Metal-graphene-metal sandwich contacts for enhanced interface bonding and work function control.

Only a small fraction of all available metals has been used as electrode materials for carbon-based devices due to metal-graphene interface debonding problems. We report an enhancement of the bonding energy of weakly interacting metals by using a metal-graphene-metal sandwich geometry, without sacrificing the intrinsic π-electron dispersions of graphene that is usually undermined by strong metal-graphene interface hybridization. This sandwich structure further makes it possible to effectively tune the doping of graphene with an appropriate selection of metals. Density functional theory calculations reveal that the strengthening of the interface interaction is ascribed to an enhancement of interface dipole-dipole interactions. Raman scattering studies of metal-graphene-copper sandwiches are used to validate the theoretically predicted tuning of graphene doping through sandwich structures.

Reducing extrinsic performance-limiting factors in graphene grown by chemical vapor deposition.

Field-effect transistors fabricated on graphene grown by chemical vapor deposition (CVD) often exhibit large hysteresis accompanied by low mobility, high positive backgate voltage corresponding to the minimum conductivity point (V(min)), and high intrinsic carrier concentration (n(0)). In this report, we show that the mobility reported to date for CVD graphene devices on SiO(2) is limited by trapped water between the graphene and SiO(2) substrate, impurities introduced during the transfer process and adsorbates acquired from the ambient. We systematically study the origin of the scattering impurities and report on a process which achieves the highest mobility (µ) reported to date on large-area devices for CVD graphene on SiO(2): maximum mobility (µ(max)) of 7800 cm(2)/(V·s) measured at room temperature and 12,700 cm(2)/(V·s) at 77 K. These mobility values are close to those reported for exfoliated graphene on SiO(2) and can be obtained through the careful control of device fabrication steps including minimizing resist residue and non-aqueous transfer combined with annealing. It is also observed that CVD graphene is prone to adsorption of atmospheric species, and annealing at elevated temperature in vacuum helps remove these species.