▎ 摘　　要

The effects of graphene-electrode coupling pattern and chemical decoration of graphene on the electron transport properties of nanoscale graphene field effect transistors (FETs) are systematically investigated. Different from the viewpoint that molecules with thiol ending groups usually connect to Au electrodes through thiolate gold bonds in molecular devices, the calculated electron transport properties of nanoscale graphene FETs at thiol-gold coupling mode are observed to be well consistent with experimental results. At the thiolate-gold coupling mode nanoscale graphene FETs exhibit pronounced bipolar FET characteristics with on-off ratios up to 320 (n type) and 650 (p type), which are much higher than those of large area graphene FETs. We propose that different coupling patterns between molecules and electrodes are essential factors responsible for the discrepancy between theoretical calculations and experimental studies. Moreover, the performance of nanoscale graphene FETs is observed to be effectively modulated by chemical decoration of graphene. In particular, their on-off ratios can be significantly increased by spacing groups between ending groups and graphene cores. Side substituents of graphene can regulate the performance of these FETs according to their electron-withdrawing ability. Potential implications for the design of high-performance nanoscale graphene FETs can be obtained from these results.