Zinc Oxide Nanowire - Nanotechnology - Lecture Slides, Slides of Nanotechnology

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ZnO Nanowire ArrayPiezoelectric NanogeneratorJung Hwan Woo

Outline 

Introduction

Piezoelectric Generator 

Harvests energy using PZ effect  Example  “Crowd Farm” – electricity generation from human footsteps in placessuch as train stations 1  Light flickering shown on YouTube 1 Wright, 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

Nanotechnology Application 

Biological application:  In-situ real-time monitoring nanosensors and nanorobots  Allows self-powered  Piezoelectric nanogenerator using zinc oxide nanowire arrays  Advantageous properties of ZnO  Piezoelectric  Semiconductive  Biologically safe and biocompatible  Diverse and abundant  Nano-applications  NWs, Nanobelts, Nanosprings, nanorings, nanobows, nanohelices  Schottky barrier between the metal and ZnO

Measurement Method 

ZnO nanowire moved by AFM tip and strained  Tensile on outer surface  Compressive on inner surface  AFM tip is Pt covered Si cone at 70°  Electric field along the z-direction within the NW is createddue to the PZ effect  PZ field direction is parallel to the z axis at the outer surfaceand anti parallel to the z axis at the inner surface AFM scan over the nanowire Wang. Z. L., et. al.

Results 

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

Results 

Power generation  ~0.5 pW per tip x 20/μm 2 ≈ 10 pW/μm 2  A NW array of size 10 μm x 10 μm would yield appreciable power for anano-device (~ 1 nW)

Changing the Material 

Direct-write piezoelectric polymeric nanogenerator with highenergy 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

Changing the material 

Results  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.

References 

Wang, Z. L., Song, J., Piezoelectric Nanogenerators Based onZinc Oxide Nanowire Arrays. Science, 2006, 312 (5771), 242-

 Chang, C., Tran, V. H., Wang, J., Fuh, Y., Lin, L., Direct-Write Piezoelectric Polymeric nanogenerator with HighEnergy Conversion Efficiency. Nano Letters, 2010, 10, 726-

G 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.

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.

G Piezoelectric Nanogenerator Review

Edson

P.

Bellido

Sosa