Super-aligned carbon nanotubes — From growth mechanism to loudspeakers

Super-aligned carbon nanotube (CNT) arrays are distinguished from normal vertically-aligned CNT arrays by their “super-aligned” nature, i.e., the CNTs in super-aligned arrays have a much better alignment than those in ordinary arrays. The key feature of a super-aligned CNT array is that continuous yarns or thin films, which are composed of a thin layer of parallelly-aligned pure CNTs, can be directly drawn from it in solid state. The as-produced yarns or thin films are transparent and highly conductive, with aligned CNTs parallel to the draw direction. Many potential applications for these have been demonstrated, for example as polarizers, transparent conducting films, and polarized light sources etc. After passing through volatile solutions or being twisted, the yarns or thin films can be further condensed into shrunk yarns. These shrunk yarns have high tensile strengths and Young's moduli, and are good candidates for thermionic and field emission electron sources. In this talk, I will present our progress in controlled synthesis, physical properties of super-aligned CNT arrays, and more applications such as high reduced brightness field emission electron source, low work function thermionic emission electron source, CNT-based Nanogrid for HRTEM, anodes for Lithium-ion Battery, incandescent displays will be demonstrated. At the end of 2007, we found that very thin carbon nanotube films, once fed by sound frequency electric currents, could emit loud sounds. This phenomenon could be attributed to a thermoacoustic effect. The ultra small heat capacity per unit area of carbon nanotube thin films leads to a wide frequency response range and a high sound pressure level. Based on this finding, we made practical carbon nanotube thin film loudspeakers, which possess the merits of nanometer thickness, transparent, flexible, stretchable, and magnet-free. Such a single element thin film loudspeaker can be tailored into any shape and size, freestanding or on any insulating surfaces, which could open up new applications of and approaches to manufacturing loudspeakers and other acoustic devices.