Date of Award
Spring 2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Engineering and Applied Science
First Advisor
Cha, Judy
Abstract
Two-dimensional (2D) materials display various exotic structural and electronic phases, with layered transition metal dichalcogenides (TMDs) presenting multiple polymorphs featuring distinct physical and chemical properties. Intercalating alkali metal ions stands out as a highly effective method for inducing structural transformations and adjusting the optical and electrical characteristics of 2D group VI TMDs. The resulting novel metastable phases hold transformative potentials for applications in electronic memories, transport devices, hydrogen gas evolution catalysts, and biological sensors. Despite numerous studies on alkali metal intercalation into 2D VI TMDs, a comprehensive understanding of the mechanistic and microscopic aspects of intercalation-induced phase changes remains elusive. This dissertation addresses fundamental materials questions on the intercalation-induced phase changes, such as the driving force and mechanism of phase transition, phase transition dynamics at the atomic level, and factors influencing phase transition pathways, with a particular focus on Mo- and W-ditellurides, relatively unexplored systems compared to their disulfide counterparts. Electrochemical lithium intercalation into 2H- and 1T′-MoTe2 flakes is investigated through in situ Raman spectroscopy, single-crystal X-ray diffraction, transmission electron microscopy, and transport measurements. The results underscore the potency of electrochemical intercalation in tuning phase stability and electron density in 2D TMDs, emphasizing the significance of phase transition pathways. Additionally, lithium-induced phase transitions in Td-WTe2 nanoflakes are probed on different substrates, highlighting the importance of heterogeneous transition pathways and interfacial engineering in modifying phase transitions. The dissertation's nanodevice approach, coupled with a multimodal in situ experimental approach, systematically explores the structure-property relationship and heterointerface effects during phase transitions of 2D TMDs induced by electrochemical intercalation. These findings carry significant implications for the development of memory devices, nanostructured metal-ion batteries, catalysts for chemical reactions, and various device applications harnessing the potential of 2D materials.
Recommended Citation
Xu, Shiyu, "In Situ Characterization of Electrochemically Intercalated Two-Dimensional Group vi Transition Metal Dichalcogenides" (2024). Yale Graduate School of Arts and Sciences Dissertations. 1353.
https://elischolar.library.yale.edu/gsas_dissertations/1353
