A DFT study of (WO3)3 nanoclusters adsorption on defective MgO ultrathin films on Ag(001)

Abstract

The structures and electronic properties of (WO₃)₃ nanoclusters adsorption on defective MgO ultrathin films on Ag(001) have been investigated by means of density functional theory (DFT) calculations including dispersion interactions. Our results show that, after deposition, the oxygen vacancy on the defective MgO/Ag(001) films is healed by one terminal oxygen atom of the (WO₃)₃ clusters through forming four O–Mg bonds. The conformation of the (WO₃)₃ nanoclusters is distorted slightly and the W₃O₃ cyclic conformation of adsorbed (WO₃)₃ nanoclusters is still maintained. The defective MgO/Ag(001) 2D films lead to enhancement of the adsorption energy between the (WO₃)₃ clusters and the substrates, compared to that on defect-free MgO/Ag(001) 2D films and a defective MgO(001) surface. It is interesting that obvious charge transfer (2.74e) occurs from the defective MgO/Ag(001) films to the 5d empty state of the (WO₃)₃ clusters, which mainly originated from spontaneous electron tunneling through the thin MgO dielectric barrier, and less from the surface defective state as the consequence of the formation of O–Mg adsorption dative bonds at the interface. In addition, compared with (WO₃)₃ nanoclusters in the gas phase, on the defect-free MgO/Ag(001) 2D films and the defective MgO(001) surface, different scanning tunneling microscopy images and vibrational spectra for depositing (WO₃)₃ nanoclusters are observed, which could help in the identification of (WO₃)₃ nanocluster adsorption on the defective MgO/Ag(001) ultrathin films in future experiments. As a consequence, our results reveal that (WO₃)₃ nanoclusters adsorption on defective MgO/Ag(001) ultrathin films provide a new avenue to tune and modify the charge state and chemical reactivity of tungsten oxide nanoclusters.