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Direct-CurrentNanogeneratorDrivenbyUltrasonicWavesAbstract:Wehavedevelopedananowirenanogeneratorthatisdrivenbyanultrasonicwavetoproducecontinuousdirect-currentoutput.Thenanogeneratorwasfabricatedwithverticallyalignedzincoxidenanowirearraysthatwereplacedbeneathazigzagmetalelectrodewithasmallgap.Thewavedrivestheelectrodeupanddowntobendand/orvibratethenanowires.Apiezoelectric-semiconductingcouplingprocessconvertsmechanicalenergyintoelectricity.Thezigzagelectrodeactsasanarrayofparallelintegratedmetaltipsthatsimultaneouslyandcontinuouslycreate,collect,andoutputelectricityfromallofthenanowires.Theapproachpresentsanadaptable,mobile,andcost-effectivetechnologyforharvestingenergyfromtheenvironment,anditoffersapotentialsolutionforpoweringnanodevicesandnanosystems.Introduction:Theoperationofnanodevicesfabricatedwithone-dimensionalnanostructures[suchasnanowires,nanotubes,andnanobelts]usuallyrequiresverylowpower,whichisprovidedbyanexternalsource,suchasabatterythatmayhavetobereplacedorrechargedregularly.Therelianceonanexternalpowersourcemaypresentalimitationforthesesystems.Variousapproacheshavebeendevelopedforenergyscavengingwithapplicationsinwirelesselectronics,suchasthermoelectric,piezoelectricthin-film,andvibrationalcantilevers.Wehaverecentlydemonstratedaninnovativeapproachforconvertingnanoscalemechanicalenergyintoelectricenergybypiezoelectriczincoxide(ZnO)nanowire(NW)arrays.BydeflectingthealignedNWswithaconductiveatomicforcemicroscopy(AFM)tipincontactmode,themechanicalenergycreatedbythedeflectionforcewasconvertedintoelectricitywiththeuseofthepiezoelectricpropertiesoftheNWs.Toimprovethepowergenerationcapabilitiesofthesystem,itisnecessarytoreplacetheAFMtipwithasimplersourceofmechanicalenergythatcanactuatealltheNWssimultaneouslyandcontinuously.WesolvedtheseproblemsbyusingultrasonicwavestodrivethemotionoftheNWs,leadingtotheproductionofacontinuouscurrent.Figure1.Nanogeneratorsdrivenbyanultrasonicwave.(A)Schematicdiagramshowingthedesignandstructureofthenanogenerator.AlignedZnONWsgrownonasolid/polymersubstratearecoveredbyazigzagelectrode.Thesubstrateandtheelectrodearedirectlyconnectedtoanexternalload.(B)AlignedZnONWsgrownonaGaNsubstrate.Thegoldcatalystparticlesusedforthegrowthhadbeenmostlyvaporized;thus,thefinalNWswerepurelyZnOwithflattopends.(C)Zigzagtrenchedelectrodefabricatedbythestandardetchingtechniqueafterbeingcoatedwith200nmofPt.Thesurfacefeaturesareduetononuniformetching.(D)Cross-sectionalSEMimageofthenanogenerator,whichiscomposedofalignedNWsandthezigzagelectrode.(Inset)AtypicalNWthatisforcedbytheelectrodetobend.