Investigation of growth parameter influence on hydrothermally grown ZnO nanowires using a research grade microwave

Hydrothermal growth methods allow for low-temperature synthesis of ZnO nanowires (NWs) directly on a variety of novel substrates required for proposed flexible substrate applications such as power-harvesting fabrics. Although hydrothermal growth opens up a new realm of application possibilities, a major drawback of this method is growth time up to 20 hours or longer have been reported as necessary to yield desired NW morphologies. The use of microwave heating of the nutrient solution has recently been reported to speed the growth process. Although hydrothermal growth temperature has been reported to be a critical process variable, the conventional microwave used previously did not offer a direct method of controlling process temperature. Using a research grade microwave oven, equipped with integrated temperature control, the impact of growth temperature, growth time, and solution concentration on ZnO nanowire length, diameter, aspect ratio, growth orientation, density and wire morphology is investigated. Using a microwave with infrared temperature control, results demonstrate that ZnO NW growth time can be decreased significantly compared to traditional hydrothermal methods, that growth rate may be easier to control with temperature, rather than microwave power, and that by controlling the growth parameters that we can tailor NW morphology for a given application.