Concentration dependence of radiation-induced changes in the optical properties of Ge<Subscript>x</Subscript>As<Subscript>40−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>60</Subscript> films

Radiation-induced changes in the optical properties of chalcogenide glasses in the Ge-As-S system are investigated as a function of the concentration. Theoretical calculations are performed with due regard for possible constraints on the range of variation in the number of homobonds and heterobonds upon their switching in the structural network of chalcogenide glasses. The experimental data are obtained upon irradiation of Ge_xAs_40?xS₆₀ thin films with fast electrons (6 MeV). The possible mechanism of structural transformations responsible for the specific features in the concentration dependence of the change in the band gap of chalcogenide glasses is discussed.     

Adsorption of functionalized benzoic acids on MgSO4.H2O (100).

Using a combination of ab initio and semiempirical methods, adsorption problems on surfaces with large unit cells and low symmetry can still be studied. Here, a hybrid approach of density functional theory (DFT) and Hartree-Fock (HF) was used. As an example, we determined the geometry and the electronic properties of benzoic acid (BA), salicylic acid (SA) and para-salicylic acid (p-SA) adsorbed on MgSO(4).H(2)O (100), which are used as conditioner molecules for the electrostatic separation of minerals. Contrary to general expectations, these molecules are chemisorbed, with binding energies around 1.9 eV, forming bonds through the carboxylic O atom of the COOH groups in a nonplanar geometry, although the surface is a stoichiometric wide-band-gap insulator and the molecules stay intact. In contrast, a planar adsorption geometry turned out to be nonbonding. Bonding takes place by means of surface-molecule resonances due to the overlap of the valence band with molecular orbitals, assisted by a small charge-transfer molecule to the surface of around 0.15e. These combined interactions cause an intramolecular twist between the COOH group and the benzene ring.     

Electronic structure of the organic semiconductor copper phthalocyanine: experiment and theory

The electronic structure of the organic semiconductor copper-phthalocyanine (CuPc) has been determined by a combination of conventional and resonant photoemission, near-edge x-ray absorption, as well as by the first-principles calculations. The experimentally obtained electronic valence band structure of CuPc is in very good agreement with the calculated density of states results, allowing the derivation of detailed site specific information.     

The electronic structure of cobalt phthalocyanine

The electronic structure and morphology of organic semiconducting cobalt-phtalocyanine (CoPc) films in situ prepared on the Au(001)-5×20 superstructure have been studied by a combination of experimental and theoretical work. The CoPc molecular film was characterized by photoemission spectroscopy (PES, valence band and core-level). The experimental results were simulated and have been explained in the framework of density functional theory (DFT) calculations. The C 1s and N 1s core level spectra were analyzed by taking into account the fact that both types of atoms have different nonequivalent positions in the molecule. And finally, the experimentally obtained electronic valence band structure of CoPc is in very good agreement with ab initio density of state results, allowing a detailed site-specific insight into the system.     

Effect of electron irradiation on InSb microcrystals

The results of experimental studies of electrophysical properties of heavily doped n-InSb whiskers exposed to electron irradiation (13 MeV, 300 K) are reported. The limiting electrophysical parameters and the problem of the Fermi-level pinning in irradiated InSb are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 42–45, February, 2006.     

Spin-polarized transport and thermopower of organometallic nanocontacts

We present a theoretical study of the length dependence of both conductance and thermopower of organometallic vanadium-benzene molecules (V _nBz_n+1) sandwiched between magnetic Co(100) electrodes. We show that the molecules with n≥3 are efficient spin filters. Namely, we find that the zero bias conductance of the majority electrons is small and decays exponentially with increasing length of the molecule and is in the tunneling regime while the minority electrons show metallic conductance. We show furthermore that the thermopower strongly depends on the length of the molecules and can even change sign as a function of length and temperature.