Metal-insulator transition on the V2O5(001) surface: Theory and experiment

Several vanadium oxides undergo a metal-to-insulator transition (MIT) in the bulk, e.g., V2O3 at ∝150 K, VO2 at 340 K, whereas V2O5 is a semiconductor. Experimental evidence for a thermally induced surface insulator-metal transition (MIT) at the V2O5(001) surface at 350-400 K is presented. This surface exposes vanadyl (V=O) double rows along the [010] direction. Using density functional theory (DFT) in combination with statistical thermodynamics, the facile reduction along the rows was predicted. The experimentally observed MIT transition expands preferentially in the direction of these rows. We then used the Monte Carlo method to simulate the reduced V2O5(001) surface at a given temperature and defect concentration. We typically find areas with a random distribution of isolated defects and others with up to 5 sites forming [010] oriented trenches. Using calculated band gaps for reduced V2O5 structures as obtained with DFT+U, we construct band gaps maps which agree with those derived from scanning tunneling spectroscopy data; only the areas with defective rows are metallic