Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering & Materials Science (ENAS)
First Advisor
Cha, Judy
Abstract
Two-Dimensional (2D) materials are atomically thin and encompass a wide range of material classes and functionalities. The reduced dimensionality yields unique optical, electronic, and magnetic properties in the mono- and few-layer limit, attractive for a variety of device applications. However, precise control of the electronic and magnetic properties of 2D materials is a persistent barrier to their incorporation into market optoelectronic technologies. For example, traditional doping methods, though well-optimized for bulk materials, can introduce negative steric effects into 2D materials and degrade device performance. In contrast, the tuning of 2D materials through surface functionalization is a promising alternative that is both powerful and nondestructive. Yet, understanding of the doping mechanism is largely limited to categorization of molecular dopants as n- or p-type based on the relative position of the HOMO or LUMO of the molecule in relation to the Fermi level of 2D host. Systematic studies to examine factors beyond redox potential for molecular doping are critically lacking. In this dissertation, 2D materials are synthesized and fabricated into monolayer and heterostructure nanodevices to systematically study factors which impact the doping efficiency of organic molecular dopants. We establish a methodology combining field-effect transistor measurements and spectroscopic characterizations to estimate the doping powers of the molecular dopants, with good agreement with calculations. Using this methodology, we determine that multiple factors beyond reduction potential influence molecular doping power such as the size and binding mode of the dopant molecule, as well as interactions between the molecules and 2D materials and among the molecules themselves. We achieve unprecedented doping of molybdenum disulfide (MoS2) via surface functionalization using molecules with small size and high surface coverage. Finally, we investigate the change in doping power for light-sensitive molecular dopants anchored to 2D substrates. These findings provide a versatile pathway to rigorously study the charge transfer dynamics between a wide variety of molecular dopants and 2D materials. Our goal is to inform the materials engineering community of sub-3nm transistor devices utilized in applications for optoelectronics, energy storage, and sensing technologies.
Recommended Citation
Reed-Lingenfelter, Serrae, "Electronic Property Tuning and External Stimuli Control of Two-Dimensional Materials via Surface Functionalization" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1097.
https://elischolar.library.yale.edu/gsas_dissertations/1097
