  The evolution in the surface morphology of epitaxial graphene films and
6H-SiC(0001) substrates is studied by electron channeling contrast imaging.
Whereas film thickness is determined by growth temperature only, increasing
growth times at constant temperature affect both internal stress and film
morphology. Annealing times in excess of 8-10 minutes lead to an increase in
the mean square roughness of SiC step edges to which graphene films are pinned,
resulting in compressively stressed films at room temperature. Shorter
annealing times produce minimal changes in the morphology of the terrace edges
and result in nearly stress-free films upon cooling to room temperature.
