Origin of spatial charge inhomogeneity in graphene.

Abstract

In an ideal graphene sheet, charge carriers behave as two-dimensional Dirac fermions Topographic corrugations and charge puddles in graphene are two of the most significant types of disorder in this new material. Topographic corrugations 2-4 , for example, have been suggested as a cause for the suppression of anticipated antilocalization 5 . Electron and hole puddles 6 have similarly been blamed for obscuring universal conductivity in graphene 7 . These issues are part of a puzzle regarding the factors that limit graphene's mobility We explored the inhomogeneous graphene charge density by spatially mapping the Dirac point (that is, the charge neutral point in the density of states of undoped graphene). The graphene local density of states at the Dirac point shows a local minimum, which is reflected by a dip in the tunnelling spectra of graphene Charge puddles can also be probed by spatially mapping the tunnelling differential conductance, dI /dV , for a fixed sample-tip bias held slightly below V D . This technique reduces data acquisition time by an order of magnitude and is particularly suited for measuring large graphene areas containing multiple charge puddles. The basis for using this second technique to measure charge puddles is illustrated i