Stoichiometry and disorder influence over electronic structure in nanostructured VOx films

摘要

We present and discuss the role of nanoparticles size and stoichiometry over the local atomic environment of nanostructured VOx films. The samples have been characterized in situ using X-ray absorption near-edge structure (XANES) spectroscopy identifying the stoichiometry-dependent fingerprints of disordered atomic arrangement. In vanadium oxides, the ligand atoms arrange according to a distorted octahedral geometry depending on the oxidation state, e.g. trigonal distortion in V2O3 and tetragonal distortion in bulk VO2. We demonstrate, taking VO2 as a case study, that as a consequence of the nanometric size of the nanoparticles, the original ligands symmetry of the bulk is broken resulting in the coexistence of a continuum of distorted atomic conformations. The resulting modulation of the electronic structure of the nanostructured VOx as a function of the oxygen content reveals a stoichiometry-dependent increase of disorder in the ligands matrix. This work shows the possibility to produce VOx nanostructured films accessing new disordered phases and provides a unique tool to investigate the complex matter.