Preparation of VO2@SiO2 nanoparticles. First, VO2 nanoparticles were pretreated with poly(vinylpyrrolidone) (PVP) K-30. Then, the VO2@SiO2 core-shell structure was prepared by the hydrolysis of TEOS, which is known as the modified Sto¨ber growth method. Finally, the prepared sample was collected by centrifugation and washed with deionised water and ethanol several times 19.