E-Thesis 175 views 51 downloads
Electronic and structural properties of Au contacts on ZnO nanowires. / Alexander M Lord
Swansea University Author: Alexander M Lord
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Zinc Oxide has emerged from an unspectacular past in the field of electronics to become one of the most widely researched materials for future devices. Here we investigate the growth and electrical properties of semiconducting ZnO nanowires for future application in the field of Nano-Devices and pre...
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Zinc Oxide has emerged from an unspectacular past in the field of electronics to become one of the most widely researched materials for future devices. Here we investigate the growth and electrical properties of semiconducting ZnO nanowires for future application in the field of Nano-Devices and present a solution to control the behaviour of the electrical contacts. ZnO nanowires (NWs) from initial growth experimentation and optimisation have been thoroughly characterised both structurally and electrically. Structural characterisation revealed the high quality of nanowires from vapour phase and hydrothermal growth that translated to similar measurements of nanowire resistivity. We have confirmed the results of atomic resolution dark field imaging with simulations that no Au catalyst contaminates ZnO nanowires, which makes the material more desirable than Silicon or GaAs. Within the limits of the dark field imaging the interface of the catalyst particle and the nanowire is abrupt, clean and intimate, with no Au diffusion, interfacial layers or roughness. Electron microscopy reveals the Au has an epitaxial relationship with the ZnO and is solid during growth. Using fabrication and contamination free nanoprobe measurements (four-probe scanning tunnelling microscope) in vacuum a transition from rectifying to Ohmic is dependent on contact size and not the materials or structural variations. We have shown this with the application of the nanoprobe on free standing as-grown catalysed ZnO nanowires. Using the most common nanowire growth methods the structure has been thoroughly characterised to allow the interpretation of electrical measurements of resistivity and Au end contacts. A regime of size dependent contacts to ZnO nanowires provides the necessary knowledge and requirements to fabricate ZnO nanowire devices with controlled properties and function. This is a major hurdle for nanodevices overcome without complicated or difficult processing steps. A nanodevice can be fabricated from a substrate, with contacts, in one- step and with tailored interface properties by controlling the catalyst particle size.
Faculty of Science and Engineering