Large-scale growth of highly oriented ZnO nanorod arrays in the Zn-NH3•H2O hydrothermal system

Large-scale highly oriented ZnO nanorod arrays were directly grown on zinc foil through a simple hydrothermal reaction of Zn foil with aqueous ammonia at 100 degrees C. The products were characterized with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was found that the ZnO nanorods were single crystalline with the wurtzite structure and grown in the [0001] direction, and have a controllable diameter in the range of 250-100 nm with lengths of up to 4.0 mu m by varying the growth time. The ammonia plays a key role in the formation of ZnO nanorod arrays, and a possible mechanism is also proposed to account for the growth of the ZnO nanorod arrays. The ZnO nanorod arrays exhibited a UV emission with peak at 396 nm and a blue green emission with a peak at 488 nm. The UV and blue green emissions are considered to originate from the exciton transition and the transition between the oxygen vacancy and interstitial oxygen, respectively. In addition, the UV and blue green emission intensities can be adjusted by changing the growth time.