Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Physics

Date of Defense

10-28-2021

Graduate Advisor

Philip Fraundorf

Co-Advisor

Julia E. Medvedeva

Committee

Eric H. Majzoub

Deborah H. Santamore

Alexey Yamilov

Abstract

Elemental carbon has important structural diversity, ranging from nanotubes through graphite to diamond. Previous studies of micron-size core/rim carbon spheres extracted from primitive meteorites suggest they formed around such stars via the solidification of condensed carbon-vapor droplets, followed by gas-to-solid carbon coating to form the graphite rims. Similar core/rim particles result from the slow cooling of carbon vapor in the lab. The long-range carbon bond-order potential was used to computationally study liquid-like carbon in (1.8 g/πœπ¦πŸ‘) periodic boundary (tiled-cube supercell) and containerless (isolated cluster) settings. Relaxations via conjugate-gradient and simulatedannealing nucleation and growth simulations using molecular dynamics were done to study nucleation seed formation, structural coordination, and the latent heat of fusion. Atomistic results, which agree with independent DFT studies, show an energy preference for pentagon nucleation seeds, sp and sp2 coordination, and a bond defining gap in nearest neighbor histograms. Latent heat of fusion values of 𝟏. πŸŽπŸπŸ“ Β± 𝟎. πŸŽπŸ•πŸ– eV/atom (𝟏. πŸπŸ•πŸ– Β± 𝟎. πŸŽπŸ“πŸ‘ eV/atom at fixed pressure) were determined which agree with values previously determined by separate experimental and computational studies. Analytical models of nucleation and growth derived from classical nucleation theory links the onset of solidification to the interface/bulk energy ratio, predict cluster size distributions, and suggest a role for saturation during slow (e.g. stellar atmosphere) cooling. The low-pressure analytical model predictions for graphene sheet density and mass weighted average are supported by experimental observations of pre-solar and lab-grown specimens.

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