Controlling Surface Potential of Graphene Using dc Electric Field

In this work, we study surface potential of graphite deposited on SiO 2 /Si substrate using Kelvin Probe Force Microscopy (KPFM) and Electric Force Microscopy (EFM). The amplitude modulated KPFM (AM-KPFM) shows that the graphene layer work function is 4.69±0.02 eV, whereas frequency modulated KPFM (FM-KPFM) revealed 4.50±0.02 eV. The work function indifference of 0.19±0.02 eV was attributed to the superior resolution of FM-KPFM and higher detection sensitivity of AM-KPFM. Subsequent EFM mapping suggests that the phase monotonically increases with increasing applied dc bias voltage in the range from -5 V to 5 V. This phase shift is ascribed to the induced charge polarization at tip-graphene surface due to interatomic interactions induced by dc field effects.