The effects of atomic oxygen exposure on electrical and field emission properties of ZnO nanowires were investigated. It was found that the turn-on field of ZnO nanowires increased after exposure to atomic oxygen. Measurement of electrical conductivity of single nanowire showed that the ozone exposure decreased the conductivity of the ZnO nanowire. Ultra-violet photoelectron spectroscopy results indicated that the ozone exposure increased the work function. Photoluminescence and X-ray photoelectron spectroscopy results suggested that ozone exposure reduced the oxygen vacancy concentration, which leads to the change in the work function and conductivity. We propose that the change of field emission properties is mainly caused by the changes in the surface work function. (c) 2012 Elsevier B.V. All rights reserved.