Density functional theory study of the OH, Cl and H2O coadsorption on the step-defect Al2O3 film surface

Abstract

Density functional theory has been performed on the step-defect Al2O3 film surfaces with the OH, Cl and H2O molecules coadsorption. Three kinds of step-defect (Al, O2, Al3) surfaces are optimized and the adsorption energy, the binding energies of film and adsorbates are calculated. The energy properties are similar in H2O or Cl coadsorption configurations, but have obvious differences for the OH group coadsorption configuration due to large numbers of adsorbate species and numbers. After structural relaxation, most of the step-defect surfaces could be easily hydroxylated. The Al3 step-defect surfaces are easier to be corroded by H2O and coadsorption molecules due to lots of unsaturated dangling bonds, some H2O molecules are located into the step-defect, surface Al atoms collapse inside the steps and several inner O atoms move outside the film. When the Cl exists in the aqueous solution, it would restrict H2O molecules from dissociating into OH groups. Moreover, the dissociation and recombination of H2O molecules could be promoted by OH groups.