Size-dependent field-emission characteristics of ZnO nanowires grown by porous anodic aluminum oxide templates assistance

The field-emission electrical properties of hydrothermally synthesized zinc-oxide nanowires grown on SiO2–Si substrate are reported. Vertically aligned single-crystalline emitters with distinct length L and diameter D are realized by controlling the assisted growth of porous anodic aluminum oxide (AAO) templates. Field-emission measurement revealed that these field emitters exhibited controllable turn-on field Eto and the field enhancement factor β. Sample with feature size of L = 500 nm and D = 80 nm was prepared and then used as a basis for examining the size effect. Lower Eto and higher β were observed consistently for increasing the aspect ratio L/D. The enhanced properties of Eto = 1.48 V/μm and β up to 6100 are achieved for L/D = 53 (L = 1600 nm and D = 30 nm). Optimal characterizing parameters of Eto and β will be reached while pursuing extreme L/D practically. Factors such as the geometric limit of AAO template manufacture and the filling efficiency of ZnO into AAO pores will exert influence on the size-dependent effect.