High-quality PMMA/ZnO NWs piezoelectric coating on rigid and flexible metallic substrates.

• New piezoelectric structures were deposited on flexible and rigid metallic substrates. • Well-aligned ZnO nanowires were successfully grown by the hydrothermal method. • The structure on the flexible substrate has shown the highest piezoelectric coefficient. • PMMA/ZnO NWs/Ti is a promising piezoelectric structure for nano energy harvesters. This paper reports the comparative study of piezoelectric nanostructures deposited on metallic flexible substrate versus rigid substrates as a new architecture for energy harvesters. Rigid metallic substrates are multi-layered types of Pt/Ti/SiO 2 /Si or Au/Ti/SiO 2 /Si while Ti foil is a flexible metallic substrate. The active piezo-layer consisted of a vertical ZnO nanowires (ZnO NWs) array grown by the hydrothermal method at low temperature, on a previously deposited crystalline seed (nucleation) sol-gel layer and covered with a layer of polymethylmethacrylate (PMMA). The new obtained nanostructures have been characterized in different stages of preparation by X-Ray Diffraction, Scanning and Transmission Electron Microscopy, Atomic Force Microscopy, Spectroscopic Ellipsometry. The piezoelectric performance of PMMA/(ZnO NWs)/Ti structures was evaluated by measuring the d 33 coefficient. Results show that ZnO nanowires have successfully grown on the flexible substrates with a piezoelectric coefficient four times greater than on rigid substrates. By improving vertical integration of ZnO NWs on flexible metallic substrate, PMMA/(ZnO NWs)/Ti affordable nanostructures open the way towards integration in wireless or defence technologies and in wearable or implantable biomedical systems as efficient harvester. [ABSTRACT FROM AUTHOR]