lecture 6 oms

Lecture VI.

Carbon-based nanostructures and Superconductors Buckyballs, Nanotubes, Graphene

Organic Superconductors

Nanocarbon

C60, CNT’s

Synthesis and e-beam lithography

Graphene (synthesis, relativistic

QM nature, transport)

Aligned Carbon Nanotubes

AAO template CNT array in AAO

CVD @ CAER, Dr. Rodney Andrews Group

TEM of smallest MWNT

AA4 CNT- MWNT with a 2 nm inner diameter

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.

A carbon nanotube is a honeycomb lattice rolled

up into a cylinder. Although carbon nanotube 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.

Figure 1 Two unit vectors

a1

a2

a1

a2

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.

Figure 2 Schematic diagram of carbon

nanotube of chirality (3, 3)

Graphene

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

Graphene Production Goes Industrial

Band Structure of Graphene

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.

• Magnetoconductance

Other Materials with (Possible) Dirac Fermions

Organic Superconductors

lecture 6 oms

Technology

chiral nanotube

graphene sheet

graphene production

band structure of graphene

difference of n

unit vectors a1 a2 a1

chiral index

aao cvd