Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Prof. Seong-Gon Kim

Committee Member

Seong-Gon Kim

Committee Member

Mark A. Novotny

Committee Member

R. Torsten Clay

Committee Member

Henk F. Arnoldus, Steven Gwaltney

Date of Degree

8-6-2021

Original embargo terms

Worldwide

Document Type

Dissertation - Open Access

Major

Physics

Degree Name

Doctor of Philosophy

College

College of Arts and Sciences

Department

Department of Physics and Astronomy

Abstract

The first-principles density functional theory (DFT) was implemented to investigate the structural, electronic and magnetic properties of vanadium (V) substituted and chalcogen (Se) vacancies in tungsten diselenide (WSe 2 ) monolayer, novel two dimensional (2D) monolayer (ML) structures in binary compounds ZnX (X= As, Sb, and Bi), and novel 2D electrides on transition metal-rich mono-oxide or chalcogenides, based on Perdew-Burke-Ernzerhof (PBE) exchange functional employed in Vienna Ab-Initio Simulation Packages (VASP). The inherent defect in 2D transition metal dichalcogenides (TMDCs) contains unavoidable substitutional defects and a certain amount of chalcogen vacancies. This type of defect affects the electronic and magnetic properties of 2D-TMDCs. To account for this fact, we demonstrated using DFT that the V-doped WSe 2 monolayer exhibits long-range ferromagnetic order. Further, the chalcogenide (Se) vacancies clustered around V-atom enhance the ferromagnetic properties of the system consistent with experimental findings. This dissertation explores the important role of Se-vacancies in the magnetic properties of the V-doped WSe 2 monolayer and proposes a method to enhance the magnetic properties of such 2D non-magnetic van der Waal (vdW) materials. In the second study, we have attempted theoretically to engineer the monolayer structure in II-V binary compounds ZnX with orthorhombic symmetry. We proved the dynamical stability of the bulk and ML structures manifested by the absence of imaginary frequencies in phonon dispersion curves. Our calculations on the density of states (DOS), and band structures using GGA indicate the increasing value of bandgap as well as the transition from indirect to direct bandgap while going from bulk to monolayer structure of ZnX. Our theoretical calculations will represent an archetype of novel 2D semiconductors on ZnX. Next, we have tailored using DFT, the structural and electronic properties of the 2D electrides that belong to transition metal-rich mono-oxide and chalcogenides with hexagonal (Hf 2 X; X = O, S, Se, Te), and orthorhombic (Ti2S and Zr2S) symmetry thereby introducing novel electrides to the electride family. The Bader charge analysis, electron localization function (ELF), projected DOS, and the calculated value of low work functions provides sufficient theoretical shreds of evidence to prove these materials as electrides.

Sponsorship

National Research Foundation of Korea

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