The optical properties of carbon nanotubes are highly relevant for materials science. The way those materials interact with electromagnetic radiation is unique in many respects, as evidenced by their peculiar absorptionphotoluminescence fluorescenceand Raman spectra.
Carbon nanotubes are unique "one-dimensional" materials, whose hollow fibers tubes have a unique and highly ordered atomic and electronic structure, and can be made in a wide range of dimension. The diameter typically varies from 0. However, the length can reach Applications of carbon nanotubes in optics and photonics are still less developed than in other fields.
Some properties that may lead to practical use include tuneability and wavelength selectivity. Potential Frågor och svar that have been demonstrated include light emitting diodes LEDs[3] bolometers [4] and optoelectronic memory. Apart from direct applications, the optical properties of carbon nanotubes can be very useful in their manufacture and application to other fields.
Spectroscopic methods offer the possibility of quick and non-destructive characterization of relatively large amounts of carbon nanotubes, yielding detailed measurements of non-tubular carbon content, tube type and chirality, structural defects, and many other properties that are relevant to those other applications.
A single-walled carbon nanotubes SWCNT can be envisioned as strip of a graphene molecule a single sheet of graphite rolled and joined into a seamless cylinder. The structure of the nanotube can be characterized by the width of this hypothetical strip that is, the circumference c or diameter d of the tube and the angle α of the strip relative to the main symmetry axes of the hexagonal graphene lattice.
This angle, which may vary from 0 to 30 degrees, is called the "chiral angle" of the tube. Alternatively, the structure can be described by two integer indices nm that describe the width and direction of that hypothetical strip as coordinates in a fundamental reference frame of the graphene lattice.
If the atoms around any 6-member ring of the graphene are numbered sequentially from 1 to 6, the two vectors u and v of that frame are the displacements from atom 1 to atoms 3 and 5, respectively. Those two vectors have the same length, and their directions are 60 degrees apart.
The chiral angle α is then the angle between u and w. All geometric properties of the tubesuch as diameter, chiral angle, and symmetries, can be computed from these indices. The type also determines the electronic structure of the tube. Specifically, the Frågor och svar behaves like a metal if m — n is a multiple of 3, and like a semiconductor otherwise.
These tubes have mirror symmetry, and can be viewed as stacks of simple closed paths "zigzag" and "armchair" paths, respectively. The optical properties of carbon nanotubes are largely determined by their unique electronic structure.
The rolling up of the graphene lattice affects that structure in ways that depend strongly on the geometric structure type nm. A characteristic feature of one-dimensional crystals is that their distribution of density of states DOS is not a continuous function of energy, but it descends gradually and then increases in a discontinuous spike.
These sharp peaks are called Van Hove singularities. In contrast, three-dimensional materials have continuous DOS.