Characterization and performance analysis of Li-doped ZnO nanowire as a nano-sensor and nano-energy harvesting element

A complete investigation of the effect of Li doping on the physical, material, electromechanical and piezoelectric properties of ZnO nanowires (NWs) is presented. Low temperature hydrothermal growth technique is used to grow vertically aligned crystalline ZnO NWs doped with different concentrations of Li. Characterization techniques reveal considerable physical, material and electromechanical property modifications of the ZnO NWs due to the incorporation of Li dopants. Atomic Force Microscope is utilized to apply controlled amount of force on the fabricated NWs to assess their piezoelectric response. More than twenty two-fold improvement is observed in sensitivity due to the combined effect of modifications in NW geometry and piezoelectric properties with the addition of Li. Finite element method simulations were performed to decouple the individual effect of Li doping on the NW size and on the piezoelectric coefficient and to see how much each effect plays a role in the sensitivity improvement. It is estimated that the changes in the material and electromechanical properties alone are responsible for more than seven-fold improvement in the sensitivity. The impact of 'kick-out' diffusion mechanism of Li in ZnO is one of the major factors responsible behind this sensitivity improvement. It is also observed that there is an optimum level of Li doping concentration which can lead to the best piezoelectric performance by the ZnO NWs. The novelty of this work lies on the detailed analyses to illustrate the physics and impact of Li dopants in ZnO NW structures from a piezoelectric point of view towards improving their application as a nano-sensing and nano-energy harvesting element.