Photodetection and piezoelectric response from hard and flexible sponge-like ZnO-based structures

In this work a comprehensive characterization of sponge-like nanostructured zinc oxide films is proposed, with a marked attention to the exhibited sensing properties. Sponge-like zinc oxide films were grown on different kinds of hard and flexible substrates, by a two-step process involving a room temperature sputtering deposition of metallic sponge-like zinc films, followed by a low-temperature oxidation treatment. This method allowed growing films with thickness of a few micrometers. The material presented a polycrystalline porous structure with randomly oriented grains. After the formation of top electrodes, the sensing properties of the samples were assessed. In particular, the films exhibited UV sensing capability, with photocurrents up to four orders of magnitude higher than the current values measured in dark conditions. The material also showed considerable piezoelectric response: the mechanical stimulus exerted by the impact of a water drop delivered on its surface generated intense piezoelectric output voltage peaks, thus proving material sensing capability. A maximum average output power density of 2.4 nW/cm(2) was calculated. Such interesting properties make sponge-like ZnO a promising smart material for sensing and energy harvesting applications. (C) 2013 Elsevier Ltd. All rights reserved.