Gold, Platinum, and Aluminum Nanodisk Plasmons: Material Independence, Subradiance, and Damping Mechanisms

Abstract

Localized surface plasmon resonances (LSPR) are collective electronic excitations in metallic nanoparticles. The LSPR spectral peak position, as a function of nanoparticle size and material, is known to depend primarily on dynamic depolarization and electron structure related effects. The former gives rise to the well-known spectral red shift with increasing nanoparticle size. A corresponding understanding of the LSPR spectral line width for a wide range of nanoparticle sizes and different metals does, however, not exist. In this work, the radiative and nonradiative damping contributions to the LSPR line width over a broad nanoparticle size range (40-500 nm) for a selection of three metals with fundamentally different bulk dielectric properties (Au, Pt, and Al) are explored experimentally and theoretically. Excellent agreement was obtained between the observed experimental trends and the predictions based on electrostatic spheroid theory (MLWA), and the obtained results were successfully related to the specific band structure of the respective metal. Moreover, for the first time, a clear transition from a radiation damping dominated to a quenched radiation damping regime (subradiance) in large nanoparticles was observed and probed by varying the electron density through appropriate material choice. To minimize inhomogeneous broadening (commonly present in ensemble-based spectroscopic measurements), a novel, electron-beam lithography (EBL)-based nanofabrication method was developed. The method generates large-area 2D patterns of randomly distributed nanodisks with well-defined size and shape, narrow size distribution, and tunable (minimum) interparticle distance. In order to minimize particle-particle coupling effects, sparse patterns with a large interparticle distance (center-to-center ≥6 particle diameters) were considered.

Refractometric biosensing based on optical phase flips in sparse and short-range-ordered nanoplasmonic layers

“…In brief, the analytical polarizability of a gold ellipsoid is used together with the modified long wavelength approximation to represent the responses of individual nanoparticles. [26][27][28] The only fitting parameter used was the effective refractive index surrounding the nanoparticles, located at an interface, which was tuned to match the resonance wavelength to an experimental transmission spectrum (Supplementary Fig. S2).…”

Plasmon–Interband Coupling in Nickel Nanoantennas

“…As we have found earlier for other metals, the agreement between experiment and theory is more than reasonable in view of the simplifying assumptions in the model. 3 From the measured and calculated data we make three main interesting observations. For decreasing disk size the LSPR is spectrally shifted towards the IBT resulting in (i) decreasing extinction efficiency of the low-energy (LE) peak (intuitively attributed to the LSPR), (ii) increasing extinction efficiency for the high-energy (HE) peak (intuitively attributed to the IBT), and (iii) a spectral shift of the latter towards higher energies as the LSPR "approaches".…”

Metal hydrides for smart window and sensor applications

“…Nanoparticles that support LSPR interact very strongly with near-visible light via effi cient light absorption and scattering and are very sensitive to several structural parameters, such as nanoparticle size and shape as well as to the chemical nature of the used metal itself. 46 Furthermore, the polarization of the electronic system of the plasmonic nanoparticle creates local strongly enhanced electromagnetic fi elds (with respect to the incoming light fi eld), as illustrated in Figure 7 b-c. In this way, a spatially nanoconfi ned sensing volume, extending a few tens of nanometers from the plasmonic particle surface, is created.…”