High contrast imaging and thickness determination of graphene with   in-column secondary electron microscopy
  We report a new method for quantitative estimation of graphene layer thicknesses using high contrast imaging of graphene films on insulating substrates with a scanning electron microscope. By detecting the attenuation of secondary electrons emitted from the substrate with an in-column low-energy electron detector, we have achieved very high thickness-dependent contrast that allows quantitative estimation of thickness up to several graphene layers. The nanometer scale spatial resolution of the electron micrographs also allows a simple structural characterization scheme for graphene, which has been applied to identify faults, wrinkles, voids, and patches of multilayer growth in large-area chemical vapor deposited graphene. We have discussed the factors, such as differential surface charging and electron beam induced current, that affect the contrast of graphene images in detail. 
Vidya Kochat, Atindra Nath Pal, Sneha E. S., Arjun B. S., Anshita   Gairola, S. A. Shivashankar, Srinivasan Raghavan and Ari...
cond-mat.mes-hall