UC Merced

Low-dimensional materials have attracted significant attention in the field of materials science and technology. These materials, characterized by their limited dimensions in one, two or three directions, exhibit exceptional properties different from those of their bulk counterparts. This deviation results from the interaction of quantum effects, surface interactions, and unique electronic structures, creating a wide range of innovative applications in various fields such as electronics, photonics, energy storage and more. This study not only reveals the scientific complexities of their behavior but also paves the way for disruptive innovations that could transform industries and transform our interactions with the world around us. In this work, I have studied different classes of low-dimensional materials such as bulk and monolayer transition-metal dichalcogenides, one-dimensional organic-metal halide hybrids, organic metal halide nanoribbons, Bi$_2$Te$_3$ and HfTe$_5$.

In the opening chapter, I lay the groundwork by discussing fundamental theories crucial for our subsequent calculations. These theories encompass density functional theory, density functional perturbation theory, GW and Bethe-Salpeter equations and other fundamental concepts on Raman, and calculation methods for elastic tensors. Chapter 2 delves into a comprehensive analysis of the impact of introducing Ni into the bulk phases of MoS$_2$, with a particular focus on the mechanism supporting low wear for lubrication applications. This chapter also presents systematic doping studies conducted through first-principles calculations. Chapter 3 narrows the focus to examine the consequences of Ni doping on the monolayer phases of MoS$_2$, revealing the induction of various known and novel distorted phases. These induced phases bring forth unique properties, including those of ferroelectric materials, multiferroic semimetals, ferromagnetic polar metals, and the presence of multiple gaps in conduction bands. These findings have promising implications for applications in spintronics, intermediate band solar cells, and non-linear optics. In Chapter 4, the attention shifts to a low-energy nine-layer phase within transition-metal dichalcogenides, where we explore methods for characterizing this phase through Raman spectroscopy and powder diffraction. Additionally, we investigate its potential applications in piezoelectricity and valleytronics. Next Chapter 5 delves into understanding the anisotropic properties of one-dimensional organic-metal halide hybrids and the mechanism of broadband emission. This chapter introduces an innovative approach for determining exciton-phonon coupling and the self-trapped exciton structure using excited state forces within a GW/Bethe-Salpeter framework. Chapter 6 offers a concise overview of my contributions to other collaborative works on low-dimensional materials, encompassing organic-metal halide hybrids, organic metal halide nanoribbons, Bi$_2$Te$_3$ and HfTe$_5$. Finally, I conclude with reflections on the potential of low-dimensional materials, their current progress, and future prospects.