Thermochromic light scattering from particulate VO2 layers

Abstract

Particulate layers of thermochromic (TC) VO 2 were made by reactive DC magnetron sputtering of vanadium onto In 2 O 3 :Sn-coated glass. The deposits were characterized by scanning electron microscopy, atomic force microscopy and Xray diffraction. Specular and diffuse optical transmittance and reflectance were recorded in the 300-2500-nm wavelength range and displayed pronounced TC effects. These properties could be reconciled with a semi-quantitative model based on Lorentz-Mie theory applied to the distribution of particle sizes and accounting for particle shapes by the Grenfell-Warren approach with equal-volume-to-area spheres.

Thermochromic Oxide-Based Thin Films and Nanoparticle Composites for Energy-Efficient Glazings

“…SEM top-view (a) and atomic force microscopy (AFM) image (b) of a particulate VO2 layer on ITO-coated glass. The maximum peak height of the deposit was ~190 nm [74].…”

“…The sublayer of ITO on the glass substrate is of significance also because it broadens the process window for making VO 2 deposits with TC properties. Figure 6 shows images taken by SEM and atomic force microscopy (AFM) of a particulate VO 2 film on ITO-coated glass and demonstrates a layer of highly irregular nanoparticles with sizes of the order of 1 µm [74]; we come back to these films in Section 5 below.…”

“…The calculations used the equal-volume and equal-volume-to-area Figure 16. Distributions of the number N eq of equivalent sphere radii for the data shown in Figure 6b [74].…”

“…The calculations used the equal-volume and equal-volume-to-area approximations in Figure 16. Data are given for the semiconducting state at τ < τ c (a,c) and the metallic state at τ > τ c (b,d) [74].…”

“…Specifically, the study employed the particulate layer depicted in Figure 6 [74], and the shown AFM image was quantified with regard to individual particle volumes V p and surface areas S p by use of available computer code [111]. In order to formulate a theoretical model of light-scattering data, the individual particles were modelled by use of two different sets of equivalent sphere radii: either equal-volume spheres represented by r eq = (3V p /4π) 1 / 3 or equal-volume-to-area spheres represented by r' eq = 3V p /S p .…”