Use in Computer ICs
The structure of each nanotube determines its properties. In turn, its structure depends on the orientation and the number of the hexagons that form the tube:
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The first nanotube is made by coiling a graphene sheet about points A and B. In this case the vector between A and B is known as (4 × a1) + (4 × a2), or (4, 4). This is a typical (n, m) value for an armchair nanotube. [n.b. (n, m) values are the convention used to describe the structure of a nanotube.] |
The second nanotube is made by coiling a graphene sheet about points A and C. In this case the vector between A and C is known as (4 × a1) + (0 × a2), or (4, 0). This is a typical (n, m) value for a zigzag nanotube. [8,9,10,11] |
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The first nanotube, or “armchair” nanotube, conducts electricity like any metal, with a very low resistance. This is because the electronic wave functions (caused by the bonds between the carbon atoms), are lined up at right-angles to the flow of electrons, and do not interfere:
The second, or “zigzag” nanotube, acts as a semiconductor, as the wave functions interfere with the movement of electrons, making it difficult for a current to flow:
These two types of nanotube can be easily combined by introducing a ‘kink' into a nanotube [7,8]:
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To do this, a pentagon (5 sided), and a heptagon (7 sided), need to be introduced on opposite sides of the nanotube. Due to the angles between each bond, the whole molecule ‘twists'. In this example, the top armchair nanotube is a conductor and the bottom zigzag nanotube is a semiconductor. This conductor-semiconductor pair has the same effect as a rectifying diode, i.e. current can only flow in one direction. |
Using ‘Molymod' from the chemistry department, and knowledge I had gained from my research, I was able to construct some models of nanotubes:
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All the tubes are zigzag tubes (they are easier to make), and so all would in theory semi-conduct. The left hand tube has complete “bucky”-style ends, and is a (5, 0) tube. On the right hand side, the top tube (standing) is a (4, 0) tube, and the lowest tube (bottom) is a (3, 0) tube. The middle nanotube shows one hexagon highlighted (built with purple bonds). Notice each hexagon is end-to-end around the circumference. This confirms it is a zigzag nanotube.