Title page for ETD etd-12152009-191229


Type of Document Dissertation
Author Chen, Kai
Author's Email Address kaichen@vt.edu
URN etd-12152009-191229
Title Self-organization on Nanoparticle Surfaces for Plasmonic and Nonlinear Optical Applications
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Robinson, Hans D. Committee Chair
Davis, Richey M. Committee Member
Heflin, James R. Committee Member
Khodaparast, Giti A. Committee Member
Keywords
  • ionic self-assembly multilayer (ISAM) film
  • dithiocarbamate
  • convective self-assembly
  • surface functionalization
  • localized surface plasmon resonance
Date of Defense 2009-12-02
Availability unrestricted
Abstract
This dissertation is about fabrication and functionalization of metal nanoparticles for use in plasmonic and nonlinear optical (NLO) applications. In the first two chapters, I describe a series of experiments, where I combined silver nanoparticles fabricated by nanosphere lithography with ionic self-assembled multilayer (ISAM) films, tuning the geometry of the particles to make their plasmonic resonances overlap with the frequency of optical excitation. The designed hybrid metallic/organic nanostructures exhibited large enhancements of the efficiency of second harmonic generation (SHG) compared to conventional ISAM films, causing a modified film with just 3 bilayers to be optically equivalent to a conventional 700-1000 bilayer film.

SHG responses from Ag nanoparticle-decorated hybrid-covalent ISAM (HCISAM) films were investigated as the next logical step towards high-χ2 ISAM films. I found that the plasmonic enhancement primarily stems from interface SHG. Interface effects were characterized by direct comparison of SHG signals from PAH/PCBS ISAM films and PAH/PB HCISAM films. Though interface &chi2 is substantially smaller in PAH/PCBS than in PAH/PB, plasmonically enhanced PAH/PCBS films exhibit stronger NLO response. I propose that the structure of PAH/PB film makes its interface more susceptible to disruptions in the nanoparticle deposition process, which explains our observations.

During the fabrication of monolayer crystals for nanosphere lithography, I developed a variation of the technique of convective self-assembly, where the drying meniscus is restricted by a straight-edge located approximately 100 μm above the substrate adjacent to the drying zone. This technique can yield colloidal crystals at roughly twice the growth rate compared to the standard technique. I attribute this to different evaporation rates in the thin wet films in the two cases. I also found that the crystal growth rate depends strongly on the ambient relative humidity.

Finally, dithiocarbamate (DTC)-grafted polymers were synthesized and employed to functionalize surfaces of Au nanopartciles. PAH-DTC shows greater stability in different environments than PEI-DTC. I also investigated the stability of PAH-DTC coated particles in suspensions with UV-Vis spectroscopy and autotitration. The covalently bonded PAH-DTC enhances the colloidal stability of the Au nanoparticles and enables subsequent ISAM film deposition onto the particles.

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