Spectroscopic investigation of the interfacial dynamics in metal/semiconductor heterostructure, liquid metals, and ionic liquids
Date
2021
Authors
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Publisher
University of Delaware
Abstract
Surfaces and interfaces play a central role in processes ranging from environmental chemistry and biological function to electrochemistry, heterogeneous catalysis, and solar energy conversion. Understanding the interfacial dynamics at the molecular level is critical to inform the design and innovation of the novel functional materials which lead to applications in multiple fields in industry as well as in academia. Recent development and applications of advanced spectroscopic techniques have accumulated a large amount of knowledge and have led to major advances in fundamental understanding of these interfacial processes. ☐ In this thesis, explorations into the interfacial dynamics of novel functional materials are demonstrated and discussed with detailed relationships between surface atomic- and electronic-level structure and chemical reactivity. Specifically, in Chapters 2 and 3, a versatile strategy was designed and demonstrated to achieve precise control of plasmonic Au/Cu2O heterostructure arrays. The ultrafast transient absorption measurements revealed that Au/Cu2O heterostructures showed charge carrier transfer from the Au nanoparticle to the Cu2O semishell when the metal was selectively excited at the plasmonic frequency. In Chapter 4, the liquid-gas interface of gallium-indium eutectic (eGaIn) and liquid bismuth were examined in the presence of oxygen and water vapor. Experimental results showed similar Ga2O3 outer layer and Ga2O inter layer formation under both gas environments at the eGaIn-gas interface. Despite similar product formation, significant differences are observed in the pressure-dependence and adsorbate-induced binding energy shifts. At the liquid Bi-gas interface, oxygen remained unreactive up to 10^-4 Torr, whereas above this pressure oxidation was observed forming Bi2O3. The onset of oxidation was at significantly higher exposure compare to the solid Bi interface. In Chapter 5, the impact of water vapor on the electrochemical shift at ionic liquid (IL)-gas interfaces was investigated. Upon introducing water vapor, the electrochemical shift approached 1 eV/V from 0.9 eV/V as a function of increasing water vapor pressure, indicating a decrease in the IL ohmic drop as the IL/water mixture become more conductive. ☐ Overall this dissertation strives to highlight the exploration on interfacial dynamics of novel functional material systems with advanced spectroscopic techniques which could enhance our understanding and help identify novel applications. The projects that are presented here have been performed in two research groups with different focuses.
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Keywords
AP-XPS, Heterostructure, Ionic liquids, Liquid Metals, Metal/Semiconductor