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(OR)(4)](n) (R = Bu-t, n = 1 (1), R = Et, n = 3 (2), R = Me, n = 4 (3)). Use of [V((OBu)-Bu-t)(4)] (1) produced thin films of monoclinic VO2 (Ml) at 700 and 800 degrees 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 degrees 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 degrees C (700 degrees C) and 65 degrees C (800 degrees C), much lower than the transition temperature observed in single crystal material (68 degrees 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 2 and 3), involving monomeric, dimeric, and oligomeric species. Use of 2 and 3 as single precursors produced thin films of crystalline V2O3 consisting of nanosheets (5 nm) with a flower-like morphology.