Silica opal photonic crystals

D. Kang, J.E. Maclennan, N.A. Clark, A.A. Zakhidov, R.H. Baughman, Electro-optic behavior of liquid-crystal-filled silica opal photonic crystals Effect of liquid-crystal alignment Phys. Rev. Lett. 86, 4052-4055 (2001)... 

FIGURE 22.42 Random laser emission spectrum of a DOO-PPV in toluene solution that is infiltrated into an opal photonic crystal. The inset shows the opal, which is composed of silica spheres in an FCC lattice and the laser excitation and collection geometries. (From Poison, R.C., Chipouline, A., and Vardeny, Z.V., Adv. Mater., 13, 760, 2001. With permission.)... 

An ordered arrangement of particles, colloidal crystals, is found in a wide range of scales. Opal is a typical colloidal crystal with an ordered arrangement of silica particles." Photonic crystals have been developed for the control of optical properties." A variety of supercrystals and superlattices consisting of nanoparticles are fabricated through self-assembly." When the unit particles are an amorphous material and the crystal lattices of each unit particle are not oriented, the colloidal assembly is not regarded as a mesocrystal (Fig. Ig). In contrast, colloidal crystals... 

Photonic crystals have only been studied in the laboratory for two decades, but naturally occurring examples exist, with the best known being the gemstone opal. Opals consist of tiny spheres of silica arranged in a face centred cubic structure. These are thought to have formed from colloidal silica solutions, and the colour depends on the size of the spheres. 

Another nice example of nanostructuring an MIP layer is the work published by Wu et al. [138, 139] who developed a label-free optical sensor based on molecularly imprinted photonic polymers. Photonic crystals were prepared by self-assembly of silica nanospheres. The space between the spheres was then filled with MIP precursor solution. After polymerization, the silica was dissolved, leaving an MIP in the form of a 3D-ordered interconnected macroporous inverse polymer opal (Fig. 15). The authors were able to detect traces of the herbicide atrazine at low concentrations in aqueous solution [139]. Analyte adsorption into the binding sites resulted in a change in Bragg diffraction of the polymer characterized by a color modification (Fig. 15). 

Another important method for photonic crystal fabrication employs colloidal particle self-assembly. A colloidal system consists of two separate phases a dispersed phase and a continuous phase (dispersion medium). The dispersed phase particles are small solid nanoparticles with a typical size of 1-1000 nanometers. Colloidal crystals are three-dimensional periodic lattices assembled from monodispersed spherical colloids. The opals are a natural example of colloidal photonic crystals that diffract light in the visible and near-infrared (IR) spectral regions due to periodic modulation of the refractive index between the ordered monodispersed silica spheres and the surrounding matrix. 

The simplest photonic crystal is nature s opal. The artificial opal is composed of monodispersed spheres of a dielectric, usually silica. Considerable work has been done using latex or polystyrene spheres, but we largely will restrict ourselves here to ceramics. In producing high-quality photonic crystals, care must be taken in each of the three main steps particle synthesis, sedimentation, and sintering. 

Templates used in the fabrication of photonic crystals basically need to be removed in the final stage of the process. There are many organic solvents that can dissolve polymers that are generally used as template, and it is also possible to remove a polymer template by biuning it out. Silica template, which is also widely used particularly in fabricating inverted opals, can be removed by dissolving it with hydrofluoric acid. 

Shroden R.C., Al-Daous M., Stein A. Self-modification of spontaneous emission by inverse opal silica photonic crystals. Chem. Mater. 2001 13 2945-2950 Soten I., Miguez H., Yang S.M., Petrov S., Coombs N., Tetreault N., Matsuura N., Ruda H.E., Ozin G.A. Barium titanate inverted opals-synthesis, characterization, and optical properties. Adv. Funct. Mater. 2002 12 71-77... 

The sol-gel method was widely used in the preparation of photonic materials and structures during the last decades. The design and preparation of hybrid nanocomposites for photonics are widely described in Refs [7,145-147]. The wide range of photonic structures prepared using the sol-gel method include colloidal crystals based on silica or polystyrene spherical particles [148,149], photonic crystals [150-152], photonic bandgap materials [153-155], and opals based on the deposition of silica, titania, and/or ceria in the voids of an ordered array of PMMA spheres [156]. A more extensive overview of photonic materials by sol-gel method can be found in Chapter 28. 

A polymer gel based on an (inverse) opal was applied in order to obtain shorter switching times, which are also desirable for electrochemical color display purposes [346]. Hence, an all-color display was developed that, dependent on the applied potential, could reversibly switch between blue, green, red, and black. Here, crosslinked polyferrocenylsilane gels were partly swollen with glutaronitrile electrolyte. The degree of swelling was controlled electrochemically. Subsequently, the distance between the voids formed by the silica beads, which were etched by hydrofluoric acid treatment, could be altered. It should be mentioned that there are also other concepts for electrically switchable photonic crystals that are not directly connected to electrochemically induced solvation [347-349]. 

Ordered macroporous materials (OMMs) are a new family of porous materials that can be synthesized by using colloidal microspheies as the template. - The most unique characteristics of OMMs are their uniformly sized macropores arranged at micrometer length scale in three dimensions. Colloidal microspheres (latex polymer or silica) can self assemble into ordered arrays (synthetic opals) with a three-dimensional crystalline structure. The interstices in the colloidal crystals are infiltrated with a precursor material such as metal alkoxide. Upon removal of the template, a skeleton of the infiltrated material with a three-dimensionally ordered macroporous structure (inverse opals) is obtained. Because of the 30 periodicity of the materials, these structures have been extensively studied for photonic applications. In this paper, the synthesis and characterization of highly ordered macroporous materials with various compositions and functionalities (silica, organosilica, titana, titanosilicate, alumina) are presented. The application potential of OMMS in adsorption/separation is analyzed and discussed. 

An interesting variation on template deposition is to self-assanble ordered nanostructures (e.g., surfactants) and microstructures (e.g., polystyrene or Si02 beads) on the surface of an electrode and then electrodeposit into the self-assembled pores. The order in the resulting nanostructure is imposed by the self-assembled layer, not by the substrate. Schwartz and coworkers have extended this idea to the use of crystalline protein masks to produce ordered nanostructures of metals (such as Ni, Pt, Pd, and Co) and metal oxides (such as Cu20). Braun and coworkers have used the electrodeposition of materials into self-assembled colloidal crystals or silica or polymer opals. The template is then removed (see Figure 17.11) to produce an inverse opal. This type of templating produces periodic microstructures that can be used to produce functional photonics. Figure 17.11 shows the production of CdSe and Ni inverse opals by electrodeposition into a colloidal crystal with subsequent removal of the colloidal crystal template. ... 

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