An explorative study was performed on sputter-deposited thermochromic (TC) VO 2 films exposed to heat treatment under dry and humid conditions. The ambient conditions were harsh and 80-nm-thick VO 2 films rapidly converted to non-TC V 2 O 5 . It was found that a 30-nm-thick sputter-deposited Al oxide top coating provided good protection and delayed the oxidation for more than one day upon heating in dry air at 300 °C and that protection occurred for several days at 95 % relative humidity and 60 °C. The thickness of the Al oxide was important and, expectedly, increased thickness yielded enhanced protection. Our results are important for TC fenestration as well as for other technical applications.

Modern buildings tend to be ''energy guzzlers'' and have indoor environments with unhealthy air. Glazing with TiO 2 /VO 2 bilayer coatings (1) exhibits enhanced photocatalytic air purification compared with single-layer TiO 2 due to heating from the underlying infrared-absorbing VO 2 film, (2) is thermochromic thanks to the VO 2 and admits less solar energy inflow when there is a cooling demand, and (3) has significantly improved luminous transmittance as a result of antireflection due to TiO 2. These coatings were deposited by reactive DC magnetron sputtering onto heated glass; they were nanocrystalline, and the anatase phase prevailed in TiO 2. The VO 2 coatings showed well-developed thermochromism. The photocatalytic degradation rate of stearic acid was almost doubled for the TiO 2 /VO 2 bilayer film compared with that for single-layer TiO 2. Our results demonstrate an important, and hitherto unexplored, synergy between photocatalysis, thermochromism, and high luminous transmittance which exploits spectral-selective material properties for solar illumination.

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Articles you may be interested inThermochromic VO2 nanorods made by sputter deposition: Growth conditions and optical modeling J. Appl. Phys. 114, 033516 (2013); 10.1063/1.4813876 Effect of O2 gas partial pressure on mechanical properties of Al2O3 films deposited by inductively coupled plasma-assisted radio frequency magnetron sputtering J. Vac. Sci. Technol. A 30, 051511 (2012); 10.1116/1.4746013Correlation of temperature response and structure of annealed V O x thin films for IR detector applications Thermochromic thin films of VO 2 were produced by reactive DC magnetron sputtering and were characterized by atomic force microscopy, scanning electron microscopy, x-ray diffraction, spectrophotometry, and resistance measurements. Depositions took place onto substrates of glass with and without layers of electrically conducting ITO (i.e., In 2 O 3 :Sn) and nonconducting SnO 2 . The substrate conditions were of large importance; thus, VO 2 could be prepared on ITO within a significantly wider process window of oxygen partial pressure than for the other substrates and could yield highly granular deposits. VO 2 films on ITO typically showed some lattice compression. Our results are valuable for the preparation and implementation of thermochromic glazings, which are of importance for energy efficient buildings.

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