Atmospheric Flash Annealing of Low-Dimensional Vanadium Nanolayers Sputtered on Glass Substrates

A simple approach to attain low-dimensional, highly transparent VO2-based thermochromic coatings on glass substrates is reported. This two-step procedure comprises the initial deposition of DC magnetron-sputtered vanadium films and the subsequent flash annealing of such layers in air atmosphere. The careful control of the thermal treatment parameters and characterizations carried out by scanning electron microscopy and variable temperature Vis-NIR spectrophotometry allowed the optimization of VO2 yields for 12.5 nm and 25 nm thick layers. The impact of layer thickness and the nature of the thermal treatment itself on the thermochromic features of such systems were also evaluated. In this sense, the resulting systems developed asymmetric transmittance vs. temperature hysteresis loops as well as a surprisingly advantageous lowering of the phase transition temperature, which is achieved without the incorporation of dopants. The most promising results were obtained for a 12.5 nm thick layer flash annealed at 475 degrees C, which, despite having a moderate solar modulation ability (similar to 2%), could be a potential candidate for smart windows applications given its high Vis-NIR transparency (> 60%) coupled with its low transition temperature of 16 degrees C below the standard value for pure VO2.