Band gap modulation of SrTiO3 upon CO2 adsorption

Abstract

Herein, CO₂ chemisorption on SrTiO₃(001) surfaces is studied using ab initio calculations to establish new chemical sensing mechanisms. It was found that CO₂ adsorption opens the band gap of the material. However, the mechanisms are different: the CO₂ adsorption on the TiO₂-terminated surface neutralizes the surface states at the valence band (VB) maximum, whereas for the SrO-terminated surface it suppresses the conduction band (CB) minimum. For the TiO₂-terminated surface, the effect is explained by the passivation of dangling bonds, whereas for the SrO-terminated surface, the suppression is caused by surface relaxation. Modulation of the VB states implies a more direct change in charge distribution, and thus, the induced change in the band gap is more prominent at the TiO₂ termination. Further, it has been shown that both CO₂ adsorption energy and surface band gap are strongly dependent on CO₂ coverage, suggesting that the observed effect can be utilized in sensing applications for a wide range of CO₂ concentrations.