Optical and Field Emission Properties of Transparent Flexible ZnO Nanowire Films

Large-area field emitter arrays have important applications in flat-panel displays, light sources, gas sensors, and vacuum pressure sensors, where achieving high field emission currents and current densities over large areas is critical. In this study, well-aligned ZnO nanowires (NWs) were grown on a flexible substrate by the carbothermal reduction process and the vapor–liquid–solid (VLS) method. The ZnO NWs were single-crystalline wurtzite structures that showed a preferential growth orientation along the c-axis. The length and diameter of the ZnO NWs were 0.6 μm and 50 nm, respectively. The experimental results from field emission studies indicated that an emitter constructed from well-aligned, grass-like ZnO NWs exhibited a turn-on field of 16.1 Vμm−1 and a field enhancement factor of β = 1073, and demonstrated a consistent single linear slope in a Fowler–Nordheim (F–N) plot, which indicates that the field emission from ZnO emitters is a barrier-tunneling, quantum mechanical process. In addition, the field emission properties of curved ZnO/Al-doped ZnO (ZnO/AZO) flexible field nanoemitters were also investigated in this study. The results show that the turn-on field and enhancement factor of ZnO NWs on AZO flexible substrates decrease as the bending angle increases owing to an increase in the total resistance of the AZO layer.