A convenient method to fabricate sputtered thermochromic VO₂ nanoparticles by SiO₂ microspheres for smart windows

To enhance the practical utility of Vanadium dioxide (VO₂) for thermochromic smart window applications, researchers have exerted numerous endeavors to improve its luminous transmittance (T_lum), and solar modulation ability (ΔT_sol), lower the phase transition temperature (T_t), and narrow the thermal hysteresis curve (ΔT). In this study, thin hexagonal periodic perforated metal Vanadium films were prepared by magnetron sputtering using SiO₂ microspheres as templates. Subsequently, the thin metal Vanadium film was subjected to rapid thermal annealing (RTA), developing a densely packed hexagonal network structure composed of VO₂ nanoparticles. The formation of the nanoparticles was driven by increased surface mass transport during annealing and the imperative to reduce the system’s surface energy. Compared with the planar VO₂ film, the two-dimensional nanostructure increases T_lum from 29.98 to 61.82%, decreases T_t from 55.91 to 44.44 °C, decreases ΔT from 15.18 to 4.98 °C, and slightly attenuates the ΔT_sol from 5.92 to 3.84%. These enhancements are attributable to the reduced refractive index, the improved uniformity in particle size distribution, and the localized surface plasmon resonance (LSPR) effect. Moreover, the thermochromic properties were further augmented through a layer-by-layer stacking process. These findings underscore the potential for advancing the integration of VO₂ particles in smart window technologies, thereby broadening their application prospects.