  There is a tunable band gap in ABC-stacked few-layer graphene (FLG) via
applying a vertical electric field, but the operation of FLG-based field effect
transistor (FET) requires two gates to create a band gap and tune channel's
conductance individually. Using first principle calculations, we propose an
alternative scheme to open a band gap in ABC-stacked FLG namely via single-side
adsorption. The band gap is generally proportional to the charge transfer
density. The capability to open a band gap of metal adsorption decreases in
this order: K/Al > Cu/Ag/Au > Pt. Moreover, we find that even the band gap of
ABA-stacked FLG can be opened if the bond symmetry is broken. Finally, a
single-gated FET based on Cu-adsorbed ABC-stacked trilayer graphene is
simulated. A clear transmission gap is observed, which is comparable with the
band gap. This renders metal-adsorbed FLG a promising channel in a single-gated
FET device.
