review article piezoelectric nanowires in energy...

Review ArticlePiezoelectric Nanowires in Energy Harvesting Applications

Zhao Wang1 Xumin Pan1 Yahua He1 Yongming Hu1 Haoshuang Gu1 and Yu Wang2

1Hubei Collaborative Innovation Centre for Advanced Organic Chemical Materials Faculty of Physics and Electronic ScienceHubei University Wuhan Hubei 430062 China2Department of Applied Physics and Materials Research Center the Hong Kong Polytechnic University Kowloon 999077 Hong Kong

Correspondence should be addressed to Haoshuang Gu guhshhubueducn and YuWang apywangpolyueduhk

Received 4 December 2014 Accepted 14 April 2015

Academic Editor Sule Erten-Ela

Copyright copy 2015 Zhao Wang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Recently the nanogenerators which can convert the mechanical energy into electricity by using piezoelectric one-dimensionalnanomaterials have exhibited great potential in microscale power supply and sensor systems In this paper we provideda comprehensive review of the research progress in the last eight years concerning the piezoelectric nanogenerators withdifferent structures The fundamental piezoelectric theory and typical piezoelectric materials are firstly reviewed After that theworking mechanism modeling and structure design of piezoelectric nanogenerators were discussed Then the recent progressof nanogenerators was reviewed in the structure point of views Finally we also discussed the potential application and futuredevelopment of the piezoelectric nanogenerators

1 Introduction

Recently portable and wireless micro- and nanoscaleddevices have been widely used in environmental monitor-ing medical implants defense technology industrial safetyand personal electronics such as the nanowire-based gasand chemical sensors [1 2] and programmable nanowirecircuit for nanoprocessors [3] Until now most of themicronanodevices are still working under the driving of con-ventional power sources such as the lion batteries Althoughthe long-term performance and miniaturization of batterieshave been largely improved in recent years the relativelylarger size unavoidable recharging or replacing process maylead to a lot of problems during the fabrication and operationprocess For example the batteries in heart pacemaker needto be replaced after the 6ndash11 yearsrsquo usage which would makethe patient suffering from the surgery and lower their livesrsquoquality Moreover hydrogen sensors have already been usedfor detecting the leakage and concentration of hydrogengas in many fields such as the nuclear power station andgenerator sets The complex power supply lines will lead tohigh potential hazard and limit the development of wirelesssensor networks Therefore the development of novel power

supply systemswithout recharging or replacing problems andmicronanoscaled dimensions has become an attractive topic

In the ambient environment and industrial process mostof the energies such as optical heat mechanical vibration andchemical reaction are wasted The highly efficient harvestingand conversion of such energies may not only be used forbuilding the self-powered devices but also promote thedevelopment of clean and renewable energy sources Amongthem mechanical energy is abundant in the environmentincluding the mechanical vibration hydraulic pressure airflow and rain drops They can be harvested and convertedinto electric output energy through the ldquopiezoelectric effectrdquowhich is so called ldquopiezoelectric electricity generationrdquo Actu-ally this effect has already been practically used inmacroscaledevices For example by installing piezoelectric bulk materi-als such as Pb(ZrTi)O

3(PZT) ceramics and Pb(MgNb)O

3-

PbTiO3(PMN-PT) crystals under the highways the pressure

from the moving vehicles can be converted into electricpowers which is strong enough to illuminate the cautionlights on the highways

In the last decade the development on the synthesistechnique of the piezoelectric nanomaterials has promotedthe miniaturization of the piezoelectric generators [4 5]

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015 Article ID 165631 21 pageshttpdxdoiorg1011552015165631

2 Advances in Materials Science and Engineering

70

60

50

40

30

20

10

02006 2007 2008 2009 2010 2011 2012 2013 2014

Year

Num

ber o

f pub

licat

ions

(a)

2006 2007 2008 2009 2010 2011 2012 2013 2014

Year

2500

2000

1500

1000

500

0

Num

ber o

f cita

tions

(b)

Figure 1 Publication (a) and citation (b) about the piezoelectric nanogenerators according to the data enquired inThomson Reuters ISIWebof Knowledge

Wang and Song firstly reported the piezoelectric ldquonanogener-atorsrdquo in 2006 which can generate impulsive output voltagewith several millivolts by bending a ZnO nanowire with theatomic force microscopy (AFM)rsquos tip [6] This nanogener-ator has attracted great interest of researchers due to thegreat potential in the application of micronanoscaled powersupply systems However the energy conversion efficiencyand output power of this early-stage device are too low tobe applied In the last 8 years researchers have done greatefforts on improving the device performance including theemploying of several kinds of piezoelectric materials withhigher piezoelectric properties [7ndash9] the design of devicestructures [10 11] and the hybrid of nanogenerators withother types of energy harvesters [12 13] Moreover somenovel applications such as the active chemical sensors werealso developed by using the nanogenerators [14 15] As shownin Figure 1 the publication and citation number of researchworks have largely increased from the first report in 2006

In this paper we firstly reviewed the fundamental the-ory about the piezoelectricity and piezoelectric materialsin Section 2 Then the working mechanism modeling andstructural design and the fabrication and performance of thepiezoelectric nanogenerators based on different structureswere discussed After that the application of piezoelectricnanogenerators in recent years was briefly reviewed Finallythe future development of the nanogenerators was alsodiscussed

2 Piezoelectricity and Piezoelectric Materials

21 Definition and Physics of Piezoelectricity Piezoelectriceffect is a unique property of certain crystals where theywill generate an electric field or current if subjected tophysical stress The direct piezoelectric effect was discoveredby brothers Pierre Curie and Jacques Curie in 1880 After thatthe same effect was observed in reverse where an imposedelectric field on the crystal will put stress on its structure

The process whereby the piezoelectric effect takes placeis based on the fundamental structure of a crystal lattice

Crystals generally have a charge balance where negative andpositive charges precisely cancel each other out along therigid planes of the crystal lattice When this charge balanceis disrupted by applying physical stress to the crystals theenergy is transferred by electric charge carriers creatinga current in the crystal With the converse piezoelectriceffect the applying of an external electric field to the crystalwill unbalance the neutral charge state which results inmechanical stress and the slight readjustment of the latticestructure Therefore piezoelectricity is the linear interac-tion between the mechanical and electrical properties ofthe dielectric materials [10] For electrical properties therelationship between the electric displacement (119863

119894) and the

electric field (119864119895) can be interpreted as

119863119894=

3sum119895=1120576119894119895119864119895 (1)

where the coefficient 120576119894119895is the permittivity of the dielectric

materialsThe permittivity coefficient is a second-rank tensorrepresented by a 3times 3matrix However thematrix is symmet-ric (120576119894119895= 120576119895119894) and there are atmost 6 independent coefficients

For mechanical properties the relationship between stressand strain under small deformations can be interpreted as

119879119894119895=

3sum119896119897=1119888119894119895119896119897119878119896119897 (2)

where 119888119894119895119896119897

is the elastic stiffness of the material Equation (2)can also be interpreted reversely as

119878119894119895=

3sum119896119897=1119904119894119895119896119897119879119896119897 (3)

where 119904119894119895119896119897

is the elastic compliance of the materials Becausethe stiffness and compliance coefficients relate to the second-rank tensor stress and strain they are fourth-rank tensorsHowever due to the symmetric stress and strain (119879

119894119895= 119879119895119894

119878119894119895= 119878119895119894) the number of 119888

119894119895119896119897can be reduced to 36 [10]

Advances in Materials Science and Engineering 3

Table 1 Typical piezoelectric material in different category

Category Typical materialsNatural crystals Berlinite (AlPO4) sucrose quartz Rochelle salt topaz and tourmaline-group mineralsNatural materials Bone tendon silk wood enamel dentin DNA and viral proteinsSynthetic crystals Gallium orthophosphate (GaPO4) langasite (La3Ga5SiO14) and diisopropylammonium bromide (DIPAB)

Synthetic ceramics BaTiO3 PbTiO3 Pb(ZrTi)O3 KNbO3 LiNbO3 LiTaO3 Na2WO3 ZnO Ba2NaNb5O5 Pb2KNb5O15 and soforth

Lead-free piezoceramics (KNa)NbO3 BiFeO3 Bi4Ti3O12 Na05Bi05TiO3 and so forthPolymers Polyvinylidene fluoride (PVDF)Organic nanostructures Self-assembled diphenylalanine peptide nanotubes (PNTs)

In reduced notation the piezoelectric constitutive equa-tion can be interpreted as [10]

119863119894= 120576119879

119894119895119864119895+119889119894119869119879119869

119878119868= 119889119868119895119864119895+ 119904119864

119868119869119879119869

(4)

where the superscripts 119879 and 119864 mean the coefficients areat constant stress and electric field respectively The 119889

119894119869

in (4) is the piezoelectric straincharge constant Underthe one-dimensional simplified hypothesis the piezoelectricconstitutive equation can also be interpreted as follows

119878 = 119904119864119879+119889119864

119863 = 119889119879+ 120576119879119864

(5a)

119878 = 119904119863119879+119892119863

119864 = minus119892119879+119863

120576119879

(5b)

119879 = 119888119864119878 minus 119890119864

119863 = 119890119878 + 120576119878119864

(5c)

119879 = 119888119863119878 + ℎ119863

119864 = minus ℎ119878 +119863

120576119878

(5d)

Among them 119889 119890 119892 and ℎ are piezoelectric constant and canbe linked as

119889 = 120576119879119892 = 119904119864119890

119890 = 120576119878ℎ = 119888119864119889

119892 =119889

120576119879= 119904119863ℎ

ℎ =119890

120576119878= 119888119863119892

120576119879= 120576119878+119889119890

(6)

22 Typical Piezoelectric Materials Until now several kindsof materials have exhibited piezoelectricity including both

natural and synthetic materials which are listed in Table 1Among them piezoelectric ceramics crystals and polymerswere most developed and useful piezoelectric materialsPiezoelectric ceramics usually refer to polycrystalline mate-rials that consisted of irregular collective small grains andare prepared through the solid-state reaction and sinter-ing process Under the poling electrical field the disor-dered spontaneous polarization in piezoelectric ceramicscan be realigned and keep the remnant polarization afterthe removal of external field As a result the piezoelectricceramics can exhibit macropiezoelectric property Piezo-electric crystals which refer to single-crystalline materialsare usually unsymmetrical in structure and therefor exhibitpiezoelectric property

The piezoelectric ceramics exhibit high piezoelectricconstant and permittivity and can be prepared into designedarchitectures which makes them suitable for the applica-tion in high-power energy transducer and wideband filtersHowever the poor mechanical quality factor high electricalloss and low stability of the piezoelectric ceramics limitedtheir application in high-frequency devices Comparativelythe natural piezoelectric crystals such as quartz exhibit lowerpiezoelectric properties and dielectric constant Moreoverthey are limited in size due to the cuts of crystals Howeverthe mechanical quality factor and stability of quartz crystalsare relatively higher than ceramics Therefore quartz crystalsare always used in high-frequency filters transducers andother standard frequency controlling oscillators Besidesthe quartz crystals the high-quality perovskite piezoelectricsingle crystals such as the Pb(A

13B23

)O3-PbTiO

3(A =

Zn2+ Mg2+ B = Nb5+) with much higher piezoelectricconstant (119889

33sim 2600 pCN) electromechanical coupling

coefficient (11989633sim 095) and strain (gt17) have also

been obtained since 1997 [16 17] These single crystals arenew-generation piezoelectric materials for high performancepiezoelectric devices and systems including ultrasound med-ical imaging probes sonars for underwater communicationsand sensorsactuators However the size and shape of thepiezoelectric single crystals are difficult to be preciously con-trolled during the growth process which limit the practicalapplication in many fields such as the microscaled actuatorsand composite metamaterials

Furthermore the piezoelectric polymers such as polyvi-nylidene fluoride (PVDF) with high flexibility low density


and resistance as well as relatively higher piezoelectricityvoltage constant (119892) have also attracted much attention inrecent years [18 19] Unlike the piezoelectric ceramic andcrystals the intertwined long-chain molecules in polymersattract and repel each other when an electric field is appliedPVDF has exhibited great potential in the application ofacoustic ultrasound measurements pressure sensors andignitiondetonations However the relatively low piezoelec-tric strain constant (119889) of PVDF limited the application intransducers

23 Applications of Piezoelectric Materials Nowadays piezo-electric materials have been widely used in the industrialmanufacturing automotive industry and medical instru-ments as well as information and telecommunication fieldsand so forth According to the operation mode of the piezo-electric devices the application of piezoelectric materials canbe classified as follows

(1) SensorsThrough the direct piezoelectric effect the piezo-electric materials can be used for the detection of pressurevariations in longitudinal transversal and shear modes Themost commonly used application of piezoelectric sensors isin the sound form such as the piezoelectric microphonespiezoelectric pickups in acoustic-electric guitars and detec-tion of sonar waves Moreover the piezoelectric sensors canalso be used with high-frequency field such as the ultrasonicmedical imaging or industrial nondestructive testing Inaddition the piezoelectric sensors were also employed inpiezoelectric microbalance and strain gauges

(2) Actuators On contrary to piezoelectric sensors theworking of actuators is usually based on the reverse piezo-electric effect to induce tiny changes in the width of thepiezoelectric materials by applying high electric fields Dueto the relatively high precision of the width changes thepiezoelectric actuators are always used in accurate posi-tioning For example the piezoelectric motors with highaccuracy have already been used in optical devices trans-portation and aerospace techniques robots medical devicesbiology and nanomanipulation fields such as the atomicforce microscopes (AFM) scanning tunneling microscopes(STM) autofocusing camera lens inkjet printers CTMRIscanners and X-ray shutters

(3) Frequency ControllingDevicesCrystal oscillator is an elec-tronic oscillator circuit that uses the mechanical resonance ofa vibrating piezoelectric crystal to create an electrical signalwith a very precise frequency The frequency can be used toprovide a stable clock signal for digital integrated circuitsMoreover the piezoelectric materials have also been usedin high-frequency resonators and filters such as the surfaceacoustic wave devices and film bulk acoustic resonators

(4) High Voltage and Power Sources By applying the externalmechanical stimulates the piezoelectric ceramic or crystalscan generate potential differences with thousands of voltsin amplitude Therefore piezoelectric materials can be usedas high voltage and power sources The most commonly

application is the piezoelectric ignitionsparkers such asthe cigarette lighters Moreover the piezoelectric materialshave been employed for energy harvesting applications Forexample the energy from human movements and vehiclemovements in public places can be harvested and convertedinto electricity for lighting the lamps Recently themicroscaleenergy harvesters were developed for harvesting the small-scale mechanical energies by using the piezoelectric nano-materials which is called ldquopiezoelectric nanogeneratorsrdquoThenanogenerators can be used for charging the batteries ordirectly driving some low-power microdevices The recentprogress of piezoelectric nanogenerators will be reviewed inthe next section

3 Piezoelectric Nanowires for EnergyHarvesting Applications

The first research work about the piezoelectric nanogener-ators was reported by Wang and Song in 2006 After thatnumerous research works have been conducted about theworking mechanism structural modeling and design andperformance optimization of the piezoelectric nanogener-ators Until now several kinds of flexible nanogeneratorshave been developed which could be used for harvest-ing that varies mechanical energies from the environmentor human bodies The output electrical energy has beenincreased from several millivolts to several hundred voltswhich is enough for driving a light-emission diode (LED)liquid crystal display (LCD) and wireless data transmittingdevice In this section the author briefly reviewed theworking mechanism modelingsimulations and the exper-imental progress of piezoelectric nanogenerators accordingto the structure of the nanogenerators including the vertical-aligned nanowire arrays the lateral-aligned nanowire net-works and the nanowire-based nanocomposites

31 Vertical-Aligned Nanowire Arrays

311 Working Mechanism and Structural Modeling Two dif-ferentworkingmodels can be used for describing theworkingprocess of the nanogenerators based on vertical-alignednanowire arrays including the lateral bending and verticalcompression Due to their different electrical andmechanicalconfigurations the workingmechanism is different in certaindegrees but with one consistent basis the coupling of thesemiconductor behavior and the piezoelectric property of thepiezoelectric nanowire

Figure 2 illustrated the working mechanism of the nano-generator based on a bending nanowire induced by an AFMtip [20] As shown a Schottky barrier was built up betweenthe nanowire and the AFM tip due to the difference ofworking function and electron affinity The system was inan equilibrium state and no voltage output was generatedwhen the nanowire is not bent by the AFM tip Once thenanowire was bent by the scanning AFM tip the asymmetricpiezoelectric potential would be generated due to the stretchand compression of the inner and outer side of the nanowireThe piezoelectric potential in the nanowire changed the


T

T T

G

G G G G

minus

VB

CB

e

e

e e

e

ee

e

ee

EF

ΦSB

V998400minus

V998400+

V998400998400minusV998400998400minus

V998400998400+V998400998400+

T T

(a) (b) (c) (d)

minusminus +

VB

Pt ZnO Ag

CB

Symbol of piezoelectricnanogenerator

e

EF

qVNG

Cath

ode +

Ano

de

asymp

(e)

Figure 2 The band diagram for understanding the charge output and flow processes in a nanogenerator with lateral bending model (a)Before bending (b) nanowire bent by the tip with the tip point at the stretched surface (c) tip scans across the nanowire and reaching themiddle point (d) tip reaching the compressed surface of the nanowire (e) energy-band diagram for the nanogenerator presenting the outputvoltage and the role played by the piezoelectric potential (Reproduced from [20] with the permission from WILEY-VCH Verlag GmbH ampCo KGaA Weinheim)

profile of the conduction band As shown in Figure 2(b)the local positive piezoelectric potential at the contact areawould lead to a slow flow of electrons from ground to thetip through the external load which resulted in the chargeaccumulation in the tip When the tip was moved to themiddle part of the nanowire the local potential dropped tozero and resulted in a back flow of the accumulated electronsthrough the load to the ground (Figure 2(c)) After that if thetip wasmoved to the compressive part of the nanowire a localnegative piezoelectric potential would raise the profile of theconduction band and led to an electron flow from the 119899-typeZnO to the tipTherefore a circular flowof electronswould begenerated and exhibited output current in the measurementdevices [23]

For nanogenerators with vertical compressed nanowirearrays the piezoelectric nanowires were connected by a pairof electrodes on the top and bottom end with at least oneSchottky contact in the interface The compressive deforma-tion was induced symmetrically along the longitude of thenanowires As a result the piezoelectric potential should be

well-distributed along the axial direction of the nanowireTherefore its working mechanism was different from thebendingmodels As shown in Figure 3 the alternative electricoutput could be attributed to the back and forth flow ofelectrons in the external circuit driven by the piezoelectricpotential [23 24] Without the external stress the system wasin an equilibrium state and no voltage output would be gen-erated (Figure 3(a)) Once the nanowire was compressed byexternal force the piezoelectric potential would be inducedalong the nanowire Consequently the conduction band edgeand Fermi level of the negative-potential side would be raisedby the piezoelectric field as shown in Figure 3(b) Due to theSchottky barrier on both sides of the nanorod the electroncould not pass through the interface between the nanowireand electrodes to compensate the energy difference andwould flow through the external circuit to the electrode on thecounter sideTherefore an impulsive electric output would begenerated The electrons were then accumulated due to theSchottky barrier and reached an equilibrium state with thepiezoelectric field to make the Fermi energy back to the same


Au Au

RL

120601B

(a)

eminus

Au Au

V+p Vminus

p

120601BΔEp

(b)

Au Au

V+p Vminus

pminus +

120601B

(c)

eminus

Au Au

minus +

120601B

(d)

Volta

ge (m

V)

Time (s)

20

10

0

minus10

minus200 5 10

(e)

Figure 3 Band diagram for understanding the charge output and flow process in the nanogenerator with compressed nanowire (a) Beforepressing (b) Nanowire vertically compressed by external force (c) Equilibrium state under strain state (d) Release of pressure (e) Outputvoltage

level which led to no more electrical output in the externalcircuit (Figure 3(c)) When the compression was released asshown in Figure 3(d) the piezopotential was vanished whichwould break the equilibrium state Therefore the energydifference would be induced on the opposite direction andlead to an impulsive negative electrical output signal

Because of the complex and expensive fabrication andcharacterization and integration process of piezoelectricnanogenerators the accurate modeling and performancesimulation about the electromechanical conversion behaviorof the nanowires were important before the experimentalworks For example Falconi and coauthors have conductedfinite element method (FEM) simulation works to estimatethe output potential and stored electrostatic energy of aZnO nanowire under various deformation configurationswith different positions of the contacts [10 11] In order tosimplify the FEM modeling process the nonlinear behaviorof Schottky contact uncertain load in the external circuitnonzero electrical conductivity of piezoelectricmaterials andparasitic effectswere neglectedThe simulationwas simplifiedas to qualitatively compare the static piezoelectric potentialgenerated by nanowire with different structureTheir simula-tion result suggested that the electrode contact configurationwould have great impact on the piezoelectric potential of abending nanowire Because the highest strain was distributedat the bottom regain of the nanowires the highest piezo-electric potential difference between the electrodes can beobtained when the electrodes were set up on both sides at thebottom of the nanowire However it is difficult to obtain thiskind of nanoscaled electrodes in practical experiments Theyalso compared the performance of bending nanowires withthe vertically compressed nanowires and found that the latterone exhibited higher energy conversion efficiency than thebending nanowires with the same electrode configurationsAccording to their results the vertical compression modelwith relatively higher electrical output and simplified struc-tures is more suitable for the practical applications than thebending models However the influence of free charge in thenanowires to the electromechanical conversion efficiencywasnot considered in this work which has been reported to be akey issue for the piezoelectric nanogenerators

Recently the polarization screening effects induced bythe free charge carriers have been regarded as an importantissue for optimizing the electromechanical conversion effi-ciency of the piezoelectric nanowires However it was verydifficult to precisely control the concentration of dopant inpiezoelectric nanowires in practical experiments Thereforethe computer analysis through FEM can be used to predictthis effect For example Gao and Wang have investigatedthe behavior of free charge carriers in a bent piezoelectricsemiconductive nanowire under thermodynamic equilib-rium conditions [25] They found that the positive side ofthe bent nanowire would be partially screened by the freecharge carriers because the conduction band electrons wouldbe accumulated at the positive side under the piezoelectricpotential Therefore the potential in positive side is muchlower than the negative side Moreover Falconi et al haveinvestigated the screening effect in a vertically compressednanowire and found that the piezoelectric potential wouldbe almost completely screened by the free charge carriers ata higher level of donor concentrations They also confirmedthat the length of the vertically compressed nanowire did notsignificantly affect the maximum value of the piezoelectricpotential while the relative dielectric constant surroundingthe nanowire would significantly influence the output voltage[26]

312 Fabrication and Performance of Vertical IntegratedNanogenerators After finding that the AFM tip-inducedlateral bending of nanowire (ZnO GaN CdS InN and ZnS)can generate impulsive voltage output [27ndash31] another kindof nanogenerator with similar mechanism was carried outIn this device the AFM tips were replaced by a zigzag topelectrode to bend the nanowires [32] Qin et al have alsoreported a similar nanogenerator with two fibers coated bythe ZnO nanowire arrays [21] As shown in Figure 4 theyentangle the fibers and brush the nanowires with each otherto make the ZnO nanowires bending This nanogeneratorcan generate voltage with approximately 1mV in amplitudeAlthough these early-stage nanogenerators have attracted alot of attention the complicated fabrication process as well as


+minus

Fixed end

Fixed end

Pulling string

Fibre coveredby ZnO NWs

Fibre covered by ZnO Stretchingdirection

Spring Fixed end

NWs and coated with Au

(a)

(b)

(c)

I II

Fibre base

Fibre base

Au coatedZnO NWs

ZnO NWs

(d)

I II

Stretching direction

V+

Vminus

(e)

I II


V+V+

VminusVminus

(f)

Figure 4 Design and electricity-generating mechanism of the fibre-based nanogenerator driven by a low-frequency external pulling force(Reproduced from [21] with the permission of Nature Publishing Group)

the low electrical output and poor stability makes them notsuitable for practical application

According to the modeling discussed above the verticalcompress of nanowires could generate higher output voltagethan the top-bottom contacted bending nanowires Xu et alhave fabricated a vertical nanowire array integrated nano-generator (VING) [33] As shown in Figure 5 the device wasfabricated by packaging the vertical-aligned ZnO nanowirearray with polymethyl methacrylate (PMMA) and connectedthe nanowire with top-bottom flat electrodes which cangenerate several tens ofmillivolts in amplitude under externalpressures The fabrication process of the VING is muchsimpler than the bending type nanogenerators Moreoverthe packaging of PMMA can largely increase the robustnessof the devices Due to the easy synthesis process of ZnOnanowire arrays ZnO VING has become the most populardesign among the reported nanogenerators Several improve-ments have been carried out by researchers For example Kimet al have demonstrated a ZnO VING based on cellulosepaper substrates which could increase the thermal stabilityof the VINGs [34] Choi and coworkers have reported a ZnO

VING based on transparent and flexible graphene electrodes[35] The nanogenerator can be fully rolled for the energyharvesting and converting processThe output current of thisdevice is up to 2-3mAcm2 under nonrolling and rollingstate Besides the conventional VINGs some novel designson the architecture of VINGs have been demonstrated byresearchers For example Hu et al have fabricated a ZnOVING which is a free-standing cantilever beam made ofa five-layer structure [36] By depositing the ZnO seedCrlayers on the top and bottom surfaces of the polyester (PS)substrate the densely packed ZnO nanowire texture filmswere synthesized and then covered by PMMA as blockinglayer Finally the top electrodes were deposited on top ofboth PMMA layers and the whole system was packaged byPDMSThe layered VINGs can generate open-circuit voltageup to 10V and short-circuit current up to 06 120583A when it wasstrained to 012 at a strain rate of 356s

As mentioned above the free charges in 119899-type ZnOnanowires will screen the piezoelectric potential That willdecrease the output voltage of the ZnO nanogenerators


(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)

Figure 5 (a) Schematic diagramof the fabrication process of theVING (b)Theoutput voltage of theVINGunder different external pressures[Reproduced from [22] with the permission from Nature Publishing Group]

Until now two major approaches have been employed fordecreasing of the screening effect Firstly it can be real-ized by improving the intrinsic properties of ZnO throughpretreatment and surface passivation and so forth Forexample Hu et al have improved the single-layered VINGsrsquoperformance with maximum output voltage up to 20V andoutput current up to 6120583Aby treating the ZnOnanowireswithoxygen plasma or annealing in air [37] Moreover the outputperformance of the ZnO nanorod based nanogeneratorscould also be improved by inducing the ultraviolet light topassivate the surface [38] A similar work was also reportedby Lin et al where the output of CdS nanowire can be

modified by using a white light stimulation [27] Secondlythe screening effect could also be suppressed by changing thestructure of the devices For example Zhu and coworkershave reported a novel design of ZnO VING [39] It couldgenerate high electrical output (119881OC = 58V 119868SC = 134 120583A)due to the new structures due to the thin layer of PMMAbetween the top of the nanowires and the top electrodeswhich could provide a potential barrier of infinite heightThebarrier could prevent the induced electrons in the electrodesfrom internal leaking through the interface between metaland semiconductor The segmentation of nanowire arraysalso guaranteed that the native free-charge carriers within the


nanowires that are not directly compressed will be isolatedfrom the compressed nanowires (Figure 6) This part of thenanowireswill not be involved in the screening effect and pre-serving the piezoelectric potential from further degradationBesides the structure design some other method such as thetreatment to the piezoelectric nanowire could also decreasethe screening effect

As known the piezoelectric constant is critical for theelectromechanical conversion efficiency of the piezoelectricnanowires The relatively low piezoelectric constant of ZnOlimited the performance of the nanowire in the VINGsPerovskite piezoelectric materials such as Pb(ZrTi)O

3(PZT)

exhibited much higher piezoelectric constant than ZnOmaterials which may lead to higher energy conversionefficiency and electric output of the nanogenerators Forexample the PZT nanowire array could generate higheroutput voltage than the ZnO nanowires with the samedevice architectures [40] However the difficult synthesisprocess of the perovskite nanowire arrays has limited theresearch and development of such kind of nanogeneratorsThe flexibility was also limited by the substrate used formaterial growth (eg NbSrTiO

3single crystals) Gu et al

have provided a feasible way to overcome the problem offlexibility where the ultra-long PZT nanowire arrays werefabricated by stacking the lateral-aligned PZT nanofiberslayer by layer and connected by top-bottom electrodes [7]This device produced ultra-high output voltage up to 209Vtogether with the current density of 235 120583Acm2 whichcould instantaneously power up a commercial LED withoutany energy storage unit Moreover Kang and coworkers havereported a lead-free piezoelectric nanogenerator based onvertically aligned KNN nanorod arrays The nanogeneratorexhibited a stable high power density of sim101120583Wcm3 [41]

32 Lateral-Aligned Nanowire Networks

321 Working Mechanism and Structural Modeling In thistype of devices the deformation of the nanowires wasalways induced by the laterally bending of the nanowireseither through the bending of substrate or through thepressure applied along the radical direction of the nanowiresUnlike the local bending of nanowires in the vertical-aligned nanogenerators the nanowires were uniformly bentin these processes Due to the ultra-high aspect ratio of theone-dimensional nanostructure the uniform lateral bendingbehavior of the nanowires can be regarded as the lateralstretching by neglecting the strain distribution along theradical direction Therefore the working mechanism of thenanogenerators based on lateral-aligned nanowires was thesame as the compressed nanowires mentioned in the abovesection

In Falconirsquos work they also compared the energy con-version behavior of the laterally stretched nanowire with thevertically compressed ones [26] They have found that thelaterally bent nanowire can generate higher output voltagethan the later one However the external forces were directlyapplied on the nanowires In practical devices the nanowireswere usually packaged by soft polymers such as PDMS

silicone to protect them from the physical damage Theexternal forces need to be applied on the packaging layersrather than on the nanowires Therefore the distributionof the applied forces on the nanowires will be differentAs a result the influence induced by the packaging layershould be taken into account during the modeling of thenanogenerators Figures 7 and 8 show the modified modelsof nanogenerators with silicone packaging layers for verticaland lateral packaged devices respectively The silicone is10 120583m in thickness and 150 in width comparing with thediameter of the nanorod In vertically compressed modelthe nanorod was vertically standing fixed at the end andpackaged by the silicone An external force along the axialdirection of the nanorod was applied on the top surfaceof the silicone Under the compressing force the nanorodwas vertically compressed and generated a piezoelectricpotential of sim350mV between the top surface and the bottomsurface

In lateral stretching model the nanorod with the samepiezoelectric parameters was laterally positioned betweentwo Au electrodes and packaged by the siliconeThe pressurewas applied on the top surface along the radial directionof the nanorod As shown in Figure 8(c) the nanowire wasbent under the radial compressing force The piezoelectricpotential difference can be calculated to be sim274V byintegrating the electric field along the axial direction of thenanorod These results indicated that the lateral assemblednanorods can generate much higher piezoelectric potentialthan the vertical assembled ones under the same externalpressure which may provide the insight for the design ofpiezoelectric nanogenerators

322 Fabrication and Performance of Laterally IntegratedNanogenerators The first lateral type of piezoelectric nano-generator is reported by Wang and coauthors in 2007 [44]This device is based on the voltage generation of an individualBaTiO

3nanowire under periodic tensile mechanical load

which is fabricated by placing a BaTiO3nanowire onto a

piezoelectric flexure stage by using nanomanipulation tech-nique The lateral strain was applied by moving the mobilebase of the stage by using a piezo stack driving by externalvoltage fixing the other base The fabrication process of theflexure stage is complex and expensive due to the smalldimension On the contrary lateral nanogenerators based onflexible polymer substrates such as the polyimide (PI) filmshave exhibited much simpler fabrication process and higherperformance

Yang et al have reported a laterally integrated nano-generator (LING) based on laterally packaged piezoelectricfine wires [42] The ZnO fine wire lying on the PI substratewas fixed to electrodes at both ends The bending of thesubstrate would result in a stretch behavior of the wire andlead to a drop in the piezoelectric potential along the wireTherefore an impulsive and alternative output would begenerated by the charge flow in the external circuit Thenanogenerator based on single fine wire can generate outputopen-circuit voltage and short-circuit current of 60ndash70mVand 1000ndash1100 pA in peak to peak amplitude respectively


(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)

Figure 6 (a)The fabrication process of the segmented ZnO nanowire VINGs (b)The generated electrical signal and FEM simulation results[Reproduced from [39] with the permission of American Chemical Society]


Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod

0minus50minus100minus150minus200minus250minus300minus350 Pi

ezop

oten

tial (

mV

)

(d)

Figure 7 FEM static simulation of the electromechanical conversion behavior of a vertically compressed device (a) Schematic diagram ofmodel (b) The deformation of silicone (c) The deformation of nanorod (d) The piezoelectric potential of nanorod

FixedFixed

NanorodAu

Au

Silicone

FA = 1 times 106 Nm2

10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)

Figure 8 Static simulation of the electromechanical conversion behavior of a lateral stretch device (a) Schematic diagram (b) Deformationof silicone (c) Deformation of nanorod (d) Piezoelectric potential of nanorod


Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de

Growth direction of ZnO nanowires

Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)

Figure 9 The structural characterization and output performance of the ZnO LINGs (a) Schematic diagram (b) Local SEM image(c) Photograph of a packaged device (d) Output open-circuit voltage (e) Output short-circuit current (Reproduced from [42] with thepermission from Nature Publishing Group)

Moreover the potassium sodium niobate (KNN) nanorod-based LINGs were fabricated by our group As known thepiezoelectric constant of the biocompatible KNN is muchhigher than ZnO and the free charge carrier density inKNN is lower than ZnO The KNN nanogenerators mayhave higher electromechanical conversion efficiency thanZnO-based nanogenerators In our KNN-LINGs the KNNnanorods synthesized by hydrothermal and parallel con-nected by interdigitated electrodes (IDEs) on a flexible PIsubstrate The PDMS packaged KNN LINGs can generateparallel open-circuit voltage of about 01 V under finger press-ing or bending movements [23 45] However the fabricationprocess of such devices is complex which would limit thelarge-scale fabrication of the nanogenerators

In order to improve and simplify the fabrication processof LINGs Zhu and coauthors have carried out a scalable

sweeping-printing-method for fabricating flexible deviceswith ZnO nanowire array which were connected by parallelstripe type of electrodes [22] The generated open-circuitvoltage was up to 203V due to the series connection ofnanowires while a peak output power density of 11mWcm3was obtained Another method for one-step fabrication ofZnO nanowire networks was reported by Xu and coworkers[33] As shown in Figure 9 the nanowires were directlysynthesized between the AuCr and Au electrodes by low-temperature chemical method and were oriented-alignedwith parallel to the substrate surface By this direct integrationprocess more than 700 rows of nanowires can be connectedin series to increase the output of the nanogenerator whichis up to 12 V in open-circuit voltage and 26 nA in short-circuit current at a strain rate of 213s and strain of019


PZT nanofibersPDMS polymer

Platinum finewires electrodes

Silicon substrate

sim05mm

Extraction electrodes

Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)

Voltagegenerated fromfast knocking PZT

nanogenerator

Teflon stack

+

minus

System vibration inresonant frequency

minus010 05 1 15 2 25 3 35 4

Time (s)

(b)

Figure 10 The PZT nanofiber-based LING (a) and the generated open-circuit voltage (b) (Reproduced from [43] with the permission fromAmerican Chemical Society)

Recently the development of electrospinning techniqueshas promoted the application of the ultra-long piezoelectricnanofibers in the energy harvesting devices which couldalso realize the large-scale fabrication of the LINGs [43 46]For example Chen et al have demonstrated a 16 V LINGbased on electrospun PZT nanofibers [43] As shown inFigure 10 the PZT nanofibers were directly fabricated on theIDEs by electrospinning and annealing process After PDMSpackage and poling the PZT LING can generate open-circuitvoltage up to 16 V under the pressure from a Teflon stackor human finger However the flexibility of the PZT LINGwas limited by the substrate due to the high-temperatureannealing process Wu and coauthors have fabricated a PZTtextile nanogenerator with parallel-aligned PZT nanofiberstransferred from the substrate to a polyethylene terephthalate(PET) film [47] The wearable LING can generate open-circuit voltage and short-circuit current up to 6V and45 nA respectively Moreover the lead-free Mn-doped KNNnanofibers were used for fabricating the flexible LINGs bytransferring the annealed KNN nanofibers onto a flexiblepolyether sulfone (PES) substrate through PDMSThis deviceexhibited sim03 V output voltage and sim50 nA output currentunder a bending strain [48]

Polyvinylidene fluoride (PVDF) nanofibers were alsoemployed in LINGs Compared with the inorganic per-ovskite piezoelectric materials PVDF nanofibers exhibitedbetter flexibility lightweight biocompatibility and ultra-longlengths which is more suitable for fabricating biocompatibleand flexible nanofiber-based nanogenerators (Figure 11) [4657] As known the electrospun PVDF nanofibers couldtransform from nonpolarized 120572-phase to polarized 120573-phasestructures under the ultra-high electrical field Chang andcoworkers have demonstrated a LING based on a singlePVDF nanofiber fabricated by a near-field electrospinningprocess [58] Under mechanical stretching the nanogener-ator exhibited repeatable and consistent electrical outputs

with energy conversion efficiency higher than the PVDFthin-film based nanogenerators The open-circuit voltageand short-circuit current of this nanogenerator are 5ndash30mVand 05ndash3 nA respectively In order to increase the outputthey have fabricated 500 parallel nanofibers and connectedthem with comb-shape electrodes on flexible substrate toamplify the current outputs [59] The peak current wasincreased to 35 nA with 02mV in peak voltage Zhao andco-authors have demonstrated a hybrid LING that consistedof the piezoelectric PVDF nanofibers fabricated by far-field electrospinning process [14] The PVDF nanofiberswere patterned into lateral-aligned arrays on the substrateand were poled with high field (200 kVcm) for 15minThe output voltage and current can be increased from15 to 20mV and 02 to 03 nA by increasing the strainrate of the device respectively A detailed review aboutthe nanofiber-based LINGs until 2012 was demonstratedby Chang et al [46] Moreover poly(vinylidenefluoride-co-trifluoroethylene) nanofibers have also been employed forhigh-performance flexible piezoelectric nanogenerators [6061] These devices can also be used for mechanical energyharvesting and ultra-highly sensitive sensing of pressureZeng et al have combined theNaNbO

3 PVDF and the elastic

conducting knitted fabric nanofibers to obtain all fiber basednanogenerators which could generate output voltage of 34 Vand current of 44 120583A at 1Hz and a maximum pressure of02MPa [62]

33 Nanowire-Composite Recently a novel type of piezoelec-tric nanogenerators based on nanowire-polymer compositeshas attracted researcherrsquos attentionThe fabrication process ofsuch devices ismuch simpler thanVINGandLING Basicallythe device consisted of four functional layers including thetop and bottom electrodes the flexible substrate and mostimportantly the nanowire-composite layer The multilayerstructure of these devices was similar to the piezoelectric


Gold electrode

Nanofibers

Current flow

Flexible polymersubstrate

VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff

Near-field electrospinning

PDMS

VampI

(c)

Figure 11 Schematic diagram (a) photograph (b) and fabrication process (c) of a PVDF LING (Reproduced from [46] with the permissionfrom Elsevier)

Table 2 The energy conversion performance of the reported nanogenerators based on nanowire composite

Piezoelectric materials Polymer Output voltage Strain Strain rate Reference

Piezoelectric semiconductor ZnO nanowires PMMA 2V 011 367s [49]GaN nanowires PMMA 12V mdash mdash [50]

BaTiO3 Nanotubes PDMS 55V mdash mdash [51]ZnSnO3 Nanobelts PDMS 53V 01 16Hz [52]

Lead-free niobatesNaNbO3 nanowires PDMS 32V 023 128s [9]

LiNbO3 nanowires PDMS sim04V 0093 (e31)00168 (e33)

mdash [53]

KNbO3 nanowires PDMS 105 V mdash mdash [54]

Lead-based piezoelectrices PMN-PT nanowires PDMS 78V mdash mdash [55]PZT nanowires PDMS 7V mdash mdash [56]

ceramics Although the piezoelectric properties of the com-posite may be lower than the ceramics the polymer matrixlargely increased the flexibility of the devices

For VINGs the device fabrication was largely limited bythe assembly process of the nanowire arrays Therefore mostof the investigation of VINGs was focused on ZnO nanowirearrays while LINGs were also suffering from the sameproblem However the nanowire-composite can be easilyobtained by directly mixing the as-synthesized nanowireswith the polymer matrix such as the PDMS Therefore itwas a general structure for building nanogenerators Table 2listed the reported nanowire-composite nanogenerators withdifferent piezoelectric materials For example Hu and coau-thors have demonstrated the high output nanogenerators byrational unipolar assembly of conical ZnO nanowires [49]The macroscopic piezoelectric potential across the thicknessof the nanogenerator with output voltage up to 2V can beproduced under a compressive strain of 011 at a strain rate

of 367s A similar structure was also reported by Jung etal by using NaNbO

3and GaN nanowires composited with

PDMS between a pair of electrodes respectively [9 50] Theoutput voltage and current density of the NaNbO

3-based

device are up to 32 V and 72 nAunder a compressive strain of023 (Figure 12) Recently Xu et al have reported the PMN-PT nanowire-based nanocomposites and nanogenerators[55] The output voltage and current density of this PMN-PTcomposite nanogenerator are up to 78V and 458 120583Acm2Moreover PZT nanowires have also been employed forbuilding the nanocomposites nanogenerators and the outputvoltage was up to 7V with manual bending This devicecan also be used to harvest the energy from the vibrationof the cantilevered at the low frequency range [56] Thiskind of nanogenerators has exhibited high output togetherwith simple and low-cost fabrication process without anymicrofabrication process and can be considered as a rationaloption for the large-scale fabrication of nanogenerators


(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)

Figure 12 The structure and characterization of NaNbO3nanogenerators (a) Photograph of NaNbO

3nanowire powder (b) Structural

diagram of the NaNbO3nanogenerators (c) AFM and SEM images (d) The working mechanism of the NaNbO

3nanogenerators

(Reproduced from [9] with the permission from American Chemical Society)

34 Application of Piezoelectric Nanogenerators In recentyears several research works about the harvesting of differentmechanical energies by the piezoelectric nanogeneratorshave been conducted by researchers which promoted theirpractical applications in various fields For example thenanogenerators can be used to harvest the biomechanicalenergies from the bending of a human finger folding andreleasing of a human elbow the running motion of a livinghamster [63] (Figure 13) Moreover an in vivo nanogeneratorthat can convert the mechanical energy from the breath andheartbeat of a living rat into electrical outputs have alsobeen reported [65] Besides the energy from the human andanimal bodies many kinds of mechanical energies in theenvironment can also be harvested by the nanogeneratorsincluding the mechanical pressures from a moving vehicle[64] and raindrops [66] as well as the vibration inducedby liquid and air flows [67ndash71] According to the above-mentioned behavior several kinds of applications based onthe piezoelectric nanogenerators have been demonstratedincluding the power sources for driving microelectronic

devices the active sensors the self-powered sensors andsome hybrid cells for energy sources

341 Power Source for Driving Electronic Devices As knownpiezoelectric nanogenerators have been viewed as one of themost promising candidates in the microscale power supplysystems for driving the microelectronic devices Howeverthe electrical output of the piezoelectric nanogenerators isactually generated due to the back and forth motion ofelectrons in the external circuit driving by the piezoelectricpotential Therefore it is necessary to convert the alternativeand impulsive electrical output signals into direct-current(DC) signals to drive the electronic devices for exampleby bridge rectifiers In the early-stage ZnO nanogeneratorsthe output voltage and power density are limited Thereforea charge storage unit such as a capacitor was usually usedfor the accumulation of electric energy generated by thenanogenerators After the charging process the system canbe used for driving some electronic devices such as LED


20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)

minus10 minus05 00 05 10

Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)

Figure 13The application of single wire nanogenerator for harvesting the biomechanical energies (a) Finger bending (b) Hamster running(c) Rat breath (d) Rat heartbeat (e) I-V characteristic (f) Generated current from the heartbeat of rat [Reproduced from [63 64] with thepermission from American Chemical Society and Copyright WILEY-VCH Verlag GmbH amp Co KGaA Weinheim]


and wireless data transmitters [22 36] Recently the outputvoltage and power density of the nanogenerators have beenlargely improved by researchers The output power couldmeet the requirement of some devices such as the LEDand LCD screens Several nanogenerators based on ZnOor PZT materials have been employed as the power sourcefor such devices without any rectifying and charge storageunits which can simplify the external circuit and decreasethe dimension of the system [7 49 64] There are alsosome research works about the nanogenerators based onpiezoelectric thin films for driving the microdevices Forexample Hwang and coworkers have demonstrated a self-powered cardiac pacemaker powered by a flexible singlecrystalline PMN-PT thin filmTheoutput current and voltageof the flexible film harvester reached 145 120583A and 82Vrespectively by harvesting the periodic mechanical motionsof bending and unbending [72]

342 Active Sensors Many experimental results have provedthat the output voltage and current of the nanogenerators areclosely related to the applied strain and strain rateThereforethe nanogenerators can also be employed as active sensors forthe strain-related mechanical matters with voltagecurrent asthe sensing parameters For exampleHu et al have integrateda nanogenerator onto a tirersquos inner surface The deformationof tire during the moving of vehicles could be harvested andconverted into output electric signals Because the change oftire-pressure and speed of the vehicle may lead to changeof the strain and strain rate of the nanogenerator it canbe used as the tire-pressure sensor and speed sensor ofthe moving vehicle [64] Lin and coworkers have integrateda nanogenerator onto an elastic spring by growing ZnOnanowire arrays on the surface of the spring Under a cycliccompressive force applied to the spring the nanogeneratorproduced a stable AC output voltage and current whichare linearly responding to the applied weight on the springTherefore the nanogenerator can serve as an active sensor fora self-powered weight measurement [73]

Besides the solid contact between the external load andthe nanogenerators the device can also be used for the sens-ing of air flows Zhang et al have demonstrated a compositenanogenerator which can convert the vortex motion in theatmosphere into electricity [69] The device can be used todetect the win-speed according to the Karman vortex streetprinciple Lee et al used a super-flexible nanogenerator forthe harvesting of the energy from the gentle wind whichcould also be used as an active deformation sensor for thedetecting of both wind and human skin motions [67]

As mentioned above the free charge carrier inside thepiezoelectric nanowireswill lead to the polarization screeningeffect and decrease the piezopotential This mechanism canalso be employed for building active sensors based on thevariation of charge carriers for example the oxide gassensor or chemical sensors Zhu et al have reported aseries of research works about the piezoactive chemicalsensors based on ZnO piezoelectric nanowire arrays fordetecting the humidity hydrogen H

2S ethanol and glucose

in the environment Because the adsorption of such chemical

matters (H2in Figure 14) on the surface of the ZnO will lead

to the introduction of free charge carriers to the nanowiresthe polarization screening effect will be modified and resultin the decrease of output voltage to the external circuitfrom the nanogenerators [74 75] The investigation of suchactive sensors may largely promote the research on self-powered sensor system and the development of modernsensor networks

343 For Driving Self-Powered Sensors The output voltageand current can be used not only as the active sensingparameters in self-powered sensors but also as the drivingsource in several kinds of sensors in which the input voltageor current will be changed with the sensing parametersof the sensors especially the resistance-type semiconductorsensors For example Xu and coworkers have integratedthe ZnO VINGs with a nanowire-based pH sensor andUV sensor respectively The partial voltage on the sensorpart generated by the VING changed with the resistanceof the sensing nanowire both in different pH environmentand under the irradiation of the UV light [33] Wu et alhave also reported the self-powered UV sensor based onnanogenerators with PZT textiles and nanowire respectively[47 76]

The difference between the above-mentioned self-powered sensors and the nanogenerator-driven electronicdevices is that the former one did not need high electricpower density which is essential for the operation inlatter ones By integrating both parts with the outputof nanogenerator as both the power source and sensingparameter the researchers have fabricated completedself-powered sensor systems For example Lee et al havedemonstrated a self-powered environment sensor systemdriven by a nanogenerator [67] The generated electricalpower can light up a LED indicator when the sensor partbased on single wall carbon nanotubes is exposed to highconcentration of mercury ions in water solution Li and Xiahave integrated ZnO VINGs with both the sensor unit anda wireless transmitter unit [77] In this system the signaldetected by a phototransistor can be transmitted wirelesslyby a single transistor RF transmitter under the driving of thenanogenerator

344 Hybrid Cells for Harvesting Multiple Energies Underthe demand of long-term energy needs and sustainabledevelopment devices that can harvest multiple types ofenergies have also been developed For example Hansenand coauthors have integrated the piezoelectric nanogener-ators with the enzymatic biofuel cell which can harvest thebiochemical energy in biofluid Both unit can be used forharvesting the energy available in vivo and can work simulta-neously or individually for boosting output and lifetime [12]Moreover Xu and Wang have developed a fully integratedsolid-state compact hybrid cell that consisted of an organicsolid-state dye-sensitized solar cell (DSSC) and piezoelectricnanogenerator in one compact structure for concurrentlyharvesting both solar and mechanical energy using a singledevice In addition to enhancing the open-circuit voltage the


Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)

Dry air200ppm 400ppm

600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)

Figure 14 The active H2sensors based on ZnO VINGs ((a)ndash(e)) The schematic diagram of the synthesis process and working mechanism

of the sensor (f) A photograph of the as-fabricated sensor (g) The output voltage of the sensor with exposure to different concentration ofhydrogen gas (h)The linear relationship between the hydrogen concentration and output voltage (Reproduced from [16] with the permissionfrom Elsevier)

hybrid cell can add the total optimum power outputs fromboth the solar cell and the nanogenerator [78]

4 Future Development of Nanogenerators

Although there have been numerous research works aboutthe fabrication performance and application of piezoelectricnanogenerators the following listed several crucial issues stillrequired to be further improved

(i) Increase of output power density

(ii) The integration packaging of energy storage unit withthe nanogenerators

(iii) Optimization on harvesting efficiency of mechanicalenergy from various working conditions

(iv) Optimization of electromechanical conversion effi-ciency through structural design

(v) Long-term stability mechanical strength and chemi-cal stability of the nanogenerators

Moreover there are also some problems still required tobe solved for the application of nanogenerators which arelisted as follows

(i) The structural design to guarantee the long-term sta-bility and mechanical strength of the active chemicalsensors

(ii) The harvesting method of mechanical energy togenerate stable output voltage for the active sensorswhich is crucial for the accuracy of the sensing results

(iii) The integration and packaging of nanogenerator andsensing unit for the self-powered systems

(iv) Temperature drift during the sensing process foractiveself-powered sensors

(v) The integration of active or self-powered system withdate processing and transmitting systems


5 Conclusions

In this paper we provide a comprehensive review of thepiezoelectric nanogenerators in the last 8 years According tothe mechanical configuration of the piezoelectric nanowiresthere are three major models for the nanogenerators includ-ing the lateral bending model vertical compression modeland the lateral stretching models For some devices theworking mechanism of the nanogenerators may be due tothe coupling of lateral bending and stretching models Basedon these basic models three major types of nanogeneratorswere fabricated by researchers Among them the VINGswere mostly investigated due to the higher output and theproven fabrication technique of ZnO nanowire arrays theLINGs with the highest energy conversion efficiency havealso been investigated in recent years with the developmentof electrospinning techniques the nanowire-composite typenanogenerators with simplest fabrication process and highelectrical output have exhibited great potentials By harvest-ing the mechanical energies such as the muscle movementheartbeats airwater flow and solid pressures and rain dropsthe nanogenerators can be used as the power source fordriving micronanodevices and self-powered sensors as wellas the active sensors for the detection the variation ofstrain-related physical phenomenon and chemical condi-tions Moreover the piezoelectric nanogenerators can beintegrated with other energy harvesting devices for buildinghybrid cells Although numerous efforts have already beendone for promoting the practical application of piezoelectricnanogenerators there are some critical issues which stillneed to be further resolved for example the energy inte-gration of nanogenerators for high output power sourcesthe structural design for increasing the energy harvestingefficiency in different conditions and the development ofpracticable integrated self-powered systems with improvedstability and reliability Furthermore the long-term stabilityand standard testing method of the nanogenerators still needto be concerned in the future studies

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors thank Professor Yang Luo in East China Nor-mal University for the discussion about the finite elementanalysis works This work was financially supported bythe National Science Foundation of China (Grant nos11474088 61274073) the National High-Tech Research andDevelopment Program of China (863 Program Grant no2013AA031903) the Applied Basic Research Project ofWuhan (Grant no 2014010101010006) and the Natural Sci-ence Foundation of Hubei Province in China (Grant no2014CFB557)

References

[1] F Patolsky andCM Lieber ldquoNanowire nanosensorsrdquoMaterialsToday vol 8 no 4 pp 20ndash28 2005

[2] J Huang and Q Wan ldquoGas sensors based on semiconductingmetal oxide one-dimensional nanostructuresrdquo Sensors vol 9no 12 pp 9903ndash9924 2009

[3] H Yan H S Choe S Nam et al ldquoProgrammable nanowirecircuits for nanoprocessorsrdquoNature vol 470 no 7333 pp 240ndash244 2011

[4] P M Roslashrvik T Grande and M-A Einarsrud ldquoOne-dimensional nanostructures of ferroelectric perovskitesrdquoAdvanced Materials vol 23 no 35 pp 4007ndash4034 2011

[5] Z L Wang ldquoFrom nanogenerators to piezotronicsamdasha decade-long study of ZnO nanostructuresrdquoMRS Bulletin vol 37 no 9pp 814ndash827 2012

[6] Z L Wang and J Song ldquoPiezoelectric nanogenerators based onzinc oxide nanowire arraysrdquo Science vol 312 no 5771 pp 242ndash246 2006

[7] L Gu N Cui L Cheng et al ldquoFlexible fiber nanogenerator with209 v output voltage directly powers a light-emitting dioderdquoNano Letters vol 13 no 1 pp 91ndash94 2013

[8] J Kwon W Seung B K Sharma S-W Kim and J-H AhnldquoA high performance PZT ribbon-based nanogenerator usinggraphene transparent electrodesrdquo Energy and EnvironmentalScience vol 5 no 10 pp 8970ndash8975 2012

[9] J H Jung M Lee J-I Hong et al ldquoLead-free NaNbO3

nanowires for a high output piezoelectric nanogeneratorrdquo ACSNano vol 5 no 12 pp 10041ndash10046 2011

[10] C Falconi G Mantini A DrsquoAmico and V Ferrari ldquoModelingof piezoelectric nanodevicesrdquo in Piezoelectric Nanomaterials forBiomedical Applications G Ciofani and A Menciassi EdsNanomedicine and Nanotoxicology chapter 4 pp 93ndash133Springer Berlin Germany 2012

[11] G Mantini Y Gao A DrsquoAmico C Falconi and Z L WangldquoEquilibrium piezoelectric potential distribution in a deformedZnO nanowirerdquoNano Research vol 2 no 8 pp 624ndash629 2009

[12] B J Hansen Y Liu R Yang and Z L Wang ldquoHybridnanogenerator for concurrently harvesting biomechanical andbiochemical energyrdquo ACS Nano vol 4 no 7 pp 3647ndash36522010

[13] Y Yang H Zhang Z-H Lin et al ldquoA hybrid energy cell for self-powered water splittingrdquo Energy and Environmental Sciencevol 6 no 8 pp 2429ndash2434 2013

[14] Y Zhao X Lai P Deng et al ldquoPtZnO nanoarray nanogenera-tor as self-powered active gas sensor with linear ethanol sensingat room temperaturerdquoNanotechnology vol 25 no 11 Article ID115502 2014

[15] Y Fu W Zang P Wang L Xing X Xue and Y ZhangldquoPortable room-temperature self-poweredactive H

2sensor

driven by human motion through piezoelectric screeningeffectrdquo Nano Energy vol 8 pp 34ndash43 2014

[16] P Han W Yan J Tian X Huang and H Pan ldquoCut direc-tions for the optimization of piezoelectric coefficients of leadmagnesium niobate-lead titanate ferroelectric crystalsrdquoAppliedPhysics Letters vol 86 no 5 Article ID 052902 2005

[17] K K Rajan M Shanthi W S Chang J Jin and L C LimldquoDielectric and piezoelectric properties of [0 0 1] and [0 11]-poled relaxor ferroelectric PZNndashPT and PMNndashPT singlecrystalsrdquo Sensors and Actuators A Physical vol 133 no 1 pp110ndash116 2007


[18] H Ohigashi ldquoElectromechanical properties of polarizedpolyvinylidene fluoride films as studied by the piezoelectricresonance methodrdquo Journal of Applied Physics vol 47 no 3 pp949ndash955 1976

[19] E Pukada ldquoHistory and recent progress in piezoelectric poly-mersrdquo IEEE Transactions on Ultrasonics Ferroelectrics andFrequency Control vol 47 no 6 pp 1277ndash1290 2000

[20] Z L Wang ldquoTowards self-powered nanosystems from nano-generators to nanopiezotronicsrdquo Advanced Functional Materi-als vol 18 no 22 pp 3553ndash3567 2008

[21] Y Qin X Wang and Z L Wang ldquoMicrofibre-nanowire hybridstructure for energy scavengingrdquo Nature vol 451 no 7180 pp809ndash813 2008

[22] G Zhu R Yang S Wang and Z L Wang ldquoFlexible high-output nanogenerator based on lateral ZnO nanowire arrayrdquoNano Letters vol 10 no 8 pp 3151ndash3155 2010

[23] Z Wang Y Hu WWang D Zhou Y Wang and H Gu ldquoElec-tromechanical conversion behavior of K

05Na05NbO3nanorods

synthesized by hydrothermal methodrdquo Integrated Ferroelectricsvol 142 no 1 pp 24ndash30 2013

[24] Z L Wang R Yang J Zhou et al ldquoLateral nanowirenanobeltbased nanogenerators piezotronics and piezo-phototronicsrdquoMaterials Science and Engineering R Reports vol 70 no 3ndash6pp 320ndash329 2010

[25] Y Gao and Z L Wang ldquoEquilibrium potential of free chargecarriers in a bent piezoelectric semiconductive nanowirerdquoNanoLetters vol 9 no 3 pp 1103ndash1110 2009

[26] C Falconi G Mantini A DrsquoAmico and Z L Wang ldquoStudyingpiezoelectric nanowires and nanowalls for energy harvestingrdquoSensors and Actuators B Chemical vol 139 no 2 pp 511ndash5192009

[27] Y-F Lin J Song Y Ding S-Y Lu and Z LWang ldquoAlternatingthe output of a CdS nanowire nanogenerator by a white-light-stimulated optoelectronic effectrdquo Advanced Materials vol 20no 16 pp 3127ndash3130 2008

[28] C-T Huang J Song W-F Lee et al ldquoGaN nanowire arrays forhigh-output nanogeneratorsrdquo Journal of the American ChemicalSociety vol 132 no 13 pp 4766ndash4771 2010

[29] Y-F Lin J Song Y Ding S-Y Lu and Z L Wang ldquoPiezo-electric nanogenerator using CdS nanowiresrdquo Applied PhysicsLetters vol 92 no 2 Article ID 022105 2008

[30] M-Y Lu J Song M-P Lu C-Y Lee L-J Chen and Z LWang ldquoZnOndashZnS heterojunction and ZnS nanowire arrays forelectricity generationrdquo ACS Nano vol 3 no 2 pp 357ndash3622009

[31] C-T Huang J Song C-M Tsai et al ldquoSingle-inn-nanowirenanogenerator with upto 1 v output voltagerdquo Advanced Materi-als vol 22 no 36 pp 4008ndash4013 2010

[32] X Wang J Song J Liu and Z L Wang ldquoDirect-currentnanogenerator driven by ultrasonic wavesrdquo Science vol 316 no5821 pp 102ndash105 2007

[33] S Xu Y Qin C Xu Y Wei R Yang and Z L Wang ldquoSelf-powered nanowire devicesrdquo Nature Nanotechnology vol 5 no5 pp 366ndash373 2010

[34] K-H Kim K Y Lee J-S Seo B Kumar and S-W Kim ldquoPaper-based piezoelectric nanogenerators with high thermal stabilityrdquoSmall vol 7 no 18 pp 2577ndash2580 2011

[35] D Choi M-Y Choi W M Choi et al ldquoFully rollable transpar-ent nanogenerators based on graphene electrodesrdquo AdvancedMaterials vol 22 no 19 pp 2187ndash2192 2010

[36] Y Hu Y Zhang C Xu L Lin R L Snyder and Z L WangldquoSelf-powered system with wireless data transmissionrdquo NanoLetters vol 11 no 6 pp 2572ndash2577 2011

[37] Y Hu L Lin Y Zhang and Z L Wang ldquoReplacing a battery bya nanogenerator with 20 v outputrdquo Advanced Materials vol 24no 1 pp 110ndash114 2012

[38] T T Pham K Y Lee J-H Lee et al ldquoReliable operationof a nanogenerator under ultraviolet light via engineeringpiezoelectric potentialrdquo Energy and Environmental Science vol6 no 3 pp 841ndash846 2013

[39] G Zhu A C Wang Y Liu Y Zhou and Z L WangldquoFunctional electrical stimulation by nanogenerator with 58 voutput voltagerdquoNano Letters vol 12 no 6 pp 3086ndash3090 2012

[40] S Xu B J Hansen and Z L Wang ldquoPiezoelectric-nanowire-enabled power source for driving wireless microelectronicsrdquoNature communications vol 1 article 93 2010

[41] P G Kang B K Yun K D Sung et al ldquoPiezoelectric powergeneration of vertically aligned lead-free (KNa)NbO

3nanorod

arraysrdquo RSC Advances vol 4 no 56 pp 29799ndash29805 2014[42] R Yang Y Qin L Dai and Z LWang ldquoPower generation with

laterally packaged piezoelectric finewiresrdquoNatureNanotechnol-ogy vol 4 no 1 pp 34ndash39 2009

[43] J Chang M Dommer C Chang and L Lin ldquoPiezoelectricnanofibers for energy scavenging applicationsrdquo Nano Energyvol 1 no 3 pp 356ndash371 2012

[44] Z Wang J Hu A P Suryavanshi K Yum and M-F YuldquoVoltage generation from individual BaTiO

3nanowires under

periodic tensile mechanical loadrdquo Nano Letters vol 7 no 10pp 2966ndash2969 2007

[45] ZWang H Gu Y Hu et al ldquoSynthesis growthmechanism andoptical properties of (KNa)NbO3 nanostructuresrdquo CrystEng-Comm vol 12 no 10 pp 3157ndash3162 2010

[46] X Chen S Xu N Yao and Y Shi ldquo16 V nanogenerator formechanical energy harvesting using PZT nanofibersrdquo NanoLetters vol 10 no 6 pp 2133ndash2137 2010

[47] W Wu S Bai M Yuan Y Qin Z L Wang and T Jing ldquoLeadzirconate titanate nanowire textile nanogenerator for wearableenergy-harvesting and self-powered devicesrdquo ACS Nano vol 6no 7 pp 6231ndash6235 2012

[48] H B Kang J Chang K Koh L Lin andY S Cho ldquoHigh qualityMn-doped (NaK)NbO

3nanofibers for flexible piezoelectric

nanogeneratorsrdquo ACS Applied Materials amp Interfaces vol 6 no13 pp 10576ndash10582 2014

[49] Y Hu Y Zhang C Xu G Zhu and Z L Wang ldquoHigh-output nanogenerator by rational unipolar assembly of conicalnanowires and its application for driving a small liquid crystaldisplayrdquo Nano Letters vol 10 no 12 pp 5025ndash5031 2010

[50] L Lin C-H Lai Y Hu et al ldquoHigh output nanogenerator basedon assembly of GaN nanowiresrdquoNanotechnology vol 22 no 47Article ID 475401 2011

[51] Z-H Lin Y Yang J M Wu Y Liu F Zhang and ZL Wang ldquoBaTiO

3nanotubes-based flexible and transparent

nanogeneratorsrdquo Journal of Physical Chemistry Letters vol 3 no23 pp 3599ndash3604 2012

[52] J M Wu C Xu Y Zhang Y Yang Y Zhou and Z L WangldquoFlexible and transparent nanogenerators based on a compositeof lead-free ZnSnO

3triangular-beltsrdquo Advanced Materials vol

24 no 45 pp 6094ndash6099 2012[53] B K Yun Y K Park M Lee et al ldquoLead-free LiNbO

3

nanowire-based nanocomposite for piezoelectric power gener-ationrdquo Nanoscale Research Letters vol 9 no 1 article 4 2014


[54] J H Jung C-Y Chen B K Yun et al ldquoLead-free KNbO3ferro-

electric nanorod based flexible nanogenerators and capacitorsrdquoNanotechnology vol 23 no 37 Article ID 375401 2012

[55] S Xu Y-W Yeh G Poirier M C McAlpine R A Registerand N Yao ldquoFlexible piezoelectric PMN-PT nanowire-basednanocomposite and devicerdquo Nano Letters vol 13 no 6 pp2393ndash2398 2013

[56] Z Zhou H Tang andH A Sodano ldquoScalable synthesis ofmor-photropic phase boundary lead zirconium titanate nanowiresfor energy harvestingrdquo Advanced Materials vol 26 pp 7547ndash7554 2014

[57] B-S Lee B Park H-S Yang et al ldquoEffects of substrateon piezoelectricity of electrospun poly(vinylidene fluoride)-nanofiber-based energy generatorsrdquo ACS Applied Materials ampInterfaces vol 6 no 5 pp 3520ndash3527 2014

[58] C Chang V H Tran J Wang Y-K Fuh and L Lin ldquoDirect-write piezoelectric polymeric nanogenerator with high energyconversion efficiencyrdquo Nano Letters vol 10 no 2 pp 726ndash7312010

[59] C Jiyoung and L Liwei ldquoLarge array electrospun PVDFnanogenerators on a flexible substraterdquo inProceedings of the 16thInternational Solid-State Sensors Actuators and MicrosystemsConference (TRANSDUCERS rsquo11) pp 747ndash750 June 2011

[60] Z Pi J Zhang C Wen Z-B Zhang and D Wu ldquoFlexiblepiezoelectric nanogenerator made of poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) thin filmrdquo Nano Energyvol 7 pp 33ndash41 2014

[61] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[62] W Zeng X-M Tao S Chen S Shang H LW Chan and S HChoy ldquoHighly durable all-fiber nanogenerator for mechanicalenergy harvestingrdquo Energy and Environmental Science vol 6no 9 pp 2631ndash2638 2013

[63] R Yang Y Qin C Li G Zhu and Z L Wang ldquoConvertingbiomechanical energy into electricity by a muscle-movement-driven nanogeneratorrdquoNano Letters vol 9 no 3 pp 1201ndash12052009

[64] Y Hu C Xu Y Zhang L Lin R L Snyder and Z L Wang ldquoAnanogenerator for energy harvesting from a rotating tire and itsapplication as a self-powered pressurespeed sensorrdquo AdvancedMaterials vol 23 no 35 pp 4068ndash4071 2011

[65] Z Li G Zhu R Yang A C Wang and Z L Wang ldquoMuscle-driven in vivo nanogeneratorrdquo Advanced Materials vol 22 no23 pp 2534ndash2537 2010

[66] R Guigon J-J Chaillout T Jager andG Despesse ldquoHarvestingraindrop energy experimental studyrdquo Smart Materials andStructures vol 17 no 1 Article ID 015039 2008

[67] S Lee S-H Bae L Lin et al ldquoSuper-flexible nanogeneratorfor energy harvesting from gentle wind and as an activedeformation sensorrdquoAdvanced FunctionalMaterials vol 23 no19 pp 2445ndash2449 2013

[68] D-A Wang and H-H Ko ldquoPiezoelectric energy harvestingfrom flow-induced vibrationrdquo Journal of Micromechanics andMicroengineering vol 20 no 2 Article ID 025019 2010

[69] R Zhang L Lin Q Jing et al ldquoNanogenerator as an activesensor for vortex capture and ambient wind-velocity detectionrdquoEnergy and Environmental Science vol 5 no 9 pp 8528ndash85332012

[70] C Sun J Shi D J Bayerl and X Wang ldquoPVDF microbelts forharvesting energy from respirationrdquo Energy and EnvironmentalScience vol 4 no 11 pp 4508ndash4512 2011

[71] Z Li and Z LWang ldquoAirliquid-pressure and heartbeat-drivenflexible fiber nanogenerators as a micronano-power source ordiagnostic sensorrdquo AdvancedMaterials vol 23 no 1 pp 84ndash892011

[72] G-T Hwang H Park J-H Lee et al ldquoSelf-powered cardiacpacemaker enabled by flexible single crystalline PMN-PTpiezoelectric energy harvesterrdquo Advanced Materials vol 26 pp4880ndash4887 2014

[73] L Lin Q Jing Y Zhang et al ldquoAn elastic-spring-substratednanogenerator as an active sensor for self-powered balancerdquoEnergy amp Environmental Science vol 6 no 4 pp 1164ndash11692013

[74] D Zhu Y Fu W Zang Y Zhao L Xing and X XueldquoPiezoactive humidity sensing of CeO

2ZnO and SnO

2ZnO

nanoarray nanogenerators with high response and large detect-ing rangerdquo Sensors and Actuators B vol 205 pp 12ndash19 2014

[75] R Yu C Pan J Chen G Zhu and Z L Wang ldquoEnhancedperformance of a ZnO nanowire-based self-powered glucosesensor by piezotronic effectrdquo Advanced Functional Materialsvol 23 no 47 pp 5868ndash5874 2013

[76] S Bai Q Xu L Gu F Ma Y Qin and Z L Wang ldquoSinglecrystalline lead zirconate titanate (PZT) nanomicro-wire basedself-poweredUV sensorrdquoNanoEnergy vol 1 no 6 pp 789ndash7952012

[77] D Li and Y Xia ldquoElectrospinning of nanofibers reinventing thewheelrdquo Advanced Materials vol 16 no 14 pp 1151ndash1170 2004

[78] C Xu and Z L Wang ldquoCompact hybrid cell based on a convo-luted nanowire structure for harvesting solar and mechanicalenergyrdquo Advanced Materials vol 23 no 7 pp 873ndash877 2011

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


70

60

50

40

30

20

10

02006 2007 2008 2009 2010 2011 2012 2013 2014

Year

Num

ber o

f pub

licat

ions

(a)

2006 2007 2008 2009 2010 2011 2012 2013 2014

Year

2500

2000

1500

1000

500

0

Num

ber o

f cita

tions

(b)

Figure 1 Publication (a) and citation (b) about the piezoelectric nanogenerators according to the data enquired inThomson Reuters ISIWebof Knowledge

Wang and Song firstly reported the piezoelectric ldquonanogener-atorsrdquo in 2006 which can generate impulsive output voltagewith several millivolts by bending a ZnO nanowire with theatomic force microscopy (AFM)rsquos tip [6] This nanogener-ator has attracted great interest of researchers due to thegreat potential in the application of micronanoscaled powersupply systems However the energy conversion efficiencyand output power of this early-stage device are too low tobe applied In the last 8 years researchers have done greatefforts on improving the device performance including theemploying of several kinds of piezoelectric materials withhigher piezoelectric properties [7ndash9] the design of devicestructures [10 11] and the hybrid of nanogenerators withother types of energy harvesters [12 13] Moreover somenovel applications such as the active chemical sensors werealso developed by using the nanogenerators [14 15] As shownin Figure 1 the publication and citation number of researchworks have largely increased from the first report in 2006

In this paper we firstly reviewed the fundamental the-ory about the piezoelectricity and piezoelectric materialsin Section 2 Then the working mechanism modeling andstructural design and the fabrication and performance of thepiezoelectric nanogenerators based on different structureswere discussed After that the application of piezoelectricnanogenerators in recent years was briefly reviewed Finallythe future development of the nanogenerators was alsodiscussed

2 Piezoelectricity and Piezoelectric Materials

21 Definition and Physics of Piezoelectricity Piezoelectriceffect is a unique property of certain crystals where theywill generate an electric field or current if subjected tophysical stress The direct piezoelectric effect was discoveredby brothers Pierre Curie and Jacques Curie in 1880 After thatthe same effect was observed in reverse where an imposedelectric field on the crystal will put stress on its structure

The process whereby the piezoelectric effect takes placeis based on the fundamental structure of a crystal lattice

Crystals generally have a charge balance where negative andpositive charges precisely cancel each other out along therigid planes of the crystal lattice When this charge balanceis disrupted by applying physical stress to the crystals theenergy is transferred by electric charge carriers creatinga current in the crystal With the converse piezoelectriceffect the applying of an external electric field to the crystalwill unbalance the neutral charge state which results inmechanical stress and the slight readjustment of the latticestructure Therefore piezoelectricity is the linear interac-tion between the mechanical and electrical properties ofthe dielectric materials [10] For electrical properties therelationship between the electric displacement (119863

119894) and the

electric field (119864119895) can be interpreted as

119863119894=

3sum119895=1120576119894119895119864119895 (1)

where the coefficient 120576119894119895is the permittivity of the dielectric

materialsThe permittivity coefficient is a second-rank tensorrepresented by a 3times 3matrix However thematrix is symmet-ric (120576119894119895= 120576119895119894) and there are atmost 6 independent coefficients

For mechanical properties the relationship between stressand strain under small deformations can be interpreted as

119879119894119895=

3sum119896119897=1119888119894119895119896119897119878119896119897 (2)

where 119888119894119895119896119897

is the elastic stiffness of the material Equation (2)can also be interpreted reversely as

119878119894119895=

3sum119896119897=1119904119894119895119896119897119879119896119897 (3)

where 119904119894119895119896119897

is the elastic compliance of the materials Becausethe stiffness and compliance coefficients relate to the second-rank tensor stress and strain they are fourth-rank tensorsHowever due to the symmetric stress and strain (119879

119894119895= 119879119895119894

119878119894119895= 119878119895119894) the number of 119888

119894119895119896119897can be reduced to 36 [10]







119863119894= 120576119879

119894119895119864119895+119889119894119869119879119869

119878119868= 119889119868119895119864119895+ 119904119864

119868119869119879119869

(4)


119894119869


119878 = 119904119864119879+119889119864

119863 = 119889119879+ 120576119879119864

(5a)

119878 = 119904119863119879+119892119863

119864 = minus119892119879+119863

120576119879

(5b)

119879 = 119888119864119878 minus 119890119864

119863 = 119890119878 + 120576119878119864

(5c)

119879 = 119888119863119878 + ℎ119863

119864 = minus ℎ119878 +119863

120576119878

(5d)


119889 = 120576119879119892 = 119904119864119890

119890 = 120576119878ℎ = 119888119864119889

119892 =119889

120576119879= 119904119863ℎ

ℎ =119890

120576119878= 119888119863119892

120576119879= 120576119878+119889119890

(6)




13B23

)O3-PbTiO

3(A =




















T

T T

G

G G G G

minus

VB

CB

e

e

e e

e

ee

e

ee

EF

ΦSB

V998400minus

V998400+

V998400998400minusV998400998400minus

V998400998400+V998400998400+

T T

(a) (b) (c) (d)

minusminus +

VB

Pt ZnO Ag

CB


e

EF

qVNG

Cath

ode +

Ano

de

asymp

(e)






Au Au

RL

120601B

(a)

eminus

Au Au

V+p Vminus

p

120601BΔEp

(b)

Au Au

V+p Vminus

pminus +

120601B

(c)

eminus

Au Au

minus +

120601B

(d)

Volta

ge (m

V)

Time (s)

20

10

0

minus10

minus200 5 10

(e)







+minus

Fixed end

Fixed end

Pulling string



Spring Fixed end


(a)

(b)

(c)

I II

Fibre base

Fibre base

Au coatedZnO NWs

ZnO NWs

(d)

I II


V+

Vminus

(e)

I II


V+V+

VminusVminus

(f)







(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)







3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









119863119894= 120576119879

119894119895119864119895+119889119894119869119879119869

119878119868= 119889119868119895119864119895+ 119904119864

119868119869119879119869

(4)


119894119869


119878 = 119904119864119879+119889119864

119863 = 119889119879+ 120576119879119864

(5a)

119878 = 119904119863119879+119892119863

119864 = minus119892119879+119863

120576119879

(5b)

119879 = 119888119864119878 minus 119890119864

119863 = 119890119878 + 120576119878119864

(5c)

119879 = 119888119863119878 + ℎ119863

119864 = minus ℎ119878 +119863

120576119878

(5d)


119889 = 120576119879119892 = 119904119864119890

119890 = 120576119878ℎ = 119888119864119889

119892 =119889

120576119879= 119904119863ℎ

ℎ =119890

120576119878= 119888119863119892

120576119879= 120576119878+119889119890

(6)




13B23

)O3-PbTiO

3(A =




















T

T T

G

G G G G

minus

VB

CB

e

e

e e

e

ee

e

ee

EF

ΦSB

V998400minus

V998400+

V998400998400minusV998400998400minus

V998400998400+V998400998400+

T T

(a) (b) (c) (d)

minusminus +

VB

Pt ZnO Ag

CB


e

EF

qVNG

Cath

ode +

Ano

de

asymp

(e)






Au Au

RL

120601B

(a)

eminus

Au Au

V+p Vminus

p

120601BΔEp

(b)

Au Au

V+p Vminus

pminus +

120601B

(c)

eminus

Au Au

minus +

120601B

(d)

Volta

ge (m

V)

Time (s)

20

10

0

minus10

minus200 5 10

(e)







+minus

Fixed end

Fixed end

Pulling string



Spring Fixed end


(a)

(b)

(c)

I II

Fibre base

Fibre base

Au coatedZnO NWs

ZnO NWs

(d)

I II


V+

Vminus

(e)

I II


V+V+

VminusVminus

(f)







(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)







3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

















T

T T

G

G G G G

minus

VB

CB

e

e

e e

e

ee

e

ee

EF

ΦSB

V998400minus

V998400+

V998400998400minusV998400998400minus

V998400998400+V998400998400+

T T

(a) (b) (c) (d)

minusminus +

VB

Pt ZnO Ag

CB


e

EF

qVNG

Cath

ode +

Ano

de

asymp

(e)






Au Au

RL

120601B

(a)

eminus

Au Au

V+p Vminus

p

120601BΔEp

(b)

Au Au

V+p Vminus

pminus +

120601B

(c)

eminus

Au Au

minus +

120601B

(d)

Volta

ge (m

V)

Time (s)

20

10

0

minus10

minus200 5 10

(e)







+minus

Fixed end

Fixed end

Pulling string



Spring Fixed end


(a)

(b)

(c)

I II

Fibre base

Fibre base

Au coatedZnO NWs

ZnO NWs

(d)

I II


V+

Vminus

(e)

I II


V+V+

VminusVminus

(f)







(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)







3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Au Au

RL

120601B

(a)

eminus

Au Au

V+p Vminus

p

120601BΔEp

(b)

Au Au

V+p Vminus

pminus +

120601B

(c)

eminus

Au Au

minus +

120601B

(d)

Volta

ge (m

V)

Time (s)

20

10

0

minus10

minus200 5 10

(e)







+minus

Fixed end

Fixed end

Pulling string



Spring Fixed end


(a)

(b)

(c)

I II

Fibre base

Fibre base

Au coatedZnO NWs

ZnO NWs

(d)

I II


V+

Vminus

(e)

I II


V+V+

VminusVminus

(f)







(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)







3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




+minus

Fixed end

Fixed end

Pulling string



Spring Fixed end


(a)

(b)

(c)

I II

Fibre base

Fibre base

Au coatedZnO NWs

ZnO NWs

(d)

I II


V+

Vminus

(e)

I II


V+V+

VminusVminus

(f)







(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)







3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a)

60

40

20

0

minus20

minus40

minus600 50 100 150 200 250

Time (s)

Volta

ge (m

V)

0MPa 125MPa

25MPa

375MPa

5MPa625MPa

(b)







3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






3(PZT)















(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a)

40

30

20

10

0

40

30

20

10

0

0 2 4 6 8 10 12

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

)

60 61 62 63 64

Time (s)

Time (s)

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

121086420

92 93 94 95 96

Curr

ent (120583

A)

Curr

ent (120583

A)

F(t) F(t)

eminus

eminus

eminus

eminus

eminus

eminus

eminus

eminus

Topelectrode

PMMA

ZnO NWs

Bottomelectrode

eminus eminus

eminuseminuseminus

eminus

eminus

eminuseminus

eminus

eminus

eminuseminuseminus

eminuseminus

Max 00

minus10

minus20

minus30

minus40

minus50

Min minus58648

(b)



Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Silicone

Nanorod

Fixed end

10120583m 5120583m

FA= 1 times

106 Nm

2

(a)

Compressed

SiliconeSilicone

1210080604020 D

ispla

cem

ent (120583

m)

(b)

NanorodNanorod

Compressed

Fixed

6050403020100 D

ispla

cem

ent (

pm)

(c)

Grounded

Compressed

Nanorod


ezop

oten

tial (

mV

)

(d)


FixedFixed

NanorodAu

Au

Silicone


10120583

m

5120583m

(a)

05

0

10

15

20

Fixed

Silicone

Disp

lace

men

t (120583

m)

(b)

GroundedFixed

Nanorod

100

80

60

40

20

0

Disp

lace

men

t (nm

)

(c)

GroundedFixed

Nanorod

25

20

15

10

05

0

Piez

opot

entia

l (V

)

(d)



Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Au

ZnO nanowire

Cr

ZnO seed

(a)

Cr el

ectro

de


Au el

ectro

de

2120583m

(b)

05 cm

(c)

12

06

00

minus06

0 5 15 25 35

Time (s)

Time (s)

Volta

ge (V

)

Volta

ge (V

) 07

00

minus07

77 84 91

(d)

Time (s)

Time (s)

20

0

minus20

20

0

minus20

0 10 20 30 40

89 96

Curr

ent (

nA)

Curr

ent (

nA)

(e)








Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Silicon substrate

sim05mm


Vo

(a)

06

05

04

03

02

01

0

Volta

ge (V

)


nanogenerator

Teflon stack

+

minus


minus010 05 1 15 2 25 3 35 4

Time (s)

(b)









Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Gold electrode

Nanofibers

Current flow


VampI

(a) (b)

-+-+ -+ -+ -+-+ -+

AuPR

CrSiO2

Polymer substrate

Liftoff


PDMS

VampI

(c)








mdash [53]








3-based



(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a)

1 cm

(c)

50120583m 40120583m

Electrode

Electrode

Piez

oele

ctric

pot

entia

l (V

)

E

F(t)

minus

+

1 cm

(b)

(d)




3nanogenerators






20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20

0

minus20

Volta

ge (m

V)

0 10 20 30 40 50 60 70 80

Time (s)

Time (s)

20

10

0

Volta

ge (m

V)

393 396 399

100

0

minus100Vo

ltage

(mV

)

108 110 112 114

Time (s)

(c) (d)

40

35

30

25

20

15

10

05

00

Curr

ent (120583

A)


Voltage (mV)

(e) 20

15

10

5

0

minus5

minus10

minus15

minus20

0 5 10 15

Time (s)

Curr

ent (

pA)

15

10

5

0

minus5

minus10

minus15

minus2048 51

Time (s)

Curr

ent (

pA)

(f)

(b)(a)















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















Ti foil

(a)

ZnO NW

(b)

SnO2ZnO NW

(c)

Silver paste

Kapton

Copper

Al foil

(d)

Force

Voltmeter

H2

(e) (f)


600ppm800ppm

08

04

00

minus04

minus08

0 100 200 300

Time (s)

Volta

ge (V

)

(g)

08

06

04

02

0 200 400 600 800

Volta

ge (V

)

Concentration (ppm)

Fitting

(h)


















5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




5 Conclusions




Acknowledgments


References

















2sensor











05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










05Na05NbO3nanorods




















3nanorod





3nanowires under
















3

























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


























2ZnO and SnO

2ZnO













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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