Defect modification to improve field emission of ZnO NRs by coating ultrathin Pt films

Ultrathin platinum (Pt) films are coated on the surface of ZnO NRs grown on Fe alloy substrates and display excellent field emission performance with the turn-on field Eto as low as 0.40 V/μm and the threshold field Ethr down to 2.62 V/μm. By coating ultrathin Pt films on the surface of the ZnO NRs, this not only helps to modify the linear defects on the outer surface of ZnO NRs, but also suppresses random electron emission along the defect directions. At an external electric field, a large amount of electrons are transported to the top of ZnO NRs where a highly localized electric field is caused, which results in enhanced field emission. Besides, ZnO NRs grown on Fe alloy substrates have a low interfacial contact resistance and intend to reduce the barrier between the substrate and the ZnO. Meanwhile, metal Pt films can help to obtain emitting centers that ensure highly conductive paths for the electrons from the ZnO NRs towards the vacuum, which effectively decrease the barrier between the ZnO and the vacuum. Finally, a schottky contact of Fe-ZnO and matched Fermi levels of ZnO-Pt contribute to the enhanced current emission efficiency. This work may help the development of the practical electron sources and advanced devices based on ZnO field emitters.