DFT study of electronic properties of N-doped ZnO and ZnO/Cu(111) bilayer films

The electronic properties of N-doped ZnO/Cu(111) bilayer films have been studied by using the DFT+U method including dispersion contributions and compared to that of free-standing ZnO bilayer films. The substitution of a lattice O ion in free-standing ZnO bilayer by a N atom results in oxidation state of N of -2, while the oxidation state of N becomes -3 when it replaces a lattice O in a ZnO/Cu(111) bilayer film. The extra negative charge of N in N:ZnO/Cu(111) compared to freestanding N:ZnO is due to an electron transfer from the Cu support. The difference in oxidation state of the N dopant is demonstrated by the analysis of the Bader charge, of the magnetization, and of the density of states. The changes in electronic properties of the doped ZnO films were evaluated by adsorbing CO and H2 molecules. The results show that the adsorption energies are significantly enhanced in N-doped ZnO/Cu(111) compared to the unsupported N:ZnO bilayer counterpart. This reflects the effect of the ZnO/Cu(111) interface in improving adsorption and possibly catalytic properties and the role of the N-dopant in activating the oxide film.