Search

Microresonators (MRs) comprising spherical particles of amorphous silicon dioxide with diameters of 2.0 and 3.5 μm coated with a 60-nm-thickness luminescent coat of amorphous hydrogenated silicon carbide (a-Si: C: H) were produced. Enhancement and modification of the continuous wide photoluminescence spectrum of the a-Si: C: H in the visible-near-infrared region at room temperature into a line spectrum displaying intense narrow bands with positions coinciding with the whispering-gallery modes of spherical MRs were demonstrated. [ABSTRACT FROM AUTHOR]

The Shape of the branches for the thermal hysteresis loop of the electrical conductivity for the opal-VO2 composite shows a size dependence near the semiconductor-metal phase transition. The steps observed on the heating and cooling branches of the loop are determined by collective phase transitions in separate monodisperse groups of VO2 nanocrystals within opal voids. [ABSTRACT FROM AUTHOR]

Three-dimensional magnetic photonic crystals, based on an artificial opal matrix with embedded magnetite Fe3O4, were investigated in both transmission and reflection in the near-infrared and visible spectral range. A strong enhancement of the polar Kerr effect and a modification of the Faraday effect have been found near the photonic band gap at about 1.8 eV. Surprisingly the shapes of the loops of magnetic hysteresis measured by magnetic circular dichroism were found to depend on the wavelength of light. This observation has been explained using a model where two types of magnetite particles have different coercive fields. [ABSTRACT FROM AUTHOR]

Three-dimensional magnetophotonic crystals (MPCs) based on artificial opals infiltrated by yttrium iron garnet (YIG) are fabricated and their structural, optical, and nonlinear optical properties are studied. The formation of the crystalline YIG inside the opal matrix is checked by x-ray analysis. Two templates are used for the infiltration by YIG: bare opals and those covered by a thin platinum film. Optical second-harmonic generation (SHG) technique is used to study the magnetization-induced nonlinear-optical properties of the composed MPCs. A high nonlinear magneto-optical Kerr effect in the SHG intensity is observed at the edge of the photonic band gap of the MPCs. [ABSTRACT FROM AUTHOR]

A method has been developed for the synthesis of calcium carbonate particles with the use of mesoporous silica particles as a template. Hydrosols of the synthesized CaCO3 particles are unstable with respect to aggregation at neutral pH values and coagulate to yield aggregates with submicron sizes. A procedure of electrostatic stabilization by adding an aqueous FeCl3 solution has been proposed for the preparation of aggregatively stable hydrosols. It has been shown that this procedure of stabilization leads to the peptization of the aggregates and makes it possible to obtain individual calcium carbonate nanoparticles with sizes of 50−80 nm. The obtained CaCO3 nanoparticles are porous, thereby making it possible to use their stable hydrosols in medicine. [ABSTRACT FROM AUTHOR]

The morphology of monodisperse spherical mesoporous silica particles with a regular pore structure is studied with atomic force microscopy. The size of nanotubes is found: the internal diameter is 2.6 nm, the external diameter is 4.8 nm, and the wall thickness is 1.1 nm. A method for assessing the strength parameters of highly porous materials is proposed. The calculated Young's modulus of a nanotube along its axis is 91.7 GPa. [ABSTRACT FROM AUTHOR]

Silicon is now the most important material in modern solid-state electronics. Regular systems of silicon nanoclusters containing up to 10[sup 14] cm[sup -3] elements were obtained in a sublattice of opal (SiO[sub 2]) voids. By using three-dimensional dielectric matrix-carriers similar to opal, it may be possible to obtain three-dimensional ensembles of semiconductor nanodevices. Various parameters of these "opal-silicon" nanocomposites were measured. [ABSTRACT FROM AUTHOR]

A correction to the article "Enhancement of optical and magneto-optical effects in three-dimensional opal/Fe3O4 magnetic photonic crystals" that was published in the October 14, 2008 issue is presented.

Scanning tunneling microscopy and scanning tunneling spectroscopy (STS) are used to investigate the local electronic behavior of Pt-Si nanostructures fabricated in an opal matrix formed by silica spheres of 250 nm diameter. Si and Pt are regularly distributed inside the opal pores and form nanoscale metal-semiconductor-metal junctions. Normalized differential conductance curves enable us to study the distribution of Pt and Si and to detect the presence of regions showing a surface band gap in the range 0.5-0.8 eV, possibly associated with the formation of silicides. STS appears as a suitable technique for the electrical characterization of opal-based nanostructures. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nanostructured submicron calcium carbonate particles with sizes of 500 ± 90 and 172 ± 75 nm have been synthesized by mass crystallization in aqueous solutions with addition of glycerol, as well as a mixture of polyethylene glycol, polysorbate, and a cellular medium. CaCO3:Si:Fe nanoparticles 65 ± 15 nm in size have been obtained by template synthesis in pores of silica particles. The crystal structure and polymorphism of these particles are studied, and the influence of the size and structure of particles on the efficiency of their loading with a chemotherapy agent, as well as its release under model conditions at different рН, is determined. [ABSTRACT FROM AUTHOR]

The effect of 3-methacryloxypropyltrimethoxysilane (MPTMOS) on the nucleation of silica particles synthesized in a water−ethanol−ammonia−tetraethoxysilane (TEOS) mixture by the Stöber−Fink−Bohn method has been studied. It has been shown, using atomic force microscopy, that, as the content of MPTMOS in a TEOS + MPTMOS precursor mixture is increased from 0 to 12.5 mol %, the final silica particle size decreases from 470 to 10 nm, because the number of nucleation centers increases by several orders of magnitude. In contrast to TEOS, hydrolysis of MPTMOS yields a smaller amount of deprotonated orthosilicic acid monomers, the condensation of which is hindered by electrostatic repulsion. The polycondensation of electrically neutral products of MPTMOS hydrolysis gives rise to a larger number of nucleation centers in the reaction mixture. [ABSTRACT FROM AUTHOR]

We have developed a technique for the preparation of submicron spherical micro- and mesoporous silica particles via basic hydrolysis of organosilanes in an ethanol–water–ammonia mixture in the presence of cylindrical alkyl amine micelles. The particles synthesized in the presence of diethoxy(3-glycidyloxypropyl)methylsilane have been shown to contain cylindrical SiO2 nanochannels with an inner diameter of 3 nm, characteristic of nanostructured M41S-type materials, but with a smaller wall thickness (0.5 instead of 0.7 nm). Owing to this, the specific surface area and volume of pores increased from 750 to 1200 m2/g and from 0.5 to 0.7 cm3/g, respectively. The addition of 3-(methacryloyloxy)propyltrimethoxysilane to the reaction mixture leads to further increase in these parameters (up to 1400 m2/g and 0.8 cm3/g) owing to micropore formation in the nanochannel walls. [ABSTRACT FROM AUTHOR]

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]

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 Bragg reflection spectra of photonic crystals based on the opal–semiconductor (GaP, GaN) composites are studied. An approach is developed which provides a means for characterizing the opal-like structures. The approach is based on examination of the Bragg reflection spectral features and of the conditions for multiwave Bragg diffraction. The shape of the Bragg spectra is analyzed in the context of the approximation of a periodic planar-layered medium taking into account sintering and axial compression of the a-SiO2 spheres that constitute the three-dimensional opal lattice. The diameters and the coefficient of compression of the spheres are determined with regard to the spectroscopic structural invariant suggested in the study for defining the conditions for observation of multiwave Bragg diffraction at the system of the {111} planes. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Сomposite particles based on monodisperse spherical mesoporous silica particles (MSMSPs) are synthesized by noncovalent binding of organic active components (propidium iodide fluorescent dye and Radakchlorin photosensitizer) from aqueous solutions. Hybrid particles with a core-shell structure are synthesized, which are MSMSPs filled with Fe3O4 and coated with mesoporous silica, the internal surface of which is modified by Fluorescein isothiocyanate (FITC) fluorescence dye by means of chemisorption. The toxicity and penetration of the obtained particles into the cells of the HeLa and K-562 cell lines were studied. The effective photodynamic action of MSMSPs containing Radachlorin in mesopores is demonstrated, which indicates the promise of using the synthesized composite particles for medical purposes. [ABSTRACT FROM AUTHOR]

Abstract: Monodisperse carbon nanodots and nanodiamond particles were studied by AFM method. Particle size distributions were calculated using AFM and DLS data. The results obtained correspond to TEM measurements. It was demonstrated that AFM allows detecting nanoparticles with sizes less than 2 nm. The average size of the particles for both samples was found to be ~4 nm. It was found that PSD for CND and DND was symmetric and asymmetric, correspondingly. Such difference can be understood in terms of different crystal structure perfection and the specific aspects of nanosized carbon preparation technology. [ABSTRACT FROM AUTHOR]

The results of spectroscopic studies of the diffraction anomalies (the so-called resonant Wood anomalies) in spatially periodic hybrid structures based on chalcogenide Ge2Sb2Te5-coated opal films of various thickness are presented. A theoretical analysis of spectral-angular dependencies of the Wood anomalies has been made by means of a phenomenological approach using the concept of the effective refractive index of the waveguiding surface layer. [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]

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 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]

We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 ( λ=442 nm, I0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 ( λ=532 nm, I0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: LD=0.18 μm. [ABSTRACT FROM AUTHOR]

Abstract: We report the experimental investigation of the non-steady-state photoelectromotive force in porous glass filled with GaN nanoparticles. The sample is illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependencies of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths , 532nm. The conductivity of the material is measured: and . [Copyright &y& Elsevier]

Abstract: Synthetic opal crystals were infiltrated with concentrated (1–10 mM) aqueous solutions of iron porphyrin (FeTPPS). The assemblies of nanoscale blocks of 25–30 nm, which have been clustered into rod-like structures of size 100–150 nm typical of FeTPPS, were observed on the surface of silica spheres (diameter nm). Optical properties of infiltrated photonic crystals were investigated on the samples immersed into liquids. The absorption bands of FeTPPS were located in the vicinity of opal stop band, the position of which was tuned by varying the effective refractive index of opal immersed in various liquids. The absorption bands of FeTPPS were strongly influenced by ethanol presumably due to the formation of chemical bonds between sulfonic groups of FeTPPS with silanol groups on the surface of silica spheres and with ethoxy groups in ethanol environment. Data have shown that FeTPPS is a perspective material for the development of hybrid magnetophotonic devices based on the opal photonic crystals. [Copyright &y& Elsevier]

Abstract: Artificial opals made of silica spheres and infiltrated with aqueous solution of iron porphyrin (FeTPPS) possessing the absorption band in a visible spectral range were studied. The structural, optical and magnetic properties of composite structures were investigated. Bulk samples of opal structure were obtained by sedimentation technique from colloidal solution of SiO2 spheres of diameter 240 and 245 nm. The structure of the samples was examined by atomic force microscopy. The properties of photonic crystals were demonstrated by optical measurements in transmission and reflection modes. The stop band was observed in the region 510–550 nm. In samples annealed at 900 °C the width of the stop band increased to ∼70 nm. Aqueous solutions of FeTPPS of concentration ∼1.0 mM and various pH-values were used for infiltration. The infiltration has led to a change of photonic characteristics, position of the stop band and dependence on light incidence angle. The absorption bands typical of FeTPPS were observed in the vicinity of the stop band. The photonic properties of infiltrated opal structures were determined to depend on the acidity of aqueous solution, which was used in technological procedure. Magnetic properties of FeTPPS-infiltrated opal samples, which have been studied at 5–300 K in magnetic fields up to 5 T, were discussed. From magnetic measurements it followed that magnetic Fe–Fe interactions have practically vanished in hybrid samples and Fe centers should be treated as isolated ones. [Copyright &y& Elsevier]

Nanocrystalline GaP and amorphous GaPN solid solution have been synthesized in voids of artificial opal. The opal–GaP and opal–GaPN composites obtained clearly demonstrate properties of photonic crystals. The reflection spectra of the opal–GaPN composite exhibit specific features related to multiple Bragg diffraction on two systems of {111} planes, parallel and nonparallel to the surface of the photonic crystal. The study of photoluminescence spectra revealed a considerable modification of the emission band of the opal–GaPN composite, which was attributed to the influence of the photonic band gap. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We have developed a colloidal crystal templating method for preparation of diamond films with 2D and 3D ordered porous structures. The technological process involved breaks down into (a) impregnation into the pores of silica colloidal crystal (opal) films of detonation nanodiamond (DND) particles from their hydrosol; (b) microwave plasma-enhanced chemical vapor deposition (MWPECVD) regrowth with diamond of pores with high DND filling; (c) Ar(+) ion dry etching of fragments of shells of coalesced diamond crystallites which form in the course of MWPECVD on the surface of the SiO(2) beads making up the outer surface of a film and (d) wet etching of the SiO(2) template in aqueous HF solution. The final samples are either connected to the substrate or free-standing films of various thicknesses having 2D or 3D ordered porous structures. The morphology of the diamond films fabricated by this method replicates the pore network of the opal template. Raman measurements confirm the diamond structure of the synthesized ordered porous material.