Substrate-controlled allotropic phases and growth orientation of TiO₂ epitaxial thin films

TiO₂ thin films were grown by pulsed laser deposition on a wide variety of oxide single-crystal substrates and characterized in detail by four-circle X-ray diffraction. Films grown at 873 K on (100)-oriented SrTiO₃ and LaAlO₃ were (001)-oriented anatase, while on (100) MgO they were (100)-oriented. On (110) SrTiO₃ and MgO, (102) anatase was observed. On M-plane and R-plane sapphire, (001)- and (101)-oriented rutile films were obtained, respectively. On C-plane sapphire, the coexistence of (001) anatase, (112) anatase and (100) rutile was found; increasing the deposition temperature tended to increase the rutile proportion. Similarly, films grown at 973 K on (100) and (110) MgO showed the emergence, besides anatase, of (110) rutile. All these films were epitaxically grown, as shown by φ scans and/or pole figures, and the various observed orientations were explained on the basis of misfit considerations and interface arrangement.