First principles study of tunable band gap in bi layer Graphene (BLG)

Abstract

Graphene being two-dimensional crystalline form of carbon hold great promise for nanoscale electronics and photonics. Graphene's promise can't be realized unless a band gap is introduced. As with monolayer Graphene, bilayer Graphene also has a zero band gap and thus has attracted considerable attention for its study. The structure and electrical properties of bi layer Graphene (BLG) sheets adsorbed with metals are studied using first-principles calculations. There is a tunable band gap in BLG by applying a vertical electric field, but the operation of BLG requires two gates to create a band gap and tune channel's conductance individually. The band gap is generally proportional to the charge transfer density. Using first principle calculations, we propose an alternative scheme to open a band gap in ABC-stacked BLG via single-side adsorption. We find that the band gap of ABC-stacked BLG can even be opened if the bond symmetry is broken. A clear transmission gap which is comparable with the band gap is observed in simulated single-gated SnCl4-adsorbed ABC-stacked bilayer Graphene. The adsorption of BLG on SnCl4 is a weak physisorption, but a band gap can be opened. Calculations of electron density show a weak coupling between Graphene substrate and SnCl4 metal and a shift in the Fermi level is also observed. This fundamental study helps in BLG device study due to inevitable Graphene/metal contact which renders metal-adsorbed BLG a promising channel in single-gated devices.