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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