Modification of green synthesized ZnO nanorods for actuation application

Abstract

Zinc oxide (ZnO) nanostructures as amazing piezoelectric materials have been recently extensively investigated in order to harvest energy. ZnO nanorods with hexagonal wurtzite structure oriented along c-axis were grown on the glass substrate by combining the facile sol–gel and chemical bath deposition techniques. Zinc acetate dihydrate as a Zn2+ source, ethanol and acetone as solvents were used in the sol preparation without using any organic stabilizer additive. ZnO sol's structure was characterized by FTIR spectroscopy. Particles forming the sol were analyzed to be zinc (hydroxo and/or oxo) acetate, according to the characterization results. The influence of the binary solvent system on the stability and optical properties of the particles as well as morphological properties of ZnO grains were studied. The positive effect of an optimum percentage of acetone in the precursor sol which reduced the zinc (hydroxo and/or oxo) acetate dissolution and ensured the particles stabilization could subsequently be understood. Dense ZnO grains with high aspect ratio on the seed layer which led to vertically aligned ZnO nanorods were obtained using the sol with 1:1 ratio of EtOH and acetone. To increase the piezoresponse of the nanorods, their crystal structure needed to be modified. Therefore, they were subjected to oxygen plasma in order to reduce oxygen vacancies and repair the crystal structure (defects) of the as-grown n-type ZnO nanorods. Photoluminescence analysis was used to analyze the crystal before and after the plasma treatment. Piezoresponse Force Microscopy (PFM) has also been employed to evaluate the reverse piezoelectric response of the nanorods as an actuator before and after plasma treatment. The magnitude and phase RMS value increase of 27% and 143% was observed after plasma treatment.