Interesting Properties of Strained or Defective Graphene
Acknowledgement to
National Research Foundation, Andrew Wee TS, Antonio Castro Neto, O. Barbaros Contributions by
Lu Jiong (NUS), Su chenliang (NUS) Candy Lim Yixuan (NUS)
Kian Ping LOH
Department of Chemistry, National U of Singapore Graphene Research Centre
ACS NANO 2013 7(10), 8350
Graphene (dry)
Grown by dry CVD process Planar structure
High π electron density bonding interactions
Governed by - interactions
Graphene-oxide (wet)
Wet chemistry, from graphite Non-stoichiometric COx
Complex interplay of ionic and non-ionic intercations
Nature Nanotechnology 5, 2010, 574 Science 324, 2009, 1312
Pioneers: Rodney Ruoff, (U Texas) Byung Hee Hung (SKKU)
A giant polyaromatic framework that can mediate multiple interactions
A consequence of graphene being a soft membrane is that it can be strain-
engineered to become highly corrugated by modifying its adhesion to the
substrate.
As a soft membrane – Graphene is easily rippled
I. Nanoripples
Nanoripple density ~ 1.5 per um
CVDG/SiO2 with high density nanoripples
Typical Cu surface after growth
Step edges (terrace) density~ 2.5 per um
Zhao wang et. al.
Electron-flexural phonon scattering in such partially suspended graphene devices
introduces anisotropic charge transport and limits charge mobility. Influence of Flexural phonon is reduced under tension. Applying weak strain may be enough
Guangxin Ni, O. Barbaros, ACS NANO, 6(2012) 1158
1. Periodically Strained Graphene
as a Reaction Breadboard
RT
1300 K for 3-5 mins
40 nm Single crystal graphene
2 nm
Θ> 1ML C60
T > 1000 oC
Annealing 3 mins
Graphene Moire Superstructure on Ruthenium:
A Strained Reaction Breadboard
buckling instability
due to the compressive strain between lattice- mismatched Ru and G
produces moire pattern
One inspiration from looking at the periodic blisters on the Moiré superlattice is the
remarkable resemblance of these blisters to an ordered array of nano-bubbles !!
d. H adsorption at room temperature, random cluster e. After annealing to 300 deg C, ordered cluster
on bright regions of moire = hump.
f,g: after annealing to cause H desorption
Hump region is a sink for diffusing H atoms Yu Wang and K. P. Loh, ACS NANO, 4, 6146 (2010)
Moire Superlattice as Reaction Breadboad:
Example 1: Selective Hydrogenation Occurs on the Hump Region of the Moire
Superlattice
C60 in the hump
C60 in the valley
C60 in the rim
In one unit cell,
Rim: hump: valley = 6:1:1 A
B
Reaction Breadboard
Example 2: Contrasting Potential Energy Landscape on the Moire Surface
Rotation of C60 frozen on Moire Valley BUT free Rotation of C60 on Moire Hump Jiong Lu, K. P. Loh, ACS Nano, 2012, 6 (1), pp 944–950
Using the Graphene Moiré Pattern for the Trapping of C60 and Homoepitaxy of Graphene Jiong Lu, K. P. Loh, ACS Nano, 2012, 6 (1), pp
944–950
C60: electron acceptor
Bonded most favorably to hcp site due to back transfer Of electron from metal to Graphene
2. Engineering Strain in
Graphene by forming Bubbles
(a) Couple dirac particles to strain via pseudomagnetic field
(b) How to control such strain
patterns at the nanoscale ?
1. Graphene blisters are formed due to the uniform compressive strain associated with the lattice-mismatched ruthenium and
graphene.
2. Oxidation releases Elastic Strain and Moire Blisters sinter to form bubbles
Engineer Graphene Nanobubble
from the Moire Blisters
150x150 nm
•Defective Moire Pattrern due to sub-surface defects on metal
•Bubbles are more inclined to appear on defective Moire Site
Transforming Graphene Moire Blisters into Geometric Nanobubbles
Jiong Lu, Antonion C. Neto, Kian Ping Loh*, Nature Communcations, 8;3:823.(2012)
Bubbles appear on site that has defective
Moire pattern, and these can be seeded by
Ion Beam Irradiation
L: 3.0 nm Triangular 3-D STM image
Transforming Graphene Moire Blisters into Geometric Nanobubbles Jiong Lu, Antonion C. Neto, Kian Ping Loh*,
Nature Communcations, 8;3:823.(2012)
Decouple graphene and
merging of 5 blisters
5.65 ??虠蹽 皐 ?皐?r
0.00 ??虠蹽 皐 ?皐?ü
5.56 Å
0
5.65 ??虠蹽 皐 ?皐?r
0.00 ??虠蹽 皐 ?皐?ü
3.05 Å
0
Merging of 7 blisters to form hexagonal bubbles
(B)
8.26 ??虠蹽 皐 ?皐?(
0.00 ??虠蹽 皐 ?皐?'
8.26 Å
0 Merging Continuous bubbles Bubbles dots
more O2 High T
STS: More-like free-standing graphene
Transforming Graphene Moire Blisters into Geometric Nanobubbles,
Jiong Lu, Antonion C. Neto, Kian Ping Loh*, Nature Communcations, 8;3:823.(2012)
Sintering the Moire Blisters to Make Geometrically well defined Graphene Bubbles With Giant
Pseudomagnetic Field
pseudo-magnetic fields as large as 650 T and electronic gaps of order of 0.8 eV.
the LL energy expected in graphene scales according to E/B1/2
The electronic gaps associated with these
pseudo-magnetic fields are of the order ΔE(eV)
≈ 0.03 [B(T)]1/2 and hence they vary from 0.3 eV to 0.8 eV
Strain field higher at the edges of graphene bubble versus the center
This results in shifts of the Landau level peaks in the STS curves towards higher energies for regions of bubbles near the edges
A B C
3. Observing Chemistry Inside Graphene
Nanobubbles
A hydrothermal anvil made of graphene bubbles ?
No clear insight into how graphene interfaces with diamond
GRAPHENE NANOBUBBLE MAT FORMED ON DIAMOND
A hydrothermal Anvil made of Graphene nanobubbles on diamond
Candy Su, Kian Ping Loh*
Nature Communications 4, 1556, (2013)
The pressure that is built up in a typical Graphene nanobubble of 2 nm in height and 10 nm in radius is calculated to be
approximately 1 GPa
1st order
Diamond phonon
peak G
D 2D
1150 cm-1 (mixed sp2/sp3 and
transpolyacetylene D peak Graphene 1360 cm-1
Red shift upon the formation of bubbles - These
observations suggest that the lattice of graphene is biaxially strained
Before heating
After heating to induce bubble formation
Cyclic voltammetry of Fe(CN)63-/4- redox couple
• Inner sphere redox couple ,
sensitive to density of electronic states and surface microstructure
• Charge transfer rate calculated follows the order of
GNBs on diamond> Diamond> flat G on diamond
Outward rotation of orbitals enhances local density of states and bestows higher
reactivity on the outer surface of the GNB,
however Inner surface is less reactive pz orbital isosurface wavefunction of flat and curved graphene calculated using density functional theory (DFT, at B3LYP/6-31G*).
Graphene Bubbles are
electrochemically more active than flat surface !!
Strong hydrogen bonding results in a
weakening of the OH oscillator, a red shift in energy and a broadening of the spectral peak
.A hydrothermal Anvil made of Graphene nanobubbles on diamond
Candy Su, Kian Ping Loh*
Nature Communications 4, 1556, (2013)
Probing the bonding dynamics of
water trapped within Graphene nanobubbles using FTIR:
Bench top hydrothermal anvil cell
The critical temperature of water is 647 K,, 2 MPa
A significantly reduced dielectric constantof supercritical water allows it to act as an aggressive solvent for organic material
DIAMOND CAN BE CORRODED
BY SUPERHEATED WATER !
The pressure that is built up in a graphene nanobubble 2 nm in height
and 10 nm in radius is calculated to be approximately 1 GPa
Calibrating the pressure inside the bubbles using pressure sensing
molecules
IR-active modes in polyphenyl molecules that become inactive upon the phase transition from the twisted to the planar
conformation.
Upon planarization, certain IR-active peaks become IR-forbidden.
We would expect to see 6 modes disappear from the spectrum if p-terphenyl belongs to the C2h group, 29 modes if it belongs to the D2 group, and 51 modes if the
molecule has C2 symmetry. These
‘‘disappearing peaks’’
comprise a special subset of vibrational modes
Monitoring the vanishing of out-of-plane vibrational modes in P-Terphenyl: “ pressure
induced flatterning of the molecules”
Similarly, by increasing the temperature, certain out-of-plane modes of p-terphenyl were found to disappear. These peaks are indicated by arrows.
The recovery of these peaks are also observed upon cooling of the sample.
100 200 300 400 500 690
695 840 850 860
Wavenumber (cm-1 )
Temperature (oC)
600 800 1000 1200 1400 1600
Transmittance (Arb.)
Wavenumber (cm-1)
25oC 500oC
Cooled (25oC)
What is the pressure in Graphene Nanobubbles?
Graph plotted based on values that has been reported
Phy. Rev. B 45, 12682-12690.
J. Chem. Phys. 99, 3137-3138.
J. Chem. Phys. 114, 5465-5467.
Phys. Rev. Lett. 82, 3625-3628.
100 200 300 400 500
0.3 0.6 0.9 1.2 1.5
Pressure (GPa)
Beyond temperature (
o
C)Based on our experiments and with reference from previously reported values, we could draw a correlation between temperature and
pressure.
Using this relationship that we derive, we can heat the sample with C60 and determine the pressure at which it undergoes polymerization.
biphenyl
terphenyl
Oligomerization/Polymerization of Fullerene: Pressure-driven [2+2] Cycloaddition
[2+2] cycloaddition of C60 is symmetry forbidden due to mismatch of MOs.
-Molecular C60: 4 sharp IR modes
-Intermolecular bonding (lowers symmetry) changes vibrational spectra drastically
-Phase transformation of C60 in GNB under different stages of polymerization
Angewandte Chemie
Candy Lim, Kian Ping Loh*
(Accepted) 2013
4. Technological Implications of
Graphene Nanobubbles (a) Optical effects
(b) Surface Tension effects
Part II
• Porous Graphene Oxide
• Highly defective relative to CVD
graphene/mechanically exfoliated graphene
to improve its catalytic efficiency Study its catalytic origin
Probing the Catalytic Activity
of Graphene Oxide and its origin ,
Chen Liang Su and Kian Ping Loh* et. al., Nature Communications, 3, 1298 (2012)
K. P. Loh JACS., 2011, 133 (23), pp 8888
K. P. Loh, Nature Chemistry 2, 12, 1015 (2011) K. P. Loh JACS, 2010, 132, 41, pg 14481
K. P. Loh. Angewandte Chemie International Edition, 49 (37), 2010, pp 6549
K. P. Loh JACS., 2012, DOI: 10.1021/ja211433h
K. P. Loh JACS., 2010, 132 (32), pp 10976 K. P. Loh JACS., 2009, 131 (46), pp 16832
K. P. Loh JACS., 2008, 130 (44), pp 14392
GRAPHENE OXIDE MEDIATES MULTIPLE SYNTHETIC TRANSFORMATION
Seeding Ice Growth At Room temperature
Using Nano Graphene Oxide
Zheng Yi and K. P. Loh
Angewandte Chemie 2013
52, Issue 33, 8708–8712
Hot spots for catalytic action!
All these “imperfections” help to mediate its catalytic properties!
Perfect Graphene
Solid Acid
Solid base
Oxidative nature
N
B N
N
N
O
O OH
O OH OH HO R2N
Amine
Pyridine
O O
O
O Defective Graphene COOH
SO3H
Spin
Red-ox sites
Su C. and Loh, K. P. Acc. Chem. Res. DOI: 10.1021/ar300118v.
These complex cocktails
of functionalities may act in concert during catalysis via hydrogen bonding, ionic
complexation, radical stabilization etc.
Isolated debris
Element Graphite GO ba-GO
Mn 45.085 ppmb 304.6516 ppm < 1.0 ppm
Fe 1050.1785 ppm 204.2784 ppm 96.3118 ppm
Zn 94.8833 ppm 35.71 ppm 2.5735 ppm
Au 3.7233 ppm 1.8551 ppm N. D.
Ru N. D. N. D. N. D.
ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy) Analysis of GO, Graphite and ba-GO.a
a20 mg sample was dissolved by 2 ml of mixture acid (HCl : HNO3 = 3 : 1) and diluted to 10 ml by 5% DI water. bMetal/Sample = 1μg/g.
Before After
Metal impurities were removed.
Su, C. and Loh, K. P. Nat. Commun. 3 : 1298
Solvent free
ba-GO that is low-cost, non-polluting, reusable Open Air
90 oC, 12 h 5wt%
NH2 N
1 2
ba-GO, O2
Oxidative coupling of benzyl amine as the model reaction
Solvent free (only reactant)
Heterogenous Catalyst that is low-cost, non-polluting, reusable Open Air (safe)
Simply heating Low catalyst-loading
(Efficiency)
An ideal model
Su, C. and Loh, K. P. Nat. Commun. 3 : 1298
N-Benzylbenzaldimines
Carbocatalyst
ba-GO Nano Au/C
Heterogeneous: self-support
Active catalyst: ba-GO Active catalyst: Au
Heterogeneous: carbon support Total catalyst loading: 5 wt% Total catalyst loading: ~250 wt%
Active catalyst loading: 5 wt% Active catalyst loading: ~2 wt% Au
Reaction Temperature: 363 K Reaction Temperature: 373 K Price of GO/ba-GO: <1 $/g Price of bulk Au: >40$/g
Oxidant: Open Air Oxidant: 5 bar O2
Solvent free Solvent: PhMe
6th reuse: 93% yield 3rd reuse: 68% yield
Therefore, this carbocatalyst can be an ideal replacement for metal catalyst.
Journal of catalysis, 2009, 138-144
Gold catalyst
Vs
1. Holes could be created and enlarged by the strong base-etching process 2. Some unique functionalities might be introduced in the defects: e. g. spin electron from the non-bonding π electron states are likely to be created at the edges.
The change of morphology before and after base treatment
0.0 0.2 0.4 0.6 0.8 1.0
Quenched GO
Yield%
ba-GO
a b
c d
Electron Spin Resonance (ESR) measurements confirm the present of unpaired electrons
Edge Spin
This suggests that radical states at the edge sites are important in the catalysis besides carboxylic acid groups
44% yield
15% yield
89% yield
Controlling the acidic functionalities is important for the reactivity
The significant contribution of the carboxylic acids in this catalysis could be confirmed
Synergistic effect of acidic groups and spins
H2O2 was detected by the UV- visible absorption spectra (Adding DPD and POD.)
The oxygen radical was trapped by the DMPO spin- trapped EPR spectra
Probing the Catalytic Activity of Graphene Oxide Chen Liang Su and Kian Ping Loh* et. al.,
Nature Communications, 3, 1298 (2012)
Conclusions
• Strained structures like graphene bubbles afford new energy landscape
• The graphene bubbles can be used as a hydrothermal cell for studying reaction
dynamics at high pressure and temperature
• Defective, porous graphene oxide can be
effective carbocatalyst
45 1. Face-to-Face Transfer of Graphene Films on Silicon Wafer
Libo Gao, A.H. Castro Neto, Kian Ping Loh*
Nature (2013) Accepted
2. Order-Disorder Transition in a 2-D B-C-N alloy
Jiong Lu, Kai Zhang, Tze Chien Su,, A. H. Castro Neto, Kian Ping Loh*
Nature Communictions (In print, ASAP)
3.Graphene Oxide as a Chemically Tuneable Platform for Optical Applications Kian Ping Loh*, Bao QL, Eda G, Manish Chowalla.
Nature Chemistry, 2, 12, 1015-1024 (2010)
4.Transforming Fullerene Molecules into Graphene Quantum dots, Jiong Lu, Pei Shan Emmeline and Kian Ping Loh*,
Nature Nanotechnology, 6, 247–252, (2011)
5.Graphene as broadband polarizer Q. Bao, Y. Wang, D. Y. Tang, Kian Ping Loh*
Nature Photonics, 5, 411–415 (2011)
6.Transforming Graphene Moire Blisters into Geometric Nanobubbles, Jiong Lu, Antonion C. Neto, Kian Ping Loh*,
Nature Communcations, 8;3:823.(2012)
7. Probing the Catalytic Activity of Graphene Oxide and its origin,
Chen Liang Su and Kian Ping Loh* et. al., Nature Communications, 3, 1298 (2012)
8.A hydrothermal Anvil made of Graphene nanobubbles on diamond Candy Su, Kian Ping Loh*
Nature Communications 4, 1556, (2013)
9. High Yield exfoliation of 2-D chalcogenides using Na Naphthanelide Jian Zheng, Kai Zhang, Kian Ping Loh* et. a. Nature Communications
10. The chemistry of ultra-thin transition metal dichalcogenide nanosheets
Manish Chhowalla, Goki Eda, Kian Ping Loh et. al. Nature Chemistry 5, 263 (2013)
References