E. Yu. Trofimova

Synthesis of monodispersed mesoporous spheres of submicron size amorphous silica

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 m2/g, whereas the pore volume and average diameter are equal to 0.63 cm3/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%.

Effect of tetraethoxysilane pretreatment on synthesis of colloidal particles of amorphous silicon dioxide

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 SiO2 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 SiO2 particles.

Two-dimensional light diffraction from thin opal films

This paper reports on experimental and theoretical investigations of light diffraction from thin films of synthetic opal. The diffraction patterns have been studied visually and recorded in different scattering geometries with the films illuminated with white unpolarized light. The diffraction pattern obtained with the film illuminated with a light beam along the [111] axis, which is normal to the film surface, has C6 symmetry and consists of six strong reflections arranged symmetrically with respect to the incident beam. This pattern becomes substantially more complicated when the film is illuminated by white light at an arbitrary angle to the [111] axis. An experimental study of the spectral response and angular relations of the diffraction patterns has established a fairly full pattern of transformation of diffraction reflections obtained under variation of the angle of light incidence on an opal film. The remarkably good matching of experimental and calculated data provides compelling evidence for light diffraction from thin opal films being two-dimensional.

Fluorescent monodisperse spherical particles based on mesoporous silica containing rhodamine 6G

Fluorescent monodisperse spherical silica (SiO2) particles with a regular mesoporous structure containing encapsulated Rhodamine 6G (R6G) dye have been synthesized. The as-synthesized particles have been coated with SiO2 and SiO2-CTAB (cetyltrimethylammonium bromide, C16H33N(CH3)3Br) shells in order to prevent uncontrolled release of the dye from pores. The kinetics of R6G release from the pores of silica particles has been studied. It has been found that the particles synthesized by adding CTAB and R6G to the reaction mixture, as well as the particles coated with the SiO2-CTAB shell, are characterized by the maximum duration of dye release from the pores, which is probably associated with the formation of chemical bonds between R6G and CTAB molecules.

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.

Spherical microresonators with luminescent a-Si: C: H coating

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.

Diagnostics of Living Cells under an Atomic Force Microscope Using a Submicron Spherical Probe with a Calibrated Radius of Curvature

The relief and mechanical elasticity of living cells from lines A549 and L41 are studied. To minimize the destructive effect of the atomic force microscope on the cell and improve the measuring accuracy of the elasticity module, special probes with a single colloid amorphous SiO2 nanogranule at their tips are employed. A procedure for preparing such probes is demonstrated.

Preparation of Colloidal Films with Different Degrees of Disorder from Monodisperse Spherical Silica Particles

The process of coagulation of suspensions of monodisperse spherical silica particles driven by appropriate coagulants (NH4Cl, HCl, C16H33N(CH3)3Br) has been studied. Films of photonic crystals and photonic glasses have been grown by the sedimentation method. The possibility of controlling the degree of structural disorder in colloidal films by properly varying the resistance of the water suspension of particles to aggregation has been demonstrated.

Controlling optical response of Opal/Ge2Sb2Te5 hybrid film structures

Hybrid film structures of the photonic crystal (opal)/glassy chalcogenide semiconductor (Ge2Sb2Te5) 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 Ge2Sb2Te5 film.

Small-angle X-ray diffraction investigation of twinned opal-like structures

Small-angle X-ray diffraction from synthetic opal films has been investigated as a function of the orientation of the sample. All the observed (hkl) diffraction reflections have been interpreted. The reconstruction of the reciprocal lattice of the studied opal films has been carried out. The diffraction patterns and scattering intensity profiles along chains of reciprocal lattice points have been calculated. It has been shown that, in the reconstructed reciprocal lattice of the opal films, the appearance of chains of partially overlapping nodes that are oriented along the direction Γ → L is caused by two factors: the small thickness of the film and the existence of stacking faults in it.