Carbon Nanotubes

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 Youngs
  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/carbons
pacing2.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.jp
g 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/pub
lications/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/tubefe
t.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 Adam
s, Thomas A. Physical Properties of Carbon
Nanotubes. n. pag. Online. Internet. 21 Apr.
2001. Available http//www.pa.msu.edu/cmp/csc/n
tproperties/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/C
onferences/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/1
1/1/9. 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.h
tm. 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/i
ntro.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/c
ap04.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