The structural and electrical properties of VO2 nanowires synthesized on Si3N4/Si substrates or molybdenum grids by a catalyst-free vapour transport method were investigated. The grown VO2 nanowires are single crystalline and rectangular-shaped with a preferential axial growth direction of [1 0 0], as examined with various structural analyses such as transmission electron microscopy, electron diffraction, X-ray diffraction, and X-ray photoelectron spectroscopy. In particular, it was found that growing VO2 nanowires directly on Si3N4 deposited molybdenum transmission electron microscopy grids is advantageous for direct transmission electron microscopy and electron diffraction characterizations, because it does not involve a nanowire-detachment step from the substrates that may cause chemical residue contamination. In addition to structural analyses, VO2 nanowires were also fabricated into field effect transistor devices to characterize their electrical properties. The transistor characteristics and metal-insulator transition effects of VO2 nanowires were investigated. (c) 2007 Elsevier Ltd. All rights reserved.