carbon nanotubes stephanie reich fachbereich physik, freie universität berlin
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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!
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