7. TEM of smallest MWNT
We have fabricated CNT
arrays in AAO template
with varying pore diameter.
Our observations indicate
that, CNT inner core
diameter decreases with
decreasing AAO pore
diameter, while the wall
thickness remains almost
the same.
AA4 CNT- MWNT with a 2 nm inner diameter
11. Obtaining Graphene
• Micromechanical cleavage from bulk graphite (on
oxidized Si)
• Thermal decomposition of 4-H SiC (Si terminated
surface) in UHV
• Vapor deposition from hydrocarbons (e.g. CVD from
xylene as is done for CNT’s)
• Pulsed Laser Deposition
• Exfoliation by Ultasonification of Graphite and Spin-
on Coating
• Plasma-enhanced Chemical Vapor Deposition
12.
13.
14.
15.
16.
17.
18.
19.
20. A carbon nanotube is a honeycomb lattice rolled
up into a cylinder. Although carbon nantoube seems to
have a 3D structure, it can be considered as 1D because of
their small size, which is in size of nano-order. The
specifying of carbon naonotube is very simple.
To define the structure, 2 numbers known as the
chiral index is used. In Fig. 1, 2 unit vectors, a1 and a2, are
defined on the hexagonal lattice. These 2 vectors define
the chiral vector Ch, and equation is shown below.
Ch= n a1+m a2≡ (n, m), (n, m are integers, 0≤|m|≤n)
(n, m) is called the chiral index, or it is just called
chirality. The example of (3, 3) is shown in Fig. 2.
This chirality is important because it tells the
characteristic of a carbon nanotube. For example, if the
difference of n and m is the multiple of 3, then that carbon
nanotube is metal. If not, it is semiconductor.
21.
22.
23.
24. The first two of these, known as “armchair” (top left)
and “zig-zag” (middle left) have a high degree of
symmetry. The terms "armchair" and "zig-zag" refer
to the arrangement of hexagons around the
circumference. The third class of tube, which in
practice is the most common, is known as chiral,
meaning that it can exist in two mirror-related forms.
An example of a chiral nanotube is shown at the
bottom left.
The structure of a nanotube can be specified by a
vector, (n,m), which defines how the graphene sheet
is rolled up. This can be understood with reference to
figure on the right. To produce a nanotube with the
indices (6,3), say, the sheet is rolled up so that the
atom labelled (0,0) is superimposed on the one
labelled (6,3). It can be seen from the figure that m =
0 for all zig-zag tubes, while n = m for all armchair
tubes.
25.
26. To calculate the band structure of
CNT’s, it is useful to discuss
graphene first.
We’ll then do a simple
modification to this calculation for
CNT’s.
46. Left: Diagram of the Brillouin zone of graphite. Center: Dirac fermions in
momentum space near corner H of the Brillouin zone are characterized by
a sharply linear Λ-shaped dispersion relation, similar to that found in
graphene. Right: As a result of interlayer interactions, other regions of
momentum space (near corner K) display a parabola-shaped dispersion,
signifying the existence of quasiparticles with finite mass whose energy is
quadratically dependent on momentum.
80. Left: Diagram of the Brillouin zone of graphite. Center: Dirac fermions in
momentum space near corner H of the Brillouin zone are characterized by
a sharply linear Λ-shaped dispersion relation, similar to that found in
graphene. Right: As a result of interlayer interactions, other regions of
momentum space (near corner K) display a parabola-shaped dispersion,
signifying the existence of quasiparticles with finite mass whose energy is
quadratically dependent on momentum.
100. Can Graphene be a Superconductor?
• Plasmon-mediated SC possible (Uchoa et al)
PRL 98 146801 (2007)
• Proximity effect supercurrents observed
(Heersche et al) Solid State Comm.143, 72
(2007)
• SC consistent with LAMH resistive transition
theory in Single-walled CNT (Zhao) PRB 71
113404 (2005)
