Field Emitters: Epitaxial ZnO Nanowire-on-Nanoplate Structures as Efficient and Transferable Field Emitters (Adv. Mater. 40/2013) (original) (raw)

As materials with a tremendously wide variety of potential applications, ZnO nanostructures have attracted a lot of attention in recent years. Among them, vertical one-dimensional (1D) ZnO nanostructures such as nanowires, nanorods, and nanotips have been considered as excellent candidates for electron fi eld emitters as they have low work functions, high aspect ratios, high mechanical stability, and high conductivity. The fi eld emission (FE) performance of such materials is highly affected by their intrinsic physical and structural parameters, such as alignment, density, uniformity, and tapering. After being stimulated by an applied electric fi eld and before reaching the counter electrode, electrons have to pass through the interface between the 1D ZnO structure and substrate. However, irrespective of the synthetic route used (whether chemical or physical), all known vertical ZnO emitters prepared on heterogeneous substrates demonstrate a so-called 'dead' layer, which is associated with a low crystallinity and poorly ordered region at the emitter-substrate interface. To date, this is one of the major and universal obstacles hindering the wide use of 1D ZnO in electronic and optoelectronic devices, such as solar cells, photodetectors, light-emitting diodes, and fi eld emitters. Obviously, growing 1D ZnO epitaxially on ZnO subtrates would provide a sharp and highquality interface, which is favorable for FE performance. However, no single-crystal ZnO wafers with low cost are available for the moment, and the related technology also needs to be improved. Therefore, achieving the high-quality interface with the substrate is still a major challenge for the electronic and optoelectronic applications based on 1D ZnO nanomaterials.