Field emission property improvement of ZnO nanowires coated with amorphous carbon and carbon nitride films

In this paper, we report an approach to prepare a new type of field emitter made up of ZnO nanowires coated with an amorphous carbon (a-C) or carbon nitride film (a-CN_x). The coated ZnO nanowires form coaxial nanocables. The best field emission properties, which showed a very low turn-on electric field of 1.5 V µm^-1 and an emission current density of 1 mA cm^-2 (enough to produce a luminance of 300 cd m^-2 from a VGA FED with a typical high-voltage phosphor screen efficacy of 9 lm W^-1) under the field of only 2.5 V µm^-1, have been obtained from the a-CN_x coated ZnO nanowire field emitter among three kinds of emitters: a-C coated ZnO nanowires, a-CN_x coated ZnO nanowires and uncoated ZnO nanowires. Microstructures and crystal configuration were investigated by scanning electron microscopy, x-ray diffraction and transmission electron microscopy. Band edge transition without any significant photoluminescence peak relating to intrinsic defects has been observed by photoluminescence measurement. The superior properties of the field emission are attributed to the low work function of the coated carbon nitride film and good electron transport property of the ZnO nanowires with an extremely sharp tip.