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overview of piezoelectric nanogeneratorws
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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 Effect
Piezoelectric nanogenerators based on zno nanowirearrays
The new field of nanopiezotronics
Piezoelectric Effect
Stress applied to wire
Piezoelectric nanogenerators for selfpowered nanostructures
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