Redistribution Of Silicon Research Articles

Первичное почвообразование на субстратах разного гранулометрического состава в посттехногенных экосистемах таёжной зоны

The paper focuses on the primary soil formation under automorphic conditions in the middle taiga sub-zone of the European North-East of Russia (Komi Republic) on the post-technogenic territories (quarries for the extraction of minerals (construction sand)) with different soil materials (ancient alluvial sands; fluvioglacial sands and sandy loams, moraine loams). In the quarries, the processes of soil formation and vegetation cover development are interdependent and are affected by the properties of soil-forming rocks. Along with the improvement of soil properties (from sandy loam to loam), the biometric parameters of pine stands increase; in the ground cover, dominating lichens are replaced by mosses, and then by grasses. The biogenic accumulation rates of organic matter increase along with the transition of soil material to fine-textured. In automorphic conditions, the accumulation rate of Corg. in soil of sandy quarry under sparse young lichen pine forest reaches 0.1, in sandy loam under young forb-moss pine forest – 0.3, in loam under young grass-forb pine forest – 0.6 t/ha/year. Already in the first succession decades, every study soil demonstrates weakly expressed processes of eluviation and illuviation (the beginning of podzolization). These processes are evidenced by morphological signs (the appearance of bleached quartz grains and whitish patches under organic horizon and in its lower part), redistribution of silicon, iron, and aluminum compounds, as well as of silty particles proportion.

Silicon redistribution, acid site loss and the formation of a core–shell texture upon steaming SAPO-34 and their impact on catalytic performance in the Methanol-to-Olefins (MTO) reaction

SAPO-34 is a commercially-implemented silicoaluminophosphate catalyst for selective high yield production of ethene and propene from methanol, but high temperature regeneration in the presence of steam leads to its deactivation. A comprehensive investigation of the effect of prolonged hydrothermal treatment on the structure and properties of SAPO-34 explains the changes in its catalytic methanol-to-olefins (MTO) performance. Microcrystalline powdered SAPO-34 (ca. 3 µm crystals, Al17.1P15.6Si3.3O72) and two batches of larger single crystals of SAPO-34 of different Si concentration (20–100 µm; Al17.3P14.7Si4.0O72 and Al17.7P12.3Si5.9O72) were steamed (pH2O = 0.95 atm) at 873–1023 K for up to 240 h. The acidity (NH3-TPD), crystallinity (PXRD), framework cation environment (solid-state 27Al, 29Si and 31P MAS NMR) and porosity were followed for all materials; larger crystals were amenable to single crystal X-ray diffraction, FIB-SEM and synchrotron IR microspectroscopy, including operando study during methanol and dimethyl ether conversions. Some level of steaming improved the lifetime of all SAPO-34 materials in MTO catalysis without affecting their olefin selectivity, although more severe conditions led to the formation of core–shell structures, microporosity loss and eventually at 1023 K, recrystallization to a dense phase. All these irreversible changes occurred faster in crystals with higher Si contents. The initial increase in catalytic lifetime results from an activated reduction in acid site density (Eact = 146(18) kJ mol−1), a result of redistribution of Si within the SAPO framework without porosity loss. Operando IR with online product analysis during methanol conversion suggests similar reaction pathways in calcined and steamed crystals, but with greatly reduced methoxy group densities in the latter. The gradual development of optically dark crystal cores upon progressive steaming was shown by FIB-SEM to be due to the formation of regions with meso- and macropores, and these were shown by IR mapping to possess low hydroxyl densities.

Механохимически синтезированные никельсодержащие алюмосиликатные модификаторы для триботехнических алюминиевых сплавов

Silumins are promising antifriction alloys for the manufacture of friction units. They have a low density, high wear and corrosion resistance. However, they own low hardness and strength, which leads to the need to develop modifying and strengthening additives. Aluminosilicates have a density close to silumin and can be used for its strengthening, but they are characterized by low wettability by metals. To improve wettability, it is necessary to modify the aluminosilicates with metals. The aim of this work is to study the mechanochemical synthesis of aluminosilicate/Nickel composites and modification of silumin using them. Structural changes in powder mixtures of natural aluminosilicates with Nickel during high-energy mechanical processing in a planetary ball mill, as well as in alloys of the composition silumin + potassium fluoroborate and silumin + potassium fluoroborate + aluminosilicate/Nickel obtained by hot pressing of mechanoactivated powders, were studied using Fourier-infrared spectroscopy and x-ray diffraction analysis. It is shown that mechanical activation of a mixture of silumin + potassium fluoroborate powders leads to a redistribution of silicon during sintering with the formation of large primary silicon crystals and a decrease in micro hardness by ~ 20 %. Mechanical activation of aluminosilicates with Nickel leads to the formation of composite powders with the removal of OH groups and the formation of SiO2 framework structures. The use of such a modifier during sintering of the silumin alloy leads to the formation of a homogeneous fine structure of the alloy with the grinding of eutectic and primary silicon grains, which increases the micro hardness of the alloy by 1.5 times.

Structure and Optical Properties of Magnetron-Sputtered SiO<sub>x</sub> Layers with Silicon Nanoparticles

The properties of SiOx layer prepared by magnetron sputtering is studied by photoluminescence Auger and SIMS methods. The depth distribution of emission characteristics and chemical composition is obtained. It is shown that as-sputtered SiOx layers are non-emitted and characterized by homogeneous enough chemical composition. High-temperature annealing in nitrogen atmosphere stimulates not only the Si nanocrystal formation but also the redistribution of silicon and the appearance of Si depleted region near layer-substrate interface. The last process is found to be dependent on excess Si content. It is found that decrease of silicon content in the depth of annealed layers is followed by the decrease of particle sizes that is proved by the blue shift of photoluminescence maximum. The possible reasons of the appearance of Si depleted region are discussed.

RBS Investigation of Ion Implanted SiSiO2 Structures Irradiated with 20 MeV Electrons

AbstractSummary: The influence of high‐energy electron irradiation on the redistribution of silicon and oxygen atoms in implanted SiSiO2 structures has been investigated by Rutherford backscattering spectroscopy (RBS). Two groups of SiSiO2 samples implanted with different doses of silicon ions (1 × 1012 cm−2 and 1 × 1016 cm−2) are used. The ion energy of 15 keV is chosen to produce maximum radiation defects at the SiSiO2 interface. The structures are then irradiated with 20 MeV electrons for different durations (from 60 s up to 120 min). After electron irradiation, the redistribution of the oxygen and silicon atoms in the samples implanted with 1 × 1012 cm−2 Si+ ions is negligible: significant redistribution of these atoms is found only in SiSiO2 samples implanted a with dose of 1016 cm−2. These results demonstrate that the structural changes at the silicon surface of implanted SiSiO2 samples, which take place after electron irradiation, depend more strongly on the implantation dose than on the electron dose irradiation.RBS spectra of SiSiO2 samples implanted with silicon ions and subsequently electron irradiated.imageRBS spectra of SiSiO2 samples implanted with silicon ions and subsequently electron irradiated.

Investigation of distribution and redistribution of silicon in thin doped gallium-arsenide layers grown by molecular beam epitaxy on substrates with (100), (111)Ga, and (111)As orientations

The distribution of silicon in GaAs was investigated by secondary-ion mass spectrometry (SIMS) before and after the thermal annealing of thin doped GaAs layers grown by molecular beam epitaxy on substrates with (100), (111)Ga, and (111)As orientations. The surface relief pattern of the grown epitaxial films was studied by atomic-force microscopy both inside and outside the ion-etching crater developed during the SIMS analysis. Features of the surface relief inside the crater are revealed for various orientations. Changes observed in the shape of doping profiles are explained both by the features of the development of the surface relief during the ion etching accompanying the SIMS analysis and by an accelerated diffusion of Si over the growth defects.

Special features of electrical activation of 28Si in single-crystal and epitaxial GaAs subjected to rapid thermal annealing

Concentration profiles of 28Si implanted in single-crystal and epitaxial GaAs were determined by measuring the C-V characteristics after the postimplantation rapid thermal annealings for 12 s at T=825, 870, and 905°C. The temperature dependence of Hall mobility of electrons in the Si-implanted layers subjected to the same annealings was determined by the Van der Pauw method within the range of 70–400 K. As distinct from conventional thermal annealing (for 30 min at 800°C), the rapid thermal annealing brings about a diffusive redistribution of silicon to deeper layers of GaAs for the materials of both types, with the diffusivity of silicon being twice as high in single-crystal GaAs as that in GaAs epitaxial layers. Analysis of temperature dependence of electron mobility in ion-implanted layers following a rapid thermal annealing indicates a significantly lower concentration of the defects limiting the mobility as compared to the case of a conventional thermal annealing for 30 min.

Activation and distribution of silicon implanted in gallium arsenide as a result of isothermal radiation annealing

The method of capacitance-voltage characteristics is used to investigate the concentration profiles n(x) of 28Si, implanted in GaAs [E=50 and 75 keV, F=(1.88–6.25)×1012 cm−2] after “photonic” and “electronic” annealing with a protective dielectric coating covering the surface and without it. It is shown that in contrast to thermal annealing (800 °C, 30 min), after photonic and electronic annealing diffusive redistribution of silicon into the interior of the GaAs sample is observed. The diffusion coefficient D and degree of activation η increase as the temperature is increased in the case of photonic annealing and as the power is increased in the case of electronic annealing. The values of the activation energy of the processes for D and η for radiation annealing (photonic and electron) are lower than the corresponding values for thermal annealing. The values of D and η after photonic and electronic annealing without the protective dielectric coating are higher than with it.

Observation of silicon redistribution during TiAl3 formation in aluminum alloy/titanium bilayers

Titanium is commonly used as an underlayer to aluminum alloy metal lines in integrated circuit applications, primarily for reliability considerations. The Ti/Al bilayer scheme may exhibit improved electromigration resistance as a combined result of two factors. In the first case, should a void form in Al line, the Ti layer would be capable of carrying a part of the increased current load, effectively shunting the current around the void. The second effect that Ti has is the improvement of the (111) crystallographic texture when compared to Al deposited directly on SiO2 (1). However, the fact that Al and Ti react to form the high resistivity intermetallic TiAl3 at temperatures above 350° C, represents a potentially serious limitation to the practical use of this system. One solution is to alloy the aluminum with silicon, which is known to retard the rate of formation of TiAl3 (2). We propose two mechanisms for the decreased reaction rate involving the diffusion of the Si into the TiAl3 where it acts as a barrier to Al diffusion.

Low temperature diffusion effects on microstructural changes in thick gold films on silicon

The formation of a silicon oxide layer and the microstructural changes in thick sputtered deposited gold films on Si(111) substrates were studied by scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods. Redistribution of silicon, gold and oxygen was analysed by Auger electron spectroscopy and secondary-ion mass spectrometry sputter profiling and electron probe microanalysis. It was found that structures formed during low temperature annealing in air up to 250°C consist of several separated zones. In the outer structure zone a thick porous silicon oxide layer with a needle-like structure is honeycombed with columnar gold grains, thus forming a mixed zone. The thickness of the gold and silicon oxide zone increases with increasing temperature until the substantial gold grain growth at the Au Si interface zone impedes the release of silicon atoms and their further outdiffusion and oxidation.

Kinetic diagrams for austenitizing high-strength cast iron

1. Kinetics for α→γ-transformation are governed by the silicon content in HC, redistribution of silicon between austenite and ferrite, and cast iron heating rate. This dependence expands the transformation range and causes formation of austenite which is inhomogeneous with respect to carbon and silicon concentration. 2. A dependence has been established for the temperature for the start and finish of austenite formation on silicon content in HC and its heating rate. The kinetic diagram plotted makes it possible to select a schedule for high-speed heating of castings for hardening with a given silicon content.

Uphill diffusion of the components of carbon and alloy steels during homogenization

1. Uphill diffusion of the components is observed fairly often in steels — during homogenizing annealing of Fe-C-Mn-Si alloys, e.g., in which the manganese content substantially exceeds the silicon content, and during prolonged heating for normalization. 2. Incomplete homogenization of the steel sometimes increases the chemical and structural heterogeneity. In those cases it is better not to homogenize the steel or to continue annealing until homogenization is complete. 3. Steels with a balanced concentration of carbide-forming and non-carbide-forming elements should evidently not be homogenized, since the redistribution of silicon in microvolumes of the metal disrupts the “balance” attained.

Austenizing gray cast iron

1. Austenizing of cast iron is related to the redistribution of silicon between the austenite formed and the remaining ferrite. The most intense redistribution of silicon occurs in ferritic cast irons with large graphite inclusions. The redistribution of silicon between phases is very rapid during the α→γ transformation, because the diffusion rate of silicon in a single-phase matrix is considerably slower than the diffusion rate of carbon. Therefore, we can ascertain that the main factor slowing down the austenizing of ferritic cast iron containing large graphite inclusions is the difficulty with which the ferrite with a high concentration of silicon is carburized. 2. Austenizing of ferritic cast iron, particularly in the case of rapid heating to high temperatures, leads to a microliquation of silicon entirely different from the original one. This affects the formation of the structure of the matrix during subsequent cooling of cast iron and also repeated austenizing. 3. The heating of ferritic cast iron containing large graphite inclusions leads first to the formation of austenite with a concentration of carbon considerably lower than the eutectic concentration (0.1–0.2%). The carburizing of austenite is very slow. Therefore, most of the austenite is transformed into ferrite when cast iron is cooled in air. A considerable part of the austenite is transformed into ferrite even when small samples are quenched in brine. The austenite is rapidly carburized when pearlitic cast iron or cast iron with highly branched graphite inclusions is heated. In all cast irons the high-silicon areas of austenite are carburized slowest — the dendrite branches and the central areas of the colonies. This is due to the fact that silicon increases the activity of carbon and therefore slows down its diffusion into austenite and ferrite. Silicon increases the rate of the diffusion of carbon from ferrite or austenite.