Positioning of the Fermi level in graphene devices with asymmetric metal electrodes

To elucidate the effect of the work function on the position of the Dirac point, we fabricated graphene devices with asymmetric metal contacts. By measuring the peak position of the resistance for each pair of metal electrodes, we obtained the voltage of the Dirac point V_g^Dirac (V) from the gate response. We found that the position of V_g ^Dirac (V) in the hybrid devices was significantly influenced by the type of metal electrode. The measured shifts in V_g ^Dirac (V) were closely related to the modified work functions of the metal-graphene complexes. Within a certain bias range, the Fermi level of one of the contacts aligned with the electron band and that of the other contact aligned with the hole band.