Shape Matters: Plasmonic Nanoparticle Shape Enhances Interaction with Dielectric Substrate

Abstract

Numerical analyses of the ultraviolet and visible plasmonic spectra measured from hemispherical gallium nanostructures on dielectric substrates reveal that resonance frequencies are quite sensitive to illumination angle and polarization in a way that depends on nanostructure size, shape, and substrate. Large, polarization-dependent splittings arise from the broken symmetry of hemispherical gallium nanoparticles on sapphire substrates, inducing strong interactions with the substrate that depend sensitively on the angle of illumination and the nanoparticle diameter.

How an oxide shell affects the ultraviolet plasmonic behavior of Ga, Mg, and Al nanostructures

“…3 For hemispherical nanoparticles located on a sapphire substrate, that can be considered experimentally relevant in surface enhancement techniques (bottom row of Figs.3a and 3b) [11,13,14], the plasmonic performance is substantially modified by the geometry and the substrate. In general, interactions with the dielectric substrate tend to red shift the dipolar resonance with respect to the isolated sphere of the same radius [11]. For aluminum and magnesium the absorption is stronger for the hemispherical case than for the spherical case, probably due to the volume reduction of the metallic core.…”

“…In this way, with the former we mimic experimental conditions for colloidal chemistry and with the latter, the typical experimental conditions for metallic nanostructures on substrates made of either Ga or Mg [11][12][13][14]. Although the typical Al NP geometry is usually not hemispherical, we use this geometry to facilitate comparison.…”

“…In previous studies, the plasmonic performance of various metals in the UV has been analyzed. Among them, aluminum (Al) [3,[6][7][8][9][10], gallium (Ga) [7,[10][11][12][13], magnesium (Mg) [7,14], and rhodium (Rh) [15][16][17] were identified as particularly promising candidates for UV plasmonics, with properties approaching those of silver (Ag) and gold (Au) widely used for plasmonic applications in the VIS-NIR [10,18]. However, the efficiencies of these metals depends sensitively on the surrounding dielectric environment, and all of them, except Au and Rh, form native oxides that wrap the NP with a shell, whose thickness depends on both the metal and the environmental exposure conditions (temperature and pressure).…”

Immunosensing platform based on gallium nanoparticle arrays on silicon substrates

“…During the last years, there has been an increasing attention to nanostructures based on Ga because of the wide tunability of the resonance energy from the UV to the IR spectral region, the simplicity of the preparation methods, the resilience of the metal plasmon to the oxidation in ambient conditions, the spectral splitting of its resonant modes due to the hemispherical geometries, and the dependence of the oscillatory modes on the polarization of the incident light (Albella et al 2011;Wu et al 2007). Thanks to those properties, their effective use have been demonstrated in different applications, such as Surface-Enhanced Raman Spectroscopy (SERS), fluorescence spectroscopy, and photo-induced degradation studies of biomolecules, showing large UV local enhancement factors compared to Au or Ag nanoparticles (Yang et al 2013).…”

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…Aggregates, which are random assemblies of nanoparticles, can have multiple resonances depending on their size and shape, especially when the interaction between particles is strong [18,53,56,57]. This is also true for triangles, stars, cubes and cages [37,42,46,48,58].…”