Epitaxial growth and surface characterization of TiO₂ anatase

Titanium dioxide TiO₂ is semi-metallic in nature and has several optical and photocatalytic applications. We study the step-by-step formation of anatase phase of TiO₂ grown on SrTiO₃ (001) using plasma-assisted molecular beam epitaxy (MBE) growth, and explore the effects of growth temperature, substrate choice and lattice mismatch on the growth pattern. Initially, the nucleation of 3D islands in the TiO₂ anatase phase is observed, identified by the appearance of transmission spots in the reflection high energy electron diffraction (RHEED) image. Previous studies suggested that these 3D structures may appear due to the migration and self-organization of Sr ions into the epitaxially strained TiO₂ layer. Upon further TiO₂ deposition, the RHEED pattern evolves into a series of streaks, signaling a smoother stepped surface, with a (4x1) surface reconstruction. Lastly, we study the electronic properties using low-temperature scanning tunneling microscopy/spectroscopy and ex-situ magnetization measurements. Our experiments shed light on the nanoscale structural and electronic information of the films, complementary to the electronic characterization by bulk probes.