Exploring condensed phases in engineered semiconducting nanocrystals

Banerjee, Progna

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https://hdl.handle.net/2142/102911 Copy

Description

Title

Exploring condensed phases in engineered semiconducting nanocrystals

Author(s)

Banerjee, Progna

Issue Date

2018-11-27

Director of Research (if dissertation) or Advisor (if thesis)

Jain, Prashant

Doctoral Committee Chair(s)

Cooper, S

Committee Member(s)

• Abbamonte, Peter
• Ertekin, Elif
• Gruebele, Martin

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

nanocrystals, cation exchange, batteries, phase transitions, doping, quantum dot, solid electrolyte, nanoscale materials, plasmon, scattering, nanoscale transformations

Abstract

The Jain lab employs a topotactic method called cation exchange to produce semiconductor nanocrystals (NCs) in novel morphologies, compositions, and crystallographic phases. My dissertation research focuses on the understanding of the physical properties and phase transitions of these new nanomaterials prepared by cation exchange. In Chapter 1, I 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 Chapter 2, I discuss how ultrasmall copper selenide (Cu2-xSe) NCs prepared by cation exchange of cadmium selenide NCs exhibit a disordered cationic sub-lattice under ambient conditions. This behavior is quite unlike larger NCs or the bulk, suggesting an interesting effect of crystallite size and strain on the stability of super-ionic phases. In Chapter 3, I describe my investigations of Li-doping of Cu2-xSe NCs and how this doping influences the crystal structure and consequently the phase transition behavior. A close-to-ambient-temperature transition from the non-superionic to superionic phase transition also appears to be present in the final lithium selenide (Li2Se) NCs formed from this doping reaction. In Chapter 4, I explain on the basis of optical spectra measurements and density functional theory (DFT) calculations how HgSe NCs, prepared using cation exchange in a novel wurtzite phase, differ from their natural zinc-blende counterparts. The latter is a semi-metal, whereas the newer phase obtained from cation exchange is found to have an inverted band structure along with a finite band-gap, making it a potential 3D topological insulator. In Chapter 5, I extend the understanding of ion exchange reactions to an “anion exchange” process in zinc oxide (ZnO) NCs. As a detour from the central thesis of my dissertation, in Chapter 6, I present my work on electrodynamic simulations of optical properties of nanostructures, which helped demonstrate that localized surface plasmons can be imaged in real space with nanometer resolution using a scanning tunneling microscope (STM) coupled to a laser.

Graduation Semester

2018-12

Type of Resource

text

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http://hdl.handle.net/2142/102911

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Copyright 2018 PROGNA BANERJEE

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