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Direct-Current Nanogenerator Driven by Ultrasonic Waves
Abstract: We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output.The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap.The wave drives the electrode up and down to bend and/or vibrate the nanowires.A piezoelectric-semiconducting coupling proce converts mechanical energy into electricity.The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires.The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems.Introduction: The operation of nanodevices fabricated with one-dimensional nanostructures [such as nanowires, nanotubes, and nanobelts] usually requires very low power, which is provided by an external source, such as a battery that may have to be replaced or recharged regularly.The reliance on an external power source may present a limitation for these systems.Various approaches have been developed for energy scavenging with applications in wirele electronics, such as thermoelectric, piezoelectric thin-film, and vibrational cantilevers.We have recently demonstrated an innovative approach for converting nanoscale mechanical energy into electric energy by piezoelectric zinc oxide(ZnO)nanowire(NW)arrays.By deflecting the aligned NWs with a conductive atomic force microscopy(AFM)tip in contact mode, the mechanical energy created by the deflection force was converted into electricity with the use of the piezoelectric properties of the NWs.To improve the power generation capabilities of the system, it is neceary to replace the AFM tip with a simpler source of mechanical energy that can actuate all the NWs simultaneously and continuously.We solved these problems by using ultrasonic waves to drive the motion of the NWs, leading to the production of a continuous current.Figure 1.Nanogenerators driven by an ultrasonic wave.(A)Schematic diagram showing the design and structure of the nanogenerator.Aligned ZnO NWs grown on a solid/polymer substrate are covered by a zigzag electrode.The substrate and the electrode are directly connected to an external load.(B)Aligned ZnO NWs grown on a GaN substrate.The gold catalyst particles used for the growth had been mostly vaporized;thus, the final NWs were purely ZnO with flat top ends.(C)Zigzag trenched electrode fabricated by the standard etching technique after being coated with 200 nm of Pt.The surface features are due to nonuniform etching.(D)Cro-sectional SEM image of the nanogenerator, which is composed of aligned NWs and the zigzag electrode.(Inset)A typical NW that is forced by the electrode to bend.
