Interdependence of Structure, Morphology, and Phase Transitions in CVD Grown VO₂ and V₂O₃ Nanostructures

Phase selective chemical vapor deposition of nanostructured vanadium dioxide (VO₂) and sesquioxide (V₂O₃) was achieved by deploying [V­(O<i>R</i>)₄]_<i>n</i> (<i>R</i> = ^<i>t</i>Bu, <i>n</i> = 1 (<b>1</b>), <i>R</i> = Et, <i>n</i> = 3 (<b>2</b>), <i>R</i> = Me, <i>n</i> = 4 (<b>3</b>)). Use of [V­(O^<i>t</i>Bu)₄] (<b>1</b>) produced thin films of monoclinic VO₂ (M1) at 700 and 800 °C consisting of anisotropic nanostructures with high crystallinity and small hysteresis in the metal-to-semiconductor transition (MST). Film morphologies manifested strong dependence on growth temperatures and exhibited pronounced texturing effects at high temperatures (>700 °C). The microstructure of the films was found to significantly affect the MST behavior of VO₂ films. DTA measurements of VO₂ films showed MST at 63 °C (700 °C) and 65 °C (800 °C), much lower than the transition temperature observed in single crystal material (68 °C). Precursors were characterized in the solid state (XRD) and solution state (temperature dependent EPR, NMR) to reveal an association–dissociation equilibrium in solution (complexes <b>2</b> and <b>3</b>), involving monomeric, dimeric, and oligomeric species. Use of <b>2</b> and <b>3</b> as single precursors produced thin films of crystalline V₂O₃ consisting of nanosheets (5 nm) with a flower-like morphology