Direct Piezoelectric Potential Measurement of ZnO Nanowires Using a Kelvin Probe Force Microscope

Precise measurements of the piezoelectric signals are essential for tailoring the properties of ZnO nanowire (NW) based energy conversion devices. We characterize three-dimensional piezoelectric potential profiles of NW arrays using a kelvin probe force microscope (KPFM). A specific device composed of vertically aligned ZnO NWs and thermal responsive polymers is designed for the KPFM test to eliminate surface roughness influence and to avoid mechanical vibrations. The KPFM images show increasing contrasts between the NW and polymer area with the rising temperature, revealing the accumulation of piezoelectric charges. The piezoelectric signals measured by KPFM are around 10 times larger than those measured using external electric circuits.