Role of shape in substrate-induced plasmonic shift and mode uncovering on gold nanocrystals

Abstract

A number of plasmonic devices and applications, such as chemical and biological sensors, plasmon-enhanced solar cells, optical nanoantennas, metamaterials and metasurfaces, require the deposition of plasmonic metal nanocrystals on various substrates. Because the localized plasmon resonance modes, energies and strengths are strongly dependent on the dielectric function of the surrounding environment, the substrate is expected to largely affect the plasmonic properties of supported metal nanocrystals. Therefore, understanding the effects of the substrate on the plasmonic properties of metal nanocrystals and the roles of the involved factors will be crucial for designing various plasmonic devices that are made of metal nanocrystals deposited on different substrates. Herein we report on our study and results of the effects of substrates with distinct dielectric functions on the plasmonic properties of three types of Au nanocrystals. A combination of experiments and numerical simulations shows that the presence of a substrate causes plasmonic shifts as well as the appearance of new plasmon modes. The plasmonic shifts and the emergence of new plasmon modes are found to be dependent on the particle shape of Au nanocrystals and in turn on the fractional particle surface area that is in contact with the supporting substrate. For Au nanospheres and nanorods, plasmonic shifts, less than 100 nm, are observed on the scattering spectra by changing the supporting substrate from indium tin oxide to silicon. In comparison, a giant spectral shift of more than 300 nm is obtained for Au nanoplates. Moreover, silicon substrates induce the emergence of an out-of-plane quadrupolar mode of Au nanoplates, which interacts with an out-of-plane octupolar mode to give rise to a distinct Fano resonance. The Fano resonance is found to become stronger as the thickness of Au nanoplates is decreased. These results are of great importance for understanding the plasmonic properties of noble metal nanocrystals supported on various substrates, and for designing novel plasmonic nanostructures with desired optical properties and functions.

Effect of Surface Plasmon Coupling to Optical Cavity Modes on the Field Enhancement and Spectral Response of Dimer-Based sensors

“…However it was shown that for large enough particles, strong diffractive coupling can occur even in an asymmetric configuration 29 , 57 , 58 . Furthermore, additional peaks at the blue side of the original resonance can arise 59 – 61 . We first consider the cavity resonances for a FP cavity that is partially filled with glass (SiO 2 ) of refractive index of 1.45.…”

Influence of the CTAB surfactant layer on optical properties of single metallic nanospheres

“…It was reported previously that the asymmetry of the environment may cause hybridization of the plasmonic modes of the nanoparticle if their spectral positions are close [23]. This effect was studied for different metallic nanoparticles [23][24][25][26][27], however the possible modulation of the optical properties due to the CTAB layer around the nanoparticles was not considered. Also, important to note that in majority of studies the optical properties of the metallic nanospheres are simulated using Mie theory and effective refractive index approximation which does not include all mentioned effects.…”

Optical Plasmon Resonances in Arrays of Au Nanoclusters

“…Однако такой способ требует прозрачной подложки, например кварца, сапфира или стекла. Действительно, большинство работ, исследующих ЛППР, представляют результаты для металлических нанокластеров, размещенных на прозрачной подложке, например [12; 13], только немногие имеют дело с непрозрачным материалом подложки, таким как кремний [14][15][16][17][18]. Определение частотного положения ЛППР для плазмонных структур на непрозрачных подложках является непростой задачей из-за сложности разделения излучения рассеянного плазмонами и обратного отражения от подложки [19].…”

“…Максимумы в расчетных спектрах поглощения плазмонных образцов использованы для определения энергий ЛППР в массивах нанокластеров Au на непрозрачных подложках. Наши результаты согласуются с литературными данными, полученными ранее альтернативными методами для нанокластеров Au идентичной формы на различных подложках [11][12][13][14][15][16][17].…”