Integrated multilayer nanogenerator fabricated using paired nanotip-to-nanowire brushes

We present a new approach to a nanogenerator (NG) that is composed of integrated, paired nanobrushes made of pyramid-shaped metal-coated ZnO nanotip (NTP) arrays and hexagonal-prism-shaped ZnO nanowire (NW) arrays, which were synthesized using a chemical approach at <100 °C on the two surfaces of a common substrate, respectively. The operation of the NGs relies on mechanical deflection/bending of the NWs, in which resonance of NWs is not required to activate the NG. This largely expands the application of the NGs from low frequency (approximately the hertz range) to a relatively high frequency (approximately the megahertz range) for effectively harvesting mechanical energies in our living environment. With one piece of such a structure stacked in close proximity over another to form a layer-by-layer matched brush architecture, direct current is generated by exciting the architecture using ultrasonic waves. A four-layer integrated NG is demonstrated to generate an output power density of 0.11 μW/cm ² at 62 mV. The layer-by-layer assembly provides a feasible technology for building three-dimensional NGs for applications where force or pressure variations are available, such as a shoe pad, an underskin layer for airplanes, and next to a vibration source such as a car engine or tire.