Transformations in inorganic nanomaterials: role of defects, surfaces, and size

As our ability to synthesize and manipulate nanomaterials increases, so does our ability to investigate the properties and transformations of materials as they evolve in size from precise clusters akin to molecules to extended solids exhibiting bulk-like properties. In this thesis, we look at a how critical features of nanomaterials like size, shape, surface chemistry or ligand shell, and defect profile affect properties and transformations on the nanoscale. In Chapter 1, we investigate the mechanism of cation exchange in an ensemble of CdSe nanocrystals with Ag+ and Cu+ in solution. We find that the generation of defects induced by non-native cations is a critical intermediate in the exchange reaction and that positive co-operativity stemming from interactions between charged defects results in an abrupt chemical transformation of the entire nanocrystal, i.e. a particle-by-particle exchange rather than an atom-by-atom mechanism. In Chapter 2, we leverage the high sensitivity of excitonic absorption of ultrasmall CdSe clusters to changes in surface chemistry to optically probe cation exchange and identify a stable, long-lived intermediate in the cation exchange transformation. The stability of the intermediate was found to be dependent on the ligand coating on the initial clusters, leading to a better understanding of how ligand passivation can play a role in chemical reactions occurring at the solid-liquid interface. In Chapter 3, we probe how the optical and structural properties of the semiconductor, cuprous selenide are affected by a decrease in crystallite size and find an ultrasmall form of cuprous selenide in which a disordered phase, known to exist in the bulk at high temperature, is stable at ambient conditions suggesting that the order-to-disorder phase transition temperature is depressed in ultrasmall Cu2Se clusters. Finally, in Chapters 4 and 5, we explore how the structure of metamolecules consisting of complex assemblies of hexagonal Au nanoplates and Au nanospheres affects their localized surface plasmon resonance properties. . We find using electrodynamic simulations combined with correlated electron microscopy/optical spectroscopy at the single-construct level that the nature and strength of plasmonic coupling within the resulting assembly is strongly dependent on the site of attachment of the nanosphere/s and the nanosphere size. In addition to the large, regio-selective polarizability of Au nanoplates, we also uncover a synergy in the polarizing effect of multiple nanospheres. The dissertation ends with an outlook of the scientific impact and potential future studies that may emanate from the work presented here.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2016

Author dc:creator

• White, Sarah Langlois

Contributors dc:contributor

• Jain, Prashant K.
• Murphy, Catherine J.
• Shim, Moonsub
• Lu, Yi

• cation exchange
• nanomaterials
• quantum dots
• clusters
• superionic
• plasmonic sensors
• discrete-dipole approximation

Statement dc:rights

• Copyright 2016 Sarah Langlois White

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/90930

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/90930