High performance VO2 thin films growth by DC magnetron sputtering at low temperature for smart energy efficient window application

VO2 thin films were deposited on soda-lime glass substrates through DC-reactive magnetron sputtering at substrate bias voltage of -160 V and a low substrate temperature of 200 degrees C. The crystal structure, electrical and optical performances, evolution of vibrational modes, and surface morphology of the films were characterized via X-ray diffraction, four-point probe method, UV/VIS/NIR spectrophotometer, ellipsometry, Raman scattering measurements, and scanning electron microscopy, respectively. The obtained results show that the films have preferred orientation of VO2 (011) lattice. The change in film resistivity is nearly 1.5 orders of magnitude after heating the film from 25 degrees C to 80 degrees C. The phase transition temperature of the film is approximately 50 degrees C, which is lower than 68 degrees C of VO2 crystal. Compressive stress in the VO2 films maybe the real reason for this result. The maximum visible transmittance shows as higher as 40%, and the IR switching efficiency can reach 50% at 2500 nm. Raman band variation and the switching characteristics of optical constants also confirmed the good thermochromic properties of VO2 films. (C) 2015 Elsevier B.V. All rights reserved.