Influence of Substrate Orientation on the Growth of Graphene on Cu Single Crystals

A systematic study of graphene growth on on-axis Cu(100) and Cu(111) single crystals oriented within 0.1$^{\circ}$ from the surface normal and a vicinal Cu(111) crystal oriented 5$^{\circ}$ off-axis has been performed. Initial attempts to grow graphene by heating each crystal to 900 $^{\circ}$C in UHV, followed by backfilling the chamber with C$_{2}$H$_{4}$ at pressures up to 5 x 10$^{-3}$ Torr did not result in graphene formation on either the on-axis Cu(100) or on-axis Cu(111) surfaces. For the vicinal Cu(111) surface, epitaxial graphene was formed under the same growth conditions. By backfilling the chamber with C$_{2}$H$_{4}$ before heating to the growth temperature, epitaxial graphene was formed on both the on-axis Cu(100) and off-axis Cu(111) surfaces, but not the on-axis Cu(111) surface. By using an argon overpressure, epitaxial overlayers could be achieved on all three Cu substrates. These results indicate that the most catalytically active sites for the dissociation of ethylene are the step edges, followed by the Cu(100) terraces sites and the Cu(111) terrace sites. The need for an argon overpressure to form graphene the on-axis Cu(111) surface indicates that the Cu sublimation rate is higher than the graphene growth rate for this surface.