1. What is graphene?
In late 2004, graphene was discovered by Andre Geim and Kostya Novoselov (Univ. of Manchester).
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.

2. Electrons move freely across the plane through delocalized pi-orbitals
Molecular structure of graphene
Carbon
2D graphene sheet
bucky ball
CNT
3D graphite
Electrons move freely across the plane through delocalized pi-orbitals

3. 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 K Ef K’
Pz anti bonding
Conduction band
Fermi energy
Pz bonding
Valence band
2DEG

4. 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

5. Optical properties of graphene
Optical transmittance control: transparent electrode
Reduction of single layer: 2.3%
F. Bonaccorso et al. Nat. Photon. 4, 611 (2010)

6. Force-displacement measurement
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)

7. 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 Ar1atm,1450~1650°C
Terrace size increase.
Nat ACS nano,2011
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
Low temperature growth
:below 1000°C
Unform growth : Capet like (Large area)
Si CMOS compatible process.
“Transfer required”
Pros&
Cons

8. Large area graphene K. S. Kim et al. Nature 457, 706 (2009)
S. Bae et al. Nat. Nano. 5, 574 (2010)

9. PSCs with graphene anodesb
5.1
3.3 Al
4.3
TiOx
8.0 eV
6.0
PC71BM
5.4
GR/PEDOT:
PSS (DT)
5.0
PTB7
-F40
PEDOT
:PSS
PCE (%)
Device
Substrate
Electrode
Method
Voc (V)
Jsc (mA cm-2) FF
Average
Best
PSC
Glass
ITO
RF sputtering
0.68
14.1
0.61
5.80 ± 0.06
5.86 GR CT
0.65
11.1
0.55
2.69 ± 1.80
3.92 DT
12.1
0.67
4.85 ± 0.24
5.49
PET
0.64
14.3
0.52
4.52 ± 0.18
4.74
12.5
0.60
4.57 ± 0.21
4.81

10. PLEDs with graphene anodes
5.4
2.4
4.8 eV
4.3 Ca
2.9
5.1
GR/PEDOT:
PSS (DT) SY Al
PEDOT
:PSS

11. PLEDs with graphene or ITO anodes
2 cm
Device
Substrate
Electrode
Method
LEmax (lm W-1)
CEmax (cd A-1)
VT (V)
Lmax (cd m-2)
PLED
Glass
ITO
RF sputtering
1.87
5.15
4.5
4750 GR CT
1.37
3.69
3150 DT
4.14
4.0
4000