PIEZOELECTRIC NANOGENERATORS BASED ON ZNO NANOSTRUCTURES

CHE 105Group 7

Taylor McCulloughDoug Suitt

Leopoldo 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 coefficient

d33 = P/ (polarization/stress)

Electromechanical Coupling K33 = Electric energy out/Mechanical energy in

https://www.americanpiezo.com/knowledge-center/piezo-theory/piezoelectric-constants.htmlhttp://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 piezotronics—A 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, R829–R858.

Nanostrucure For Device Nanowires

W 1-100 nm

AR > 20 Nanorods

W 1-100 nm

AR > 1, < 20

Nanobelts W 30-300

nm AR 5-10

Thin Films

Wang, Z. L. Zinc oxide nanostructures: growth, properties and applications. J. Phys.: Condens. Matter 2004, 16, R829–R858.

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 efficiency

Controlled 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. (υ = 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, 33–71.   

Wang, Z. L. From nanogenerators to piezotronics—A 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.

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 strain–piezopotential relationship along bent zinc oxide microwires. Nano Energy 2013, 2, 1225-1231

Flexoelectricity

Can occur in any material Inhomogeneous strain

Stress gradient Large effect at nanoscale Negligable in bulk

Potential due piezo & flexo effect

Potential due piezoeffect only

Liu, C, Hu, S, Shen, S. Effect of flexoelectricity 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

electrode Zigzag 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 nanogenerators—Harvesting 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, 3553–3567

Different Nanowire configurations

NW 1 & 2 Push/deflection from

top electrode NW 3

In motion due to stimulation by ultrasound wave

NW 4 Direct compression

Getting Higher Current & Voltage

Wang, Z. L. Towards Self-Powered Nanosystems: From Nanogenerators to Nanopiezotronics Adv. Funct. Mater. 2008, 18, 3553–3567

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

ReferencesWang, 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, R829–R858.Wang, Z. L. ZnO nanowire and nanobelt platform for nanotechnology. Materials Science and

Engineering,  2009, 64, 33–71.      Wang, Z. L. From nanogenerators to piezotronics—A decade-long study of ZnO nanostructures.

MRS Bulletin, 2012, 37, 814-827 Clausthal University of Technology. Zinc oxide nanowires for photonic applications.      <http://www.lac.tu-clausthal.de/en/arbeitsgruppen/angewandte-photonik-lac/projekte/zinc-oxide-nanowires-for-photonic-applications/> (Accessed February 27th 2014)                                 Wang, Z. L. et al. Lateral nanowire/nanobelt based nanogenerators, piezotronics and

piezo-phototronics. Materials Science and Engineering 2010, 70, 320-329.Geng, D, Pook, A, Wang, X. Mapping of strain–piezopotential relationship along bent zinc oxide

microwires. 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 flexoelectricity 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 nanogenerators—Harvesting ambient mechanical energy at the

nanometer scale. Nano Energy 2012, 1, 13-24.Kumar, B, Kim, S. W. Energy harvesting based on semiconducting piezoelectric ZnO

nanostructures. Nano Energy 2012, 1, 342-355.Environmental Protection Agency. Nanobelts and Nanorods.<http://www.epa.gov/radiation/docs/cleanup/nanotechnology/chapter-3-nano-belts.pdf> (Accessed February 27th 2014)