Surface-architecture-controlled ZnO nanowires were grown using a vapor transport method on various ZnO buffer film coated c-plane sapphire substrates with or without Au catalysts. The ZnO nanowires that were grown showed two different types of geometric properties: corrugated ZnO nanowires having a relatively smaller diameter and a strong deep-level emission photoluminescence (PL) peak and smooth ZnO nanowires having a relatively larger diameter and a weak deep-level emission PL peak. The surface morphology and size-dependent tunable electronic transport properties of the ZnO nanowires were characterized using a nanowire field effect transistor (FET) device structure. The FETs made from smooth ZnO nanowires with a larger diameter exhibited negative threshold voltages, indicating n-channel depletion-mode behavior, whereas those made from corrugated ZnO nanowires with a smaller diameter had positive threshold voltages, indicating n-channel enhancement-mode behavior.
Flexible materials and devices could be exploited in light-emitting diodes, electronic circuits, memory devices, sensors, displays, solar cells and bioelectronic devices. Nanoscale elements such as thin films, nanowires, nanotubes and nanoparticles can also be incorporated into the active films of mechanically flexible devices. Large-area devices containing extremely thin films of molecular materials represent the ultimate scaling of flexible devices based on organic materials, but the influence of bending and twisting on the electrical and mechanical stability of such devices has never been examined. Here, we report the fabrication and characterization of two-terminal electronic devices based on self-assembled monolayers of alkyl or aromatic thiol molecules on flexible substrates. We find that the charge transport characteristics of the devices remain stable under severe bending conditions (radius ≤ 1 mm) and a large number of repetitive bending cycles (≥1,000). The devices also remain reliable in various bending configurations, including twisted and helical structures.
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