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Photonic Crystals (photonic + crystal)
Kinds of Photonic Crystals Terms modified by Photonic Crystals Selected AbstractsAnalysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum OxidxeADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Sang-Wan Ryu Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source] Silicon-Based Near-Visible Logpile Photonic CrystalADVANCED MATERIALS, Issue 37 2010Ganapathi Subramania A nanocavity structure is embedded inside a silicon logpile photonic crystal that demonstrates tunable absorption behavior at near visible wavelengths well beyond the absorption edge of silicon. This is due to silicon's indirect bandgap resulting in a relatively slow increase in the absorption of silicon with decreasing wavelength. Our results open up the possibility of utilizing the wide, complete three dimensional photonic gap enabled by the large refractive index of silicon to create three dimensional photonic crystal based devices well into the visible regime. [source] Photonic Crystal Formed by the Imaginary Part of the Refractive IndexADVANCED MATERIALS, Issue 24 2010Juntao Li A periodic array of dye-doped disks that form a 2D photonic lattice is fabricated and characterized. The array was generated by interference lithography, and the voids of the template were filled by SU8 without doping. This creates a photonic lattice with a uniform real part of the refractive index, but a periodically modulated imaginary part. The structure is characterized by diffraction measurements; the structure only diffracts light in the spectral range where the dye absorbs, hence acts like a truly imaginary index photonic crystal. [source] Log-Pile TiO2 Photonic Crystal for Light Control at Near-UV and Visible WavelengthsADVANCED MATERIALS, Issue 4 2010Ganapathi Subramania Three-dimensional photonic crystals with an omnidirectional bandgap at visible frequencies can have significant impact on solid-state lighting and solar-energy conversion. Using a procedure based on multistep electron-beam lithographic processing, a 9-layer log-pile photonic crystal is fabricated composed of 70-nm-wide titanium dioxide rods with 250-nm lattice spacing that exhibit a stacking direction bandgap between 400,nm and 500,nm (see image). [source] Internally Referenced Ammonia Sensor Based on an Electrochemically Prepared Porous SiO2 Photonic Crystal,ADVANCED MATERIALS, Issue 22 2007H. King An oxidized porous silicon photonic crystal possessing two reflectance peaks is infused with bromothymol blue, yielding a pH-responsive ammonia vapor sensor. One reflectance peak overlaps the absorbance band of the deprotonated dye while the other appears in a "clear" spectral region. Simultaneous monitoring of both reflectance peaks corrects for large changes in probe light intensity. [source] A Two-Dimensional KTiOPO4 Photonic Crystal Grown Using a Macroporous Silicon Template,ADVANCED MATERIALS, Issue 17 2006A. Peña 2D KTiOPO4 photonic crystals are fabricated using a silicon membrane of air holes as a template. Columns of KTiOPO4 are grown by liquid-phase epitaxy from a substrate into such air holes. The crystallographic orientation of the columns is the same as that of the substrate. The photonic-crystal properties of the fabricated structures and their capability to generate second-harmonic light are experimentally demonstrated. [source] Self-Assembled Silica Photonic Crystal as a Liquid-Crystal Alignment Layer and its Electro-optic Applications in Fabry,Perot Cavity Structures,ADVANCED MATERIALS, Issue 19 2004Y. Ha Microgrooves on self-assembled photonic-crystal (PC) films align liquid crystals (LCs) without any additional rubbing or surface treatment. Nematic (see Figure and inside cover) or twisted-nematic LCs can be formed, depending on the relative orientation of the microgrooved films. A LC Fabry,Perot (FP) cavity was fabricated using these PC films, and electro-optic tuning of FP cavity modes is demonstrated. [source] Microwave Studies of Photonic Crystals,ADVANCED ENGINEERING MATERIALS, Issue 11 2006F. Kuchar Experimental and numerical investigations on photonic crystals with millimeter dimensions and the lowest photonic bands in the microwave range are reported. Negative refraction, right-handed and left-handed behavior of the modes in the photonic crystal and the effect of positional disorder are analyzed. [source] Photonic Crystals in BioassaysADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Yuanjin Zhao Abstract Photonic crystal (PC) based bioassay techniques have many advantages in sensitive biomolecular screening, label-free detection, real-time monitoring of enzyme activity, cell morphology research, and so on. This study provides an overall survey of the basic concepts and up-to-date research concerning the very promising use of PC materials for bioassays. It includes the design and application of PC films, PC microcarriers, PC fibers, and PC optofluidics for fluorescence enhancement or label-free bioassays. Emphasis is given to the description of the functional structures of different PC materials and their respective sensing mechanisms. Examples of detecting various types of analytes are presented. This article promotes communication among chemistry, biology, medicine, pharmacy, and material science. [source] Dimer-Based Three-Dimensional Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Ian D. Hosein Abstract The self-assembly of polystyrene dimer- and spherocylinder-shaped colloids is achieved via controlled drying on glass and silicon substrates. 3D monoclinic colloidal crystal structures are determined from scanning electron microscopy images of sections prepared using focused ion-beam (FIB) milling. Full photonic bandgaps between the eighth and ninth bands are found for a systematic range of colloidal dimer shapes explored with respect to the degree of constituent lobe fusion and radius ratio. The pseudogap between bands 2 and 3 for spherocylinder-based monoclinic crystals is also probed using normal incidence reflection spectroscopy. [source] Tunable Colors in Opals and Inverse Opal Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Carlos I. Aguirre Abstract Colloidal photonic crystals and materials derived from colloidal crystals can exhibit distinct structural colors that result from incomplete photonic band gaps. Through rational materials design, the colors of such photonic crystals can be tuned reversibly by external physical and chemical stimuli. Such stimuli include solvent and dye infiltration, applied electric or magnetic fields, mechanical deformation, light irradiation, temperature changes, changes in pH, and specific molecular interactions. Reversible color changes result from alterations in lattice spacings, filling fractions, and refractive index of system components. This review article highlights the different systems and mechanisms for achieving tunable color based on opaline materials with close-packed or non-close-packed structural elements and inverse opal photonic crystals. Inorganic and polymeric systems, such as hydrogels, metallopolymers, and elastomers are discussed. [source] High Quality Factor Metallodielectric Hybrid Plasmonic,Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Xindi Yu Abstract A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer,gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic,photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic,photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated. [source] Photonic Crystals: Three-Dimensional Nanostructures for Photonics (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Mater. Over the last decade, direct laser writing via two-photon absorption turned from a laboratory curiosity into a versatile technique for the fabrication of 3D nano-and microstructures. Especially, in the field of nanophotonics novel structures could be fabricated and tested for agreement with theory. G. von Freymann and co-workers review recent progress in the field on page 1038. The cover image displays a potpourri of complex 3D nanostructures for photonics. Cover artwork by M. S. Rill. [source] Site-Selective Self-Assembly of Colloidal Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Sanna Arpiainen Abstract A scalable method for site-selective, directed self-assembly of colloidal opals on topologically patterned substrates is presented. Here, such substrate contains optical waveguides which couple to the colloidal crystal. The site-selectivity is achieved by a capillary network, whereas the self-assembly process is based on controlled solvent evaporation. In the deposition process, a suspension of colloidal microspheres is dispensed on the substrate and driven into the desired crystallization sites by capillary flow. The method has been applied to realize colloidal crystals from monodisperse dielectric spheres with diameters ranging from 290 to 890,nm. The method can be implemented in an industrial wafer-scale process. [source] Lattice-Registered Two-Photon Polymerized Features within Colloidal Photonic Crystals and Their Optical Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2008Erik C. Nelson Abstract In this work we demonstrate a significant advance in the introduction of embedded defects in 3D photonic crystals by means of two-photon polymerization. We have developed the ability to precisely position embedded defects with respect to the lattice of 3D photonic crystals by imaging the structure concurrently with two-photon writing. Defects are written with near-perfect lattice registration and at specifically defined depths within the crystal. The effect of precise defect position on the optical response is investigated for embedded planar cavities written in a photonic crystal. The experimental data are compared to spectra calculated using the Scalar Wave Approximation (SWA). [source] Cover Picture: Assembly of Wiseana Iridovirus: Viruses for Colloidal Photonic Crystals (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 8 2006Mater. Abstract Assembly of colloids is a versatile tool for micro- and nanofabrication. Natural and artificially engineered viruses offer the opportunity to expand the functionality and versatility of such assemblies. The cover shows optically iridescent, thin polycrystalline arrays (background) as well as bulk pellets (inset right) that exhibit reversible hydration-dependent reflection spectra, as reported by Vaia and co-workers on p.,1086. The films and pellets were created in vitro with classical colloid-assembly techniques from Wiseana iridescent virus (inset, center) harvested from infected Wiseana spp larvae (inset, left). In,vitro assembly of Wiseana iridescent virus (WIV) yields iridescent pellets and films with structural color more vivid than in the native insect. WIV is icosahedral in shape, 140,nm in diameter, with 30,nm long fibrils attached to the outer surface, and exhibits a surface charge ca.,1/6th that of a comparable polymer colloid. The low surface charge and tethered chains on the virus surface allow the facile modification of the interparticle distance. Directed sedimentation yields predominantly an amorphous liquid-like packing of the virus. Such samples exhibit a broad reflection band that is angle independent and for which the broad maximum can be reversibly shifted from blue towards red with increased hydration. Slow sedimentation and flow-assisted assembly methods produce thin films with a polycrystalline morphology that exhibit narrower, more intense reflectivity peaks, which are hydration and angle dependent. This study points toward the potential of viral particles for photonic crystals where their unique structural features (icosahedral symmetry, extreme monodispersity, precise surface functionalization, and tethered surface chains of low surface-charge density) may lead to superior control of optical properties of their assembled arrays. [source] Selectively Transparent and Conducting Photonic CrystalsADVANCED MATERIALS, Issue 5 2010Paul G. O'Brien Selectively transmissive and conductive 1D photonic crystals (PCs) are fabricated by alternately depositing sputtered ITO and spin-coated ATO nanoparticle films. These Bragg reflectors exhibit broad and intense Bragg peaks (tunable via the thickness of their ITO layers) over their stop gap but are highly transmissive over remaining spectral regions of the visible and infrared spectrum. [source] 3D Bi-chiral Photonic Crystals: Three-Dimensional Bi-Chiral Photonic Crystals (Adv. Mater.ADVANCED MATERIALS, Issue 46 200946/2009) Bi-chiral photonic crystals are tailored man-made solids inspired by blue-phase cholesteric liquid crystals. They possess two types of chirality, leading to four different types of bi-chiral structures. In naturally occurring blue-phase liquid crystals, only two of these are thermodynamically stable. On p. 4680, Michael Thiel and co-workers fabricate all four via direct laser writing. [source] Three-Dimensional Bi-Chiral Photonic CrystalsADVANCED MATERIALS, Issue 46 2009Michael Thiel Four different types of bi-chiral photonic crystals are experimentally realized and characterized (see figure). In these 3D bi-chiral photonic crystals one type of handedness stems from the motif (the spirals in our case) and the other one from the corner, that is, from the fictitious skeleton onto which the motif is arranged. In nature only two of these types of bi-chiral photonic crystals exist. We realized all four bi-chiral combinations for the first time. [source] Photonic Crystals: Patterned Polymeric Domes with 3D and 2D Embedded Colloidal Crystals using Photocurable Emulsion Droplets (Adv. Mater.ADVANCED MATERIALS, Issue 37 200937/2009) The inside cover shows a scheme for the preparation of photonic dome patterns, SEM images of a dome pattern, and a single dome decorated with 2D colloid array, as fabricated in work reported on p 3771 by Seung-Man Yang and co-workers. The background is an optical microscopy image of patterned photonic domes, which can be used as a near-field microlens array. The greenish color of the domes corresponds to the photonic bandgap. [source] Rare-Earth Spontaneous Emission Control in Three-Dimensional Lithium Niobate Photonic CrystalsADVANCED MATERIALS, Issue 34 2009Airán Ródenas Spontaneous emission inhibition of erbium ions at 1.5,µm wavelength is obtained by tailoring direct femtosecond-laser-written 3D photonic structures inside lithium niobate laser crystals. This technique allows for engineering of the structure symmetry and filling fraction by spatially inscribing laser-induced amorphous voxels inside the crystalline sample. [source] Photonic Crystals: Silicon Direct Opals (Adv. Mater.ADVANCED MATERIALS, Issue 28 200928/2009) The inside cover shows an image of a porous silicon direct opal fabricated by magnesiothermic reduction. Using chemical vapor deposition to infill the porous structure, a nonporous silicon opal can be obtained. The optical properties of opals formed with this method, reported by Cefe López and co-workers on p. 2899, demonstrate the high quality of the final product. [source] Fabrication of 3D Photonic Crystals of Ellipsoids: Convective Self-Assembly in Magnetic FieldADVANCED MATERIALS, Issue 19 2009Tao Ding Three-dimensional photonic crystals of ellipsoidal colloidal particles are prepared by direct convective self-assembly from suspension with the aid of a magnet. The magnetic field provides the orientational order, which is additionally needed for these colloidal particles with symmetry lower than spherical. The positional order is provided by the convection, just as for spherical colloids. [source] Dual Tuning of the Photonic Band-Gap Structure in Soft Photonic CrystalsADVANCED MATERIALS, Issue 18 2009Masaki Honda A dually tunable photonic crystal composed of thermosensitive gel particles confined in a pH-sensitive inverse-opal gel is reported. The position of the photonic band-gap can be thermally regulated, while its intensity is dramatically changed by pH. Reversible, independent, and extensive switching of the position and intensity of the photonic band-gap could be achieved using independent external stimuli. [source] Stacking the Nanochemistry Deck: Structural and Compositional Diversity in One-Dimensional Photonic CrystalsADVANCED MATERIALS, Issue 16 2009Leonardo D. Bonifacio Abstract One-dimensional photonic structures, known as Bragg stacks or Bragg reflectors or Bragg mirrors, represent a well-developed subject in the field of optical science. However, because of a lack of dynamic tunability and their dependence on complex top-down techniques for their fabrication, they have received little attention from the materials science community. Herein, we present recent and ongoing developments on the way to functional one-dimensional photonic structures obtained from simple bottom-up techniques. We focus on the versatility of this new approach, which allows the incorporation of a wide range of materials into photonic structures. [source] Porous One-Dimensional Photonic Crystals Improve the Power-Conversion Efficiency of Dye-Sensitized Solar CellsADVANCED MATERIALS, Issue 7 2009Silvia Colodrero The solar-to-electric power-conversion efficiency (,) of dye-sensitized solar cells can be greatly enhanced by integrating a mesoporous, nanoparticle-based, 1D photonic crystal as a coherent scattering layer in the device. The photogenerated current is greatly improved without altering the open-circuit voltage of the cell, while keeping the transparency of the cell intact. Improved average , values between 15% and 30% are attained. [source] Terahertz Photonic Crystals Based on Barium Titanate/Polymer Nanocomposites,ADVANCED MATERIALS, Issue 19 2008Joseph Lott Polymeric materials with engineered refractive indices for applications in the THz regime can be fabricated and processed by conventional melt-processing of inorganic nanomaterials and conventional host polymers. The approach opens up new opportunities for the creation of optical elements to manipulate the technologically relevant THz radiation, for example photonic crystals. [source] Microfabrication of Three-Dimensional Photonic Crystals of SiO2,Al2O3 Ceramics and Their Terahertz Wave PropertiesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2008Weiwu Chen Dense three-dimensional microphotonic crystals of SiO2,Al2O3 ceramics were fabricated using microstereolithography and successive sintering process. The forming dimensional tolerance for a 50 vol% ceramic paste is 10 ,m and sintering shrinkage is around 12%. Diamond-type photonic crystals with lattice constants of 500 and 125 ,m were formed and sintered successfully. The band gaps of the samples were measured and compared with the theoretically calculated band diagram. [source] Synthesis of Colloidal Photonic Crystals with High Nonlinear Optical Performance: Towards Efficient Second-Harmonic Generation with Centrosymmetric Structures,ADVANCED MATERIALS, Issue 22 2007A. Molinos-Gómez Chemically modified colloidal photonic crystals with high nonlinear optical performance have been prepared by a novel, very efficient solid-phase based synthesis, opening up a new field of nonlinear optical second-harmonic Generation with centrosymmetric organic structures (see figure). [source] Woodpile Metallic Photonic Crystals Fabricated by Using Soft Lithography for Tailored Thermal Emission,ADVANCED MATERIALS, Issue 6 2007J.-H. Lee Woodpile metallic photonic crystals are fabricated by using soft lithography and electrodeposition (see figure) for tailored thermal emission. This method produces a highly layered full-metallic structure with excellent structural fidelity. By adding a homogeneous monolithic backplane to the conventional woodpile structure, the difficulty of alignment in layer-by-layer fabrication is alleviated, while preserving characteristic enhanced thermal emission. [source] | ||||||||||||||||||||||||||||||||||