Thermal evaporation synthesized zinc oxide nanowires for improved morphological and structural properties

Abstract

Considering the immense fundamental and applied interests of the zinc oxide nanowires (ZnONWs), this study produced these nanowires (NWs) on the glass substrates by the standard thermal evaporation technique. The as-deposited samples were characterized systematically at the room temperature via diverse analytical instruments. The main aim was to optimize the growth parameters to achieve vertically aligned ZnONWs that have not been fully explored yet. The influence of different deposition or growth parameters (such as the growth temperatures, growth times, oxygen gas flow rates and substrate positions) on the structures and morphologies of the proposed ZnONWs were determined. The longer growth time was utilized to obtain highly aligned ZnONWs that are useful for various practical applications. To deposit the ZnONWs, 1 gram of high purity (99.99%) zinc (Zn) powder was spread in an alumina boat, placed on the alumina boat holder which was then put in the glass tube of the thermal evaporator. The lengths and diameters of the NWs were found to be significantly affected by the variations of the growth temperatures and times. The growth temperature of 500°C was shown to be optimum to produce the strong vertical alignments of the NWs on the substrate surface. The transmission electron microscopy (TEM) images of the as-deposited samples revealed the growth of long ZnONWs with uniform morphological distribution and crystalline structures. In addition, the lengths of the NWs were first increased with the increase in the growth duration and then broken, scattered as well as bent on the substrate surface at longer time. The growth time of 20 min was observed to be ideal to attain the vertically aligned NWs on the substrate surface. Moreover, an increase in the oxygen gas flow rate caused an imbalance in the NWs growth directions with strong misalignment. Besides that, the higher oxygen gas levels led to a reduction in the Zn contents in the deposited NWs. The changes in the substrate positions in the thermal evaporation glass chamber (near the gas inlet, in the centre of the furnace and near the gas outlet) were found to influence the NWs growth, wherein the boat placement at the central region of the evaporator tube produced the optimum vertical alignments of the ZnONWs. It was concluded that by carefully adjusting the growth parameters of the thermal evaporation process the structures and morphologies of the vertically aligned ZnONWs can be tailored. The current findings may be useful for the progress of the ZnONWs production essential for different applications.