GRAPHENE PASSING THROUGH - NTUAold.chemeng.ntua.gr/seminars/download/Athens January 2011.pdf ·...

FROM FULLERENES TO

GRAPHENE PASSING THROUGH

CARBON NANOTUBES: SYNTHESIS, PROPERTIES AND SYNTHESIS, PROPERTIES AND

APPLICATIONS OF quasi-NEW

ALLOTROPES OF CARBON.

Simone MussoSimone Musso

spsp22 and spand sp33 hybridizationshybridizations

sp3sp2

Carbon, having an electron configuration 1s2 2s2 2p2, forms a great variety ofcrystalline and disordered structures because it can exist in three differenthybridizations, sp3, sp2, sp1.

Planar geometry

Tetrahedral geometry

Cubic, sp3

hybridization

Diamond

3.4 ÅPlanar, sp2

hybridization

Graphite

Allotropic forms of CAllotropic forms of C

Planar geometry

Tetrahedral geometry


Cubic, sp3

hybridization

Diamond

3.4 ÅPlanar, sp2

hybridization

Graphite

Nanotube

Fullerene

Nanotube/Fullerene sp2 + sp3 character

Physical and chemical properties are a direct consequence of the carbon-carbon bonds and lattice configuration


Cubic, sp3

hybridization

Diamond

3.4 ÅPlanar, sp2

hybridization

GraphiteGraphene


Carbon NanotubeFullerene

Discovery of fullerene or buckyballDiscovery of fullerene or buckyball

H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl and R. E. Smalley, Nature 318 (1985) 162–63.

Discovery of fullereneDiscovery of fullerene

Before the C60 structure was considered beyond doubt, a sufficientamount of material had to be prepared for detailed spectroscopicanalysis, but a lack of funds stopped the research6..

Then, in 1990 Kratschmer and Huffman developed an arc dischargetechnique:

DC Arc-discharge

W. Krätschmer, L. D. Lamb, K. Fostiropoulos and D. R. Huffman, Nature 347 (1990) 354–58.

ddp ≈≈≈≈ 20 VI = 100-200 AT° →→→→ 4000-6000°CHe or Ar (600mbar)

Characterization of fullereneCharacterization of fullerene

MS

XRD

W. Krätschmer, L. D. Lamb, K. Fostiropoulos and D. R. Huffman, Nature 347 (1990) 354–58.

UV-VisFT-IR

FullerenesFullerenes

C540

C960

C240

C

8.34 Å ; 7.66 Å

Different fullerenes can be separated

C60 (bucky ball)

d= 7.1 Å

C70 (rugby-ball shaped)Different fullerenes can be separated by means of chromatographic

column.

Fullerene propertiesFullerene properties

� Fullerenes are non-toxic and are soluble in several organic solvents.

�Fullerenes are quite stable. However the spherical curvature producesangle strain that allows fullerenes to undergo characteristic reactions ofaddition to double bonds (hybridization turns from sp2 to sp3).

�C60 in organic solvents exhibits 5 stages of reversible oxidation/reduction,hence fullerene can work either as electrophiles or nucleophiles.

CHEMICAL REACTIVITY

hence fullerene can work either as electrophiles or nucleophiles.

C60F18

Image created by Chris Ewels, www.ewels.info


Fullerenes, packed in fcc structure, can be intercalated with alkali andalkaline-earth metal atoms which provide electrons to the conductionband (from semi-conducting to metallic behavior). In 1991 potassium-doped fullerene (K3C60) revealed superconducting behavior at 18K.

DERIVATIVES: EXOHEDRAL, ENDOHEDRAL and ON-SITE DOPING

L. Forrò and L. Mihaly, Rep. Prog. Phys. 64 (2001) 649-699.


DERIVATIVES: EXOHEDRAL, ENDOHEDRAL and ON-SITE DOPING

� In the endohedral doping a foreign atom is inserted in the inner cavity(M @ C60). This doping can be performed either by ion implantation orcoevaporation of C and metal in arc discharge system.

� The on-site doping is achieved by replacing one carbon atom with anitrogen atom ((C59N)2 azafullerene).

CNTs !!!

Image created by Chris Ewels, www.ewels.info L. Forrò and L. Mihaly, Rep. Prog. Phys. 64 (2001) 649-699.

Fullerenes applicationsFullerenes applications

� Hydrogen or oxygen storage: hydrogenation of fullerene produceshydrides. The reaction is reversible and can be catalyzed with metals (lowpressure).

� Catalyst: fullerene promotes the conversion of methane into higherhydrocarbons and inhibits coking reactions.

� Sensor: fullerene based capacitors can be used to detect ppm of H2S� Sensor: fullerene based capacitors can be used to detect ppm of H2Sin N2, ppm of water in isopropanol.

� Diamond precursor: fullerene can be transformed to diamond at highpressure (RT) or can be used as a diamond nucleation center during CVD.

� Alloy strengthening/hardening (Ti), improvement of electricalconductivity of Cu alloys.

� Biomedical field: inhibition of human HIV replication and HIV-1protease. Biological antioxidant (radical sponge).


Cubic, sp3

hybridization

Diamond

3.4 ÅPlanar, sp2

hybridization

Graphite


FullereneCarbon Nanotube

Discovery of CNTsDiscovery of CNTs

Many scientific papers start citing ‘‘the discovery of Many scientific papers start citing ‘‘the discovery of carbon nanotubes by Iijima in 1991. . .’’carbon nanotubes by Iijima in 1991. . .’’

Arc-discharge: from endohedral fullerene to CNTs

S. Iijima, Nature 354, (1991) 56


First TEM evidences of nanoFirst TEM evidences of nano--sized carbon tubessized carbon tubes

L.V. Radushkevich, V.M. Lukyanovich, Zurn. Fisic. Chim. 26, (1952) 88

First TEM evidences of nanoFirst TEM evidences of nano--sized carbon tubessized carbon tubes

What are CNTs?What are CNTs?

Rolled graphene sheet

Diameter: 0,7 - 100 nm

Length: from few tens of nm up to several mm

EvenEven ifif thethe curvaturecurvature causescauses aa higherhigher strainstrain energy,energy, aa defectdefect freefree CNTCNThashas anan overalloverall lowerlower energyenergy statestate thanthan graphitegraphite becausebecause danglingdanglingbondsbonds areare removedremoved.. ThisThis explainsexplains highhigh thermalthermal stabilitystability andand chemicalchemicalinertnessinertness..

CNTs classificationCNTs classification

SWCNTs classificationSWCNTs classification

Zig-zag

Chiral

n −−−− m ≠≠≠≠ 3 ×××× integer

Semi-conductor behavior

depending on the diameter.

A CNT is characterized by its Chiral Vector (A CNT is characterized by its Chiral Vector (CChh))= = n n ââ11 + + m m ââ22

and by the Chrial Angle (and by the Chrial Angle (θθθθθθθθ) with respect to the zig zag axis) with respect to the zig zag axis

Armchair

Chiral

n −−−− m = 3 ×××× integer Metallic

conductor behavior

Armchair (5,5)

θθθθ = 30°°°°

Zig Zag (9,0)

θθθθ = 0°°°°

SWCNTs classificationSWCNTs classification

θθθθ = 0°°°°

Chiral (10,5)

0°°°° θθθθ < 30°

CharacterizationCharacterizationHR-TEMSEM

200 400 600 800

0

20

40

60

80

100

Weight derivative [%/°C]

Temperature [°C]

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Air 20°C/min

Weight [%

]

TGA

Temperature [°C]

10 20 30 40 50 60 70 80 90 100

(*)

(004)

(100)

(*)

(002)

Intensity (arb.unit)

2θ (°)

XRD

500 1000 1500 20000

200

400

600

800

1000

1200

1400

1600

1800

Raman shift (cm-1)

Intensity (a.u.)

Raman spectroscopy

1344 cm-1

D peak

1591 cm-1

G peak

RBM

Properties of defect free CNTsProperties of defect free CNTs

Young’s modulus

(GPa)

Tensile Strength

(GPa)

Density

(g/cm3)

MWCNT 1200 ∼150 2.6

SWCNT 1054 75 1.3

SWCNT bundle 563 ∼150 1.3

Graphite (in-plane) 350 2.5 2.2-2.6

Steel 208 0.4 7.8

Thermal conductivity Electrical conductivityThermal conductivity

(W/mK) RT

Electrical conductivity

(A/cm2)

MWCNT ∼3000 ≤109

SWCNT ∼6000 Depends on the chirality

SWCNT bundle ∼3000 ≤109

Graphite (in-plane) ∼1700 ≤109

Diamond 2000 - 2500

Copper 401 106

FunctionalizationFunctionalization

Chemical functionalization can be used to tune CNTs properties.

� Composite – improving compatibility matrix/filler

� Biomedical – improving biocompatibility, drug delivery, diagnosis6

Chemical (KMnO4, HNO3-H2SO4) or plasma oxidation change surface properties while producing lattice defects (removable by annealing).

Van der Waals interactions with porphyrin or pyrene derivatives are less effective.

CNT properties/applicationsCNT properties/applications

CNT synthesisCNT synthesis

High temperature methods

� Arc Discharge

� Laser ablation

These techniques generate small amount of high quality CNTs by sublimation ofgraphite in presence of catalyst particles.

Gas phase (vapor phase) methods

� Chemical Vapor Deposition (CVD) and plasma enhanced-CVD (PECVD)

During CVD a conventional heat source is used to form CNTs by thermal cracking ofhydrocarbons. A plasma source is used in PE-CVD to create a glow discharge whichprovokes a low temperature precursor dissociation

Nanoparticles of Co, Ni or Fe are necessary to catalyze the growth

CNT synthesisCNT synthesis

Gas or low bp liquids can be

used. The CVD technique is

simple, low-cost, easily scalable

for commercial production and

allows to produce large amounts

of CNTs with high purity.

CVD

PECVD

V= -600VT° →→→→ 400-800°CAr or N2 (0.1-30 Torr)

Plasma discharge sources:

- direct current (DC),

- alternating current (AC),

- radio frequency (RF),

- hot-filament aided with DC,

- microwaves

We do like gas phase techniquesWe do like gas phase techniques

CVD allows to produce cm long CNTs. With direct spinning is also possible thesynthesis of very long CNT ropes in situ.

Ya-Li Li et al., Science 304 (2004) 276 S. Musso et al. Carbon 45 (2007) 1133-1136

CNT growth mechanismCNT growth mechanismTwo theories for the carbon-metal interaction:

� Dissolution and saturation of carbon atoms in metal nanoparticles andprecipitation of carbon.

� The catalyst provokes dehydroaromatization (DHA) of cyclic molecules ofhydrocarbon.

Base growth mechanism is dueto a strong adhesion of thecatalyst to the substrate.

Tip growth mechanism is due to aweak adhesion of the catalyst tothe substrate.

Tip growth mechanismTip growth mechanism

Stephan Hofmann et al., Nanoletters 7 (2007) 602

TOXICITYTOXICITY

Small CNT

Factors influencing the safety of CNTs in vivo.

Big CNT


Cubic, sp3

hybridization

Diamond

3.4 ÅPlanar, sp2

hybridization

GraphiteGraphene


Carbon NanotubeFullerene


GraphiteGraphene

Nanotube Fullerene

� Graphene was largely studied from a theoretical point of view.

� The unsuccessful attempts to synthesize it seemed to confirm the theory that truly two-dimensional crystals (any kind of crystal) could not exist.

� In 2-D the thermal vibration of the atoms should lead to a displacementcomparable to interatomic distance (thermodynamically unstable).

� The very large perimeter-to-surface ratio of 2-D crystals promotes a collapse.

Discovery of Graphene?... Not yet6Discovery of Graphene?... Not yet6

Epitaxial Growth by CVD

Graphene and few layers of graphene are grown on Ni

Graphene is not free-standing and its properties are strongly affected bysubstrate:� Significant charge transfer from the substrate to the epitaxial graphene

� Hybridization between the d orbitals of the substrate atoms and π orbitals ofgraphene, which significantly alters the electronic structure of the epitaxialgraphene.

Discovery of GrapheneDiscovery of Graphene

K.S. Novoselov et al., Science 306 (2004) 666-669

Free-standing graphene films (10 µµµµm in size) were

prepared by mechanical exfoliation (repeated peeling) of

small mesas of highly oriented pyrolytic graphite (HOPG).

MultiMulti--layers graphenelayers graphene

� The electronic structure of graphene rapidly evolves with the number oflayers, approaching the 3D limit of graphite at 10 layers.

� Only graphene and its bi-layer has simple electronic spectra: they are bothzero-gap semiconductors (or zero-overlap semimetals).

� For three or more layers, the spectra become more complicated, severalcharge carriers appear, and the conduction and valence bands start notably

J.C. Meyer et al., Nature 446 (2007) 60-63

charge carriers appear, and the conduction and valence bands start notablyoverlapping. This allows single-, double and few (3 to <10) layer graphene to bedistinguished as three different types of 2D crystals (‘graphenes’).

� Thicker structures should be considered as thin films of graphite.

CharacterizationCharacterization

HR-TEM

500 nm

2 nm

J.C. Meyer et al., Nature 446 (2007) 60-631 nm


AFM-STM topography

STM

M.I. Katsnelson, MaterialsToday 10 (2007) 20-27A. Charrier et al., J. Appl. Phys. 92 (2002) 2479-2484

AFM


Nanobeam e-diffraction

J.C. Meyer et al., Nature 446 (2007) 60-63

Since graphene is microscopically corrugated the e-diffraction peaks of graphene become broader whileincreasing the tilt angle.

The elastic strain can intrinsically provide thethermodynamic stability of the film.


2D (G’)

Raman analysis

Raman spectra of graphene flakes. 2D (G') Raman peak changes in shape width andposition for an increasing number of layers reflecting a change in electron bandstructure and electron-phonon interactions.

A.C. Ferrari et al., Phys. Rev. Lett. 97 (2006) 187401


Confocal Raman

Confocal Raman map (2D band center of mass position).1, 2, 3 and 4- layered flakes can be easily distinguishedwhen using a color palette scale.

Chemical Vapor Deposition

High yield graphene synthesisHigh yield graphene synthesis

CVD (or PE-CVE) of carbon precursor is used to deposit graphene on thin layer of

nickel (1 1 1) over silicon substrate. The graphene can be transferred to various

substrates, demonstrating viability for numerous electronic applications.

K.S. Kim et al., Nature 457 (2009) 706-710

Other graphene synthesisOther graphene synthesis

Hydrazine reduction

� Silicon carbide (6H-SiC) is heated between 1080 and 1320°C giving the

growth of graphene. The face of the SiC used for graphene creation, Si-

terminated or C-terminated, highly influences the thickness, mobility and

carrier density of the graphene.

Silicon carbide sublimation

� Graphene oxide paper is reduced to single-layer graphene in a solution of pure hydrazine (NH2-NH2).

� Gram-quantities of graphene are produced by the reduction of ethanol bysodium metal, followed by pyrolysis of the ethoxide product, and washingwith water to remove sodium salts.

Sodium reduction of ethanol

Unfolding CNTs

� Graphene ribbons are produced by cutting and unfolding CNTs viachemical etching (KMnO4-H2SO4) o plasma etching.

Graphene properties/applicationsGraphene properties/applications

Charge carriers (electrons and holes) have high density (1013 cm-2) and highmobility (15000 cm2V-1s-1) at RT, and the mobility weakly depends ontemperature (only impurity scattering):

� Ballistic field effect transistor (high speed electronic devices)

Electrical properties

K.S. Novoselov et al., Science 306 (2004) 666-669

Rather modest on-off conductance ratio of ~30 at RT


The transistor conductance can be significantly altered (106 on-off ratio at RT)by a reversible chemical modification. In presence of humidity the electric fieldchanges the graphene to graphane (hydrogenated derivative, 3.5 eV of bandgap) and graphene oxide (-OH, insulator).

� Non volatile memory application.


T.J. Echtermeyer et al., IEEE Electronic Device Letters 29 (2008) 952


Graphene chip can double the frequency of an electromagnetic signal.

� Graphene chips can transmit data faster than standard silicon chips,consuming less energy and having a higher S/N ratio.

Graphene has high electrical conductivity, high optical transparency, mechanicalstrength and flexibility.

� Touchscreens, liquid crystal displays, organic photovoltaic cells,


Touchscreens, liquid crystal displays, organic photovoltaic cells,stretchable electrodes.

K.S. Kim et al., Nature 457 (2009) 706-710


Graphene has an incredibly high surface area to mass ratio.

� Ultra-capacitors with great energy storage density.

Graphene has electrical conductivity can be tuned by gas molecule absorption.

� High sensitive gas sensors.

Graphene stripes, called graphene nanoribbons (GNRs), have electrical


Graphene stripes, called graphene nanoribbons (GNRs), have electricalproperties that depends on the un-bonded edges.

� Armchair GNRs are semiconductors with a band gap that increases withthe decreasing of the width.

� Research is being done to create quantum dots by changing the width ofGNRs at select points along the ribbon, creating quantum confinement.


High thermal conductivity (~ 5000 Wm-1K-1)

� Heat sinks.

Graphenen is very strong (Young’s modulus 0.5 TPa) and stiff (elastic constant1-5N/m).

� NEMS applications as pressure sensors or resonators.� NEMS applications as pressure sensors or resonators.

� Nanocomposites

Small spin-orbit interaction and near absence of nuclear magnetic moments incarbon. GNRs in the zig-zag orientation, at low temperatures, show spin-polarized edge currents.

� Spintronics (magnetoelectronics) applications


Graphene oxide is obtained by oxidizing (KMnO4-H2SO4) and chemicallyprocessing graphite/graphene. The graphene oxide flakes dispersed in watercan give well-ordered structure with exceptional mechanical properties.

� Nanocomposites

H. Chen et al., Adv. Mater. 20 (2008) 3557-3561

S. Stankovich et al., J. Mater. Chem. 16 (2006) 155

Thank you for your Thank you for your attention!attention!

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