Self-Recovery of Carbonate-Contaminated Strontium Titanate (100) Vicinal Surfaces Imaged by Tip-Enhanced Raman Spectroscopy

Strontium titanate (SrTiO₃) as a model perovskite has significant applications in catalysis, carbon capture, and advanced electronics. On SrO-terminated (100) surfaces, carbon dioxide (CO₂) is a common chemisorption, altering the electronic and chemical properties. This study employed tip-enhanced Raman spectroscopy (TERS) and density functional theory (DFT) simulations to explore this CO₂ chemisorption. The (100) surface of SrTiO₃ exhibits two distinct terminations, SrO and TiO₂ with nominally almost the same heights (0.2 nm). Height scans of hydrothermally treated (100) SrTiO₃, show values closer to 0.3 and 0.1 nm, where we attribute the difference in height to the selective adsorption of ambient CO₂ on one of the terminations. The TERS analysis shows the presence of a 1071 cm⁻¹ Raman peak (characteristic of carbonate vibration), localized exclusively at the SrO terrace, confirming that CO₂ preferentially adsorbs onto SrO. Both experimental and DFT results indicate that this CO₂ monolayer alters the binding energy between the SrO and TiO₂ terminations. This leads to spontaneous yet slow delamination of SrO and the emergence of SrCO₃ nanograins on a purely TiO₂-terminated crystal surface. The interpretation is in quantitative agreement with respective volumes of layers and grains throughout the process.