ORCID

0000-0002-4634-0946

Keywords

STM, MoS2, NiTe2, 2D, FDSS, Raman

Abstract

This research investigates the electronic, structural, and ferroic properties of two-dimensional (2D) materials, focusing on transition metal dichalcogenides (TMDs) and metal thio- and selenophosphates (MTPs). Using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), Raman spectroscopy, and photoluminescence spectroscopy (PL), this work explores how dimensional confinement, substrate interactions, and thickness-dependent effects influence material behavior. Advancements in STM probe fabrication for high-resolution molecular imaging are also presented, with implications for nanoelectronics and quantum materials.

The first study examines monolayer MoS2 on metallic substrates (gold and graphite). Raman spectroscopy revealed substrate-induced strain and charge transfer in MoS2 on Au. STM and STS on MoS2/graphite heterostructures primarily reflected the underlying graphite, highlighting challenges in probing specific layers and the impact of substrate interactions on electronic properties.

The second study focuses on NiTe2, a semimetal TMD. Low-temperature STM/STS revealed multiple electronic features near the Fermi level. Au-assisted exfoliation enabled imaging of thin NiTe2 on Au(111), which exhibited hexagonal, rectangular, and grain boundary patterns, likely resulting from the polycrystalline Au substrate. These observations emphasize the influence of substrate morphology on structural properties.

The third study investigates ferroelectric and strain-dependent behavior in MTPs CuInP2S6 (CIPS) and CuCrP2S6 (CCPS). Piezoresponse force microscopy and Raman spectroscopy revealed strain-modulated ferroelectric properties in CIPS and layer-dependent vibrational behavior in CCPS, offering insights into thickness-induced modifications in ferroic behavior.

The final study presents a field-directed sputter sharpening (FDSS) technique adapted for in-situ fabrication of ultra-sharp STM probes. A custom adapter enabled reliable production of probes with sub-2 nm radii, validated via atomic-scale imaging of C60 molecules. This advancement enhanced tip performance while minimizing contamination and downtime.

Together, these studies advance understanding of how reduced dimensionality, substrate interactions, and spatial confinement affect low-dimensional materials, with implications for future quantum and electronic applications.

Completion Date

2025

Semester

Spring

Committee Chair

Ishigami, Masahiro

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Physics

Identifier

DP0029344

Document Type

Dissertation/Thesis

Campus Location

Orlando (Main) Campus

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