Carbon nanotubes

1
Carbon nanotubes
Stephanie Reich Fachbereich Physik, Freie
Universität Berlin
2
Pure sp2 sp3 carbon
1991
iron age
2004
4 cen BC
1985

3
Single-walled carbon nanotubes
diameter 1 5 nm, length up to cm

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

4
Single-walled carbon nanotubes

• Growth of carbon nanotubes
• Zone folding fundamentals
• Electronic properties
• Optical properties
• Nanotube vibrations
• (Functionalization)

5
Nanotube growth

• 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

http//home.hanyang.ac.kr/, www.seas.upenn.edu
6
Chemical vapor deposition

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

Hata, Science (2004) Zhang, Nat Mat (2004)
Milne
7
Nanotube growth

• 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

http//home.hanyang.ac.kr/, www.seas.upenn.edu
8
Nanotube structure

• nanotube diameter d chiral angle T determine
  microscopic structure

9
Nanotube structure

• nanotube diameter d chiral angle T determine
  microscopic structure

10
Chiral vector - (n,m) nanotube
c n a1 m a2 8 a1 8 a2
a2
a1

• nanotube diameter d chiral angle T determine
  microscopic structure
• specified by the chiral vector c around the
  circumference

11
Chiral vector - (10,0) nanotube
c n a1 m a2 10 a1
a2
a1

• nanotube diameter d chiral angle T determine
  microscopic structure
• specified by the chiral vector c around the
  circumference

12
Nanotube structure
(8,8) (6,6) (10,0) (8,3)

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

13
Quantum confinement

• circumference periodic boundary conditions
• ? p diameter/p (p integer)

14
Confined phase space
K
?
M
15
One-dimensional Brillouin zone
16
Band structure (10,0) tube
17
Metal or semiconductor? (n-m)/3

• quantization in (n,0)
• n1 allowed lines between G and M
• G 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

(10,0) semiconductor (9,0) metal
18
Metal semiconductor in experiment
E
k
19
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

20
Graphene a semimetal

• valence and conduction band touch in a single
  point

21
HOMO LUMO

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

22
Metal or not?

• three nanotube families metal
  semiconductor small gap semiconductor la
  rge gap

23
Electronic properties of nanotubes

• quantum confinement
• band gap depends on structure
• most properties depend on band gap

E
k
metal semiconductors
24
Optical properties of nanotubes

• Every nanotube colorful
• Bulk nanotube samples black

25
Transitions between subbands

valence
conduction
26
Chirality from luminescence

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

27
Chirality from luminescence
?

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

28
Nanotubes, optics excitons

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

29
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
30
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
RBM
HEM
D mode
D mode
31
Electron-phonon coupling

• doping hardens phonon frequencies
• metallic into semiconducting spectrum?
• bundling effect?

semiconducting
metallic
32
Phonon softening

• vibration periodically opens and closes a band
  gap
• softening of the phonon frequencies
• phonon dispersion is singular
• q k1 k2

33
Phonons limit nanotube transport

• ballistic transport
• resistance approaches quantum limit 13kO/channel
• no scattering by defects
• ballistic transport breaks down by hot phonons
• phonon emission faster than decay

34
Functionalization

• change nanotube properties
• solubility
• composite materials
• sensitivity reactivity
• tune pristine properties
• electron interaction
• defects
• vibrations

35
Quintessential nanotubes

• Many different nanotube structures
• Porperties differ vastly
• Essential ingredients
• Quantum confinement pick properties
• Large surface area manipulate properties
• sp2 carbon bond ultra-strong material
• We cannot control the type of tube

36
Summary

• Nanotube properties depend on their
  structurethere 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

37
Thanks to

• TU BerlinChristian ThomsenJanina Maultzsch
• MITMichael StranoFrancesco StellacchiJing Kong
• KITFrank Hennrich
• University of CambridgeStefan HofmannJohn
  Robertson

• 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 Malic (SfB)Megan Brewster (MIT, NSF)

38
The end

• Thank you!