Theses and Dissertations

Date of Award

8-1-2024

Document Type

Thesis

Degree Name

Master of Science in Interdisciplinary Studies (MSIS)

Department

Physics

First Advisor

Nicholas Dimakis

Second Advisor

Efrain Ferrer

Third Advisor

M. Jasim Uddin

Abstract

In this study, we conducted a comprehensive investigation on computational simulations and analyses of heterostructures formed by two-dimensional (2D) molybdenum disulfide (MoS2) and graphene (Gr) on various metal coated substrates, including gold (Au), copper (Cu), nickel (Ni), and platinum (Pt). The frequency-dependent dielectric function (ɛ(ω)), refractive index (n), and reflectivity (R) are determined using light polarization parallel and perpendicular to the c axis of the 2D layers. Our findings reveal that MoS2/Au, MoS2/Cu, and MoS2/Pt heterostructures exhibit a direct bandgap at the K-point of the Brillouin zone, whereas their corresponding MoS2/MoS2/Metal structures present an indirect bandgap. The reduced interlayer spacing in MoS2/MoS2/Ni enhances electronic coupling between MoS2 layers and the Ni substrate, significantly altering the band structure through energy level shifts and band alignment changes. A Dirac point at the Fermi level is revealed by the band structure study of MoS2/Gr/Au and MoS2/Gr/Cu, suggesting that these heterostructures have only minor alterations brought about by interactions. By comparison, the MoS2/Gr/Pt and MoS2/Gr/Ni systems show a modest band gap of 0.15 eV and 0.16 eV, respectively, along with a slight displacement of the Dirac point toward the conduction band. The observed shift and the corresponding band gaps indicate a more robust connection between the metallic substrates (Ni and Pt) and graphene, which could potentially modify the heterostructures' electrical characteristics. Flat bands are observed on sulfur vacancies in MoS2/Au structures. The optical properties exhibit peaks in the infrared and visible regions, decreasing towards the ultraviolet region. Similar optical behavior is noted for the parallel components of the electric field in all three cases of sulfur vacancy on MoS2/Au. In the low energy range (0−5.5 eV), the dielectric function exhibits anisotropic behavior for both the real and imaginary parts for almost all the structures; in the upper range (> 5.5 eV), it exhibits isotropic behavior. In all configurations, there is a small electron transfer per atom from graphene to Au and MoS2, reinforcing graphene's p-type semiconductor characteristics in the heterostructures and heterointerfaces. Similarly, charge transfer from Metals to MoS2 confirms MoS2 as an n-type semiconductor. Among the configurations studied, MoS2/Gr/Pt exhibits the highest work function, correlating with the lowest electrical conductivity. Hence, this work intends to investigate the heterostructures' distinctive physical property features with wide-ranging applications in optoelectronics, integrated nano photonics, electro catalytic and photo-electrochemical energy generation.

Comments

Copyright 2024 Shishir Timilsena. https://proquest.com/docview/3116184141

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