecules suggest that the geometry of molecules play an important role in the template effect of the SiC nanomesh.
Appears in Collections:Ph.D Theses (Open)

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