Piezoelectric Nanogenerators Based on Zno Nanostructures Akdnfldl

Piezoelectric nanogenerators based on Zno nanostructures

CHE 105Group 7Taylor McCulloughDoug SuittLeopoldo Torres

Big Picture

Why are nanogenerators important

Future devices at the nanoscale need power

Need environmentally friendly renewable energy sources

Nature is already producing an enormous amount of energy essentially wasted

Imagine turning the mechanical enery produced by walking, heartbeat, blood flow and random vibrations into energy

Benefits of ZnO

Most diverse and abundant nanostructures

Very robust material

Biofriendly, biocompatable and non-toxic

Coupled piezoelectric and semiconducting properties

Large bandgap in the visible range

At The Nanoscale

Much higher Piezoelectric coefficient than bulk

Higher purity allows for higher strain

Higher aspect ratio

Flexoelectric effect contributes

Piezoelectric Properties

Some needed definitions

Aspect Ratio

Lmajor / Wminor = L/D

Piezoelectric coefficientd33 = P/ (polarization/stress)

Electromechanical CouplingK33 = Electric energy out/Mechanical energy in

https://www.americanpiezo.com/knowledge-center/piezo-theory/piezoelectric-constants.html

http://www.piceramic.com/pdf/KATALOG_english.pdf

http://dspace.library.drexel.edu/bitstream/1860/86/14/thompson_thesis.pdf

Self powered nanotech

ZnO Nanostructures

Wang, Z. L. Nanostructures of Zinc Oxide. Materials today 2004, 6, 26-33.

More ZnO structures

Wang, Z. L. Nanostructures of Zinc Oxide. Materials today 2004, 6, 26-33.

Wang, Z. L. From nanogenerators to piezotronicsA decade-long study of ZnO nanostructures. MRS Bulletin, 2012, 37, 814-827

Nanostrucure and properties

ZnO extremely versatile

Nanowires

Nanorods

Nanobelts

Nanoshells

Nanoring

Nanohelixes

Nanospirals

Nanosprings

Nanobows

Nanopropellers

Wang, Z. L. Zinc oxide nanostructures: growth, properties and applications. J. Phys.: Condens. Matter 2004, 16, R829R858.

Nanostrucure For Device

Nanowires

W 1-100 nm

AR > 20

NanorodsW 1-100 nm

AR > 1, < 20

NanobeltsW 30-300 nm

AR 5-10

Thin Films

Wang, Z. L. Zinc oxide nanostructures: growth, properties and applications. J. Phys.: Condens. Matter 2004, 16, R829R858.

Which is best?

In nanogenerators we need:

High voltage

Related to D33 coefficient

Proportional to strain deflection and 1/AR

High current Governed by impurities

Controlled by crystal size/shape

High efficiencyControlled by device design

i) The NW/NB can be subjected to extremely large elastic deformation without plastic deformation or fracture.
ii) Due to their small diameter, NWs/NBs are most likely free of dislocations, and thus, expected to have a high resistance to fatigue, possibly extending the lifetime of the device.
iii) NWs/NBs can be bent under an extremely small applied force. This is unique for harvesting energy created by weak mechanical disturbance. ( = 1-1000+ HZ)

Zno Crystal structure

ZnO crystal structures

Wurtzite

Rutile

Perovskite

Spinel

Clausthal University of Technology. Zinc oxide nanowires for photonic applications.

Wang, Z. L. ZnO nanowire and nanobelt platform for nanotechnology. Materials Science and Engineering, 2009, 64, 3371.

Wang, Z. L. From nanogenerators to piezotronicsA decade-long study of ZnO nanostructures. MRS Bulletin, 2012, 37, 814-827

Why Wurtzite?

Wurtzite crystal structure

Unsymmetrical (no center symmetry)

Charge separation not balanced

Dipole moment induced

Potential created

Wang, Z. L. et al. Lateral nanowire/nanobelt based nanogenerators, piezotronics andpiezo-phototronics. Materials Science and Engineering 2010, 70, 320-329.tetrahedrally coordinated O2 and Zn2+ are stacked layer by layer

along the c-axis. It has a hexagonal unit cell (a = 0.3296 and

c = 0.52065 nm)

Piezoelectric Effect

Apply a uniform strain

Distortion of lattice ions

+V on tensile side V on compressive

Ions cannot move/recombine

Potential exists while strain is present

http://www.beg.utexas.edu/aec/workshop200805/Tues3/6_Yang.pdf

Geng, D, Pook, A, Wang, X. Mapping of strainpiezopotential relationship along bent zinc oxide microwires. Nano Energy 2013, 2, 1225-1231

crystal is connected to an external load, the electrons in the circuit

are driven to ow to partially screen the piezopotential, which is

the energy conversion process. Therefore, the principle of the

nanogenerator is the transient ow of electrons in external load as

driven by the piezopotential created by dynamic straining (Fig. c on the right).

On the other hand, if the material is also a semiconductor, the

piezopotential acts as a gate voltage that can tune/gate the

transport process of the charge carriers under the driving force of

an externally applied voltage (Fig. 1d). The device fabricated based

on this principle is called the piezotronic device.

The piezopotential in a ZnO NW under different straining has

been investigated using the perturbation theory and nite element

method (FEM) [3335]. As shown in Fig. 2a, the length of the

nanowire is taken as 1.2mm and the side length of the hexagon is

100 nm. At both ends, about 100 nm is preserved as the unstrained

part that serves as the contacting part of ZnO NW with the electrode

in a real device. When a uniform stretching force of 85 nN is applied

alongc-axis, the NW is elongated for 0.02 nm with a tensile strain of

2 105

. The piezopotential distribution can be obtained with FEM

if we ignore the doping or conductivity in ZnO, as shown in Fig. 2b.

The potential drop from the +c-axis side to the c-axis side is

approximately 0.4 V. When the NW is compressed with the same

amount of force, the compressive strain becomes 2 105 and

potential difference remains 0.4 V while the potential distribution is

reversed with the +c-axis side having lower potential (Fig. 2c).

The above-calculated results need to be modied if we include

the contribution made by the free charge carriers in the NW

contributed by dopants or intrinsic defects. The intrinsic point defect

in an as-grown ZnO NW always shows an n-type semiconducting

behavior. The inuence of the free charge carriers (electrons in an n-type ZnO NW) on the piezopotential has been investigated under a

thermodynamic equilibrium condition [34]. Driven by the piezo-electric eld, the free charge carrier will redistribute to tentatively

screen the positive piezopotential zone. Considering the donor

concentration to be around 1017 cm3

, which is typical for an as-grown NW, the charge carriers will accumulate at the positive

potential side (+c-axis side in a stretched NW or c-axis side in a

compressed NW) and the negative potential side is not signicantly

affected. As a result of this charge redistribution, the positive

potential is clearly screened while the negative potential region is

still preserved. The negative piezopotential in the NW can be

effective for nanogenerator and piezotronics.

Flexoelectricity

Can occur in any material

Inhomogeneous strain

Stress gradient

Large effect at nanoscale

Negligable in bulk

Potential due piezo & flexo effectPotential due piezoeffect only

Liu, C, Hu, S, Shen, S. Effect of exoelectricity on electrostatic potential in a bent piezoelectric nanowire. Smart Mater. Struct 2012, 21, 1-12.

Nanogenerator Device

Conductive electrode substrate (grounded)

Nanowires grown vertically

Silicon zigzag top electrodeZigzag for both Piezo/flexo effects

Pt coated for metal -semiconductor shottky barrier contact

Wang, Z. L. et al. Piezoelectric Nanogenerators for Self-Powered Nanodevices. IEEE Pervasive computing, 2008, 7, 49-55.

Wang, X. Piezoelectric nanogeneratorsHarvesting ambient mechanical energy at the nanometer scale. Nano Energy 2012, 1, 13-24.

Accumulation & Releasing mechanism

Shottky contact with stretched side

Reverse bias diode no current flow

Charge acumulates and is preserved

Contact with both Forward bias current flows

Wang, Z. L. Towards Self-Powered Nanosystems: From Nanogenerators to Nanopiezotronics Adv. Funct. Mater. 2008, 18, 35533567

Different Nanowire configurations

NW 1 & 2

Push/deflection from top electrode

NW 3In motion due to stimulation by ultrasound wave

NW 4Direct compression

Getting Higher Current & Voltage

Wang, Z. L. Towards Self-Powered Nanosystems: From Nanogenerators to Nanopiezotronics Adv. Funct. Mater. 2008, 18, 35533567

Device Performance

Using vertically grown ZnO nanowires they have developed a nanogenerator capable of outputing 58V and 134 microamps

References

Wang, Z. L. Nanostructures of Zinc Oxide. Materials today 2004, 6, 26-33.Wang, Z. L. Zinc oxide nanostructures: growth, properties and applications. J. Phys.: Condens. Matter 2004, 16, R829R858.Wang, Z. L. ZnO nanowire and nanobelt platform for nanotechnology. Materials Science and Engineering, 2009, 64, 3371. Wang, Z. L. From nanogenerators to piezotronicsA decade-long study of ZnO nanostructures. MRS Bulletin, 2012, 37, 814-827 Clausthal University of Technology. Zinc oxide nanowires for photonic applications. (Accessed February 27th 2014) Wang, Z. L. et al. Lateral nanowire/nanobelt based nanogenerators, piezotronics andpiezo-phototronics. Materials Science and Engineering 2010, 70, 320-329.Geng, D, Pook, A, Wang, X. Mapping of strainpiezopotential relationship along bent zinc oxidemicrowires. Nano Energy 2013, 2, 1225-1231Wang, Z. L. et al. Piezoelectric Nanogenerators for Self-Powered Nanodevices. IEEE Pervasive computing, 2008, 7, 49-55.Liu, C, Hu, S, Shen, S. Effect of exoelectricity on electrostatic potential in a bent piezoelectric nanowire. Smart Mater. Struct 2012, 21, 1-12.Jiang, X, Huang, W, Zhang, S. Flexoelectric nano-generator: Materials, structures and devices. Nano Energy 2013, 2, 1079-1092.Wang, Z. L, Song, J. H. Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays. Science 2006, 312, 242-246.Wang, X. Piezoelectric nanogeneratorsHarvesting ambient mechanical energy at the nanometer scale. Nano Energy 2012, 1, 13-24.Kumar, B, Kim, S. W. Energy harvesting based on semiconducting piezoelectric ZnOnanostructures. Nano Energy 2012, 1, 342-355.Environmental Protection Agency. Nanobelts and Nanorods. (Accessed February 27th 2014)


Piezoelectric nanogenerators based on zno nanowirearrays

The new field of nanopiezotronics


Stress applied to wire

Piezoelectric nanogenerators for selfpowered nanostructures

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Piezoelectric Nanogenerators Based on Zno Nanostructures Akdnfldl