Effect of Er doping on the In ₂ O ₃ (001) surface for H ₂ S, NO ₂ , and CO detection: a DFT study

The impact of Erbium (Er) doping on the gas sensing performance of the In₂O₃(001) surface toward H₂S, NO₂, and CO was rigorously investigated using density functional theory (DFT) calculations. Analysis based on adsorption energy, Bader charge transfer, and density of states (DOS) confirms that Er doping selectively enhances the surface reactivity toward NO₂. Key results demonstrate a marked improvement in NO₂ binding strength: the adsorption energy increases significantly from -0.37 eV on the pristine surface to -0.61 eV on the Er-doped surface. This stronger chemisorption is supported by enhanced electron withdrawal from the surface by NO₂, with the charge transfer increasing from -0.38 e (pristine) to -0.46 e (Er-doped). Furthermore, TDOS and PDOS analyses confirm the appearance of new, strong electronic states near the Fermi level only after NO₂ adsorption on the doped surface, indicating robust electron coupling. Conversely, Er doping weakens the interaction with the other test gases. For H₂S, the adsorption energy reduces from -0.53 eV to -0.42 eV, and charge transfer drops sharply from +0.40 e to +0.09 e. CO adsorption remains weak, with the energy decreasing slightly from -0.25 eV to -0.19 eV. These findings indicate that Er-doped In₂O₃(001) surfaces exhibit enhanced selectivity, making them highly promising candidates for selective NO₂ detection.