Ultrathin Ruthenium Films on Graphene Buffered SiO2 via Quasi Van der Waals Epitaxy

In this study, we demonstrate a quasi van der Waals epitaxy approach to prepare an epitaxial Ru ultrathin film on large-scale, single-crystalline, monolayer graphene. Physical and epitaxial properties of the bulk, near surface, and surface of ultrathin Ru films were comprehensively studied using various structural, morphological, compositional, and electrical characterization techniques. We confirm that Ru can epitaxially grow on single-crystalline, monolayer graphene using magnetron sputtering at an elevated temperature of 600 degrees C. The epitaxial Ru films with film thickness ranging from 94.2 nm down to 3.9 nm show the (0001) out-of-plane orientation. The epitaxial relationships between Ru and graphene are out-of-plane Ru(0001) || graphene(0001) and in-plane Ru[11 (2) over bar0] || graphene[11 (2) over bar0]. All the Ru films show smooth surfaces with a root-mean-square roughness of less than 0.8 nm and have a negligible oxide layer on the surface. The Ru films on graphene demonstrate significantly reduced electrical resistivity compared to their counterparts grown on bare SiO2, which show a polycrystalline nature. For 7.1 to 3.9 nm film thicknesses, the resistivity of Ru on graphene shows a 38 to 45% resistivity decrease from that of the Ru film on bare SiO2 without graphene. Our observations suggest the existence of the above classical van der Waals interaction between Ru and graphene. On the other hand, graphene is capable of effectively blocking the interdiffusion/interaction between Ru and SiO2 during a 1000 degrees C annealing process.