Structural and electronic properties of few-layer graphenes from frist-principles

Using first-principles calculation method, it is found that the calculated layer spacing for the two-layer AB stacked FLG is only 2.725{\AA}, which is substantially reduced from the calculated value of 3.257{\AA} for bulk graphite. The average interlayer spacing for 2-, 3-, 4-, 5-, 6-, 7- and 8-layer FLG's are found to oscillate and approach that of the bulk graphite. The two-layer AA stacked FLG is found to remain metallic for the external electric potential up to 4.5Volts considered in this study. In contrast, the two-layer AB stacked FLG is found to exhibit a semi-metal-semiconductor transition under an external electric potential qualitatively in agreement with previous theoretical studies. However, the energy gap is not limited at 0.3eV as obtained in previous first-principles calculation due to the substantially reduced interlayer spacing. The threshold of the semi-metal-semiconductor transition is 0.04 Volts. The external electric potential also induced energy gaps in 3- and 4-layer AB stacked FLG's. However, in these two thicker FLG's, the induced energy gaps are small within 0.1eV. Based on this study, only the two-layer FLG is useful as a nanoscale electronic switch.