Graphene-induced Ge (001) surface faceting

Faceted Ge surfaces result from the growth of a graphene overlayer on Ge (001) by chemical vapor deposition. The surface exhibits four-fold symmetry after faceting, with the surface normal of the facets tilted towards 11001 from the average surface normal. X-ray reflectivity measurements allow the facet angles, directions, and symmetry to be measured precisely as a function of deposition conditions. Graphene grown from a CH4 precursor in a H-2/Ar carrier atmosphere at temperatures from 870 to 920 degrees C yields facets on the Ge surface with an average facet angle of 7.70 degrees +/- 0.07. Additionally, a distribution of facet angles is observed with an angular spread of approximately +/-1 degrees. The facet pattern has four-fold symmetry over a large area with no indication of the formation of competing facets from reflectivity measurements. The facet angle tends toward the {107} facet of Ge with slight variation as a function of temperature indicating that the facet angles are dominated by surface energetics. The slight dependence on temperature is accompanied by a reconstruction of the surface into {001} facets under slow-cooling conditions, suggesting that the surface diffusion kinetics and temperature dependence have an important role in the formation of the faceted surface structure at lower temperatures. (C) 2016 Elsevier B.V. All rights reserved.