Bottom up method for Bottom up method for preparing nanostructures: preparing nanostructures:

growth of carbon growth of carbon nanotubesnanotubes

Akos KukoveczAkos Kukovecz

Universität Wien 2002Universität Wien 2002

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Talk layoutTalk layout

• Carbon nanotube basicsCarbon nanotube basics• Overview of the synthesis techniquesOverview of the synthesis techniques• NT growth theories & modelsNT growth theories & models• Application oriented growth – examplesApplication oriented growth – examples• PurificationPurification

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Carbon nanotube basicsCarbon nanotube basics

(10,5) SWCNT(10,5) SWCNT

SWCNT: rolled-up graphene sheetSWCNT: rolled-up graphene sheet

diameter: ~0.7-3 nm, length > 500 nmdiameter: ~0.7-3 nm, length > 500 nm

C(n,m) : chiral vector diameter, electrical C(n,m) : chiral vector diameter, electrical propertiesproperties

From the website of Dr. Maruyama.From the website of Dr. Maruyama.

R. Saito et al.: Physical Properties of Carbon Nanotubes, Imperial Press, London, 1999,R. Saito et al.: Physical Properties of Carbon Nanotubes, Imperial Press, London, 1999,

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SWCNT morphologySWCNT morphology

Synthesis yields entagled mat of nanotube bundlesSynthesis yields entagled mat of nanotube bundles

Science, Science, 273273, 483., 483.

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Multi wall carbon Multi wall carbon nanotubesnanotubes

Co-axial set of increasing diameter SWCNTsCo-axial set of increasing diameter SWCNTs

• Easier synthesis than SWCNTsEasier synthesis than SWCNTs• Accurate quality control is evenAccurate quality control is even more difficult more difficult

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Talk layoutTalk layout

• Carbon nanotube basicsCarbon nanotube basics• Overview of the synthesis techniquesOverview of the synthesis techniques• NT growth theories & modelsNT growth theories & models• Application oriented growth – examplesApplication oriented growth – examples• PurificationPurification

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Synthesis of multi wall Synthesis of multi wall tubestubes

d.c. arcd.c. arc

SetupSetup

ParameterParameterss

• d.c. arc, 20 V, 100 Ad.c. arc, 20 V, 100 A• 500 torr He 10 ml/s500 torr He 10 ml/s• electrode distance 1 mmelectrode distance 1 mm• ~3000 °C in plasma~3000 °C in plasma

PropertiesProperties

• No catalyst neededNo catalyst needed• MWCNT in cathode MWCNT in cathode deposit, deposit, • dd = 2-25 nm, = 2-25 nm, ll 1 1 mm

• Co/graphite: 100 nm, 60 Co/graphite: 100 nm, 60 mm

• Co/SiOCo/SiO22: 30 nm, 10 : 30 nm, 10 mm

• Fe: more amorphous Fe: more amorphous carboncarbon• Ni, Cu: no nanotubesNi, Cu: no nanotubes

•5-10 % C5-10 % C22HH22, C, C66HH66 in N in N22, , ArAr• Co (Fe, Ni) @ MgO, Co (Fe, Ni) @ MgO, AlAl22OO33, SiO, SiO22, zeolites, , zeolites, graphite etc.graphite etc.• 700-1100 °C, 1 atm700-1100 °C, 1 atm

Vapor deposition (CVD)Vapor deposition (CVD)

APA APA 6767 1. 1.

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SWCNT synthesisSWCNT synthesis

Catalyst?Catalyst?nono

Exotic Exotic methodsmethods

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Exotic SWCNT synthesis I.Exotic SWCNT synthesis I.

CH3

CH3

CH3

N

TPA is template forTPA is template forAlPOAlPO44-5 synthesis-5 synthesis

AlPOAlPO44-5 is a zeolite-5 is a zeoliteanalogoue analogoue

Pyrolysis (550 Pyrolysis (550 °°C) C) transforms TPA into SWCNTtransforms TPA into SWCNT

AlPOAlPO44--55

PyrolizedPyrolized

APA APA 6969 381. 381.

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Exotic SWCNT synthesis II.Exotic SWCNT synthesis II.Coalescence of CCoalescence of C6060 molecules into SWCNT within the molecules into SWCNT within the

nanospace of a larger SWCNT (peapod system).nanospace of a larger SWCNT (peapod system).

Heating: vacuum, 1000 Heating: vacuum, 1000 °°C, 14 hoursC, 14 hours

From the website of Dr. Maruyama.From the website of Dr. Maruyama.

CPL CPL 337337 48. 48.

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SWCNT synthesisSWCNT synthesis

Catalyst?Catalyst?nono

Exotic Exotic methodsmethods

yesyes

In situ generated?In situ generated?nono

CVDCVD

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Chemical vapor deposition Chemical vapor deposition (CVD)(CVD)

Unique:Unique: NT growth location controlled! NT growth location controlled!

ParametersParameters CatalystCatalyst ProductProduct

800-1000 800-1000 °°CCCHCH44: 1 dm: 1 dm33/min/min

• strong metal-support strong metal-support interactioninteraction

• large surface arealarge surface area• large mesopore large mesopore

volumevolume

Fe/Mo @ aluminaFe/Mo @ alumina

Co @ MgOCo @ MgO

SWCNTSWCNT

d=1.4 nm, l>10 d=1.4 nm, l>10 mm

NTs grow from the metal clusters.NTs grow from the metal clusters.Metal clusters can be positioned by Metal clusters can be positioned by e.g. litography, ink printing, laser etching...e.g. litography, ink printing, laser etching...

APA APA 6767 1. 1.

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SWCNT synthesisSWCNT synthesis

Catalyst?Catalyst?nono

Exotic Exotic methodsmethods

yesyes

In situ generated?In situ generated?nono

CVDCVD yesyes

Starting phase?Starting phase?solidsolid

• d.c. arc discharged.c. arc discharge• pulsed laser vaporization (PLV)pulsed laser vaporization (PLV)

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d.c. arc discharged.c. arc dischargeSWCNTs: in soot, collarett.SWCNTs: in soot, collarett.

Conditions: as for MWCNT.Conditions: as for MWCNT.

Anode contains catalyst!Anode contains catalyst!

Good SWCNT yield:Good SWCNT yield:Co, Co/Ni, Co/Fe, Ni/Y, Ni/FeCo, Co/Ni, Co/Fe, Ni/Y, Ni/Fe

Product:Product: diameter control not straightforwarddiameter control not straightforwardtubes often covered with amorphous carbontubes often covered with amorphous carbon

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Pulsed laser vaporization Pulsed laser vaporization (PLV)(PLV)

target Collectorlaser

He (Ar)

ParametersParameters TargetTarget ProductProduct

T = 1200 °CT = 1200 °C2 successive 2 successive

pulsespulses

GraphiteGraphite

+0.5% catalyst (Ni, +0.5% catalyst (Ni, Co)Co)

SWCNTSWCNT

d=1.4 nm, l>10 d=1.4 nm, l>10 mm

Good diameter control, little amorphous carbon.Good diameter control, little amorphous carbon.APA APA 6767 1. 1.

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SWCNT synthesisSWCNT synthesis

Catalyst?Catalyst?nono

Exotic Exotic methodsmethods

yesyes

In situ generated?In situ generated?nono

CVDCVD yesyes

Starting phase?Starting phase?solidsolid

• d.c. arc discharged.c. arc discharge• pulsed laser vaporization (PLV)pulsed laser vaporization (PLV)

gasgas

• flame pyrolysisflame pyrolysis• gas phase gas phase decomposition decomposition

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NT yield < 1%NT yield < 1%Mostly SWCNTsMostly SWCNTs

Flame pyrolysisFlame pyrolysisContinuous productionContinuous production, familiar plant engineering -> CHEAP!, familiar plant engineering -> CHEAP!

SWCNTs grow in sooting flame: OSWCNTs grow in sooting flame: O22+fuel+catalyst. +fuel+catalyst.

Fuel: CFuel: C22HH22, C, C66HH66 1-3 dm 1-3 dm33/min + x(2-4) O/min + x(2-4) O22

Catalyst: ferrocenes, metallocenes, Fe(NOCatalyst: ferrocenes, metallocenes, Fe(NO33))33

TTflameflame=1200 =1200 °°C, p=80 Torr, t=250 msC, p=80 Torr, t=250 ms JPC B JPC B 104104 9615. 9615.

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Gas phase catalytic Gas phase catalytic decompositiondecomposition

Continuous productionContinuous production -> low cost! -> low cost!Carbon sources: hexane, benzene, acetylene, CHCarbon sources: hexane, benzene, acetylene, CH44, , CO,...CO,...Catalyst precursors: metal-carbonyls & Catalyst precursors: metal-carbonyls & metallocenesmetallocenes

HiPCO processHiPCO process

CO: CO: 10 atm 10 atm 1 1

dmdm33/min/minFe(CO)Fe(CO)55: 5 ppm: 5 ppm

d = 0.7-1.4 nmd = 0.7-1.4 nml > 1 l > 1 mm

Boudouard: 2 Boudouard: 2 CO CO

C + COC + CO2 Treshold: 500 Treshold: 500 °C°C

n Fe(CO)n Fe(CO)55 = Fe = Fenn + 5n CO Treshold: 250 + 5n CO Treshold: 250 °C°C

CPL CPL 313313 91. 91.

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Talk layoutTalk layout

• Carbon nanotube basicsCarbon nanotube basics• Overview of the synthesis techniquesOverview of the synthesis techniques• NT growth theories & modelsNT growth theories & models• Application oriented growth – examplesApplication oriented growth – examples• PurificationPurification

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Nanotube growth theoriesNanotube growth theoriesAre they really so different?Are they really so different?

Common points:Common points:

• All go to atomization temperatureAll go to atomization temperature

Hexagonal spHexagonal sp22 graphite is the most graphite is the moststable form of carbon.stable form of carbon.

• Constrain :Constrain :Steric limit / catalyst presentSteric limit / catalyst present

Nanotubes insteadNanotubes insteadof graphene sheets!of graphene sheets!

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Possible growth Possible growth arrangementsarrangements

Root growth: VLSRoot growth: VLSTip growth: scooterTip growth: scooter

CCCC

CC

Gro

wth

dire

ction

Gro

wth

dire

ction

CC CC

CC

Gro

wth

dire

ction

Gro

wth

dire

ction

CC CC

CC

Gro

wth

dire

ction

Gro

wth

dire

ction

SkullcapSkullcap

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Tip growth: scooter modelTip growth: scooter model

Co (Ni) atom cycles: Co (Ni) atom cycles: C atoms add to hexagonsC atoms add to hexagons

Co (Ni) atom stops (e.g. gets too large): Co (Ni) atom stops (e.g. gets too large): Dangling bonds make pentagons, close dome.Dangling bonds make pentagons, close dome.

TEM: no metal in NT tipTEM: no metal in NT tip

Topics in Appl. Phys. Topics in Appl. Phys. 8080 55. 55.

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Root growth: VLS modelRoot growth: VLS model

Vapor-Liquid-Solid (VLS) modelVapor-Liquid-Solid (VLS) model

Carbon from vapor phase dissolves in Carbon from vapor phase dissolves in liquid metal nanocluster, then segregates liquid metal nanocluster, then segregates on cluster surface to give solid nanotubes.on cluster surface to give solid nanotubes.

NTs grow radially from NTs grow radially from Ni-carbid partice.Ni-carbid partice.

TEMTEM

PRL PRL 8787 275504. 275504.

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Root growth: MD Root growth: MD simulationsimulationI. NucleationI. Nucleation

Red: Red: CoCoGray: Gray: CC

2000 K2000 KHomogeneous distr.Homogeneous distr.

1500 K1500 KC segregates to surfaceC segregates to surface25 ps25 ps

Aromatic Aromatic ringsrings

1500 K1500 K

15 ps15 ps

5 new C enter the tube5 new C enter the tube

II. GrowthII. Growth PRL PRL 8787 275504. 275504.

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Skullcap growth: MD Skullcap growth: MD simulationsimulation

Ni cluster (blue): d=1.2 nmNi cluster (blue): d=1.2 nmFree C atoms come from gas.Free C atoms come from gas.

From the website of Dr. Maruyama.From the website of Dr. Maruyama.CPL CPL 260260 471. 471.

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Talk layoutTalk layout

• Carbon nanotube basicsCarbon nanotube basics• Overview of the synthesis techniquesOverview of the synthesis techniques• NT growth theories & modelsNT growth theories & models• Application oriented growth – examplesApplication oriented growth – examples• PurificationPurification

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Application oriented growth: CVDApplication oriented growth: CVDElectronic industry can not use random NT mats!Electronic industry can not use random NT mats!

SWCNT network between Si pillarsSWCNT network between Si pillars

SWCNT gas sensorSWCNT gas sensor

10 ppm range10 ppm range

0.1 % range0.1 % range

• Field emission Field emission displaysdisplays

• FET mass productionFET mass production

APL APL 8181 2261. 2261.

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Talk layoutTalk layout

• Carbon nanotube basicsCarbon nanotube basics• Overview of the synthesis techniquesOverview of the synthesis techniques• NT growth theories & modelsNT growth theories & models• Application oriented growth – examplesApplication oriented growth – examples• PurificationPurification

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Nanotube purificationNanotube purification

I.I. Contaminants: catalyst metal & amorphous Contaminants: catalyst metal & amorphous carboncarbon

II.II. Removal: metals by dissolving in acid (HCl, Removal: metals by dissolving in acid (HCl, HNOHNO33))

carbon by selective oxidation (Ocarbon by selective oxidation (O22, , wet air, wet air, HNO HNO33, , HH22OO22 etc.) etc.)

III.III. Challanges: Challanges: NTs not soluble in any NTs not soluble in any solventsolvent

sonication can break NTssonication can break NTs

thin NTs sensitive to thin NTs sensitive to oxidationoxidation

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Thanks for your attention!Thanks for your attention!

AkoskaAkoska®®