6. Carbon nanostructures: fullerenes and carbon nanotubes

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C is unique in its versatility

Diamond (sp3 Carbon):-hardest material-perfect insulator or semiconductor when doped

Graphene (sp2 Carbon):-soft material-highly anisotropic

Acetylene (sp1 Carbon):

Fullerenes (C60):Diameter = 0.71 nmSMALLEY 1985

Nanotubes:Metallic or SemiconductingDiameter: 0.5 - 50 nmLength: < 50 µmIIJIMA 1991

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Carbon materials

•19th century: 1st fibre by T. A. Edison(from bamboo filaments)•1950s introduction of carbon reinforced materials(composites)•PAN (polyacrylonitrile) fibres•C-whiskers•vapor phase grown (CVD)•1985 discovery of fullerenesand conjecture of Smalley of the possible existence of1d fullerenes•discovery by Iijima with TEM breakthrough

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Graphene

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⇒

Single perfect sheet of graphite (so called graphene)

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“”

LCAO bandstructure of graphene

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Reciprocal lattive of graphene and the -point

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Fullerenes

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◆

C20+2n

⇒12 pentagonal ringsn hexagonal rings

Coordination number =3, ∼sp2

hybridization

C60

C70 C

78

C78

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◆

- 12 pentagons and 20 hexagons

- Icosahedral (Ih) point group symmetry (5-fold rotation axis)

- σ and π bonds, two bond lengths 1.40 Å and 1.45 Å

- Found first in astronomic spectra, then obtained in carbon-arc shoot (end of 80´s)

C60

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C60 , buckminsterfullerene

•Solid C60

, FCC close packing

3 Å

10 Å

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Solid C60

•Van der Waals bonds between molecules

•FCC lattice

• low T: oriented C60

-molecules

•High T: rotation of C60

-molecules

molecular bonding

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C60 solids

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C60

doped solid

M3C60 , M=alcaline metal

metal ortype II superconductor, as the lattice parameter is changed

fcc, semiconductor 0.5 eVC60

Molecule

Solid

HOMO

εFsemiconductor

metal

semiconductor

LUMO

band-gap

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M3C

60 compounds are superconducting (Type II)

- Relatively high Tc (45 K for pure (Tl2Rb)C

60),

higher than other intermetallic as Nb3Ge

- a↑ ⇒ g(εF) ↑ ⇒ Tc↑

(BCS) 19

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Atoms encapsulated in C60

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Carbon nanotubes

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Produced in DC-arc struck between two carbon electrodes (Iijima, NEC,

Tsukuba 1991)

Single-walled nanotube(usually concentric

multi-walled nanotubes)

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The first experimental electron microscope images published, S. Iijima , Nature (1991), reporting the discovery of carbon nanotubes.

First electron microscope image and diffraction pattern from single-walled carbon nanotubes [S. Iijima & T. Ichihashi Nature 363, 603 (1993).]

The smallest CN

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Carbon nanotubes: types and description

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Nanotube geometry

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Nanotube = wrapped sheet of graphite

Chiral vector

A A’

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(5, 5) armchair nanotube

(9, 0) zigzag nanotube

(10, 5) chiral nanotube

Armchair nanotubes n=m , chiral angle 30°. Zigzag nanotubes , either nor m are zero, chiral angle is 0°. Chiral nanotubeschiral angles intermediate between 0° and 30°

http://physicsweb.org/article/world/11/1/9#world-11-1-9-6

,diameter

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Carbon nanotubes: band structure

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1D bands of CN

Bandstructure of a (10; 10) armchair carbon nanotube. The shaded region is the 1: Brillouinzone. Note, each band is doubly degenerate, except for the ones crossing E = 0 and the ones withmaximal and minimal energy. There are in total 40 bands.

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1D character

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Metallic and semiconducting nanotubes

Zig-zag-tube Arm-chair-tube

metalsemimetal semiconductor

e--pockets

graphite 1. BZ

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1D model

a)Zig-zag tube

- 1 BZ of graphite: elctron pockets at K ⇒ metallic

- Tubes: periodicity around the axis → allowed -values on lines

- If n=3p, p ∈ integer ⇒ line of allowed -points intersects K

⇒ metallic zig-zag -wire (3p,n)- If n=3p+1, 3p+2 ⇒ semiconductor

b)Arm-chair tube

- Line of allowed -points intersects K⇒ metallic⇒ transistors?

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Carbon nanotubes: properties and applications

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Single-wall carbon nanotubes are also expected to be very strong and to resist fracture under extension, just as the carbon fibers commonly used in aerospace

applications

Unlike carbon fibres, however, single-wall

nanotubes are remarkably flexible.

Mechanical properties

Ultimate material in strength

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Ruoff et al. Science 287, 637 (2000)

Mechanics, pulling...

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Viola Barwich & Ernst Meyer, Basel

SFM tips

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Vibrating Carbon Nanotubes

Ebbesen et al, Nature 381, 678 (1996)

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Raman (radial breathing modes)

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NanoelectronicsElectronic properties

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Nanotube transistors

Gate (Si)

SiO2

Source (Au) Drain(Au)

Nanotube

FET at

room temperature

SET a 4 K

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FET (unipolar)

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5540

1D electronic properties: quantization of conductance

de Heer’s experiment

Optical properties

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Nanotube lights (different colors).Light emission when an electric field is applied

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Nanotubes for better TV screens

Aligned carbon nanotubes into different patterns

New flat screens, longer lasting, more energy efficient, thinner and flexible.

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Fullereness (C60) encapsulated in single wall CNs

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ReferencesScience and Application of Nanotubes, edited by D. Tomanek and R. J. Enbody,(Kluwer Academic/Plenum Publishers, 1999)

M. S. Dresselhaus, G. Dresselhaus and P. C. Eklund, Science of Fullerenes andCarbon Nanotubes; Academic Press: New York, 1996.

Carbon Nanotubes, edited by M.S. Dresselhaus, G. Dresselhaus and Ph. Avouris(Springer, Berlin Heidelberg, New York 2001)

Physics Today, May 1999, p22

Physics World, Vol.13, Issue 6, June 2000

R. Saito, G. Dresselhaus and M. S. Dresselhaus, Physical Properties ofCarbon Nanotubes; Imperial College Press: London, 1998, 1999, 2001.

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