Temperature-induced metal-semiconductor transition in W-doped VO2 films studied by photoelectron spectroscopy

We present a photoemission study on reactively sputtered W-doped VO 2 films by high-resolution photoelectron spectroscopy. The valence band spectra and core-level lines were analyzed below and above transition temperature on vanadium dioxide films with different tungsten concentrations. It is shown that increase in tungsten content in the film results in decreased transition temperature and smeared metal-semiconductor transition. The centroid and the width of the valence band in the semiconducting state are found to be dependent on tungsten concentration in the film. In the metallic state the valence band width increases and becomes asymmetric demonstrating clearly Fermi edge. The V-2p and O-1s core-level lines exhibit broadening upon going through metal-semiconductor transition which is assigned to the interaction of core-level hole with d band in the final state. Detailed analysis of tungsten 4d core-level line revealed the tungsten valence to be 6+<span id="MathJax-Element-1-Frame" class="MathJax_SVG" style="font-size: 90%; display: inline-block; position: relative;" tabindex="0" role="presentation" data-mathml=" 6 + "> and 5+ <span id="MathJax-Element-2-Frame" class="MathJax_SVG" style="font-size: 90%; display: inline-block; position: relative;" tabindex="0" role="presentation" data-mathml=" 5 + "> .