Optical properties of nanostructured metal films
TL;DR: The reflection spectra of the films at normal incidence were recorded as a function of film thickness and the spectra correlated with the local visual appearance of the film and the surface structure from SEM, showing a single reflectivity dip at a wavelength just below the sphere diameter consistent with surface-plasmon grating-like behaviour.
Abstract: Nanostructured metal films of platinum, gold and silver up to 675 nm thick we prepared by electrochemical deposition through templates of 700 nm diameter polystyrene spheres assembled as hexagonal close packed monolayer on an evaporated gold surface followed by removal of the template by dissolution in tetrahydrofuran. The reflection spectra of the films at normal incidence were recorded as a function of film thickness and the spectra correlated with the local visual appearance of the film and the surface structure from SEM. For thin films, below one quarter sphere height, the spectra show a single reflectivity dip at a wavelength just below the sphere diameter consistent with surface-plasmon grating-like behaviour. For the thicker films several reflectivity dips are observed which move towards longer wavelength with increasing film thickness. This behaviour is shown to be consistent with a model in which light reflected from the top of the structure interferes with light reflected from within the spherical segment cavities in the film.
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TL;DR: This work has shown that coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface can be associated with surface plasmons, which have potential applications in miniaturized optical devices, sensors, and photonic circuits.
Abstract: Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8
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1,219 citations
TL;DR: A review of the plasmon-enhanced Raman spectroscopy (PERS) field can be found in this paper, where a new generation of hotspots that are generated from hybrid structures combining PERS-active nanostructures and probe materials are discussed.
Abstract: Since 2000, there has been an explosion of activity in the field of plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In this Review, we explore the mechanism of PERS and discuss PERS hotspots — nanoscale regions with a strongly enhanced local electromagnetic field — that allow trace-molecule detection, biomolecule analysis and surface characterization of various materials. In particular, we discuss a new generation of hotspots that are generated from hybrid structures combining PERS-active nanostructures and probe materials, which feature a strong local electromagnetic field on the surface of the probe material. Enhancement of surface Raman signals up to five orders of magnitude can be obtained from materials that are weakly SERS active or SERS inactive. We provide a detailed overview of future research directions in the field of PERS, focusing on new PERS-active nanomaterials and nanostructures and the broad application prospect for materials science and technology. Assisted by rationally designed novel plasmonic nanostructures, surface-enhanced Raman spectroscopy has presented a new generation of analytical tools (that is, tip-enhanced Raman spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy) with an extremely high surface sensitivity, spatial resolution and broad application for materials science and technology.
1,158 citations
TL;DR: The concept of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) in detail is introduced in detail because it overcomes the long-standing limitations of material and morphology generality encountered in traditional SERS.
Abstract: Core–shell nanoparticles are at the leading edge of the hot research topics and offer a wide range of applications in optics, biomedicine, environmental science, materials, catalysis, energy, and so forth, due to their excellent properties such as versatility, tunability, and stability. They have attracted enormous interest attributed to their dramatically tunable physicochemical features. Plasmonic core–shell nanomaterials are extensively used in surface-enhanced vibrational spectroscopies, in particular, surface-enhanced Raman spectroscopy (SERS), due to the unique localized surface plasmon resonance (LSPR) property. This review provides a comprehensive overview of core–shell nanoparticles in the context of fundamental and application aspects of SERS and discusses numerous classes of core–shell nanoparticles with their unique strategies and functions. Further, herein we also introduce the concept of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) in detail because it overcomes the long...
741 citations
TL;DR: In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self-assembly.
Abstract: Photonic crystals have proven their potential and are nowadays a familiar concept. They have been approached from many scientific and technological flanks. Among the many techniques devised to implement this technology self-assembly has always been one of great popularity surely due to its ease of access and the richness of results offered. Self-assembly is also probably the approach entailing more materials aspects owing to the fact that they lend themselves to be fabricated by a great many, very different methods on a vast variety of materials and to multiple purposes. To these well-known material systems a new sibling has been born (photonic glass) expanding the paradigm of optical materials inspired by solid state physics crystal concept. It is expected that they may become an important player in the near future not only because they complement the properties of photonic crystals but because they entice the researchers' curiosity. In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self-assembly.
606 citations
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TL;DR: The reflectance and the phase change on reflection from semiconductor-metal interfaces (including the case of metallic multilayers) can be accurately described by use of the proposed models for the optical functions of metallic films and the matrix method for multilayer calculations.
Abstract: We present models for the optical functions of 11 metals used as mirrors and contacts in optoelectronic and optical devices: noble metals (Ag, Au, Cu), aluminum, beryllium, and transition metals (Cr, Ni, Pd, Pt, Ti, W). We used two simple phenomenological models, the Lorentz-Drude (LD) and the Brendel-Bormann (BB), to interpret both the free-electron and the interband parts of the dielectric response of metals in a wide spectral range from 0.1 to 6 eV. Our results show that the BB model was needed to describe appropriately the interband absorption in noble metals, while for Al, Be, and the transition metals both models exhibit good agreement with the experimental data. A comparison with measurements on surface normal structures confirmed that the reflectance and the phase change on reflection from semiconductor-metal interfaces (including the case of metallic multilayers) can be accurately described by use of the proposed models for the optical functions of metallic films and the matrix method for multilayer calculations.
3,629 citations
TL;DR: In this article, the spontaneous crystallization of monodisperse silica spheres into close-packed arrays is exploited for optical characterization of planar materials with diffractive optical properties.
Abstract: Materials whose dielectric constant varies spatially with submicrometer periodicity exhibit diffractive optical properties which are potentially valuable in a number of existing and emerging applications. Here, such systems are fabricated by exploiting the spontaneous crystallization of monodisperse silica spheres into close-packed arrays. By reliance on a vertical deposition technique to pack the spherical colloids into close-packed silica−air arrays, high quality samples can be prepared with thicknesses up to 50 μm. These samples are planar and thus suitable for optical characterization. Scanning electron microscopy (SEM) of these materials illustrates the close-packed ordering of the spherical colloids in planes parallel to the substrate; cross-sectional SEM micrographs of the arrays as well as optical methods are used to measure sample thickness and uniformity. Normal-incidence transmission spectra in the visible and near-infrared regions show distinct peaks due to diffraction from the colloidal layer...
1,997 citations
TL;DR: By assembling a thin layer of colloidal spheres on a silicon substrate, this work can obtain planar, single-crystalline silicon photonic crystals that have defect densities sufficiently low that the bandgap survives.
Abstract: Photonic bandgap crystals can reflect light for any direction of propagation in specific wavelength ranges1,2,3. This property, which can be used to confine, manipulate and guide photons, should allow the creation of all-optical integrated circuits. To achieve this goal, conventional semiconductor nanofabrication techniques have been adapted to make photonic crystals4,5,6,7,8,9. A potentially simpler and cheaper approach for creating three-dimensional periodic structures is the natural assembly of colloidal microspheres10,11,12,13,14,15. However, this approach yields irregular, polycrystalline photonic crystals that are difficult to incorporate into a device. More importantly, it leads to many structural defects that can destroy the photonic bandgap16,17. Here we show that by assembling a thin layer of colloidal spheres on a silicon substrate, we can obtain planar, single-crystalline silicon photonic crystals that have defect densities sufficiently low that the bandgap survives. As expected from theory, we observe unity reflectance in two crystalline directions of our photonic crystals around a wavelength of 1.3 micrometres. We also show that additional fabrication steps, intentional doping and patterning, can be performed, so demonstrating the potential for specific device applications.
1,649 citations
TL;DR: Three-dimensional crystals of air spheres in titania with radii between 120 and 1000 nanometers were made by filling the voids in artificial opals by precipitation from a liquid-phase chemical reaction and subsequently removing the original opal material by calcination and are a new class of photonic band gap crystals for the optical spectrum.
Abstract: Three-dimensional crystals of air spheres in titania (TiO 2 ) with radii between 120 and 1000 nanometers were made by filling the voids in artificial opals by precipitation from a liquid-phase chemical reaction and subsequently removing the original opal material by calcination. These macroporous materials are a new class of photonic band gap crystals for the optical spectrum. Scanning electron microscopy, Raman spectroscopy, and optical microscopy confirm the quality of the samples, and optical reflectivity demonstrates that the crystals are strongly photonic and near that needed to exhibit band gap behavior.
1,532 citations
TL;DR: The examples presented demonstrate the compositional diversity possible with this technique and could have applications in areas ranging from quantum electronics to photocatalysis to battery materials.
Abstract: Titania, zirconia, and alumina samples with periodic three-dimensional arrays of macropores were synthesized from the corresponding metal alkoxides, using latex spheres as templates. In a fast, single-step reaction, the monomeric alkoxide precursors permeate the array of bulk polystyrene spheres and condense in air at room temperature. Close packed, open-pore structures with 320- to 360-nanometer voids are obtained after calcination of the organic component at 575 degreesC. The examples presented demonstrate the compositional diversity possible with this technique. The resulting highly structured ceramics could have applications in areas ranging from quantum electronics to photocatalysis to battery materials.
1,426 citations