Papers by Keyword: Electronic Excitations

Abstract: Polycrystalline C₆₀ saturated with molecular hydrogen and nitrogen were studied using the spectral-luminescent method of registration in the quantum counting mode at a low temperature of 20 K. Previously, it was found that the temperature limit of the adsorption crossover (the transition from the diffusion mechanism of intercalation - physisorption to chemical interaction - chemisorption) for fullerite C₆₀ in an H₂ atmosphere is about 250 °C [1], and in an N₂ atmosphere – 420 °C [2], respectively. At saturation temperatures above those indicated, the process of chemical interaction of impurity molecules and the fullerite matrix occurs with the formation of new compounds. Therefore, saturation was carried out at temperatures of 300 °C for hydrogen and 450 °C for nitrogen under a pressure of 30 atm. For the first time, the results of registration of photoluminescent radiation at low temperatures from new substances based on fullerite C₆₀ are presented. A mixture of weakly saturated fulleranes C₆₀H_X was obtained by saturation of hydrogen from the gas phase at a temperature close to the sorption crossover temperature, and their low-temperature photoluminescence was identified for the first time. The analysis of the "blue" shift of the beginning of the spectrum of such radiation allowed us to more accurately attribute the obtained material to the initial segment of the fullerane series. The presence of radiation of the azafullerene dimer (biazafullerene) (C₅₉N)₂ in the spectra of the reaction products of C₆₀ with N₂ was also detected. It was shown that for polycrystalline samples of C₆₀ saturated in a nitrogen atmosphere, the characteristic luminescence of biazafullerene with a maximum at 1.53 eV determines the intensity and shape of the entire short-wave part of the emission spectrum of the complex of synthesized substances.

Abstract: Spatial distributions of a potential established inside a crystal by an externally applied potential are investigated theoretically in Pd and PdH. The calculations were performed in the framework of the linear-response approach with full inclusion of the electron band structure obtained within a self-consistent pseudopotential scheme. Analysis shows that in clean palladium the potential amplitude is maximal at the octahedral sites of the fcc lattice where the hydrogen ions predominantly reside. On the other hand the corresponding amplitude is significantly lower at the palladium ion positions. We observe drastic modifications in the screening properties in Pd upon hydrogen absorption. Nevertheless, the potential amplitude in PdH is also small at the Pd sites, whereas that at the H sites is significantly larger. However, in PdH the H ions are located at places where a local shallow minimum in the induced potential amplitude is observed. These results only slightly depend on the magnitude of the momentum transfer.

Abstract: The electronic excitations and electron absorption spectra of polychlorinated dibenzo-p-dioxins (PCDDs) were investigated by the time-dependent density functional theory (/DFT). The main spectral features were interpreted on the basis of the electronic structure of PCDDs by fully considering the possible interference of coexist organic molecules for the electron spectra. With the numbers of benzene rings in aromatic molecules increasing, the excitation energies decrease. The excitation energies of the compounds with three or four benzene rings (phenanthrene or fluoranthene) fall into the electronic transition regions of PCDDs. Therefore these compounds were not possible differentiate from the electron spectra of PCDDs. Furthermore, with the amounts of benzene rings extending to surpass three and four, the energies decease continuously and run beyond of the transition energy ranges of PCDDs. Thus the electron excitation energies of those aromatic molecules with three or four benzene rings were in the range of PCDDs, acting as the possible interferential substances for the detecting of PCDDs.

Abstract: The effect of electron dose rate on phase separation induced by electronic excitation in GaSb nanoparticles has been studied in order to see whether a nonlinear relation between density of excited states introduced and the efficiency of the phase separation is found or not. The phase separation to two phases consisting of an antimony core and a gallium shell proceeds after incubation time with increasing electron dose and does only at the dose rate above a threshold value. It is suggested that such nonlinear behaviors take place as a cooperative phenomenon among electronic-excitation effect, nano-size effect and temperature.

Abstract: Characteristic features of radiation damage in insulators for fusion reactors are that those materials are exposed to synergistic radiation damage of elastic displacements and electric excitation with the presence of an electric field. This paper describes the nucleation-and-growth of radiation-induced defects and their stability in oxide ceramics, such as magnesium-aluminate spinel (MgAl2O4) and alpha-alumina (α-Al2O3). Microstructure evolution in these oxides is shown through transmission electron microscopy for the formation process of dislocation loops under synergistic irradiation with displacements and ionizing radiation, the stability of dislocation loops, and the nucleation-and-growth process of loops with an applied electric field.