Field emission properties of carbon nanotubes directly grown on a well-polished oxygen- free copper substrate by chemical- vapor deposition (CVD) were studied. Ni was sputtered on the copper substrate as catalyst, and the reactant gas was acetylene. From scanning electron microscopic and transmission electron microscopic images, the as- grown carbon nanotubes are seen to be bamboo structure with branches. Efficient field emission of CNTs is measured by a diode configuration, and the maximum current is 4.8 mA corresponding to a lowelectric. eld of 6.7 V/mu m(the emission area is about 3.14 mm(2)). The diffusion between nickel and copper substrate is found to cause the loss of catalyst based on X- ray diffraction pattern of the surface of the substrate. (C) 2008 Elsevier B. V. All rights reserved.