Optical limiters and diffraction elements based on a COANP-fullerene system: Nonlinear optical properties and quantum-chemical simulation

The results of optical study and quantum-chemical simulation of a conjugated organic system, 2-cyclooctylamino-5-nitropyridine (COANP)-fullerene, performed to determine its potential for application as a limiter of visible and near-IR laser radiation and as a material for diffraction elements in systems for reversible recording of optical information, are presented. Complexation between a COANP molecule and fullerene is considered as one of the main mechanisms responsible for the corresponding properties of this system. For the first time, nonlinear optical characteristics of COANP-C₆₀ and COANP-C₇₀ systems are comparatively studied and the intermolecular interaction between a COANP molecule and fullerene is analyzed on the quantum-chemical level.     

Computational modeling of amorphous silica. 4. Modeling the initial structures. Aerogel

A qualitative classification algorithm for constructing large clusters of aerogel model structures is used. According to this algorithm, aerogel is classified with polysilicas characterized by a packing of long chains of silicon-oxygen tetrahedra. A model of the aerogel structure is suggested, according to which aerogel is described as a set of cross-linked chains forming double or more complex ribbons. This model is in agreement with the conclusions drawn from analysis of the vibration spectra of its components. Institute of Surface Chemistry, Ukrainian Academy of Sciences. Russian University of Peoples' Friendship. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 35–38, May–June, 1994. Translated by O. Kharlamova     

Computer modeling of amorphous silica structures

An algorithm for large cluster construction for quantum-chemical modeling of amorphous silica structures is suggested. The algorithm is based on the conception that different species of disperse amorphous silica, namely aerosil, silica gel and aerogel are different polymorphic forms; that these polymorphic modifications can be classified by Libau's crystallochemical classification of silicates; that each classification mode is determined by the manufacturing method. The structure models presented are obtained in accordance with the algorithm and are in line with the chemical reactions forming the basis of commercial manufacturing of the products.     

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Coherent neutron inelastic scattering intensifies for two low-frequency Γ₄ internal modes in anthracene-d₁₀ have been measured at several different Brillouin zone centres. These intensifies have been used to determine the eigenvectors of the two modes involved. It is shown that the motion in both cases is a combination of a butterfly motion (B) and a twisting motion (T). The energy proportions in these two modes are 0.97B and 0.03T (±0.01) for the mode at 3.16 THz and 0.94T and 0.06B (±0.04) for the mode at 4.60 THz. This experimental result strengthens our reliance on model calculations for the assignment of phonon frequencies measured by neutron coherent inelastic scattering.     

Noise-induced escape on time scales preceding quasistationarity: New developments in the Kramers problem

Noise-induced escape from the metastable part of a potential is considered on time scales preceding the formation of quasiequilibrium within that part of the potential. It is shown that, counterintuitively, the escape flux may then depend exponentially strongly, and in a complicated manner, on time and friction. (c) 2001 American Institute of Physics.     

Studies on photoinduced effects in pulse-electrodeposited Ag/Hg-1212/CdSe hetero-nanostructures

Metal/superconductor/semiconductor (Ag/Hg-1212/CdSe) hetero-nanostructures have been fabricated using pulse-electrodeposition technique and are characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and Ag/Hg-1212/CdSe heterojunctions is measured in dark and under laser irradiation at room temperature. The nature of the junction formed and built-in-junction potentials were determined. The increase in carrier concentration across the junction due to photo-irradiation has been observed.