  Optical reflection microscopy is one of the main imaging tools to visualize
graphene microstructures. Here is reported a novel method that employs
refractive index optimization in an optical reflection microscope, which
greatly improves the visibility of graphene flakes. To this end, an immersion
liquid with a refractive index that is close to that of the glass support is
used in-between the microscope lens and the support improving the contrast and
resolution of the sample image. Results show that the contrast of single and
few layer graphene crystals and structures can be enhanced by a factor of 4
compared to values commonly achieved with transparent substrates using optical
reflection microscopy lacking refractive index optimization.
