Solar Energy Materials and Solar Cells, Vol.125, 291-296, 2014
Thermochromic VO2 thin films deposited by HiPIMS
Thermochromic VO2 windows have the potential of managing heat transfer in an efficient way. However, several problems such as a high transition temperature 68 degrees C and high deposition temperatures (over 400 degrees C) limit their applicability. We present a novel approach for the fabrication of thermochromic VO2 films in which High Power Impulse Magnetron Sputtering (HiPIMS) is used for deposition. Indeed, HiPIMS is known for its high ionization degree of sputtered species that allows one to control the evolution of the film microstructure by ion bombardment. The optical and other physical properties of the obtained HiPIMS VO2 coatings are first presented. Based on spectrophotometry, ellipsometry, AFM, SEM, TOF-SIMS, Raman spectroscopy and XRD results, we show that it is possible to deposit dense stoichiometric crystalline VO2 films at lower substrate temperatures (300 degrees C) compared to other approaches. These films exhibit a high infrared modulation (Delta T-2500 (nm) of 61% between 30 degrees C and 90 degrees C), low surface roughness (R-rms. under 10% of total thickness for films approximately 100 nm thick), and lower transition temperatures than the bulk material (T-c down to 50 degrees C for thicker films). (C) 2014 Published by Elsevier B.V.
Keywords:High power impulse magnetron sputtering;Smart windows;Optical properties;Microstructure;Thermochromism;Vanadium dioxide