What is graphene?

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What is graphene?
In late 2004, graphene was discovered by Andre Geim and
Kostya Novoselov (Univ. of Manchester).
- 2010 Nobel Prize in Physics
Q1. How thick is it?
 a million times thinner than paper
(The interlayer spacing : 0.33~0.36 nm)
Q2. How strong is it?
 stronger than diamond
(Maximum Young's modulus : ~1.3 TPa)
Q3. How conductive is it?
 better than copper
(The resistivity : 10−6 Ω·cm)
(Mobility: 200,000 cm2 V-1 s-1)
But, weak bonding between layers
Seperated by mechanical exfoliation of 3D graphite crystals.
1
Molecular structure of graphene
2D graphene sheet
Carbon
Electrons move freely across the
plane through delocalized pi-orbitals
bucky ball
CNT
3D graphite
2
Electronic structure of graphene
Effective mass (related with 2nd derivative of E(k) )  Massless
Graphene charged particle is massless Dirac fermion.
 Zero gap semiconductor or Semi-metal
Pz anti bonding
Conduction band
Ef
K
Fermi energy
K’
Pz bonding
Valence band
2DEG
K
K’
3
Electrical properties of graphene
High electron mobility at room temperature: Electronic device.
Si Transistor, HEMT devices are using 2D electron or hole.
μ (mobility) = vavg / E
(velocity/electric field)
Jdrift ~ ρ x vavg
4
Optical properties of graphene
Optical transmittance control: transparent electrode
Reduction of single layer: 2.3%
F. Bonaccorso et al. Nat. Photon. 4, 611 (2010)
5
Mechanical properties of graphene
Mechanical strength for flexible and stretchable devices
Young’s modulus
=tensile stress/tensile strain
Diamond ~ 1200 GPa
Force-displacement measurement
C. Lee et al. Science 321, 385 (2008)
6
Graphene growth by chemical vapor deposition
SiC sublimation
Metal catalysis
CVD
Ni: non uniform multi Cu: uniform single
 Cu: layer by layer growth
Current
Status
Solid Carbon : Low temp.
Nat.mat.2009.203. Ar1atm,1450~1650°C
Terrace size increase.
Nat.2010.549.
Pros&
Cons
High temperature growth
:1200~1500°C
Non-uniform growth
in Step edge and terrace.
High cost SiC wafer
: SiC growth on Si
No transfer required
ACS nano,2011
Low temperature growth
:below 1000°C
Unform growth : Capet like (Large area)
Si CMOS compatible process.
“Transfer required”
7
Large area graphene
K. S. Kim et al. Nature 457, 706 (2009)
S. Bae et al. Nat. Nano. 5, 574 (2010)
8
PSCs with graphene anodes
b
-2
Current density (mA cm )
PEDOT PTB7 TiOx Al
:PSS -F40
3.3
4.3
5.4
4.3
4.3
5.0
5.1
6.0
GR/PEDOT:
PSS (DT)
PC71BM 8.0 eV
0
-4
IPCE (%)
a
50
CT
DT
25
0
400 600 800
 (nm)
-8
-12
0.0
0.2
0.4
0.6
Voltage (V)
PCE (%)
Device
Substrate
Electrode
Method
Voc (V)
Jsc (mA cm-2)
FF
Average
Best
ITO
RF sputtering
0.68
14.1
0.61
5.80 ± 0.06
5.86
CT
0.65
11.1
0.55
2.69 ± 1.80
3.92
DT
0.68
12.1
0.67
4.85 ± 0.24
5.49
ITO
RF sputtering
0.64
14.3
0.52
4.52 ± 0.18
4.74
GR
DT
0.64
12.5
0.60
4.57 ± 0.21
4.81
Glass
GR
PSC
PET
9
OR'
x
y
z
Ca Al
0
100
0
50
-2
J (mA cm )
50
CT
DT
0
0
2
4
6
8
10
12
14
-1
4.3
4.8 eV
2.0
-2
2.9
GR/PEDOT: 5.4
PSS (DT)
150
4
Voltage (V)
2.4
5.1
200
L (cd m )
PEDOT SY
:PSS
Luminous efficiency (lm W )
RO
-1
OR
250
CE (cd A )
-2
OR'
Current density (mA cm )
PLEDs with graphene anodes
1.6
1.2
3
10
1
10
0
0.8
5
10
V (V)
CT
DT
0.4
0.0
-3
0
3
6
Voltage (V)
9
12
10
-1
Luminous efficiency (lm W )
250
-2
L (cd m )
-2
Current density (mA cm )
PLEDs with graphene or ITO anodes
200
150
100
3
10
1
10
0
5
10
V (V)
50
0
0
2
4
6
8
10
12
2.0
1.6
1.2
2 cm
0.8
ITO
GR/PEDOT:PSS (DT)
0.4
0.0
-2
Voltage (V)
Device
PLED
Substrate
Glass
0
2
4
6
8
10
12
Voltage (V)
Electrode
Method
LEmax (lm W-1)
CEmax (cd A-1)
VT (V)
Lmax (cd m-2)
ITO
RF sputtering
1.87
5.15
4.5
4750
CT
1.37
3.69
4.5
3150
DT
1.87
4.14
4.0
4000
GR
11

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