First-principles study of CO and OH adsorption on in-doped ZnO surfaces

Abstract

We present a first-principles computational study of CO and OH adsorption on non-polar ZnO (1010) surfaces doped with indium. The calculations were performed using a model ZnO slab. The position of the In dopants was varied from deep bulk-like layers to the surface layers. It was established that the preferential location of the In atoms is at the surface by examining the dependence of the defect formation energy as well as the surface energy on In location. The adsorption sites on the surface of ZnO and the energy of adsorption of CO molecules and OH-species were determined in connection to In doping. It was found that OH has higher bonding energy to the surface than CO. The presence of In atoms at the surface of ZnO is favorable for CO adsorption, resulting in an elongation of the C-O bond and in charge transfer to the surface. The effect of CO and OH adsorption on the electronic and conduction properties of surfaces was assessed. We conclude that In-doped ZnO surfaces should present a higher electronic response upon adsorption of CO.

Effect of Zinc Oxide Modification by Indium Oxide on Microstructure, Adsorbed Surface Species, and Sensitivity to CO

“…Here we report on the experimental investigation of nanocrystalline In 2 O 3 -modified zinc oxide: materials microstructure, distribution of the additive, concentration of surface OH-species and chemisorbed oxygen, sensor response to CO and reactivity to the target gas in relation to the indium oxide amount in ZnO/In 2 O 3 . The sensitivity to CO correlated to the concentration of surface oxidizing species, OH-groups and to the reactivity of the surface to CO in presence of segregated In 2 O 3 species, in agreement with the theoretical results in Saniz et al (2018).…”

“…and/or lattice distortions upon incorporation of In(III) into ZnO, because of the difference of ionic radii of Zn(II) (0.60 Å) and In(III) (0.62 Å) in tetrahedral coordination (Shannon, 1976). This assumption is in line with the change of Zn-O bond length following the introduction of In, as shown by DFT (Saniz et al, 2018). Previously, the solubility of In in similarly prepared nanocrystalline ZnO(In) was estimated to be 1 at.% In Vorobyeva et al (2017).…”

“…Furthermore, the annealing temperature of 450 • C might be not enough for the elimination of amorphous phase and crystallization of ZnO(In) as a solid solution. Noteworthy, the preferred segregation of In atoms on a model ZnO surface, rather than incorporation into the bulk, was suggested by firstprinciples calculations (Saniz et al, 2018).…”

“…It was found that the adsorption of CO and OH-species would be enhanced in the presence of In atoms on the surface. Moreover, interatomic bond elongation and charge transfer from the adsorbed CO molecule to the In-doped surface was predicted, suggesting that the electronic state of Zno would have improved sensitivity to CO (Saniz et al, 2018). Here we report on the experimental investigation of nanocrystalline In 2 O 3 -modified zinc oxide: materials microstructure, distribution of the additive, concentration of surface OH-species and chemisorbed oxygen, sensor response to CO and reactivity to the target gas in relation to the indium oxide amount in ZnO/In 2 O 3 .…”

“…This work is focused on the effect of zinc oxide modification by indium oxide on sensitivity and surface reactivity to CO. Saniz et al (2018) reported on the DFT-modeling of impurity atoms formation in 4 wt.% In-doped Zno slabs, showing that the localization of In at the surface of zinc oxide is energetically favorable. It was found that the adsorption of CO and OH-species would be enhanced in the presence of In atoms on the surface.…”