Nanotechnology – technology in everything

CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING

Nanotechnology – technology in everything

Gehan AmaratungaEngineering Dept.

Cambridge University


The scale of the physical world


Contact CEN

AN

O

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NO


Nanotechnology todaywill generate $4 trillion by Lux Research (2008) estimates that:

nanotechnology was incorporated in:$1.1 trillion worth of products in 2007 and $3.1 trillion in 2008

$1 trillion of 2007 nanotechnology product revenue was generated by advances in existing semiconductor process techniques

Advances to 90 nm, 65 nm nodes

Nanotechnology products 2015!


What does the 50 nm node in electronic devices mean?

Man made electronics are approaching the size of biological organisms

Transistor for 90 nm node (Source: Intel) Influenza virus (Source: CDC)


Integrated Circuit AdvancesContinued progress to 90 nm, 65 & 45 nm nodes has brought semiconductor manufacture into the world of nanotechnology

Moore’s law dictates we must halve the size of a transistor every 24 months

This means reducing smallest dimension by factor of 0.7Some existing components (dielectric) have already reached their limits

Continuation of Moore’s law requires real progress in alternative nanotechnology materials, structures and devices


Nanotechnology – consumer products today

Appliances Batteries Heating, Cooling and Air Large Kitchen Appliances Laundry & Clothing Care

Automotive Coatings Electronics and Computers

Audio , Television, CamerasComputer Hardware , displaysMobile Devices and Communications

Food and Beverage Cooking Storage

• Goods for Children – Toys and Games

• Health and Fitness – Clothing, Sporting Goods – Sunscreen – Cosmetics, Personal Care – Filtration

• Home and Garden – Cleaning – Construction Materials – Home Furnishings – Luggage – Luxury – Paint


Nanotechnology – some examples

Photo by David Hawxhurst-Woodrow Wilson International Center for Scholars


Nanotechnology products - today

Nanotechnology consumer products inventory August 2008

– 803 products on the market

– 279% increase since 2006

– Health & fitness largest category


Nano products – Health & Fitness Category

Data courtesy Wilson of Woodrow International Centre for Scholars


Nano-products today

Over 235 products now use silver nano-particles for self-cleaning

Wound dressingsCosmeticsFood storageAir purifiersPersonal care


Nanotechnology – Enabled by ‘seeing’

The invention of the Atomic Force Microscope (AFM) and electron microscope (EM) have enabled us to see into the nano world and begin to manipulate individual atoms.

C60 on Si (111)

Graphite superlattice5 nm periodicity


Nanotechnology in spaceFuture space applications include:

High strength CNT materials for a space elevator(foreseen by Arthur C. Clarke in ‘Fountains of Paradise’ set

in Sri Lanka – elevator starts from top of Sigiriya!)The only material exhibiting the required strength today

CFE guns to replace existing “thrusters”Lighter and lower energy requirements

Courtesy of NASA

CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING ePECePEC

Nanocomposites for Photovoltaic Energy Harvesting

and Storage

Gehan A. J. Amaratunga

Electrical Engineering Division, Engineering Dept,

University of CambridgeCambridge UK

Electronics, Power & Energy Conversion


What is the difference between PV energy generation and energy

harvesting? (1) PV Energy generation: An alternative

to conventional electricity generation technologies for grid connected power

(2) PV Energy harvesting: capturing light energy in an opportunistic manner from the environment. Generally lower intensity than direct sunlight and aimed at providing an energy source for distributed electronic environments


Solar PV Energy Generation – An ‘expensive’ technology?

€ 30 billion solar market by 201030% global solar market growth since 1996 – 50% since 2003Demand so high, prices have gone up!

0

200

400

600

800

1000

1200

MW

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2007 2008 2009 2010

Year


Solar PV generation almost entirely Si cell based


Alternative cell technologies which are ‘cheaper’ not required for growth of solar power generation. A new Si industry growing rapidly with massive investment in

new capacity


PV Energy harvesting requires alternative and ‘cheap’ cell technologies as they have to be deployed in environments which are unsuitable for Si – e.g flexible substrates such as clothing

Powering of autonomous sensing and communication electronics for information gathering

Sensing your

environment

Gateway to cellular/IP networks

Local

Sensors

Other devices

Computing

Memory

Services

Communities

Content

Global

Physical objects in future intelligent

environments

Physical objects in future intelligent

environments

Future “wearable”personal trusted devices

Future “wearable”personal trusted devices

Physical and digital worlds fuse

Physical and digital worlds fuse

Sensing, computing and communication


Nanocomposite cells

In a nanomposite cell the semiconducting element is scaled to nanometer scale dimensions – e.g a 50nm dia wire – and dispersed in a polymer( flexible) matrix.

The cell performance is determined by the ‘ensemble’ behaviour of the semiconducting nanowires


Materials when taken down to the < 50nm scale can exhibit physical and chemical properties not seen in bulk phases – e.g.

CNT vs graphite Accepting that synthesis can be carried out on a large

scale, exploitation of these properties will require:(1) Technologies for placement, contacts,integration etc

of individual objects with scales < 50nm in at least two dimensions.

OR(2) Dispersion of nanoscale particles in a host matrix,

with ‘ensemble’ behaviour of the particles in the matrix enabling enhanced physical/chemical performance. The Nanocomposite


MWCNT NEMS Switch: Gate voltage applied to deflect suspended CNT to makecontact with source.

source drain

gate 0 1 2 3 410-13

10-12

10-11

10-10

10-9

10-8

10-7

0 1 2 3 4

10-13

10-12

10-11

10-10

10-9

10-8

10-7

-

-

-

-

-

-

-

- ---

Sour

ce/D

rain

Cur

rent

(A

)

Gate Bias (V)

Drain -0.5V, Gate 0 to -4VDrain 0.5V, Gate 0 to 4V

Example of Category 1 Research at Cambridge:

S.N. Cha et al, APL 2005


Deterministically and spatially controlled growth of CNTs for ‘ensemble’ field emission.

Arrays

Electronsource

Electronsource

Examples of Category 1/2 Research at Cambridge


Nanocomposite Research – Category 2

Specially suited for energy conversion and storage:

(i) Polymer – CNT solar cells(ii) Supercapcitors(iii) Batteries/fuel cells


Zinc Oxide Nanowires

Z.L. Wang, MRS Bulletin 32 (2007)

Direct wide bandgap material (3.37 eV)Large exciton binding energy (60 meV)Transparent and semi-conductingPiezoelectric, pyroelectricPhotoconductingBio-safe and biocompatibleMany structures….


Zinc Oxide Nanowire Growth (CVD)

ZnO (s) + C (s) Zn (gas) + CO (gas)

Hongjin Fan et al. Nanotechnology 17 (2006)

Silicon

Sapphire


CNT@Cambridge Grouphttp://www-g.eng.cam.ac.uk/cnt/

Zinc Oxide Nanowire Characterization

2.58 Å

< 001 >

30 40 50 60 70 80

(11

2)

(10

3)

(11

0)

(10

2)

(10

1)

(00

2)(1

00

)

cou

nts

position (2-Theta)

300 400 500 600 700

4.0 3.5 3.0 2.5 2.0photon energy (eV)

inte

nsity

(a.

u.)

wavelength (nm)

266 nm at 298K

01-100002


Hydrothermal ZnO Nanowire Synthesis

Step 1: Spin coat zinc acetate

Step 2: NW growth in solution

Zinc salt hydrolysis,HMTA

90º C

High density, yield, quality nanowires Economic and environmental Any type of substrate can be used Scalable to large area


30 40 50 60 70 80(0

04)

(11

2)

(10

3)

(10

2)

(110

)

(00

2)(1

01)

Co

unt

s

position (2-Theta)

(10

0)

ZnO Nanowire Characterization

300 400 500 600 700

4.0 3.5 3.0 2.5 2.0

photon energy (eV)

inte

nsity

(a.

u.)

wavelength (nm)

266 nm at 298 K


= 800 – 1080 cm2/Vs

ON/OFF ~ 106


ZnO Nanowire Electrical Properties

= 18 - 44 Ω.cm


SWNT Thin Films with ZnO NWs

1 2 30

25

50

75

100

Tra

nsm

itta

nce

(%

)

Photon energy (eV)

Untreated (800 ohms/sq.)

HNO3treated (450 ohms/sq.)

ZnO Nanowires

SWNT TF

Parekh, Fanchini, Eda, Chhowalla APL 90 (2007)

1000 2000 3000 4000

wavenumber (cm-1)

C=CC=O CH

OH

Inte

nsity

(ar

b. u

n.)

HNO3 Treated

Untreated

SWNT Network


ZnO NW - SWNT TF OPVs

-0.2 0.0 0.2 0.4 0.6-3

-2

-1

0

1

2 SWNT-ZnO light SWNT-ZnO dark

Cu

rre

nt D

en

sity

(m

A/c

m2 )

Voltage (V)

Voc = 460mVIsc = -2.31FF ~ 0.6

Eff. ~ 0.64

400 500 600 7000

10

20

30

Ext

ern

al Q

ua

ntu

m E

ffici

en

cy (

%)

Wavelength (nm)

100 mW/cm2

Unalan et al. to be submitted

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

4.2 eV

7.4 eV

5.1 ev

PEDOT

En

erg

y [e

V]

LUMO or Ec

HOMO or Ev

Work

P3HT AuS-SWNTM-SWNT

e- h+

5.2 eV

3.53 eV

4.8 eV

5.4 eV

4.5-5.0 eV

5.0 ev

ZnO

Substrate


Use of nanostructured electrodes to have ‘area’

concentrator cells.For fixed material, target is large h but small d, l

Cell 1: interpenetrated junction Cell 2: interpenetrated electrodes


Vertically aligned CNT – a-Si:H cell

CNT

a-Si:H (n-i)

ITO

W

Fig 2. A schematic diagram showing the periodic CNT arrays offer multiple absorption opportunities in amorphous silicon photovoltaic cell.


a-Si:H on CNT cell

Periodic CNT array

a-Si: H and ITO coated CNT array



Fabrication sequence for CNT/a-Si:H/ITO cell

I Deterministic MWCNT growth II Conformal n+ and i-a-Si:H III – ITO transparent contact IV Completed array(hole collector)


500 nm

MWCNTa-Si:H

ITO

Capacitance enhancement

(i) with CNT (ii) no CNT

40 nm

TEM and EDX


Performance of photovoltaic devices with and without CNTs arrays when illuminated with normal incident light. (b) Performance of solar cell with dot pattern CNTs electrode when illuminated with light from different incident angles


Wavelength dependency of Isc

enhancement

Ⅰ Ⅱ

Ⅰ Ⅱ

PV-1

PV-2

Filtered PV response

PV-1 PV-2


PV cell on flexible carbon fibre fabric

Electrospun carbon fibre

ZnO nanowires gown directly on fibre

‘black dye’ light absorber

Ionic counter electrode


Flexible carbon fabric

SEM image of the carbonized carbon fibre fabric with an average diameter of 1.16 µm.

10m


ZnO grown directly on carbon fibre


PV Cell


A room temperature processed solar cell on flexible substrate

A novel ionic liquid was synthesized by grafting polyvinylalcohol (PVA) with ionic liquid 1-butyl-3-vinylimidazoliumbromide (VIC4Br) under the irradiation of a 60Co-γ source.


Ionic liquid based solid dye sensitised PV cell


Reverse process – Light emission from ZnO NW composite

Flexible & transparent deviceCheap and simple to fabricate, at low temperature (max. 150ºC)Fully solution processable, no vacuum required.

Device Structure

220nm


LED Fabrication – Hydrothermal NW growth

Step 1: Hydrothermal Growth of ZnO nanowires on ITO coated glass

Simple, low temperature method High density, yield, quality nanowires Economic and environmental Any type of substrate can be used Scalable to large area Controllable dimensions

Greene et al. Nano Lett. 5 (2005)

Kim et al. APL 89 (2006)Vayssieres et al. Adv. Mater 15 (2003)


Optical Properties Transmission Spectra Photoluminescense spectra

300 400 500 600 700

4,0 3,6 3,2 2,8 2,4 2,0

Inte

nsity (a.u

.)

Wavelength (nm)

Hydrothermal NW PL266nm laser at 298K

400 500 600 700 800 9000

20

40

60

80

100

3,6 3,2 2,8 2,4 2,0 1,6

% T

ran

sm

issio

n

Wavelength (nm)

Transmission spectrum-ZnO wires on ITO+glass


LED Fabrication

No plasma

1 min

3 min 6min

Step 1: Hydrothermal Growth of ZnO nanowires on ITO coated glassStep 2: Spin coat insulating layer, dry and etch the tips


LED FabricationStep 1: Hydrothermal Growth of ZnO nanowires on ITO coated glassStep 2: Spin coat insulating layer, dry and etch the tipsStep 3: Spin coat organic p-type layer

poly(styrenesulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS)

• Highly p-doped hole injection layer

• Water based solvent

•Highly stable


LED structureStep 1: Hydrothermal Growth of ZnO nanowires on ITO coated glassStep 2: Spin coat insulating layer, dry and etch the tipsStep 3: Spin coat organic p-type layerStep 4: Evaporate metal contact


LED diode Characteristic

-2 -1 0 1 2 3 4 5 6 7 8 9

0

-2

-4

-6

-8

Curr

ent (m

A/c

m2 )

Forward Bias (V)


Light Emission

350 400 450 500 5500

300

600

900

409.25

450.72

479.84

Inte

nsity

(A

u)

Wavelength (nm)

•Narrow band emission•Emission Threshold: ~9V

A. Nadarajah et al. Nanoletters, December 2007

???


Origin of ultra-sharp emission peak at 450nm

Al PEDOT:PSS ZnO ITO

-7

-6

-5

-4

-3

Ener

gy(e

V)

4.1eV

3.3 eV

5.3 eV

4.2 eV

7.6 eV

4.7 eV

Estimated Fermi Levels

Energy levels for materials used

Device under forward bias

• Due to the large barrier, electron and hole accumulation occurs outside the depletion layer

• At this point, recombination probability is high.

~450nm


450nm

•ZnO is known to posses defect states, specially so, on solution grown wires• If one on these defects emits at 450nm, even though intensity may be low, if it is long lived, it can be constructively amplified by ZnO NW cavity.

Oriented ZnO NW acting as cavity for light Amplification

Experimental length ~220nm


Energy Storage : Two aspect are important – energy density and power

density

1 10 100 1,000 10,000

1

10

100Li ion

Ni MHNi CdPb

Activated C

CNT goal

batteries

super-caps

capacitors

Ene

rgy

dens

ity (

Wh/

kg)

Power Density (W/kg)

Ragone Plot


Capacitive energy storage




1E+01

1E+00

1E-02 1E+00 1E+01 1E+03 1E+041E-01 1E+02

1E+03

1E+02

1E+04

1E+05

1E+06

EML

HEL

BUS

PFNTPL Film Cap

Ultracap

Ultracap CHPS Lithium Ion

Lithium Ion

Nickel Metal Hydride

Ultracap

Lead AcidFlywheel

Flywheel

SMES

Compulsator 10ms 2sec

0.1 hr100 hr

Watt hours per kg

Wat

ts p

er k

gRevised Energy and Power Densities Chart

Points from previous chartNew SMES points

2

4

15

69

8

3

7AFS Flywheel

Virial Limit

Commercial ultracapsLaboratory ultracaps


Ragone plot and battery discharge curve


Li ion BATTERY TECHNOLOGY TRENDS

800Wh/L

20102008

550Wh/L

800Wh/L

20102008

550Wh/L

EN

ER

GY

SO

UR

CES

New Lithium-based chemistries provide potential for further battery capacity improvement.

A major limitation of Li ion batteries remains their loss of capacity with time irrespective of the number of charge-discharge cycles. A capacity loss of 20% per year is common.


A Practical solution would be an integrated device in which it appears as if

a Li ion battery is connected in parallel

with a supercapacitor

+ +

-

-


Solid Li ion batteries

No liquid electrolyte ( Li salt in an organic solvent) – allows removal of metal casing required to contain liquid. Light weight batteries.But solid electrolyte does not take up Li very well – ion conducting polymer composite, higher internal resistance.Energy density can be enhanced by increasing Li take up of the anode – currently intercolated carbon.


Solid Supercapacitors

Enhanced Electrode areas with solid High relative permittivity dielectric.

Nanocomposite of electrode and dielectric?

Pioneering a new nanocomposite system which results in an interpenetrating Li-ion battery and supercapcitor network.


New method for bulk production of nanocarbon materials which can be

suitable for energy storage applications

Nature, 506 (414), 2001

Nano-onions


Carbon nanohorns: Bulk synthesis by arc in liquid nitrogen.

Enhanced take up of metal/catalyst particles. Suitable for both Li-ion anode and Pt catalyst on electrode for fuel cells

Nanotech.546(15)2004


Synthesis of Nanohorn-metal

composite

Carbon 95(42)2004

CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERINGELECTRONICS, POWER ANDENERGY CONVERSION GROUP

CNH Ongraphite

CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERINGELECTRONICS, POWER ANDENERGY CONVERSION GROUP

NP agglomerates are 20-100nm diameter spherical structures with concave and convex curves inside the structure.Distance between the graphene sheets, d=0.376nm compared to ordinary graphite 0.336nm. Chemical and surface energy differences are expected because of the highly curved surface structures, and possible edge formations at the surface


Surface Area Measurements of SWNHs

ELECTRONICS, POWER ANDENERGY CONVERSION GROUP

Nitrogen adsorption isotherms taken at 77K for as-produced and modified SWNH (oxidized in air at 350ºC).

1000 ~1500 m2/g



Joint programme with Nokia to explore flexible energy storage systems



Conclusions

Polymer nanocomposites can significantly enhance the performance of organic photovoltaic devices.The same concept of distributed and interpenetrating junctions can be extended to electrodes and ion conducting polymers. These would be applicable in Li-ion batteries and supercapacitors.New nanomaterial structures which can be synthesised by bulk methods should be explored in nanocomposites for energy storage.Engineered structures, such as vertically aligned and optimally placed carbon MWCNTs, could form the back bone for enhanced supercapacitors.


ConclusionsPolymer nanocomposites allow the opportunity to use inorganic semiconductors in nanowire form for ubiquitous energy harvesting photovoltaic devices.High electronic quality ZnO nanowires grown on SWNTs and carbon fibres are suitable for charge separation with polymer and dye absorbers.Oriented nanowires and nanotubes allow an additional degree of freedom for optical design of PV cells. Narrow band width light emission observed from oriented ZnO/PDOT:PSS heterojunction diodes


AcknowledgementsCambridge

Emrah Unalan, Pritesh Hiralal, Hang Zhou, Daniel Kuo, Shavari Dalal, Nalin Rupesinghe, Sai Giridhar, Tim Butler

Nokia Cambridge Research CentreDi Wei, Alan Colli, Markku RouvalaRutgersManish ChhowallaTokyo Institute of TechnologyKenichi Suzuki, Akihiko TaniokaNagoya Institute of TechnologyYasuhiko Hayashi

Financial SupportSamsung Advanced Institute of Technology;Nokia – Cambridge Strategic Research Alliance in

Nanotechnology