Height (nm)H

(1)

CHEMICALLY DERIVED GRAPHENE CHEMICALLY DERIVED GRAPHENE:

ELECTRONIC AND MECHANICAL PROPERTIES

PROPERTIES

Cristina Gómez-Navarro

Universidad Autónoma de Madrid

Max-Planck-Institute for Solid State Research

(2)

Why Graphene?

Single layer of graphite

Extraordinary properties

•One atom thick: real 2D material

y p p

•Electronic band structure, transport properties

Semi-metal with field effect

μ~100.000 cm²/Vs

High quality: Ballistic transport on micron scale Semi metal with field effect

•Mechanical properties

High strength of carbon-carbon bond 2D flexible but stiff films

(3)

Applications: Proof of concept devices

FET: graphene ribbons

Han, PRL 2007

Transparent electrodes

Wang, nanoletters 2008

Gas sensors

Schein, Nature Materials 2007

Bio devices

Mohanty, nanoletters 2008

NEMS El t h i l R t

NEMS: Electromechanical Resonators

Bunch, Science 2007

(4)

Current ways to obtain Graphene

• Mechanical exfoliation of graphite.

•Very simple method but:Very simple method, but:

•High multilayer/monlayer ratio.

•Finding monolayers time consuming

Not applicable Not applicable

to technology yet

Novoselov et al Nature, 2005

•Epitaxial growth on silicon carbide and metals

Berger et al Science 2006

•Limited to certain substrates

•Uniformity, size domain?

•UHV, high temperatures

Berger, et al Science, 2006 Land, Surface Science, 1992

•Chemical approach:

Vi hit id G hit id il l d

•Via graphite oxide: Graphite oxide, easily layered

•Mainly monolayers Solution based

Inexpensive, scalable, substrates

Stanovich et al Nature , 2006

•Solution based

•Reducing graphite oxide on surface?

(5)

Initial idea

Graphite oxide: graphite functionalized with epoxy

C O C C O

1

^st

: Synthesizing graphite oxide

C-O-C and hydroxyl C-OH groups in the interlayer and C-OH -COOH groups at the edges of the graphene sheets.

Graphite o ide la ers are eas to separate in ater leading to “graphene o ide”

2

^nd

: Adsorption of single GO layers on surface

Graphite oxide layers are easy to separate in water…leading to “graphene oxide”

Solution process

2 : Adsorption of single GO layers on surface

300nm

3

^rd

: Reducing GO by chemical procedures on surface Hydrazine or hydrogen plasma

Q lit d ti f h bt i d t h thi t ?

Schniepp et al J Phys. Chem. B, 110, 8535, 2006

Quality and properties of graphene obtained trough this route?

(6)

AFM imaging of GO

0 5 1.0 1.5 2.0 2.5

Height (nm)

single double on single double

700nm _{6 0 0 n m} _{6 0 0 n m}

100 200 300 400

-0.5 0.0

H 0.5

X (nm)

700nm

1 st layer h~ 1 0±0 1nm

Very high mono\multilayer ratio

1 st layer h 1.0±0,1nm 2nd layer h ~ 0,8±0,1nm

Very high mono\multilayer ratio

h in agreement with theoretical expectation

(7)

Electronic transport GO

Electrodes by e-beam lithography

1 0µm

IV curves as a function of reduction time with hydrazine

Time of

1.0µm

400nm

3 0x10^-10

4,0x10^-10 Iwithouthydraz

4 0x10^-9 6,0x10^-9 1,5x10^-7 2,0x104,0x10^-7^-6

8

1,0x10

^-7

Iwithouthydraz I5hvapor

I5hdisol

Time of reduction

Before reduction good insulator

1,0x10^-10 2,0x10^-10 3,0x10

(A) 0,0

2,0x10^-9 4,0x10

I(A)

0,0 5,0x10^-8 1,0x10^-7

I(A)

0,0 2,0x10^-6

I(A)

0,0 5,0x10

^-8

(A)

I5hdisol I22hdisol

-2 0x10^-10 -1,0x10^-10

I 0,0

9

-4,0x10^-9 -2,0x10^-9

I

-1,5x10^-7 -1,0x10^-7 -5,0x10^-8

I

4 0x10^-6 -2,0x10^-6

I

-5,0x10

^-8

I(

Reduction improves conductivity 3 orders of magnitude

-10 -8 -6 -4 -2 0 2 4 6 8 10 -3,0x10^-10

2,0x10

X Axis Title

-10 -8 -6 -4 -2 0 2 4 6 8 10 -6,0x10^-9

X Axis Title

-10 -8 -6 -4 -2 0 2 4 6 8 10 -2,0x10^-7

X Axis Title

-10 -8 -6 -4 -2 0 2 4 6 8 10 -4,0x10

X Axis Title

-3 -2 -1 0 1 2 3

-1,0x10

^-7

Bias Voltage(V)

Fixed channel length Maximum in conductivity after 24h of NH or 5 sec H plasma

(8)

Electronic transport reduced GO

10M _{RT vacuum}

RT air

Ambipolar behaviour similar to pristine graphene

6M 8M

R(Ω)

Ambipolar behaviour similar to pristine graphene

Conductivity: σ=0.1-1 S/cm

S D

Bias V

Gate V

60 40 20 0 20 40 60

2M

4M Mobility: μ=-0.1-1 cm²/Vs

n e μ =¹σ

For high quality graphene μ=1.000-100.000 cm²/Vs

-60 -40 -20 0 20 40 60

Gate Voltage(V)

-18 experimental data

-21 -20 -19

18 p

linear fit

(I/A)

Temperature dependence indicates a hopping transport mechanism

T₀ ⎟⎞¹n

⎜⎛

25 -24 -23

Ln( -22

Hopping e

T

I I

0

⎟⎠

⎜⎝

=

0.14 0.16 0.18 0.20 0.22 0.24 -25

T^-1/3 (K^-1/3)

(9)

High resolution imaging of GO

GO on HOPG

1 0 0 n m

1.7nm

AFM: wrinkling STM: ordered\disordered regions

(10)

Raman spectroscopy: GO

5x10³

before reduction

G/D ratio:

sp

²

carbon domain size of ~ 5-6 nm

2x10³ 3x10³ 4x10³

(counts)

before reduction 24h N₂H₄

G band D band

Ferrari et al Phys Rev B 2000

1200 1400 1600 1800

0 1x10³

I 2x10

w ave number (cm^-1)

Ferrari et al. Phys Rev B 2000 Tuinstra et al. J Chem Phys 1970

w ave number (cm )

Model

Graphene islands

-19

-18 experimental data

linear fit

-24 -23 -22 -21 -20

Ln(I/A)

STM

1.7nm ^0.14 ^0.16 ^0.18 ^0.20 ^0.22 ^0.24

-25

T^-1/3 (K^-1/3)

Hopping conduction

Defect regions

Gomez-Navarro et al. Nanoletters 7 3499 2007

(11)

2nd step: Chemical Vapor Deposition of ethylene 2nd step: Chemical Vapor Deposition of ethylene

•High T

•Decomposition of C H

•Decomposition of C

₂

H

₄

•obtaining atomic C

to be incorporated in vacancies to be incorporated in vacancies

•High T facilitates healing

Flow ethylene for 3 min at 800 ºC

(12)

CVD treated GO: improved conductivity

3 0

After CVD conductivity increases two orders of magnitude

2.2 2.4 2.6 2.8 3.0

ds / μA

Conductivity: σ=20-200 S/cm Mobility: μ~50-100 cm

²

/Vs

7

8 GO

reduced GO CVDGO

-16 -12 -8 -4 0 4 8 12 16

1.4 1.6 1.8

I d2.0

V / V

4 5 6

CVDGO

pristine graphene

u nts

VG / V

2 3 4

Co u

10^-4 10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 0

1

10 10 10 10 10 10 10 10 10

σ / Scm

^-1

Lopez et al. Advanced Materials, 2009

(13)

CVD treated GO: Raman and coductivity

/G

80 100 120

Scm-1

6x10⁴ 7x10⁴

G

u.

D

-15

-14 Experimental Data

Linear Fit

hopping transport High D/G ratio Correlation D/G conductivity

20 40 60

onductivity / S

4x10⁴ 5x10⁴

Intensity / a.

-18 -17 -16

LnI ds (A)

n

T T

e I I

1 0 ⎟⎠⎞

⎜⎝

=

⎛

1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50

Co 0

D/G Intensity Ratio 1000 1250 1500 1750

3x10⁴

Raman shift / cm^-1

0,15 0,20 0,25 0,30 0,35 0,40

-19

T^-1/3 (K^-1/3)

e I I =

₀

New smaller graphene regions

Oxidized/

defective Graphene

regions

defective regions CVD created graphene

regions

CVD GO

RGO

(14)

Conclusions on electrical transport

• GO routes provides access to a large scale production of graphene monolayers.

• Reduction improves conductivity in 3 orders of magnitude

• CVD of ethylene increases conductivity in 2 orders of magnitude.

• CVDGO still contains a considerable amount of defects.

6 7

8 GO

reduced GO CVDGO

pristine graphene

• Large range of conditions for improvement.

3 4 5

Counts

700nm

10^-4 10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ 0

1 2

10^-4 10^-3 10^-2 10^-1 10⁰ 10¹ 10² 10³ 10⁴ σ / Scm^-1

Gomez-Navarro et al. Nanoletters 2007 Lopez et al. Advanced Materials 2009

(15)

GO: mechanical properties

A

δ

Au Au

SiO₂ SiO₂

)

3

/ ( 32 Ew t l

K

_eff

= + 17 T / l

Correlation between conductivity

40 F

ff

Force Constant Young modulus,

built-in tensions

_1.6

Correlation between conductivity and elastic modulus

20 30 40

(nN)

Force curves

E=0.3 TPa

0 6 0.8 1.0 1.2 1.4

(S/cm)

0 10 20

F(

δ

T=4 nN

0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0.0

0.2 0.4

σ 0.6

0 10 20 30 40 50 60 70 Z piezo displacement (nm)

K

₁

, K

₂

, K

₃

…

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 E (TPa)

Gomez-Navarro et al. Nanoletters 2008

(16)

Height (nm)H

CHEMICALLY DERIVED GRAPHENE CHEMICALLY DERIVED GRAPHENE:

ELECTRONIC AND MECHANICAL PROPERTIES

PROPERTIES

Cristina Gómez-Navarro

Universidad Autónoma de Madrid

Max-Planck-Institute for Solid State Research

Why Graphene?

Single layer of graphite

Extraordinary properties

•One atom thick: real 2D material

y p p

•Electronic band structure, transport properties

•Mechanical properties

Applications: Proof of concept devices

FET: graphene ribbons

Transparent electrodes

Gas sensors

Bio devices

NEMS El t h i l R t

NEMS: Electromechanical Resonators

Current ways to obtain Graphene

• Mechanical exfoliation of graphite.

•Epitaxial growth on silicon carbide and metals

•Chemical approach:

Vi hit id G hit id il l d

•Via graphite oxide: Graphite oxide, easily layered

•Mainly monolayers Solution based

•Solution based

•Reducing graphite oxide on surface?

Initial idea

1

: Synthesizing graphite oxide

2

: Adsorption of single GO layers on surface

2 : Adsorption of single GO layers on surface

3

: Reducing GO by chemical procedures on surface Hydrazine or hydrogen plasma

Q lit d ti f h bt i d t h thi t ?

Quality and properties of graphene obtained trough this route?

AFM imaging of GO

700nm 6 0 0 n m 6 0 0 n m

700nm

Very high mono\multilayer ratio

Very high mono\multilayer ratio

Electronic transport GO

IV curves as a function of reduction time with hydrazine

1,0x10

0,0 5,0x10

-5,0x10

-1,0x10

Electronic transport reduced GO

Ambipolar behaviour similar to pristine graphene

Ambipolar behaviour similar to pristine graphene

Temperature dependence indicates a hopping transport mechanism

Hopping e

I I

=

High resolution imaging of GO

GO on HOPG

1 0 0 n m

AFM: wrinkling STM: ordered\disordered regions

Raman spectroscopy: GO

G/D ratio:

sp

carbon domain size of ~ 5-6 nm

Model

STM

Hopping conduction

2nd step: Chemical Vapor Deposition of ethylene 2nd step: Chemical Vapor Deposition of ethylene

•High T

•Decomposition of C H

•Decomposition of C

H

•obtaining atomic C

to be incorporated in vacancies to be incorporated in vacancies

•High T facilitates healing

Flow ethylene for 3 min at 800 ºC

CVD treated GO: improved conductivity

After CVD conductivity increases two orders of magnitude

700nm _{6 0 0 n m} _{6 0 0 n m}