1 Tuning the graphene work function by electric field effect
We report variation of the work function for single and bi-layer graphene devices measured by scanning Kelvin probe microscopy (SKPM). Using the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene. High conductivity1,2 and low optical absorption3,4 make graphene an attractive material for use as a flexible transparent conductive electrode5-8. This atomically thin carbon layer provides the additional benefit that its work function can be adjusted by the electric field effect (EFE). Since the band alignment of two different materials is determined by their respective work functions, control over the graphene work function is the key to reducing the contact barriers of graphene top electrode devices9, 10. Previous scanning probe based studies11-13 reveal that the work function of graphene is in a similar range to that of graphite, ~4.6 eV14, and depends sensitively on the number of layers15, 16. However, the active