Microstructure of heteroepitaxially grown RuO₂ thin films on MgO by pulsed-laser deposition

Conductive ruthenium oxide (RuO₂) thin films with a room-temperature resistivity of 35μΩcm and a residual resistivity ratio above 5 have been heteroepitaxially grown on MgO(100) substrates by pulsed-laser deposition. The heteroepitaxial growth of RuO₂ on MgO is confirmed by both the strong in-plane and the strong out-of-plane orientation of the film with respect to major axes of the substrate. The orientation relationship between the RuO₂ film and the MgO substrate, deduced from both X-ray and electron diffraction, is (110)_RuO2 ∥ (100)_MgO and [001]_RuO2 ∥ [011]_MgO) (and [|1|10]_RuO ∥ [0|1||1|]_MgO). High-resolution electron microscopy reveals that the epitaxial RuO₂ film contains two variants that are consistent with the X-ray diffraction measurement.