Optical Properties of Single-Wall Carbon Nanotubes

平均半径为0.55，0.65和1.0 nm的单壁纳米管的拉曼散射光谱表明，石墨中对应于E模的光学声子峰随纳米管尺寸的变化出现多次分裂<2g>.这些分裂构成了第一个实验证据的独特功能的纳米管，它们表现出离散和直径依赖的分散体所产生的圆柱对称性。在450 ~ 800 nm波长范围内测量了平均直径为1.1 nm的单壁纳米管中光学声子的共振拉曼散射。散射强度在690 nm附近表现出异常，在纵向分量中为最小值，在横向分量中为最大值。我们的光传输测量也表现出在相同的光子能量范围内的下降。这些反常现象是由入射激光束与纳米管中的区带折叠电子结构共振引起的。这些结果构成了由纳米管的圆柱对称性产生的统计密度临界点的直接实验证据。

Raman scattering spectra of single-wall nanotubes with mean radii 0.55,0.65 and 1.0 nm show size-dependent multiple splittings of the optical phonon peak corresponding to E_<2g> mode in graphite. These splittings constitute the first experimental evidence for the unique feature of nanotubes that they exhibit discrete and diameter-dependent dispersions arising from their cylindrical symmetry. The observed dispersion is well explained on the basis of graphite, and shows possibilities of predicting and controlling the basic property of nanotubes in the zone-folding scheme.Resonant Raman scattering from optical phonons in single-wall nanotubes of mean diamater 1.1 nm has been measured in the wavelength of incident laser beam between 450 nm and 800 nm. The scattering intensities exhibit anomalies in the vicinity of 690 nm, being a minimum in the longitudinal components and a maximum in the transverse. Our optical transmission measurement also exhibits a dip in the same photon energy range. The anomalies are caused by the incident laser beam resonant with the zone-folded electronic structures in nanotubes. These results constitute a direct experimental evidence of the critical point in the density of ststes produced by the cylindrical symmetry of nanotubes.