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.