CNT Research: from Academic Wonder to Industrial Exploration

Carbon nanotubes (CNT) are nano-scale tubular structures which consist of seamless cylindrical shells of graphitic sheets. They were first found by professor Sumio Iijima in the arcdischarge soot between graphite electrodes in 1991 [1]. As a newly discovered carbon allotrope, CNTs have drawn worldwide attentions by their unique electrical, mechanical, and thermal properties. Seven years after their discovery, CNTs were synthesized in the form of arrays by chemical vapor deposition (CVD) [2,3]. For the first time in the history, billions of CNTs were aligned in the vertical direction on a substrate, and their growth position can be controlled by catalyst pattern design [3]. In 2002, we discovered a new type of CNT array, which is named the super-aligned CNT array. This kind of array was composed of clean, straight and defectfree CNTs, and there exist strong Van de Waals forces between adjacent nanotubes. Due to this unique feature, when one picks a strand of CNTs by tweezers or adhesive tapes, continuous long yarns or films can be simply pulled out from the array [4], as shown in figure 1. This discovery had enabled us to produce macroscopic materials with pure CNTs with a quick and easy dry spin process, as shown in figure 2. In 2005, we scaled up the substrate size of the CNT arrays from 1 inch to 4 inches, which could provide CNT films as wide as 10 cm [5]. Figure 1. The mechanism of dry spinning CNT yarns and films from super-aligned CNT arrays. The CNT yarns and films are composed of sparse parallel CNTs along the pulling direction. With the large percent of the vacancy between CNTs, the as drawn films can have transparency up to 90%. Therefore, CNT films can be used as a new type of transparent conductive film which have potential applications in liquid crystal displays and touch panels. The CNT films also have superb flexibility which is desired in flexible IT products. Figure 2. a) Spinning CNT film. b) A SEM image of the CNT film. c) A CNT film shrink into a fiber when passing through a drop of ethanol. d) A SEM image of the CNT fiber.