First-principles Study Of Modulating Band Gap Of H-BN Sheet

The studies of low-dimensional nanomaterials open a new way for the problems ofenergy and environmental pollution. As a green renewable energy, solar energy hasreceived great attention. The dreamful dramatics is that a miraculous stuff asphotocatalysts is capable of split water into H2and O2with sunlight. However, theabsorption of the solar spectrum is only4%due to the large band gap of thephotocatalysts. Like graphene, BN is layered hexagonal-honeycomb structure with a wideband gap of4.5eV. In this thesis, we try to manipulate the band gap of layered BN filmthrough electric field and strain. Our results include:1. We demonstrate the possibility of modulating the band gap of bilayer BN sheet inthe entire visible light energy window. Our density functional calculations show that theband gap can be tuned in a broad range, from0.3eV to4.5eV, by applying electric fieldfrom-0.015au to0.015au. More interestingly, we found that the photo-excited electronsand holes are well separated in the BN bilayer, which can thus be a promisingphotocatalyst for water splitting. We further revealed that the bad gap reduction can betriggered by the inherent electric field on metal surfaces when they are used to support theBN bilayer.2. In gernal, the strain is always induced due to the lattice mismatch when the BNgrown on supported materials. We systematic study the strain effect on the band structureof layered BN films. We found that the band gap of BN films is linear reduced with thetensile strain, independent on the stacking configuration and the number layer of layeredBN film. Our results indicate that the band structure of BN film is determined byinteraction of B-N in inter-layer of a single BN layer and the interaction of intra-layer ofBN sheet can be neglected.