Yu. A. Agafonov

The mechanism of carbon dioxide hydrogenation on copper and nickel catalysts

The mechanism of the reaction of CO2 with H2 on copper and nickel catalysts was studied by means of isotope, non-steady-state, and steady-state methods. Staged schemes of the process were proposed. The slow step of CO formation on the test catalysts is the reaction of the adsorbed carboxylate complex with a hydrogen atom. It was shown that hydrogen adsorption on the copper catalyst is dissociative in character. A formyl complex and hydrogen are involved in the slow step of methane formation on the nickel catalyst. It was found that the methane formation proceeds via a consecutive scheme through CO.

Multilayer gratings efficiency: numerical and physical experiments

Abstract Recently the possibility of focusing, imaging and spectroscopy with Fresnel zones etched on a flat multilayer substrate instead of a curved substrate has been shown. This is now known as Bragg-Fresnel Multilayer lenses (BFML). Lamellar gratings etched in a multilayer (LMG) are the basic type of Bragg-Fresnel optics. In this paper we describe important points in the fabrication, computer simulation, and testing of the LMs. They can be very interesting as a spectroscopic device with a relatively high dispersion and efficiency. We develop a rigorous theory of diffraction combined with the layer-by-layer differential integration numerical method. The agreement with experimentals results obtained for a lamellar grating with several period and various etched depths in a W/Si multilayer is very good. The main result is an increase of the effective extinction depth ( t ext ) in short-period gratings which gives a possibility to increase the absolute diffraction efficiency of the LGM practically from 30% to 60% in the first order with a totally suppressed zero order.

Elliptical multilayer Bragg-Fresnel lenses with submicron spatial resolution for X-rays

Abstract Elliptical Bragg-Fresnel multilayer lenses (BFML), designed and fabricated at the Institute of Microelectronic Technology (Russian Academy of Science) have been used for two-dimensional focusing of the white X-ray synchrotron beam at LURE (Orsay France). For two fixed beam energies (8 keV and 12.4 keV), the spot size produced was approximately 1 μm as determined from a high resolution photographic plate. A fluorescence X-ray scanning microprobe based on these BFML lenses was also tested. The transmitted signal registered during the scan of a test object shows less than 1 μm resolution with 8 keV output photon energy. 2D scanning images with submicron resolution of test objects in transmission mode at 8 keV and 12.4 keV beam energies are presented.

Comparison of modal and differential methods for multilayer gratings

Abstract Modal theory is applied in calculating the lamellar multilayer grating performances. Comparison of numerical results obtained with the differential and modal methods is performed. Both methods give the same values of diffraction order efficiency and are in good agreement with experimental data. Tungsten-carbon multilayer gratings having a 4 μm lamellar period and a 3 nm bilayer spacing for a 0.154 nm wavelength were used as the test object. The diffraction properties of multilayer gratings are discussed using reciprocal space and dispersive surfaces representation. A strong dependence of the multilayer grating properties on the lamellar period and the optical characteristics of multilayer grating materials are shown.

INTERBALL magnetotail boundary case studies

Abstract We present two examples of INTERBALL-1 data near both the high and low-latitude tail magnetopause (MP) under disturbed conditions. For the high-latitude case, MAGION-4 data determine the scales of the MP current sheets which are in the order of 100–500 km for the main ones, 50–200 km for Flux Transfer Events (FTEs) and a few km for the fine structures and ULF turbulence. The MP speed was 15–30 km/s. The energetic protons in the magnetosheath (MSH) provide evidence of reconnection upstream of the spacecraft (S/C). The tailward flows grow for the northward MSH magnetic field when the reconnection site is believed to be shifted tailward of the cusp. The inner boundary layer (BL) after the disturbance consists of tailward and earthward flowing plasma of MSH origin and cold mantle plasma flowing tailward The earthward flow is evidence of reconnection tailward of the S/C, which is regarded as a specific feature of the disturbed conditions. Local production of a plasma-sheet-like plasma at high latitudes is argued based on the inner BL plasma characteristics. The following features are observed in both cases: (a) FTEs for both northward and southward MSH fields; (b) waves in the current sheet vicinities over ten mV/m and 15 nT peak-to-peak; (c) electron fluxes with scales down to a few km with extra heating especially parallel to the magnetic field; (d) outer turbulent boundary layers with a deflected magnetic field; (e) ions with time-energy dispersion-like features and deflected ion fluxes. In the downstream dawn region at the transition between the low-latitude boundary layer and the plasma sheet (LLBL/PS), multiple MP encounters are observed. In the LLBL parallel electron intensifications correlate with ULF magnetic fluctuations.

Structure, electrical and magnetic properties, and the origin of the room temperature ferromagnetism in Mn-implanted Si

The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 1016 cm−2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account for only a few percent of the total Mn content. The main part of Mn is fixed in Mn15Si26 nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than by a Mn impurity.

Kinetics and mechanism of the oxidative dehydrogenation of isobutane on cobalt, nickel, and manganese molybdates

The kinetics of oxidative dehydrogenation of isobutane in the presence of atmospheric oxygen on manganese molybdate has been studied. The experiments have been carried out in a circulation flow reactor at 470–530°C. The form of kinetic equations and the mechanism of the formation of isobutene, carbon oxides, and cracking products on manganese molybdate are similar to those found previously for the same reaction on cobalt and nickel molybdates. The highest yields of isobutene and propene (isobutane cracking products) are achieved on Co0.95MoO4. The mechanism of the process has been investigated by the unsteady-state response method. Manganese molybdate contains the largest amount of reactive oxygen, whereas nickel molybdate contains the smallest amount of reactive oxygen. The earlier conclusion that molybdate lattice oxygen and chemisorbed oxygen play the main role in the formation of iso-C4H8 and in deep oxidation processes, respectively, is confirmed.

Kinetics of carbon monoxide methanation on nickel catalysts

The kinetics of CO methanation in excess H2 on CaO- and CeO2-doped nickel catalysts supported on Al2O3 and TiO2 was studied at atmospheric pressure in a temperature range of 180–240°C. It was found that the same rational fractional rate equation corresponding to the reaction taking place at high surface coverages, is valid for all of the catalysts. The activity of nickel catalysts in the methanation reaction and their adsorption capacity with respect to reaction mixture components depend on the nature of the support and dopants.

Reaction mechanism of CO methanation on nickel catalysts, as studied by isotopic and nonstationary methods

Kinetic isotope effects were measured upon the replacement of hydrogen by deuterium in the reaction of carbon monoxide methanation on nickel catalysts supported on TiO2 and γ-Al2O3. Data on the mechanism of the process were obtained with the use of a nonstationary method. A step-scheme was proposed, in which the interaction of oxygen-containing compounds with hydrogen is a slow step of the process.

Ferromagnetism of Mn-Implanted Silicon: Magnetization and Magnetooptic Faraday Effect

Manganese-implanted silicon plates of both n and p types have been obtained by implanting 195-keV manganese ions with doses from 1 × 1015 to 2 × 1016 cm−2. According to magnetic measurements by a vibrating sample magnetometer and a SQUID magnetometer, all of the samples exhibit a ferromagnetic ordering at room temperature. The magnetooptic Faraday effect is manifested in the spectral region 1–6 μm in the temperature interval 80–305 K. The characteristic features of the field and temperature dependences of magnetization and the spectrum of the Faraday effect indicate a percolation type of magnetic ordering at low temperatures and a crucial role of the exchange between delocalized p-type carriers and Mn ions at temperatures above 100 K.