Carbon Nanotube Synthesis

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Carbon Nanotube Synthesis and Processing
Y. Tzeng ELEC 7970 Summer 2003
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The Nanotube Site
Maybe the most significant spin-off product of
fullerene research, leading to the discovery of
the C60 "buckyball" by the 1996 Nobel Prize
laureates Robert F. Curl, Harold W. Kroto and
Richard E. Smalley, are nanotubes based on carbon
or other elements. These systems consist of
graphitic sheets seamlessly wrapped to cylinders.
With only a few nano-meters in diameter, yet
(presently) up to a milli-meter long, the
length-to-width aspect ratio is extremely high. A
truly molecular nature is unprecedented for
macroscopic devices of this size. Accordingly,
the number of both specialized and large-scale
applications is growing constantly.
http//nanotube.msu.edu/
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Nanoscale Science Laboratory Single-crystals
of single-walled Carbon nanotubes
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Molecular model of a buckyball. They have a
diameter of approximately 1 nm (10-9 m),which
means we would need about 1024 buckyballs to fill
a normal football! (Courtesy Prof Richard
Smalley)
Simulated structure of a carbon nanotube made up
primarily of graphite hexagons. Courtesy of
Richard Smalley's picture gallery.
http//www-g.eng.cam.ac.uk/nano/nanotube.htm
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Synthesis methods for carbon nanostructures
The CVD techniques It is a chemical deposition
(the deposition can be led for severaldays)
through pyrolysis (the sample and the surrounding
are heated, typicallyaround 700 C) of a
hydrocarbide (acetylene, ethylene, benzene...)
overa template substrate (for example, iron
nano-particules embedded in silica). See for
instance Z. W. Pan et al. - Very long carbon
nanotube-nature, vol. 394, 13 aug. 1998
Krätschmer arc methods It is the most widely
used method to synthesize carbon nanostructure
because it is rather simple to undertake in
laboratory. The principle is to submit 2 graphite
electrodes to a high currentdischarge (typically
20V, 50A) inside an enclosure filled with inert
gas(helium, argon...) at low pressure (between 50
and 700 mbar). Metallicparticles can be added in
the initial electrodes to catalyse single
wallnanotubes. See W. Krätschmer, L.D. Lamb, K.
Fostiropoulos, D.R. Huffman , Solid C60 a new
form of carbon - Nature 347, 354-358 (1990) and
C. Journet et al.- Large scale production of
single-walled carbon nanotubes by the
electric-arc technique - Nature 388 21 aug. 1997
http//membres.lycos.fr/thomaslaude/methods.htm
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The laser ablation methods It is rather similar
to the arc method and was in fact the first one
tobe developed. Studies (mainly in Rice
university) have proved that it canlead to very
similar structures to those obtained by the arc
method fullerenes, nanotube multi or
mono-layered, onions... The main differences are
The material is submitted to a laser ablation
instead of an arc discharge. (The laser is
usually a pulsed YAG laser.) No tube of
reasonable length has ever been synthesized
without some catalysing particles. This tends to
say that a certain local anisotropy is
necessaryto grow tube. Particles are collected
through a carrier gas on a cool plate far fromthe
target. A secondary heating is usually added.
See A. Thess et al. - Crystalline ropes of
metallic carbon nanotubes- science, vol. 273, 26
july 1996
http//membres.lycos.fr/thomaslaude/methods.htm
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STEM image of a nanotube crystal. Each linear
fringe corresponds to a single wall nanotube
1.6nm in diameter
Schematic showing the transformation of C60
molecules to single wall nanotubes and then
nanotube crystals.
SEM image of 4 nanotube crystals growing from a
molybdenum substrate. Each crystal is about 200nm
in diameter
http//www-g.eng.cam.ac.uk/nano/nanotube.htm
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http//www.ornl.gov/odg/tubemain.html
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http//www.ornl.gov/odg/tubemain.html
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http//www.iljinnanotech.co.kr/en/material/r-4-3.h
tm
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TEM images of rope for the single-walled
nanotubes synthesized by laser- vaporization
method
SEM image of single-walled carbon nanotubes
synthesized by laser- vaporization method
Schematic diagram of laser vaporization
apparatus for the synthesis of multiwalled
nanotubes.
http//www.iljinnanotech.co.kr/en/material/r-4-2.h
tm
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SEM images of multiwalled carbon nanotubes
synthesized by arc-discharge method.
Schematic diagram of arc-discharge apparatus.
TEM image of single walled carbon nanotubes
synthesized by arc-dischargemethod.
SEM image of single walled carbon nanotubes
synthesized by arc-discharge method.
Deposit of carbon nanotubes and carbonaceous
particles using arc-discharge.
http//www.iljinnanotech.co.kr/en/material/r-4-1.h
tm
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Thermal CVD of Carbon Nanotubes
SEM images of carbon nanotubes grown by thermal
CVD method.
TEM images of carbon nanotubes grown by thermal
CVD method.
http//www.iljinnanotech.co.kr/en/material/r-4-4.h
tm
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Vapor Phase Growth of Carbon Nanotubes
TEM images of carbon nanotubesgrown by vapor
phase growth method.
SEM images of carbon nanotubes grown by vapor
phase growth method.
http//www.iljinnanotech.co.kr/en/material/r-4-5.h
tm
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Electrolysis MWNTs are synthesized using this
method which involves the electrolysis of molten
lithium chloride using a graphite cell in which
the anode was a graphite crucible. The
temperature of the graphite crucible is
approximately 600 oC in the Ar atmosphere. MWNTs
with 2-10 nm in diameter and 0.5 or more in
length are synthesized when DC power at less than
3-20A and 20 V is applied. Amorphous carbons and
encapsulated CNTs are synthesized as by-products.
http//www.iljinnanotech.co.kr/en/material/r-4-6.h
tm
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Flame synthesis In this method, combustion heat
is a heating source of carbon nanotubes produced
from combustion of CH4 in the small amount of
oxygen atmosphere. MWNTs and SWNTs are
synthesized by flowing hydrocarbon source like
C2H2 and catalytic precursors in the diffusion
flame atmosphere. As the temperature range of
600-1300 oC is not uniform in the Flame
atmosphere, the tubes contain a great amount of
amorphous carbons and show poor crystallinity. It
facilitates mass production and is promising in
the application to electrolytic materials.
http//www.iljinnanotech.co.kr/en/material/r-4-6.h
tm
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http//www.iljinnanotech.co.kr/en/material/r-4-6.h
tm
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http//www.iljinnanotech.co.kr/en/material/r-4-6.h
tm
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• Purification process of MWNTs synthesized by
  arc-discharge    1)As-prepared MWNTs   
  2)Ultrasonic dispersion in surfactants      
  (2CMC SDS or 0.2 benzalkouim chloride)   
  3)Decantation æ Sediment    4)Comminution and
  redispersion    5)Centrifugation at 5000rpm for
  10 min æ Sediment    6)Filtration   
  7)Oxidation at 760ªc    8)Purified nanotubes

• Purification process of SWNTs synthesized by
  arc-discharge    1)As-prepared carbonaceous
  Sample    2)Oxidation     3)Dilute HNO3
  reflux    4)Filtration    5)Oxidation    
  6)Ultrasonic dispersion in surfactants      
  (2CMC SDS or 0.2 benzalkouim chloride)   
  7)Centrifugation at 5000rpm for 10 min æ
  Sediment    8)Oxidation     9)Purified
  nanotubes

http//www.iljinnanotech.co.kr/en/home.html
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• Purification of SWNTs using electrophoresis   
  1)As-prepared carbonaceous Sample   
  2)Ultrasonic dispersion in detergent (1 aquet) 
    3)Electrical adsorption on the selected
  electrode       using electrophoresis (Ti,
  coated glass, ITO-glass)    4)Repeat above steps

• Manufacturing of field emitting device using
  SWNTs based  on the electrophoresis   
  1)Purified SWNTs    2)HNO3 reflux for 16 hours 
    3)Ultrasonic dispersion for 2 hours   
  4)Filtration    5)Ultrasonic dispersion in
  surfactants       (2CMC SDS or 0.2 benzalkouim
  chloride)    6)Suspension solution   
  7)Electrical adsorption on the selected electrode
        using electrophoresis (Ti, coated glass,
  ITO-glass)

• Size control of SWNTs produced by arc
  discharge    1)Purified SWNTs    2)Aqua regia
  reflus for 16 hours    3)Ultrasonic dispersion
  for 2 hours    4)Filtration    5)Ultrasonic
  dispersion in surfactants      (2CMC SDS or 0.2
  benzalkouim chloride)    6)Suspension solution

http//www.iljinnanotech.co.kr/en/home.html
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Carbon Nanotubes - A Time Line
(http//www.pa.msu.edu/cmp/csc/nttimeline.htm)
1991    Discovery of multi-wall carbon nanotubes
 "Helical microtubules of graphitic carbon", S.
Iijima, Nature 354, 56 (1991) 1992
   Conductivity of carbon nanotubes  "Are
fullerene tubules metallic?", J. W. Mintmire, B.
I. Dunlap and C. T. White, Phys. Rev. Lett. 68,
631 (1992)"New one-dimensional conductors -
graphitic microtubules", N. Hamada, S. Sawada and
A. Oshiyama, Phys. Rev. Lett. 68, 1579
(1992)"Electronic structure of graphene tubules
based on C60", R. Saito, M. Fujita, G.
Dresselhaus and M. S. Dresselhaus, Phys. Rev. B
46, 1804 (1992) 1993    Structural rigidity of
carbon nanotubes  "Structural Rigidity and Low
Frequency Vibrational Modes of Long Carbon
Tubules", G. Overney, W. Zhong, and D. Tománek,
Z. Phys. D 27, 93 (1993) 1993    Synthesis of
single-wall nanotubes  "Single-shell carbon
nanotubes of 1-nm diameter", S Iijima and T
Ichihashi Nature, 363, 603 (1993)"Cobalt-catalyse
d growth of carbon nanotubes with
single-atomic-layer walls", D S Bethune, C H
Kiang, M S DeVries, G Gorman, R Savoy and R
Beyers, Nature, 363, 605 (1993) 1995
   Nanotubes as field emitters  "Unraveling
Nanotubes Field Emission from an Atomic Wire",
A.G. Rinzler, J.H. Hafner, P. Nikolaev, L. Lou,
S.G. Kim, D. Tománek, P. Nordlander, D.T.
Colbert, and R.E. Smalley, Science 269, 1550
(1995).
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1996    Ropes of single-wall nanotubes
 "Crystalline ropes of metallic carbon
nanotubes", Andreas Thess, Roland Lee, Pavel
Nikolaev, Hongjie Dai, Pierre Petit, Jerome
Robert, Chunhui Xu, Young Hee Lee, Seong Gon Kim,
Daniel T. Colbert, Gustavo Scuseria, David
Tománek, John E. Fischer, and Richard E. Smalley,
Science 273, 483 (1996). 1997    Quantum
conductance of carbon nanotubes  "Individual
single-wall carbon nanotubes as quantum wires",
SJ Tans, M H Devoret, H Dai, A Thess, R E
Smalley, L J Geerligs and C Dekker, Nature, 386,
474 (1997). 1997    Hydrogen storage in
nanotubes  "Storage of hydrogen in single-walled
carbon nanotubes", A C Dillon, K M Jones, T A
Bekkendahl, C H Kiang, D S Bethune and M J Heben,
Nature, 386, 377 (1997). 1998    Chemical
Vapor Deposition synthesis of aligned nanotube
films  "Synthesis of large arrays of
well-aligned carbon nanotubes on glass", Z F Ren
et al., Science, 282, 1105 (1998). 1998
   Synthesis of nanotube peapods  "Encapsulated
C60 in carbon nanotubes", B.W. Smith, M.
Monthioux, and D.E. Luzzi, Nature 396, 323
(1998). 2000    Thermal conductivity of
nanotubes  "Unusually High Thermal Conductivity
of Carbon Nanotubes", Savas Berber, Young-Kyun
Kwon, and David Tománek, Phys. Rev. Lett. 84,
4613 (2000).
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2000    Macroscopically aligned nanotubes
 "Macroscopic Fibers and Ribbons of Oriented
Carbon Nanotubes" , Brigitte Vigolo, Alain
Pénicaud, Claude Coulon, Cédric Sauder, René
Pailler, Catherine Journet, Patrick Bernier, and
Philippe Poulin, Science 290, 1331 (2000).
2001    Integration of carbon nanotubes for
logic circuits  "Engineering Carbon Nanotubes
and Nanotube Circuits Using Electrical
Breakdown", P.C. Collins, M.S. Arnold, and P.
Avouris, Science 292, 706 (2001). 2001
   Intrinsic superconductivity of carbon
nanotubes  M. Kociak, A. Yu. Kasumov, S. Guéron,
B. Reulet, I. I. Khodos, Yu. B. Gorbatov, V. T.
Volkov, L. Vaccarini, and H. Bouchiat , Phys.
Rev. Lett. 86, 2416 (2001).
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Nanohorns Single-walled carbon cones with
morphologies similar to those of nanotube caps
were first prepared by Peter Harris, Edman Tsang
and colleagues in 1994 (they were not discovered
by NEC scientists, as stated in a recent press
release). They were produced by high temperature
heat treatments of fullerene soot - click here to
see a typical image. Sumio Iijima's group
subsequently showed that they could also be
produced by laser ablation of graphite, and gave
them the name "nanohorns". This group has
demonstrated that nanohorns have remarkable
adsorptive and catalytic properties, and that
they can be used as components of a new
generation of fuel cells. For details see the NEC
press release and this news item from CNN.
http//www.rdg.ac.uk/scsharip/tubes.htm
August 30, 2001 NEC uses Carbon Nanotubes to
Develop a Tiny Fuel Cell for Mobile Applications
The developed tiny fuel cell, classified as a
polymer electrolyte fuel cell (PEFC), utilizes
the carbon nanohorns as electrodes for catalyst
support. It is observed that very fine platinum
catalyst particles are dispersed on the surfaces
of the carbon nanohorns. The size of the platinum
particle is less than half of that supported on
the ordinary activated carbon (acetylene black)
by the same method. The size of the catalyst
particle is one of the most important factors
that determine the performance of the fuel cell,
and it is considered that, the finer the size the
better performance.
http//www.nec.co.jp/press/en/0108/3001.html
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Nano-test-tubes Among the highlights of nanotube
research to date is the demonstration that tubes
can be opened and filled with a variety of
materials including biological molecules. For
more details see the website of Oxford's Carbon
and Nanotechnology Group
A High Resolution Transition Electron Micrograph
of Small Ruthenium Metal Crystals Inside
Single-Walled Carbon Nanotubes.
A High Resolution Transition Electron Micrograph
of Samarium Oxide Inside a Multi-Walled Carbon
Nanotube.  
http//www.chem.ox.ac.uk/icl/catcentre/nanogrp.htm
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(a) HRTEM image of a 2x2 KI crystal in a 1.4nm
diameter SWNT (b) structural representation of
(a) (inset end-on view) Reconstructed image of
a 3x3 KI crystal in a 1.6nm SWNT (d) Structural
representation of (c) (inset end-on view).
Recently, we showed that 2x2 and 3x3 atomic layer
thick KI crystals can be formed in SWNTs as a
function of their diameter. These crystals
frequently have reduced co-ordination (e.g. the K
and I atoms in the 2x2 crystal are 44
coordinated) and exhibit lattice distortions
compared to the bulk halide. An enhanced HRTEM
image-restoration technique developed by Angus
Kirkland and Owen Saxton at Cambridge University
makes possible an atom-by-atom reconstruction of
these crystals, the first time that
crystallography has been attempted on such a
scale.
http//www.chem.ox.ac.uk/researchguide/jsloan.html
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Hydrogen Storage in carbon Nanotubes
The ability to produce high-capacity hydrogen
storage systems has been a long sought after goal
for a number of industries, particularly the
space and automobile sectors. Such organisations
are interested in using hydrogen-powered fuel
cells to propel fuel efficient and
environmentally friendly vehicles. Current
technology for hydrogen storage methods involve
compressing the gas in high-pressure cylinders or
the conversion of metals to metal-hydrides, but
at the present these procedures are to bulky or
too heavy for practical transport
applications. Carbon nanotubes may offer a
potential solution to this problem as it has been
suggested pores of molecular dimensions can
adsorb large quantities of gasses owing to the
enhanced density of the adsorbed material inside
the pores, a consequence of the attractive
potential of the pore walls. http//www.chem.ox.a
c.uk/icl/catcentre/HStorage.htm
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Chemical modification of single-walled carbon
nanotubes (SWNTs).
3D image of gold colloids covalently attached to
the walls of a single-walled carbon nanotube. The
diameter of the tube is approximately 1.3 nm
http//www.chem.ox.ac.uk/researchguide/kscoleman.h
tml
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Carbon Nanotube Bioelectrochemical
TransducersCarbon nanotubes (buckytubes)
exhibit unique mechanical, structural and
electrical properties. Their size and tuneable
electronic properties render them attractive
candidates for use as the wiring components in
nanoscale circuitry. We, with Malcolm Green,
Jeremy Sloan and Karl Coleman, have been able to
controllably modify single-walled nanotubes with
Quantum Dots, metalloproteins and enzymes. The
electrochemical communication between immobilized
molecules, nanotube and external circuit are
being analysed.
http//www.chem.ox.ac.uk/researchguide/jjdavis.htm
l
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A compendium of the currently accepted physical
properties of Carbon Nanotubes. This page is
intended for a general audience, nanotube
researchers, and the interested public. Compiled
by Thomas A. Adams II as a part of the honors
chemistry research project
Jump To Introduction Quick Facts
Equilibrium Structure Optical Properties
Electrical Transport Thermal Transport
Elastic Behavior References Glossary
Other Projects Contact
http//www.pa.msu.edu/cmp/csc/ntproperties/
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Nanotubes form different types, which can be
described by the chiral vector (n, m), where n
and m are integers of the vector equation R na1
ma2 .                                         
             The chiral vector is determined by
the diagram at the left. Imagine that the
nanotube is unraveled into a planar sheet. Draw
two lines (the blue lines) along the tube axis
where the separation takes place. In other words,
if you cut along the two blue lines and then
match their ends together in a cylinder, you get
the nanotube that you started with. Now, find any
point on one of the blue lines that intersects
one of the carbon atoms (point A). Next, draw the
Armchair line (the thin yellow line), which
travels across each hexagon, separating them into
two equal halves. Now that you have the armchair
line drawn, find a point along the other tube
axis that intersects a carbon atom nearest to the
Armchair line (point B). Now connect A and B with
our chiral vector, R (red arrow). The wrapping
angle    (not shown) is formed between R and
the Armchair line. If R lies along the Armchair
line (   0), then it is called an "Armchair"
nanotube. If   30, then the tube is of the
"zigzag" type. Otherwise, if 0lt   lt30 then it
is a "chiral" tube. The vector a1 lies along the
"zigzag" line. The other vector a2 has a
different magnitude than a1, but its direction is
a reflection of a1 over the Armchair line. When
added together, they equal the chiral vector R.
Adapted from 23
http//www.pa.msu.edu/cmp/csc/ntproperties/
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Ballistic Conductance In 1998, Stephan Frank et
al. experimented on the conductance of nanotubes.
5 Using a SPM, he carefully contacted nanotube
fibers with a mercury surface. His results
revealed that the nanotube behaved as a ballistic
conductor
with quantum behavior. The MWNT conductance
jumped by increments of 1 G0 as additional
nanotubes were touched to the mercury surface.
The value of G0 was found to be 1/12.9 k -1,
where G0 2e2/h . The coefficent of the
conductance quantum was found to have some
suprising integer and non-integer values, such as
0.5 G0. Later, in 1999, Sanvito, Kwon, Tománek,
and Lambert, 4 used a scattering technique to
calculate the ballistic quantum conductance of
MWTNs. They found that their results explained
these unexpected conductance values found by
Frank in 1998. Sanvito et al. stated that some of
the quantum conductance channels were blocked by
interwall reactions. Also, the interwall
reactions of MWNTs were found to redistribute the
current over individual tubes across the
structure nonuniformly.
http//www.pa.msu.edu/cmp/csc/ntproperties/
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Resistivity and Maximum Current
Density Relatively early in the research of
nanotubes, Thess et al. calculated the
resistivity of ropes of metallic SWNTs to be in
the order of 10-4 -cm at 300 K. 2 They did
this by measuring the resistivity directly with a
four-point technique. One of their values they
measured was 0.34 x 10-4, which they noted would
indicate that the ropes were the most highly
conductive carbon fibers known, even factoring in
their error in measurement. In the same study his
measurements of the conductivity, Frank et al.
5 was able to have reach a current denisty in
the tube greater than 107 A/cm2. Later, Phaedon
Avouris 12 suggested that stable current
densities of nanotubes could be pushed as high as
1013 A/cm2.
http//www.pa.msu.edu/cmp/csc/ntproperties/
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The study by Wilder et al. showed that nanotubes
of type n-m3l, where l is zero or any positive
integer, were metallic and therefore conducting.
The fundamental gap (HOMO-LUMO) would therefore
be 0.0 eV. All other nanotubes, they showed,
behaved as a semi-conductor. The fundamental
gap, they showed, was a function of diameter,
where the gap was in the order of about 0.5 eV.
Their data showed that the energy gap reflected
the graph at right (adapted from 23. This graph
can be modelled by the function
Egap2 y0 acc / d Where y0 is the C-C tight
bonding overlap energy (2.7 0.1 eV), acc is the
nearest neighbor C-C distance (0.142 nm), and d
is the diameter. This shows that the fundamental
gap ranged from around 0.4 eV - 0.7 eV, which
they said was in good agreement with the values
obtained from one-dimentional dispersement
relations. They concluded that the fundamental
gap of semi-conducting nanotubes was determined
by small variations of the diameter and bonding
angle (determined by the twist, see Equilibrium
Structure for more information.)
http//www.pa.msu.edu/cmp/csc/ntproperties/
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Also that year, Che, Cagin, and Goddard 6
numerically calculated the thermal conductivity
of a (10, 10) nanotube to approach 2980 W/m-K as
the current applied to it is increased (see
figure at right.) In 2000, Berber, Kwon, and
Tomànek 16 determined the thermal conductivity
of carbon nanotubes and its dependence on
temperature. They confirmed the suggestion of
Hone et al. in 1999 by suggesting an unusually
high value of 6,600 W/m-k for the thermal
conductivity at room temperature. They theorized
that these high values would be due to the large
phonon mean free paths, which would concur with
Hone's model suggested above. Both groups stated
that these values for thermal conductivity are
comparable to diamond or a layer of graphite.
http//www.pa.msu.edu/cmp/csc/ntproperties/