Tip induced doping effects in local tunnel spectra of graphene

TL;DR

This study investigates how an STM tip can locally dope single-layer graphene, affecting its tunneling spectra, with the doping tunable via a back-gate, revealing charge inhomogeneity and doping-dependent spectral features.

Contribution

It demonstrates tip-induced doping effects in graphene's local spectra and explains the spectral features as arising from tip and bias voltage dependent doping.

Findings

Two minima in spectra shift oppositely with doping

One minimum varies with square root dependence, the other linearly

Spatial charge inhomogeneity affects local spectra

Abstract

We report on tip induced doping in local tunnel spectra of single layer graphene (SLG) with tunable back-gate using room temperature scanning tunneling microscopy and spectroscopy (STM/S). The SLG samples, prepared on silicon dioxide surface by exfoliation method and verified by Raman spectra, show atomically resolved honeycomb lattice. Local tunnel spectra show two minima with a clear evolution in the position of both with doping by the back gate. A similar variation in spectra is also observed spatially due to charge inhomogeneity. With doping the two minima move in opposite directions with one showing nearly a square root dependence and the other a linear dependence on gate voltage. We explain these features as arising from the STM tip induced and bias voltage dependent doping in SLG.