Model-Free Unraveling of Supported Nanoparticles Plasmon Resonance Modes

Abstract

Plasmonics of Ag, Au, and Zn nanoparticles supported on Al 2 O 3 (0001), TiO 2 (110), and ZnO(0001) substrates has been probed by surface differential reflectivity spectroscopy (SDRS) during vapor deposition growth. Parallel and perpendicular interfacial susceptibilities (ISs), or "optical thicknesses", which characterize only the dielectric response of the film, are derived from experimental spectra in p-and spolarization using an inversion procedure based on Kramers−Kronig transform. The consistency of the approach is checked against sum rules. Plasmonic contributions are unraveled by decomposing ISs into damped oscillators and identified with the help of dielectric simulations of truncated supported spheres or spheroids. Beyond the common Drude behavior of Ag, Au, and Zn, the comparison between the three metals demonstrates the paramount role of interband transitions in the ISs profiles. While gold and silver show free electron plasmon modes, zinc exhibits polarization modes of bound electrons. However, despite those differences, the resonant modes that are identified herein are universal for supported particles. Particle shape, equilibrium aspect ratio, image field, polydispersity, and interface-induced damping are discussed by analyzing changes in frequencies, oscillator strengths, and broadenings. Deposit-induced band gap absorption for semiconductor substrate and switches from growth to coalescence regimes are evidenced. Static and dynamic coalescence are characterized by power law exponents as a function of particle size. Therefore, the unique framework that is proposed opens strong prospects in the optical characterization of growth, metal/ semiconductor interfaces, and gas adsorption.

Examining Substrate-Induced Plasmon Mode Splitting and Localization in Truncated Silver Nanospheres with Electron Energy Loss Spectroscopy

“…41,53 We assign the peak located at 2.8 eV in both experiment and simulation to a quadrupole-like mode, Q z , aligned perpendicular to the substrate. 28 Plane-wave simulations (Figure 3c) show that this mode is only excitable when the incident electric field has a component normal to the substrate, indicating that Q z is polarized normal to the substrate, in agreement with previous studies. 28 The experimental and simulated EELS maps (Figure 3d and 3e) for the Q z mode are only in qualitative agreement because Q z is weakly excited in simulation and it lies on the blue shoulder of the D xy peak, making the simulated EELS map at 2.8 eV a superposition of these two modes.…”

“…28 Plane-wave simulations (Figure 3c) show that this mode is only excitable when the incident electric field has a component normal to the substrate, indicating that Q z is polarized normal to the substrate, in agreement with previous studies. 28 The experimental and simulated EELS maps (Figure 3d and 3e) for the Q z mode are only in qualitative agreement because Q z is weakly excited in simulation and it lies on the blue shoulder of the D xy peak, making the simulated EELS map at 2.8 eV a superposition of these two modes. A quadrupole-like mode polarized parallel to the substrate (Q xy ) has been reported to exist in truncated Ag nanospheres in the quantum size regime; 28 however, we do not observe this mode.…”

Periodic Arrays of Diamond‐Shaped Silver Nanoparticles: From Scalable Fabrication by Template‐Assisted Solid‐State Dewetting to Tunable Optical Properties

“…Already, the same nanoparticle put into inhomogeneous environment (like a neighboring substrate) can exhibit strong quadrupole and higher order modes. In case of supported or partially embedded nanoparticles, numerical simulations are required to analyze their optical properties . For objects larger than the optical wavelength, retardation effects come into play even for simple spheroidal shapes.…”

Charge Transfer at Hybrid Interfaces: Plasmonics of Aromatic Thiol-Capped Gold Nanoparticles

“…21 In particular, the broadening of the plasmon band when the particle diameter decreases in the range 2À10 nm is described only by a size-dependent damping rate Γ D , due to an enhanced surface scattering, which scales with the surface/volume ratio. 36 However, and contrary to silver, 45 the screening of conduction electrons by the more localized d electrons in gold cannot be neglected in the visible/near-UV region since the two interband 5d f 6sp transitions at 330 and 470 nm overlap with the localized surface plasmon. This results in a sizable discrepancy between the Drude model and the absorption profile when interband transitions are neglected ( Figure S9b).…”