Li-ZnO Nanowire Carpet as a Micro-Newton Force Sensor with Nanometer Resolution

ZnO nanowires offer nanometer resolution with high piezoelectric coefficient as force sensors. There is, however, much room to improve the sensitivity with addition of substitutional impurities. Here, the effect of p-type Li-doping on vertically-aligned crystalline piezoelectric ZnO nanowires (NWs) is investigated. The NWs are used as an elementary material to fabricate micro-Newton force sensors based on undoped and Li-doped ZnO nanostructures. The novelty of this work lies on the doping of ZnO NWs with Li that improves its performance by altering the physical and material properties. Scanning Electron Microscope (SEM) images illustrate that the force sensors can realize nanometer scale resolution. X-ray diffraction (XRD) and Raman spectroscopy depict that most of the Li atoms are incorporating into the ZnO structure as substitutional dopants, thus improving the piezoelectric properties. An Atomic Force Microscope (AFM) is operated in contact mode to apply mu N range mechanical force to the nanowires. It is shown that the sensitivity of ZnO NW sensor increases from 0.033 mV/mu N to 0.102 mV/mu N when doped with Li.