Chemically functionalized carbon nanotubes (see Figure) are shown to produce composites with improved uniformity and dispersion. At low nanotube loading, a significant enhancement of the mechanical properties can be obtained. Moreover, the polymer/nanotube composites show efficient load transfer between the fillers and the matrix.

Carbon nanotube (CNT) field emitters are now being evaluated for a wide range of vacuum electronic applications. However, problems including short lifetime at high current density, instability under high voltage, poor emission uniformity, and pixel-to-pixel inconsistency are still major obstacles for device applications. We developed an electrophoretic process to fabricate composite CNT films with controlled nanotube orientation and surface density, and enhanced adhesion. The cathodes have significantly enhanced macroscopic field emission current density and long-term stability under high operating voltages. The application of this CNT electron source for high-resolution x-ray imaging is demonstrated.

Currently a significant amount of research activity is directed towards synthesis of 1D nanostructures including carbon nanotubes (CNTs) and inorganic nanorods.[1] Several general approaches such as the vapor±liquid±solid transformation process [2] have been developed that are very successful in stabilizing a large number of materials with considerable control in uniformity. The unique geometry and novel properties of the nanotubes and nanorods make them attractive building blocks for new functional materials and devices. Recent experiments have demonstrated their potentials as high-resolution microscopy probes, [3,4] conducting fibers, [5±7] and high performance composite fillers. [8,9] Although considerable progress has been made in the synthesis of nanostructured materials, development in this field in general is hindered by the lack of bottom±up manufacturing processes that can efficiently assemble functional structures and devices using these nanostructured building blocks.Here we report a dielectrophoresis [10] method to manipulate, align, and assemble 1D nanostructures using alternating current (AC) electric field. Pre-formed CNTs dispersed in water are assembled into micro-electrodes and sub-micrometer diameter fibrils with variable lengths from~1 lm to over 1 cm. The CNTs within the fibril are bonded by van der Waals forces and are aligned along the fibril axis. The method affords fine control of the fibril length and is capable of parallel fabrication of many fibrils using the same source. The short fibrils can potentially be used as the probes for scanning probe microscopes (SPMs) and the long fibrils as electrodes and conducting wires. Scanning electron microscope (SEM) images of a singlewall carbon nanotube (SWNT) fibril drawn from the suspension are shown in Figure 1. The fibril is about 100 lm in length and 0.2 lm in diameter. One end of the fibril is anchored to the apex of the W tip. Close examination showed that at the interface individual SWNT bundles adhered on the surface of the W tip and coagulated into a thin fibril comprising of only a few SWNT bundles in the radial direction (Fig. 1b). The surface of the fibril is smooth and the diameter is uniform throughout. Since the SWNT bundles used arẽ 2 lm in length and 30±50 nm in diameter, the morphology indicates that the SWNT bundles are aligned along the longitudinal axes of the fibril and in the direction of the electrical field. The very end of the fibril comprises only a single SWNT bundle as shown by the SEM image in Figure 1d. Except at a few points over the entire length, the fibril surface is remarkably free of nanoparticles, amorphous carbons, and other impurities that are ubiquitously present even in the purified SWNTs.The diameter of the fibril depends on several parameters such as the drawing rate, the electrical field gradient, the sharpness of the W tip, and the concentration of the suspension. The length of the fibril is controlled by the distance the W tip travels. Turning off the field or withdrawal of the tip at a rate faste...