Growth behavior of Al-doped zinc oxide microrods with times

We investigated the growth behavior of Al-doped zinc oxide (ZnO) microrods grown on ZnO seed layers at various growth times. During the initial 3 h (region I), the randomly oriented microrods grew on the surface of the substrate because of the weak acidity of the initial solution (pH similar to 5.5). Between 3 h and 6 h (region II), when the pH was close to neutrality, a dominant growth of Al-doped ZnO (AZO) microrods with tapered shape occurred. After that the vertical growth of the microrods reached a certain equilibrium, a selective etching of the side nonpolar plane, rather than the top polar plane, dominantly occurred between 6 h and 12 h (region III), thus leading to the formation of the microrods of cylindrical shape. From 12 h to 24 h (region IV), the pH value was saturated, and the morphology of the microrods did not significantly change. As a result, owing to the change of the pH value, the growth behavior of the AZO microrods appeared significantly different when increasing the time. (C) 2015 Elsevier Ltd. All rights reserved.