THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Thursday, November 17, 2016

11:30 AM
in MoSE 4100F

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Yiren Wu

"Colloidal Hybrid Nanocrystals: Syntheses, Properties, and Applications"

Committee Members:

Prof. Dong Qin, Advisor, MSE

Prof. Zhiqun Lin, MSE

Prof. Vladimir Tsukruk, MSE

Prof. Angus Wilkinson, CHEM

Prof. Donggang Yao, MSE

Abstract:

Bimetallic nanocrystals have received significant interest in recent years because of their enhanced properties relative to the monometallic counterparts. By controlling the ratios of elements and their spatial distributions, one can engineer and enrich the properties of bimetallic nanocrystals, greatly expanding their scope of applications. In this proposal, I will develop Ag-based bimetallic nanocrystals and hybrid nanostructures with integration of plasmonic and catalytic properties for surface-enhanced Raman scattering (SERS) and related applications. Specifically, I will design synthetic routes involving the use of Ag nanocrystals as well-defined seeds for the heterogeneous nucleation and deposition of a different metal in a process known as overgrowth. When the seed (made of Ag) and the metal (M) to be deposited share the same lattice structure and have closely matched lattice constants, the overgrowth will become epitaxial. Under optimal conditions, the epitaxial overgrowth would allow for the generation of bimetallic nanocrystals with an exquisite control over their size, shape, morphology, and structure, including Ag@M core-frame nanocubes. Alternatively, when silica-coated Ag nanocrystals are employed as seeds, hybrid Ag/M/SiO2 nanostructures will be obtained. By combining the strong SERS activity of Ag nanocrystals and the catalytic properties of M, I will demonstrate the use of these bimetallic and hybrid nanostructures as unique SERS probes for in-situ monitoring of Pd- or Au-catalyzed reduction of 4-nitrothiophenol and the Ag-catalyzed oxidation reaction of 4-aminothiophenol on the surface of nanocrystals by SERS. In addition, I will turn the synthesis of Ag@M core-frame bimetallic nanocrystals into a model system for investigating the fundamentals involved in the heterogeneous nucleation and overgrowth of metal nanocrystals. My central hypothesis is that the vibrational frequency of a metal-sensitive SERS probe can serve as a distinctive reporter for the metal being deposited on the surface of a Ag nanocrystal, with a detection limit well below one monolayer. To validate my hypothesis, a novel class of molecular probes will be developed for analyzing the heterogeneous nucleation and early-stage deposition of a metal, such as Pd, Pt, Ir, Rh, or Ru, on the edges of Ag nanocubes by SERS.