A. V. Nashchekin

Monodisperse spherical mesoporous silica particles: fast synthesis procedure and fabrication of photonic-crystal films

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 250-1500xa0nm has been developed. The synthesis is fast (taking less than 1xa0h) 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 ∼15xa0nm 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 3.1xa0±xa00.15 and 2.3xa0±xa00.12xa0nm, respectively. The specific surface area and the pore volume of MSMSP were, depending on synthesis conditions, 480-1095xa0m(2)xa0g(-1) and 0.50-0.65xa0cm(3)xa0g(-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.

Formation of Silver Nanoparticles on the Silicate Glass Surface after Ion Exchange

It has been experimentally shown that water vapor thermal treatment of silicate glasses with silver ions introduced by ion exchange leads to the formation of a silver nanoparticle layer with a high packing density on the glass surface. The results of studying the morphology of samples by atomic force and electron microscopy and X-ray spectral analysis of the composition of nanoparticles, as well as the optical density and luminescence spectra in different stages of the treatment, are presented. Mechanisms explaining the processes responsible for silver nanoparticle formation upon water vapor thermal treatment on the glass surface after ion exchange are proposed.

Melt synthesis and structural properties of opal-V2O5 and opal-VO2 nanocomposites

A method has been proposed for filling bulk and film opals with V2O5 and V2O5: W melts under the action of capillary forces. The VO2 and VO2: W (1.8 mol %) compounds have been synthesized from the V2O5 and V2O5: W precursors in opal pores. The phase composition and morphology of the nanocomposites prepared have been investigated. It has been revealed that, in the opal-V2O5 composite, the filler compound has a texture formed by the directional crystallization of the melt in pores of the opal film. The tunable photonic crystal heterostructure opal/opal-VO2 has been synthesized using liquid chemical etching.

Specific features of the formation of vanadium oxide micro- and nanocrystals during gas-phase synthesis

A modified method of gas-phase synthesis of vanadium oxide micro- and nanocrystals was developed. The morphology of the crystals obtained and its dependence on the synthesis conditions are analyzed. The method is shown to permit the growth of rod-shaped crystals rectangular in cross section, whiskers, crystals with a rectangular cavity, and also lamellar crystals and planar ordered textures consisting of oriented rodshaped crystals. The microcrystals synthesized were used to study the mutual reversible transformation of various vanadium oxides using oxidation and reduction reactions.

Track technology for creating the arrays of nickel microtips, micronozzles, and microtubes

A method for obtaining surface arrays of nickel objects (microtips, micronozzles, and microtubes) with preset geometric parameters by means of a track technology has been developed using the data of scanning electron microscopy. It is shown that Ni microtips with a radius as small as 10–25 nm can be obtained, which allows these microobject arrays to be used as multiple-tip field emission cathodes capable of providing high emission current densities.

Monodisperse spherical meso–macroporous silica particles: Synthesis and adsorption of biological macromolecules

Monodispersed spherical silica particles, including large mesopores (over 10 nm) and macropores (up to 100 nm) were obtained by chemical etching in an autoclave. A method for introducing globular protein myoglobin molecules into the pores is developed. The method of filling is based on a high adsorption capacity of the developed internal pore structure of the particles. The structure and adsorption properties of the materials are studied.

Investigation of the morphological features of silver nanoparticles in the near-surface layers of glass when they are synthesized by heat treatment in water vapor

This paper presents the experimental results of synthesizing silver nanoparticles in the near-surface layers of glasses by heat treatment in water vapor. It is shown that the presence of a cracked layer on the glass surface has a substantial effect on the shape of the silver nanoparticles, and this manifests itself in the absorption spectra of the glasses. It is established that, when silver is introduced by thermal diffusion from a film, the silver nanoparticles have the shape of oblate ellipsoids in nanocracks and on the glass surface, whereas they acquire a spherical shape in the volume of the glass. It is shown that, when silver is introduced into glass by ion exchange and the glass is later heat-treated in water vapor, part of the silver emerges onto the glass surface, forming a structured film.

Fabrication of the structures with autocatalytic CdTe nanowires using magnetron sputtering deposition

We report the possibility of autocatalytic synthesis of highly crystalline perfect CdTe nanowires by magnetron presputtering deposition through the windows in ultrathin layers of SiO2. The photoluminescence spectra of obtained CdTe nanowires exhibit an emission band in the 1.4–1.7 eV region, indicating crystalline perfection of the nanowires.

Specific features of thermal dissolution of silver and gold thin films in silicate glass

It has been shown experimentally that the thermal dissolution of silver and gold thin films in silicate glass is accompanied by the formation of a monolayer of silver and gold micro- and nanocrystals, respectively, on the surface of the glass. These processes occur at temperatures well below the melting temperature of the metal. Microcrystals are formed predominantly at the edges of islands of the metal film, where there is a sufficient amount of the material for their growth. Silver and gold nanocrystals are formed in the case when atoms of the metal dissolved in the glass repeatedly emerge on the glass surface. Silver and gold dissolved in the glass exist not only in the form of atoms and ions but also in the form of charged and neutral molecular clusters.

Synthesis and modification of micro-and nanorods of vanadium oxides

A method for the gas-phase synthesis of single-crystalline micro-and nanorods of vanadium pentoxide (V2O5) has been developed based on the thermal decomposition of vanadium chloride vapor. Using this technique, it is possible to obtain separate micro-and nanorods (with thicknesses ranging from 50 nm to 5 μm and a length of up to 7 mm), planar arrays, and three-dimensional structures. The temperature dependence of the resistance of individual microrods of vanadium oxides in various degrees of oxidation has been measured.