Arrays of well-aligned ZnO nanorods were synthesized on a Si substrate at 600 degreesC by 193 nm pulsed laser ablation of a ZnO target in low pressures of oxygen. Electron microscopy and X-ray diffraction revealed highly c-axis aligned, ultra-thin, needle-like nanorods with tip diameters <50 nm growing vertically from the substrate. Many of the rods appear to be capped by particles, which high-resolution transmission electron microscopy shows to be ZnO also. It is suggested that these derive from post-growth crystallisation of oxygen rich molten zinc droplets that cap the nanorods during growth- indicating a vapour-liquid-solid growth mechanism. The room temperature photoluminescence spectra of these samples show strong, narrow bandwidth UV emission similar to380 nm and only weak visible emission. (C) 2004 Elsevier B.V. All rights reserved.