Field emission enhancement of ZnO nanorod arrays with hafnium nitride coating

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved with hafnium nitride (HfNx) coating under proper sputtering condition. HfNx films with various composition have been coated on ZnO nanorod arrays using a reactive direct current (DC) magnetron sputtering system. Morphology and crystal configuration of the ZnO nanorod arrays were investigated by scanning electron microscopy and X-ray diffraction. The field emission properties of the coated and uncoated ZnO nanorod arrays were characterized. The as-grown ZnO nanorod arrays showed a turn-on electric field of 6.60 V μm− 1 at a current density of 10 μA cm− 2 and an emission current density of 1 mA cm− 2 under the field of 9.32 V μm− 1. While the turn-on electric field of the coated ZnO nanorod arrays sharply decreased to 2.42 V μm− 1, an emission current density of 1 mA cm− 2 under the field of only 4.30 V μm− 1 can be obtained. A method to accurately measure the work function of the coated films was demonstrated.