[{VOCl2(CH2(COOEt)2)}4] as a molecular precursor for thermochromic monoclinic VO2 thin films and nanoparticles

Abstract

The synthesis of thermochromic monoclinic vanadium(IV) oxide (VO₂ (M)) thin films and vanadium oxide nanocrystals from a molecular precursor, [{VOCl₂(CH₂(COOEt)₂)}₄] is described. Thin films were synthesised using aerosol assisted chemical vapour deposition (AACVD) onto glass substrates at high temperatures and were subsequently characterised and tested for thermochromic efficiency. The film's suitability as smart, energy efficient window coatings was investigated by calculating their solar modulation potential. Thin films were also doped with tungsten to lower their metal to semiconductor transition temperature (MST) through the addition of tungsten(VI) phenoxide during the AACVD process, lowering the MST from a typical ∼70 °C for an undoped VO₂ (M) thin film to ∼50 °C for a typical W-doped example. The optimum deposition temperature of 550 °C produced films with thermochromic properties (solar modulation of 15.9%) comparable to the highest values reported. In addition, vanadium oxide nanostructures were synthesised using the thermal decomposition of [{VOCl₂(CH₂(COOEt)₂)}₄] and their shape controllably tailored by varying surfactant concentration and type. Thin films and nanostructures were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS). Thermochromic measurements were measured using UV-Vis spectroscopy with a variable temperature stage.