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Part II. Introduction of Graphene Part II. Introduction of Graphene 1 Graphene (Mother of all‐graphitic form) 2D honeycomb lattice Graphene 0D 1D 3D blkbulky bllball NtbNanotube Graphite 22 Geims et al, Nature Materials,Vol.6 183, 2007 History of Graphene • Early: Thlheoretical description • 1962: Named by Hanns‐Peter Boehm (Graphite + ‐ene) • 2004: Single‐atom‐thick, free‐standing graphene is extracted (by Andre Geim and Konstantin Novoselov, Manchester University, U.K.) • 2005: Anomalous quantum Hall effect was observed • 2010: Nobel prize in Physics for Andre Geim and Konstantin NlNovoselov • Now: Stimulate wide researches and be applied to various fields 3 From ggpraphite to ggpraphene Graphene Mono‐atomic layer~1nm (10‐9 m) Graphite Multilayer carbon atom 2010 The Nobel Prize in Physics Prof. Andre Geim and Konstantin Novoselov at the U. Manchester for groundbreaking experiments regarding the 2‐D material graphene Graphite Graphene Graphene Atomic‐thick layer of carbon atom Zero bandgap Massless Dirac fermions K. S. Novoselov, A. K. Geim. Science (2004) High transparency and Flexible Low Resistivity about 10‐6 Ω∙cm, (< siliver) Ultrahigh high mobility (1000~300000cm2V‐1S‐1) etc… 6 A. K. Geim, Science (2009) Nair et al., Science, (2008) Bae. S et al. Nat. Nanotechnol. (2011) Atomic structure of graphene • The atomic structure, two‐dimensional crystals • The thinnest Materials Kraner et al. Chem. Rev. 2010,110,132 Rao et al, Angew. Chem., 2009,48,7752 Electronic Structure of Graphene • All C atoms are sp2‐bonded to adjoining C atoms • sp2 electrons form σ bonds – Form the honeycomb net of C atoms • Delocalized p electrons form π bonds C atom 2 2 2 2s 2px 2py 2pz sp sp sp p …… Graphene …… sp2 sp2 sp2 sp2 sp2 sp2 sp2 Delocalized p σ‐bonded π ‐bonded 8 Tight‐binding Unit cell Nearest neighbor EH k Analytic solution: E k 2 p JMC 21, 3335 (2011)1 S k π* 2nd‐nearest σπ π • π and π* merge at K, leading the metallic behavior of graphene • It is also called “Dirac point” • Bonds with adjacent atoms are most important, therefore the “nearest‐neighbor tight‐binding description” is usually used Phys. Rev. B 66, 035412 (2002) 1‐2. Fundamental Properties of Graphene 10 Band Structure of Graphene Dirac point π* π* π π • The valence band and the conduction band meet at Dirac point – Metallic behavior – “Semi‐metal” or “zero‐bandgap semiconductor” • Linear E‐k dispersion near Dirac point – “Massless” electrons and holes 11 Graphene AbilAmbipolar tttransport Au Au Yuanbo Zhang, et al., Nature(2005) Graphene 300nm SiO2 N+ Si Hole branch Electron branch K. S. Novoselov, et al., Nature (2005) Disadvantage of graphene 1. Low on/ off ratio FiFermi Dirac 2. Usually P‐type in air energy point 3. Poor air stability Negative bias Positive bias 12 Doped graphene 1. Covalent functionalized or 2. Surface charge transferred doping substitutional doping Xinran Wang, etal. Science (2007) J.–H. Chen. et al. Nature (2008) McCreary, K. etal. Appl. Phys. Lett. 2011 Dacheng Wei, etal. Nano lett. (2009) YWYu, W. etltal. Nano LttLett. 2011 Wang, Y.; etal. J. Phys. Chem. C (2008) Most of doping methods could considerably damage carrier mobilities of graphene. The doping level could not easily be easily controlled. The doping devices are very vulnerable to environment, especially for n‐type doping. 13 High transparency of Graphene Dirac point Electronics • Zero effec tive mass near the Dirac poiitnt • High carrier mobility >15,000 cm2/ V‐1s‐1 • Low Resistivity about 10‐6 Ω∙cm, (< siliver) • etc… Optics e2 1. One atomic layer absorption 2.3% c 2. High transparency Nair et al., Science, (2008) 14 Great potential for electronic and optoelectronic applications! 14 Optoelectronics application of Graphene • Transparent conddiucting eldlectrode TOUCH PANEL SOLAR CELL Light emitting diode Bae, S. et al. De Arco, L. G. et al Nature Nanotech. 4, 574–578 (2010). ACS Nano 4, 2865–2873 ()(2010) • Ultra fast Photodetector Matyy,ba, P. et al. ACS Nano 4, 637–642 (2010). 15 Xia, F. et al. Nature Nanotech. 4, 839–843 (2009). Thermal conductivity of graphene The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction. Nano Letters, 2008,Vol.8, 902 Mechanical properties of graphene 1. These experiments establish graphene as the strongest material ever measured. 2. The results show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime. Hones et al, Science,Vol. 321, p385, 2008 Synthesis of Graphene • Mechanical exfoliation • Epitaxial g rowth on silicon carbide • Epitaxial growth on metal substrates • Reduction of graphene oxide => solution processible, mass producible, Novoselov et al., Science (2004) simple and cheap Graphene/Cu Solution process Graphene/SiC de Heer et al, Science (()2006) Ruoff et al., Science, vol. 324, Sasha Stankovich, et al., Nature 442, pp1312-1314, 2009 282-286, 2006 18 Exfoliation process – In 2004, Andre Geim and Konstantin Novoselov suggest this method[4] – Use tapes to split one layer of C atoms from graphite and form graphene flake – Free‐standing graphene – Demonstrate the first graphene transistor – 2010 Nobel Prize in Physics Novoselov, K. S.; Geim, A. K. et al, Science 306 (5696), 666 (2004) 19 How to find the atomic layer “graphene” from repeatedly split graphite crystals by adhesi ve tape Epitaxial Graphene on SiC substrate by Chemical Vapor Deposition STM image of a CVD‐EG layer grown on a 4HSiC(0001) substrate Strupinski, W. et. al., Nano Lett. 2011, 11, 1786–1791 IBM wafer‐scale epitaxial graphene J. Vac. Sci., B. 28, 985,2010 21 Large area fabrication of graphene on Cu by using CVD processes Graphene grown on Cu foil Ruan, G. et. al., ACS Nano 2011, 5, 7601‐7607. 10 cm Ruoff et al., Science, vol. 324, pp1312-1314, 2009 Fabrication process of CVD graphene 10 cm Cockroach leg Ruan, G. et. al., ACS Nano 2011, 5, 7601‐7607. Chemical exfoliation of graphene from reduced graphene ooidexide GO Reduced GO Reduction 2 Distorted sp3 sp Insulator‐like Metallic‐like (planar) Eda et al. Nature Nanotech. 3 270‐274 (2008) Atomic and electronic structure of GO/Graphene GO nanoshtheet Graphene Ideal structure Reduction Insulator‐like Metallic‐like Distorted sp3 sp2 (planar) O 2 3 O sp /sp hybrid ( Real structure) Epoxide group HO O OH O O OH O HO O OH O HO Carboxyl group OH O OH O O O HO O O O Sp2‐like O 3 O sp ‐like OH OH O O OH HO O 25 Akasay et al, J of Phys. Chem. B Lett., 110, 8535,25 2006 Transfer of graphene Two Traditional Transfer Methods for CVD Graphene in the World PMMA Transfer Method Roll to Roll Transfer Method Small area Large area Lee, W. H., et. al, J. Am. Chem. Soc. , 2010, 133 , 4447 Bae, S., et. al., Nat. Nanotech., 2010, 5, 574 Roll‐to‐roll production of 30‐inch graphene films for transparent electrodes Bae, S., et. al., Nat. Nanotech., 2010, 5, 574 Processes of large‐area CVD graphene film transferred onto arbitrary substrate Graphene Growth Graphene Transfer Graphene Film PMMA method Cu foil Etching Organic support protection Graphene on Cu foil R2R method A critical step Yu Wang et al, ACS Nano, 2011, 5 , 9927–993729 Bae, S., et. al., Nat. Nanotech., 2010, 5, 574 Problems of PMMA and R2R Transfer Methods Difficulty in handling PMMA method stack problem PMMA residual PMMA protection Organic Residue R2R method adhesive cracks cracks Thermal released tape 1. undesired mechanical defects 2. organic adhesive from tape Junmo Kang et al, ACS Nano, 2012, 6, 5360. Xuesong Li et al, Nano Lett., 2009 , 9 , 4359–436330 Can we transfer graphene with no organic residue ??? Using electrostatic attraction Electrostatic generator Adv. Mater. 25, 4521, (2013) Clean‐Lifting Transfer (CLT) Technique Adv. Mater. 25, 4521, (2013) 1. Clean (No contamination) 2. Continuous (No folds, cracks, or holes). SiO2/Si wafer Flexible PET substrate 31 32 High quality CVD graphene of transferred by the CLT technique SEM AFM 1. Clean 2. Uniform morphology 3. No significant macroscopic defects, Wrinkles from the Cu foil XPSRaman analysis analysis Raman mapping PMMA I / I ~0060.06 R2R D G CLT PMMA or other functional groups ts ty on graphene in PMMA or R2R ii nn 1. High quality transfer method 2. Good uniformity Cou Intens 280 284 288 292 Binding1200 energy 1800 (eV) 2400 3000 33 Raman Shift (cm-1) CLT of graphene by a screen protector 34 Characterizations of garphene Raman Spectra of graphene Idifiidentification of t he l ayer numb er o f grap hene CVD graphene grown on Ni Graphene fron mechanical exfoliation of HOPG 2D band G bbdand No D band D band trilayer trilayer I G / I 2D ~1.25 bilayer bilayer I G / I 2D ~1.05 I G / I 2D ~040.4 monolayer monolayer A. Reina et. al., Nano Lett. 9 (2009) 3035. 36 A. C. Ferrari et al., PRL 97, 187401 (2006) AFM and STM image of graphene AFM images of graphene on SiO2 STM images of graphene/Ir(111) EitlExperimental calltdlculated Voloshina, E. N. Science Report, 2013, 3, 1 Photothermal reduction method for GO and r‐GO AFM of GO (a) TEM of GO (b) 2 10nm 1 0 Height (nm) -1 -2 0.0 Height 1.7 μm (c) (d) 1.0 reduced 0min graphite reduced 45min nce GO s) aa reduced 180min tt 0.8 RGOR-GO 0.6 0.4 reduction zed absorb ty (arb. uni ii ii Xe Lamp 0.2 Inens Normal 0.0 300 450 600 750 900 1050 1200 Wavelength (nm) 1200 1400 1600 1800 2000 2200 -1 Mild reduction processes Raman shift (cm ) 38 Electrical properties of graphene Tunable electrical and optical platform of graphene Atomically thin structure Tunable electronic structure EilEasily modltddulated by eltillectrical, or chilhemical , optical and mechilhanical method s IR Nano imaging Electrical gating Chemical Doping B.
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