Electrical Properties of Novel and Engineered Two-Dimensional Materials

Abstract

Layered materials are a class of matter in which atomic layers are bonded to one another via van der Waals (vdW) forces. Due to these weak, out-of-plane interactions, we can exfoliate layered materials even down to monolayer thicknesses. Confinement of electron interactions to two dimensions (2D) has led to the rise of new exciting physical properties which are largely inaccessible in three dimensions. Additionally, we can create new artificial interfaces which do not occur naturally, by creating hetero structures of the exfoliated materials. Therefore, assembling vdW materials with highly-tunable properties have been at the epicenter of innovative material and physics research over the past two decades. This dissertation reports on the methods for electrical and optical characterization of some of these novel two dimensional materials. Increasing the amount of electronic and ionic charge that can be rapidly accumulated in and recovered from a material is the preeminent chemical challenge for electrochemical energy storage devices like supercapacitors and batteries. In the first two parts of this thesis, I will reveal the role of the interface during intercalation processes by creating heterostructures with finite, discrete hetero-layers. Here, we demonstrate the electro-intercalation of lithium at the level of singular “vdW number of constituent layers,” comprised of deterministically stacked hexagonal boron nitride (hBN), graphene, and molybdenum dichalcogenide layers. Such engineered functional vdW heterostructures enable the direct resolution of intermediate stages in the intercalation of discrete heterointerfaces and the extent of charge transfer to individual layers. Also, we develop operando optical microscopy to investigate the dynamics of ion diffusion into thin graphite to estimate upper diffusion limits. Furthermore, developing new quantum materials has a crucial role in advancing quantum technology. Advances in crystal growth methods provide scientists opportunities to invent new layered materials with phenomenal electrical and optical properties. In the second part of this thesis, I will present electrical characterization of novel layered materials, such as metal organic frameworks (MOFs), a new allotrope of carbon—so called graphullrene, and CeSiI as new 2D heavy fermions candidates. I will present novel device fabrication techniques and electron transport characterizations based on these low-dimensional quantum materials. The results in this thesis provide new methodologies and offer novel approaches to manipulating the charge density in the 2D limit and to explore the electrical properties of quantum materials.