3 years ago

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

Interdependence of Structure, Morphology, and Phase Transitions in CVD Grown VO2 and V2O3 Nanostructures
David Graf, Sanjay Mathur, Johannes Schläfer, Axel Klein, Simon Garbe
Phase selective chemical vapor deposition of nanostructured vanadium dioxide (VO2) and sesquioxide (V2O3) was achieved by deploying [V(OR)4]n (R = tBu, n = 1 (1), R = Et, n = 3 (2), R = Me, n = 4 (3)). Use of [V(OtBu)4] (1) 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 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.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b01018

DOI: 10.1021/acs.chemmater.7b01018

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