Date of Award

8-2020

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. Asghar Kayani

Second Advisor

Dr. Ramakrishnan Guda

Third Advisor

Dr. Sung Chung

Fourth Advisor

Dr. Muralidhar K Ghantasala

Keywords

Embedded gold nanoparticles, metal enhanced photoluminescence

Abstract

Noble metal nanoparticles (MNPs) have attracted great attention in electronics, solar cells and catalysis. Their unique optical properties and biocompatibility makes them useful in biological applications like imaging, drug delivery, therapy and diagnostic. At the surface of MNPs the collective oscillation of free electrons resonates with a particular wavelength of incident light, generating the Localized Surface Plasmons Resonance (LSPR). LSPR results in absorption and scattering of incident light. Scattering results in reflecting photons and absorption leads to enhanced photoluminescence and quenching of fluorophores, if the fluorophore is in the vicinity of MNPs.

Most of the studies in this regard have been carried out using chemically synthesized metal nanoparticles of different crystallinity, sizes and shapes. One problem with this approach is the possibility of direct chemical interaction between the fluorophore and metal nanoparticle that results in quenching of photoluminescence intensity. Moreover, using chemical means, it is difficult to control the distance between the nanoparticle and the fluorophore.

In this dissertation, efforts are made to understand the LSPR of Au-NPs implanted within quartz substrate. The size and the concentration of MNPs were optimized with increasing ion beam fluence leading to a decreased inter-nanoparticle distance. Moreover, we employed post implantation annealing of implanted substrates at 800 °C to investigate the diffusion and heating effect on the concentration of Au-NPs within the substrates.

Rutherford Backscattering Spectrometry (RBS) measurements are used to obtain the depth profile and concentration of gold within the quartz substrate. The formation of Au-NPs is characterized by UV-visible spectroscopy measurements. LSPR peaks of Au-NPs were observed, that confirmed the formation of embedded Au-NPs. Moreover, increase in the size and concentration of Au-NPs was clearly observed as the fluence of Au within quartz substrate increased or annealing of the substrates is carried out. During the annealing, slight diffusion of Au away from the surface of the substrate was observed that increased with annealing time, however, implanted Au maintained the concentration.

Steady-state measurements of lead halide perovskite nanocomposites CsPbX (X = Cl3, Br3, Br2I and I3) in the vicinity of Au-NPs were carried out to study the interaction between perovskites and embedded Au-NPs. PL enhancement of CsPbX (X = Cl3, Br3, Br2I and I3) was observed on implanted substrates with the fluence ranging from 2.0 x 1016 to 5.0 x 1016 Au-atoms/cm2 and quenching was observed on substrates implanted with higher fluence. The overlap of PL emission and Au-NPs absorption also played a significant role in PL quenching.

Access Setting

Dissertation-Campus Only

Restricted to Campus until

3-31-2021

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