Research On The Chirality And Related Physical Properties Of Carbon Nanotubes

The chiral indices of a carbon nanotube fully determine its molecular structure, andtherefore have a strong link with many aspects of its physical properties. With thedeepening of research on carbon nanotubes, research on the chirality and relatedphysical properties of carbon nanotubes is drawing people’s attention. This paperdescribes our research on the synthesis and characterization of ultra-long carbonnanotubes, the unambiguous determination of chiral indices of carbon nanotubes, andthe measurement of physical properties of carbon nanotubes with known chiral indices.We first studied the synthesis of ultra-long carbon nanotubes by chemical vapordeposition. We tried both the “fast heating” and thermostatic processes and obtainedcarbon nanotubes with high density, high length, and high parallelism. Furthermore, byadjusting the proportion of carbon source during the growth, we realized the control ofthe density and length of ultra-long carbon nanotubes. We also tried to control thenumber of walls of ultra-long carbon nanotubes, by optimizing the proportion of carbonsource or changing the composition and the preparation methods of catalysts. We alsostudied the growth mechanism of ultra-long carbon nanotubes both experimentally andtheoretically.We discovered and developed a method to observe ultra-long carbon nanotubes byoptical microscope with the assist of water vapor condensation. When warm watervapor reaches the sample, it tends to condense along carbon nanotubes, since the nucleialong carbon nanotubes are denser than that on substrates. The micro droplets formedalong carbon nanotubes can be observed under an optical microscope, and stretched theoutlines of carbon nanotubes. We further extend this simple and efficient opticalimaging technique to other nanomaterials and nanostructures.We studied the methods to precisely determine the chiral indices of carbonnanotubes by transmission electron microscope. We first designed and fabricated aspecialized kind of silicon nitride micro-grids, which can be used as the substrates forcarbon nanotubes growth. These micro-grids greatly improved our efficiency ofpreparing and characterizing the samples. We optimized the process of obtaining thehigh-resolution images and electron diffraction patterns of carbon nanotubes, and compared several methods to obtain chiral indices of carbon nanotubes. Experimentsshowed that by the “intrinsic layer line spacing” method the chiral indices ofsingle-walled and double-walled carbon nanotubes can be obtained uniquely andunambiguously.On this basis, we tried to measure the electronic properties of carbon nanotubeswith known chiral indices. For ultra-long carbon nanotubes and lattice-guided carbonnanotubes, we designed and fabricated two specialized kinds of silicon nitridemicro-grids respectively. The determination of chiral indices and the measurement ofelectronic properties of one carbon nanotube were integrated on a micro-grid. Weoptimized the related techniques and obtained preliminary measurement results.