Formation of Tungsten Oxide Nanowires by Electron-Beam-Enhanced Oxidation of WS2 Nanotubes and Platelets

Oxidation of van der Waals-bonded layered semiconductors plays a key role in deterioration of their superior optical and electronic properties. The oxidation mechanism of these materials is, however, different from non-layered semiconductors in many aspects. Here, we show a rather unusual oxidation of tungsten disulfide (WS₂) nanotubes and platelets in a high vacuum chamber at a presence of water vapor and at elevated temperatures. The process results in formation of small tungsten oxide nanowires on the surface of WS₂. Utilizing real-time scanning electron microscopy we are able to unravel the oxidation mechanism, which proceeds via reduction of initially formed WO₃ phase into W₁₈O₄₉ nanowires. Moreover, we show that the oxidation reaction can be localized and enhanced by an electron beam irradiation, which allows for on-demand growth of tungsten oxide nanowires.