Dissertations, Theses, and Capstone Projects

Date of Degree

6-2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Chemistry

Advisor

Maria C. Tamargo

Committee Members

Christophe Testelin

Nicolas GIovambattista

Stepehen O'Brien

Subject Categories

Materials Chemistry

Keywords

Molecular beam Epitaxy, topological insulators, altermagnets, Curie temperature

Abstract

Accepting Dr. Feynman’s invitation to control matter at the atomic scale, this thesis presents work on materials grown via molecular beam epitaxy (MBE) where one can grow highly, ordered thin films with atomic-layer precision. This technique provides the user significant control over the growth parameters and subsequent properties observed. MBE grown MnSb2Te4 and MnTe materials systems were investigated for their unique physical properties, topological and altermagnetic properties, respectively, which are desirable in several expanding and developing fields, including quantum computing, spintronics, and magnonics. This dissertation had four aims: 1) defect engineering of quantum topological materials, in particular 3D topological insulators of the form V2VI3 (where V= Bi/Sb, VI= Se/Te) by doping with and incorporating large amounts of Mn using molecular beam epitaxy (MBE), 2) elucidating the band structure of the MnSb2Te4 using ARPES as a function of composition and magnetic transitions observed in this complex material system. This work sought to understand how the type and distribution of defects related to Mn incorporation foster the desired electrical and magnetic properties, and 3) investigation of MnTe altermagnet growth on unconventional substrates. This work observed how optimizing certain growth parameters: high Mn flux ratio and reduced growth rate significantly enhances Curie temperature (TC) in MnSb2Te4 up to 100K, the highest for this material system. This work sought to understand the mechanisms in the growth that promotes this property. Structural and electrical analysis revealed significant Mn incorporation and random distribution throughout the crystal under a high Mn flux ratio and slow growth rate regime birthed a new material system: (Sb2−yMnyTe3)1-x (Mn1+ySb2-yTe4)x. This work vii probed this new material system, demonstrating how significant disorder in the excess Mn distribution affected its magnetic properties and band structure. Finally optimized growths of thin film α-MnTe, an altermagnetic material that is receiving much attention currently was pursued. We tuned the MBE growth conditions to yield pure, single phase α-MnTe on InP(111)A, which was thoroughly verified by different structural analysis tools and continued to refine these parameters to grow on new interfaces and substrates.

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