Epitaxial growth of bronze phase titanium dioxide by molecular beam epitaxy

Bronze phase titanium dioxide (TiO₂-B) has an ideal open structure for applications in high-rate lithium-ion batteries, but high quality and water-free TiO₂-B is difficult to synthesize since TiO₂-B is energetically less stable compared to other TiO₂ polymorphs. Using CaTi₅O₁₁ as a template layer can help stabilize TiO₂-B phase, but it is still challenging to avoid the formation of TiO₂ anatase (TiO₂-A) impurity phase. Here we show the synthesis of phase pure TiO₂-B films by in situ engineering of the surface quality of the buffer layer using molecular beam epitaxy (MBE). By applying surface sensitive in situ reflection high-energy electron diffraction (RHEED), the formation of the impurity TiO₂ anatase phase on the surface of CaTi₅O₁₁ buffer layer can be monitored and eliminated in real time, leaving a clean template surface for the growth of phase pure TiO₂-B films.