Injector-like ZnO nanostructures with different areal density and morphology (one or two needles) have been synthesized by the vapor-phase transport method. The cone-shape base of the injector-like ZnO nanostructure plays an important role in field emission. It holds up the needle to obtain a higher aspect ratio, separates the emission needles from each other to minimize the screening effect, and also reduces the risk of reaching an excessive temperature which is considered to be a cause of nanostructure breakdown. The sample with a long, sharp needle and medium areal density has the best FE performance due to the above three reasons. Moreover, the simulation of emission current density is in relatively good agreement with our experimental results. It shows that the highest current density is obtained when the spacing between the neighboring nanostructures is similar to the height for the single needle nanostructures. The nanostructures with double needles even reach higher emission current density when the space is two times the nanostructure's height. Injector-like ZnO nanostructures exhibit a good field emission property and have great potential for applications in field emission devices.
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