| Summary: | 碩士 === 臺灣大學 === 材料科學與工程學研究所 === 98 === In this research, the band profiles of graphene and graphene related materials (graphane and graphene oxide) have been investigated. Graphene, constructed by a single layer of graphite, has been developed in recent years. This two-dimension material is promising in photovoltaic heterojuction since its good conducting properties. Due to the reversible hydrogenation and oxidation process, the interface of graphene, graphene oxide and graphane is a key factor to investigate heterojunctions. We use first principle calculations to evaluate the band alignment properties of interfaces, such interfaces as semi-infinite contact, layer-layer contact and quantum dot of graphene. The charge transfer between two sides of heterostructures is also discussed. In some conditions, the spatial confinement in graphene quantum dot results in optical excitations inside the dot.
We also investigate the optical transitions of silicon-germanium core-shell nanowires. With different core diameter and shell thickness, we illustrate the variation of fundamental band gap energy and the direct-indirect transition on band structure calculation. Through the parallel-polarization absorption spectrum, we found that the core property plays an important role on the optical transition. A method called the band-resolved absorption density analysis technique is developed to investigate the mechanism of the optical transition processes.
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