Plasmons in strongly coupled metallic nanostructures.

This review provides a perspective on the recent developments in the transmission of light through subwavelength apertures in metal films. The main focus is on the phenomenon of extraordinary optical transmission in periodic hole arrays, discovered over a decade ago. It is shown that surface electromagnetic modes play a key role in the emergence of the resonant transmission. These modes are also shown to be at the root of both the enhanced transmission and beaming of light found in single apertures surrounded by periodic corrugations. This review describes both the theoretical and experimental aspects of the subject. For clarity, the physical mechanisms operating in the different structures considered are analyzed within a common theoretical framework. Several applications based on the transmission properties of subwavelength apertures are also addressed.

http://digital.csic.es/bitstream/10261/47904/1/Light%20passing.pdf

Light passing through subwavelength apertures

Spherical silicon nanoparticles with sizes of a few hundreds of nanometers represent a unique optical system According to theoretical predictions based on Mie theory they can exhibit strong magnetic resonances in the visible spectral range The basic mechanism of excitation of such modes inside the nanoparticles is very similar to that of split-ring resonators, but with one important difference that silicon nanoparticles have much smaller losses and are able to shift the magnetic resonance wavelength down to visible frequencies We experimentally demonstrate for the first time that these nanoparticles have strong magnetic dipole resonance, which can be continuously tuned throughout the whole visible spectrum varying particle size and visually observed by means of dark-field optical microscopy These optical systems open up new perspectives for fabrication of low-loss optical metamaterials and nanophotonic devices

Magnetic light

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

1. Health care is a human right. 2. The care of the individual is at the center of health care, but the whole system needs to work to improve the health of populations. 3. The health care system must treat illness, alleviate suffering and disability, and promote health. 4. Cooperation with each other, those served, and those in other sectors is essential for all who work in health care. 5. All who provide health care must work to improve it. 6. Do no harm.

https://www.journalacs.org/article/S1072-7515(00)00768-7/pdf

Is this a practical approach

Noble metal films deposited over two-dimensional arrays of polystyrene nanospheres constitute a confirmed class of efficient and cost-effective substrates for surface enhanced Raman scattering (SERS). In this paper, we perform scanning confocal SERS microscopy to investigate the spatial (lateral) variations of the SERS enhancements on gold films over nanospheres (AuFoN) substrates. By constructing SERS imaging maps with a resolution down to the diffraction limit, the local SERS efficiency is found to vary on two different scales. First, the local SERS efficiency is periodically modulated (intensity ratios of 2−3) by the periodic AuFoN surface topography (as demonstrated by correlation with atomic force microscopy imaging of the same sample area); second, randomly distributed SERS hot-spots are observed, at which the SERS intensity is 1 to 2 orders of magnitude larger than at adjacent regions. Furthermore, these hot-spots exhibit fluctuating behavior, characteristic of single-molecule SERS sensitivity. The...

Mapping the SERS Efficiency and Hot-Spots Localization on Gold Film over Nanospheres Substrates

High-sensitivity strain gauges based on single wires of close-packed 14 nm colloidal gold nanoparticles are obtained by a novel variant of convective self-assembly (CSA). This CSA mode named stop-and-go CSA enables the fabrication of nanoparticle wires only a few micrometers wide, separated by distances that can be easily tuned over tens to hundreds of micrometers. Nanoparticle wires are obtained in a single step by direct deposition of nanoparticles from suspensions onto flexible polyethylene terephthalate films, without any lithographic prepatterning. When connected between two electrodes, such single nanoparticle wires function as miniature resistive strain gauges. The high sensitivity, repeatability, and robustness demonstrated by these single-wire strain gauges make them extremely promising for integration into micro-electromechanical systems or for high-resolution strain mapping.

High-Sensitivity Strain Gauge Based on a Single Wire of Gold Nanoparticles Fabricated by Stop-and-Go Convective Self-Assembly

Spherical silicon nanoparticles were prepared by laser ablation of a single crystal Si wafer immersed in 95% ethanol with a pulse duration shorter than the time of electron−phonon relaxation (from 35 to 900 fs). The size distribution depends on the pulse duration as well as the width of the size distribution, which increases with the increase of the laser pulse duration. High resolution transmission electron microscopy performed on 20−40 nm particles showed polycrystalline particles made up mainly of silicon (α-Si) crystallites with the diamond structure and in some cases cubic silicon carbide (SiC) inclusions. Electron energy loss spectroscopy data on the large particles are very similar to bulk Si. Raman analysis extended to small frequencies showed a downshift and an asymmetrical broadening of the first-order Si optical peak with respect to bulk Si in good agreement with a spatial confinement in 5−10 nm crystallites. The photoluminescence spectra present a maximum of emission band at about 640 nm.

Silicon Nanoparticles Produced by Femtosecond Laser Ablation in Ethanol: Size Control, Structural Characterization, and Optical Properties

High-sensitivity resistive strain gauges based on electron tunneling in assemblies of gold colloidal nanoparticles are fabricated and characterized. The active area of these strain gauges consists in well-defined arrays of parallel, few micrometer wide wires of close-packed 18 nm gold nanoparticles. These nanoparticle wires are obtained by convective self-assembly (CSA) on flexible polyethylene terephtalate substrates, without any lithographic prepatterning. The fine control over the thickness and the width of the nanoparticle wires through the substrate temperature and the meniscus speed during the CSA process allows demonstrating the strong impact of the dimensionality (2D or 3D) of the nanoparticle assembly on the strain gauge sensitivity. Wires made of a single monolayer of nanoparticles turn out to give strain gauges about three times more sensitive than those made of multilayers. This work shows that the simplicity and versatility of convective self-assembly over other alternative methods make this ...

Monolayered Wires of Gold Colloidal Nanoparticles for High-Sensitivity Strain Sensing

Surface-enhanced Raman spectroscopy (SERS) is a technique that has become widely used for identifying and providing structural information about molecular species in low concentration. There is an ongoing interest in finding optimum particle size, shape and spatial distribution for optimizing the SERS substrates and pushing the sensitivity toward the single-molecule detection limit. This work reports the design of a novel, biocompatible SERS substrate based on small clusters of anisotropic silver nanoparticles embedded in a film of chitosan biopolymer. The SERS efficiency of the biocompatible film is assessed by employing Raman imaging and spectroscopy of adenine, a significant biological molecule. By combining atomic force microscopy with SERS imaging we find that the chitosan matrix enables the formation of small clusters of silver nanoparticles, with junctions and gaps that greatly enhance the Raman intensities of the adsorbed molecules. The study demonstrates that chitosan-coated anisotropic silver nanoparticle clusters are sensitive enough to be implemented as effective plasmonic substrates for SERS detection of nonresonant analytes at the single-molecule level.

https://iopscience.iop.org/article/10.1088/0957-4484/23/5/055501/pdf

Cosmin Farcau

Papers

Mapping the SERS Efficiency and Hot-Spots Localization on Gold Film over Nanospheres Substrates

High-Sensitivity Strain Gauge Based on a Single Wire of Gold Nanoparticles Fabricated by Stop-and-Go Convective Self-Assembly

Silicon Nanoparticles Produced by Femtosecond Laser Ablation in Ethanol: Size Control, Structural Characterization, and Optical Properties

Monolayered Wires of Gold Colloidal Nanoparticles for High-Sensitivity Strain Sensing

Chitosan-coated anisotropic silver nanoparticles as a SERS substrate for single-molecule detection.