Electron and phonon in carbon nanostructures: a local study with scanning

tunneling spectroscopy

Lucia Vitali

Max-Planck Institut für Festkörperforschung, Stuttgart,Germany

Spectroscopy on atomic scaleInelastic electron

tunneling spectroscopy:

Point contact spectroscopy:

Scanning Tunneling Spectroscopy:

Co and H-Co on Cu(111) TbPc2 on Cu(111)

Self-assembling, lithography, transport, …

Carbon allotropes

diamond (3D) planar graphite C60 (0D)1985

single-walled carbon nanotube (1D)1991

Graphene2004

Graphene 2D conductor, linear electron band, electron velocity independent on energy, high carrier

mobility, QHE at RT, gas sensor, …,

Metallic, superconducting, isolating transition (doping level), Endohedral fullerenes (Metal

or N): Magnetism and superconductivity

Electronic, mechanical and electrical new properties: Quasi 1D (model system for

physicists!) , metallic or semiconductor, supports large current flux, high carrier mobility, electron

field emitters, CNT-FET, Single electron transistors

high young modulus, high tensile strength, gas sensors, gas storage, …,

Fullerenes

CNT

Novel fascinations on Carbon

Semiconducting SWCNTs as components of FETs

* S.J. Wind, J. Appenzeller, R. Martel, V. Derycke & Ph. Avouris; Appl. Phys. Lett. 80 (2002), 3817.

donor-acceptor hybrids: natural photosynthesis

NT-based Ultra-capacitors

Z. Chen et al., Science 5768, 1735 (2006)

Integrated Logic Circuit Assembledon a Single Carbon Nanotube

Scanning Tunneling Microscopy & Spectroscopy

dI/dV~ρel

6K-STM

Preparation chamber

LHe-Cryostat

STM

Ch

T

(n,n)

(n,0)

a1a2

roll-up vector:

Ch = na1 + ma2 ≡ (n,m)

metallic if (n-m) = 3q

semiconducting if (n-m) ≠ 3q

q:integer

chiral (n,m)

zigzag (n,0)

armchair (n,n)

Structure of single-wall carbon nanotubes (SWCNTs)

-Impurity atom

-Strain, different bond strength

Spatial resolution

A.M.Rao et al. Science 275.187.1997

Raman Spectroscopy

A.Mews et al. Adv.Mat.12.1210.2000

Confocal Raman Spectroscopy

A.Hartschuh et al. PRL.90.095503.2003

Near-Field Raman Spectroscopy

0.14µm

1

10

100

1000

Nea

r F

ield

Ram

an S

pect

rosc

opy

Con

foca

l Ram

an S

pect

rosc

opy

Ram

an S

pect

rosc

opy

nm

10Å

10Å

1

10

100

1000

Inel

asti

c E

lect

ron

Tun

nelin

g Sp

ectr

osco

py

Nea

r F

ield

Ram

an S

pect

rosc

opy

Con

foca

l Ram

an S

pect

rosc

opy

Ram

an S

pect

rosc

opy

nm

Spectroscopy technique: Localprobe of lattice dynamics (vDOS)

Inelastic Electron Tunneling Spectroscopy

- Carbon nanotubes (SWCNT)

- Graphite (HOPG)

Electron Tunneling Spectroscopy

dI/dV~ρel+ρin

Elastic tunneling Inelastic tunneling

SWCNT on Au/mica

+ =

Acknowledgment:* M.Knez , Y.W.Fan for the sample preparation

Recipe:Disperse SWCNT in Dichlorethane, Sonicate and centrifuge.Deposit the solution on Au substrates

10Å

....to tube diameter ?

From STM images....

X

Metallic tube∆E=6γ0aC-C/d∆E~1.38V

Diameter ~15.4Å

(14,8) tube

Determination of (n,m)

-0.9 -0.6 -0.3 0.0 0.3 0.6 0.9 1.20

1

2

3

4

5

6

7

0.8V

-0.58V

dI/d

V[n

A/V

]V

Φ=10°Chirality Θ=20°

(n,0)

(9,0) tube - metallic

-1,0 -0,5 0,0 0,5 1,00,0

0,2

0,4

den

sit

y o

f sta

tes [

arb

.un

its]

energy / γ0

-3

-2

-1

0

1

2

3

π/sqr(3)a0

E(

k x )

/ γ

0

kx

E1-1´

-0,8 -0,4 0,0 0,4 0,80,0

0,2

0,4

den

sit

y o

f sta

tes [

arb

.un

its]

energy / γ0

-3

-2

-1

0

1

2

3

0 π/sqr(3)a

E(

kx )

/ γ 0

kx

(10,0) tube - semiconducting

Egap

Energy separation between the first vHs singulatities:

∆E=2γ0aC-C/d semiconducting∆E=6γ0aC-C/d metallic

γ0= 2.5 eV tight-binding overlap energyaC-C=1.42Å lattice constant

10Å

ωRBM=C/d

d

ω

Dependence of the radial breathingmode on the SWCNT diameter

0 10 20 30 40 50

d2 I/dV

2

mV

T = 6K

dt = 21.45Å

dt = 16.47Å

dt = 19.32Å

dt = 18Å

dt = 19.78Å

dt = 9.02Å

dt = 12.26Å

dt = 10.51Å

dt = 21.5Å C=262meV*ÅC~270-290meV*Å D.Sanchez-Portal et al PRB.59.12678.1999J.Kurti et al. PRB.58.R8869.1998

0.04 0.06 0.08 0.10 0.12

12

16

20

24

28

32

(9,4)

(17,14)

(22,9) (17,6)

(14,4)

(9,7)

RB

M (m

eV)

1/diameter (Å-1)

Local properties:

Intramolecular-junctionTube cap

20Å

Ph.Lambin, V.Meunier, Appl.Phys.A 68.263.(1999)

10Å

Tube crossings

50Å

(16,4) (19,4)

Å

High

Low

Local probe: Intra-molecular junction or 5/7 pairs

Phon

onen

ergy

(mV)

(16,4) (19,4)

Å

Local probe: Intra-molecular junction or 5/7 pairs

High

Low

Phon

onen

ergy

(mV

)

Local probe: Nanotube capping

„Neck“

Cap

Intermolecular-junction

10Å

(17,14) (9,7)

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

RS

dI/d

V

V

Electronic structure

(9,7)

(17,14)

Å

Nanotube capping: d2I/dV2

meV

RBM

PRL.93.136103.2004

Theory for RBM(powered by C.S.Jayanthi et al)

(5,5)+C60

-finite length: A tube can sustain an RBM only if its length exceeds 3.5nm.

-capped region: Transforms from radial to tangential character inside the tube

PRL.93.136103.2004

Crossed Nanotube Junctionpressure induced local metallization

Phys. Rev. Lett. 96, 086804 (2006)

If a (9,2) tube crosses a bundle...

1. DOS

bI II III

Å

eV

A

I II III

PRL 96, 086804 (2006)

1.1 DOS: Local pressure-induced metallization

d(9,2)=8.2Åbundle~15Å

=Tube compressed of ~35%

at the crossing junction

Pressure at crossing junction=15GPa(Assuming Bulk modulus=35GPa)

c

I II III

b

I II III

0 50 100 150

10

8

12

Å

Å

Å

eV

I II III

a

dI/d

V

PRL 96, 086804 (2006)

1.2 DOS: Image-charges

Å

eV

A

I II III

Contact potential ∆=∆holes-∆image

∆V=∆Q/CTS

∆V=60meVCTS~0.1aF

∆Q= additional 0.025hole/nm(= ~25% total charge transferred )

Å

meV

I II III

c

b

Å

meV

I II III a dI/d

V2

2d

I/d

V2

2

I II III

2. Vibrational density of states

G-band

RB-mode

HOPG

IETS of HOPG

Phonons+

Plasmon

The total density of phonons can be detected with STM-IETS

DFT powered

byL.Wirtz, A.Rubio

Experiment

PRB 69, R121414, (2004)

-Enhancement of the phonon modes at K

Phonon assisted tunneling processElectron transmission probability

Κ// Γ M K

Tran

smis

sion

pro

babi

lity

Take home message

- Inelastic Tunneling Spectroscopy as probe of lattice dynamics (vDOS)1. HOPG (phonon assisted tunneling process)2. SWCNT: RBM + G band

- Map of the vibration frequencies along the tube1. vibrational modes vs. tube structural changes

(i.e. 5/7 pairs or tube deformations)2. charge transfer

You for your attention!

Acknowledgments

M.Burghard, M.A.Schneider, K.Kern, C.Riedl, U.Starke

@MPI-Stuttgart & Uni Erlangen

L.Wirtz, A.Rubio, @San Sebastian & Institute for

Microelectronics and Nanotechnology,Villeneuve d'Ascq

Lei, Liu, C.S.Jayanthi, S.Y.Wu@University of Louisville