Effect of Power Level on Rapid Microwave-assisted Hydrothermal Synthesis of Vertically Aligned ZnO Nanowires

In this paper, we investigate the effect of applied microwave power level on the longitudinal growth rate of the ZnO nanowires grown hydrothermally for semiconductordevices applications. Our observations from the cross-sectional SEM images of the grown nanowire arrays revealed that, incontrast to the expectations, although for low microwave powerlevels, the longitudinal growth of ZnO nanowires continued its rising trend by increasing the process time, but when higherpowers applied to the system, despite the observation of higher growth rates, the axial growth of the nanowires stopped atlonger growth times. As in our system, it was impossible to grow nanowires with length more than 1.2 μm at 450W power level ornanowires longer than 700 nm at 850W applied power without refreshing the growth solution. The reason for this problem is that although the nanowires growth rate increases, the formation of ZnO in the bulk solution also increases and thus leads to a considerable speed-up in the loss of precursor materials. So, using the highest possible power level in this method is not cost effective and it must be optimized