Topological annealing of carbon nanostructures : a new structure evolution algorithm

Abstract

With this methodology, tangible gains in materials science are acquired. All-carbon voltage monitors are discovered, their fabrication analyzed, and ways to confirm these theoretical results empirically are discussed. Flaws are revealed in contemporary carbon logic gate designs, and more chemically feasible versions are demonstrated. Properties such as electrical transport and bond length are accurately predicted using topology alone, without the usually required calculations based on density functional theory or molecular dynamics. Synthesis pathways to exotic and undiscovered allotropes, such as Haeckelite, are proposed. The long-standing mystery of experimentally observed ratios of carbon nanotube chiralities is partially elucidated. These are a few of the practical impacts of the research presented in this thesis, displaying the great utility of the ATAC methodology, and its premise to enable material design and discovery.

In this thesis, the author provides a model for simulating the irradiation and annealing of carbon nanostructures, for understanding these transformations, and for predicting the resulting structures. A Metropolis Monte Carlo method is employed to replicate empirically observed defects in sp2 carbon under elevated energy conditions emerging from electronic irradiation. By using elementary defects as the fundamental units of transformation, it is possible to simulate processes with much longer time scales than allowed by traditional molecular dynamics. The algorithm developed to achieve these goals is known as the Accelerated Topological Annealing of Carbon, or ATAC.

In the course of coding the fundamental principles of ATAC, the author has investigated several avenues of scientific inquiry including parameterizations of graph theory, spintronics, energy barriers, and other interesting and applicable phenomena. With the algorithm itself, the configuration space of various combinations of welded carbon nanotubes, C60 molecules, and graphene sheets were probed, characterizing both the intermediate transformations and final configurations.