Simulation of the sublimation process in the preparation of photochromic WO3 film by laser microprobe mass spectrometry

It is known that electrophotochromism of a WO3 film dramatically depends on its microstructure. To probe the influence of the microcomposition and the microstructure on the electrophotochromism of the VE-WO3 film, we employed a method based on laser microprobe mass spectrometry to simulate the sublimation process of WO3 with conditions mimicking those in vacuum evaporation. Both positive and negative ion clusters containing no more than six tungsten atoms were generated from direct laser vaporization of WO3 powder. The fragment valence calculation on the ion clusters showed that a valence of six was the ideal oxidation state for tungsten. The X-ray photoelectron spectroscopy results also confirmed the formation of stoichiometric units in the deposited film. Based on experimental results, (WO3)x, especially (WO3)3 and (WO3)4, were found to be the major component units in the vacuum evaporated (VE) film.