  The inability to grow large well ordered graphene with a specific number of
layers on SiC(0001) is well known. The growth involves several competing
processes (Si desorption, carbon diffusion, island nucleation etc.), and
because of the high temperatures, it has not been possible to identify the
growth mechanism. Using Scanning tunneling microscopy and an initially vicinal
6H-SiC(0001) sample, we determine the sequence of microscopic processes that
result in the formation of bilayer graphene. Adjacent steps retract with
different speeds and the carbon released produces characteristic "fingers" when
a step of higher speed catches up with a slower moving step. These processes
are based on different rates of Si desorption from steps and can be avoided if
faster heating rates are used. We also show that faster rates lead to single
layer graphene films extending over many microns.

Materials Science