Carbon nanotubes

Stephanie ReichFachbereich Physik, Freie Universität Berlin

Pure sp2 & sp3 carbon

iron age

4 cen BC

1985

1991

2004

U. Bristol

Single-walled carbon nanotubes

Nanotubes are not one, but many materials Nanotubes consist only of surface atoms

diameter: 1 – 5 nm, length: up to cm

Single-walled carbon nanotubes

Growth of carbon nanotubes

Zone folding & fundamentals

Electronic properties

Optical properties

Nanotube vibrations

(Functionalization)

Nanotube growth

http://home.hanyang.ac.kr/, www.seas.upenn.edu

grow out of a carbon plasma

laser ablation arc discharge chemical vapor deposition

metal catalysts nickel, cobalt, iron …

carbon tubes diameter ~ 1 nm length 500 nm – 4 cm

industrial scale production started 2005 since 2009 large scale

Chemical vapor deposition

Hata, Science (2004); Zhang, Nat Mat (2004); Milne

long tubes & high yield high quality high degree of control during growth

Nanotube growth

http://home.hanyang.ac.kr/, www.seas.upenn.edu

grow out of a carbon plasma

laser ablation arc discharge chemical vapor deposition

metal catalysts nickel, cobalt, iron …

carbon tubes diameter ~ 1 nm length 500 nm – 4 cm

industrial scale production started 2005 since 2009 large scale

Carbon nanotubes (Wiley, 2004) , Freitag group

Nanotube structure

nanotube diameter d & chiral angle Θ determine microscopic structure

Carbon nanotubes (Wiley, 2004)

Nanotube structure

nanotube diameter d & chiral angle Θ determine microscopic structure

Carbon nanotubes (Wiley, 2004)

Chiral vector - (n,m) nanotube

nanotube diameter d & chiral angle Θ determine microscopic structure

specified by the chiral vector c around the circumference

c = n a1 + m a2 = 8 a1 + 8 a2

a1

a2

Carbon nanotubes (Wiley, 2004)

Chiral vector - (10,0) nanotube

nanotube diameter d & chiral angle Θ determine microscopic structure

specified by the chiral vector c around the circumference

c = n a1 + m a

2 = 10 a1

a1

a2

Carbon nanotubes (Wiley, 2004)

Nanotube structure

typical samples contain 40 – 100 different chiralities controlling chirality during growth is impossible

(8,8) (6,6) (10,0) (8,3)

Carbon nanotubes (Wiley, 2004)

circumference – periodic boundary conditions

= diameter/p (p integer)

Quantum confinement

Carbon nanotubes (Wiley, 2004)

Confined phase space

K

M

Carbon nanotubes (Wiley, 2004)

One-dimensional Brillouin zone

Carbon nanotubes (Wiley, 2004)

Band structure (10,0) tube

M K M

Ener

gy

(eV)

Wave vector

-6

-4

-2

0

2

4

6

8

10

Ene

rgy

(eV

)

/a

Carbon nanotubes (Wiley, 2004)

Metal or semiconductor? – (n-m)/3

(10,0) semiconductor (9,0) metal quantization in (n,0) n+1 allowed lines

between and M

K = 2/3 KM = 1/3

metals(3,0), (6,0), (9,0), (12,0) …

semiconductors(2,0), (4,0), (5,0), (7,0) …

general conditionmetallic if (n-m)/3 = integer

Metal & semiconductor in experiment

E

k

Concept of zone folding

quantization along the circumference

reduced phase space find nanotube properties by

reference to graphene works for

electrons, phonons, and other quasi-particles

interactions, e.g., electron-phonon coupling

central concept of nanotube research

Reich, Carbon nanotubes (Wiley, 2004)

Graphene – a semimetal

valence and conduction band touch in a single point

-8

-4

0

4

8

12

graphene

Ener

gy

(eV)

K M

Reich, Carbon nanotubes (Wiley, 2004)

HOMO & LUMO

HOMO & LUMO are degenerate Nanotube chiral vector compatible with HOMO/LUMO wave function?

three nanotube families

metal

semiconductor

small gap

semiconductor

large gap

Metal or not?

Electronic properties of nanotubes quantum confinement band gap depends on structure most properties depend on band gap

k

E

metal semiconductors

Optical properties of nanotubes

Every nanotube – colorful Bulk nanotube samples – black

1.0 1.1 1.2 1.3

(8,6)

(6,5)(7,6)

(10,2)

(9,4)

Energy (eV)

Transitions between subbands

-1.0 -0.5 0.0 0.5 1.0

Dens

ity o

f sta

tes

Energy (eV)

valence conduction

1.0 1.1 1.2 1.3

(8,6)

(6,5)(7,6)

(10,2)

(9,4)

Energy (eV)

Bachilo, Science (2002)

Chirality from luminescence

every (n,m) nanotube has specific pairs of transition energy use this for assignment

0.6 0.8 1.0 1.2 1.4 1.6 1.80.0

0.5

1.0

1.5

2.0

2.5

Ener

gy

(eV)

Tube diameter (nm)

Bachilo, Science (2002)

Chirality from luminescence

(6,6)

(8,4)

(10,0)?

luminescence detects semiconducting tubes, metallic not some tubes were not observed

E. Malic, M. Hirtschulz

Nanotubes, optics & excitons

chirality, electron-electron, and electron-hole interaction sensitive to environment

200 300 400 1200 1400 1600

Raman shift (cm 1)

Raman scattering on carbon nanotubes (Springer, 2006)

Phonons in carbon nanotubes

100 – 1000 vibrations strong coupling to

electronic system radial-breathing mode

(RBM) high-energy mode (HEM) D mode

twiston and low-energy phonons

RBM HEM

D mode

Phonons in carbon nanotubes

100 – 1000 vibrations strong coupling to electronic

system radial-breathing mode

(RBM) high-energy mode (HEM) D mode

twiston and low-energy phonons

characterizie nanotubes presence metallic/semiconductor chirality

RBM HEM

D mode

RBM HEM

D mode

H. Farhat

Electron-phonon coupling

doping hardens phonon frequencies

metallic into semiconducting spectrum?

bundling effect?

semiconducting

metallic

Kohn (1959)

Phonon softening

vibration periodically opens and closes a band gap

softening of the phonon frequencies

phonon dispersion is singular

q = k1 – k2

Yang PRL (2000); Javey Science (2003)

Phonons limit nanotube transport

ballistic transport resistance approaches

quantum limit 13kΩ/channel

no scattering by defects

ballistic transport breaks down by hot phonons

phonon emission faster than decay

Functionalization

change nanotube properties

solubility composite materials sensitivity &

reactivity

tune pristine properties

electron interaction defects vibrations

Summary

Nanotube properties depend on their structure;there is no „typical nanotube“

Growth of carbon nanotubes produces many different tubes = different materials

Nanotube absorb light & show infrared luminescence

Particularly strong electron-phonon coupling

Functionalize nanotubes for further tailoring

Thanks to…

Cinzia Casiraghi (AvH)Antonio Setaro (FUB)Vitalyi Datsyuk (BmBF)

Rohit Narula (FUB) Sebastian Heeg (ERC)Oliver Schimek (DFG)Asaf Avnon (SfB)Thomas Straßburg (BmBF)Stefan Arndt (BmBF)

Ermin Malić (SfB)Megan Brewster (MIT, NSF)

TU BerlinChristian ThomsenJanina Maultzsch

MITMichael StranoFrancesco StellacchiJing Kong

KITFrank Hennrich

University of CambridgeStefan HofmannJohn Robertson

The end

Thank you!