  Non-destructive and rapid evaluation of graphene directly on the growth
substrate (Cu foils) by dark field (DF) optical microscopy is demonstrated.
Without any additional treatment, graphene on Cu foils with various coverages
can be quickly identified by DF imaging immediately after chemical vapor
deposition growth with contrast comparable to scanning electron microscopy. The
improved contrast of DF imaging compared to bright field optical imaging was
found to be due to Rayleigh scattering of light by the copper steps beneath
graphene. Indeed, graphene adlayers are readily distinguished, due to the
different height of copper steps beneath graphene regions of different
thickness.
