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Unformatted text preview: 11-5-07 Carbon NanotubesStrength over density makes cnts more attractive.Because most engineering applications utilize rather large structures, ie building, bridge, space elevator, since we are dealing at the nano scale, that transition might not happen in the next few years, however focusing on the functional and electrical properties of CNTs, we are much closer to working devices and even commercial possibilities. In order for C60to close up, need pentagons for the closing up of the structures. Band Stucture: (diagrams on slide)oIn graphite- There is basically no band gap present except a funnel type structureonly a few electrons can go through without additional energy input.oBut CNTs arent graphite, they are made from graphite. If you look at a semimetal, if you take a few atoms away, it makes changes in the band gap structure.oIn CNTs, there are less atoms participating, because it is made from a layer of graphite. oThe smaller diameter of the CNT, there less atoms that are involvedthe more distant the valence and conduction band itgreater band gap.oElectronic properties are going to be either metallic or semi-conducting based on directionality and the diameter. Electrical propertiesoMetallicIf 2n +m =3q q is an integerN, m refer to diameter and folding directionMetallic when n=moSemiconductor in the other cases....
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- Fall '07