A composite material that leads to self organization of mesogen-coated gold nanospheres is synthesized and shows enhanced anisotropic optical properties due to synergistic effects of the mesogens intrinsic birefringence and its ability to drive the self-assembly process into highly anisotropic architectures with densely packed nanospheres. Such nanoengineered matter sustains a response beyond that achievable by its individual constituents, i.e., a metamaterial.

The self-assembly of nanoparticles into hierarchical architectures is currently attracting a lot of interest due to their potential applications in a wide range of fields like nanophotonics, nanoelectronics or catalysis. In the present chapter, we discuss the potential of metal nanospheres for the bottom-up fabrication of optical metamaterials. Controlling the spatial arrangement of the nanoparticles in these composites offers a promising route to engineer unique optical responses originating from their collective plasmonic resonance. Here we explore experimentally how different types of NP arrangements can give rise to distinct macroscopic effective properties, including both electric and magnetic optical responses. For each of the structures investigated, we propose a brief overview of the current state-of-the-art of the appropriate bottom-up fabrication methods and analyze their optical properties in details. First, the optical constants of “bulk” amorphous nanoparticle metamaterials are investigated by ellipsometry, demonstrating that controlling the nanoparticle filling fraction provides an efficient route to tune the metamaterial permittivity. As an example of a potential application, the realization of a hybrid plasmonic Bragg mirror is discussed. Finally, we focused on the fabrication and characterization of dense spherical nanoclusters that can sustain a magnetic response at optical frequencies. In doing so, we demonstrate the possibility to engineer the permeability of nanocluster-based metamaterials, thereby opening interesting perspectives for the realization of isotropic negative index materials operating in the visible.

An invisibility cloak has been designed, realized and characterized. The cloak hides free-standing sub-wavelength three-dimensional objects at the short wavelength edge of the visible spectrum. By a bottom-up approach the cloak was self-assembled around the object. Such fabrication approach constitutes a further important step towards real world applications of cloaking; leaving the realm of curiosity. The cloak and the way it was fabricated opens an avenue for many spectacular nanooptical applications such as non-disturbing sensors and photo-detectors, highly efficient solar cells, or optical nanoantenna arrays with strongly suppressed cross-talk to mention only a few. Our results rely on the successful combination of concepts from various disciplines, i.e. chemistry, material science and plasmonics. Consequently, this work will stimulate these fields by unraveling new paths for future research.

Nowadays for the sake of convenience most plasmonic nanostructures are fabricated by top-down nanofabrication technologies. This offers great degrees of freedom to tailor the geometry with unprecedented precision. However, it often causes disadvantages as well. The structures available are usually planar and periodically arranged. Therefore, bulk plasmonic structures are difficult to fabricate and the periodic arrangement causes undesired effects, e.g., strong spatial dispersion is observed in metamaterials. These limitations can be mitigated by relying on bottom-up nanofabrication technologies. There, self-assembly methods and techniques from the field of colloidal nanochemistry are used to build complex functional unit cells in solution from an ensemble of simple building blocks, i.e., in most cases plasmonic nanoparticles. Achievable structures are characterized by a high degree of nominal order only on a shortrange scale. The precise spatial arrangement across larger dimensions is not possible in most cases; leading essentially to amorphous structures. Such self-assembled nanostructures require novel analytical means to describe their properties, innovative designs of functional elements that possess a desired near-and far-field response, and entail genuine nanofabrication and characterization techniques. Eventually, novel applications have to be perceived that are adapted to the specifics of the self-assembled nanostructures. This review shall document recent progress in this field of research. Emphasis is put on bottom-up amorphous metamaterials. We document the state-of-the-art but also critically assess the problems that have to be overcome.

The electromagnetic response of metamaterial can be managed by combining resonances and interferences of different materials and on different lengths scales. In our contribution we study composite metamaterials containing resonant plasmonic metallic nanoparticles that show organization. The material bases its non-conventional properties on short distance self-organization by mesogens that form a liquid crystal material. We analyze the properties of such materials with a structural model containing organized nanoparticles. Theoretically insight of the electromagnetic properties is provided and we give details on their optical properties.

In a recent comment arxiv:1310.1503 Miller et al. noted that a cloak we previously presented (Scientific Reports 3, 2328) that exploits a scattering cancellation technique to render an optically small dielectric particle invisible suffers from increased extinction. According to Miller et al. this disqualifies the terminology of a cloak. We concur with the crux of the comment but wish to stress that we never claimed nor suggested a reduction in extinction. A scattering cancellation cloak cancels scattering. The issue, therefore, seems to be whether the structure should be called a cloak or not. We understand a cloaked object as an object that is not perceived by an external observer. We argue that optically small particles are much easier seen in a scattering configuration whereas it is difficult to perceive them in extinction; providing justification to the terminology as used.

A first characterization of newly realized micro periodic structures including metallic nanoparticles is reported. The original mixture, generally utilized for the realization of polymer-liquid-crystal-polymer-slices gratings (POLICRYPS), has been enriched with a small amount of silver nanoparticles. The obtained structure shows a spectral response that strongly depends on the polarization of the probing light. These first structures are oriented to the fabrication of devices with metamaterial properties.

We introduce a novel bottom-up approach to fabricate by self assembly a metamaterial from metallic nanoparticles in a two-step process. In the first step, a metamaterial made of densely packed silver nanoparticles is required. The material dispersion with increasing nanoparticle densities, from dispersed to randomly packed nanoparticles, was measured by spectroscopic ellipsometry, demonstrating high permittivity values in the visible. In the second step, this material was used to prepare spherical clusters by a method based on oil-in-water emulsion. The optical properties of these clusters were equally investigated by spectroscopic means. Comparisons with rigorous numerical simulations clearly indicate that, depending on the cluster size, their spectral response can be unambiguously associated with the excitation of a magnetic dipole resonance. As a consequence, such spherical clusters are promising building blocks for future metamaterials possessing a magnetic response in the visible range. (C) 2012 Optical Society of America

We investigate experimentally metallic nanoparticle composites fabricated by bottom-up techniques as potential candidates for optical metamaterials. Depending on the plasmonic resonances sustained by individual NPs and their nanoscale organization into larger meta-atoms, various properties might emerge. Here, the focus of our contribution is on the fabrication and optical characterization of silver NP clusters with a spherical shape. We start with the characterisation of the "bulk" dielectric constants of silver NP inks by spectroscopic ellipsometry for different nanoparticle densities (i.e from strongly diluted dispersions to solid randomly packed films). The inks are then used to prepare spherical nanoparticle clusters by an oil-in water emulsion technique. The study of their optical properties demonstrates their ability to support Mie resonances in the visible. These resonances are associated with the excitation of a magnetic dipole, which constitutes a prerequisite to the realization of metamaterials with negative permeability.

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.

In this work, the physical and optical properties of gold nanoparticles functionalized with laterally grafted nematic ligands were studied. In particular, the influence of the nanoparticle size on the mesomorphic behavior and optical properties of the composite was investigated. To obtain an in-plane alignment of the mesogens, thin oriented films were prepared by shearing and characterized by polarized absorption spectroscopy. While the sub-2nm nanoparticle thin film only showed birefringence due to a strong damping of the plasmon resonance, larger NPs exhibit a strong dichroism with a shift of the NP plasmon resonance by about 50 nm. These results demonstrate the possibility to obtain a bulk NP metamaterial with tunable plasmonic properties by chemical engineering of the NP ligands.

We report on the fabrication and characterization of a micro periodic structure realized in soft-composite materials containing metallic nanoparticles. The particles are used to infiltrate a passive polymer template realized by combining a holographic curing setup and a microfluidic etching process. In other experiments, small amounts of nanoparticles are dissolved in the original mixture utilized for the realization of polymer-liquid-crystal-polymer-slices gratings (POLICRYPS); this enables to fabricate POLICRYPS-like structures showing novel electromagnetic properties. Obtained structures are characterized in term of impinging probe polarization in the UV/visible range. Correlation between the optical response and external perturbations (electric field, temperature) is also reported. These first attempts are oriented to the fabrication of devices with tunable metamaterial properties.

The transmission of light through a hole was thought to be very weak when all of the lateral dimensions of the hole were much smaller than the wavelength of the light.The discovery of enhanced transmission has changed this view, raising fundamental questions and leading to many practical applications ranging from photonics to chemical sensing. A key feature of the transmission process is the activation of surface plasmons. In this article, we review the present understanding of this phenomenon and illustrate its potential through several examples of applications in different fields.

We present a material concept based on nanoparticles clusters sandwiched between polymer layers and arranged in a thin film stack to combine. In this way we achieved to combine plasmonic resonances and multilayer interference and realized thin film bulk materials with unconventional optical properties. The technology is based on spin coating and polymerization and leads to high quality films with specific optical features. Samples with a variety of parameters were prepared and characterized by angle resolved spectroscopy. We present details how cluster concentration and multilayer interference influence the optical properties if such metamaterials.

We discuss our latest achievements in fabricating, characterizing and theoretically understanding metamaterials and plasmonic elements that are made from closely packed metallic nanoparticles and which are fabricated with bottom-up approaches that rely on self-organization.

Keywords: Nanophotonics, Plasmonics Reference EPFL-CONF-175255 Record created on 2012-02-28, modified on 2017-05-10

We investigate numerically the effect of a finite metal film thickness on the propagation characteristics of the channel Plasmon polariton (CPP) and wedge plasmon polariton (WPP) modes, both in a symmetric and asymmetric environment. We observe that decreasing the metal thickness results in an improvement of the field localization near the groove tip and an increase of the losses for both types of mode. This behavior stems from the typical symmetric charge distribution of both modes across the metal film. When considering an asymmetric dielectric environment, the CPP mode is found to evolve into short range Plasmon modes propagating along the groove walls, in contrast to the WPP mode which remains essentially confined at the tip apex. These results can be useful to tailor the properties of such plasmon modes, using the metal thickness as the variable parameter.

Keywords: Nanophotonics, Plasmonics Reference EPFL-CONF-175247 Record created on 2012-02-28, modified on 2017-05-10

We detail the role of single nanometric apertures milled in a gold film to enhance the fluorescence emission of Alexa Fluor 647 molecules. Combining fluorescence correlation spectroscopy and lifetime measurements, we determine the respective contributions of excitation and emission in the observed enhanced fluorescence. We characterize a broad range of nanoaperture diameters from 80 to 310 nm, and highlight the link between the fluorescence enhancement and the local photonic density of states. These results are of great interest to increase the effectiveness of fluorescence-based single molecule detection and to understand the interaction between a quantum emitter and a nanometric metal structure.

The excitation of surface plasmon polaritons (SPP) by focusing a laser beam on single subwavelength holes opened in a thin gold film is studied both experimentally and theoretically. By means of leakage radiation microscopy, quantitative measurements of the light-SPP coupling efficiency are performed for holes with different sizes and shapes. The system is studied theoretically by using a modal expansion method to calculate the fraction of the incident energy which is scattered by the hole into a surface plasmon. We demonstrate that a single subwavelength hole can be used to generate SPP with an efficiency up to 28%.