The effects of tetrafluoro methane (CF4) and oxygen (O-2) plasmas on the morphology and field emission of copper oxide (CuO) nanowires are investigated. The tip diameter of nanowires is found to be reduced and the tips sharpened by both plasmas. Furthermore, O-2 plasma removes the amorphous layer on the surface of as-grown nanowires, while CF4 plasma treatment deposits a thick amorphous coating which results in a decrease in the surface work function. All these factors contribute to the large enhancement of the field emission performance after the plasma treatment. (c) 2005 Elsevier B.V. All rights reserved.