Electrodeposition and formation mechanism of ZnO tubular structure

Zinc oxide (ZnO) microtubes and nanotubes were prepared on indium-tin oxide (ITO) substrates and ZnO buffer layer/ITO substrates respectively by a two-step approach, which involves the electrodeposition of ZnO rods from Zn(NO₃)₂ and hexamethylenetetramine aqueous solution and subsequently selective dissolution from ethylenediamine aqueous solution to form tubular structure. The phase structure and morphology of ZnO films were investigated by the X-ray diffraction and scanning electron microscope. The results indicate that ZnO rods turn into ZnO trumpets at the beginning of etching, and then develop to ZnO tubes. The formation mechanism of tubular structure is discussed. Firstly, the metastability of (0001) plane leads to preferential etching in (0001) plane. Secondly, the unbalanced distribution of defects in ZnO rods resulted in selective etching in the center of the rods. The annealing experiments testify the formation mechanism.