Vanadium oxide surface studies

The vanadium oxides can exist in a range of single and mixed valencies with a large variety of structures. The large diversity of physical and chemical properties that they can thus possess make them technologically important and a rich ground for basic research. Here we assess the present status of the microscopic understanding of the physico-chemical properties of vanadium oxide surfaces. The discussion is restricted to atomically well-defined systems as probed by surface techniques. Following a brief review of the properties of the bulk oxides the electronic and geometric structure of their clean single crystal surfaces and adsorption studies, probing their chemical reactivity, are considered. The review then focuses on the growth and the surface properties of vanadium oxide thin films. This is partitioned into films grown on oxide substrates and those on metal substrates. The interest in the former derives from their importance as supported metal oxide catalysts and the need to understand the two-dimensional overlayer of the so-called “monolayer” catalyst. On the single crystal metal substrates thin oxide layers with high structural order and interesting properties can be prepared. Particular attention is given to ultrathin vanadium oxide layers, so-called nano-layers, where novel phases, stabilised by the substrate, form.     

Structural and electronic comparative analysis of aminopyridazines showing anti-GABA activity. Crystal structure of 2-(carboxy-3′-propyl)-3-amino-6-cyclohexylpyridazinium bromide.Ab initio Mulliken population analysis of the 6-phenyl-substituted analog compared to GABA

The crystal structure of 2-(carboxy-3-propyl)-3-amino-6-cyclohexylpyridazinium bromide has been determined by single-crystal X-ray diffraction techniques and refined by full-matrix least squares. The compound crystallized in the tri-clinic space groupP ¯1 witha=10.275(1),b=11.215(1),c=7.082(1) Å,=91.84(1),=102.21(1), =106.77(1)°, andZ=2. FinalR-factor is 0.045. The main structural results are very similar to the ones observed for the 6-phenyl analog. These two compounds are GABA-A antagonists.Ab initio molecular orbital calculations, with STO-3G and 4-31G basis sets, suggest that the exocyclic nitrogen accurately mimics the nitrogen atom of GABA.     

Structural and spectroscopic study on imidazole-copper(II)-N-protected amino acid complexes. Crystal and molecular structure of tetrakis(imidazole)copper(II)bis(N-tosylvalinate)

A pink-red air-stable, crystalline compound of empirical formula [Cu(Im)₄(N-tsval)₂] (Im=imidazole; ts=4-toluenesulfonyl group, hereafter abbreviated as tosyl;N-tsval=N-tosylvalinate monoanion) was synthesized and characterized by means of structural and spectroscopic measurements. The crystal structure of the compound was determined from three-dimensional diffractometer data. The crystals are monoclinic, space groupC2/c, a=18.952 (5),b=12.372 (2),c=17.594 (3) Å,=93.77 (2)°,Z=4. The structure was solved by the heavy-atom method and refined through least-squares calculations toR=0.035 for 2284 observed reflections. The coordination about the copper atom is elongated octahedral, with four imidazole molecules as equatorial ligands and two sulfonic oxygens in axial positions.     

Beryllium diffusion across GaAs/(Al,Ga)As heterojunctions and GaAs/AlAs superlattices during MBE growth

Beryllium diffusion during MBE growth of (Al, Ga)As layers, (Al, Ga)As/GaAs heterojunctions and GaAs/AlAs superlattices has been studied by electrochemical C-V and secondary ion mass spectrometry (SIMS) concentration profiling, in conjunction with transmission electron microscopy. Diffusion times were comparatively short since they were limited to part of the growth sequence, so non-equilibrium effects had a significant influence. The results are consistent with an interstitial-substitutional mechanism in which lattice site incorporation becomes more difficult with increasing band gap enthalpy. Incorporation involves a kick-out reaction which leads to the observed disordering of the superlattices.     

Radiattonal capture of neutrons by deuterons n + d →3H + λ and P-odd nuclear forces

P-odd polarizational phenomena are considered in the radiative capture of neutrons by deuterons: n + d ³H + . It is shown that, in the general case, 18 different P-odd asymmetries of the angular distribution of quanta arise in the collision of arbitrarily polarized neutrons with a deuteron target characterized by vector and tensor polarizations. The P-odd contribution to the density matrix of the quanta formed in the capture of polarized neutrons by unpolarized deuterons is determined by eight real structural functions, while the P-odd dependence of the Stokes parameters of the photons on the tensor polarization of the deuterons is characterized, in the general case, by ten structural functions. In slow-neutron capture, the number of P-odd correlations is reduced.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 23–26, March, 1987.     

Estimating gas temperature in the channel of a high-temperature jet discharge in air

Consideration is made of determining gas temperature in the channel of a high-frequency jet discharge in air over the intensity distribution of lines for the rotational spectrum band for the transition A² X²II (0-0) in the radiation of hydroxyl. It is shown that the branches R₂ and Q₁ of this band are the most useful for temperature measurements at atmospheric pressure. Within error limits, the temperature in the discharge channel as determined from the lines of the R₂-branch is T_gas = (3120 ± 70) and (3380 ± 90) K in the cross sections of the discharge at a distance of 3 and 30 mm, respectively.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–7, February, 1987.     

Selecting the duration of excitation pulses for an electroluminescent thin-film matrix

The factors influencing the optimum selection of the excitation pulse width of thin-film electroluminescent devices is examined. It is shown that to excite an individual cell, a pulse width of 5–7 sec is sufficient, but to excite the matrix, the pulse width is determined by the independence of the conducting layer and the dimensions of the matrix. Formulas are cited for engineering calculations of the required pulse width.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 59–62, December, 1987.