(Figure a,b) shows the schematic of the setup to measure the electrical properties of the Ag/ZnO contacts and the optical image of the Ag/ZnO nanocable affixed to the probe. Forward I-V characteristics from as-grown Ag/ZnO nanocables and those annealed at 400°C in air for 1 h are shown in (Figure c,d). The I-V characteristics exhibit well-defined rectifying behavior of a Schottky barrier diode structure, which mainly reflects current transport across the metal-semiconductor interface. It is described by the thermionic emission relation:
Great efforts have been made to synthesize ZnO nanowires (NWs) as building blocks for a broad range of applications because of their unique mechanical and mechanoelectrical properties. However, little attention has been paid to the correlation between the NWs synthesis condition and these properties. Here we demonstrate that by slightly adjusting the NW growth conditions, the cross-sectional shape of the NWs can be tuned from hexagonal to circular. Room temperature photoluminescence spectra suggested that NWs with cylindrical geometry have a higher density of point defects. In situ transmission electron microscopy (TEM) uniaxial tensile-electrical coupling tests revealed that for similar diameter, the Young's modulus and electrical resistivity of hexagonal NWs is always larger than that of cylindrical NWs, whereas the piezoresistive coefficient of cylindrical NWs is generally higher. With decreasing diameter, the Young's modulus and the resistivity of NWs increase, whereas their piezoresistive coefficient decreases, regardless of the sample geometry. Our findings shed new light on understanding and advancing the performance of ZnO-NW-based devices through optimizing the synthesis conditions of the NWs.
Synthesis And Characterization Of Individual ZnO Nanowires
AB - One dimensional nanostructures are useful materials for investigating the dependence of electrical and thermal transport or mechanical properties on dimensionality and size reduction (or quantum confinement). These materials are expected to play an important role as both interconnects and functional units in fabricating electronic, optoelectronic, electrochemical and electromechanical nanodevices. Nanowire-like structures are the ideal system for studying the transport process in one-dimensionally (1D) confined objects, which are of benefit not only for understanding the fundamental phenomena in low dimensional systems, but also for developing new generation nanodevices with high performance. ZnO is one of the most fascinating material that has a diverse group of growth morphologies, such as nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires, nanocages etc. As with any semiconductor, 1-D ZnO nanostructures provide an attractive candidate system for fundamental quantization and low-dimensional transport studies. The large surface area of the nanorods and bio-safe characteristics of ZnO makes them attractive for gas and chemical sensing and biomedical applications, and the ability to control their nucleation sites makes them candidates for micro-lasers or memory arrays. The ability to control the synthesis of high quality ZnO nanowires leads to potential applications in UV photodetection, gas sensing, light-emitting nanodevices and transparent electronics. Therefore the controlled and large scale synthesis of these one dimensional nanomaterials are of potential importance. Various methods as thermal evaporation, wet chemical, laser ablation, hydrothermal etc have been widely imployed for the growth of ZnO nanostructures. This review represents the review of current research activities on the synthesis of ZnO nanorods (or nanowires) and the various growth process and mechanism have been discussed. Some possible application of these nanomaterials are also discribed.
Journal of Nanoscience and Nanotechnology
Large-scale vertically aligned ZnO nanowires with high crystal qualities were fabricated on thin graphene oxide films via a low temperature hydrothermal method. Room temperature photoluminescence results show that the ultraviolet emission of nanowires grown on graphene oxide films was greatly enhanced and the defect-related visible emission was suppressed, which can be attributed to the improved crystal quality and possible electron transfer between ZnO and graphene oxide. Electrochemical property measurement results demonstrated that the ZnO nanowires/graphene oxide have large integral area of cyclic voltammetry loop, indicating that such heterostructure is promising for application in supercapacitors.