Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates

The effect of point defects and interactions with thesubstrateare shown by density functional theory calculations to be of significantimportance for the structure and functional properties of hexagonalboron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG)and Ni(111) substrates. The structure, surface chemistry, and electronicproperties are calculated for h-BN systems with selected intrinsic,oxygen, and carbon defects and with graphene hybrid structures. Theelectronic structure of a pristine monolayer of h-BN is dependenton the type of substrate, as h-BN is decoupled electronically fromthe HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111)substrate, metallic-like behavior is predicted. These different film/substratesystems therefore show different reactivities and defect chemistries.The formation energies for substitutional defects are significantlylower than for intrinsic defects regardless of the substrate, andvacancies formed during film deposition are expected to be filledby either ambient oxygen or carbon from impurities. Significantlylower formation energies for intrinsic and oxygen and carbon substitutionaldefects were predicted for h-BN on Ni(111). In-plane h-BCN hybridstructures were predicted to be terminated by N-C bonding.Substitutional carbon on the boron site imposes n-type semiconductivityin h-BN, and the n-type character increases significantly for h-BNon HOPG. The h-BN film surface becomes electronically decoupled fromthe substrate when exceeding monolayer thickness, showing that thesurface electronic properties and point defect chemistry for multilayerh-BN films should be comparable to those of a freestanding h-BN layer.