Solid-State Dewetting of Tungsten-Doped Vanadium Dioxide Nanoparticles: Implications for Thermochromic Coatings

Doped vanadium dioxide (VO₂) nanoparticles (NPs) have significant potential for applications requiring temperature-dependent emissivity, reflectivity, or transmission. Thermochromic coatings in particular enable energy-saving smart windows and passive thermal radiators but are subject to tight performance constraints. A major challenge is preparing uniform layers of NPs, over large areas, with controllable size distributions and transition temperatures (<i>T</i> _c). We describe the growth and transition characteristics of randomly distributed undoped and W-doped VO₂ NPs formed by solid-state dewetting. Sizes and size distributions are controlled by anneal time, as particles grow via Smoluchowski aggregation before oxidizing into V₂O₅; shapes are determined by the interfacial energies between VO₂ (V₂O₅) and the silicon substrate. Tungsten dopants concentrate at the NP surface, increasing the energy barrier for and slowing the rate of dewetting, aggregation, and oxidization. Surprisingly, the doped NPs exhibit lower <i>T</i> _c and sharper hysteresis than comparably doped thin films. These results advance our capacity to engineer doped VO₂ NPs, yield valuable insights into VO₂-substrate interactions, and highlight the distribution of W-dopants in VO₂ NPs.