A template-free electrochemical deposition route to ZnO nanoneedle arrays and their optical and field emission properties

We report a soft and template-free electrochemical deposition method for preparing wafer-scale ZnO nanoneedle arrays on an oriented gold film coated silicon substrate. It has been shown that the ZnO nanoneedles possess single-crystal wurtzite structure and grow along the c-axis perpendicularly on the substrate. Raman and resonant Raman scattering studies have confirmed that the ZnO nanoneedles are of good crystal quality. The room temperature photoluminescence spectrum of such ZnO nanoneedle arrays exhibits a strong ultraviolet emission but negligible visible emission. The time-resolved photoluminescence spectral analysis discloses the excitonic origin of the ultraviolet emission. The field electron emission study, showing notable emission current in a moderate turn-on field, demonstrates potential applications of such ZnO nanoneedle arrays in field emission display, devices. The formation of such a ZnO nanoneedle array is attributed to the formation of { 0001}-oriented ZnO nuclei on the oriented gold coated silicon substrate and preferential growth along < 0001 >.