Two-dimensional phases of silicon on silicon carbide

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Wu, Hsin-Ju
First, Phillip N.
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2D materials have been widely studied since single layer graphene, a 2D atomic honeycomb structure with unusual electronic properties, was obtained. Graphene grown on SiC by thermal decomposition is of interest because of its potential for fine control of the epitaxial growth directly on a crystalline semiconductor substrate. Control of this growth has been obtained by introducing Si vapor into the growth environment. Other work has shown that this approach is valuable for the production of unique nanostructures of graphene; in this work, we explore the possibility to grow 2D thin films of silicon on the SiC substrate. An understanding of growth dynamics and surface phases is of interest for the creation of electronic-grade graphene on SiC, but there is also the potential for electronically useful 2D phases of silicon. For instance, the Si 2D honeycomb structure, silicene, is considered a potential next-generation material for electronic devices. In this thesis, we describe experiments undertaken in order to understand growth dynamics and Si surface phases in the pre-graphene regime of quasi-equilibrium growth, determined by the temperature and Si vapor pressure. A novel LEED pattern (√43 x √43 R7.6 degree) for a complex 2D Si structure is found on both the Si-terminated and C-terminated faces of SiC. The hexagonal structure and epitaxial matching constraints are consistent with silicene, but ultimately we show that a different structure is a more likely explanation. Based on experimental data and established structures from other research groups, a model for the newly-discovered phase of Si on SiC(0001) is proposed. By comparing growth conditions and other experimental data collected, we conclude that the structure contains three tetramers similar to the Si-rich 3 x 3 structure and three bridge-atom formations, reducing the number of dangling bonds to just three per unit cell. Empirical methods underlying the development of this model are discussed. Similar approaches are potentially of use for other 2D phases of Si on SiC.
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