ORCID Identifier(s)

0000-0001-6003-1499

Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics and Applied Physics

Department

Physics

First Advisor

Muhammad N Huda

Second Advisor

Ali Koymen

Abstract

Silicon carbide (SiC) is a technologically significant material. A recent report on the abundance of C60 fullerenes in interstellar space, along with the presence of SiC precursors, sparked interest in potentially similar SiC nanostructures. C60 and C70 fullerenes were found experimentally and are an exceptionally stable form of carbon. As Si and C have similar valence electron configurations, it has been long envisioned that Si and SiC could also form similar fullerene-type structures. In this dissertation, Si30C30 fullerene-derived clusters were studied from the first principles theory, starting from an ideal Si60 fullerene template with various arrangements of silicon and carbon atoms and then relaxing them without any symmetry constraint. Hydrogen passivation was considered as well to model the effect of ligands that may be available during chemical synthesis processes. We have found that, after passivation, the relative stability order of different configurations of Si30C30 clusters (isomers) changed compared to the unpassivated structures, while some structures collapsed. We have also noticed several Si–Si and Si–C double bonds on the unpassivated structures. Endohedral doping of several transition metal atoms (Fe, Nb, Hf, Ta, and W) atoms in C60, C70, Si30C30 (sphere structure), and Si35C35 structures was then considered. The doping was found to increase binding energy compared to original structures without doping. On the other hand, Fe, Nb, Hf, Ta, and W atoms in the center of C60, C70, Si30C30 (sphere structure), and Si35C35 structures maintained a significant value of magnetic moments. With hydrogen passivation, the magnetic moment on W atom was enhanced. Moreover, rare-earth atoms (La, Ce, Pr, and Nd) have been studied as doping atoms in C60, C70, Si30C30 (sphere structure), and Si35C35 structures. They help to increase the stability of structures and decrease the diameter. Also, Pr and Nd doped atoms hold a high value of magnetic moments inside fullerenes. We present ab initio molecular dynamic (AIMD) simulation on endohedral doping structures in Si30C30 (sphere structure), and Si35C35 structures. Overall, the result shows the magnetic moment decreases on some of the transition metals (Nb, Hf, Ta, and w) and rare-earth (La and Ce) atoms as the temperature increases. On the other hand, the Fe, Pr, and Nd atoms maintain the value of magnetic moments at Si30C30 (sphere structure) while the temperature increases up to 300K. For Si35C35 structures, the Nd atom has showed a good value of magnetic moment up to 300K. The overall spherical nature was maintained for the SiC fullerenes as the temperature increases. Our study in the dissertation provides a fundamental understanding of the SiC fullerenes, their stabilities and magnetic moments at room temperature. The study will motivate their synthesis and applications in electronic and magnetic devices in near future.

Keywords

SiC fullerenes, Magnetic moments of fullerenes, Endohedrally doped fullerenes, Rare-earth doped fullerenes, Stability of silicon-carbide fullerenes

Disciplines

Physical Sciences and Mathematics | Physics

Comments

Degree granted by The University of Texas at Arlington

Included in

Physics Commons

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