| A single-walled carbon nanotube (SWCN) is a hollow cylinder of a single shell carbon atoms. The smallest SWCNs that can ever be manipulated are 4 angstroms in diameter, which are grown by pyrolysis of hydrocarbon molecules in one-dimensional channels of zeolite single crystals (Tang, 1998). These carbon nanotubes are mono-sized and parallel in alignment. They offer the opportunity to study the intrinsic anisotropic physical properties of 4 A SWCNs in the form of macroscopic samples.; The followed experimental results presented in the thesis are intimately connected with the successful fabrication of 0.4-nm SWCNs. In Chapter 3, I present the measurements of polarized optical absorption spectra. Three possible structures: (5, 0), (4, 2), and (3, 3) contribute to three bands at 1.37, 2.1, and 3.1 eV in optical absorption spectra. The direct correspondence between chiralities and absorption bands is identified by density functional calculations.; In Chapter 4, I develop a symmetry-adapted lattice-dynamical model for SWCNs, which can calculate the phonon dispersions efficiently for any nanotube chirality. The model is applicable, but not limited to 0.4-nm SWCNs. The programming codes are included in the Appendix. In Chapter 5, I show that features of the resonant Raman spectrum can be assigned to van Hove singularities in calculated phonon density of states. In the low-frequency region, two peaks at 510 and 550 cm -1 are attributed to the radial breathing modes of the (4, 2) and (5, 0) tubes. After removing the zeolite framework, the radial breathing mode frequencies downshift by ∼10 cm-1.; The electronic properties of 0.4-nm SWCNs can be modified by adding electrons one by one to their discrete electronic states through Li doping. In particular, the tube zeolite composite exhibits very high lithium affinity. The Li doped 0.4-nm SWCNs are candidates of high temperature superconductors in view of the superconductivity in pure 0.4-nm SWCNs below 15 K. In Chapter 6, I provide various experimental characterizations of Li doped 0.4-nm SWCNs. We demonstrate that up to 10 wt% of Li can be doped into the tube zeolite composites. We do observe the evidence of superconductivity at higher temperature.; Improvement of the quality of 4 A SWCNs is a fundamental subject of the research. By doping small amount of Si into the framework of aluminophosphate, higher quality 4 A nanotubes can be grown in the channels of the framework. Silicon doped aluminophosphate (SAPO-5) molecular sieves act as "shape-selective catalysts" in the grown process of 4 A SWCNs, which is confirmed by our infrared vibration spectra. The first-principles calculations also indicate that SAPO-5 provides more favorable environments for the nanotube growth. These endeavors are reported in Chapter 7.; Finally, I summarize the thesis and propose the future works in Chapter 8. |
