Morphology control and improved field emission properties of ZnO tetrapod films deposited by electrophoretic deposition

High-quality ZnO tetrapods with different morphologies were synthesized via thermal evaporation of a surface-modified Zn powder in an oxygen/argon mixed gas. The morphology, including the size and shape of the individual legs of ZnO tetrapods, was, easily altered by adjusting the proportion of oxygen in the carrier gas and the reaction temperature of the furnace. A correlation between the experimental parameters and the product morphologies was proposed and discussed. Moreover, the influence of the deposition time on the field emission (FE) characteristics of ZnO-tetrapod cathodes fabricated by the electrophoretic deposition (EPD) method was investigated. The results show that ZnO-tetrapod cathodes grown for 15 min have the best field emission properties, with a turn-on field of 2.01 V/μm, a threshold field of ∼3.8 V/μm, a current density of 1.96 mA/cm2 at a field of ∼4.62 V/μm, and a field enhancement factor as high as 1.1×104. The low threshold field and marked enhancement in β were attributed to the small radius of curvature, the high aspect ratio, and, perhaps more importantly, the proper density distribution of ZnO tetrapods.