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Nanotip fabrication of zinc oxide nanorods and their enhanced field emission properties

The ZnO nanorods on ZnO/Si substrates were synthesized by using the low temperature growth aqueous solution method. The chemical and plasma etching treatments were carried out on the as-grown ZnO nanorods to provide the nanorods with various tip angles. The crystal structure and morphology of the ZnO nanorods were examined by x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The nanorods grew along the [0001] direction and had various tip angles formed after the above etching processes. The field emission properties of the ZnO nanorods with tip angles of 110° and 85° are: the turn-on electric fields (at the current density of 10 µA cm−2) are about 3.03 and 1.70 V µm−1, respectively, while field enhancement factors are 1972 and 3513, respectively. The lifetime measurement result indicates the turn-on field of the ZnO nanostructures reaches a stable value during 1000 cycle times. The enhanced field emission properties are believed to benefit from decreased tip angle of the nanorod emitter.