Synthesis of density-controlled ZnO nanoneedle arrays on a flexible substrate by addition of Al salts and use of microwave irradiation

We synthesized density-controlled ZnO nanoneedle arrays on a flexible substrate (Teflon) by the addition of aluminum chloride to the growth solution and application of microwave irradiation at 95 °C for 30 min. The density of ZnO nanoneedles on the substrate could be controlled by adjusting the concentration of aluminum chloride added to the reaction solution. After the reaction, the only species observed in the bulk solution were zinc aluminum layered double hydroxides (ZnAl:LDHs); these ZnAl:LDHs played a critical role in controlling the ZnO density on the substrate. On the basis of our results, we propose a mechanism for the density-controlled growth of ZnO nanoneedles.