▎ 摘　　要

The fabrication of atomically smooth metal films on oxide substrates is a considerable challenge because most deposition methods used on metals do not work properly on supporting oxides. Here we report an alternative procedure based on thermal laser epitaxy of materials. We present results for 15-nm-thick ruthenium films grown on c-plane sapphire and for graphene-coated ruthenium films. Helium diffraction was used as a sensitive probe of the surface crystallinity of the grown films, in addition to atomic force microscopy (AFM). Surface quality has been examined for samples prepared using different growth parameters. Our observation of high-helium reflectivity and narrow diffraction peaks from graphene demonstrates the presence of flat ruthenium film domains, with a very low density of defects over lateral scales of microns, which is consistent with the AFM results. The absolute helium reflectivity measured under optimal growth conditions is 5%. These results pave the way to fabricating ultrasmooth, transparent metallic films on top of sapphire by thermal laser epitaxy.