Researcher(s)
- Benjamin Gunderman, Physics, Stony Brook University
Faculty Mentor(s)
- Lars Gundlach, Department of Chemistry and Biochemistry, Department of Physics and Astronomy, University of Delaware
Abstract
Incident light on sub-wavelength metallic nanoparticles (NPs) induces oscillations of their electron clouds, known as localized surface plasmons (LSPs), which reach their maximum amplitude at resonance and have a time duration in the femtosecond scale. Transient absorption spectroscopy (TAS) in the ultrafast regime has been implemented to study the plasmonic effects on the dynamics of the charge carriers within the NPs. Recent results from the Gundlach group have shown a stimulated emission signal of localized surface plasmon polaritons from Au and Ag nanoparticles (NPs), being more prominent from the silver samples. However, pure Ag NP arrays degrade easily under environmental conditions. To address this, Ag/Au alloy samples with up to 75% Ag were synthesized using nanosphere lithography and measured under TAS, showing that the signals were similar to those obtained for bare Au NPs. Therefore, we fabricated alloy NP arrays with higher concentrations of Ag (80% and 90%). Homogenizing the alloys require high-temperature annealing, necessitating capping the arrays with SiO2. To remove the SiO2 cap, substrates were immersed in a NaOH solution with 100 µL of diethylamine to prevent Ag etching. The decapping time, temperature, and concentration were varied, as no single set of these parameters had previously been consistently successful. Decapping success was evaluated by UV-Vis absorption spectroscopy, where successful decapping was indicated by a narrowing, intensification, and slight blue shift of the LSPR peak. While some samples showed marginal spectral improvement post-decapping, the majority exhibited little change or significant weakening of the LSPR peak. SEM analysis of the degraded samples suggested partial decapping, which exposed the Ag to etching by OH- ions. Moving forward, we will test different aspects of the decapping procedure using Ag thin films and dewetted Ag thin films as simpler analogs for the nanoparticle arrays. This includes evaluating the efficacy of diethylamine protection and the OH- etching rates of Ag. Additionally, we will explore alternative decapping agents to improve the process and minimize Ag degradation.