2011 05 18 SwissNanoConvention Fasel

8/9/2019 2011 05 18 SwissNanoConvention Fasel

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Materials Science& Technology

Roman Fasel

GrapheneGraphene

an extraordinaryan extraordinary nanomaterialnanomaterial

Empa - Swiss Federal Laboratories for

Materials Science and Technology

nanotech@surfaces Laboratory

8600 Dbendorf , Switzerland

and

Department of Chemistry and Biochemistry

University of Bern

OutlineOutline

Whats all the hype about? Why graphene? Hype or hope?

what is graphene? structure and properties

how to make it? fabrication methods

what is it useful for? potential applications

controlling electronic properties of graphene graphene nanoribbons


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What isWhat is graphenegraphene??

2-dimensional

hexagonal lattice ofcarbon

sp2 hybridized carbonatoms

Basis for C60 (buckyballs), nanotubes, andgraphite

Among strongest bonds

in nature (7.4 eV/C)

A. K. Geim & K. S. Novoselov. The rise of graphene. Nature Materials 6 183-191 (2007)

What isWhat is graphenegraphene??

Linear dispersion, as describedby Dirac cone

Charge carriers behave likerelativistic particles described bythe Dirac equation for spin 1/2particles(massless Dirac fermions)

High charge carrier velocity of106 m/s

Graphene is a zero band gap

semiconductor


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Electronic properties ofElectronic properties of graphenegraphene

ambipolar: charge carrier concentrationcontinuously tunable from electrons to holes

Fast decay of resistivity with increasingcharge carrier density indicates very highcharge carrier mobility

Carrier concentrations up to 1013 cm-2

Opens field for terahertz electronics

A. K. Geim & K. S. Novoselov. The rise of

graphene. Nature Materials 6 183 (2007)

Resist ivity vs. gate voltage

Ambipolar electric field effect

vd: carrier drift velocity: charge carrier mobilityE: applied electric field

Optical properties ofOptical properties of graphenegraphene

Light absorption linear with number ofgraphene layers

2.3% absorption per layer

Absorption almost independent of photonenergy

Direct consequence of bandstructurearound EF

Application as conductive, opticallytransparent electrode

Resistive touchscreens, transparentflexible displays,

Bonaccorso et al.,

Graphene photonics and optoelectronics,

Nature Photonics 4, 611 (2010)

Tran

smittance(%)

wavelength (nm)


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GrapheneGrapheness SuperlativesSuperlatives

Strongest materials ever measured

Thinnest flexible membrane ever created

Impermeable to gases

Record value for RT thermal conductivity

Ballistic transport over micrometers at RT Current density six order of magnitude higher than that of Cu

Room temperature Quantum Hall Effects

Graphene Contender

Elastic modulus 1060 GPa 500 (WC)

Fracture strength 130 GPa 3.6 (Kevlar)

Electron mobility 200000 cm2V-1sec -1 1000 (Si), 8500 (GaAs)

Electr. resistivity 1x10-8 cm 1.610

8 (Ag)Thermal conduct. 5000 Wm-1K-1 400 (Cu), 2000 (diamond)

Specific surf. area 2630 m2g-1

Permeability impermeable even to He

O. Grning (Empa)

S. Unarunotai et al., Adv. Mater. 22, 1072 (2010)

GrapheneGraphene synthesissynthesis

Micromechanical cleavage ofbulk graphite via adhesive tapeNovoselov et al., Science 306, 666 (2004)

AFM

A.K. Geim & K. S. Novoselov.

The rise of graphene.

Nature Materials 6, 183 (2007)


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CVDCVD graphenegraphene: Large scale growth on thin Cu or Ni foils: Large scale growth on thin Cu or Ni foils

R. Ruoff et al., J. Am. Chem. Soc. 133, 2816 (2011)

X. Li et al., Science 324, 1312 (2009)

Roll-to-roll transfer of graphene filmsfrom a thermal release tape to a PETfilm at 120 C.

S. Bae et al.,

Nature Nanotechnology 5, 574 (2010)

Graphene-PET touch-screen

CVDCVD graphenegraphene for transparent electrodesfor transparent electrodes


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YQ Wu et al. Nature 472, 74-78 (2011)

GrapheneGraphene r.fr.f. transistor on DLC substrate. transistor on DLC substrate

Cut-off frequencies of 155 GHz achieved on40 nm device using short gate lengths

Electronics: Industry-compatible graphene transistors

Nature 472, 4142 (2011)

Maximumf

requencyofoscillation

cut-off frequency

GrapheneGraphene for electronic applicationsfor electronic applications

M Liu et al. Nature (2011); doi:10.1038/nature10067

GrapheneGraphene--based waveguidebased waveguide--integrated optical modulatorintegrated optical modulator

Au Pt

GrapheneSi

broad optical bandwidth (1.351.6m)

small device footprint (25m2)

high operation speed (1.2GHz at 3 dB)under ambient conditions

essential for optical interconnects forfuture integrated optoelectronic systems

PaperPaper that'sthat's strongerstrongerthanthan steelsteel

A. R. Ranjbartoreh et al.,

Advanced mechanical properties of graphene paper,

J. Appl. Phys. 109, 014306 (2011)

high hardness ( 217 kgf/mm2) (2x carbon steel)

high yielding strength ( 6.4 TPa) (nx carbon steel)

outstanding bending rigidity

high elastic modulus under bending


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Grapheneincreasesstrength and

stiffness ofcomposites

Aerospace,medical implants

Composites Tunableresonators

Environmentaland biomedicalsensors

Mechanical

components

Photo-detectors,OLEDs,metamaterials

Solar cells

Opto-electronics

Optical

components THz transistor?

Mostly analogsystems

Interface tocells asbioelectrodes

.

Ultrafast

electronics LCD displays,touch screens

ITOreplacement?

Flexibleelectronics

Transparent

electronics

Potential impactPotential impact

ChallengesChallenges

production mass production tailored to application / further processing

defects avoid defects (intrinsic properties), defect engineering

contacts electrical resistance between device electrodes and graphene

channel

bandgap engineering of electronic properties

handling 2D material

substrate interactions (free standing / supported / suspended)


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ControllingControlling thethe electronicelectronic propertiesproperties ofof graphenegraphene

pristine graphene: semimetal

graphene antidot lattice e-beam-based structuring energy gap of ~6 mV for antidot lattice

of a few tens of nm

graphene nanoribbons (GNR) e-beam-based structuring

semiconducting energy gap visible at4 K for ribbons of ~20 nm width

~100 meV gap for unzippednanotubes

C.-H. Park et al, Nature Physics 4, 213 (2008)

GrapheneGraphene nanoribbonsnanoribbons

X. Li et al.,

Science 319,1229 (2008)

It is still a challenge to achieve sub-10nm GNRs

It is difficult to control the edge morphology by top-down methods

RT applications require characteristic GNR widths of 1 - 3 nm!

The bottom-up approach constitutes the only meansfor the fabrication of such fine structures!

from CNT unzipping / chemically derived / lithographically pattefrom CNT unzipping / chemically derived / lithographically patternedrned

M. Y. Han et al., PRL 98, 206805 (2007); L. Jiao et al., Nature 458, 877 (2009); D. V. Kosynkin et al., Nature 458, 872 (2009)

V. Barone et al.,Nano Lett. 6 2748 (2006)

E

g

(eV)

W (nm)

on/off ratio

energy gap

(exp.)

energy gap

(calc.)


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Covalent assembly of suitably programmed molecular precursors

RR

BottomBottom--up approach toup approach to graphenegraphene nanostructuresnanostructures

R

R

R

RR+

Geim, Science 320, 356 (2008)

intermolecular

C-C coupling

intramolecular

cyclodehydrogenation

use metal surface astemplate (and catalyst)

UHV conditions

BottomBottom--upup fabricationfabrication ofof nanographenesnanographenes

Nature 466, 470 (2010)

30 nm

6,11-dibromo-1,2,3,4-tetraphenyltriphenylene

Dehalogenation

& C-C coupling

on Au(111) or

Ag(111) surface

Surface-assisted

cyclodehydrogenation


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Atomically preciseAtomically precise graphenegraphene nanoribbonsnanoribbons ((GNRsGNRs))

10,10-dibromo-9,9-

bianthryl

T1 T2 > T1

2 V, 20 pA, 298 K

1.9 V, 80pA, 5 K 0.86 nm

Step 1

Coupling to linear polymer

on Au(111): 200 C

Step 1 Step 2

-1.5 V, 500 pA, 35 K

Atomically preciseAtomically precise GNRsGNRs

Step 2

Cyclodehydrogenation induced bysecond annealing step: 400 C

Apparent height: 4 1.8

-3V, 30 pA, 5 K

Unit cell is halved to a = 4.2

width

0.7

4n

m

N=7 armchair nanoribbonEgap=1.6 eV

J. Cai et al., Nature 466, 470 (2010)


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TuningTuning thethe Band Gap inBand Gap in GrapheneGraphene NanoribbonsNanoribbons

N=9

N=11

(3p+1) N=7: ~3.8 eV / 1.6 eV

(3p+2) N=11: ~0.9 eV / 0.2 eV

(3p) N=9: ~2.0 eV / 0.7 eV

N=7

GW / LDA

Yang et al., PRL 99, 186801 (2007)

33--fold GNR junctionfold GNR junction

U=-2 V, I=0.02 nA, T=115 K

J. Cai et al., Nature 466, 470 (2010)


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Thermally stable up to at least 550C

Single-atom-wide pores with sub-nanometer periodicity (7.4 )

Periodically missing phenyl groups

turn semimetallic graphene into asemiconductor with Egap = 2.40 eV

M. Bieri et. al, Chem. Commun., 6919 (2009)

PorousPorous graphenegraphene

GrapheneGraphene -- Hype or Hope ?Hype or Hope ?

From: http://en.wikipedia.org/wiki/Hype_cycle

PositiveHype

NegativeHype

difficult to make predictions on realistic applications in the positive hype phase


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Peter Antoinette (CEO Nanocomp)

Thank you for your kind attention.Thank you for your kind attention.

M t i l S i & T h l

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2011 05 18 SwissNanoConvention Fasel