Property and Phase Tuning in Two-Dimensional Materials by Surface Functionalization and Intercalation
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Reduced dimensionality and weak van der Waals interactions make two-dimensional (2D) materials highly responsive to chemical modification, providing an exceptional platform for controlling electronic behavior. This tunability creates opportunities to control carrier density, alter interfacial interactions, and access emergent structural and electronic states relevant to future electronic, sensing, and energy technologies. However, a deeper understanding is still needed of how chemical modification reshapes the relationship between a material’s structure and properties. This dissertation addresses that challenge through surface functionalization and electrochemical intercalation. First, surface functionalization of the transition metal dichalcogenide (TMD) MoS2 is used to examine how interfacial chemistry shapes charge transfer in 2D devices. Transport measurements show that electron doping cannot be explained by molecular reducing strength alone, while also introducing new photosensitive molecules for photo-induced functionalization of 2D materials. Second, electrochemical lithium intercalation is used to study phase transitions in the TMD MoTe2, where experimental studies are needed to clarify behavior that does not always follow theoretical predictions. Using in situ Raman spectroscopy and transport measurements, this work shows that phase evolution depends strongly on local structure, device geometry, and interfacial environment. Finally, electrochemical lithium intercalation of the layered rare-earth tritelluride LaTe3 is investigated using amultimodal in situ approach combining Raman spectroscopy, 4D scanning transmission electron microscopy, electron energy-loss spectroscopy, theoretical calculations, and electrochemical measurements. These experiments resolve multiple previously unknown and distinct structural and electronic regimes during lithiation. Together, these studies show how chemical modification can be used to tune existing properties and access new material states. By establishing structure-property relationships in molecularly functionalized and electrochemically intercalated layered systems, this dissertation provides new insight into the design of tunability of electronic platforms.