Simulation and fabrication of binary colloidal photonic crystals and their inverse structures
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High refractive index contrast silicon colloidal photonic crystals having a different topology to those previously reported have been synthesized. A new process of colloidal‐crystal templating based on micromolding in inverse silica opals (MISO) is used (see Figure), and photonic crystals so built present a full photonic bandgap, as indicated by band structure calculations.
Colloidal crystal
Refractive index contrast
Photonic bandgap
Yablonovite
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Silica and polystyrene spheres were randomly mixed, and ordered into a densely packed photonic crystal. Reflectance spectrum measurements revealed that the L-point pseudobandgap linearly red-shifts as the polystyrene sphere composition increases.
Polystyrene
Colloidal crystal
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We report on the fabrication and characterization of opal-based photonic crystal heterostructures. These heterostructures are created by using multilayer deposition of silica and polystyrene spheres. In the specific the fabricated structures involved both different lattice constant and dielectric function. Scanning electron microscopy (SEM) and NIR-VIS transmittance and reflectance spectroscopy are used to characterize the systems. The SEM images show good ordering of the two-layer colloidal crystals constituting the heterostructures. The transmittance and reflectance spectra measured from the (111) plane of the heterostructure show that the composite colloidal photonic crystals have double photonic stop bands that matches the stop bands of the individual photonic crystals. This behaviour can be seen as a superposition of the properties of each individual layer.
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Polystyrene
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Colloidal photonic crystal heterostructures, composed of two opaline photonic crystal films of silica spheres with different diameters, are fabricated by a two-step spin-coating method. Scanning electron microscopy (SEM) and UV-vis spectrophotometer are used to characterize the heterostructures. The SEM images show good ordering of the two-layer colloidal crystals constituting the heterostructures. The transmission spectra measured from the (111) plane in the heterostructure show that the composite colloidal photonic crystals have double photonic stop bands. Furthermore, when the sizes of the silica spheres used for fabricating the composite photonic crystal are slightly different, the transmission spectrum shows that the composite photonic crystals have more extended bandgap than that of the individual photonic crystals due to partial overlapping of its two photonic stop bands.
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Spin Coating
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We describe two different ideas for novel architectures based on photonic crystals of sub-micron colloids. The first involves the formation of photonic superlattices from colloidal photonic crystals. The superlattice periodicity induces the formation of minibands due to folding of the photonic band structure. This represents the first instance in which mid-gap states have been incorporated into a colloidal photonic crystal via a specifically engineered structural modification. The second idea involves applying the superprism concept to three-dimensionally periodic structures. Near a photonic band edge, the diffraction angle is extremely sensitive to the wavelength and propagation direction of the incident light. We analyze this effect in the context of macroporous polymer thin films formed from colloidal crystal templates.
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Yablonovite
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Photonic metamaterial
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A novel photonic crystal in which the refractive index of the interstitial void region in a colloidal crystal is gradually changed with respect to the specific direction of the crystal was proposed. This was achieved by infiltrating polymers using the interfacial-gel polymerization with high refractive index dopants. Therefore, the resulting colloidal photonic crystal has a gradually varying stop-band at different positions of the crystal when the incident light was normal to the [111] crystallographic axis. This structure could be a kind of tunable photonic crystals based on the positional variations. The optical properties and potentials for other photonic applications will be investigated.
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Yablonovite
Photonic metamaterial
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A (001) oriented three-dimensionally periodic photonic crystal, free of cracks, has been fabricated via a modified template-assisted colloidal self-assembly method with polystyrene spheres. Analysis of the opal-type crystals has revealed the structure to be noncubic. This is a face-centered tetragonal (fct), (001) oriented photonic crystal. The optical properties of the crystals have been characterized at near-normal incidence by reflectance spectroscopy. It is found that the photonic stop band shifts to shorter wavelengths compared with an identical cubic structure oriented along the (001) direction. We have also simulated the stop band behavior of such fct crystals and their inverse silicon analogs, revealing that the polymer opal could provide an inverse template for the formation of photonic crystals with a complete band gap.
Tetragonal crystal system
Colloidal crystal
Yablonovite
Polystyrene
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Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text E. Istrate and E. H. Sargent, "Phase change in reflection from colloidal photonic crystals: Experimental measurements," in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, Technical Digest (CD) (Optica Publishing Group, 2004), paper IThL3. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
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Summary form only given. A colloidal crystal of submicron-sized polystyrene spheres in water may serve as a photonic crystal owing to the dielectric contrast between the constituent materials. Such photonic crystals exhibit strong attenuation in regions of the transmission spectrum (stop bands) arising from Bragg diffraction of light by the crystal planes. Stop bands in polystyrene colloidal crystals have been observed and studied extensively for both FCC and BCC crystal phases. Photonic crystals also modify the photonic dispersion relation near the stop band. In addition, defect states can be introduced into the stop band of a colloidal photonic crystal by substitutional doping with microspheres of different size or dielectric strength. We have significantly improved the Mach-Zehnder interferometer used in a previous dispersion study. We report the application of the improved instrument to the study of dispersion in a colloidal crystal with defect states present.
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Polystyrene
Crystal (programming language)
Stopband
Yablonovite
Photonic metamaterial
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A series of monodispersed P(St-MMA-AA) colloids with diameters from 200 nm to 500 nm was synthesized successfully using emulsion polymerization. The corresponding colloidal crystals were fabricated and investigated. UV-Vis reflectance spectra showed that the band gaps of the obtained colloidal crystals accord well with Bragg law. The height, phase and spectrum 2D images of the obtained binary colloidal crystals were studied using different modes of atom force microscopy.
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Emulsion polymerization
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