Finite element method calculations of ZnO nanowires for nanogenerators

The bending of a nonconducting piezoelectric ZnO nanowire is simulated by finite element method calculations. The top part is bent by a lateral force, which could be applied by an atomic force microscope (AFM) tip. The generated electrical potential is 0.3 V. This relatively high signal is, however, difficult to measure, due to the low capacitance of the ZnO nanowire (4x10^{-5} pF) as compared to the capacitance of most preamplifiers (5 pF). A further problem arises from the semiconducting properties of experimentally fabricated ZnO nanowires which causes the disappearance of the voltage signal within picoseconds.