Regulating the surface morphology and improving the thermochromic properties of VO₂ films by introducing Cu-Ag and Cu-Zr nanoparticles into the VO₂/VO₂/VO₂ structure

In this work, Cu-Ag and Cu-Zr bimetallic nanoparticles (NPs) were embedded into VO₂/VO₂/VO₂ tri-layer films by using pulsed laser deposition. The results showed that Cu-Ag and Cu-Zr NPs have a significant regulating effect on the crystallinity and surface morphology of VO₂ films. In comparison to Cu-Ag NPs, Cu-Zr NPs exhibit a much milder degree of surface morphology regulating influence on VO₂ films. The introduction of Cu-Ag and Cu-Zr nanoparticles leads to a completely different surface morphology of VO₂ films. Owing to the ability to adjust the surface of the VO₂ film to be granular, the resulting local surface plasmon resonance effect effectively modulates the spectral curve, thereby enhancing the thermochromic properties of the composite films. Both Cu-Ag and Cu-Zr NPs can significantly improve the thermochromic properties of VO₂ films. And high luminous transmittance (T_lum = 74.6%) and high solar modulation ability (ΔT_sol = 8.4%) were simultaneously achieved when the pulse number for depositing Cu-Zr NPs was 100. Additionally, the transmission spectrum of the composite films was simulated by using the finite-difference-time-domain method, and the growth mechanism of the composite films was explored. This work provides a guidance on controlling the morphology of VO₂ films by Cu-based bimetallic NPs, which will promote the application of VO₂ films in smart windows.