Vacuum-annealed Cu contacts for graphene electronics

We present transfer length method measurements of the contact resistance between Cu and graphene, and a method to significantly reduce the contact resistance by vacuum annealing. Even in samples with heavily contaminated contacts, the contacts display very low contact resistance post annealing. Due to the common use of Cu, and its low chemical reactivity with graphene, thermal annealing will be important for future graphene devices requiring non-perturbing contacts with low contact resistance.