  Confocal laser scanning microscopy (CLSM) is a non-destructive,
highly-efficient optical characterization method for large-area analysis of
graphene on different substrates, which can be applied in ambient air, does not
require additional sample preparation, and is insusceptible to surface charging
and surface contamination. CLSM leverages optical properties of graphene and
provides greatly enhanced optical contrast and mapping of thickness down to a
single layer. We demonstrate the effectiveness of CLSM by measuring
mechanically exfoliated and chemical vapor deposition graphene on Si/SiO2, and
epitaxial graphene on SiC. In the case of graphene on Si/SiO2, both CLSM
intensity and height mapping is powerful for analysis of 1-5 layers of
graphene. For epitaxial graphene on SiC substrates, the CLSM intensity allows
us to distinguish features such as dense, parallel 150 nm wide ribbons of
graphene (associated with the early stages of the growth process) and large
regions covered by the interfacial layer and 1-3 layers of graphene. In both
cases, CLSM data shows excellent correlation with conventional optical
microscopy, atomic force microscopy, Kelvin probe force microscopy, conductive
atomic force microscopy, scanning electron microscopy and Raman mapping, with a
greatly reduced acquisition time. We demonstrate that CLSM is an indispensable
tool for rapid analysis of mass-produced graphene and is equally relevant to
other 2D materials.
