Enhanced cold field emission of large-area arrays of vertically aligned ZnO-nanotapers via sharpening: experiment and theory.

Large-area arrays of vertically aligned ZnO-nanotapers with tailored taper angle and height are electrodeposited on planar Zn-plate via continuously tuning the Zn(NH3)4(NO3)2 concentration in the electrolyte. Experimental measurements reveal that the field-emission performance of the ZnO-nanotaper arrays is enhanced with the sharpness and height of the ZnO-nanotapers. Theoretically, the ZnO-nanotaper is simplified to a "charge disc" model, based on which the characteristic macroscopic field enhancement factor (γC) is quantified. The theoretically calculated γC values are in good agreement with the experimental ones measured from arrays of ZnO-nanotapers with a series of geometrical parameters. The ZnO-nanotaper arrays have promising potentials in field-emission. The electrochemical synthetic strategy we developed may be extended to nanotaper arrays of other materials that are amenable to electrodeposition, and the "charge disc" model can be used for quasi-one-dimensional field emitters of other materials with nano-sized diameters.