Studies of Exotic Electronic, Optical, and Electrochemical Properties in Nanoparticle Assembly and Graphene

Authors

Jay Min Lim, University of Nebraska-LincolnFollow

First Advisor

Ravi Saraf

Date of this Version

8-2024

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Mechanical Engineering and Applied Mechanics

Under the supervision of Professor Ravi Saraf

Lincoln, Nebraska, August 2024

Comments

Copyright 2024, Jay Min Lim. Used by permission

Abstract

It is well known that exotic properties and phenomena emerge as structural dimensions shrink to nanoscales. We self-assembled one-dimensional chains of gold nanoparticles in solution and quantified the growth process by monitoring the redshift of localized surface plasmon resonance (LSPR). Curiously, the redshift stopped while the chains continued to rearrange as manifested by gradual reduction in the LSPR peak. Using electromagnetic simulations, we quantitatively explained the phenomena as a rapid “addition-polymerization” followed by a sharp transition to “condensation-process.” Next, recognizing the significant electric field enhancement in the interparticle gap, a photoluminescent-active Eu³⁺ ion was used to probe Surface-Enhanced Photoluminescence (SEPL) in the hotspots. Remarkably, in the LSPR-stable regime, SEPL intensity continued to increase. Electromagnetic simulation revealed that, all hotspots are not made equal where the location of the gap in the chain matters. The observation is consistent with the growth process and explains the SEPL spectrum. Counterintuitively, on breaking the chains from ≥15 to ≤6 nanoparticles, SEPL intensity increased. Interchain plasmonic interaction estimated by simulation explains this unforeseen amplification of hotspot enhancement.

Monolayer of these chains was deposited to form nanoparticle necklace network (N³). The N³ exhibits gating leading to an all-metal transistor with high gain. The gating mechanism of N³ sharply transitioned from Coulomb blockade to classical critical percolation behavior at ~140 K.

Lastly, electrochemical redox on pristine graphene, known to be otherwise inert was discovered and studied. The strong π-π interaction was shown to incite the redox of methylene blue (MB) on graphene. Interestingly, using an in-house opto-electrochemical instrument called SEED, concomitant structural and electrochemical measurements quantitatively showed anisotropic redox behavior where the MB molecules docked at specific orientation on graphene for redox.

The discovery of these interesting properties in nanoparticle assembly and graphene offers exciting opportunities for advancing nanotechnology. These findings can pave the way for rational design of highly sensitive devices for a wide range of applications such as biosensors, chemical sensors, living transistors and electrocatalytic electrodes.

Advisor: Ravi Saraf