An influence of the adsorbed molecules layer on the localized surface plasmons in the spherical metallic nanoparticles

Abstract

An influence of the adsorbed molecules layer on the optical characteristics of the spherical metallic nanoparticles has been studied in the work. In order to do this one considers the additional term which takes into account the scattering of electrons at the interface between metal and adsorbate. The analytical expressions for the frequency dependences for the parameter of coherence loss due to the scattering at the interface “metal – adsorbed layer” have been obtained. It has been found that the presence of the adsorbed molecules results in the electron scattering anisotropy, and, hence, in the anisotropy of the optic response of such systems. The result of the indicated anisotropy is the appearance of the additional maximum in the infrared part of the spectrum in the frequency dependences for the optical characteristics. An evolution of the frequency dependences for the components of the polarizability tensor and the absorption cross-section and scattering cross-section for the two-layer spherical nanoparticles of the type “metal – adsorbate” under the variation of their geometrical parameters has been analyzed. It has been shown that the weak maximum of the real, imaginary parts and the module of the transverse component of the polarizability tensor and the absorption and scattering cross-sections in the infrared part of the spectrum appears due to inducing of the local density of the states by adsorbate. The reason of the shift of the maxima of the absorption cross-section and scattering cross-section for the nanoparticles of the constant sizes with the cores of different metals has been found. It has been demonstrated the existence of the small-scale oscillations at the frequency dependences for the components of the polarizability tensor and at the absorption and scattering cross-sections, caused by an oscillating contribution of the surface electron scattering. The dependence of the location and the value of the maximum of the absorption cross-section for the particle “metal – adsorbate” with the constant geometrical parameters and content on the dielectric permittivity of the medium, in which the nanoparticle is situated, has been proved.

Optical and thermal effects in the neighborhood of the spherical layered nanoparticle of the ``metallic core – J-aggregate shell'' structure

“…For the third maximum (𝜆 (3) max ≈ 480 nm for Ag@TC and 𝜆 (3) max ≈ 550 nm for Au@TC), and ℏ𝜔 (3) res = 2.11 eV for Ag@TC and ℏ𝜔 (3) res = 1.62 eV for Au@TC, which correspond to 𝜆 (3) max ≈ 765 nm and 𝜆 (3) max ≈ 590 nm, i.e., the theoretical and experimental values 𝜆 (3) max are close for Au@TC while the values 𝜆 (3) max are significantly different for Ag@TC the values differ significantly. In our opinion, this can be associated with the fact that the theoretical values of resonant frequencies ℏ𝜔 (𝑖) res were estimated in non-dissipative approximation, while under an increase of the wavelength (decrease of the frequency) of the incident light for the particles of the indicated size, the relaxation processes, associated with the electron scattering both by the surface of the particle and with the additional chemical damping at the interface "metal -J-aggregate" interface (see, for example, [74,75]), may be essential. Nevertheless, the authors are aware that this issue requires a more detailed research and will be the subject of subsequent works of the authors.…”