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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) 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 Ar1atm,1450~1650°C Terrace size increase. Current Status Solid Carbon : Low temp. Nat 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 Al 4.3 TiO x 8.0 eV PC 71 BM 5.4 GR/PEDOT: PSS (DT) PTB7 -F40 PEDOT :PSS PCE (%) DeviceSubstrateElectrodeMethodV oc (V)J sc (mA cm -2 )FFAverageBest PSC Glass ITORF sputtering ± GR CT ± DT ± PET ITORF sputtering ± GRDT ±

10 PLEDs with graphene anodes eV 4.3 Ca 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 sputtering GR CT DT


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