Vertically aligned epitaxial KNbO3 nanorod array for piezoelectric energy harvester and second harmonic generator

Vertical alignment of one-dimensional piezoelectric/ferroelectric materials is highly required to take full advantage of their unique electrical and optical properties for various applications. Here, we report the piezoelectric nanogenerator (NG) and second harmonic generator (SHG) applications of a vertically aligned single-crystalline KNbO3 (KNO) nanorod (NR) array on a conducting Nb:SrTiO3 substrate. A simple, cost-effective hydrothermal method at low temperature enables growth of ultra-long orthorhombic KNO NR array with a high piezoelectric coefficient. A corona-poled KNO NR array-based NG generates stable piezoelectric power under the compressive force. The open-circuit voltage and closed-circuit current almost linearly increase. In addition, the KNO NR array emits bright and sharp red, green, and blue visible light under the shining of infrared light. The SHG intensity is strongest along the KNO NR direction and weakest perpendicular to the NR direction. These results imply that the vertically aligned KNO NR array could be useful for an environment-friendly pressure sensor and a full-color display application. (C) 2015 Elsevier Ltd. All rights reserved.