Temperature induced shape change of highly aligned ZnO nanocolumns

Vertically well-aligned ZnO nanocolumns were grown on Al2O3 (0 0 0 1) substrates via metalorganic chemical vapor deposition without using any metal catalyst. Their morphology was investigated as a function of the growth temperature (Tg), which was found to be a key processing parameter to control their shape. At Tg⩾450°C, vertically well-aligned ZnO nanocolumns started to grow. It was found that a higher Tg yielded slimmer, needle shaped nanocolumns, whereas a lower Tg yielded thicker nanocolumns.