Carbon Nanotubes Joey Sulpizio, Rice University

1. Carbon Nanotubes Joey Sulpizio, Rice University Introduction Carbon nanotubes comprise an extraordinary class of organic macromolecules. These molecules are basically cylindrical sheets of sp2 hybridized carbon. Carbon nanotubes are very long in relation to their width and can contain millions of carbon atoms per molecule. The amazing structure of these molecules allows for a variety of interesting physical properties such as high tensile strength, thermal conductivity, and electrical conductivity. There is a wide range of possible applications for carbon nanotubes, including electronics, probing, and structural support. History In 1991, Japanese scientist Sujimo Iijima of NEC discovered carbon nanotubes. Iijima, an electron microscopist, was studying materials deposited on the cathode during the arc-evaporation synthesis of fullerenes. Arc-evaporators are devices used for evaporating and condensing substances between electrodes. On examination of the central core of the cathodic deposit, Iijima found a variety of closed graphene structures which included many never discovered nanoparticles including carbon nanotubes. Single-walled and multi-walled nanotubes were later produced in bulk using this arc-evaporation method. The arc-evaporation method was modified in 1993 by adding metals such as cobalt to the graphite electrodes to produce single-walled-nanotubes, which are the subject of much research today. In 1996, the Smalley group of Rice University found an alternative method for producing carbon nanotubes using laser-evaporation of graphite in a way similar to their preparation for C60. This method gave a relatively high yield and formed tubes aligned in bundle-like ropes. • Properties • Average diameter of single-walled tubes 1.2-1.4 nm • Distance from opposite carbon atoms (line 1) 2.8 A • Analogous carbon atom separation (line 2) 2.46 A • Parallel carbon bond separation (line 3) 2.45 A • Carbon bond length (line 4) 1.42 A • Average density 1.36 g/cm3 • High thermal conductivity ~2000W/m/K • Delocalized pi electron system (aromatic) due to sp2 hybridization • Lateral flexibility related to reversible buckling of the atomic layers • High axial strength and stiffness, with Young’s modulus ~1TPa and maximum tensile strength ~30 GPa • Metallic or semi-conducting depending on helicity, with metallic fundamental gap at 0 eV and semi-conducting gap ~0.5 eV Maximum Current Density ~1013 A/m2 • Diamagnetic with axial magnetization susceptibility • Fairly chemically inert http://www.pa.msu.edu/cmp/csc/ntproperties/carbonspacing2.gif Fig 5. Nanotube carbon spacing diagram http://cnst.rice.edu/tube_1010.jpg Fig 1. A computer drawing of a carbon nanotube • Applications • Structural elements in bridges, buildings, towers, and cables • Material for making lightweight vehicles for all terrains • Heavy-duty shock absorbers • Open-ended straws for chemical probing and cellular injection • Nanoelectronics including batteries capacitors, and diodes • Microelectronic heat-sinks and insulation due to high thermal conductivity • Quantum wires and single-electron transistors due to electrical properties • Nanoscale gears and mechanical components • Electron guns for flat-panel displays • Nanotube-buckyball encapsulation coupling for molecular computing with high RAM capacity http://www.cnrs.org/cw/en/pres/compress/n384a6a.jpg Fig 6. Optical microscope view of a nanotube structural fiber -white line is 25 um http://focus.aps.org/v3/st35f1.jpg Fig 7. Atoms inside a nanotube act as a semi-conductor junction Fig 2. Diagram of laser used for laser-vaporization nanotube synthesis xhttp://www.sigmaxi.org/amsci/articles/97articles/fig03nanotube.gif?37,64 Fig 9. A carbon nanotube transistor http://www.nas.nasa.gov/Groups/Nanotechnology/publications/MGMS_EC1/simulation/normal.gif Fig 8. Nanotubes as gears • Structure • Cylindrical carbon fullerene cages consisting of only hexagons and pentagons Fig 3 • Helical structure related to mechanisms of formation • Either multi-walled or single-walled • Single-walled tubes are either armchair, zig-zag, or chiral in structure Fig 4 • Helical shape described by chiral vector (n,m) Fig 5 http://www.aip.org/physnews/graphics/images/tubefet.jpg References “Researchers Explore Applications for Carbon Nanotubes.” Online APS News. (1997): n. pag. Online. Internet. 21 Apr. 2001. Available: http://www.aps.org/apsnews/0697/11962c.html Adams, Thomas A. Physical Properties of Carbon Nanotubes. n. pag. Online. Internet. 21 Apr. 2001. Available: http://www.pa.msu.edu/cmp/csc/ntproperties/main.html. Collins, Philip, Hiroshi Bando, and A. Zettl. “Nanoscale Electronic Devices on Carbon Nanotubes.” Fifth Foresight Conference on Molecular Nanotechnology. (1997): n. pag. Online. Internet. 21 Apr. 2001. Available: http;//www.foresight.org/Conferences/MNT05/Papers/Collins. Dresselhaus, Mildred, Peter Eklund, and Riichiro Saito. “Carbon Nanotubes.” Physics World. (1998): n. pag. Online. Internet. 21. Apr. 2001. Available: http://physicsweb.org/article/world/11/1/9. Harris, Peter J F. “Carbon Nanotube Science and technology.” A Carbon Nanotube Page. n. pag. Online. Internet. 21 Apr. 2001. Available: http://www.rdg.ac.uk/~scsharip/tubes.htm. Liu, J. “Fullerene Pipes.” Science. (1998): n. pag. Online. Internet. 21 Apr. 2001. Available: http://cnst.rice.edu/pipes.pdf Tomanek, David. The Nanotube Site. n. pag. Online. Internet. 21 Apr. 2001. Available: http://www.pa.msu.edu/cmp/csc/nanotube.html. Yakobsin, Boris, and Richard Smalley. “Fullerene Nanotubes: C1,000,000 and Beyond.” American Scientist. (1997): n. pag. Online. Internet. 21 Apr. 2001. Available: http://www.sigmaxi.org/amsci/articles/97articles/intro.html http://www.phys.psu.edu/~crespi/research/carbon.1d/images/nanotube-70.gif Fig 3. Nanotube fullerene structure http://www.sigmaxi.org/amsci/articles/97articles/cap04.html Fig 4. Types of single-walled nanotube: 1-armchair 2-zig-zag 3-chiral Fig 5. Diagram of the Chiral vector, where R = na1 + ma2 http://www.pa.msu.edu/cmp/csc/ntproperties/hex.gif