Carbon nanotubes - Department of Physics & Astronomy

```Carbon nanotubes
• John, Sarah, Doug
Carbon nanotubes
Main interest:
1. Prototypes for a onedimensional quantum wire.
2. Strength
Who found first nanotube?
1970: Morinobu Endo-- First carbon filaments of nanometer
dimensions, as part of his PhD studies at the University of
Orleans in France. He grew carbon fibers about 7 nm in
diameter using a vapor-growth technique. Filaments were not
recognized as nanotubes and were not studied.
1991:Sumio Iijima-- NEC Laboratory in Tsukuba-- used highresolution transmission electron microscopy to observe carbon
nanotubes.
Graphite
Hexagonal graphite:
I.
Graphite has a structure containing layers of atoms
arranged at the corners of contiguous hexagons.
II.
(not to be confused with hexagonal close packed).
III. The ease with which layers slide against each other is
consistent with the much larger distance between carbon
atoms in different layers (335 pm) than between carbon
atoms in the same layer (142 pm).
IV. The lattice constant a = 246.6 pm
V.
C=669 pm
Graphite
Graphite
What is tube rolled out of ?
An ideal nanotube can be thought of as a hexagonal network
of carbon atoms that has been rolled up to make a cylinder.
width: nanometer: "capped" with half of a fullerene
molecule.
length: microns
How to roll the nanotube ?
1. A carbon nanotube is
based on a twodimensional graphene
sheet.
2. The chiral vector is
defined on the
hexagonal lattice as
Ch = nâ1 + mâ2,
3. Chiral angle
4. Role/cap off
Different types of nanotubes
(n, 0) or (0, m) and
have a chiral angle of
0°, armchair
nanotubes have (n, n)
and a chiral angle of
30°, while chiral
nanotubes have
general (n, m) values
and a chiral angle of
between 0° and 30°.
What are the main properties?
1. Diameter of nanotube
2. Chiral angle
Both depend on n and m.
Diameter=length of chiral vector divided by 4
(has to do with the capping)
Interesting thought from paper.
Quote: “Since each unit cell of a nanotube contains a number of hexagons,
each of which contains two carbon atoms, the unit cell of a nanotube contains
many carbon atoms. If the unit cell of a nanotube is N times larger than that of
a hexagon, the unit cell of the nanotube in reciprocal space is 1/N times
smaller than that of a single hexagon. “
Let us break this down!
Interesting thought from paper.
Then in reciprocal space:
(pi/L) = (pi/a N) = (pi/a)(1/N)
For k space
Dispersion relation in nanotubes
5,5
9,0
10,0
Some thoughts:
E(kx, ky)
Then because we have a cylinder:
E(kxn , ky)
Where
Kxn = ((2*pi) /P) * n
n=1,2,3 …(1-D bands)
How to make nanotubes?
Rice University group (1996)-- produce bundles of ordered single-wall
nanotubes :
1.
Prepared by the laser vaporization of a carbon target in a furnace at 1200
°C.
2.
Cobalt-nickel catalyst helps the growth of the nanotubes, presumably
because it prevents the ends from being "capped" during synthesis.
3.
By using two laser pulses 50 ns apart, growth conditions can be maintained
over a larger volume and for a longer time. This scheme provides more
uniform vaporization and better control of the growth conditions.
4.
Flowing argon gas sweeps the nanotubes from the furnace to a water-cooled
copper collector just outside of the furnace.
Catherine Journet, Patrick Bernier and colleagues at the University of Montpellier in
France: carbon-arc method to grow arrays of single-wall nanotubes.
Look like ?
Scanning electron microscope: looks like a mat of carbon ropes
Ropes are between 10 and 20 nm across and 100 µm long.
Transmission electron microscope: each rope is found to consist
of a bundle of single-wall carbon nanotubes aligned along a
single direction.
X-ray diffraction, which views many ropes at once, shows that
the diameters of the single-wall nanotubes have a narrow
distribution with a strong peak.
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