The growth mechanism of VO2 multilayer thin films with high thermochromic performance prepared by RTA in air

In this paper, the multilayer thin films with SiNx/NiCr/NiCrOx/VO2/NiCrOx/NiCr/SiNx structure were prepared by reactive magnetron sputtering at room temperature and subsequently rapid thermal annealing (RTA) in air. The effects of annealing temperature on the microstructure and thermocheromic performance of the VO2 multilayer thin films were systemacially investigated by UV-Vis-NIR, XRD, SEM, XPS and TEM. The results showed that the crystalline VO2 multilayer thin films can be obtained as the temperature rose from room temperature to 301 °C within 6 s, and the high thermochromic performance with solar modulation (∆Tsol) of 17.2%, luminous transmittance (Tlum) of 26.9% and phase transition temperature (Tc) of 60 °C can be acquired as the temperature rose from room temperature to 571 °C within 10 s, which indicates the VO2 multilayer thin films show the good antioxidation. Based on growth mechanism of VO2 multilayer thin films, it can be found that the atomic diffusion may form crystal nucleation and induce the rapid crystallization of VO2 thin film at low temperature, the drastic diffusion reaction results in the degeneration of crystallinity and performance of VO2 film with increasing temperature. Finally, the unbalance of interfacial stress lead to the rupture of the films, and the VO2 was completely oxidized into V2O5. The exploration of the growth mechanism provides the basis for the optimization of the film structure and annealing parameters, so as to promote the practical application of VO2 multilayer thin films with high thermochromic performance.