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Abstract
Low-dimensional quantum materials have generated substantial interest over the past several decades due to the prospect of implementing their unique electronic and optoelectronic properties within next-generation devices. Ensuring robust device performance requires a detailed understanding of these materials’ stabilities, particularly at elevated temperature operating conditions. In situ scanning transmission electron microscopy (STEM) provides the best method for comprehensively analyzing the thermal properties of low-dimensional quantum materials. In Chapter 1, a systematic overview describes the preparation and types of in situ STEM experiments best-suited for evaluating the morphological, structural, compositional, and chemical dynamic transformations at elevated temperatures for low-dimensional quantum materials. A variety of one-dimensional (1D) quantum morphology dynamics are also exhibited to illustrate the diversity of decomposition pathways within these materials. Chapter 2 focuses on exfoliated 1D TaSe3 nanoribbons through both low kV and aberration-corrected in situ STEM. The key findings demonstrate the high-temperature formation of a core-shell nanostructure consisting of loose, small grains of TaSe2 surrounding a central core of TaSe2 which eventually decomposes further into discrete Ta-intercalated TaSe2 particles. Chapter 3 describes the high temperature stability of 1D TaS3 nanoribbons evaluated through morphological and compositional in situ STEM analysis. In contrast to other MX3-type 1D materials, TaS3 exhibits exceptional thermal robustness, and evidence suggests separate decomposition pathways corresponding to the two polymorphs of TaS3. Finally, the thermal decomposition of exfoliated two-dimensional P21 nanosheets, revealed through low kV and aberration-corrected in situ STEM, is examined in Chapter 4. Decomposition sites occur at nanosheet fractures and edges, driven by a crystalline-to-amorphous phosphorus transformation at a linear rate. In aggregate, these results enrich our understanding for low-dimensional quantum material thermal dynamics to better inform design choices for devices incorporating these materials and to reveal unique nanostructural behavior to be further studied both in situ and ex situ.