Structure-Decomposition relationships of homoleptic and heteroleptic vanadium(IV) alkoxides for defined gas phase depositions of VO2 and V2O3 thin films

Abstract

A facile high yield synthesis of a novel non-oxo heteroleptic vanadium(IV) alkoxide with chelating asymmetric fluorinated ß-heteroarylacetamides (2,2,2-trifluoro-N-(pyridine-2-yl)acetamide (H-PyTFA) (1)) with the general formula [V(OtBu)2(PyTFA)2] (4) as precursor for nanostructured vanadium oxides films deposited by chemical vapor deposition (CVD) is presented here. Single crystal X-ray analysis, electron paramagnetic resonance (EPR) spectroscopy and mass spectrometry (EI-MS) revealed the unambiguous structural and electronic features of the monomeric octahedral complex 4. Comparative thermogravimetric studies with homoleptic monomeric vanadium(IV) tert–butoxide [V(OtBu)4] (2) and trimeric [V3(μ-OEt)4(OEt)8] (3) displayed the strong influence of the alkyl function in vanadium(IV) alkoxides and chelating ligands on volatility, stability and thermal decomposition pathways to different oxide phases and morphologies. We demonstrated a controlled two-step thermal decomposition of heteroleptic vanadium(IV) alkoxide (4) which offer new opportunities for a versatile growth by the enlarged ‘CVD window’ between sublimation temperature and decomposition temperature and selective self-limited growth originated from the ‘Energy trap’ between the first and second decomposition steps. Preliminary CVD experiments proofed the successful conversion of the heteroleptic precursor 4 into vanadium dioxide with ribbon-like morphology on silicon, which revealed the impact of molecular precursor engineering on crystal growth kinetics.