Transcript Piezoelectric Nanogenerators

Piezoelectric Nanogenerators Based
on Zinc Oxide Nanowire Arrays
Zhong Lin Wang1,2,3* and Jinhui Song1
14 APRIL 2006 VOL 312 SCIENCE
Presented by
Yiin-Kuen(Michael) Fuh
Outline
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Motivation & Background
Experimental design
Results
Conclusion
Motivation & Background
• Motivation—self-powered device can greatly reduce the size of
integrated nanosystems for optoelectronics, biosensors and more.
• Background—
– 1D ZnO nanomaterials
• exhibits both semiconducting and piezoelectric(PZ)
properties for electromechanically coupled sensors and
transducers.
• is relatively biosafe and biocompatible for biomedical
applications.
• exhibits the most diverse and abundant configurations of
nanostructures knownsuch as NWs, nanobelts
(NBs) ,nanosprings, nanorings, nanobows and nanohelices
(10).
– The mechanism of the power generator relies on the coupling of
piezoelectric and semiconducting properties of ZnO as well as
the formation of a Schottky barrier between the metal and ZnO
contacts.
Experimental design
(A) Aligned ZnO NWs grown on Al2O3 substrate.
(B) TEM image showing the NW
without an Au particle or with a
small Au particle at the top.
Each NW is a single crystal
and has uniform shape. Inset at
center: an electron diffraction
pattern from a NW. Most of the
NWs had no Au particle at the
top. Inset at right: image of a
NW with an Au particle
Experimental design for converting nanoscale
mechanical energy into electrical energy by a
vertical piezoelectric (PZ) ZnO NW.
(C) The base of the NW is
grounded and an external load
of RL is applied, which is much
larger than the resistance RI of
the NW. The AFM scans across
the NW arrays in contact mode
Results-Electromechanically coupled discharging
process observed in contact mode.
• (A) Topography image, NW density
~20/um2
• (B) Output voltage , Vpeak~6-9mV
• (C) A series of line profiles of the
voltage output signal when the AFM
tip scanned.
• (D) Line profiles from the topography
(red) and output voltage (blue)
images across a NW. The peak of
the voltage output corresponds
approximately to the maximum
deflection of the NW, indicating that
the discharge occurs when the tip is
in contact with the compressed side
of the NW.
• (E)Vpeak of FWHM .
• (F) Welastic=WPZD+Wvib. , WPZD~0.5CV2
=WPZD/Welastic ~17-30%
Results-Electromechanically coupled discharging
process observed in tapping mode.
• (A) Experimental setup.
• (B) Topography image
• (C) Output voltage. The
voltage output contains
no information but noise,
proving the physical
mechanism demonstrated
Theory --Transport is governed by a metalsemiconductor Schottky barrier for the PZ ZnO NW
• (A) NW coordination system.
• (B) Longitudinal strain z distribution (NW of
length 1 µm and an aspect ratio of 10).
• (C) induced electric field Ez distribution
• (D) Potential distribution due to PZ effect.
• Schottky rectifying behavior (E) is to
separate and maintain the charges as well
as build up the potential. The process in (F)
is to discharge the potential and generates
electric current.
• The PZ potential is built up in the displacing
process (G), and later the charges are
released through the compressed side of the
NW (H).
• (I) Large Au particle: The charges are
gradually "leaked" out, no accumulated
potential will be created.
Conclusion
• Self-powering nanotechnology ? Estimated power~ 10
pW/µm2 and much more power if drives resonantly!
• Use flexible substrate for scavenging energy produced
by acoustic waves, ultrasonic waves, or hydraulic
pressure/force or environment etc. for applications such
as implantable biomedical devices, wireless sensors,
and portable electronics
• Continued work published as “Direct-Current Nano
generator Driven by Ultrasonic Waves ” Science 6 April
2007:Vol. 316. no. 5821, pp. 102 – 105
• Nanogenerator is featured in the overview section in the
NSF FY 2008 budget request to congress