Single‐Particle Study: Chemical Effect on Surface Plasmon Damping in Two‐Dimensional Gold Nanoprisms

Abstract

Anisotropic plasmonic gold nanoparticles have attracted considerable attention because of their unique size-and shape-dependent absorption and scattering properties caused by localized surface plasmon resonance (LSPR) and collective oscillations of the conduction band electrons induced by interactions with incident light. In this regard, gold nanoparticles have been employed in many applications, such as plasmonic biosensors, 1-4 surface enhanced Raman spectroscopy (SERS), 5-7 and photothermal cancer therapy. 8,9 Recently, two-dimensional (2D) gold nanoparticles, such as triangular gold nanoprisms (AuNPs), have attracted considerable interest because of their large surface to volume ratio, sharp corners and edges, which can enhance the electric field significantly. 10-12 Furthermore, 2D triangular AuNPs exhibit characteristic LSPR optical properties that are different from 1D gold nanoparticles. For instance, in the visible and near-infrared (IR) regions, 2D AuNPs with large surface to volume ratio present two characteristic dipole and quadrupole resonance modes. 7,13-18 The higherorder resonance modes in 2D AuNPs are caused by the retardation effect. 13,19,20 Recently, there have been research efforts to better understand the LSPR modes observed in the AuNPs. 15,17,18 The most important factor that can affect the LSPR modes in 2D AuNPs have been found to be the aspect ratio (AR). 14,15,18 The AR is determined by the edge length divided by the thickness. For instance, typical quadrupole and dipole resonance modes are not observed clearly for thick AuNPs. 15,18 Moreover, the recent studies presented that the dipole resonance wavelength is red-shifted with increasing edge length at a fixed thickness. 14-16 Furthermore, the dipole resonance wavelength is also shifted toward a longer wavelength when the thickness is decreased at a constant edge length. 14 Despite the recent efforts to reveal the optical properties of 2D AuNPs, their optical properties are still largely unanswered at the single-particle level. For example, chemical interface damping (CID) is one of LSPR decay processes in plasmonic gold nanoparticles. 21,22 Considerable effort has been made to characterize the effect of chemical adsorption on plasmon damping in 1D gold nanoparticles at the single-particle level, 21,23-25 but our understanding of the CID effect of 2D AuNPs with large surface to volume ratio is unclear. In this regard, it is of importance to gain deeper understanding on the interaction between strong CID effects and large surface to volume ratio of 2D AuNPs with various adsorbate molecules.In this study, scattering-based dark-field (DF) microscopy and spectroscopy were employed to characterize chemical-induced scattering properties and plasmon damping of 2D AuNPs synthesized by a seedless growth method with an average edge length and thickness of 100.4 × 21.1 nm, respectively. The relative CID effect and sensitivity of the two dipole and quadrupole LSPR modes induced in single AuNPs were examined according to the adsorption of adsorbate...

Circular Polarization Conversion in Single Plasmonic Spherical Particles

“…This proposition is supported by the recent observation made by others that dipolar plasmon resonances exhibit higher damping than quadrupole ones upon adsorption of thiols. 32 In the CP scattering model developed here, a sufficient relative increase in quadrupolar contributions will indeed achieve the CP inversion.…”

“…This proposition is supported by the recent observation made by others that dipolar plasmon resonances exhibit higher damping than quadrupole ones upon adsorption of thiols. 32 In the CP scattering model developed here, a sufficient relative increase in quadrupolar contributions will indeed achieve the CP inversion. In this paper, we have demonstrated experimentally and justified by FEA that polarimetric (high-angle collection) DF far-field microscopy with // CP illumination shows significant conversion into ⊥ CP from the scattering by metal nanoparticles, such as 300 nm spherical gold particles.…”

Single-particle Correlation Study: Polarization-dependent Differential Interference Contrast Imaging of Two-dimensional Gold Nanoplates

“…Increasingly, research efforts are geared toward better comprehending the optical properties in 2D single AuNPs with large surface areas under dark-field (DF) microscopy. [29][30][31] For instance, 2D AuNPs with large surface areas were shown to present two characteristic dipole and quadrupole resonance modes in the spectral ranges between the visible and nearinfrared. 27,28,[32][33][34][35][36] Despite the recent advances in elucidating the scattering properties of the individual AuNPs, details surrounding their optical properties remain largely ambiguous.…”