Graphene is a single atomic layer of sp2-bonded C atoms densely packed into a two-dimensional
honeycomb crystal lattice. A method of forming structurally perfect and defect-free
graphene films comprising individual mono crystalline domains with in-plane lateral dimensions of up to 200 μm or more is presented. This is accomplished by controlling the temperature-dependent
solubility of interstitial C of a
transition metal substrate having a suitable
surface structure. At elevated temperatures, C is incorporated into the bulk at higher concentrations. As the substrate is cooled, a lowering of the interstitial C
solubility drives a significant amount of C atoms to the surface where
graphene islands nucleate and gradually increase in size with continued cooling. Ru(0001) is selected as a
model system and
electron microscopy is used to observe
graphene growth during cooling from elevated temperatures. With controlled cooling, large arrays of macroscopic single-crystalline graphene domains covering the entire
transition metal surface are produced. As the graphene domains coalesce to a complete layer, a second graphene layer is formed, etc. By controlling the interstitial C concentration and the
cooling rate, graphene
layers with thickness up to 10 atomic
layers or more are formed in a controlled, layer-by-layer fashion.