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Perfect 3D film photonic crystals are synthesized from submicron spherical silica particles consisting of a nonporous core and a mesoporous shell. The obtained photonic crystals with a hierarchical pore arrangement-transport macropores between particles and mesopores inside the shell-are promising for application in optical gas sensors. [ABSTRACT FROM AUTHOR]

A procedure for the synthesis of monodisperse spherical mesoporous silica particles (MSMSPs) via the controlled coagulation of silica/surfactant clusters into spherical aggregates with mean diameters of 250-1500 nm has been developed. The synthesis is fast (taking less than 1 h) because identical clusters are simultaneously formed in the reaction mixture. The results of microscopic, x-ray diffraction, adsorption and optical measurements allowed us to conclude that the clusters are ~15 nm in size and have hexagonally packed cylindrical pore channels. The channel diameters in MSMSPs obtained with cethyltrimethylammonium bromide and decyltrimethylammonium bromide as structure-directing agents were 3:1 ± 0:15 and 2:3 ± 0:12 nm, respectively. The specific surface area and the pore volume of MSMSP were, depending on synthesis conditions, 480-1095 m2 g-1 and 0.50-0.65 cm3 g-1. The MSMSP were used to grow opal-like photonic-crystal films possessing a hierarchical macro-mesoporous structure, with pores within and between the particles. A selective filling of mesopore channels with glycerol, based on the difference between the capillary pressures in macro- and mesopores, was demonstrated. It is shown that this approach makes it possible to control the photonic bandgap position in mesoporous opal films by varying the degree of mesopore filling with glycerol. [ABSTRACT FROM AUTHOR]

Hybrid film structures of the photonic crystal (opal)/glassy chalcogenide semiconductor (GeSbTe) type, which exhibit strong variations in the intensity of reflected light due to the resonant excitation of anomalous diffraction (Wood anomaly), have been synthesized. A method of controlling the resonant optical response of the obtained structures is proposed that is based on a thermoinduced phase transition from the amorphous to crystalline state in the GeSbTe film. [ABSTRACT FROM AUTHOR]

A technique has been developed for synthesis of submicron monodispersed mesoporous spheres of amorphous silica from an alcohol-water-ammonia mixture by means of tetraethoxysilane hydrolysis in the presence of hexadecyltrimethylammonium bromide. The mechanism of sphere formation from aggregates of close-packed surfactant cylindrical micelles coated by silica has been proposed. The specific surface area in the synthesized spheres is higher than 800 m/g, whereas the pore volume and average diameter are equal to 0.63 cm/g and 3 nm, respectively. The average size of particles is shown to decrease twice after the temperature of the synthesis is increased twice. According to the data of atomic force spectroscopy and dynamic light scattering, the average diameter of mesoporous spheres can be controllably varied in the range 300-1500 nm with a root-mean-square deviation of no more than 6%. [ABSTRACT FROM AUTHOR]

The effect of the time passed after tetraethoxysilane treatment with ammonia on the diameter of particles produced by tetraethoxysilane hydrolysis in alcohol-water-ammonia media is studied. The regulation the time passed after of tetraethoxysilane treatment results in the synthesis of submicron monodisperse spherical silica particles with diameters differing by a factor of two. The difference is explained by the formation of SiO particles with sizes of 10-100 nm in tetraethoxysilane during 10-30 h after treatment with ammonia. These particles enhance the concentration of nucleation centers in a reaction mixture, thus decreasing the final size of monodisperse silica spheres. Opal films with a high structural perfection and pronounced photonic crystal properties are grown based on the obtained monodisperse SiO particles. [ABSTRACT FROM AUTHOR]

The temperature evolution of copper oxide nanoparticles in the temperature range of 1.5-250 K has been investigated by thermal-neutron diffraction. CuO particles were obtained by Cu(NO) · 3HO decomposition directly in the pores of porous glass with an average pore diameter of 7 nm. The characteristic nanoparticle size and linear thermal expansion coefficients have been determined. [ABSTRACT FROM AUTHOR]

The parameters of three-dimensional photonic crystals based on opal-VO composite films in the 1.3-1.6 μm spectral range important for practical applications (Telecom standard) are numerically calculated. For opal pores, the range of filling factors is established (0.25-0.6) wherein the composite exhibits the properties of a three-dimensional insulator photonic crystal. On the basis of the opal-VO composites, three-dimensional photonic film crystals are synthesized with specified parameters that provide a maximum shift of the photonic band gap in the vicinity of the wavelength ∼1.5 μm (∼170 meV) at the semiconductor-metal transition in VO. [ABSTRACT FROM AUTHOR]

In this paper the thermal and optical properties of the SiO2/GaN synthetic opals are studied by photothermal deflection technique. This technique, used in different configurations, allows to determine the effective thermal diffusivity and the absorption spectra. [ABSTRACT FROM AUTHOR]

The crystalline and magnetic structures of γ-Fe2O3 maghemite synthesized in porous glass in the form of nanoparticles with a mean diameter of 106(2) Å have been determined by the neutrons and synchrotron radiation diffraction methods. Nanostructured maghemite with the spinel structure has vacancies in the octahedral and tetrahedral positions. The magnetic structure corresponds to the usual ferrimagnetic type. The measured magnetic moments are much lower than the moments in a usual sample. Moreover, the moments are strongly different in the octahedral and tetrahedral positions; this difference is explained by the difference in the exchange interaction for moments in different positins. [ABSTRACT FROM AUTHOR]

VO[sub 2] photonic crystals exhibiting a semiconductor-metal phase transition at 55-75°C have been synthesized by the infiltration of vanadium dioxide (VO[sub 2]) into opal crystals and the subsequent removal of SiO[sub 2] by etching. A study of the optical reflection spectra of such crystals demonstrated that they are characterized by a wide photonic band gap (in the [111] direction of light propagation) in the visible spectral range. The energy position of this band gap changes abruptly upon a phase transition. The temperature shift and hysteresis of the position of the photonic band gap were measured. Quantitative calculations of the reflection spectra of photonic crystals of opal and VO[sub 2] were performed in terms of the model of a layered periodic medium, and numerical values of the geometric parameters and optical constants of the studied three-dimensional periodic structures were obtained. [ABSTRACT FROM AUTHOR]

Three-dimensional opal-silicon composites both with a direct (with different extent of the opal voids filling with Si) and inverted structure were synthesized, and their structural analysis was carried out. The spectra of specular reflection from (111) growth surfaces of the synthesized composites were measured in the wavelength range from 400 to 900 nm. The features observed in the spectra are analyzed theoretically and interpreted as manifestations of the photonic band gap in the direction [111]; the band gap position and width can be tuned in the visible and near-infrared spectral range. [ABSTRACT FROM AUTHOR]

Results of determination of the X-Ray Mn K line shifts in nanoparticles of manganese oxides (MnO, MnO, and MnO) relative to the corresponding lines in bulk compounds are presented. Nanoparticles of manganese oxides were formed by direct synthesis in pores of borosilicate glasses with average pore diameter of 7(1) nm. [ABSTRACT FROM AUTHOR]

Single-stage synthesis has been used to obtain submicrometer monodisperse spherical mesoporous silica particles exhibiting bright wide-band luminescence in the visible spectral range. The particles have a specific surface area of 550 m/g, pore volume of 0.36 cm/g, and average pore diameter of 0.3 nm. The synthesis technology provides formation of an active inner surface (surface of mesopores), which will enable binding and retention of medicinal preparations upon their introduction into the particles. The particles are promising for application in theranostics of cancerous growths as nanocontainers simultaneously serving as biomarkers. [ABSTRACT FROM AUTHOR]