Growth behavior and interface of (In + Nb) co-doped rutile TiO₂ films prepared on m-plane sapphire substrates

(In + Nb) co-doped TiO₂ (TINO) films with a rutile structure have been prepared on m-plane sapphire substrates using a pulsed laser deposition method. The film growth mode and the atomic-scale microstructure of the TINO/sapphire heterostructure have been investigated by advanced electron microscopy techniques. The crystallographic orientation relationship of (001)[010]_rutile//(11¯00)[0001]_sapphire between the TINO films and the m-plane sapphire substrates has been determined. Across the TINO/sapphire interface, Ti(In,Nb)O₆−octahedra connect AlO₆−octahedra through either edge-sharing or corner-sharing. Misfit dislocations appear at the TINO/sapphire interface and contribute to epitaxial strain relaxation in the heterosystem. Additionally, two types of twins, (011)[100] and (031)[100], form within the films. Cation segregation occurs at the twin boundary and the TINO grain boundary. The findings here may provide a better understanding of the growth behaviors of the (In + Nb) co-doped rutile TiO₂ films prepared on other types of substrates.