Density effect and plasmon bremsstrahlung in the theory of plasmon excitation by large-angle scattered electrons

Experiments on plasmon excitation by electrons which scatter at large angles constitute one of the basic sources of information on plasmon in solids. These experiments provide spectra especially rich in detail, of electrons backscattered from targets having a comparatively perfect structure. Besides, these are the only experiments that are possible at low energies of incident electrons when no shooting of thin films can take place. In such experiments the lattice must absolutely be involved in the process of electron backscattering, since the plasmon cannot appreciably affect the direction of motion of electrons. However, the lattice not only causes the appearance of backscattered electrons, but can also affect the very process of plasmon excitation. In the present paper a theoretical treatment is given of the influence which the lattice exerts on the process of plasmon generation. This influence is displayed through two effects: the bremsstrahlung of plasmons and the density effect. These effects are due to the processes of either the plasmon emission beginning before the termination of the electron-lattice collision or the electron-lattice collision beginning before the termination of electron-plasmon collision event and to the interference of these processes. The most important result of the theory developed in the paper is that these effects lead to the broadening of the plasmon resonance line, which is of the same, or even greater, order of magnitude than that due to the traditional mechanisms.     

Sol–gel synthesis of highly effective catalyst based on cobalt tetrasulfophthalocyanine complex and silicon oxide

New hybrid materials based on silicon oxide and water soluble cobalt phthalocyanine complex were synthesized and characterized. It was shown that synthesized material exhibit pronounced catalytic activity in the R–SH type of organic compounds oxidation reaction in comparison with the individual macroheterocycle. The influence of the synthetic route of the hybrid material preparation on its catalytic efficiency was determined.     

Between Adamantane and Atrane: Intrabridgehead Interactions in the Cage‐Like Phosphane Related to a Novel Tris(homoadamantane) Ring System

Herein, we report unusual four‐center interactions in the novel cage‐like phosphane, 1,4,7‐triaza‐9‐phosphatricyclo[5.3.2.1^4,9]tridecane (CAP). This water‐soluble ligand, the first example of a tris(homoadamantane) ring system, can be considered a macrocyclic homologue of the well‐known PTA (1,3,5‐triaza‐7‐phosphaadamantane). However, ³¹P NMR spectroscopic anomalies of CAP follow those typical for the bi‐/tricyclic atrane systems. Another atrane‐like feature of CAP is the ability of one nitrogen atom to undergo out–in pyramidal inversion. The latter is associated with a substantial decrease in the intracage N?N and P?N distances. Analysis of electron density distribution [molecular electrostatic potential (MESP) and atoms‐in‐molecules (AIM) approaches] suggests that the P and N atoms in the pyramidally inverted CAP derivatives are involved in interactions resulting in accumulation of electron density at the center of the phosphane cage. The latter can reliably explain the stereoelectronic and NMR anomalies of the new ligand. The semi‐flexible CAP cage populates the structural niche between the rigid adamantine skeleton of PTA and flexible atrane systems and can be regarded as an alternative to PTA in aqueous coordination chemistry.     

Optical activity of dielectric superlattices with defects

Natural optical activity of a nonideal 1D multilayer system is considered phenomenologically and the concentration dependence of its specific rotation angle is simulated numerically. As a model system, the two-sublattice SiO₂ LC structure was chosen. Specific gyrotropy features caused by the corresponding disordering types of the studied systems were revealed. Based on the developed phenomenological theory, the frequency dependence of the specific rotation angle of the polarization plane of linearly polarized light was studied for the case of a molecular-crystal multilayer system whose layers contain pointlike defects. This creates additional possibilities for simulating optically active multilayer composite materials.     

Relationship between the spectral properties of solutions of borofluoride complex of alkylated dipyrromethene and the physicochemical parameters of solvents

Spectral and photophysical characteristics of borofluoride complex of alkylated dipyrromethene (Bodipy) are determined by means of absorption and fluorescence electron spectroscopy in various organic solvents. Dependences of the spectral and photophysical characteristics of Bodipy solutions vs. the physico-chemical parameters of solvents are obtained by linear regression analysis and the contribution from each parameter to the property under study is determined. It is established that the negative solvatochromic effect is intrinsic for Bodipy. It is concluded that specific interactions contribute substantially to the properties of the chromophore, which are determined by the electron donor properties of the solvent.     

Numerical simulation of acoustic excitations in an imperfect 1D superlattice

Features of the propagation of acoustic excitations in an imperfect 1D superlattice have been studied within the virtual crystal approximation. The dependence of the lowest acoustic band gap width of an imperfect (disordered in the composition and layer thickness) two-sublattice 1D phonon crystal on the concentration of impurity layers has been numerically simulated.     

Mechanisms of manifestation of strength upon high-speed intrusion of metal jets into metals and brittle materials

Mechanisms of manifestation of strength upon penetration of cumulative jets into metals and brittle materials have been analyzed on the basis of studying the kinetics of intrusion. In contrast to intrusion into metals, which proceeds with a smooth variation in the velocity, the process of penetration of a cumulative jet into a brittle material is intermittent: the initial stationary intrusion stops and recommences after some time in an unstable form. The revealed features have been explained from the viewpoint of radial action of a cavern in a brittle material on a cumulative jet, when the primary intrusion of a jet causes radial convergence of fragments of cavern walls and the secondary penetration through the regions of interaction. The necessary conditions for the radial action are the high strength resistance and high destruction rate of brittle material is, providing the destruction and convergence of cavern walls. The collapse of the cavern and the secondary penetration terminate with the arrival of the unloading wave at the zone of primary intrusion.