Strontium titanate (100) surfaces monitoring by high temperature in situ ellipsometry

SrTiO3 surface contamination evidenced by in situ ellipsometry monitoring. Temperature dependence of overlayer thickness d of HF-treated SrTiO3 substrate: (1) The sample was heated up (full circles) then (2) cooled down (empty square). (3) The sample was out from the chamber on air for several weeks. (4) Heating up process was repeated. Irreversible behavior during heating up and cooling down indicate the desorption process leaving clean surface with only sub-nanometric roughness. Inset is AFM topographic images of atomic steps (500 nm × 500 nm) of as HF-treated substrate, with the 1 nm height scale. This demonstrates the necessity of in situ sensitive monitoring of the surface before thin film growth and surface analysis in particularly for low temperature deposition process.