Marta Ibisate

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

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 materials, 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 photons, 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 microchips, 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 voltage. 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.

Optical study of the full photonic band gap in silicon inverse opals

An optical study of the band structure of both silicon–silica composite and silicon inverse opals is presented. The study is aimed at demonstrating the development of a full photonic band gap for a system already revealed as paradigmatic. The characterization is based on the comparison between the band structure calculations and optical reflectance spectroscopy experiments. This study is carried out for various symmetry points in the Brillouin zone, some never explored before as K, (110) and W, (210). The results show that, in accordance with the band structure, there is a certain frequency range that produces a reflectance peak regardless of orientation and can be assigned to the band gap. Similarly all other reflectance peaks can be accounted for by other band structure features.

Optical gain in DNA-DCM for lasing in photonic materials

We present a detailed study of the gain length in an active medium obtained by doping of DNA strands with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye molecules. The superior thermal stability of the composite and its low quenching permit one to obtain an optical gain coefficient larger than 300 cm(-1). We also demonstrate that such an active material is feasible for the infiltration into photonic nanostructures, allowing one to obtain fluorescent photonic crystals and promising lasing properties.

Qualitative and Quantitative Analysis of Crystallographic Defects Present in 2D Colloidal Sphere Arrays

In this work, we present a study of the typical spontaneous defects present in self-assembled colloidal monolayers grown from polystyrene and silica microspheres. The quality of two-dimensional crystals from different colloidal suspensions of beads around 1 μm in diameter has been studied qualitatively and quantitatively, evaluated in 2D hexagonal arrays at different scales through Fourier analysis of SEM images and optical characterization. The crystallographic defects are identified to better understand their origin and their effects on the crystal quality, as well as to find the best conditions colloidal suspensions must fulfill to achieve optimal quality samples.

Vanadium dioxide thermochromic opals grown by chemical vapour deposition

The semiconductor–metal transition that occurs in vanadium dioxide at 68 °C is the object of increasing interest in modern optics due to its applications in ultrafast optical devices. In a three-dimensional photonic crystal, the fine control of the structure is important for optimizing the switching magnitude and the spatial homogeneity. We report a controlled process to fabricate large-area high quality VO2–SiO2 opals with fine control over the filling volume. The method comprises two stages. The first stage is a chemical vapour deposition synthesis whereby the vanadium pentoxide is grown. The second one is a thermal annealing that allows reducing the vanadium pentoxide to vanadium dioxide. We have carried out a steady-state study of the semiconductor–metal transition, for opals with the Bragg peak around the 1.55 µm spectral region, by means of reflectance spectroscopy. As the temperature increases approaching the phase transition the intensity of the reflectance peak decreases and a small blueshift can be observed at 65 °C. When the phase transition is achieved at 68 °C the intensity of the reflectance peak decreases drastically and the Fabry–Perot oscillations disappear.

Light Emission from Nanocrystalline Si Inverse Opals and Controlled Passivation by Atomic Layer Deposited Al2O3

This work was partially supported by EU FP7 NoE Nanophotonics 4 Energy grant No. 248855; the Spanish MICINN CSD2007-0046 (Nanolight.es), CSD2008-00023 (FUNCOAT), CSD2009-00013 (Imagine), MAT2009-07841 (GLUSFA), TEC2008-06756-C03-02/TEC, CSIC PIF08-016 (Intramural Frontera), MAT2010-18432 and the Comunidad de Madrid S2009/MAT-1756 (PHAMA) projects. F. G. G. was supported by the JAE Postdoctoral Program from the CSIC. M. I. is a Ramon y Cajal researcher.

Photonic crystal microprisms obtained by carving artificial opals

A method for fabrication of photonic crystal prisms is demonstrated. The procedure is based on micromanipulation techniques, here applied to artificial opals. By means of a microgrinder an opal prism comprising a single crystal (several tens of microns in size) has been carved with three different faces: (111), (110), and (100). The faces were morphologically characterized by scanning electron microscopy and their optical reflectance spectra measured and compared with the theoretical band structure.

One-Step-Process Composite Colloidal Monolayers and Further Processing Aiming at Porous Membranes

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly (in which a silica precursor, tetraethyl orthosilicate (TEOS), is added to the base colloid) with confined growth in a wedge-shaped cell, while profiting from the advantages of both techniques. Using this method, it is possible to fabricate the composite monolayer in a single growth step. A systematic study of the influence of TEOS concentration in the initial colloid was performed in order to improve the quality of the two-dimensional crystals produced. Thus, it was demonstrated that the two methods are compatible. Furthermore, the composites were then subjected to thermal treatment so that the polymer is removed to reveal the inverse structure. After the calcination the membranes still present very good quality and so the proposed approach is effective for the fabrication of porous membranes. A comparison of reflectance spectra, between composite monolayers fabricated using this method and composites achieved by infiltrating polystyrene bare opals with silica chemical vapor deposition, is also established. The procedure presented is expected to establish the route for an easier and quicker fabrication of inverse monolayers of high refractive index materials with applications in light control.

3D photonic crystals from highly monodisperse FRET-based red luminescent PMMA spheres

Red-luminescent PMMA spheres containing a Forster resonance energy transfer (FRET) pair were synthesized via a two-step polymerization method. Two reaction parameters, time and monomer volume, are scanned in order to tune the sphere diameter in the 250–500 nm range. Further the polydispersity of the spheres is kept low, at ca. 3%, regardless of sphere diameter or dye concentration. A thorough optical characterization via spectroscopy and time resolved measurements shows a FRET efficiency of over 40% before concentration quenching effects take place, allowing for a precise tuning of their emission in the red region of the visible spectrum. The high quality of these spheres makes them suitable to fabricate self-assembled 3D photonic crystals which act as photonic environment to modify the spectral properties of the FRET pair via Bragg diffraction.

Organic Opals: Properties and Applications

The potential of organic materials in the field of photonics, from polymeric to carbonaceous systems, can be enhanced by providing them with a submicrometer structuration. This can strongly affect light–matter interaction within the material, add structural color, or allow for a tailored porosity at the micro and nanoscale. The latter would pave the way for a number of applications ranging from biosensors to lithium-ion batteries. In this sense self-assembled artificial opals have been eagerly explored over the past two decades. In the present chapter we provide a comprehensive account on the state of the art of artificial opals made from organic materials. After introducing the main materials used in the field we describe the properties, both structural and optical, of organic opals which makes them highly relevant from the point of view of applications. Finally, we list a number of potential uses which are being currently explored for these materials in different fields.