FAPESP WEEK BEIJING, Brazil-China Scientific Collaboration

April 15-18, 2014, Peking University

Graphene and Its 2D Hybrids

—— Attraction, Reality and Future

Zhongfan Liu (刘忠范)

Center for Nanochemistry (CNC)

Center for Nanoscale Science & Technology (CNST)

Beijing Science & Engineering Research Center for Low Dimensional Carbon Materials

Peking University

Nanocarbons —— The Favorite of CNC@PKU

1998-

2008-

2013-

RB Heimann, SE Evsyukov, Y Koga, 1997 Nobel Prize for C60 in 1996 and Graphene in 2010

Graphene —— The thinnest 2-D atomic crystal

Zero-gap semimetal having a giant conjugation system

Various Possible Applications

Graphene: Band Structure Evolution with Layer

Thickness and Stacks

AB stack Twisted bilayer

Monolayer Bilayer Trilayer

Massless Dirac fermions

Relativistic linear E-K

dispersion: E = pvF

pvH Fˆˆ

•

•

Parabolic E-K dispersion

Massive chiral fermions

Gap opening with E⊥

Similar linear E-K

Dirac fermions

VHS near EF due to

interlayer coupling

ABA Stacks

ABC Stacks

Parabolic dispersion

Conductivity increase

with E⊥

Parabolic dispersion

Gap opening with E⊥

Chemical Vapor Deposition (CVD)

—— A cost-effective approach for high-quality graphene

Transition Metal Catalysts for Graphene Growth

Pd

1555oC

8.9@1504oC

10.51.0V

FCC

Cu

1085 oC

0.04

3.70.5V

FCC

Ni

1455oC

2.7@1327oC

1.2-0.2V

FCC

Ag

962oC

0.04

14.90.8V

FCC

Rh

1964oC

1.5@1694oC

8.5 FCC

Ru

2334oC

3.0@1942oC

9.1 HCP

Au

1064 oC

0.08

14.51.5V

FCC

Os

3033oC

2.1@2732oC

10.2 FCC

Co

1495oC

4.1@1321oC

1.8-0.3V

HCP

Fe

1538oC

>25.0

0.8-0.4V

FCC/BCC

Pt

1768oC

2.8@1705oC

11.31.2V

FCC

Ir

2466oC

3.1@2296oC

9.4 FCC

VIIIB IB

Ni

1455oC

2.7@1327oC

1.2-0.2V

FCC

Melting point (℃)

C solubility (at.%)

Lattice mismatch(%)

Carbide formation yes or not

Redox potential (vs. SHE)

Crystalline facet

ZF Liu et al, Acc. Chem. Res., 2013, 46, 2263; 中国科学（化学）, 2013; 化学学报，2013

Noble metal foils

Rational Catalysts Design for CVD Graphene

Bimetal alloy

catalysts

Metal carbide

catalysts

c c cc c

cMoMo

cMoMo

C dissolutionNo segregation

Carbide formation

CH4CH4

Surface catalytic de-composition & growth

c cMo Mo

Ni/Mo alloy

A: Ni, Co, Fe

B: Mo, W, V

Component A

(Decomp.

Catalyst)

Component B

(Carbon trap)

BY Dai, ZF Liu et al., Nature Comm.,

2011, 2, 522

Ni-Mo CVD

Fe-Mo CVD

Co-Mo CVD

Ni-W CVD

Ni-CVD

Carbon source

decomposition zone

(1020oC)

Epitaxial growth

zone (1000oC)

Gas flow direction

K Yan, ZF Liu et al., Nano Lett. 2011, 11, 1106Two-temperature zone

van der Waals epitaxy

Cu foil

Bilayer Growth —— AB Stacked Bilayer

20 mm

20 mm

Epitaxial AB-Stacking Bilayer Growth on Monolayer Graphene

Optical image

> 2L

VBG

Mobility: ~ 550 cm2/Vs

K Yan, ZF Liu et al., Nano Lett. 2011, 11, 1106

MX Liu, YB Gao, YF Zhang, ZF Liu, Small, 2013, 9, 1360-1366

W Yan, ZF Liu, L He et al., Phys. Rev. Lett., 2012, 109, 126801

θ=0º

θ=6.9º θ=12ºθ=3.7º

θ=2.2º θ=3.0º

Bilayer graphene

on Rh(111) by APCVD

Bilayer Growth —— Twisted Bilayer

W Yan, YF Zhang, ZF Liu, L He et al.,

Phys. Rev. Lett., 2012, 109, 126801

Energy Difference of Two VHSs as a Function of Twist Angles

Mosaic Graphene：In-plane hybrid superlattice with

ubiquitous gap opening

FP Ouyang, ZF Liu, ZR Liu et al.,

ACS Nano, 2011, 5, 4023-4030

Even walls

Odd walls

Antidot Lattice & Nanomesh Mosaic Graphene with BN

RQ Zhao, ZF Liu, ZR Liu et al., J. Phys. Chem. C,

2012, 116, 21098; PCCP, 2013, 15, 803

Mosaic Graphene: Bandgap Opening with High Carrier Mobility

The intrinsic carrier mobility at room temperature

is tunable from 1.7 x 103 to 1.1 x 105 cm2 V-1 s-1 with

a bandgap of 0.38 to 1.39 eV. Some BNGs (1,4-BNG)

show ultrahigh mobility up to 6.6 x 106 cm2 V-1 s-1.

JY Wang, RQ Zhao, ZF Liu, ZR Liu, Small, 2013, 9, 1373-1378

20 mm 10 mm

in

Two-step seeding growth

K Yan, ZF Liu et al., Nature Comm., 2012, 3, 1280

Raman D/G AFM

Transport Properties

Dual Dirac Point

No additional resistance

from the junction

Doping Concentration

nd~2.7×1012 cm-2

Carrier Mobility

μi~1100-1500 cm2/V·s

μn~700-1100 cm2/V·sWafer Scale Growth & Transfer

Modulation-Doped Growth of Mosaic Graphene—— 2D hybrids of graphene and nitrogen-doped graphene

The Thinnest p-n Junction and Photocurrent Generation

Full spectral range absorption

Weak electron-phonon coupling

Carrier multiplication (multi -

exciton generation)

Broadband & ultrafast

photodetection and high-efficiency

photoelectric conversion

Photocurrent generation & modulation

Multichannel photocurrents & addition effect

K Yan, et al., Nature Comm., 2012, 3, 1280

Efficiency:

~0.1 mA/W

Plasmon-Enhanced Photoelectric Conversion for

Mosaic Graphene

D Wu, HL Peng, ZF Liu et al., JACS, 2013, 135, 10926-10929

4 fold increase (0.3 mA/W)

Asymmetrically-Doped Bilayer Graphene for

Photocurrent Generation

Nitrogen-doped

adlayer

Pristine adlayer

Y Zhou, ZF Liu et al., Small, 2014, in pressCH4 at 1000oC and CH3CN at 950oC

LEEM for

work function

0.06eV

Photocurrent Generation on Asymmetrically-Doped

Bilayer Graphene

• Electron doping

concentration: 2.7 x

1012/cm2

• Carrier mobility:

mI = 880 cm2V-1s-1

mn = 560 cm2V-1s-1

• Photocurrent

response: 0.2 mA/W

at zero bias & room

temperature,

doubling the mono-

layer junctions

• Photothermoelectric

effect and enhanced

light absorption

633nm laser

Mosaic Graphene —— Graphene/h-BN hybrids

On Rh(111)

YB Gao, YF Zhang, ZF Liu, Nano Lett., 2013, 13, 3439-3443

Experiments versus Theoretical calculation

Preferred

formation of

zigzag edge at

the boundary

Theoretical calculation

of the G-BN boundary

linking structure

Preferential Boundary Edges: Theory & Experiments

YB Gao, YF Zhang,

ZF Liu, Nano Lett.,

2013, 13, 3439-3443

CVD growth on

nanostructured surface

Folded/Wrinkled graphene

by transferring to flat surface

Self-masked

plasma etching

Graphene on Cu foil Wrinkle-Preserved Transfer GNRs Array

ZH Pan, JACS, 2011, 133, 17578; N Liu, Nano Res, 2011, 4, 996; YF Zhang, ACS Nano 2011, 5, 4014

Wrinkle Engineering: Direct Growth of Wrinkle-Designed Graphene

0.5/µm

Wrinkles, GNRs and Characterization

ZH Pan, ZF Liu et al., JACS, 2011, 133, 17578

Ion/Ioff: 30

Doping Growth of Graphene

Bulk Ni

H Wang, HL Peng, ZF Liu et al.,

Small, 2013, 9, 1316-1320 CH Zhang et al., ZF Liu et al., Adv.

Mater., 2011, 23, 1020

N-doped graphene B-doped graphene

Graphene Chemistry for Band Structure Modulation

C + X => CX

• Giant conjugated system

• Large delocalized energy

• No dangling bonds

• No geometric curvature

• Lack of functional groups

• Different layers

• Double faces

• Poor solubility

Fullerenes

(1985)

Nanotubes

(1991)

Graphene

(2004)

Conjugated structures of carbon atoms

High chemical stability

• Modulate surface properties

• Create new graphene derivatives

• Bandgap opening

• Spin control and magnetics

• Device fabrication technique

Why Graphene Chemistry ?

• Dimensionality effect in chemistry

Photochemical Bandgap Engineering of Graphene

Gaint 2D molecule

LM Zhang, L Zhou et al., Small, 2013, 9, 1134 (Review)

L Liao, ZF Liu, JACS, 2014 (Perspective)

Photochemical Approach to Bandgap Engineering

Photocatalytic oxidation

LM Zhang et al. JACS 2011, 133, 2706

Photochlorination

B Li, L Zhou, ACS NANO, 2011, 5, 5957; MM Yang,

JPCC, 2012, 116, 844; L Zhou, Small, 2013, 9, 1388

Photomethylation

JANUS Graphene：Asymmetric modification

LM Zhang et al., Nature Comm., 2013, 4, 1443

L Liao et al., Small, 2013, 9, 1348

Large Scale Continuous CVD Growth of Graphene

Roll to roll growth system

(Growth rate ~1 m2/h)Large area growth on Cu foil

Lamination machine

(A3, SG 330-SCL)

Large area transfer using electrochemical bubbling technique

(graphene/PET transparent conducting film)

XW Yang, et al., JEAC, 2013, 688, 243

Transferring Graphene from Growth Metal Substrates

PMMA-aided transfer

EC vs FeCl3

CO-intercalating adsorption

ZF Liu et al., JPCC, 2008, 112, 17741

Electrochemical etching

DL Ma et al., Nano Res, 2013, 6(9), 671-678

More and beyond Graphene

• Single crystalline domain size (from cm to wafer size?）

• Growth on insulators or nonmetals (h-BN, Sapphire, quartz, Si/SiO2)

• Low temperature growth (device fabrication compatibility)

• Large area transfer from metal surface

• Mass production with high quality and low cost

• 2D hybrid materials (BNC…)

• Bandgap opening with high mobility

• 2D chemistry with high efficiency

• Edge control (spintronics)

• New carbon allotrope (Graphyne and graphdiyne…)

• Main contributors:

Liu Nan (Segregation growth)

Dai Boya (Bimetal alloy-CVD)

Yan Kai (Epitaxial bilayer & grafting growth)

Liu Xun (on Cu-Ni alloy)

Pan Zhonghuai (Wrinkle engineering)

Zhang Chaohua (Co-segregation)

Gao Yabo (UHV-STM)

Wu Di (Mosaic graphene)

Zhou Yu (Photoconversion)

Zou Zhiyu (IVB-VIB TMCs)

Sun Jingyu (Insulating substrate)

Gao Teng (2-D hybrids)

Song Xuju (on h-BN)

Wang Huan (B-doping)

Zhao Ruiqi (Theory)

Yang Mingmei (Theory)

Wang Jinying (Theory)

Zhang Liming (Photochemistry)

Zhou Lin (Photochlorination)

Liao Lei (Photomethylation)

• Collaborators:

Kong Jing (MIT)

Chen Yulin (Oxford Univ.)

Bao Xinhe (DICP, China)

Fu Lei (Wuhan Univ.)

Duan Wenhui (Tsinghua Univ.)

He Lin (Beijing Normal Univ.)

Liu Zhirong (PKU)

Peng Hailin (PKU)

Zhang Yanfeng (PKU)

Acknowledgements