Optimizing surface treatment for Nb-doped SrTiO₃ substrates: effects on structural and chemical properties

The use of SrTiO₃ substrates with either TiO₂- or SrO-terminated surfaces is essential for growing high-quality epitaxial perovskite oxide thin films. Adding niobium to SrTiO₃ introduces novel functionalities and imparts alterations to the metallic and structural characteristics. This study thoroughly investigates the physical and chemical processes involved in the chemical etching and annealing processes. This is to achieve an atomically flat, single-terminated surface of (001)-oriented Nb-doped SrTiO₃ (Nb:STO) surfaces and to optimize their performance. Atomic force microscopy (AFM) identified the most optimal treatment regimen, pinpointing annealing at 950 °C for a duration of 6 h, coupled with a 90-s etching procedure, which achieves a well-defined step terrace structure of the substrate. Additionally, angle-resolved X-ray photoelectron spectroscopy (AR-XPS) has revealed pronounced shifts in the predominant chemical component within the near-surface region due to changes in thermal parameters, even under consistent temperatures and durations. Reflection high-energy electron diffraction (RHEED) further confirms the creation of a single-terminated surface with the specified annealing conditions. This research provides valuable insights into the surface treatment processes for Nb:STO substrates and their influence on substrates’ structural and chemical properties.