Piezoelectric properties of template-free electrochemically grown ZnO nanorod arrays

In this work, we evaluated the piezoelectric properties of the ZnO nanorods (NRs), subsequently grown by a template-free electrochemical deposition (ECD) approach. The one-step preparation method yielded in a relatively short-time synthesis large arrays of high aspect-ratio ZnO NRs, vertically aligned to the substrate and exhibiting a well-defined hexagonal symmetry coupled with an excellent crystallinity. Piezoresponse force microscopy (PFM) was employed to extract the effective piezoelectric coefficient (d ₃₃ ) of the ZnO [0 0 0 1]-oriented NRs. A mean effective d ₃₃ coefficient of 11.8 pm/V was measured over several individual NRs. The results have shown an increased piezoelectric response of the ZnO NRs, with ∼18% in respect to the ZnO bulk material, and with a factor ranging from 28% to 167% compared to similar ZnO nanostructures prepared by other counterpart techniques. Both morphology and crystalline quality of the obtained ZnO NRs, as well as the piezoelectric investigations, ranked the ECD as a promising low-cost pathway for possibly producing high quality nanostructured ZnO-based piezoelectric devices with enhanced performance.