Graphene-based materials for potential energy
applications
Yong P. Chen,
Physics, ECE and Birck Nanotechnology Center
Purdue University
yongchen@purdue.edu
http://www.physics.edu/quantum
Chen
Slide 1 of 28
JNCASR-Purdue
SymposiumYong
onP.Nanomaterials
for Energy, 4/16/2012
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Graphene: exceptional & unique material properties
High thermal conductivity
high electrical conductivity & mobility…
Geim’05
Kim’05
Dirac
electrons
Balandin’10
optical transparency
material & chemical versatility
Large surface area..
Geim’09
Marita’11
Hong’09
nanoribbons/molecules/“graphXne”, functionalization…
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 2 of 28
Graphene: potential energy applications
Energy conservation (reduce consumption)
Energy (heat) management
Energy efficient
electronics
Heat dissipation
Thermal-interface
micro/nano electronics
& macroelectronics
A. Balandin, IEEE Spectr’09…
Energy conversion & energy storage
Photovotaic
(photoelectric)
thermoelectric
Ultracapacitors, batteries…
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 3 of 28
Outline
• CVD Graphene
– Large-scale CVD graphene, electrical and thermal properties
– Graphene single crystals & grain boundaries: electrical properties
• Graphene composite
– Thermal transport
– Photoelectric properties
• More exoticas
– Double layer “excitonics”
– Nanoribbon and edge electronics
– Nanoribbon “thermotronics”
Acknowledgment: many students/postdocs, collaborators & colleagues (see slides)
$$$: NSF, IBM, ACS, NRI-MIND, NIST, DHS, DTRA, Bill Miller, Chuck Day
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 4 of 28
Si
Wanted: Scalable Production of Graphene
How is graphene made?
“scotch tape” (micromechanical exfoliation)
* easy
* great for physics/single device
BUT
* not scalable (limits practical applications)
* limit experimental possibilities
(fundamental studies)
“bottom-up”: large scale synthesis
CVD on metal:
old history: ~1960s—
transfer (Q. Yu et al., APL 2008)
“Ni graphene”: 2009(Kong, Hong,..)
“Cu graphene”: 2010(Ruoff, …)
•Sublimation of
SiC
Berger et al.’06
•Chemical Vapor
Synthesis
(CVS)/CVD …
Courtesy. B.Hong
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 5 of 28
Large-scale Graphene Grown by CVD on Cu Foils
Chemical vapor deposition (at ambient pressure)
CVD furnace @ Purdue-QMD Lab
Recipe by Q.Yu
SiO2/Si
Details see:
H. Cao et al., Appl. Phys. Lett. (2010)
W. Wu et al., Sensors & Actuators B (2010)
Yong P. Chen
Also LP CVD: X. Li et al., Science (2009)
M. Levendorf et al., Nano Lett. 9, 4479 (2009)
Lee et al., Nano Lett. (2009)
S. Bae et al., Nature Nanotech (2010)
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
6
Slide 6 of 28
Continuous Graphene Films Grown by CVD on Cu (transferred to SiO2/Si)
Spectroscopic Raman Mapping: uniformity of graphene film
Raman spectra
20*20
μm2
area
H. Cao et al., APL (2010)
100*100 μm2 area
I2D/G
3μm
2μm
G resonance
• 2D/G is sensitive to number of layers
>2: monolayer (also 2D width)
• D/G is sensitive to crystalline defects (domain)
ωin
~90% area covered
by monolaye
graphene (2D/G>2)
ID/G
ωout
D resonance
7
TEM/SEAD
STM Monolayer CVD graphene
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 7 of 28
Electronic Transport: Field effect (transistor)
H. Cao et al., Appl. Phys. Lett. 96, 122106 (2010)
FET Device
“ambi-polar” Electric Field effect
3μm
40
T=300K
Conductance(µS)
30
With:4um
Length: 60um
p-type
(holes)
20
n-type
(electrons)
10
T.Shen et al.
photo- or e-beam lithography
-60
-40
-20
0
20
40
60
Vg(V)
• Ion/Ioff >~3 (graphene: semimetal)
•μ~3000 cm2/Vs
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
8
Slide 8 of 28
“Half integer” quantum Hall effect (QHE):
electronic “hall-mark” of single-layer graphene
H. Cao et al., Appl. Phys. Lett. 96, 122106 (2010)
magnetic
field (B)
Rxy
(RHall )
Rxx
I
gate
• Rxy quantized at Rxy
−1
1 e2
= 4( N + )
2 h
with Rxx ->0
Exfoliated
K. S. Novoselov et al., (2005)
Y. Zhang et al., (2005)
CVD on Cu
H. Cao et al., (2010)
S. Bae et al., (2010)
LL filling factor v=nch/eB=4(N+1/2)
1/BN=4(e/nch)(N+1/2) “Berry phase”
Novoselov &
Jiang et al.,
Science’07
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 9 of 28
APL (2011)
Excellent
electronic
homogeneity
In polycrystalline graphene
High quality quantum Hall states in CVD graphene
[ h/2e2~12906….. Ω potential use for resistance metrology:
(with D. Newell et al. NIST)]
Scalable/large size of CVD graphene an advantage (low noise, contact R, optical studies….)
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 10 of 28
Graphene Single Crystal Grains (on poly-Cu)
• grain boundaries
• edges
Graphene crystal not aligned with Cu grain
& can grow continuously cross Cu GB
no definite epitaxial relationship with Cu
 weak graphene-Cu interaction; see also
Li & Guisinger, Nano Lett.’10 on Cu(111)
Cu GB
10 μm
10 μm
Single crystal graphene can grow on polycrystalline Cu!
Q. Yu & L. Jauregui et al.
Nature Mater, 10, 415 (2011)
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 11 of 28
Scalable Fabrication of Graphene Single Crystals
• large single crystal grains
X. Li et al JACS (2011) [LP CVD]
• Graphene Single Crystal Arrays
Seeded growth:
2nd regrowth (graphene single crystals)
Patterned graphene dots (seends)
20 μm
Q. Yu & L. Jauregui et al. Nature Mater 10, 415 (2011)
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 12 of 28
Atomically Resolved STM
Graphene
(b)
b
A
Z
Z
Verifies
d
• Single crystal grain
c
• Zigzag-oriented edges
Cu
(c)
(d)
Z
A
Z
UHV 300K STM by Jifa Tian
in Argonne CNM STM user facilities
(thanks: Nanthan Guisinger)
A
Z
Q. Yu & L. Jauregui et al.
Nature Mater, 10, 415 (2011)
Z
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 13 of 28
Raman Spectroscopy and Raman Mapping: Grain boundaries revealed!
ID(x,y)
IG(x,y)
(a)
I2D(x,y)
(b)
(c)
2μm
2μm
2μm
ID(x,y)
IG(x,y)
(d)
I2D(x,y)
(f)
(e)
2μm
L.Jauregui et al
Yong P. Chen 2μm
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide2μm
14 of 28
Electronic Transport Within and Cross grains
2
3
4
5
6
T = 300K
1
10
9
8
Device #2
7
5 μm
Cross-GB resistivity ~
10 times higher than
intra-grain resistivity!
Q. Yu & L. Jauregui et al. Nature Mater, 10, 415 (2011)
Luis Jauregui et al., Solid State Comm. 151, 1100 (2011)
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 15 of 28
Weak localization due to GBs:
Scattering & Coherence of Carriers
ID
T = 450mK
A
B
Device#4
A
B
5μm
Q.Yu & L.Jauregui et al. Nature Mater. 2011
L. Jauregui et al. Solid State Comm 2011
Weak localization requires inter-valley scattering
--consistent with prominent Raman D-peak of GB’s
WL in graphene requires intervalley scattering
(Morozov’06’ McCann’06)
Perfect flat grapheneWAL
Ripples  random “pseudo” magnetic field suppresses WAL/WL
Intervalley scattering restores time-reversal WL
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 16 of 28
Thermal Conductivity: Electro-Raman Measurement of
• suspended CVD graphene
• electric heating (only graphene):
well controlled/defined
• Raman thermometry: reads graphene T
[Balandin’07]
Variable T (77-600K)
10μm
c ∂T
= ∇.( κ∇T ) + ρJ 2
h ∂t
κ = RI2L/ (8ΔTWh)
Joule
heating
k~2000W/mK
L.A. Jauregui et al. (2010); ECS Trans. (2010)
T rise
(read by Raman)
cf also Cai et al Nano Lett.10
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 17 of 28
Thermal Conductivity of Large CVD Graphene:
Pure-Electrical Measurement
Differential thermocouple Thermo Couple Works on Large CVD Graphene!
1
2
κ G ∇T1 AG
CVD graphene
Heat flow through graphene
on glass
κ Au∇T2 AAu
W
TC L A
)
κ G = κ Au 2 1 Au = 2288 (
L2 TC1 AG
m⋅ K
Heat flow through right Au pad
Heater
Au
G
Au
For >10 different samples: 1750 – 2420 (W/m-K)
TC1
TC2
Heater
Consistency check
κ1 = κ 2
TC1
TC2
TC2 L1
= 0.95κ 2
L2 TC1 vs. κ = κ
1
2
Au/Cu
A. Sidorov, Z. Jiang et al
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 18 of 28
CVD graphene
“Seebeck”
gas sensor
• large area
• Seebeck more
sensitive than
resistance
Yong P. Chen
yongchen@purdue.edu (765) 494-0947 http://www.physics.purdue.edu/quantum
Slide 19 of 28
Thermoconductivity & Photoconductivity
of graphene-based composites
Jiuning Hu & Wonjun Park (Purdue, ECE)
Yong P. Chen (Purdue, Physics, ECE)
Thanks: X. Ruan, T. Fisher,
Background & motivation
Why Graphene?
 Excellent electrical, thermal, and mechanical properties
 Transparent (~97.7%) and conductive
 Large surface to volume ratio; easy to be functionalized
Graphene composite (r-GO composite)
 Massively productive
 Tunable properties
 Electrical conductivity: extremely low percolation
threshold concentration
 Thermal conductivity
 Photoconductivity
Wonjun Park (Purdue)
park249@purdue.edu
21
Preparation of composites
Graphite
Powder
Graphite
Oxide
Hummer’s
method
Functionalization by phenyl isocyanate
& exfoliation by ultrasonication
r-GO/polymer
composite
Addition of
polymer(polystyrene)/nanoparticle
& reduction by hydrazine
Hot pressing
Functionalized
graphene oxide
Composite
powder
Coagulation in methanol/filtering
& drying
Composite bulk
(or film)
S. Stankovich et al. Nature (2006)
Wonjun Park (Purdue)
park249@purdue.edu
22
r-GO/PS composites
r-GO/PS composite bulk
r-GO/PS powder
SEM image of 0.5 vol.% r-GO/PS
800
10 vol.% r-GO/PS
5 vol.% r-GO/PS
1 vol.% r-GO/PS
0.5 vol.% r-GO/PS
Intensity (a. u.)
700
600
500
400
300
200
100
SEM image of 5 vol.% r-GO/PS
0
1500
2000
-1
Raman Shift (cm )
Wonjun Park (Purdue)
park249@purdue.edu
23
Jiuning Hu (Purdue)
hu49@purdue.edu
24
Jiuning Hu (Purdue)
hu49@purdue.edu
25
Jiuning Hu (Purdue)
hu49@purdue.edu
26
Dark conductivity at RT
Ibias
V
Au
r-GO/PS composite
σc ~ 0.3 vol.%
S. Stankovich et al., Nature (2006)
•
•
•
Device channel size : W=1;L=1;t=1.3mm
σdark ~3 x 102 S/m for 20 vol.% of r-GO/PS composite
σdark increases by ~104 from 0.5 vol. % r-GO/PS to 20 vol. % r-GO/PS
Wonjun Park (Purdue)
park249@purdue.edu
27
Temperature dependent dark conductivity
102
σ
dark
σ (S/m)
101
100
5 vol.% r-GO/PS
1 vol.% r-GO/PS
0.5 vol.% r-GO/PS
10-1
10-2
10-3
T0.7
dark_5 vol.% ∝
σ
T
σ
T1.7
dark_1 vol.%∝
dark_0.5 vol.%∝
100
150
200
250
300
Temperature (K)
Wonjun Park (Purdue)
park249@purdue.edu
28
Photoconductivity measurement setup
Half wave
Plate
Laser Source
633 nm
Polarizing
Beam
Splitter
Lens
17.54
0.5 vol.% r-GO/PS
Ibias
Vchannel (mV)
17.52
17.50 Laser
off
17.48
Laser
on
V
Laser
off
Au
17.46
r-GO/PS composite
17.44
17.42
17.40
0
100
200
300
Cryogenic
Stage
Time (sec)
Wonjun Park (Purdue)
park249@purdue.edu
29
Photoconductivity vs r-GO concentration at RT
0.7
10-2
-3
10
P=0.3 mW
P=0.6 mW
P=0.8 mW
P=1 mW
10-4
0
5
10
15
20
Sensitivity (%)
σph (S/m)
P=0.3 mW
P=0.6 mW
P=0.8 mW
P=1 mW
0.6
10-1
0.5
0.4
0.3
0.2
0.1
0.0
r-GO concentration (vol. %)
0
5
10
15
20
r-GO concentration (vol. %)
σ=(Ibias/Vchannel)(L/Wt)
σillumination=σdark+ σph
Sensitivity=σph/σdark
Wonjun Park (Purdue)
park249@purdue.edu
30
Photoconductivity vs Laser power at RT
0.7
0.6
10
3.0x10
0.5 vol.% r-GO/PS
2.5x10-4
10-2
ph
(S/m)
σphσ(S/m)
2.0x10-4
0.5 vol.% r-GO/PS
1 vol.% r-GO/PS
2.5 vol.% r-GO/PS
5 vol.% r-GO/PS
20 vol.% r-GO/PS
1.5x10-4
10-3
1.0x10-4
-5
5.0x10
-4
0.0
0.5
0.5 vol.% r-GO/PS
1 vol.% r-GO/PS
2.5 vol.% r-GO/PS
5 vol.% r-GO/PS
20 vol.% r-GO/PS
0.4
0.3
0.2
0.1
10
0.0
0.0
Sensitivity (%)
-1 -4
0.2
0.2
0.4
0.4
0.6
0.6
0.8
1.0
0.8
Laser
Power
(mW)(mW)
Laser
Power
1.0
0.0
0.0
0.2
0.4
0.6
0.8
Laser Power (mW)
1.0
σph=APα & α~1
Wonjun Park (Purdue)
park249@purdue.edu
31
0.7
0.6
-1
10
10-2
0.5 vol.% r-GO/PS
1 vol.% r-GO/PS
2.5 vol.% r-GO/PS
5 vol.% r-GO/PS
20 vol.% r-GO/PS
10-3
0.5
0.5 vol.% r-GO/PS
1 vol.% r-GO/PS
2.5 vol.% r-GO/PS
5 vol.% r-GO/PS
20 vol.% r-GO/PS
0.4
0.3
0.2
0.1
10-4
0.0
Sensitivity (%)
σph(S/m)
Photoconductivity vs Laser power at RT
0.2
0.4
0.6
0.8
1.0
0.0
0.0
Laser Power (mW)
0.2
0.4
0.6
0.8
Laser Power (mW)
1.0
σph=APα & α~1
Wonjun Park (Purdue)
park249@purdue.edu
32
5
10-1
10-2
10-3
5 vol.% r-GO/PS @RT
5 vol.% r-GO/PS @100K
0.5 vol.% r-GO/PS @RT
0.5 vol.% r-GO/PS @100K
10-4
10-5
Sensitivity (%)
σph(S/m)
Photoconductivity at 100K
4
0.5 vol.% r-GO/PS @RT
0.5 vol.% r-GO/PS @100K
5 vol.% r-GO/PS @RT
5 vol.% r-GO/PS @100K
3
2
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Laser Power (mW)
Wonjun Park (Purdue)
0.2
0.4
0.6
0.8
1.0
Laser Power (mW)
park249@purdue.edu
33
Wonjun Park (EE PhD)
(graphene composite+)
: semiconductor/absorber
nanoparticles
SEM image of Si NP/r-GO/PS
(10/1/89 vol.%) composite
SEM image of r-GO/PS
(1/99 vol.%) composite
Dark conductivity of composites
Photosensitivity of r-GO/PS
Devices (W=1/L=1/t=1.3mm) were characterized by lock-in amplifier with a 632 nm-laser (23mW)
Superfluidic Dirac Excitons  ultra-energy-efficient devices!
excitons (electron-hole pairs)
[can Bose-condense  (excitonic) superfluid]
d
d~ few nm
Huge (~1000 K) for Dirac electrons!
Min & MacDonand et al. PRB’08;
Zhang & Joglekar PRB’08; Lozovik & Sokolic ,
JETP’08
Dissipationless interconnect
Bilayer PseudoSpin Field-Effect Transistor
S. Banerjee et al. Electron Dev . Lett. 2009
[ultralow-power switch]
PMOS
NMOS
+ + + +
-
-
-
-
Stacked Graphene
Double Layer Device
Proof of principle:
• Stacked Double layer device
• Excitonic FET devices
Graphene 1
BN
Graphene 2
Double layer field effect:
use bottom graphene
to gate top graphene
Jiuning Hu & Yong Chen(Purdue)
(few layer)
Novel electronic properties of Graphene edges and nanoribbons
•
•
•
•
Open and tunable bandgap
Semiconductor vs metallic
Edge magnetism and spintronics
…
Challenge: how to make “perfect” edge & GNRs?
Jiuning Hu (Purdue)
hu49@purdue.edu
37
Graphene Edges: A STM Study
J.Tian, H.Cao, W. Wu, Q.Yu and Y.P. Chen. Nano Lett. 11, 3663 (2011)
2Å
4.3Å
• “Zigzag all-the-way!”
• “zigzag-roughened”
edge structure
• Microscopically rough,
but locally follows zigzag
down to atomic scale
--zigzag strongly preferred
• Such studies harder in
exfoliated graphene
STM of one rare armchair
edge:
J.Tian et al Nano Lett. (2011)
intervalley scattering?
intervalley back scattering
RL/2K~0.82
K=4π/(3a); 2K= 8π/(3a)
λ2K=2π/(2K)=3a/4
RL = 4π ( 3a )
RL (2 K ) = 3 2
Why not @ zigzag edges?
Intervalley Back-scattering: why armchair but not
zigzag
Real space
Momentum-space
Intervalley scattering:
Strong @ armchair
Weak @ zigzag
weak finite due to roughness
“A”
“Z”
how to make “perfect” GNRs?
(a)
molecular precursor
[building blocks]
T1
(b)
(b2)
T2
GNR formation
[dehydrogenation]
(b3) Armchair GNR
W
(b1) dibromoanthrene
linking building blocks
[debromination]
L
(c1) tetrabromophenanthrene
(c2)
(c3) Zigzag GNR
(c)
Assemble benzene-based molecular building blocks
(eg. J. Cai et al. Nature’2010)
Radial breathing?
Q.Yu
Thermal Management with Graphene Nanoribbons
Collab: X. Ruan
42
43
44
Summary
 CVD Graphene
 Large-scale CVD graphene, electrical and thermal properties
 Graphene single crystals & grain boundaries: electrical properties
 Graphene composite
 Thermal transport
 Photoelectric properties
 More exoticas
 Double layer “excitonics”
 Nanoribbon and edge electronics
 Nanoribbon “thermotronics”
Acknowledgment: many students/postdocs, collaborators & colleagues (see slides)
$$$: NSF, IBM, ACS, NRI-MIND, NIST, DHS, DTRA, Bill Miller, Chuck Day