OS Layer Research Articles

DETERMINATION OF THE CALORIFIC VALUE OF SYSOLA OIL SHALE FROM GAMMA-GAMMA LOGGING DATA

This historical review addresses one topic in well logging. In 1983- 85 special geophysical work was carried out in the Poinga area of the Vychegda oil shale basin (OSB) in the northeastern part of the East- European Platform, to search for oil shale deposits (1). The results of the study of Sysola oil shale by using the geophysical logging are presented. The density logging data was used to predict the calorific value of oil shale. It is shown that the elementary procedure of elimination of the regional compo- nent from the measured values of the gamma-gamma log provides an excellent correlation between the predicted and true calorific values of oil shale. The regional anomalies of gamma-gamma logging data were determined using the averaging method. The local anomalies of OS layers were calculated. In our calculations not the absolute values of the measured gamma-gamma logging parameter, but relative to average ones were used. So, the accuracy increased significantly and amounted to 87-91%.

Effects of Os Inserted Layers on the Microstructures and Magnetic Properties of the FePt Films

The microstructure and magnetic properties of multilayer [Os(t)/FePt(x)]n films on a glass substrate with a 10 nm Os buffer layer by ion beam sputtering have been studied as a function of the annealing temperatures between 300 and 800 degrees C. Here, t = 0.2, 1 or 5 nm and x varied from 10, 20, 25, 50, to 100 nm with its associated n value of 10, 5, 4, 2, and 1, respectively. No diffusion evidence was found in samples with a thin Os layer and t > or = 1 nm. The average grain size of the multilayer films can be well controlled by both annealing temperature and thickness of the FePt layer by a very thin Os space layer with t > or = 1 nm. The enhancement of H(c) can be understood from the fact that for a FePt film with an Os spacer layers, the increasing number of Os layer will inhibit the grain growth of FePt grains and enriches the grain boundary. We have experimentally demonstrated that even with a very thin 1 nm Os spacer layers, the [Os(t)/FePt(x)]n multilayer films can exhibit good hard magnetic properties and are attractive candidates for ultrahigh density magnetic recording media.

Electrochemical and Spectroscopic Studies of Ethanol and Acetaldehyde Oxidation Onto Pt(110) Modified by Osmium

This paper presents the studies of ethanol and acetaldehyde electrooxidation onto Pt(110) electrode modified by different osmium coverage. These oxidation reactions were studied by in situ Fourier transform infrared spectroscopy. It was shown that the catalytic activity of Pt(110) after osmium deposition for ethanol oxidation is greater than that observed on unmodified Pt(110). It was also demonstrated that the mechanistic pathway for this reaction depends directly on the degree of osmium coverage. Thus, for low osmium coverage (θ Os ≤ 0.12), the formation of CO and CO2 is not so effective when compared with other coverage degrees, and hence the full oxidation of adsorbed ethanol to CO2 is increased when the Os is deposited in the range of 0.30–0.80 ML. Additionally, the formation of acetaldehyde is also observed in low degree of osmium coverage. For a complete osmium layer (θ Os > 1.0), the catalytic activity of the electrode for ethanol oxidation shows the lowest value. The acetaldehyde oxidation reaction on Pt(110)/Os favors the CO2 production. For electrodes covered completely by Os layer, a considerable presence of CO2 above 0.8 V was observed; in contrast with the very low quantity of adsorbed COlinear, this suggests that the CO2 can also be formed from the oxidation of a possible strongly adsorbed species at high potentials on this surface, or it can also be considered that acetaldehyde can be oxidized to CO2 by the cleavage of C–C bond.

Microstructure and ordering parameter studies in multilayer [FePt(x)/Os]n films

The microstructure, ordering parameter, and magnetic properties of multilayer [FePt(x)/Os]n films on glass substrate by dc-magnetron sputtering (with x being thickness in nm; Os with a fixed thickness 5 nm; n being the number of layers) have been studied as a function of the annealing temperatures between 300 and 900 °C. The grain size of multilayer films can be controlled by annealing temperature and thickness of the FePt layer with Os space layer. The coercivity as a function of the annealing temperature for samples with n = 1 and pure FePt behaves roughly saturated after annealing above 700 °C. However, for samples with n > 4 the value of Hc seems still increasing with increasing annealing temperature between 600 and 900 °C, and the ordering parameter decreases with increasing the number of Os layers. Our experimental results are reasonably well to describe the effect of strain-assisted transformation.

Effects of Os spacer layers on the thermal stability, microstructures, and magnetic properties of FePt films on Si(100)

The thermal stability, interlayer diffusion, and magnetic properties of FePt(100 nm) single-layer and multilayer [Os(5 nm)/FePt(25 nm)]4 films on a Si(100) substrate with/without a 10-nm-thick Os underlayer have been studied as functions of the annealing temperatures between 400 and 800 °C. The insertion of a thin Os layer into the FePt and Si(100) interface results in better thermal stability. No diffusion evidence was found in samples with an Os underlayer for annealing temperatures up to 700 °C, as seen from x-ray, transmission electron microscopy, and magnetic studies. We have experimentally demonstrated that the Os underlayer can effectively prevent the diffusion of the intermixing between the FePt layer and the Si(100) substrate for temperatures up to 700 °C. As a result of this study, the Os has potential to be a better diffusion barrier to prevent the diffusion of the FePt film on a Si(100) substrate from forming an ordered face centered tetragonal (fct) L10 hard magnetic phase.

Effect of Interface Texturing on Optical and Photoelectric Properties of Organic/Inorganic Semiconductor Heterojunctions

The effect of texturing interfaces on the optical and photoelectric properties of anisotype and isotype organic (OS)/inorganic (IS) semiconductor heterojunctions has been investigated. p-(Pentacene) and n-(methyl perylene pigment, MPP) type organic semiconductor layers were evaporated on n-GaAs and p-InP substrates, respectively, with flat substrates and the substrates textured by chemical anisotropicetching (with a microrelief of the quasigrating type). The spectra of the light reflectance and the short-circuit photocurrent for the Au/OS/IS heterostructure were measured and analyzed to distinguish the contribution of the photocurrent generated in the OS layer. A considerable enhancement of the photocurrent generated in both inorganic and organic semiconductors was found for structures with textured interface.

A framework model for grid security

Computational grids can be considered as tiered objects; following a widespread terminology, cluster grids may be grouped into enterprise grids, that in turn may belong to global grids. Therefore, computing grid security has to be “tiered” too, with the ground level remaining the OS one. In this work, we introduce a sort of unified approach, an overall architectural framework for access control to grid resources, and one that adheres as much as possible to current security principles. Current grid security implementations are viewed in the light of this model, their main drawbacks are described, and we show how our proposal is able to avoid them. We believe that a main strategy could be to adopt both PKI and PMI infrastructures at the grid layer, ensuring that an adequate transfer of authentication and authorization will be made between the Virtual Organization and Resource Provider layers. This can be achieved by extending those features at the OS layer as system applications and services.

Magnetoresistance and interlayer coupling studies in FePt/Os/FePt thin films

Effects of the Os layer on the magnetic properties of FePt/Os/FePt were investigated. The magnetic layer of FePt in the as-deposited Ta/FePt/Os/FePt/Ta thin films exhibited very strong (1 1 1) orientation in all the cases. As the thickness of Os spacer layer between 1 and 3 Å, it appeared an antiferromagnetic exchange coupling (AFC) behavior. The exchange coupling transforms to ferromagnetic when the thickness of Os spacer layer was thicker than 4 Å. Although the J value for FePt/Os/FePt thin films is −0.22 erg/cm 2, which is relatively small than that of Co/Ru system, the GMR effects could be observed. In general, the AFC in multilayer system shows the first maximum of AFC peak occurring at spacer thickness between 8 and 11 Å for most spacer materials. In our investigation, this is the first time that a clear AFC behavior observed in FePt/Os/FePt system with Os spacer thickness at 2 Å.

Effects of an Os layer on the magnetic properties of CoFe∕IrMn

The uses of Os as an antidiffusion and buffer layer in IrMn exchange coupled CoFe film were investigated. For the purpose of antidiffusion, the inserted Os layer showed a distinct improvement of S>0.9, with HC slightly increasing by 1.6 times for the CoFe∕Os∕MnOs multilayer after 400 °C annealing, even though the Os thickness was as thin as 0.3 nm. Furthermore, with a 0.3 nm Os barrier, the 350 °C annealed CoFe∕Os∕IrMn∕CoFe showed almost the same magnetic behavior as the as-deposited state, while the Hex of the upper part of the CoFe∕Os∕IrMn changed from 100 to 190 Oe. In addition, as a buffer layer, the Os buffer layer could enhance the diffraction peak intensities of IrMn(111)∕Os(002) and CoFe (111), and the Hex of CoFe∕IrMn was proportional to the Os thickness. A 120 Oe of Hex was achieved by using an 11 nm Os buffer layer in a CoFe10nm∕IrMn15nm bottom type film. These results show that Os has the potential to be an antidiffusion and buffer layer in a magnetic multilayer.

Magnetoresistance study and interlayer coupling of CoFe/Os/CoFe thin films

The CoFe/Os/CoFe thin films were deposited on natural oxidized Si(1 0 0) substrates at room temperature by an ultra-high vacuum DC-magnetron sputtering system with a base pressure less than 1×10 −8 Torr. The thickness of the ferromagnetic layers was 100 Å in all cases and a series of trilayers with Os spacer ranging from 3 to 20 Å was made. Effects of the Os layer thickness on the magnetoresistance (MR) and magnetic properties were investigated. The results showed that the magnetism switched from ferromagnetic (Os thickness=3, 5 Å) to antiferromagnetic (Os thickness=7–13 Å) and then ferromagnetic (Os thickness=20 Å) again. From the MR study, we see that the AMR ratio decreased from 4.64% to the minimum value 0.69% at 9 Å and then increased; GMR ratio increased from 0.01% to the maximum value 0.43% at 9 Å and then decreased. From the hysteresis loops, the results exhibited that coercivity increased from 16 Oe to the maximum value 92 Oe at 9 Å and then decreased, and squareness value decreased from 0.97 to the minimum value 0.17 at 9 Å and then increased. Dependence of saturation field on Os spacer-layer thickness for CoFe trilayers showed a maximum value 216 Oe at 9 Å. This suggests that the small GMR effect may be related to the small exchange coupling strength in CoFe/Os/CoFe thin films.

The effect of Os interlayers on the thermal stability of magnetic CoFe/OsMn films

The thermal stability of a multilayer structure of protection layer/Co 90Fe 10/Os ( d nm)/Os 20Mn 80 has been studied as functions of annealing temperature ( T an) and thickness of Osmium (Os) layer. The insertion of a thin Os layer between the Co 90Fe 10/Os 20Mn 80 interface shows better thermal stability. No diffusion evidence was found for samples with d ≧ 0.3 nm as examined by Auger electron spectroscopy depth profile at different annealing temperatures up to 400 °C. These samples with Os layer showed the same magnetic behavior and the hysteresis loop with squareness ( S) larger than 0.9 were observed before and after annealing.

Microstructure and magnetic properties of Co/Os/Co and Fe/Os/Fe thin films

The Co/Os/Co and Fe/Os/Fe thin films were deposited on natural oxidized Si (1 0 0) substrates at room temperature by magnetron sputtering. The thickness was kept at 100 Å for all the magnetic layers, and was varied between 3 and 20 Å for the Os layer. Effects of the Os layer thickness and microstructure on the magnetic properties of the film were investigated. The results showed that the antiferromagnetic coupling occurred for the Co/Os/Co thin films with the Os thickness between 7 and 13 Å. Due to the mismatch of Fe and Os, pinholes in the Os layer could be observed. The presence of interface roughness and pinholes reduces the antiferromagnetic interlayer exchange coupling strength and affect the dependence of the interlayer exchange coupling on the Os layer thickness. From the magnetoresistance (ΔMR) study, the largest ΔMR ratio arising from antiferromagnetic coupling for Co/Os/Co and Fe/Os/Fe thin films are about 0.45% and 0.07% respectively. The small ΔMR in Fe/Os/Fe system is explained by the large interface roughness and lattice mismatch effect.

Osmium nanoislands spontaneously deposited on a Pt(111) electrode: an XPS, STM and GIF-XAS study

Scanning tunneling microscopy (STM) characterized adlayers of spontaneously deposited osmium on a Pt(111) electrode were investigated using ex-situ X-ray photoemission spectroscopy (XPS) and in-situ grazing incidence fluorescence X-ray absorption spectroscopy (GIF-XAS). After a single spontaneous deposition, monoatomic (or nearly monoatomic) nanoislands of osmium are formed. The island diameter varies from 2 to 5 nm depending on the Os coverage, which in turn is adjusted by varying the concentration of the Os precursor salt (OsCl3) in the deposition bath and/or by the deposition time. XPS reveals three oxidation states: a metallic Os (the 4f7/2 core level binding energy of 50.8 eV), Os(IV) (51.5 eV) and Os(VIII) (52.4 eV). The metallic osmium exists at potentials below 500 mV (vs. RHE) while above 500 mV osmium is oxidized to Os(IV). Electrodissolution of osmium begins above 900 mV and occurs simultaneously with platinum oxidation. At ca. 1200 mV V versus the RHE reference, the oxidation state of some small amounts of osmium that survive dissolution is the Os(VIII). We demonstrate, for the first time, that mixed or odd valencies of osmium exist on the platinum surface at potentials higher that 800 mV. In-situ GIF-XAS measurements of an Os LIII edge also reveal the presence of three Os oxidation states. Namely, below the electrode potential of 400 mV, the X-ray fluorescent energy at maximum absorption is 10.8765 keV, and is characteristic of the metallic Os. In the potential range between 500 and 1000 mV this energy is gradually shifted to higher values, assignable to higher valencies of osmium, like Os(IV). This tendency continues to higher potentials consistent with the third, highly oxidized osmium form present, most likely Os(VIII). The variation of the “raw edge jump height” of Os with the electrode potential, which is equivalent to a drop in osmium surface concentration, demonstrates that the electrochemical stripping of Os begins below 1.0 V versus RHE, as expected from voltammetry. Also, the observed intensity of the white line of Os in the 100–400 mV region is larger than the value reported for metallic bulk Os. This discrepancy may result from the difference in the electronic properties of the metallic Os layers on Pt(111) and the metallic bulk Os: in the potential region between 100 and 400 mV, the 5d electrons in Os and Pt form a mixed electronic band, and the density of electronic states near the Fermi level, the main factor determining the white line intensity, may not be the same as in metallic bulk. The presented results on osmium adlayers are much more comprehensive than those available in our previous work due to the combined STM, GIF-XAS and XPS investigations. A nearly perfect convergence of the in situ and ex situ data is one of the main research outcomes of this project. Finally, platinum XPS spectra taken in the context of Os electrooxidation from the electrode surface are also presented and conclusions are made, that up to 900 mV platinum remain metallic, irrespective of a significant osmium oxidation on its surface.

Comparative studies on electrochemical behavior and electrocatalytic properties of heteropolyanion-containing multilayer films prepared by two methods

Two modification methods for multilayer formation, i.e. immersion growth and electrochemical growth, were studied comparatively for their influence on the electrochemical behavior and the electrocatalytic properties of the thus-fabricated SiMo11V-containing multilayer films. Electrochemical growth was proven to be a more suitable method than immersion growth in preparing uniform ultrathin multilayer self-assemblies with good functions. We investigated the effects of scan rate and pH on the electrochemical behavior of the monolayer and multilayer films. We also compared the electrocatalytic effects on the reduction of BrO3− and HNO2 by the multilayer films prepared by the two methods. Moreover, the influence of multilayer thickness and the identity of the outermost layer on the electrocatalytic properties were studied. Much higher catalytic currents appeared on the thicker multilayer films than those on the thinner ones. On the other hand, the catalytic currents became smaller when the multilayer films with SiMo11V as the outermost layer were covered with an additional quarternized poly(4-vinylpyridine) layer partially complexed with osmium bis(2,2′-bypyridine) chloride (QPVP–Os layer). These influences were believed to be due to the different quantities of electrocatalyst loaded in the multilayer films and the blocking effect of the QPVP–Os outermost layer.

Emission life and surface analysis of barium-impregnated thermionic cathodes

Emission life of small Ba-impregnated thermionic cathodes suitable for use in TV tubes is investigated systematically. Cathodes are covered with an Os layer to enhance the emissivity. They have an unusual emission life in that the emission current decreases gradually with time and then drops abruptly. The early gradual decrease in emission at high cathode temperatures is caused by the phase change of the Os layer to OsW2. A linear relationship is found to exist between the logarithm of the lifetime and the reciprocal of the cathode temperature. This life end is believed to happen after the end of the reduction reaction between BaO and the porous W body and after ceasing replenishment of the low work function Ba+-O− monolayer on the metal surface. A formula for the emission lifetime is derived from the assumption that the rate determining step is the Ba diffusion inside the pellet. Emission lifetime τ is shown to be given by τ=Ad2 exp(E/kT), where A is a constant, d is the pellet thickness, and E is the activation energy of Ba diffusion. This relation is confirmed experimentally.