Enhanced Bragg reflections from size-matched heterostructure photonic crystal thin films prepared by the Langmuir-Blodgett method

The Langmuir-Blodgett method was used to engineer photonic crystal thin films of an AB architecture. Structures were studied by transmittance and reflectance spectroscopies. For an AB structure in which the silica particle diameter B is twice that of A, reflectance features associated with the first order Bragg peak for the ``A'' domain are only observed when the structure is probed from the A side of the structure. Furthermore, this feature is enhanced in intensity compared to that for a structure consisting solely of A particles. These findings are attributed to a matching of first and second order Bragg processes

Photonic crystal thin films of GaAs prepared by atomic layer deposition

Photonic crystal thin films were fabricated via the self-assembly of a lattice of silica spheres on silicon (100) substrates. Progressive infilling of the air spaces within the structure with GaAs was achieved using trimethylgallium and arsine under atomic-layer-deposition conditions. Samples with the highest levels of GaAs infill were subsequently inverted using selective etching. Reflectance spectra are interpreted via the Bragg expression and calculated photonic band structure diagrams. For GaAs infilled and inverted samples, the relative positions of the first and second order Bragg reflections are strongly influenced by the wavelength dependent refractive index

(2+1)-dimensional photonic crystals from Langmuir-Blodgett colloidal multilayers

Angle-resolved transmission spectra of multilayers of two-dimensional colloidal crystals prepared by the Langmuir-Blodgett technique have been studied. In contrast to the light diffraction in three-dimensional colloidal crystals, optical spectra revealed only very weak correlation between layers in the Langmuir-Blodgett multilayers. Two reasons for the observed transmission minima have been identified: the diffraction at a stack of layers and the scattering of the incident beam by guided modes of the two-dimensional colloidal crystals. (c) 2006 American Institute of Physics. (DOI:10.1063/1.2234568

Understanding of transmission in the range of high-order photonic bands in thin opal film

Diffraction in the face centered cubic lattice cannot explain some minima observed in the transmission spectra of self-assembled opal films. Here, we compared them with minima observed in the transmission spectra of a hexagonal close packed monolayer of spheres of the same diameter. The identity of the sphere packing on the surface of the opal film and in the sphere monolayer was demonstrated by the light diffraction at the sample surfaces. It was shown that excitation of surface propagating modes in the opal film is responsible for the formation of additional minima in opal film transmission. (C) 2008 American Institute of Physics. (DOI: 10.1063/1.2920443

Erasing diffraction orders: Opal versus Langmuir-Blodgett colloidal crystals

The optical transmission of photonic crystals self-assembled from colloidal nanospheres in opals and assembled from two-dimensional colloidal crystals in a periodic stack by the Langmuir-Blodgett technique has been compared. Elimination of all related zero order diffraction resonances other than that from growth planes and broadening and deepening of the remaining one-dimensional diffraction resonance have been observed for samples prepared by the Langmuir-Blodgett approach, which are explained in terms of the partial disorder of a crystal lattice. (c) 2007 American Institute of Physics.(DOI:10.1063/1.2714198

Modification of emission of CdTe nanocrystals by the local field of Langmuir-Blodgett colloidal photonic crystals

A light source on the surface of a slab of 2+1-dimensional photonic crystal has been prepared by the Langmuir-Blodgett deposition of a colloidal crystal on top of a thin film containing CdTe nanocrystals. The directional enhancement of the light emission intensity in the spectral range of the photonic bandgap has been revealed through the comparative examination of the angle-resolved transmission, diffraction, and photoluminescence spectra of the prepared structures. Changes in the emission spectrum have been tentatively explained in terms of the acceleration of the radiative recombination due to the increase in the local field strength at photonic bandgap resonance and changes in the emission diagram-as arising from the wavelength dependence of the topology of the local field pattern

One-dimensional metal-organic framework photonic crystals used as platforms for vapor sorption.

We present the fabrication of one-dimensional photonic crystals (Bragg stacks) based on a microporous metal–organic framework material and mesoporous titanium dioxide. The Bragg stack heterostructures were obtained using two complementary synthesis approaches utilizing the bottom-up assembly of heterogeneous, i.e. two-component photonic crystal multilayer structures. Zeolitic imidazolate framework ZIF-8 and mesoporous titanium dioxide were chosen as functional components with different refractive indices. While ZIF-8 is intended to impart molecular selectivity, mesoporous TiO2 is used to ensure high refractive index contrast and to guarantee molecular diffusion within the Bragg stack. The combination of micro- and mesoporosity within one scaffold endows the 1D-MOF PC with characteristic adsorption properties upon exposure to various organic vapors. In this context, the sorption behavior of the photonic material was studied as a function of partial pressure of organic vapors. The results show that the multilayered photonic heterostructures are sensitive and selective towards a series of chemically similar solvent vapors. It is thus anticipated that the concept of multilayer heterogeneous photonic structures will provide a versatile platform for future selective, label-free optical sensors

Preparation and optical properties of novel bioactive photonic crystals obtained from core-shell poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Optical properties of polymer microspheres with polystyrene cores and polyglycidol-enriched shells poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) (P(S/PGL) particles with number average diameters Dn determined by scanning electron microscopy equal 237 and 271 nm), were studied before and after immobilization of ovalbumin. The particles were synthesized by emulsifier-free emulsion copolymerization of styrene and polyglycidol macromonomer (poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol)) initiated with potassium persulfate. Molar fraction of polyglycidol units in the interfacial layer of the microspheres determined by XPS was equal 42.6 and 34.0%, for the particles with Dn equal 137 and 271 nm, respectively. Colloidal crystals from the aforementioned particles were prepared by deposition of particle suspensions on the glass slides and subsequent evaporation of water. It was found that optical properties of colloidal crystals from the P(S/PGL) microspheres strongly depend on modification of their interfacial layer by covalent immobilization of ovalbumin. The coating of particles with ovalbumin resulted in decreasing their refractive index from 1.58 to 1.52