Interesting plasmonic effects can arise from the combination of small polarisable particles with graphene, related to surface plasmon-polaritons (SPPs) supported by the latter in the terahertz (THz) spectral range. The electromagnetic coupling between graphene SPPs and dipole moments of nanoparticles (NPs) deposited on top of it gives rise to optical properties that aren’t present in the individual components of this system. The NPs’ polarisability is renormalized due to the electromagnetic back action of the SPPs which are excited in graphene when an external propagating electromagnetic wave impinges on the particle. Moreover, beyond the usual dipole-dipole interaction, an indirect particle-particle coupling arises via polarisation charges induced on the graphene-covered interface by each particle – this indirect coupling oscillates with the interparticle distance. We derived coupled-dipole equations taking into account all these effects, allowing us to calculate an effective optical conductivity of the particles’ monolayer. One of the G+NPs system’s unique properties is a collective polariton mode, causing a considerable enhancement of the THz radiation absorption in graphene, while the reflection drops to nearly zero for a broad range of angles of incidence. The frequency of this resonant mode can be adjusted by changing the Fermi energy in graphene via electrostatic gating and therefore it can be used for electrically controlled reflection and transmission of THz radiation
We theoretically investigate the optical response of ensembles of polarizable metallic nanoparticles (NPs) that form (1) submonolayer films of particles adsorbed on a dielectric substrate, considered as two-dimensional (2-D) systems, and (2) thin three-dimensional (3-D) films, where NPs are embedded in a dielectric matrix. For system (1), the effect of NPs’ distance to the substrate is taken into account. In both cases, we find that short-range clustering leads to a broadening and a spectral shift of the absorption band related to the surface plasmon resonance (SPR) in individual NPs. We show that the clustering can help in achieving spectrally broad SPR bands, especially if NPs aggregate into fractal clusters, which can be interesting for some applications such as surface-enhanced Raman scattering. In particular, submonolayer films on NPs generated using the diffusion-limited aggregation algorithm produce sizable and spectrally broad absorption, which can be tuned to the visible range by choosing an appropriate capping and/or substrate material. Calculated results for thin 3-D films are compared with experimental data obtained for Au/TiO2 nanocomposite layers produced by reactive cosputtering.
KEYWORDS: Gold, Fractal analysis, Dielectrics, Particles, Transmittance, Absorption, Nanocomposites, Simulation of CCA and DLA aggregates, Nanoparticles, Surface plasmons
We theoretically investigate the optical response of ensembles of polarizable metallic nanoparticles (NPs) that form (i) submonolayer films considered as 2D systems, and (ii) thin 3D films where NPs are embedded in a dielectric matrix. In both cases we find that short-range clustering leads to a broadening and a spectral shift of the absorption band related to the surface plasmon resonance in inividual NPs. We show that clustering can help achieving spectrally broad surface plasmon resonance (SPR) bands, especially if NPs aggregate into fractal clusters, which can be interesting for some applications, such as SERS. In particular, submonolayer films on NPs generated using the dillusion-limited aggregation algorithm, produce sizable and spectrally broad absorption, which can be tuned to the visible range by choosing an appropriate substrate. Calculated results for thin 3D films are compared to experimental data obtained for Au=TiO2 nanocomposite layers produced by reactive co-sputtering
We present a flexible fluorescence lifetime imaging device which can be employed to scan large sample areas with a spatial resolution adjustable from many micrometers down to sub-micrometers and a temporal resolution of 20 picoseconds. Several different applications of the system will be presented including protein microarrays analysis, the scanning of historical samples, evaluation of solar cell surfaces and nanocrystalline organic crystals embedded in electrospun polymeric nanofibers. Energy transfer processes within semiconductor quantum dot superstructures as well as between dye probes and graphene layers were also investigated.
Non-radiative (Forster-type) energy transfer of an exciton between two quantum dots (QDs) plays an important role in artificial structures where semiconductor nanocrystal QDs play the role of building blocks. We theoretically study the effect of surrounding medium (e.g. dielectric substrate) on the transfer rate. Applying a simple model to describe the QDs, we demonstrate that the transfer rate can be strongly enhanced in the vicinity of a metal surface if the donor QD is excited in resonance with surface plasmons characteristic of this surface. Then the scaling law with the interdot distance becomes more complex than R-6 and the characteristic Forster radius can increase by an order of magnitude. We also show that transfer rate between two QDs is not exactly / R-6 even within the dipole-dipole approximation, in free space if the electron and hole in the dot are in the weak confinement regime
Optical response of a system of (nearly) identical polarizable particles, coupled by electromagnetic interactions is
studied theoretically addressing the following question: Is it possible to extract information concerning the spatial
correlations in the particles' positions from the experimentally measurable optical response of the system? The
relation between the spectral-dependent solutions of the coupled-dipole equations and the type and parameters of
the particle-particle correlation function in real space is analyzed. The physical system considered is a collection
of metallic nanoparticles distributed over a square or cubic lattice in a random-correlated way, relevant to metaldielectric
composites interesting for nanoplasmonics. We show that it is possible to propose a numerical criterium
that allows for conclusion concerning the degree of correlation in the particle positions using the (experimentally
measurable) extinction spectrum of the system.
Spectroscopy of light scattering on LO phonons confined in short-periodicical superlattices (SL) is known to besensitive to a small-scale structure existing on the interfaces [1 ]. Recently [2 ], we have developed a 1D latticedynamics model providing both mode shifts and the shape of the lines due to broadening of the interfaces. Simpleresults were obtained for two cases:
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