Effect of annealing on the spin density of dangling bonds and the structures of amorphous germanium

Electron paramagnetic resonance was used to study the dependence of the volume spin density of dangling bonds ina-Ge films produced by cathode sputtering in argon on annealing temperature. The structure of the films is determined by x-ray diffraction analysis. Two EPR lines with g=2.019 and g=2.003 are observed whose intensities change nonmonotonically with annealing temperature. The g=2.019 line is characteristic only of the amorphous state of germanium, while the g=2.003 line persists even after crystallization of the films. When the results are compared with structure data, the conclusion may be drawn that the observed lines in the EPR spectrum are related to the dangling bonds in the peripheral regions of two types of clusters. The g=2.003 line is due to dangling bonds in the peripheral region of clusters with the usual cubic packing of atoms, and the g=2.019 line is due to clusters of the hexagonal type, which is not characteristic of the normal structure of crystalline germanium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 51–57, July, 1989.     

Ag(I)/V(V) Heterobimetallic Frameworks Generated from Novel-Type {Ag(2)(VO(2)F(2))(2)(triazole)(4)} Secondary Building Blocks: A New Aspect in the Design of SVOF Hybrids

A series of new silver(I)-containing MOFs [Ag(2)(tr(2)ad)(2)](ClO(4))(2) (1), [Ag(2)(VO(2)F(2))(2)(tr(2)ad)(2)]·H(2)O (2), [Ag(2)(VO(2)F(2))(2)(tr(2)eth)(2)(H(2)O)(2)] (3), and [Ag(2)(VO(2)F(2))(2)(tr(2)cy)(2)]·4H(2)O (4) supported by 4-substituted bifunctional 1,2,4-triazole ligands (tr(2)ad = 1,3-bis(1,2,4-triazol-4-yl)adamantane, tr(2)eth = 1,2-bis(1,2,4-triazol-4-yl)ethane, tr(2)cy = trans-1,4-bis(1,2,4-triazol-4-yl)cyclohexane) were hydrothermally synthesized and structurally characterized. In these complexes, the triazole heterocycle as an N(1),N(2)-bridge links either two adjacent Ag-Ag or Ag-V centers at short distances forming polynuclear clusters. The crystal structure of compound 1 is based on cationic {Ag(2)(tr)(4)}(2+) fragments connected in a 2D rhombohedral grid network with (4,4) topology. The neighboring layers are tightly packed into a 3D array by means of argentophilic interactions (Ag···Ag 3.28 ?). Bridging between different metal atoms through the triazole groups assists formation of heterobimetallic Ag(I)/V(V) secondary building blocks in a linear V-Ag-Ag-V sequence that is observed in complexes 2-4. These unprecedented tetranuclear {Ag(2)(VO(2)F(2))(2)(tr)(4)} units (the intermetal Ag-Ag and Ag-V distances are 4.24-4.36 and 3.74-3.81 ?, respectively), in which vanadium(V) oxofluoride units possess distorted trigonal bipyramidal environment {VO(2)F(2)N}ˉ, are incorporated into 1D ribbon (2) or 2D square nets (3, 4) using bitopic μ(4)-triazole ligands. The valence bond calculation for vanadium atoms shows +V oxidation state in the corresponding compounds. Thermal stability and photoluminescence properties were studied for all reported coordination polymers.     

Regularities of Electrochemical Formation and Properties of Oxide Films on Titanium–Iron Alloys

Regularities governing the formation and properties of oxide films on titanium–iron alloys containing 10, 20, 32, 45, 60, or 80 at. % Fe are studied by the voltammetry and chronoamperometry methods coupled with local measurements of activation potentials. Dependences of the oxide film thickness on potential are found. Activation potentials for samples with oxide films formed in air and at 5 V decrease with increasing iron content in alloys.     

Experimental verification of the Stokes-Einstein relation in liquid Fe—FeS at 5 GPa

Experiments have been performed at 5 GPa on liquid Fe-FeS in order to determine Fe and S self-diffusivity as a function of temperature. The viscosity of the sample was then obtained using the Stokes-Einstein relation. The results are in excellent agreement with previous experiments where the viscosity of a material of the same composition under similar conditions was measured directly. These results support high, near-metallic, values of diffusivity and low viscosity in liquid Fe-S up to a few hundred K above the eutectic temperature, in contrast with some previous studies. Moreover, these results fully confirm the validity of the Stokes-Einstein relation between viscosity and diffusion coefficients for Fe_0.61S_0.39.     

Imaging cytoplasmic cAMP in mouse brainstem neurons

Background  

cAMP is an ubiquitous second messenger mediating various neuronal functions, often as a consequence of increased intracellular Ca²⁺ levels. While imaging of calcium is commonly used in neuroscience applications, probing for cAMP levels has not yet been performed in living vertebrate neuronal tissue before.     

Plastic Constants of Fracture

Based on the theory of an ideal rigid-plastic body, an approach is formulated for determining fracture constants on the basis of standard mechanical tests on uniaxial extension of plane and cylindrical samples. Instead of the experimentally determined characteristics of fracture of materials (dimensionless elongation and constriction of the sample during its fracture), two invariant tensor characteristics of the degree of sample deformation are introduced, which correspond to the moment of origination of a macrocrack and critical strain at the crack tip determining the process of crack propagation. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 2, pp. 147–155, March–April, 2006.     

Photoelectrochemical Study of Anodic Oxide Films on Titanium–Cobalt Alloys

Properties of anodic oxide films as a function of the composition of Ti _x –Co (x= 0, 10, 20, 30, 50, 67, 75 at. %) alloys in solutions of a borate buffer and sodium sulfate are studied by the voltammetric technique combined with photocurrent measurements. The oxide film on the alloys is shown to contain TiO₂and Co₂O₃. In a borate buffer, the oxide film presumably comprises two layers: an outer layer of cobalt oxides and an inner layer of a mixture of cobalt and titanium oxides.     

Ellipsometric Study of Anodic Oxide Films on Alloys of the Ti–Al System

Anodic oxide films (AOF) on neat titanium and on alloys of the Ti–Al system (Ti–10 at. % Al, Ti–24 at. % Al, Ti–50 at. % Al, Ti–75 at. % Al) formed in borate buffer solution are studied by ellipsometry. A model is proposed, which adequately describes the shape of the alloy surface with and without AOF. The model takes into account the roughness factor, allowing one to more correctly determine optical parameters of AOF and dependence of its thickness on anodic potential. It is found that the alloy surface roughness is effectively smoothed with increasing applied potential.