Synthesis, characterization and sensor applications of doped and mixed metal oxide nanowires

Various metallic nanowires were synthesized using template-assisted electrodeposition method, and by adjusting the chemical components in the plating solution, alloy or doped nanowires could be synthesized through co-deposition process. Metal oxide nanowires were obtained by thermally oxidizing the metallic nanowires into their corresponding metal oxide forms. Morphology of these metallic and metal oxide nanowires was characterized using optical microscope and scanning electron microscope (SEM). Elementary and crystalline analysis was conducted using energy dispersive X-ray (EDS) spectrum and X-ray diffraction (XRD). For integration purpose, dielectrophoresis (DEP) assembly was studied and adopted to nanowire system. This field effect based technique was later applied to align nanowires forming contacts with micro electrodes in sensor chip fabrication process. The sensor application of metal oxide nanowires has been investigated in a systematical and methodical manner. Both dynamic and static testing methods have been deployed to evaluate the sensor performance of different metal oxide nanowires.;Pure tin oxide nanowires were fabricated first to verify that for same sensing material, if made in the form of nanowire, it could outperform the conventional thickfilm/thin-film configuration in terms of sensitivity, response and recovery time. Then, inspired by this encouraging preliminary result, mixed tin-copper oxide nanowires were synthesized. Interesting morphology changes, i.e. rugged surfaces, of nanowires after thermal oxidation process were found as well as enhanced sensitivity comparing to pure tin oxide nanowire. Doped tin oxide nanowires provide another solution utilizing doping effect to improve the sensor performance. Catalytic dopant platinum, electroactive dopant copper, indium and nickel have been successfully introduced into tin oxide nanowires. These four types of doped tin oxide nanowires displayed not only good sensitivity and response kinetics, but also differences in selectivity. An array device that could accommodate up to four individual nanowire sensor units was developed to simultaneously gather testing data and feed to computer to build a data base. Principle component analysis (PCA) of this database further amplified the selectivity patterns of each doped tin oxide material and demonstrated this sensor array's ability of classifying chemical analyte.;In all, nanowires show many advantages such as a large variety in compositions, and capability of being efficiently assembled in a massive manner. The great potential of high surface-to-volume ratio metal oxide nanowires for solid-state gas sensing should be highlighted. The future research work should aim at exploration of other possible mixed/doped metal oxide materials, optimization of compositions and temperature effect in order to improve the sensitivity and selectivity, as well as theoretical study, simulation and modeling of the doping effects. Sensor devices featuring metal oxide nanowires as key functional component should also be given great attention; the array style device consisted of multiple nanowire sensor units needs further development toward a commercial product level. Furthermore, this prototype nanowire sensor array device may be incorporated with fluorescent polymer, surface acoustic wave (SAW) sensors to compose an electronic-nose system with data fusion technique for precise detection, discrimination and quantification of hazardous gas, chemical and explosives.