Carbon nanotubes (CNTs) have attracted increasing scientific and technological interest due to their exceptional mechanical, electrical, and magnetic properties and numerous potential applications. These properties are largely controlled by the diameter of the tubes, the number of concentric layers, and the structural chirality. Features such as a high electrical conductivity at room temperature, a large aspect ratio with a whisker-like shape, and a unique resistivity compared to metals (for which the resistance varies reversibly with temperature), make CNTs one of the most suitable candidates for field emission. [1] Indeed, excellent field-emission properties, such as a high emission current density, a low emission threshold, and a long lifetime, have been experimentally demonstrated recently. [2] However, the realistic difficulties lie in the handling and processing of nanometersized CNTs, thus, hindering their practical applications in actual field-emission devices. Macroscopic CNT films have attracted a great deal of research effort and significant results have been achieved. Large-area and aligned CNT films suitable for field emission have been synthesized mainly by chemical vapor deposition (CVD) on different substrates. [3] Membrane filtration, [4,5] magnetic arrangement, [6] electrophoretic deposition, [7] and substrate coating methods [8] have also been investigated for the preparation of CNT films. Zhang et al. have reported a solid-state process via cooperatively rotating CNTs in vertically oriented nanotube forests, and they have obtained a meter-length transparent sheets with a width of 5 cm. [9] Very recently, Song et al. have di-rectly synthesized a macroscopic single-walled CNT (SWCNT) nonwoven material by a floating CVD technique in a two-stage furnace system. [10] Although the products are large in size, its inhomogeneous morphology and poor manipulability seriously limit their use in technological applications.We demonstrate a direct approach to the large-area synthesis of 2D SWCNT films, using a CVD method. A key factor of our CVD system is the introduction of a circular gas-flow stabilizer in the quartz reaction tube, which benefits the formation of an uniform and high-quality film on the stainless-steel film collector situated downstream of the reaction tube (diameter = 50 mm). This universal technique exhibits several advantages: 1) The SWCNT film production is extremely simple compared with other methods that include post-treatments. [4][5][6][7][8][9] 2) The thickness of the film can be controlled easily by altering the reaction time.3) The films deposited on the collector are technically free standing and, thus, can be easily manipulated. When dried after being subjected to a water or acetone spray, the SWCNT films become denser and can be easily handled by hand, rather like handling a sheet of thin paper. 4) This technique can be scaled up for the large-area and low-cost synthesis of SWCNT films.Optical images of the films with different thicknesses show a variation in transparency t...
