Size- and shape-controlled synthesis of monodisperse vanadium dioxide nanocrystals

Highly monodisperse VO2 nanocrystals with finely defined sizes and shapes were synthesized for the first time by thermolysis of single source vanadium precursor in high boiling point solvents of oleic acid (OA), oleylamine (OM), and octadence (ODE). The resulting VO2 nanocrystals were characterized by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-Ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was revealed that the low valence vanadium oxide of VO2 nanocrystals was successfully synthesized via this approach, and the obtained VO2 nanocrystals displayed uniform sizes and narrow size distribution with size variation in range of approximately 4-20 nm under various synthetic conditions. The previously unknown cubic, polyhedral shaped VO2 nanocrystals were achieved as well through modulating the preparative conditions. The solvent composition and precursor concentration are found to have profound effects on the sizes and shapes of the final VO2 nanocrystals. It is expected that the obtained VO2 nanocrystals with finely controlled sizes and shapes may be valuable candidates for studying and realizing the new size- and shape- dependent optical and electrical properties of VO2 materials in the nanoscale realm, and the novel synthetic method is potentially useful for the controlled synthesis of high quality doped VO2 and other vanadium oxides nanocrystals.