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What is graphene? 1 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.

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Presentation on theme: "What is graphene? 1 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."— Presentation transcript:

1 What is graphene? 1 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 cm 2 V -1 s -1 ) In late 2004, graphene was discovered by Andre Geim and Kostya Novoselov (Univ. of Manchester). - 2010 Nobel Prize in Physics But, weak bonding between layers Seperated by mechanical exfoliation of 3D graphite crystals.

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

3 Electronic structure of graphene 3 K Ef K K’ Pz bonding Valence band Pz anti bonding Conduction band 2DEG Fermi energy Effective mass (related with 2 nd derivative of E(k) )  Massless Graphene charged particle is massless Dirac fermion.  Zero gap semiconductor or Semi-metal

4 Electrical properties of graphene 4 High electron mobility at room temperature: Electronic device. Si Transistor, HEMT devices are using 2D electron or hole. μ (mobility) = v avg / E (velocity/electric field) J drift ~ ρ x v avg

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

6 Mechanical properties of graphene 6 Young’s modulus =tensile stress/tensile strain Diamond ~ 1200 GPa Force-displacement measurement Mechanical strength for flexible and stretchable devices C. Lee et al. Science 321, 385 (2008)

7 Graphene growth by chemical vapor deposition 7 SiC sublimation Metal catalysis 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 Nat.mat.2009.203. Ar1atm,1450~1650°C Terrace size increase. Current Status Solid Carbon : Low temp. Nat.2010.549. ACS nano,2011 CVD Ni: non uniform multi  Cu: uniform single  Cu: layer by layer growth Low temperature growth :below 1000°C Unform growth : Capet like (Large area) Si CMOS compatible process. “Transfer required”

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

9 PSCs with graphene anodes 9 ba 5.1 3.3 Al 4.3 TiO x 8.0 eV 6.0 4.3 PC 71 BM 5.4 GR/PEDOT: PSS (DT) 4.3 5.0 PTB7 -F40 PEDOT :PSS PCE (%) DeviceSubstrateElectrodeMethodV oc (V)J sc (mA cm -2 )FFAverageBest PSC Glass ITORF sputtering0.6814.10.615.80 ± 0.065.86 GR CT0.6511.10.552.69 ± 1.803.92 DT0.6812.10.674.85 ± 0.245.49 PET ITORF sputtering0.6414.30.524.52 ± 0.184.74 GRDT0.6412.50.604.57 ± 0.214.81

10 PLEDs with graphene anodes 10 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 11 2 cm DeviceSubstrateElectrodeMethodLE max (lm W -1 )CE max (cd A -1 )V T (V)L max (cd m -2 ) PLEDGlass ITORF sputtering1.875.154.54750 GR CT1.373.694.53150 DT1.874.144.04000


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