Scanning tunneling microscopy of graphene on Ru(0001)

After prolonged annealing of a Ru(0001) sample in ultrahigh vacuum a superstructure with a periodicity of $\ensuremath{\sim}30\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ was observed by scanning tunneling microscopy (STM). Using x-ray photoelectron spectroscopy it was found that the surface is covered by graphitic carbon. Auger electron spectroscopy shows that between 1000 and $1400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ carbon segregates to the surface. STM images recorded after annealing to increasing temperatures display islands of the superstructure, until, after annealing to $T\ensuremath{\geqslant}1400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, it covers the entire surface. The morphology of the superstructure…