The large roughness of the UHV-annealed samples suggests that the surface is far from equilibrium
such that a transformation to a smooth morphology cannot be achieved under these conditions.
The key factor in achieving an improved growth is the significantly higher annealing temperature of 1
650◦C that is attainable for graphene formation under argon at a pressure of 900 mbar as compared with 1,280◦C in UHV