Scanning Tunneling Microscopy and Spectroscopy study of charge inhomogeneities in bilayer Graphene

Shyam K. Choudhary, Anjan K. Gupta

Published 2010-07-26Version 1

We report room temperature scanning tunneling microscopy and spectroscopy study of bilayer graphene prepared by mechanical exfoliation on SiO$_2$/Si surface and electrically contacted with gold pads using a mechanical mask. The bulk conductivity shows contribution from regions of varying electron density indicating significant charge inhomogeneity. Large scale topographic images show ripple like structures with a roughness of $\sim$1nm while the small scale atomic resolution images show graphite-like triangular lattice. Local dI/dV-V tunnel spectra have an asymmetric V-shape with the minima location showing significant spatial variation indicating inhomogeneity in electron density of order 10$^{11}$ cm-2. The minima in spectra at a fixed location also shifts linearly with the gate voltage with a slope consistent with the field induced carrier density.