Band gap modulation of SrTiO₃ upon CO₂ adsorption

Abstract

CO 2 chemisorption on SrTiO 3 (001) surfaces is studied using ab initio calculations in order to establish new chemical sensing mechanisms. We find that CO 2 adsorption opens the material band gap, however, while the adsorption on the TiO 2 -terminated surface neutralizes surface states at the valence band (VB) maximum, CO 2 on the SrO-terminated surfaces suppresses the conduction band (CB) minimum. For the TiO 2 -terminated surface, the effect is explained by the passivation of dangling bonds, whereas for the SrO-terminated surface, the suppression is caused by the surface relaxation. Modulation of the VB states implies a more direct change in charge distribution, and thus the induced change in band gap is more prominent at the TiO 2 termination. Further, we show that both CO 2 adsorption energy and surface band gap are strongly dependent on CO 2 coverage, suggesting that the observed effect can be utilized for sensing application in a wide range of CO 2 concentrations.

Interaction of SrO-terminated SrTiO3 surface with oxygen, carbon dioxide, and water

“…Our calculations start with the interaction of the CO The formation of carbonate layer on SrTiO 3 surface was recently investigated with theoretical methods by Sopiha et al 25 In their study, they have shown that the carbonate layer significantly alters the electronic properties of the SrTiO 3 surface by increasing the surface band gap. The effect has been observed on both TiO 2 and SrO terminated surfaces.…”

“…Amongst those phases the most important are the formation of surface carbonates, surface hydroxides, and physisorption or chemisorption of water molecules. [25][26][27] A knowledge of the real surface composition of ABO 3 perovskite air electrodes for solid oxide devices is crucial for the understanding of the chemical activity on the electrode surface and for the further optimization of electrode performance. Theoretical studies on surface termination of perovskites have so far been limited to the chemical composition of the investigated materials.…”

Suppression of surfaces states at cubic perovskite (001) surfaces by CO2 adsorption

“…In order to avoid dipole-dipole interaction due to the cell periodicity, 58 CO2 chemisorption on both sides of the symmetrical slabs was modeled. This model was validated for SrTiO3(001) surfaces in our recent study 31 were computed as charge densities for the states within energy limits from the conduction band minima (CBM) or VBM levels of the slabs to those of the corresponding bulk compounds.…”

“…1a), in agreement with previous reports. 31,35, 64, 65 Although these energy gap reductions were observed for most investigated surfaces, the underlying mechanisms differ significantly among them. For the BO2-terminated ABO3(001), the effect is originated from the surface states emerging above the VBM of the bulk systems, as evident from the layer-resolved LDOS and projected surface state density shown in Fig.…”

“…[27][28][29] Despite this knowledge, the exact mechanism on how the adsorption affects the surface conductivity has long remained uncertain. Recently, it has been demonstrated that molecular chemisorption on K1-yNayTa1-xNbxO3(001) 29,30 and SrTiO3(001) 31 results in the suppression of surface states emergent at their clean (001) facets. Since the existence of surface states can increase the surface conductivity [32][33][34] and even contribute to the formation of 2dimensional electron gas (2DEG), 35 this suppression might be a long-missing link between the CO2 adsorption and conductivity change during the sensing.…”