氧化锌纳米线阵列压电式纳米压电发电机

Advantageous properties of ZnO

Piezoelectric Semiconductive Biologically safe and biocompatible Diverse and abundant Nano-applications

NWs, Nanobelts, Nanosprings, nanorings, nanobows, nanohelices
Chang, C., et. al.
Changing the material

Results


Leabharlann Baidu
5-30 mV at 0.5-3 nA => 2.5-90 pW Energy conversion efficiency

~12.5% average ~21.8% peak
Chang, C., et. al.


All ZnO NWs are vertically aligned Single crystal and uniform



NW grows along the [0001] direction {0 1 -1 0} surface on the side Au evaporates during the growth or removed by the tip of the atomic force microscope (AFM) during scanning Nanowires are placed vertically on Ag plate and grounded
Changing the material

Method

Directly written by near-field electrospinning (NFES) to produce nanofibers on substrate with in situ mechanical stretching and electrical poling
AFM scan over the nanowire
Wang. Z. L., et. al.
Results

Simulated strain contour and Schottky effect
Wang. Z. L., et. al.
Results

Measured PZ effect



Q&A
• Q: Why so little advance in the topic from 2006-2010 (judging for the presentation)? There is a fundamental obstacle? Have other nanoarrays be tested? Is this the best alternative to harvest energy at the nanoscale? • A: I believe that the limitation comes from the nature of the material. The piezoelectricity can only yield little power per area. Increase in the dimension of the array could yield higher power but it will eliminate these generators for nanotechnological use. However, it is certain that this method is one of the better ways to harvest energy for nanorobots as the external power source is completely eliminated. • Q: Is the only work done? Are there many other people working on this? Was the presented work a breakthrough? • A: This topic is a hot research topic these days. There are many more papers out there, though the Science paper was a bright original idea that suggested new strategy in powering nano-devices.
Questions?
G6 Rebuttal: Piezoelectricity
Jung Hwan Woo
Comments
• Thank you all for constructive comments. I will work harder to provide future research suggestions and to include more current research being carried out. I will also include suggestions to how the experiment is performed to improve the results.
References


Wang, Z. L., Song, J., Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays. Science, 2006, 312 (5771), 242246. Chang, C., Tran, V. H., Wang, J., Fuh, Y., Lin, L., DirectWrite Piezoelectric Polymeric nanogenerator with High Energy Conversion Efficiency. Nano Letters, 2010, 10, 726731.


AFM tip is Pt covered Si cone at 70° Electric field along the z-direction within the NW is created due to the PZ effect PZ field direction is parallel to the z axis at the outer surface and anti parallel to the z axis at the inner surface
1Wright,
Nanotechnology Application

Biological application:


In-situ real-time monitoring nanosensors and nanorobots Allows self-powered

Piezoelectric nanogenerator using zinc oxide nanowire arrays
Piezoelectric Generator

Harvests energy using PZ effect Example

“Crowd Farm” – electricity generation from human footsteps in places such as train stations1 Light flickering shown on YouTube
Results

Power generation


~0.5 pW per tip x 20/µm2 ≈10 pW/µm2 A NW array of size 10 µm x 10 µm would yield appreciable power for a nano-device (~ 1 nW)
ZnO Nanowire Array Piezoelectric Nanogenerator
Outline

Introduction
Piezoelectricity

Piezo- : derived from Greek meaning press or squeeze Electricity generation by mechanical stress Reversible

Schottky barrier between the metal and ZnO
Fabrication of Nanoarrays

ZnO Nanowires grown on c plane-oriented α-Al2O3 using Au as a catalyst by vapor-liquid-solid (VLS) process
Sarah H (2007-07-25). "MIT duo sees people-powered "Crowd Farm"". MIT news. Massachusetts Institute of Technology http://web.mit.edu/newsoffice/2007/crowdfarm-0725.html
SEM (left) and TEM (right) image
Wang. Z. L., et. al.
Measurement Method

ZnO nanowire moved by AFM tip and strained


Tensile on outer surface Compressive on inner surface

Direct PZ effect and converse PZ effect
First demonstration by Pierre Curie and Jacques Curie in 1880 in the course of studying for pyroelectricity Governing equation:
Changing the Material

Direct-write piezoelectric polymeric nanogenerator with high energy conversion efficiency



In place of ZnO, Polyvinylidene fluoride (PVDF) used Advantages Higher flexibility Reduced physical resistance Good PZ Chemical stability Disadvantages α-, β-, and γ-crystalline phases exist β-PVDF is used for best PZ effect Must be mechanically stretched and electrically poled
Q&A
• Q: Could you better explain why current is measured when AFM tip exerts stress on nanowires and how it is measured? • A: For a free-standing piezoelectric nanowire under stress, one side will be compressively strained and the other tensilely stressed. This produces a flow of electron in a clockwise (or counter-clockwise) direction in a 2D model. If there is a source of electron, in this case the AFM tip, electrons from this source will be pulled to the same direction as the electron movements due to the electric field. At the same time, AFM could also measure the current out of the AFM tip.
Average peak height: ~6 to 9 mV Peak density: ~8/µm2 (captured by AFM) Nanowire density: ~20/µm2 Efficiency: ~8/20 ≈ 40% (with scanning AFM tip)
Wang. Z. L., et. al.

E = ε/d
where
E : electric field ε : strain d : PZ coefficient
http://resources.edb.gov.hk/physics/articleIE/smartmaterials/SmartMaterials_e.htm
http://en.wikipedia.org/wiki/Piezoelectricity