Photochemical Sciences Ph.D. Dissertations

Title

Photochemical energy conversion in metal-semiconductor hybrid nanocrystals

Date of Award

2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Mikhail Zamkov (Advisor)

Second Advisor

Kevin McCluney (Other)

Third Advisor

Ksenija Glusac (Committee Member)

Fourth Advisor

H. Peter Lu (Committee Member)

Abstract

My dissertation work focuses on several aspects in nanoscale materials for photocatalysis. Several nanostructured architectures were explored as detailed below.

The present work demonstrates a general strategy for coupling the near field (NF) radiation of surface plasmons to long-lived optical excitations in semiconductor nanocrystals (NCs) was investigated. A unique signature of the plasmon to exciton energy transfer was observed in photoexcitation measurements that unambiguously correlate the increase in the CdSe exciton population with the excitation of plasmon modes in Au domains. That scheme for harvesting the NF radiation of metal nanoparticles presents an excellent opportunity for extracting the evanescent emission of surface plasmons.

Furthermore, an experimental strategy was developed for monitoring the time-dependent monomer concentration during the hot-injection synthesis of Ag nanocrystals. The present approach employs Au nanoparticles as chemical probes of the Ag monomer build-up in the reaction flask. The precipitation of Ag on the surface of Au nanoparticles is diffusion–limited and results in a blue-shift of the plasmon resonance which is used to gauge the Ag monomer concentration, [Ag0]. In particular, it was shown that the nucleation rate is independent of the reaction temperature but is highly sensitive to the concentration of free ligands in solution.

Eventually, a general strategy for the synthesis of colloidal semiconductor nanocrystals (NCs) exhibiting the size dispersion below 5% was demonstrated. That approach relies on the sequential deposition of fully saturated cationic and anionic monolayers onto small-diameter clusters, which leads to focusing of nanocrystal sizes with the increasing particle diameter. The present synthesis is amenable to different types of semiconductor nanocrystals and can potentially offer a viable alternative to traditional hot-injection strategies of the nanoparticle growth.

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