Templated Techniques for the Synthesis and Assembly of Plasmonic Nanostructures

Plasmonic clusters can support Fano resonances, where the line shape characteristics are controlled by cluster geometry. Here we show that clusters with a hemicircular central disk surrounded by a circular ring of closely spaced, coupled nanodisks yield Fano-like and non-Fano-like spectra for orthogonal incident polarization orientations. When this structure is incorporated into an uniquely broadband, liquid crystal device geometry, the entire Fano resonance spectrum can be switched on and off in a voltage-dependent manner. A reversible transition between the Fano-like and non-Fano-like spectra is induced by relatively low (∼6 V) applied voltages, resulting in a complete on/off switching of the transparency window.

A plasmonic Fano switch.

Revolutionary developments in the fabrication of nanosized particles have created enormous expectations in the last few years for the use of such materials in areas such as medical diagnostics and drug-delivery, and in high-tech devices. By its very nature, nanotechnology is of immense academic and industrial interest as it involves the creation and exploitation of materials with structural features in between those of atoms and bulk materials, with at least one dimension limited to between 1 and 100 nm. Most importantly, the properties of materials with nanometric dimensions are, in most instances, significantly different from those of atoms or bulk materials. Research efforts geared towards new synthetic procedures for shape and size-uniform nanoscale building blocks as well as efficient self-assembly protocols for manipulation of these building blocks into functional materials has created enormous excitement in the field of liquid crystal research. Liquid crystals (LCs) by their very nature are suitable candidates for matrix-guided synthesis and self-assembly of nanoscale materials, since the liquid crystalline state combines order and mobility at the molecular (nanoscale) level. Based on selected relevant examples, this review attempts to give a short overview of current research efforts in LC-nanoscience. The areas addressed in this review include the synthesis of nanomaterials using LCs as templates, the design of LC nanomaterials, self-assembly of nanomaterials using LC phases, defect formation in LC-nanoparticle suspensions, and potential applications. Despite the seeming diversity of these research topics, this review will make an effort to establish logical links between these different research areas.

Nanoparticles in Liquid Crystals: Synthesis, Self-Assembly, Defect Formation and Potential Applications

Molecular sensors based on scattering spectroscopy of single gold nanoparticles can be improved three-fold by the use of gold nanoshells instead of solid gold nanoparticles. The particle plasmon resonance responds more sensitively to changes in the environment, the biological spectral window is accessible, and the scattering spectra show sharper resonances. In particular, we focus our discussion on the narrow homogeneous line width of only 180 meV.

Gold nanoshells improve single nanoparticle molecular sensors

Financial support from the Spanish Ministry of Science and Education (NAN2004-09195-C04-01 and MAT2005-05524-C02-01), and UE (NoE-Phoremost) are acknowledged.

Plasmonic Au/Co/Au Nanosandwiches with Enhanced Magneto-optical Activity†

A concept to electrically control the scattering of light is introduced. The idea is to embed noble metal nanoparticles in an electro-optical material such as a liquid crystal in order to induce a spectral shift of the particle plasmon resonance by applying an electric field. Light scattering experiments on single gold nanoparticles show that spherically shaped nanoparticles become optically spheroidal when covered by an anisotropic liquid crystal. The two particle plasmon resonances of the optically spheroidal gold nanoparticles can be spectrally shifted by up to 50 meV when electric fields of more than 10 kV/cm are applied.

Electrically controlled light scattering with single metal nanoparticles

Summary form only given. Electrically controlled switching of light is a key ingredient in modern optical communication and display systems. Up to now such optoelectronic scattering devices do not take advantage of noble metal nanoparticles, which are known to act as strong light scatterers when the frequency of the light is in the spectral range of the particle plasmon resonance. This resonance frequency not only depends on particle properties but also on the refractive index of the surrounding medium. We report on electrically controllable light scattering where electric fields are used to spectrally shift the particle plasmon resonance of spherical noble metal nanoparticles. The basic idea is that the electric field alters the refractive index of the embedding dielectric matrix. For this purpose, spherical noble metal nanoparticles are incorporated in a liquid crystal. An applied electric field aligns the liquid crystal molecules leading to an anisotropic refractive index and thus to a polarization dependent spectral shift of the particle plasmon. Light scattering spectra of an individual gold nanoparticle taken with a dark-field microscope setup are shown.

Electrically controlled light scattering

We report on electrically controlled light scattering where electric fields are used to spectrally shift the plasmon resonance of spherical noble metal nanoparticles. Applying external electric fields to the liquid crystal induces a reorientation of the molecules and therefore a reorientation of the anisotropy. This results in a field-induced shift of the plasmon peak , which may be useful for the realization of novel optoelectronic switching devices.

http://ieeexplore.ieee.org/iel5/9180/29127/01313586.pdf

H. von Poschinger

Papers

Electrically controlled light scattering with single metal nanoparticles

Electrically controlled light scattering

Electrically controlled light scattering with metal nanoparticles