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Monodisperse molybdenum-disulfide nanoparticles are synthesized in the mesopores of a template, i.e., spherical silica (mSiO2) particles. First, the pores of the mSiO2 particles are impregnated with the precursor (ammonium tetrathiomolybdate) solution. Then, MoS2 is synthesized from the precursor within the pores of mSiO2 via the annealing of particles in a H2S/H2 atmosphere under thermodynamically equilibrium conditions. To obtain individual MoS2 nanoparticles, the template material (a-SiO2) is selectively removed from the composite mSiO2/MoS2 particles via etching in HF. The average size of the MoS2 nanoparticles is determined by microscopic methods to be 3.5 nm. According to dynamic light scattering data, the nanoparticles have a low root-mean-square size scatter (18%). [ABSTRACT FROM AUTHOR]

Abstract: A nanocomposite in the form of monodisperse spherical mesoporous silica particles (mSiO2) filled with GaN:Eu3+ is synthesized by the template method. The method is based on the capillary impregnation of pores of mSiO2 particles with a melt of crystal hydrates of gallium and europium (0.22 wt %) nitrates, followed by thermal decomposition and ammonia treatment. It is shown that nanocomposite particles contain hexagonal GaN:Eu3+, are of spherical shape, monodisperse and do not coalesce with each other. The photoluminescence spectra of the mSiO2/GaN:Eu3+ particles show a group of lines characteristic of intracenter transitions in Eu3+. [ABSTRACT FROM AUTHOR]

Results obtained in an experimental study of spontaneous emission from erbium ions in a spectral range corresponding to the lower photonic band edge of distributed Bragg reflectors (1D photonic crystals) are presented. The photonic crystals were constituted of alternating quarter-wave a-Si:H and a-SiOx:H layers grown by PECVD. Erbium was introduced into the a-Si:H layers by magnetron sputtering of an erbium target in the course of structure growth. The change observed in the intensity of spontaneous emission is due to the nonmonotonic behavior of the density of optical modes near the photonic band edge. © 2005 Pleiades Publishing, Inc. [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]

The effect of hot-filament chemical vapor deposition conditions on the phase composition of diamond films grown on a silicon substrate was studied. The growth conditions providing the highest content of diamond phase at a growth rate of about 1 µm/h were ascertained. [ABSTRACT FROM AUTHOR]

Fabry-Perot microcavities tuned to a wavelength of 1.5 µm have been fabricated by means of plasma-enhanced chemical-vapor deposition on the basis of a-Si:H and a-SiO[sub x]:H. Distributed Bragg reflectors (DBRs) and the active layer were grown in a single technological cycle. The half-wave active layer was doped with erbium in the course of growth from a metal-organic compound. The high optical contrast enabled a high microcavity quality factor (Q = 355) with only three DBR periods. The intensity of erbium photoluminescence (PL) from the microcavity is two orders of magnitude higher than that of erbium emission from an identical a-Si:H layer without DBR. Transmission, reflection, and PL spectra are analyzed. It is found that the spectral shape of the line of erbium PL (transition [sup 4]I[sub 13/2] → [sup 4]I[sub 15/2]) from the microcavity virtually coincides with the shape of the resonance peak of its transmission spectrum. Theoretical calculations have been performed providing a comprehensive description of the observed experimental spectra. [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]