Hydrogen study in solids by nuclear reactions

The use of nuclear reaction methods for hydrogen or deuterium analysis and its applications to hydrogen profiling and lattice location by channelling experiments is briefly reviewed. The application of these methods to various problems such as the measurement of surface hydrogen and its stability under ion bombardment, the study of solid solutions of hydrogen metal systems obtained by implantation, and the correlation of the amount of hydrogen with the physical properties of some amorphous semiconductors, is described.     

Interfacial properties of thermally oxidized Ta2Si on Si

Many refractory metal silicides have received great attention due to their potential for innovative developments in the silicon‐based microelectronic industry. However, tantalum silicide, Ta₂Si, has remained practically unnoticed since its successful application in silicon carbide technology as a simple route for a high‐k dielectric formation. The thermal oxidation of Ta₂Si produces high‐k dielectric layers, (O? Ta₂Si)‐based on a combination of Ta₂O₅ and SiO₂. In this work, we investigate the interfacial properties of thermally oxidized (850–1050 °C) Ta₂Si on commercial silicon substrates. The implications of diffusion processes in the dielectric properties of an oxidized layer are analyzed. In particular, we observe migration of tantalum pentoxide nanocrystals into the substrate with increasing oxidation temperature. An estimation of the insulator charge and interfacial O? Ta₂Si/Si trap density is also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultra-thin SiO2 layers on TiO2: improved photocatalysis by enhancing products' desorption

A study on the photocatalytic degradation of contaminants (salicylic acid and stearic acid) on titanium dioxide films overcoated with a few monolayers of silica is presented herein. A rather uncommon situation was observed, where the presence of the thin silica layers decreased the degradation rate of stearic acid while increasing that of salicylic acid. The results were explained by addressing the effect in the presence of silica films on the desorption of the intermediate products formed in the degradation of salicylic acid. This finding, which may apply also to other aromatic compounds, may have implications on the design and operation of photocatalytic devices for indoor applications, since ultrathin layers of silica are known to be formed over time on the photocatalyst. An interesting effect of the thickness of the silica sub-nanometre layer on the degradation rate of salicylic acid was explained in terms of gradual changes in the isoelectric point. If optimized, this effect can be utilized to precisely control adsorption or desorption and accordingly to induce specificity in the photocatalytic degradation of contaminants. A methodology for preparing a molecularly imprinting photocatalyst with an inert ultrathin layer in between the imprinted sites was presented. It was found that overcoating the area in between the imprinted sites preserved the benevolent effect of imprinting. While at present the imprinting effect was moderate, there is a reason to believe that this effect can be improved considerably by controlling the type of inert overlayer.     

Low-temperature dielectric spectrum of thermally oxidized polyethylene

Three loss peaks in the dielectric spectra of thermally oxidized polyethylene at temperatures below 50°K are each apparently associated with specific species of nonvolatile oxidation products involving hydrogen atoms. We report how each is influenced by room-temperature rolling, heat treatment, isotopic substitution, and chemical attack. One, the Vincett-Phillips peak, is susceptible to attack by Cu²⁺, Fe³⁺, and HI, and is attributed to a hydroperoxide species. Its rapid and easy determination has promise in the study of polyethylene oxidation. Carson's (higher-frequency) peak is tentatively attributed to an alcohol species and a new (lower-frequency higher-temperature) peak is described but not yet attributed. A few additional observations are made on the loss peaks associated with antioxidants of the substituted phenol type, as reported by Thomas and King.     

Enhancing photoinduced hydrophilicity of micro arc oxidized TiO2 nanostructured porous layers by V-doping

This study sheds light on the effect of vanadium doping on hydrophilicity properties of micro arc oxidized TiO₂ porous layers. Pure and V-doped titania layers, with a pore size of 50–400 nm, were grown by micro arc oxidation method. Morphology and topography of the layers were studied by SEM and AFM techniques where formation of a porous structure with a rough surface was confirmed. Moreover, phase structure and chemical composition of the samples were investigated employing XRD and XPS techniques. The pure TiO₂ layers consisted of anatase and rutile phase. Vanadia phase was also detected in V-doped layers. It was also revealed that V₂O₅ not only dispersed in the TiO₂ matrix, but also doped into the crystalline lattice. Optical properties and band gap energy of the synthesized layers were evaluated by a UV-Vis spectrophotometer. Our results showed that the band gap energy decreased when vanadium was introduced into the titania lattice. Finally, hydrophilicity of the pure and the doped layers was studied under ultraviolet and visible illuminations by measuring the water contact angle on their surface. The V-doped layers, especially those which were grown under intermediate voltages, revealed an enhanced hydrophilicity when compared to the pure TiO₂ layers.     

A surface x-ray study of the structure and morphology of the oxidized Pd001 surface

The oxidation of Pd(100) and the formation of PdO was studied in situ using surface x-ray diffraction. A bulklike, epitaxial PdO film is formed at oxygen partial pressures beyond 1 mbar and sample temperatures exceeding 650 K. The main orientation is PdO(001)/Pd(001), based upon bulk reflections from the PdO film. By comparing with measurements from the Pd crystal truncation rods, we estimate an rms surface roughness of 6 A, in good agreement with previous high pressure scanning tunneling microscopy measurements. Finally, we observed the transformation from the (radical5 x radical5) surface oxide to PdO bulk oxide at 675 K and 50 mbar O(2) pressure.     

Initial surface reactions of TiO2 atomic layer deposition onto SiO2 surfaces: density functional theory calculations

We present a density functional theory (DFT) study of the initial surface reactions of TiO2 deposition onto a SiO2 substrate using atomic layer deposition (ALD). The precursors for the deposition process were chosen to be TiCl4 and H2O, and several cluster models were used for the SiO2 substrate. We predict the activation barriers, transition states, and reaction pathways of the surface reactions, and we investigate the effect of surface heterogeneity (such as the presence of siloxane bridges) on the reactivity of the SiO2 surface. Our study suggests that the concentration and arrangement of different reactive groups on the substrate will strongly dictate the process of film growth during ALD, including the film morphology and the growth rate.     

Solar thermochemical reactionsⅢ:A convenient one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles catalyzed by high surface area SiO_2 and induced by solar thermal energy

A simple,convenient and efficient method for the synthesis of 1,2,4,5-tetrasubstituted imidazole derivatives using benzoin,an aromatic aldehyde,an aromatic amine in the presence of ammonium acetate catalyzed by high surface area SiO_2 and induced by free solar thermal energy was reported.     

EDX depth profiling by means of effective layers

A new approach is described for depth profiling in stratified multilayer samples by recording energy dependent characteristic x-ray EDX(E ₀ ) curves in a scanning electron microscope. An effective layer technique replaces the x-ray excitation function of the heterogeneous target by an equivalent function of a homogeneous sample. First results of thickness determination are shown and compared to direct measurements of film thickness monitoring (FTM) and atomic force microscopy (AFM).     

A study of thin surface layers by multilayer Mössbauer spectroscopy /MMS/

A stacking Mössbauer technique, MMS has been applied for studying thin surface layers. The surface layers formed on the⁵⁷Fe film in aqueous solutions of corrosion inhibitors, such as zinc phosphate and barium metaborate, and in distilled water was studied by this method. It has been found that the corrosion is much slower in the presence of zinc phosphate and barium metaborate. XPS analysis suggests the formation of a mixed iron zinc phosphate on the surface of the⁵⁷Fe film after corrosion in a zinc phosphate solution.     

Formation of grafted surface layers on silicon dioxide particles and their investigation by means of thermoprogrammed oxidation

Silica nanoparticles are obtained according to the Stober–Fink–Bohn method, and their surfaces are chemically modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane. It is estimated that sols of porous silica nanoparticles (average sizes, 50–200 nm) form during primary chemical process; the average size of the particles can be increased to 400–500 nm by consecutive growth. Oxythermography (thermoprogrammed oxidation) measurements reveal a stepped dependence between the content of organic substance of nanoparticles and the duration of chemical modification reaction exists. It is concluded that this could be due to the formation of dense shell (or shells) as a result of sols aging between the cycles of growth; such shells impose diffusive restrictions when molecules penetrate into the pores of the internal volume of the particles.

     

A study of the surface heterogeneity and catalytic activity of catalysts by means of reaction thermodesorption

Reaction thermodesorption is studied. A generalized wiew is offered regarding the routes along which the transformations take place under the conditions of temperature-programmed desorption.

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Impedance spectroscopy study of passive layers on the surface of lead-tin and lead-tin-calcium alloys anodically oxidized in 4.8 M sulfuric acid solution

The nature of passive films, which were formed at various potentials in 4.8 M H₂SO₄ solution on the lead-tin and lead-tin-calcium alloys, is studied by the method of impedance spectroscopy. At the potentials of 1.3 and 1.7 V, the electrode impedance is presented by the equivalent circuit, which corresponds to the formation of a bilayer film consisting of lead(II) sulfate and oxide on the electrode surface. Lead(II) oxide, which forms under the layer of lead sulfate, determines a high resistance of passive layer on the electrodes of lead alloys under investigation. An introduction of tin into the lead alloys significantly decreases the resistance of passive layers. An addition of calcium to the lead-tin alloy raises the impedance of the system. At a potential of 2.05 V, a single-layer compact passive film forms on the electrodes of the test lead alloys. It consists predominantly of lead oxides PbO _x (1 < x ≤ 2), which exhibit a higher electron conductivity. An introduction of tin into the lead alloys decreases the resistance of formed films; calcium has almost no effect on the resistance of passive film under these conditions.     

A study of sulphonated and oxidized coals by thermal analysis

Earthy and xylytic brown coals from Poland have been sulphonated with 98% sulfuric acid at temperatures of 60°, 90° and 140°C. The main exothemic peak shifts to higher temperatures with increase in sulphonation reaction temperature whereas overall weight loss to 1000°C decreases. DTA curves of earthy and xylytic coals sulphonated at higher temperatures are similar, even though DTA curves of the unmodified coals differ appreciably. Thermal decomposition of earthy coal oxidized by nitric acid follows a different pattern. Nitric acid causes oxidation and depolymerization of the organic components and this is reflected in the shapes of DTA and TG curves of oxidized coals. As the nitric acid concentration and reaction temperature increase, the main exothermic peak shifts to lower temperatures (from 330°C for basic coal to 270°C for coal oxidized with 30 and 50% nitric acid). The weight loss is higher for oxidized coal than for coal unmodified by nitric acid.