What Triggers Epitaxial Growth of GaN on Graphene?

With the perspective of using two-dimensional materialsas growthsubstrates for semiconductors, we explore the nucleation of GaN nanostructureson graphene. Using plasma-assisted molecular beam epitaxy, we investigatewhat happens during the long incubation time which precedes the epitaxyof the first GaN islands. After 30 min of nitrogen plasma exposurewith no deposition, we find that graphene is modified, and we identifyC-N bonds. We measure and model the variation of the incubationtime with the growth parameters. These data support the idea thatgraphene must be modified before GaN nucleation becomes possible.We then test the adhesion at the interface between graphene and theGaN nanostructures. Our studies converge on the conclusion that GaNnanostructures nucleate on graphene from pyridinic N atoms incorporatedin the lattice, which are responsible for strong binding between thetwo materials. This work explores how a graphenemonolayer is modifiedbefore nucleation and growth of GaN nanowires by plasma-assisted molecularbeam epitaxy becomes possible on it. It is shown that the grapheneis damaged by the N plasma and that the N atoms become incorporatedinto pyridine sites before the first GaN bonds are formed. It is thoughtthat the pyridinic N atoms are the anchor points for this GaN epitaxyon graphene, which is not of the van der Waals type.