This work reports on an alternative and advantageous
procedure
to attain VO2-based thermochromic coatings on silicon substrates.
It involves the sputtering of vanadium thin films at glancing angles
and their subsequent fast annealing in an air atmosphere. By adjusting
thickness and porosity of films as well as the thermal treatment parameters,
high VO2(M) yields were achieved for 100, 200, and 300
nm thick layers treated at 475 and 550 °C for reaction times
below 120 s. Comprehensive structural and compositional characterization
by Raman spectroscopy, X-ray diffraction, and scanning-transmission
electron microscopies combined with analytical techniques such as
electron energy-loss spectroscopy bring to the fore the successful
synthesis of VO2(M) + V2O3/V6O13/V2O5mixtures. Likewise,
a 200 nm thick coating consisting exclusively of VO2(M)
is also achieved. Conversely, the functional characterization of these
samples is addressed by variable temperature spectral reflectance
and resistivity measurements. The best results are obtained for the
VO2/Si sample with changes in reflectance of 30–65%
in the near-infrared at temperatures between 25 and 110 °C. Similarly,
it is also proven that the achieved mixtures of vanadium oxides can
be advantageous for certain optical applications in specific infrared
windows. Finally, the features of the different structural, optical,
and electrical hysteresis loops associated with the metal–insulator
transition of the VO2/Si sample are disclosed and compared.
These remarkable thermochromic performances hereby accomplished highlight
the suitability of these VO2-based coatings for applications
in a wide range of optical, optoelectronic, and/or electronic smart
devices.