Abstract: Periodic density functional theory calculations using pseudopotential plane-waves were performed systematically to investigate the surface relaxation of different Al₂O₃ surfaces including α-Al₂O₃ (0001) and γ-Al₂O₃ (110), (110C), and (110D) surfaces, as well as the adsorption of CO molecules on these surfaces. Our calculated results indicate that the CO molecules tend to adsorb perpendicularly on the Al atoms at the surface through carbon atoms and interactions were observed between the CO 5σ state and the substrate. After adsorption, some electrons transferred from the CO molecules to the surface and accordingly the surface work functions of the different Al₂O₃ surfaces decreased. The adsorption results in small perturbations of the C ― O bond length and the corresponding C ― O stretching frequency was blue-shifted in all the adsorption structures. By examining the results of the CO adsorption on the different surfaces, it is clear that CO can be used as an effective probe molecule to distinguish the active adsorption sites on the different Al₂O₃ surfaces.

Key words: Al₂O₃ surface, CO molecule, Adsorption, Electronic structure