Publication date: 3rd July 2020
I employ a topotactic method called cation exchange to produce semiconductor nanocrystals (NCs) in novel morphologies, compositions, and crystallographic phases. My dissertation research focused on the understanding of the physical properties and phase transitions of these new nanomaterials prepared by cation exchange1–3. In this talk, I shall describe the countless possibilities of the exploration of physicochemical properties and applications of molecularly precise semiconductor nanoclusters, a class of materials that we were able to expand with the help of cation exchange. In particular, I shall discuss how ultrasmall copper selenide (Cu2-xSe) NCs prepared by cation exchange of cadmium selenide NCs exhibit a disordered cationic sub-lattice under ambient conditions1. Known superionic materials, such as AgI, Cu2Se etc. in their bulk form, display this phase transition at high temperatures and/or pressures, making them unsuitable for many applications. As a follow-up to this study, I shall describe my investigations of Li-doping of Cu2-xSe NCs and how this doping influences the crystal structure and consequently the phase transition behavior2. For this study to pave the way to fundamental understanding on ion transport behavior in solids, and applications as solid-state electrolytes, thermoelectrics and ultrafast electronic switches, the possible mechanism of ionic transport in these NCs remains to be investigated. As a separate demonstration on the synthesis and stabilization of a non-natural phase in NCs, I shall explain on the basis of optical spectra measurements and density functional theory (DFT) calculations how HgSe NCs3, prepared using cation exchange is found to have an inverted band structure along with a finite band-gap, making it a potential 3D topological insulator.
Prof. Prashant K. Jain (jain@illinois.edu) for expert guidance and useful discussions; Dr. Sarah White (alumnus)-collaborator and co-author; Mr. Daniel Dumett-theoretical DFT calculations; Materials Research Laboratory (MRL)-HRTEM, STEM on JEOL 2010-EF FEG and Beckman Institute for Advanced Science and Technology-Confocal Raman Microscope. Grants from ACS Petroleum Research Fund and 3M.
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