Hydration and reduction of molecular beam epitaxy grown vo _x/α-fe ₂o ₃(0001): ambient pressure study

Supported vanadium oxides processed under ambient environments have been studied by using X-ray standing wave (XSW) analysis of X-ray fluorescence spectroscopy and X-ray photoelectron spectroscopy (XPS). For the VO _x/α-Fe ₂O ₃(0001) system, hydration and hydrogen annealing have been carried out under ambient pressure. Vanadium in the hydrated oxide phase occupies two high-symmetry surface adsorption sites with distinct adsorption heights, which resembles the adsorption geometry of fully oxidized vanadium. Reduction by the hydrogen annealing enhanced the V overlayer ordering by relocating a portion of the disordered V to highsymmetry sites. The V atoms located closer to the substrate oxygen layer in the hydrated phase moved toward the substrate after hydrogen reduction, while the V in the higher adsorption site stayed at the same height. The different responses of two adsorption sites to the reduction process are discussed and related to activities of the two sites