Well-aligned ZnO nanowires were grown on Si (111) substrates pre-coated with a ZnO buffer layer. The nanowires are single-crystalline wurtzite structures with a preferential growth in the [0001] direction. Room temperature photoluminescence (PL) measurements of as-grown nanowires annealed in argon and air exhibited a strong ultraviolet emission and suppressed visible emission, affirming the presence of few defects. Field emission properties of the nanowires were investigated, and the lowest turn-on field obtained was 3.8 V/mu m at a current density of 0.1 mu A/cm(2), with a corresponding field enhancement factor beta of 1644. Current-voltage (I-V) and capacitance-voltage (C-V) measurements showed that the contact was ohmic and the ZnO nanowires were n-type, with little C-V hysteresis. (C) 2010 Elsevier B.V. All rights reserved.