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.

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

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

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

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

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)

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. 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

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

PSCs with graphene anodes b 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

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

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