title: Mechanism and energetics of O and O2 adsorption on polar and non-polar ZnO surfaces.
abstract: Polar surfaces of semiconducting metal oxides can exhibit structures and chemical reactivities that are distinct from their non-polar surfaces. Using first-principles calculations, we examine O adatom and O2 molecule adsorption on 8 different known ZnO reconstructions including Zn-terminated (Zn-ZnO) and O-terminated (O-ZnO) polar surfaces, and non-polar surfaces. We find that adsorption tendencies are largely governed by the thermodynamic environment, but exhibit variations due to the different surface chemistries of various reconstructions. The Zn-ZnO surface reconstructions which appear under O-rich and H-poor environments are found to be most amenable to O and O2 adsorption. We attribute this to the fact that on Zn-ZnO, the O-rich environments that promote O adsorption also simultaneously favor reconstructions that involve adsorbed O species. On these Zn-ZnO surfaces, O2 dissociatively adsorbs to form O adatoms. By contrast, on O-ZnO surfaces, the O-rich conditions required for O or O2 adsorption tend to promote reconstructions involving adsorbed H species, making further O species adsorption more difficult. These insights about O2 adsorption on ZnO surfaces suggest possible design rules to understand the adsorption properties of semiconductor polar surfaces.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Prashun
authors.initials: P
authors.lastname: Gorai
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Edmund G
authors.initials: EG
authors.lastname: Seebauer
authors.affiliation: Department of Mechanical Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Elif
authors.initials: E
authors.lastname: Ertekin