Dielectric function of two-phase colloid–polymer nanocomposite

Abstract

The plasmon resonance of metal nanoparticles determines their optical response in the visible spectral range. Many details such as the electronic properties of gold near the particle surface and the local environment of the particles influence the spectra. We show how the cheap but highly precise fabrication of composite nanolayers by spin-assisted layer-by-layer deposition of polyelectrolytes can be used to investigate the spectral response of gold nanospheres (GNS) and gold nanorods (GNR) in a self-consistent way, using the established Maxwell-Garnett effective medium (MGEM) theory beyond the limit of homogeneous media. We show that the dielectric function of gold nanoparticles differs from the bulk value and experimentally characterize the shape and the surrounding of the particles thoroughly by SEM, AFM and ellipsometry. Averaging the dielectric functions of the layered surrounding by an appropriate weighting with the electric field intensity yields excellent agreement for the spectra of several nanoparticles and nanorods with various cover-layer thicknesses.

Gold Nanorods Sense the Ultrafast Viscoelastic Deformation of Polymers upon Molecular Strain Actuation

“…Motion of polymers around the particles now do not substantially affect the average dielectric environment of the GNR. 53 We obtain the most direct confirmation of our interpretation by the following argument: If we change the thickness of the spacer layers, we should observe a different timing of the GNR response to the strain pulse which is given by the sound propagation time. Figure 4 presents the results for a sample with a 75 nm thick propagation layer (sample 2) that shows a nearly instantaneous red-shift.…”

Signatures of Strong Coupling on Nanoparticles: Revealing Absorption Anticrossing by Tuning the Dielectric Environment

“…In contrast, our experimental approach consists of shifting the plasmon resonance by adjusting the permittivity ϵ med of the particles’ environment. The plasmon resonance is determined by the (dipole) polarizability α of the particle in this environment: , Here ϵ mat denotes the permittivity of the nanoparticle, while the geometrical factor f takes into account the shape of the particle. The plasmon resonance occurs at the wavelength for which the denominator becomes minimal.…”

“…Due to the low thickness of about 1.25 nm for each layer, the effective ϵ med experienced by the particle is the average of the permittivity of the polymer cover and of the adjacent air. The stepwise addition of thin polymer layers then leads to an increase of the effective ϵ med , which in turn shifts the plasmon resonance. , We fabricated a separate sample for each cover thickness. This method allows a very fine-tuning of the exciton–plasmon overlap, much more precise and facile than the tuning by particle size variation.…”

“…In contrast, our experimental approach consists of shifting the plasmon resonance by adjusting the permittivity med of the particles' environment. The plasmon resonance is determined by the (dipole) polarizability α of the particle in this environment: [25,29]…”

“…This letter presents an experimental approach to determine the coupling regime of hybrid nanoparticles that successfully distinguishes the intermediate and strong coupling regimes. It describes an experimental procedure: a) to measure the real absorption spectrum of particle ensembles, and b) to determine the anticrossing relation without nanoparticle size variation, but via shifting the plasmon resonance by layer-by-layer deposition of polyelectrolytes [25]. The different coupling regimes are illustrated by two core-shell nanoparticle systems, gold nanorods and nanospeheres, which are both coated with an excitonic molecular shell.…”