Growth of high-quality ruthenium films on sapphire

We have developed and optimized a method to grow ruthenium films of unprecedented quality. Our three-step process is reminiscent of solid-phase epitaxy. First, c-cut sapphire substrates are terminated at their Al-rich √31 × √31R ± 9° reconstruction by in situ annealing. Second, 3D structured epitaxial Ru films are deposited at low temperatures by laser evaporation of Ru rods. Third, the films, thus, obtained are epitaxially transformed by high-temperature annealing. X-ray diffraction studies reveal good crystallinity of the obtained 15–60 nm-thick films: peak widths of the rocking curve are one order of magnitude smaller than those of the best published films. Scanning transmission electron microscopy and electron energy loss studies show that the interface between the sapphire substrates and the flat Ru films is atomically sharp with very limited intermixing. These results demonstrate the usefulness of postanneal processes for producing high-quality epitaxial films of elemental metals on insulating substrates.