Orbital orientation mapping of V2O5 thin films

We report the effects of growth methods on the orbital orientation in vanadium pentoxide (V2O5) thin films, an important factor to consider when selecting growth techniques for highly selective catalysts and devices. Thermal evaporation and sol-gel methods were used to synthesize the V2O5 films. The surface morphology, roughness, and orientation of the films were characterized by atomic force microscopy and x-ray diffraction. Surface electronic properties and oxidation states were assessed by x-ray photoemission spectroscopy. Polarized x-ray absorption spectroscopy demonstrated that the thermally evaporated film [which was in the (001) orientation] exhibited greater anisotropy than the (100) oriented sol-gel film. The observed increase in anisotropy agrees well with computational findings which revealed that more vanadyl bonds are present at the surface of the thermally evaporated film than at the surface of the sol-gel film. The same computational study also found that the orientation of these bonds is more parallel to the film surface in the thermally evaporated film than in the sol-gel film. The data suggest that the method of growth may be used as a controlled variable to select key film characteristics for potential applications.