Observation of nano-ripple structure of an epitaxial graphene surface in a water environment

Abstract We studied the surface morphology of epitaxial graphene on a SiC substrate in a water environment using atomic force microscopy in the tapping mode. Nano-ripple structures were observed in both the monolayer and bilayer graphene regions. The period of the nanoripple structure was ∼5 nm. The average height of the structures was 41 and 17 pm for the monolayer and bilayer graphene, respectively. The direction of the structures corresponded to the [11 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> 0] direction of the SiC crystal. The estimated area surface ratios were 1.0156 and 1.0063 for monolayer and bilayer graphene, respectively. One possible origin of the nanoripple structure is the relaxation of the compressive stresses caused by high-temperature annealing.