Physics and chemistry of advanced nanoscale materials : experiment, simulation, and theory

Citation

Kiang, Ching-Hwa (1995) Physics and chemistry of advanced nanoscale materials : experiment, simulation, and theory. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4t4q-5805. https://resolver.caltech.edu/CaltechETD:etd-10162007-105256

Abstract

This thesis discusses simulation and theory of lattice dynamics as well as experiments on novel forms of carbon.

A new crystalline AgBr interaction potential was constructed by fitting literature experimental data. The shell model was successfully used to account for the polarizabilities of the ions. This approach overcame difficulties previous investigators faced in determining the AgBr potential.

The very useful shell model was generalized to allow, for the first time, its use in dynamical simulations. The rapid shell dynamics, simulating the electron polarization, were integrated out in a generalized Born-Oppenheimer-like approach. The effective Hamiltonians were derived for both quantum and classical descriptions of the shells.

The first crystallization and characterization of a metallofullerene were performed. Endohedral metallofullerenes were synthesized and characterized. Metals such as Sc, Y, and Er that formed stable compounds in fullerene cages were synthesized and products purified. The crystal structure of Sc2C84 was determined by transmission electron microscopy study.

Experimental studies on fullerenes and related materials lead to the first example of a catalytically-grown, fullerene-like material. We discovered that single-layer carbon nanotubes can be produced by vaporizing cobalt and carbon with an electric arc in a helium atmosphere. Catalyst promoters such as sulfur, bismuth, and lead were found not only to enhance the yield of single-layer nanotubes but also to produce tubes in a diameter range not accessible with cobalt alone. Sulfur, bismuth, and tungsten were found to catalyze the formation of cobalt crystals encapsulated in graphitic polyhedra. Various carbon structures were also produced concurrently, e.g. multilayer nanotubes, strings of carbon nanocompartments, carbon nanofibers, and metal-filled nanomaterials. Nanotubes were observed to undergo real-time structural changes under electron beam heating.

A growth model of single-layer nanotube was formulated based on the experimental results. The carbon ring is regarded as the nanotube precursor, and cobalt carbide is regarded as the catalytic species that efficiently supplies carbon clusters to the open end of tube. The catalyst promoter assists the reaction by keeping the growing end open.

Thesis Files