Electronic structure and growth mechanism of carbon tubules

Abstract

A one-dimensional electronic band structure model for carbon tubules is summarized. The general structure of carbon tubules and fullerenes projected in a two-dimensional hexagonal lattice sheet with +12 defects representing the pentagonal faces. The possible caps which are fitted smoothly to a tubule can be generated by this projection method. Growth of the tubule can occur by absorbing C 2 clusters at such topological defects ( i.e. pentagonal faces) on generalized fullerenes. The tubule electronic structure is obtained from a simple tight-binding model for a single-layer carbon tubule. The model shows that approximately one-third of the tubules are metallic and two-thirds are semiconducting, depending on the tubule diameter and chirality. Metallic one-dimensional electronic energy bands are stable under a Peierls distortion. As the tubule diameter, d increases, the semiconductor energy gap decreases approximately as 1/d. The calculation of the electronic structure of two concentric tubules shows that pairs of concentric metal—semiconductor (orsemiconductor—metal) and metal—metal tubules are stable under the weak turbostratic interlayer interaction. Possible applications of concentric carbon tubules to semiconductor—metal devices are discussed.