Mildred Dresselhaus - Why are we so ...

Why are we so Excited about Carbon Nanostructures? : 

University of Zagreb Department of Physics November 19, 2008 Why are we so Excited about Carbon Nanostructures? Mildred Dresselhaus Massachusetts Institute of Technology Cambridge, MA

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Why are we so Excited about Carbon Nanostructures? Early adventures with graphene and graphite and related nanostructures Adventures with Carbon Nanotubes Graphene and Graphene Ribbons Studies of graphene edges Looking to the Future of Carbon nanostructures Outline

Graphene -the Mother of all nano-Graphitic forms : 

Graphene -the Mother of all nano-Graphitic forms A graphene sheet is one million times thinner (10-6) than a sheet of paper. Graphene is a 2D building block material for other sp2 bonded carbon materials. It can be wrapped up into 0D fullerenes, rolled into 1D nanotubes, cut into 1D graphene ribbons or stacked into 3D graphite (After A. Geim)

The Novel Electronic Structure of Graphene : 

P.R. Wallace, Phys. Rev. 71, 622 (1947) In 1957-1960 McClure extended the 2D graphene electronic structure to 3D graphite. Near the K point linear  relation and and EF where J.W. McClure, Phys. Rev, 108, 612 (1957); 119, 606 (1960) The Novel Electronic Structure of Graphene

Magnetoreflection in Graphite : 

Magnetoreflection in Graphite M.S. Dresselhaus and J.G. Mavroides. IBM Journal of Research and Development 8, 262 (1964) J.W. McClure, Phys. Rev, 108, 612 (1957); 119, 606 (1960) First magneto-optical experiment to measure energy bands at several regions of the Brillouin zone (near K and H) This experiment (1961) was enabled by the availability of a new material, highly oriented pyrolytic graphite (HOPG) from Ubbelohde (1960). Using the McClure-Slonczewski-Weiss symmetry-based E(k) model, the band parameters for the electronic structure of graphite were deduced.

Identification of Electrons and Holes in Graphite : 

Identification of Electrons and Holes in Graphite This experiment established the location for electrons and holes in graphite that we use today. Using circularly polarized radiation in the first laser magneto-optical experiment, the locations of electrons and holes in the Brillouin zone for graphite were identified P.R.Schroeder, M.S. Dresselhaus and A.Javan, Phys.Rev. Lett 20,1292 (1968)

My entry into the Nanoworld (1973) : 

My entry into the Nanoworld (1973) Hannay et al, Phys.Rev.Lett. 14, 225 (1965) Observation of superconductivity in stage 1 graphite intercalation compounds (C8K) C8K aroused much interest in carbon nanostructures since neither potassium nor carbon is superconducting. Intercalation compounds allowed early studies to be made of individual or few graphene layers in the environment of the intercalant species.

Concurrent Studies on Forerunners of Fullerenes : 

Concurrent Studies on Forerunners of Fullerenes Intercalation led to studies of ion implantation and photon irradiation and to liquid carbon studies (1983). Liquid carbon was found to be metallic T. Venkatesan et al, Phys. Rev. Lett. 53, 360 (1984) The Laser ablation process used to make liquid carbon caused the emission of large carbon clusters (like C100) rather than C2 and C3 with relatively low laser energy input. E.A.Rohlfing, D.M. Cox and A.Kaldor. J. Chem.Phys., 81, 332 (1984) A trip was made to Exxon Research Lab to discuss results. Soon (1984), Exxon published the famous result for the mass spectra. In 1985 fullerenes were discovered by Kroto, Smalley, and Curl.

Forerunners of Carbon Nanotubes : 

Forerunners of Carbon Nanotubes M.S.Dresselhaus et al., Graphite Fibers and Filaments, Springer (1988) Saito, Fujita, Dresselhaus2, Electronic structure of carbon fibers based on C60, PRB 46, 1804 (1992) In 1980, Morinobu Endo showed me vapor grown carbon fibers. At the center of carbon fibers is a multiwall carbon nanotube. The nanotube-fullerene connection was made by going from C60C70C80 CNT in a public discussion (Dec. 1990) with Richard Smalley. This idea suggested that a single wall Carbon nanotube would be interesting (August 1991) and led to calculating the electronic structure of single wall carbon nanotubes before they were ever seen.

General Relations between 1D and 2D Systems shown in terms of carbon nanotubes : 

1D van Hove singularities give high density of electronic states (DOS) at well defined energies Rolling up a 2D sheet Confinement of 1D electronic states on cutting lines 1D 2D Carbon nanotubes are metallic if a cutting line passes through the K point; otherwise they are semiconducting. DOS General Relations between 1D and 2D Systems shown in terms of carbon nanotubes K K’

Discovery of Single Wall Carbon Nanotubes : 

Discovery of Single Wall Carbon Nanotubes First synthesis and (n,m) characterization of Single Wall Carbon Nanotubes (1993) D. Bethune et al Nature 363, 605 (1993) S. Iijima and T. Ichihashi, Nature 363, 603 (1993) Identified (n,m) nanotube chirality by TEM (transmission electron microscopy)

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Why are we so Excited about carbon nanostructures? Early adventures with graphene and graphite and related nanostructures Adventures with Carbon Nanotubes Graphene and Graphene Ribbons Studies of graphene edges Looking to the Future of Carbon nanostructures Outline

Nanotube Structure : 

Rolled-up graphene layer has a large unit cell. Graphene Sheet SWNT Each (n,m) nanotube is a unique molecule. R.Saito, MS Dresselhaus, G. Dresselhaus,, Imperial College Press, 1998 Nanotube Structure

Unique Properties of Carbon Nanotubes within the Nanoworld : 

Small size: ~1 nm diameter (down to ~10 atoms around the circumference) Electronic Properties: can be either metallic or semiconducting depending on diameter and orientation of the hexagons Mechanical: Very high strength, modulus, and resiliency. Physics: model system for 1D density of electronic states. Single molecule Raman spectroscopy, luminescence and transport properties. chiral zigzag armchair graphene ribbon SWNT Unique Properties of Carbon Nanotubes within the Nanoworld

Resonance Raman Spectroscopy (RRS) : 

E = 0.94eV = 1.17eV = 1.58eV = 1.92eV = 2.41eV A.M. Rao, P.C. Eklund, R.E. Smalley, M.S. Dresselhaus, et al., Science 275 (1997) 187 RRS: R.C.C. Leite and S.P.S. Porto, PRL 17, 10-12 (1966) Raman spectra from SWNT bundles Enhanced Signal Optical Absorption e-DOS peaks diameter-selective resonance process wRBM = a / dt Confirms: Resonant DOS Each (n,m) tube has a different spectrum Resonance Raman Spectroscopy (RRS)

Resonant Raman Spectra of Carbon Nanotube Bundles : 

G-band resonant Raman spectra Diameter dependence of the Van-Hove singularities M. A. Pimenta et al., Phys. Rev. B 58, R16016 (1998) laser energy Kataura plot Metallic and semiconducting tubes have different lineshapes Resonant Raman Spectra of Carbon Nanotube Bundles

Single Nanotube Raman Spectroscopy yields Eii and (n,m) : 

The large density of states at resonance enables single nanotube spectroscopy The geometrical structure of an individual carbon nanotube can then be found R. Saito et al., Phys. Rev. B 61, 2981 (2000) Each nanotube has a unique DOS because of trigonal warping effects (wRBM, Eii)  (n,m) A. Jorio et al., Phys. Rev. Lett. 86, 1118 (2001) Single Nanotube Raman Spectroscopy yields Eii and (n,m) Single nanotube spectroscopy has since been demonstrated in photoluminescence and in Rayleigh scattering experiments.

Raman Spectra of SWNT Bundles : 

Raman Shift (cm-1) Raman Intensity o G+ G-band RBM gives tube diameter and diameter distribution Raman D-band characterizes structural disorder G- band distinguishes M from S tubes and G+ relates to charge transfer G’ band at about twice the D-band frequency provides connection of phonon to its wave vector Each feature in the Raman spectra provides complementary information about nanotubes Raman Spectra of SWNT Bundles

Band Gap Nanotube Fluorescence : 

Band Gap Nanotube Fluorescence 2n+m=constant family patterns are observed in the photoluminescence excitation-emission spectra. Identification of ratio problem Showed value of mapping optical transitions Good method to determine the (n,m) for semiconducting nanotubes in a given sample M. J. O’Connell et al., Science 297 (2002) 593S. M. Bachilo et al., Science 298 (2002) 2361. Peaks only SDS=Sodium Dodecyl Sulfate 1.0 g/cm3

Extended tight binding model : 

 Kataura plot is calculated within the extended tight-binding approximation including effects of: curvature (sss, sps, pps, ppp) long-range interactions (up to ~4Å) geometrical structure optimization The extended tight-binding model shows: Family behavior Differentiation between S1 and S2 type tubes Strong chirality dependence M 2n+m=3p S1 2n+m=3p+1 S2 2n+m=3p+2 Transition Energy (eV) Inverse Diameter (1/nm) Ge.G. Samsonidze et al., APL 85, 5703 (2004) N.V. Popov et al Nano Lett. 4, 1795 (2004) and New J. Phys. 6, 17 (2004) Extended tight binding model Kataura plot

Excitons in Carbon Nanotubes : 

2-photon excitation to a 2A+ symmetry exciton (2p) and 1-photon emission from a 1A- exciton (1s) cannot be explained by the free electron model Wang, Brus, Heinz et al. Science 308, 838 (2005) Experimental Justification for excitons The observation that excitation and emission are at different energies supports the exciton model. Excitons in Carbon Nanotubes

Non-degenerate Pump-probe Experiments : 

Non-degenerate Pump-probe Experiments Epump = 1.57±0.01eV, ~E11(6,5)+2ħwD Eprobe = around E11of (6,5) nanotube (Instrument resolution ~250fs) S. G. Chou, M.F. DeCamp, A. Tokmakoff, et al. Phys. Rev. B 72, 195415 (2005) Frequency domain Fast optics, Time domain Fast optics provides further evidence in support of the excitonic model.

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Current Research Topics Raman studies of individual double wall carbon nanotubes Raman studies of metallic carbon nanotubes as a function of gate voltage Electroluminescent emission from metallic SWNTs as a function of drain voltage

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Why are we so Excited about carbon nanostructures? Early adventures with graphene and graphite and related nanostructures Adventures with Carbon Nanotubes Graphene and Graphene Ribbons Studies of graphene edges Looking to the Future of Carbon nanostructures Outline

Graphene -the Mother of all nano-Graphitic forms : 

Graphene -the Mother of all nano-Graphitic forms A graphene sheet is one million times thinner (10-6) than a sheet of paper. Graphene is a 2D building block material for other sp2 bonded carbon materials. It can be wrapped up into 0D fullerenes, rolled into 1D nanotubes, cut into 1D graphene ribbons or stacked into 3D graphite (After A. Geim) Graphene Revisited (2004)

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Optical Transmission of Graphene Visualisation of Fine Structure Constant the fine structure constant observed “with a naked eye” Manchester, Science ‘08

Anomalous Quantum Hall Effect in 1ML Graphene : 

Anomalous Quantum Hall Effect in 1ML Graphene Half integer quantum Hall effect Factor of 4 in 4e2/h Berry’s phase of π This work attracted great attention and interest in graphene Novoselov et al., Nature 438 (197) 2005 Three anomalies:

Graphene Ribbons : 

Zigzag Special feature of graphene ribbons is that they have edges and few columns of carbon atoms along the width. Direction of cutting lines Graphene Ribbons Armchair

Electronic structure of graphene ribbons : 

Armchair Zigzag Metallic for N=3M-1 (M integer) Semiconducting for N=3M and 3M-2 Examples: Always metallic Presence of localized edge states at the Fermi level Van Hove singularities in the DOS Nakada et al., Phys. Rev. B 54, 17954 (1996). Electronic structure of graphene ribbons Metallic for N=5 and Semiconducting for N=4, 6

Graphene ribbon edges favor armchair and zigzag edge segments : 

Graphene ribbon edges favor armchair and zigzag edge segments Armchair edges are the most favored (more stable), chiral edges are least favored Higher intensity AFM signal along zigzag edge Z1 supports a high electron density of states along the zigzag edge Enoki et al., Int. Rev. Phys. Chem. 26, 609 (2007).

GNR Electrical Devices : 

GNR Electrical Devices (X. Wang et al., PRL, 2008) Vds=-1V -500mV -10mV Narrow nanoribbon devices exhibit large Ion/Ioff ratios

Raman spectra of graphene ribbons : 

Cançado et al., Phys. Rev. Lett. 93, 047403 (2004). Gruneis et al., Phys. Rev. B 67, 165402 (2003). G1 - nanographite ribbon G2 – 3D graphite substrate Strong polarization effect is observed in graphene ribbons Raman spectra of graphene ribbons

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Why are we so Excited about carbon nanostructures? Early adventures with graphene and graphite and related nanostructures Adventures with Carbon Nanotubes Graphene and Graphene Ribbons Studies of graphene edges Looking to the Future of Carbon nanostructures Outline

Raman studies on graphene ribbon edges : 

Raman studies on graphene ribbon edges The intervalley (K→K') D-band intensity depends on the edge type: large for armchair edge, smaller for zigzag edge. But the intravalley (K→K) D'-band intensity is similar for zigzag and armchair edges L. G. Cançado, et al. Phys. Rev. Letters, 93, 247401 (2004)

Images of Graphene Ribbons and Edges : 

Images of Graphene Ribbons and Edges zigzag zigzag zigzag armchair c b (a) Low magnification SEM image (b) low magnification TEM (c) Atomic resolution image Campos-Delgado, et al, Nano Letters (2008) a Zigzag and Armchair edges are clearly seen

Formation of sharp edges : 

Formation of sharp edges Clear achiral armchair and zigzag edges develop by Joule heating The amount of chiral edges decreases with annealing After 10min annealing After 20min annealing

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Why are we so Excited about carbon nanostructures? Early adventures with graphene and graphite and related nanostructures Adventures with Carbon Nanotubes Graphene and Graphene Ribbons Studies of graphene edges Looking to the Future of Carbon nanostructures Outline

Looking to the Future of Carbon Nanostructures : 

Looking to the Future of Carbon Nanostructures Synthesis Remains a main focus Control and understanding of synthesis process Control of (n,m) during synthesis, cloning etc Control of number of graphene layers and sample size Control of graphene ribbon synthesis Better samples will reveal new science Characterization and properties New techniques such as aberration corrected HRTEM allow detailed studies of defects, dopants and structures Raman studies will provide complementary technique to study nanocarbons – also HRTEM and Raman Unique studies such as separation of charge and spin transport

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Scaffold for Neuron growth Artificial muscle Applications Increasing interest in applications, especially for: Field effect transistors and transparent electrodes Nanotubes for adding resilience to lithium ion batteries Conducting reinforcement for polymers and ceramics Chemical and biosensors Muscle actuators, tissue growth scaffold Special applications of nanohorns for applications to energy and medicine Metrology science needs to be developed Health effects need to be investigated further Looking to the Future of Carbon Nanostructures Nanohorns Carbon electronics Nanotube film sensor

Thank you : 

Thank you Collaborators: G. Dresselhaus, MIT H. Son, MIT J. Kong, MIT M. Hofmann, MIT X. Jia, MIT H. Farhat. MIT A.Reina, MIT F. Villalpando, MIT M.A. Pimenta, UFMG Brazil A. Jorio, UFMG Brazil F. Plentz Filho, UFMG Brazil A. Souza Filho, UFC Brazil L.G. Cancado, Rochester G.G. Samsonidze, UC Berkeley M. Endo, Shinshu U R. Saito, Tohoku U K. Sasaki, Tohoku U Y.A. Kim, Shinshu U M. Terrones, IPICYT, Mexico

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