Metal Nanoparticle Clusters Research Articles

Spontaneous emission of a two-level atom placed within clusters of metallic nanoparticles

We present calculations of the electromagnetic local density of states and of thecorresponding spontaneous emission rate for a two-level atom placed near a metallicDrude-type nanosphere as well as within clusters of nanospheres. Our calculationsare based on a dyadic Green’s function formalism within the framework of themultiple-scattering method. We examine the convergence of the above quantitiesin terms of the angular expansion of the electromagnetic field. The frequencyand spatial dependence of the local density of states and of the correspondingspontaneous emission rate is also studied by depicting the relevant spectra for differentcluster sizes and configurations. We have found, in particular, that within thefrequency region of the surface–plasmon resonances the spontaneous emissionrate is influenced by the near field of the spheres which are closer to the atom,rendering the contribution of the farthest spheres almost negligible. Depending on thedistance from the surface of the sphere(s) the spontaneous emission rate in thecluster assumes values which can be several orders of magnitude larger than thecorresponding rate in a vacuum. Finally, we examine the differences which arise when anexperimentally available dielectric function is employed instead of the Drude type.

Plasmonic nanoclusters: a path towards negative-index metafluids

We introduce the concept of metafluids-liquid metamaterials based on clusters of metallic nanoparticles which we will term Artificial Plasmonic Molecules (APMs). APMs comprising four nanoparticles in a tetrahedral arrangement have isotropic electric and magnetic responses and are analyzed using the plasmon hybridization (PH) method, an electrostatic eigenvalue equation, and vectorial finite element frequency domain (FEFD) electromagnetic simulations. With the aid of group theory, we identify the resonances that provide the strongest electric and magnetic response and study them as a function of separation between spherical nanoparticles. It is demonstrated that a colloidal solution of plasmonic tetrahedral nanoclusters can act as an optical medium with very large, small, or even negative effective permittivity, epsilon(eff), and substantial effective magnetic susceptibility, Chi(eff) = mu(eff) -1, in the visible or near infrared bands. We suggest paths for increasing the magnetic response, decreasing the damping, and developing a metafluid with simultaneously negative epsilon(eff) and mu(eff).

Self‐Assembly of Nanoparticles on Live Bacterium: An Avenue to Fabricate Electronic Devices

Lysine-capped gold nanoparticles can be electrostatically assembled on the surface of Bacillus cerius, a Gram-Positive bacterium. The conductivity of the “gold-plated” bacteria assembly immobilized between electrodes is a function of the humidity experienced by the nanoparticles.

On the theory of optical properties of fractal clusters

A theory of optical properties of clusters of spherical metal nanoparticles characterized by an arbitrary size distribution is developed in a quasi-static dipole approximation. The equations for coupled dipoles and general relations are formulated in terms of reduced dipole moments. It is shown that the dipole resonant frequencies and amplitudes, the absorbed power, and the acting-field magnitudes strongly depend on the ratios of particle radii in a cluster. Properties of linear, planar, and three-dimensional systems are examined.