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Carbon nanotubes have been subject to a great many theoretical and experimental investigations and have many interesting properties. However, the caps found at the ends of nanotubes have been rather neglected. Previous work has established the possible caps for a given nanotube. This thesis seeks to build on this work to determine which caps are probable. Three representative nanotubes are considered: the (5,5) tube (an example of a metal); the (10,0) tube (an example of an insulator) and the (11,2) tube (for which experimental data is available). A linear scaling density matrix method based on orthogonal tight-binding theory is used for a systematic study of doubly capped nanotubes. The energetically most stable caps are found for all three tubes and the isolated pentagon rule established for fullerenes is shown to be valid for nanotube caps. No simple rule governing the stability of isolated pentagon caps is found, although the stability of (11,2) caps correlates well with the number of hexagons adjacent to just one pentagon. The local densities of states (LDOS) are calculated for the most stable cap for each nanotube. A localised state is found for the capped (5,5) tube and a resonant state is observed for the capped (11,2) tube. The LDOS for the capped (11,2) tube is compared with experimental observations and questions are raised concerning the nature of the tube observed and the limitations of STM as a method for identifying nanotube caps.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 225-238). Also available via World Wide Web.

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references.

Endohedral fullerenes are closed carbon shells encapsulating molecular or ionic species in their inner space. Obtained for the first time in 1985, endohedral metallofullerenes (EMFs) remain in focus of research for many years with a broad variety of metal atoms, endohedral cluster and cage sizes being reported. Electrochemical studies of endohedral metallofullerenes are of particular interest because of the more complex redox behavior in comparison to empty fullerenes. The EMF molecules can be considered as a combinations of positively charged cluster and negatively charged carbon shell “ligand”, and both constituents can be redox active. A cage-based electrochemical activity is more common, in particular, the most abundant nitride clusterfullerenes generally have redox-active cages. Cluster-based electrochemical activity is less common and can be revealed via unexpected redox behavior (e.g., shifted potential when compared to analogous molecules, potential metal dependence) and with the use of spectroscopic methods. Here we report electrochemical and EPR studies of three EMF families: (i) M2@C82-C3v and M2@C82-Cs dimetallofullerenes with a covalent bonding between two metal atoms, (ii) M2@C80(CH2Ph) dimetallofullerene derivatives with single-occupied metal-bonding orbital, and (iii) M2TiC@C80 EMFs with endohedral Ti(IV) (M is either Sc or Y or a lanthanide). For the first two families, the metal-metal bonding orbital has been found to be redox active: in M2@C82, the double-occupied M-M bonding orbital is involved in the first oxidation process, while in M2@C80(CH2Ph) the unoccupied component of single-occupied metal-bonding orbital acts as the LUMO, accepting one electron during the first reduction step. Thus, single electron transfer reactions in both cases lead to the changes in the magnetic properties of EMFs, which is especially well revealed by EPR spectroscopy. For the series of M2TiC@C80 EMFs, the first reduction predominantly occurs on internal Ti atom and can be described as TiIV/TiIII redox process. Due to the variation of the size of the Ti ion in different oxidation states, reduction changes the inner strain of the cluster, leading to a large variability of the TiIV/TiIII reduction potential in dependence on the size of the formally inert lanthanide metal in M2TiC@C80.

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Yung, Man Fai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references. / Yung, Man Fai. / Acknowledgements --- p.iii / Abstract --- p.iv / Preface --- p.vi / Contents --- p.vii / List of Figures --- p.x / List of Tables --- p.xii / Chapter Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Physical Origin of Optical Nonlinearity --- p.3 / Chapter 1.1.1 --- Mathematical Description --- p.3 / Chapter 1.1.2 --- Anharmonic Oscillator Model --- p.4 / Chapter 1.2 --- Nonlinear Optical Susceptibility --- p.4 / Chapter 1.2.1 --- Molecular Hyperpolarizability --- p.4 / Chapter 1.2.2 --- Macroscopic Nonlinear Susceptibility --- p.5 / Chapter 1.2.3 --- Kleinman Conjecture --- p.6 / Chapter 1.3 --- Third-Order Nonlinear Optical Process --- p.7 / Chapter 1.3.1 --- Intensity Dependent Refractive Index --- p.7 / Chapter 1.3.2 --- Physical Mechanisms --- p.8 / Chapter 1.3.3 --- Tensor Nature of Third-Order Susceptibility x(3) --- p.10 / Chapter 1.3.4 --- Conventions for Nonlinear Susceptibility --- p.11 / References --- p.12 / Chapter Chapter 2. --- Optical Kerr Effect --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Theoretical Background --- p.14 / Chapter 2.2.1 --- Pump-Probe Technique --- p.14 / Chapter 2.2.2 --- Description of Induced Birefringence --- p.15 / Chapter 2.2.3 --- Signal Transmitted through OKE --- p.17 / Chapter 2.2.4 --- Resonant OKE --- p.18 / Chapter 2.2.5 --- Third-Order Autocorrelation --- p.19 / Chapter 2.3 --- Applications --- p.20 / References --- p.21 / Tables --- p.23 / Figure Captions --- p.24 / Chapter Chapter 3. --- Nonlinear Optical Properties of Fullerenes --- p.26 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Second Harmonic Generation --- p.27 / Chapter 3.3 --- Third-Order Effects --- p.28 / Chapter 3.4 --- Reverse Saturable Absorption and Optical Limiting --- p.29 / References --- p.32 / Figure Captions --- p.34 / Chapter Chapter 4. --- Excited State Enhancement --- p.38 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- Origin and Properties of Excited State Enhancement --- p.39 / Chapter 4.3 --- Experimental Demonstrations --- p.42 / References --- p.44 / Chapter Chapter 5. --- Experimental Setup --- p.46 / Chapter 5.1 --- Introduction --- p.46 / Chapter 5.2 --- Laser System --- p.46 / Chapter 5.3 --- Optical Layout --- p.48 / Chapter 5.4 --- Sample Preparation --- p.50 / Chapter 5.5 --- Detection System --- p.51 / Chapter 5.6 --- Third-Order Autocorrelation Measurement --- p.52 / Chapter 5.7 --- Optical Limiting Measurement --- p.53 / Chapter 5.8 --- Excited State Enhancement Measurement --- p.54 / References --- p.56 / Figure Captions --- p.57 / Chapter Chapter 6. --- Results and Discussion --- p.69 / Chapter 6.1 --- Introduction --- p.69 / Chapter 6.2 --- Results of Pure Liquids --- p.69 / Chapter 6.2.1 --- Carbon Disulfide (CS2) --- p.69 / Chapter 6.2.2 --- Toluene --- p.71 / Chapter 6.2.3 --- Nitrobenzene --- p.71 / Chapter 6.3 --- Third-Order Autocorrelation of CS2 --- p.74 / Chapter 6.4 --- Results of Fullerenes C60 and C70 --- p.75 / Chapter 6.5 --- Optical Limiting of C60 --- p.78 / Chapter 6.6 --- Excited State Enhancement of Fullerenes --- p.79 / References --- p.82 / Tables --- p.85 / Figure Captions --- p.90 / Chapter Chapter 7. --- Conclusion --- p.108

Thesis (Ph. D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. 3 MPEG files (not linked from research.pdf file). Title from title screen of research.pdf file viewed on (Feb. 27, 2007). Vita. Includes bibliographical references.

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