Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials1,2, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons3,4,5,6, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips7, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage8,9,10. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 µm, produced by growing silicon inside the voids of an opal template of close-packed silica spheres that are connected by small ‘necks’ formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.

Large-scale synthesis of a silicon photonic crystal with a complete three-dimensional bandgap near 1.5 micrometres

Porous carbons that are three-dimensionally periodic on the scale of optical wavelengths were made by a synthesis route resembling the geological formation of natural opal. Porous silica opal crystals were sintered to form an intersphere interface through which the silica was removed after infiltration with carbon or a carbon precursor. The resulting porous carbons had different structures depending on synthesis conditions. Both diamond and glassy carbon inverse opals resulted from volume filling. Graphite inverse opals, comprising 40-angstrom-thick layers of graphite sheets tiled on spherical surfaces, were produced by surface templating. The carbon inverse opals provide examples of both dielectric and metallic optical photonic crystals. They strongly diffract light and may provide a route toward photonic band-gap materials.

https://science.sciencemag.org/content/sci/282/5390/897.full.pdf

Carbon Structures with Three-Dimensional Periodicity at Optical Wavelengths

We describe the recent experimental progress in the control of spontaneous emission by manipulating optical modes with photonic crystals. It has been clearly demonstrated that the spontaneous emission from light emitters embedded in photonic crystals can be suppressed by the so-called photonic bandgap, whereas the emission efficiency in the direction where optical modes exist can be enhanced. Also, when an artificial defect is introduced into the photonic crystal, a photonic nanocavity is produced that can interact with light emitters. Cavity quality factors, or Q factors, of up to 2 million have been realized while maintaining very small mode volumes, and both spontaneous-emission modification (the Purcell effect) and strong-coupling phenomena have been demonstrated. The use of photonic crystals and nanocavities to manipulate spontaneous emission will contribute to the evolution of a variety of applications, including illumination, display, optical communication, solar energy and even quantum-information systems.

Spontaneous-emission control by photonic crystals and nanocavities

Rod-coil diblock copolymers in a selective solvent for the coil-like polymer self-organize into hollow spherical micelles having diameters of a few micrometers. Long-range, close-packed self-ordering of the micelles produced highly iridescent periodic microporous materials. Solution-cast micellar films consisted of multilayers of hexagonally ordered arrays of spherical holes whose diameter, periodicity, and wall thickness depended on copolymer molecular weight and composition. Addition of fullerenes into the copolymer solutions also regulated the microstructure and optical properties of the microporous films. These results demonstrate the potential of hierarchical self-assembly of macromolecular components for engineering complex two- and three-dimensional periodic and functional mesostructures.

https://science.sciencemag.org/content/sci/283/5400/372.full.pdf

Self-Assembly of Ordered Microporous Materials from Rod-Coil Block Copolymers

We report a strategy for the production of materials with structural hierarchy. The approach employs polymer microgels as templates for the synthesis of semiconductor, metal, or magnetic nanoparticles (NPs). We show that NPs with predetermined dimensions and size-dependent properties can be synthesized by using a very delicate balance between the reaction conditions, the composition and the structure of microgel templates, and the concentration of NPs in the microgel. Postheat treatment of microgels doped with semiconductor nanoparticles reduces NP polydispersity and allows control of their photoluminescence. Microgel templates are particularly beneficial in the synthesis of polymer microspheres heavily loaded with monodisperse superparamagnetic Fe3O4 NPs. Hybrid submicrometer-size microgels have promising potential applications in photonics, catalysis, and separation technologies.

Polymer microgels: reactors for semiconductor, metal, and magnetic nanoparticles.

In this letter, we investigate the optical properties of packed monodisperse silica submicron spheres by means of optical transmission measurements. The results are compatible with a three dimensional face centered cubic order in these solid structures. The lattice parameter of these structures, and therefore their optical properties, can be easily tuned through the sphere size (between 200 and 700 nm) thus covering the whole visible and near infrared spectrum.

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Photonic crystal properties of packed submicrometric SiO2 spheres

Here we present experimental evidence of the strong modification of the CdS photoluminescence when it is embedded in a SiO2 colloidal photonic crystal. When the emitted light matches a forbidden photonic band in the matrix, inhibition of the semiconductor photoluminescence is achieved. In this work we prove the effective control of this effect by means of the photonic lattice parameter of the host. CdS was grown by chemical bath deposition and its quality has been checked employing Raman spectroscopy and x-ray diffraction. Scanning electron microscopy is used to study the morphology of the composite.

/pdf/cds-photoluminescence-inhibition-by-a-photonic-structure-3gveozv2nh.pdf

CdS photoluminescence inhibition by a photonic structure

Photonic crystal made by close packing SiO2submicron spheres

The surface of the solid structures obtained by natural sedimentation from aqueous solutions of monodisperse Si${\mathrm{O}}_{2}$ spheres is imaged by atomic force microscopy. The dynamic scaling method applied to these images leads to temporal and spatial logarithmic scalings of the surface width that is consistent with the Edward-Wilkinson interface motion equation. It suggests that the interface grows close to equilibrium by the aggregation of Si${\mathrm{O}}_{2}$ spheres which, after reaching the growing surface driven by gravity, relax to minimum potential energy sites without significant attractive particle-particle interactions.

Edward-Wilkinson Behavior of Crystal Surfaces Grown By Sedimentation of SiO2 Nanospheres.

We use photoluminescence and photoluminescence excitation experiments with and without magnetic field to study the electronic properties of InxGa1-xAs/GaAs quantum wells grown on vicinal (001) substrates. We analyze samples of a wide range of In contents (from 17% to 35%) and various misorientation angles (up to 6 degrees). The optical quality of the samples increases with the tilt angle and is explained as mainly controlled by alloy disorder. A fit of the electron-heavy-hole transitions is performed by means of a method which consists of the resolution of a two-dimensional Schrodinger equation and which includes two adjustable parameters: the In surface segregation energy E(s) and the length xi in which the hydrostatic pressure becomes biaxial as defined by the Nagai's model [J. Appl. Phys. 45, 3789 (1974)]. For a given angle and In content the differences between the PL peaks of vicinal and nominal samples present a maximum as a function of the well width, a fact which is well explained by our theoretical model. A study of the exciton dimensionality has been also carried out using models that take dimensionality into account in different manners. (C) 1997 American Institute of Physics.

R. Mayoral

Papers

Photonic crystal properties of packed submicrometric SiO2 spheres

CdS photoluminescence inhibition by a photonic structure

Photonic crystal made by close packing SiO2submicron spheres

Edward-Wilkinson Behavior of Crystal Surfaces Grown By Sedimentation of SiO2 Nanospheres.

Optical studies of highly strained InGaAs/GaAs quantum wells grown on vicinal surfaces