Seed layer-free electrodeposition and characterization of vertically aligned ZnO nanorod array film

Vertically aligned arrays of ZnO nanorod (ZNR) were rapidly synthesized on ITO glass without needing a pre-prepared seed layer of ZnO via a hexamethylenetetramine (HMT)-assisted electrodeposition route. The effect of HMT on the ZNR electrodeposition process was investigated by the cyclic voltammetric curve and the current-time curve. An electrodeposition growth model based on the capping effect of HMT-4H was proposed. The as-synthesized ZNRs possess single crystalline, a wurtzite crystal structure with markedly preferential growth orientation along [0001] direction determined by transmission electron microscopy and powder X-ray diffraction. As compared with the electrodeposited ZnO film without HMT assistance, the ZNR arrays showed the high transmittance (90%) in the visible wavelength range and the blue-shift of the band gap energy. Moreover, the presence of an optical-phonon E ₂ (high) at 437.3 cm ^-1 in Raman spectrum and strong ultraviolet emission at 376 nm but weak defect-related deep level emission in the room temperature photoluminescence spectrum also indicated that such ZNR arrays are of good crystal quality. More importantly, the rapid synthesis of ZNRs could provide the feasibility for preparation of ZnO nanotubes within a shorter time by a subsequent electrochemical dissolution process.