Porous structure of synthetic opals

Some adsorption, structural, and annihilation characteristics of synthetic opals are measured. An analysis of these characteristics makes it possible to conclude that the total porosity in opals comprises macropores, which are in essence the voids between structure-forming spheres, and nanopores connected to the substructure of the spheres. The systems of macropores and nanopores are separated by narrow channels that collapse upon the thermal treatment of opals. The sizes of primary a-SiO₂ particles and nanopores, which correspond to the voids between these particles, are estimated.     

Magnetization Distribution in Particles with Configuration Anisotropy,Prepared via Microsphere Lithography

Technical Physics - The arrays of permalloy particles with shape anisotropy, prepared via microsphere lithography, have been characterized using atomic force microscopy and magnetic force...     

Viscosity effect on the fluorescent and conformational properties of 2-N-piperidino-5-(2′,2′-dicyanovinyl)thiophene

The mechanism of deactivation of the electronic excitation energy of 2-N-piperidino-5-(2′,2′-dicyanovinyl)thiophene is studied by the methods of fluorescence and quantum chemical calculations. The increase in the fluorescence quantum yield from 0.0004 in n-hexane at room temperature to 1 in an EPA mixture at 77 K is determined by an increase in the viscosity (rigidity) of the medium hindering the rotation of molecular fragments. The efficient nonradiative process in a molecule with the probability ≤2.5×10¹¹ s^?1 results mainly from rotation about the C12–C13 bond and the transition to an intermediate state with a low-lying energy level.     

Optical properties of thin films of closely packed SiO2 spheres

Ordered, closely packed, defect-free one-, two-, and three-layer thick films of SiO₂ spheres of diameter D varying from 0.6 to 1.4 μm were obtained. Their optical transmittance and reflectance spectra were measured in the range 0.3–2.5 eV. The one-layer structures reveal a transmittance minimum whose spectral position is described by the Bragg law with the plane separation equal to the sphere radius D/2. As the number of the layers increases, a spectral feature appears which signals the formation of a photonic gap in the 〈111〉 direction of the fcc crystal lattice and is determined by the distance between the {111} planes equal to 0.816D. The spectra of two-and three-layer structures measured with a diverging light beam contain additional lines originating from the formation of photonic gaps by the {111} and {221} planes. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 6, 2002, pp. 1026–1031. Original Russian Text Copyright ? 2002 by Bazhenov, Gorbunov, Aldushin, Masalov, Emel’chenko.