Origin of the ring-shaped emission pattern observed from the field emission of ZnO nanowire: role of adsorbates and electron initial velocity

A ring-shaped pattern was observed in the field emission from ZnO nanowires. These ring patterns are different from those previously reported from metallic or carbon nanotube emitters, which occur under high current density. The influences of the applied field and anode to emitter distance on the ring-shaped pattern have been investigated. On the basis of the experiment results, an edge emission model induced by the field desorption has been proposed. Furthermore, it is found that an initial velocity is essential to obtain the desired pattern size. The initial velocity of emitting electron is estimated by using field induced hot electron emission model. Simulation results from the model are consistent with the experimental results.