Tailoring the electronic properties of low-dimensional carbon hybrids

Thomas Pichler

University of ViennaFaculty of PhysicsTokyo 5.10.2012

Acknowledgements

Vienna University group:C. Kramberger, A. Grüneis, P. Ayala,K. de Blauwe, X. Liu, R. Pfeiffer, J. Chacon, G. Ruiz, A. Briones, L. Shi, M. Sauer, P. Rohringer,F. Simon (now Budapest), A. Chernov, H. KuzmanyIFW-Dresden: M. Rümmeli, M. Knupfer, B. BüchnerSurrey University: H. Shiozawa (now Vienna Univ.), R. SilvaSynchrotron:BESSY II: D. Batchelor, P. Hoffmann, J. Fink, R. Follath, S. Krause ELETTRA: P. Lacovig, M. Dalmiglio, S. Lizzit, A. GoldoniTheory:Donestia San Sebastian: A. Rubio, C. Allicante, D. MowbrayLille Univ.: L. Wirtz, Samples:AIST: H. KatauraTokyo Metrop. Univ.: K. YanagiIFW-Dresden: M.H. R.Nagoya Univ: Y. Miyata, R. Kitaura, H. Shinohara

Funding: DFG, FWF, APART, EU

OUTLINE

Introduction/Motivation/Experimental/Applications

Part 1: Electronic structure of 1D nanostructures:Single walled carbon nanotubes (SWCNT):

a) Pristine SWCNT: nature of the metallic ground stateb) Electronics and optics with functionalized SWCNT:

Intercalation, substitution/attachment and filling

Part 2: Electronic structure of 2D nanostructures:Graphene systems:

a) Graphite revisited: A Key to Graphene and SWCNT b) GIC KC8 revisited: A key to Graphenec) Graphane, n-doped graphane: Tuneable gap, acceptor leveld) Electron dispersion, electron phonon coupling

Summary and outlook

TODAY

Introduction/Motivation/Experimental/Applications

Part 1: Electronic structure of 1D nanostructures:Single walled carbon nanotubes (SWCNT):

a) Pristine SWCNT: nature of the metallic ground stateb) Electronics and optics with functionalized SWCNT:

Intercalation, substitution/attachment and filling

Part 2: Electronic structure of 2D nanostructures:Graphene systems:

a) Graphite revisited: A Key to Graphene and SWCNT b) GIC KC8 revisited: A key to graphenec) Graphane, n-doped graphane: Tuneable gap, acceptor leveld) Electron dispersion, electron phonon coupling

Summary and outlook

Low dimensional quantum solids?

All solids are of course quantum systems

1D and 2D quantum solids:

- Mesoscopic systems with size quantization

- Quantum effects already at room temperature

- Correlation effects crucial:electron-hole, electron-electron, electron-phonon

- Instabilities in 1D and 2D systems!

Molecular carbon nanostructures are archetypical examples of perfect 1D and 2D solids

Graphene2D

Dimensionality of sp2 bonded carbon allotropes

Graphite,Mittelalter

3D

Fullerene0D

R. Curl, H. Kroto, R. Smalley, 1985Nobel prize chemistry, 1996

Carbon nanotubesIijima, 1991

1D

A. Geim, K. Novoselov, 2004Nobel prize physics, 2010

Carbyne

Diamond Graphite

A. Hirsch et al. Nature Materials 9, 868 (2010)

more？Carbon nanowire

But also …..

Motivation: Why all carbon nanostructures?

Advantages of carbon:

1. cheap, light

2. structural properties: hard, stiff, flexible, ductile,….

3. biocompatible

4. electronic properties:

insulating semiconducting semimetallic metalliczero gap semiconductor

diamond fullerenes, graphite, nanotubes nanotubes graphene

Tunable by functionalisation

Special properties of nanotubes

Electronic propertieres:

Geometry of SWCNT : 2/3 are semiconducting 1/3 metallicconductivity tunable by functionalisation

Temendous current carrying capacity: 1 billion A/cm2

no electromigration

Excellent heat conductor: twice as good as diamond

Mechanical properties:

Strength at least 100 times higher than steel Youngs modulus 1 Tpa

Flexible ultimate carbon fibers

Geometry:

High aspect ratio of 1000 to 10000, 1 nm diameter High surface area

Electronic structure of different carbon allotropes

Two 1s core electrons and 4 valence electrons (two 2s and two 2p)

σσ

σ∗σ∗

2s

2psp3

sp3

Diamond

σσ

σ∗σ∗

ππ

π∗

2s

2p

2pz

sp2

π∗

sp

2

graphitenanotubesfullerenesconj. polymers

σ-bonds: W~50 eV

π-bondsW~ 20 eV

σ−bondπ-orbital:W~ 0.5 eV

SWCNTs Hamada vector

(n,n) armchair

(n,0) zigzag

(n,m) chiral

(n,0)

(n,n)

a2

Φ

Introduction: formation of single-wall carbon nanotubes

Φ=0Φ=0Φ=0Φ=0

Φ=30Φ=30Φ=30Φ=30°°°°

0<Φ<300<Φ<300<Φ<300<Φ<30°°°°dn,m=|C|/ππππ=a(n2+m2+mn)1/2/ππππThe diameter of SWCNT (n,m) :

a=|a1|=|a2|=2.49 Å

graphene sheet

e.g. (10,10) d=1.37nm

o

A

O(A)

����

),(21 mnamanC =+= rrr

����C

����C

����a1

(n,m)

d

0.0 0.5 1.0-9

-6

-3

0

3

6

9

0.0 0.5 1.0-9

-6

-3

0

3

6

9

EF

E(K

) (e

V)

ka/π ka/π

0

-3 -2 -1 0 1 2 30

D

ensi

ty o

f sta

tes

E(k) (eV)

Introduction: electronic properties of SWCNTs

semiconductor

2πd·kn=2π·n

1/d

1/d

Eg~1/d

(10,10)

(17,0)

K KK

(kn-quantization)

Electronic properties are determined by the structu re of SWCNT

periodic boundaries

k

metal

(10,10)

(17,0)

EF

KM

K

K ΓΓΓΓ

EF

using tight binding approximation

Synthesis and purification of SWCNT and DWCNT.high vacuum CVD!

Electronic/optical properties: EELS, XAS,ARPES,Raman, PL,OAS!What happens upon functionalization?

Charge transfer vs. hybridisation: bonding environment, doping level, Fermi level shift and changes in the DOS.

Nature of the metallic ground state:

Normal Fermi liquid or a Tomonaga-Luttinger liquid?Transition 1D – 3D metal?

Electronic structure of functionalized SW(DW)CNT from high energy and optical spectroscopy

What are we doing on nanotubes ….. ?

SWCNT from laser ablation/ arc discharge

SWCNT yield and diameter distribution vs. T, p, laser pulse, gas, catalyst, …

Optimised: 70 wt% SWCNT, d=1.2-1.4 nm

Purification andopening:HNO3, H2O2,Heat treatment

semiconductingmetallic

SWCNT with no catalyst and “carbon impurities”, d=1.4 +/- 0.12 nm

Optical response of type separated bulk SWCNT

Y. Miyata et al., J. Phys. Chem. C 2008, 112, 3591 (2008)

-2 -1 0 1 2

S3,4

S*

2

S*

1

M*1

M1

S1

S2

Energy (eV)

DO

S

SemiconductingMetal

S3,4

M2,3

M*2,3

*

diameter

1.37 ± 0.08nm

Miyata et al. J Phys. Chem.C 112, 13187 (2008).

Samples

Gain from High Energy Spectroscopy

Photoemission Spectroscopy X-ray absorption and EELS

Occupied Density of States Unoccupied Density of States

Matrix element weighted DOSValence Band Conduction Band

(site selective)(site selective for RESPES)

Core Hole Effects!!!

Bonding environment

Charge Transfer

Basic Correlation Effects

Bonding environment

Charge Transfer

Basic Correlation Effects

Core Level High resolution XPS

-Doniac-Sunjic lineshape M

-Voigtian (symetric) SC

285.2 284.8 284.4 284.0 N

orm

aliz

ed In

tens

ity Binding Energy (eV)

METALLICITY MIXED SWCNT

Kramberger et al. PRB 75 (2007) 235437

0,4eV

High resolution XPS of metallicity sorted SWCNT

P.Ayala et. al. PRB 80 (2009) 205427

Core hole screening not visibly affected in metallic samples

Work functions : different in bulk metallic SWCNTs sample

Graphite

0,32 eVDoniach Sunjic

Voigtian

π*

σπ

C1s

σ*

π

π*

C 1s

EF

0 D2 D

kWhat is the electronic behavior of the 1 D system??

k

0 D

1 D

2 D

10 8 6 4 2 0

σσσσC60

SWCNTs

N

orm

aliz

ed In

tens

ity

Energy (eV)

ππππ

Graphite

High Energy Spectroscopy studies on sp2 –hybridized C structures

Site selective weighted projected DOS of the conduction band

285 290 295

σσσσ∗∗∗∗ππππ∗∗∗∗

Nor

mal

ized

Inte

nsity

Energy (eV)

VB-PES Conduction Band-XAS

Matrix element weighted DOS of the valence band

283 284 285 286 287 288

Mea

sure

d+

reso

l. br

oad.

Cal

c. D

OS

Energy (eV)C1s

π*

σ*

π

σ

Quasi „0D“: Fullerenes

Quantum Chemical calculations of molecular orbitals match experimental DOS � small core hole effects in XAS

0D

6 5 4 3 2 1 0

+ re

sol.

broa

d.M

easu

red

Cal

c. D

OS

Binding Energy (eV)

VB-PES XAS

HOMO

LUMO

T.Pichler et al. PRL 78(1997) 4249

2D: Graphite-Graphene

π

π*

C 1s

EF

2D

But: strong core hole effects in XAS of the conduction band

ππππ

TB-DOS of the valence band matches experimental DOS

VB-PES XAS

Bruhwiler et al.PRL 76

(1996)1761

XAS: Conduction band of metallicity mixed SWCNT bundles

Site selective weighted projected DOS of the conduction band Fine structure in π* resonance: S1*,S2*, S3*, and M1*. But: exitonic effects for the π* along tube axis like in graphite

282 283 284 285 286

285 290

SWCNT HOPG

Nor

mal

ized

Inte

nsity

Energy (eV)

π∗

Energy (eV)

σ∗

S1*

S2*

M1*

C1sBE

S3*

-1.0 -0.5 0.0 0.5 1.0

S2M1

Energy (eV)

M1*S1

* S2*S1

C. Kramberger et al. PRB, 75, 235437 (2007)

π

π*

C 1s

EF

vHS

vHS in DOS of conduction band: XAS fine structure

Strong excitonic effect on π* resonance (parallell), vHS only weakly affected

284 285 286 287 284 285 286 287

0 1 2 3 0 1 2 3

M*

4M*

2,3M*

1

b)

S*

2S*

3

Nor

mal

ized

Inte

nsity

Energy (eV)

ππππ∗∗∗∗

a)

S*

5

Nor

mal

ized

Inte

nsity

Energy (eV)

S*

1

ππππ∗∗∗∗

DO

S

Energy (eV)

S*

4DO

S

Energy (eV)

P. Ayala et al. PRB80, 205427 (2009)

π

π*

C 1s

EF

Valence band of a metallicity mixed SWCNT bucky paper

π

σ

High resolution angle integrated photoemission at T=35 K:

10 8 6 4 2 0

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)vHS of tubes: S1, S2, M1good agreement with TB calculations e.g. H. Ishii et al, Nature, 426, 540 (2003), H. Rauf et al.

1.5 1.0 0.5 0.0

Binding energy (eV)

M1S2

S1

-1.0 -0.5 0.0 0.5 1.0

S2 S1M1

Energy (eV)

M1*S1

* S2*

Diameter cumulative DOS in VB photoemission response

Very good agreement between PES peaks and diameter cumulative DOS!Additional life time broadening in experiment!Chemical potential for semiconducting tubes shifted by 0.1 eV!No Fermi edge in metallic SWCNT

4 3 2 1 0 4 3 2 1 0

4 2 0 -2 -4 4 2 0 -2 -4

0.5 0.0

b)

M2,3

Inte

nsity

(cp

s)

Binding energy (eV)

EF

π

M1

a)

S3,4,5

S2

Inte

nsity

(cp

s)Binding energy (eV)

EF

π

S1

DO

S

Energy (eV)

DO

S

Energy (eV)

Energy (eV)

P. Ayala et al. PRB80, 205427 (2009)

Scaling in 1D and 3D metals: gain from photoemission

Ef

1exp[(E-Ef)/kT] + 1

f(E) =

n(E) ~ E α

I(E)

1

T = 0

3D metal: Fermi-liquid

•PES shows Fermi edge

1D metal: Tomonaga-Luttinger liquid

• 1D paramagnetic metal

• correlated electron state interaction parameter g

g<< 1 repulsive Coulomb interaction

g>1 attractive interaction

power law dependence of n(E):

Photoemission intensity: I(E) ~ n(E) f(E)

n(E) ~ const, α=0, g=1

For SWCNT:

α=(g+1/g−2)/8 =0.3−0.5

α=0E α

Metallic tubes in metallicity mixed samples

T = 35K

α = 0.43, g=0.18

good agreement with theoretical predictions and results from transport measurements

1.5 1.0 0.5 0.0

0.2 0.02

log

Inte

nsity

(ar

b. u

nits

)

In

tens

ity (

arb.

uni

ts)

Binding energy (eV)

log Binding energy (eV)

α = 0.43

S1

S2

M1

Metallic SWCNT in a bundle of SWCNThave the renormalization of a Tomonaga-Luttinger liquid

semiconductingmetallic

H. Ishii et al, Nature, 426, 540 (2003); H. Rauf et al, PRL 93, 096805 (2004)

A bundle of undoped metallic SWCNT

� Undoped purely metallic SWCNT bundles are still 1D metals

No Fermi liquid!No Fermi edge for metallic SWCNT!

�Still van der Waals interaction of the tubes in a bundle!

� Implications on maximum conductivity in e.g. transparent electrodes

P. Ayala et al. PRB80, 205427 (2009)

1.5 1.0 0.5 0.0

1 0.1 0.01

log

Inte

nsity

(ar

b. u

nits

)

In

tens

ity (

arb.

uni

ts)

Binding energy (eV)

M1

log BE (eV)

αααα = 0.37

Intercalation

in-situ doping: UHV evaporation(5x10-10 mbar)Na, K, Rb, Cs and Ba SAES getters

getter

vapor

Sapphirefilm

Alkali-metal intercalation

UHVdoping

e-

e--2 -1 0 1 2

0.0

0.1

(10,10)D

OS

(eV

-1C

-1)

Energy (eV)

INTERCALATION:

doping

SCM

What happens with doping?

INTERCALATION:

doping

SCM

Is a bundle of doped metallic tubes a normal Fermi liquid or a Luttinger liquid?

What happens with doping?

Transition from a TLL to a FL

0,10 0,05 0,00 -0,05

1:20

pristine

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)

metal T=35K

Crossover to a Fermi liquid

α = 0.43

α = 0

H. Rauf et al, PRL 93, 096805 (2004)

Dependence of the power law scaling factor alpha from the degree of doping.

Where is the transition from a TLL to a FL?

0,10 0,05 0,00 -0,05

1:20

pristine

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)

metalT=35K

α = 0.43

α = 0

1,5 1,0 0,5 0,0

1 0,1 0,01

log

Inte

nsity

(ar

b. u

nits

)

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)

M1

log BE (eV)

αααα = 0.37

TLL

FL

?

Rigid band shift in metallicity mixed samples

• S1, S2 and M1 shift to higher binding energies

• power law behavior at first stable

• abrupt change at K:C = 1:125, ∆E(S1) = 0.37eV

T=35K

1.5 1.0 0.5 0.0

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)

S 2S1

M1

-1.0 -0.5 0.0 0.5 1.0

S2 S1M1 M1*S1

* S2*

1 0.1

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)

αααα = 0.43

αααα ~ 0T=35K

Doping dependence of the LL parameter α in mixed samples

0.000 0.005 0.0100.0

0.1

0.2

0.3

0.4

0.5

5

6

7

43

2o

1

∆Es1

=

0.37 eV

∆Es1

=0.3 eV

α

K / C

Power law scaling vs. intercalation:α= const. up to K/C=1/500, ∆ES1=0.25 eVα=0, g=1 above K/C=1/150, ∆ES1>0.35 eV

H. Rauf et al. PRL 93, 096805 (2004); C. Kramberger et al. PRB 79, 195442(2009)

-0.5

0.0

0.57

6 5432

1

Ene

rgy

(eV

)-1.0

-0.5

0.0

0.5

1.0

a bundle of only metallic tubes is a normal Fermi liquid!

B,N Substitution

SWCNT

BCN-SWNT, MWBNT

Substitution: Heteronanotubes

TEM of DWBN-NT

E. Borowiak-Palen et al. Chem.Comm.1, 82 (2003), CPL, 387 , 516 (2003)G. Fuentes et al. PRB 67, 35429 (2003), PRB 69, 245403 (2004), P.Ayala, et al., Reviews of Modern Physics (2010).

B-SWNT, BC3NT

C

B

Filling@SWCNTso-called “peapod”

Filling of the inner space of SWCNTs with molecules

Filling

Modified electronic properties?

What happens upon the formation of the peapods?

Charge transfer, chemical bonding

or orbital hybridisation?

Conversion to double-wall carbon nanotubes (DWCNT)?

Potential applications

Carrier tuning of SWCNT, protection for molecules and even drugs, stabilizing reactive compounds and nanocrystals, chemical reaction inside a 1D confined nano reaction tube, 1D spinchain for spin electronics, …

?

?

Examples

Fullerenes@SWCNT

C60@SWCNT :

1D C60 chain inside SWCNT (TEM,Raman)

Gd@C82@SWCNT :

Band gap modulation (STM,STS)

Dy3N@C80@SWCNT :

Charge transfer (PES)

Conversion to DWCNT(TEM, Raman)!

Organic molecules @SWCNT

TCNQ, TDAE, Anthracene@SWCNT, Metallocenes p- and n- type doping

C60@SWCNT

Estimation of the local filling ratio by TEM

Peapods: e.g. C60 filled SWCNT

>90 % filling

C60 - C60 distance 9.7 Å no C60 polymer in SWCNT

X. Liu et al., Phys. Rev. B 65, 45419 (2002), Synth. Met. 135-136, 715 (2003)

Bulk filling ratio, structure in peapods

C60

Maximum filling ratio with C60: 100% no charge transfer to C60

C1s

π*

t1g

t1u

Ferrocene filling of SWCNT and transformation to DWCNT

High filling factor after long time annealing in at 150 C

Metallocene filling and chemistry inside SWCNT

Metallocenes : TM(C5H5)2, RE(C5H5)3

CH M

Metallocene consists of

TM: Transition metal atoms

RE: Rare-earth metal atoms

Planar aromatic ligand: C5H5

Electronic & magnetic & chemical properties varying with metal atoms.

0.6 nm

0.4 nm

M = Fe : Ferrocene

Most stable metallocene~ 1.4 nm

Suitable size to be filled inside SWCNT !!!

Metallocene filling: Filling factor

Assuming a 1D ferrocene chain inside SWCNT (d =1.4 nm) with adjacent ferrocene distance ~ 0.755 nm

Fe/C ratio ~ 0.003

Filling factor ~ 35 %

0.755 nm

d = 1.4 nm

Nanochemistry in 1D: Gain from TEM

H. Shiozawa et al. Adv. Mat. (2008)

Ferrocene

Iron carbide

High resolution Overview

Iron oxide nanocrystals

50 nm

Ferrocene filled SWCNT and growth of DWCNT

• Charge transfer ∆EF=0.1 eV, ~0.2 e- per ferrocene• Power law behavior α =0.55• growth of inner tubes at ~ 600 °C

H. Shiozawa et al. Adv. Mat. (2008);PRB (2008)

2.0 1.5 1.0 0.5 0.0

720 710 300 290

x1

Fe2p

1/2

Norm

alize

d int

ensit

y

Binding energy (eV)

x20Fe

2p3/

2 C1s

Ferrocene

M1

S2

S1

B

A

Binding energy (eV)

Inte

nsity

(ar

b. u

nits

)

725 720 715 710 705

1150°C, 1h.

600°C, 2h.

FeCp2@NT

Nor

mal

ized

inte

nsity

Binding energy (eV)150 200 250 300 350

FeCp2@NT

1150°C, 1h.

Nor

mal

ized

inte

nsity

Raman shift (cm-1)

600°C, 2h.

SWCNT

290 300 310 320 330 340 350 360

(6,4)

(17,

3),(

15.6

)

(16,

2), (

14,5

), (

17,0

)

(14,

7),(

18,1

)

(13,

8),(

16,4

)

(12,

9),(

11,1

0)(1

7,2)

,(15

,5),

(18,

0)

(14,

6),(

16,3

),(1

3,7)

(17,

1),(

12,8

)

(14,

6) (11,

9),(

15,4

),(1

0,10

)

Nor

mal

ized

inte

nsity

Raman shift (cm -1)

(13,

6)

S

(16,

3)

(6,5)

0.60 0.65 0.70 0.75

Diameter difference (nm)N

orm

aliz

ed in

tens

ity

FeCp2@NT, 1150°C, 1h.

b C60

@NT, 1150°C, 15h.

(6,5)

(6,4)

DWCNT/Inner tubes: Gain from high resolution Raman

H. Shiozawa et al. Adv. Mat. (2008)Catalytic growth of inner DWCNT differs from non-catalytic!

Ferrocene

C60

Temperature induced chemical reaction in a SWCNT nanoreactor

H. Shiozawa et al. Adv. Mat. (2008); PRB (2008)

1. Ferrocene filling

MD simulation from S. Maruyama

2. Catalytic growth fromIron carbide particles

3. Iron release via defectsIron oxide nanocrystals

Ferrocene filling of metallicity sorted SWCNT

M. Sauer et al. submitted

PL of ferrocene filled Hipco SWCNT

Pristine Opened Filled

X. Liu et al. Advanced Functional Materials DOI: 10.1002/adfm.201200224 (2012)

PL of ferrocene filled Hipco SWCNT

X. Liu et al. Advanced Functional Materials DOI: 10.1002/adfm.201200224 (2012)

Summary for carbon nanostructures

Graphene and SWCNT are ideal 1D and 2D objects

Outstanding mechanical and electronic properties

Ideal systems to study basic correlation effectseven at room temperature!!!!!!

Tuneable electronic properties and interactions!!!

Interesting for both basic research and applications

….. and now finally to something completely different….

….. It´s …..

WANTED: PhD students, postdoc eager to unravel the equilibrium ground state dressed by correlations……!

The beauty of instabilities…!!!

My research groupin Vienna:

LOW DIMENSIONALQUANTUM SOLIDS

Gd@C82@SWCNTs undergo structural transformation upon heat treatment , yielding 1D Gd encapsulated nanowires.

82Gd@C82@SWCNTs→Gd@SWCNTs

P.Ayala et al., Materials Express 1,30 (2011).

• XAS response in the 3d levels of Gd and RESPES.• Stronger resonance for Gd nanowires � smaller hybridisation

82Gd@C82@SWCNTs→Gd@SWCNTs

P.Ayala et al., , Materials Express 1,30 (2011).

Combinational doping: Intercalation of peapods

Peapods: e.g. C60 filled SWCNT

in-situ filling: UHV evaporation(5x10-10 mbar)K, C60 at 120/400 CEquilibration 12 h at RT/350 CAnnealing at T=650 C

K,C60

vapor

Sapphirefilm

Filling/Intercalation

UHV

Okada et al. PRB 67, 205411;PRL 86, 3835

Electronic structure of C60 peapods: Predictions

Que PRB 66, 193405

1/gp2 = 2/gt

2 -1

αt = 0.46gt = 0.18

gp = 0.13, αp = 0.73

Calculated DOS Influence of more conduction channels

• C60-LUMO states near the Fermi level, 4 bands• noticeable increase of α expected

C60

C60-LUMO

9 8 7 6 5 4 3 2 1 0

In

tens

ity (

arb.

uni

ts)

Binding energy (eV)

pristine SWCNT pristine peapods

π

σ

hu=2.3 eV

HOMO-3,4 hg+gg=3.5 eV

Electronic structure of C60 peapods

C60 derived molecular orbitals (Mos) observedBinding energies as in bulk C60, 100% fillingPower law α=0-48-0.55 � basically no increase !!!

1.5 1.0 0.5 0.0

1 0.1

log

Inte

nsity

(ar

b. u

nits

)

Inte

nsity

(ar

b. u

nits

)

Binding energy (eV)

log Binding energy (eV)

α = 0.55

M1

S2 S1

-1.0 -0.5 0.0 0.5 1.0

t1u

H. Rauf et al., PRB 72, 245411 (2005)

Combinational doping: Intercalation of C60 peapods

Competitive charge transfer to SWCNT and C60 peas !

Raman: A g(2) of C 60-x:

- charge transfer up to C60-6

- no line phases:

0.8 <x< 5.3 average charge transfer

- charge transfer induced polymerization

0 1 2 3 4 5 61420

1430

1440

1450

1460

1470-6.5 cm-1/x

Pos

ition

Ag

(2)

( cm

-1 )

(C60

)-x

-6

-6K+

e–

T. Pichler et al., PRL 87, 267401 (2001), PRB 67, 125416 (2003).

Why carbon nanotubes?

Archetypical 1D system:

New electronic, optical and structural properties:

- Ideal 1D quantumwires- Hard, ductile Nanowires- Molecular Magnets, Spintronics- Protection for reactiveelements and molecules

- Gas storage, gas sensing- FET, VIAS, optoelectronic- Sources for field emission- Organic superconductors- Li-Ion batteries- Sensors, actuators, NT-yarns, composits, drug delivery…..

Ideal tools for nanoelectronics/optics/mechanics/(bio)chemistry