MSE PhD Proposal - Xiaojun Sun

Wednesday, September 9, at 1 p.m.

Room 3201 MoSE

Committee:

Prof. Dong Qin, Advisor, MSE

Prof. Zhiqun Lin, MSE

Prof. Meilin Liu, MSE

Prof. Vladimir Tsukruk, MSE

Prof. John Zhang, Chemistry

Title: Bimetallic Nanocrystals for Applications in Plasmonics and Catalysis

Silver nanocrystals have fascinating optical properties known as localized surface plasmon resonance, which is essential to applications such as optical sensing and imaging. For example, Ag nanocubes embrace surface-enhanced Raman scattering (SERS) properties with enhancement factors up to 106 at visible excitation wavelengths for highly sensitive detection of chemical or biological species. Unfortunately, elemental Ag is highly susceptible to oxidation under conditions that involve oxidants, halide ions, and acids. Such chemical instability often results in changes to the morphology of Ag nanocrystals, particularly at corners and edges with high energies, and ultimately compromises their performance. Additionally, the toxicity of the released Ag+ ions also limits the potential applications of Ag nanocrystals in a biological system. One potential solution to improve the chemical stability of elemental Ag is to form alloys with a more stable metal such as Au or protect the Ag nanocrystals with ultrathin Au shells. However, it is difficult to form Ag-Au alloys by reducing their precursors simultaneously in a solution phase due to their substantial difference in reactivity. It is also challenging to coat Ag nanocrystals with Au shells due to galvanic replacement. In this proposal, I aim to develop strategies to epitaxially deposit Au or Ag-Au alloys on the surface of a Ag nanocube in a fashion similar to seeded growth. I will demonstrate that integrating Ag nanocubes with Au can greatly enrich their plasmonic properties and improve their chemical stability for chemical sensing. By exploring the use of Ag nanocrystals as templates, I will fabricate Ag@Pt core-shell nanocubes or octahedra, and further etch away the Ag templates to generate Pt-based nanocages with a wall thickness of a few atomic layers and well-defined {100} or {111}facets. This new class of Pt nanomaterials hold a great potential as effective catalysts for the oxygen reduction reaction (ORR) owing to their substantially enhanced mass activity and catalytic durability.