Synthesis and characterization of metallic RuO2 heteroepitaxy films on sapphire substrates

In order to investigate the dependence of the physical properties of RuO2 films on the deposition temperature and the crystal orientation, we grew heteroepitaxy RuO2 films on sapphire substrates by using RF sputtering. As the deposition temperature was increased from 300 ?C to 650 ?C, the (100) RuO2 films on the C-plane showed an increase in the surface roughness, but decreases in the resistivity and the lattice constant. As the temperature was increased above 700 ?C, the physical properties of the RuO2 film became worse. In contrast, the (101) RuO2 film was grown on the A-plane and the R-plane, and the (001) RuO2 film was grown on the M-plane. The surface roughness of the RuO2 film was minimum on the R-plane and maximum on the M-plane, while the resistivity of the RuO2 film was minimum on the R-plane and maximum on the C-plane. Although the crystallinity of the RuO2 film along the out-of-plane direction was the best on the C-plane, the resistivity was relatively large on the C-plane because of the grain-boundary scattering caused by imperfections of the in-plane ordering.