Electronic Structure Engineering via On-Plane Chemical Functionalization: A Comparison Study on Two-Dimensional Polysilane and Graphane

Two-dimensional materials are important for electronics applications. A natural way of electronic structure engineering for two-dimensional systems is on-plane chemical functionalization. On the basis of density functional theory, we study the electronic structures of fluorine-substituted planar polysilane and graphane. We find that carbon and silicon present very different surface chemistries. The indirect energy gap of planar polysilane becomes direct upon fluorine decoration, and its gap width is mainly determined by fluorine coverage regardless of its distribution on the surface. However, the electronic structure of fluorine doped graphane is very sensitive to the doping configuration, due to the competition between antibonding states and nearly free electron (NFE) states. With specific fluorine distribution patterns, zero-dimensional and one-dimensional NFE states can be obtained. Our results demonstrate the advantages of two-dimensional silicon based materials compared with carbon based materials, in the viewpoint of practical electronic structure engineering by surface chemical functionalization.