Fine-tuning of localized surface plasmon resonance of metal nanostructures from near-Infrared to blue prepared by nanosphere lithography

Abstract

Plasmonics using metal nanoparticles (MNPs) has emerged as an important research subject in the field of photonics, electronics, and nanotechnology. Despite spectacular progress in recent years, accurate tuning and modeling of plasmon resonances over a wide spectral range using state-of-the-art fabrication methods are still challenging tasks. Here, we report on the fine-tuning of the localized surface plasmon resonance (LSPR) of metal nanoparticles over a wide spectral range from near-infrared to blue using nanosphere lithography (NSL). In this systematic study, we use NSL to fabricate triangular shaped metal nanostructures using gold, silver, copper, and aluminum. All structures were annealed up to 500 °C under a nitrogen atmosphere in order to study the effect of annealing on the LSPR. Structural changes were investigated using scanning electron microscopy and atomic force microscopy. UV-VIS spectroscopy was used to determine the LSPR spectral position for these structures. The LSPR peak position is ordered as copper, gold, silver, and aluminum (from low to high photon energy—ranging from near-infrared to blue). The rate at which the LSPR changes with respect to the increasing annealing temperature is determined to be (2.3 ± 0.3) nm/°C and (1.3 ± 0.1) nm/°C for Ag and Au, respectively, while Cu MNPs show a two-step relation with a steeper slope of (1.4 ± 0.3) nm/°C initially up to 275 °C followed by a shallower slope of (0.5 ± 0.1) nm/°C. The full width at half maximum of the LSPR increases from gold over silver and copper to aluminum. We also performed finite element method simulations to validate the experimental findings. Our results can have a significant impact in plasmonic applications where fine-tuning and accurate designing of the LSPR are important.