Synthesis, Structure, and Properties of Metastable Heterostructures Containing TiSe2
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Date
2018-06
Authors
Lygo, Alexander C.
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Preparing homologous series of compounds allows chemists to rapidly discover new compounds with predictable structure and properties. Synthesizing compounds within such a series involves navigating a free energy landscape defined by the interactions within and between constituent atoms. Historically, synthesis approaches are typically limited to forming only the most thermodynamically stable compound under the reaction conditions. Presented here is the synthesis, via self-assembly of designed precursors, of isocompositional incommensurate layered compounds [(BiSe)1+δ]m[TiSe2]m with m =1, 2, and 3. The structure of the BiSe bilayer in the m = 1 compound is not that of the binary compound, and the m = 2 and 3 are the first example of compounds where a BiSe layer thicker than a bilayer in heterostructures have been prepared. Specular and in-plane X-ray diffraction combined with high-resolution electron microscopy data was used to follow the formation of the compounds during low-temperature annealing and the subsequent decomposition of the m = 2 and 3 compounds into [(BiSe)1+δ]1[TiSe2]1 at elevated temperatures. These results show that the structure of the precursor can be used to control reaction kinetics, enabling the synthesis of kinetically stable compounds that are not accessible via traditional techniques. The data collected as a function of temperature and time enabled us to schematically construct the topology of the free energy landscape about the local free energy minima for each of the products.
Description
68 pages. Presented to the Department of Chemistry and Biochemistry and the Robert D. Clark Honors College in partial fulfillment of the requirements for the degree of Bachelor of Science June, 2018
Keywords
Physics, Chemistry, Heterostructures, 2D materials, Crystal structures, Solid-state, Kinetically formed, Metastable