A theoretical framework to analyze the optical properties of amorphous metamaterials made from meta-atoms
which are amenable for a fabrication with bottom-up technologies is introduced. The achievement of an isotropic
magnetic resonance in the visible is investigated by suggesting suitable designs for the meta-atoms. Furthermore,
two meta-atoms are discussed in detail that were fabricated by self-assembling plasmonic nanoparticles using
techniques from the field of colloidal nanochemistry. The metamaterials are experimentally characterized by
spectroscopic means and the excitation of the magnetic dipole moment is clearly revealed. Advantages and
disadvantages of metamaterials made from such meta-atoms are discussed.
Self-assembly techniques are used to build complex amorphous structures from plasmonic particles. The assembly
makes use of surface chemistry and intermolecular interactions between surfaces, surfactants, polymers and particles.
The resulting two- or three-dimensional structures have optical properties that derive from the coupling between
particles. A high control of the structural parameters on the nanometer scale can easily be achieved. In contrast to top-down
techniques relatively large areas can be prepared in a versatile manner thus paving the way to applications as
functional devices. Several structures are discussed such as layered arrays of gold nanoparticles, core-shell structures and
hierarchical structures. The optical properties of these structures are also presented and compared with simulations.
Some of the structures are of interest for plasmonic cloaking whereas other might find applications as substrates for
sensing by surface-enhanced Raman spectroscopy.
This paper is dedicated to the study of plasmonic cloaking, based on the use of appropriate core-shell systems
that may act as a cloaking devices for a finite range of frequencies. This cluster consists of an amorphous
arrangement of metallic (gold or silver) and/or polaritonic nano-particles, which could be approximated in the
quasistatic limit by an effective medium, having interesting properties such as a negative or very low permittivity
and/or permeability in the optical domain with moderate losses. We first derive the effective properties of a shell
made of such small spheres using the Maxwell-Garnett and Clausius-Mosotti formulas. We then numerically
show that a dielectric core sphere is almost made invisible at optical frequencies with a scattering reduction of
more than 70 percent. We finally derive some analytical expressions that we have compared to rigorous numerical