Silicon-rich Regions Research Articles

Regolith water storage patterns determine vegetation productivity in global karst regions

Although the distribution of vegetation productivity is largely determined by temperature and precipitation variations, the influence of the substrate condition still requires further exploration, especially in karst regions characterized by extremely shallow soil underlain by weathered bedrock. In this study, we find that the regolith in karst landscapes can behave much like soil layer in many other terrestrial landscapes and the contribution of bedrock lithology to GPP by affecting water availability is significant, but dominant chemical elements have inconsistent impacts across the selected karst regions worldwide. In karst landscapes with tropical (Savannah, Aw) and temperate (without dry season, Cf) climates, more than 80% of the grids show a significant positive correlation between available water for plants and precipitation supply, and calcium-rich areas with lower average root length tend to form higher GPP. Conversely, in karst landscapes with arid (Steppe, Bs) and temperate (Dry winter, Cw) climates, more than 70% of the grids show decoupled water availability for plants from variability of precipitation, and silicon-rich regions with deeper average root lengths contribute to higher vegetation productivity. Instead of climate regimes, the effect of bedrock lithology on vegetation productivity is mediated by how precipitation is stored and released to plants. Our results highlight that the critical role of bedrock lithology-related water storage should not be ignored in the Earth system models.

Si diffusion induced adhesion and corrosion resistance in annealed RF sputtered SiC films on graphite substrate

Silicon carbide (SiC) is one of the promising candidates for graphite protection in different applications involving high temperatures and a highly corrosive environment. An ideal Silicon carbide coating should withstand a corrosive environment without compromising its adhesion. Herein, RF magnetron sputtered silicon-rich SiC thin films were deposited on a graphite substrate followed by annealing at 1000 °C, 1200 °C, and 1400 °C in an inert atmosphere. The impact of annealing temperature on microstructure, adhesion and chemical stability of SiC thin films was demonstrated. Different analytical techniques like Scanning electron microscopy (SEM), X-Ray Diffraction (XRD), Fourier's Transform Infrared (FTIR) spectroscopy and nano-indentation were used to study microstructural evaluation and mechanical characteristics. Moreover, the electrochemical analysis (Tafel and Electrochemical impedance spectroscopy) was performed in 3.5% NaCl solution. The microstructural analysis revealed that the amorphous SiC thin film turned into a crystalline and dense film upon annealing. Scanning electron micrographs showed that silicon-rich regions at SiC film surface started to disappear as Si diffuses into graphite matrix at elevated temperatures. Both these factors contributed to improvement in the adhesion of SiC coating with graphite substrate as annealing temperature increased. In addition, the nano-indentation hardness of 5.2 GPa was obtained for as grown sample, which decreased at 1000 °C, and then increased at 1200 °C and 1400 °C. Furthermore, the electrochemical analysis confirmed the enhancement in corrosion resistance upon annealing at a temperature of 1200 °C and 1400 °C due to Si diffusion and film compactness in these samples.

Electronegativity and doping in Si1-xGex alloys

Silicon germanium alloys are technologically important in microelectronics but also they are an important paradigm and model system to study the intricacies of the defect processes on random alloys. The key in semiconductors is that dopants and defects can tune their electronic properties and although their impact is well established in elemental semiconductors such as silicon they are not well characterized in random semiconductor alloys such as silicon germanium. In particular the impact of electronegativity of the local environment on the electronic properties of the dopant atom needs to be clarified. Here we employ density functional theory in conjunction with special quasirandom structures model to show that the Bader charge of the dopant atoms is strongly dependent upon the nearest neighbor environment. This in turn implies that the dopants will behave differently is silicon-rich and germanium-rich regions of the silicon germanium alloy.

Structural and mechanical evolution of TiAlSiN nanocomposite coating under influence of Si3N4 power

Abstract In this study, we have reported the microstructural and mechanical properties of nanocrystalline Titanium Aluminum Nitride (TiAlN) embedded in amorphous Silicon Nitride (Si 3 N 4 ) nanocomposite films. The films were deposited on Si substrate by using DC\RF reactive magnetron co-sputtering of TiAl and Si 3 N 4 targets by varying power to the Si 3 N 4 target. The films were investigated using grazing incident X-ray diffraction (GIXRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), stylus profiler and nanoindentation. GIXRD shows the formation of crystalline cubic Ti 3 AlN phase in the films. With the increase in Si 3 N 4 power, crystal growth of TiAlN diminishes. FESEM micrographs showed the uniformly distributed, well developed, sharp-edged, irregular shaped grains on the surface of the films. The silicon-rich region was observed at inter-grain boundary region and the micrographs visualize the presence of amorphous Si 3 N 4 on the edge of crystal grains. The amorphous content increases with Si 3 N 4 power. EDS confirms the presence of all elements in the films. The optimum mechanical properties were observed at 70 W Si 3 N 4 target power. Hardness, elastic modulus, elastic recovery and resistance to plastic deformation of film rises from 40 W to 70 W target power and then reduces at 90 W.

Design and fabrication of functionally graded in-situ aluminium composites for automotive pistons

Engineering components with location specific properties are being designed and fabricated successfully using functionally graded materials (FGM). The present investigation aims at design, fabrication and evaluation of functionally graded automotive piston using in-situ primary silicon reinforced A390 aluminium composite by centrifugal casting technique with a view of obtaining improved thermo mechanical properties at specific locations. The dies are designed and fabricated so as to obtain the primary silicon rich region towards the head portion of the piston. FGM pistons with A390 and A390-0.5%Mg are produced. They are characterised along the vertical cross section of the piston from piston head towards the skirt by microstructural, chemical, mechanical, thermal and tribological characterisations methods. The results are also compared with that of gravity cast piston. Microstructure and chemical composition analysis of FGM piston shows graded distribution of primary silicon from the head portion of the piston towards skirt and a eutectic composition in the skirt region. That yields an increase in hardness towards the head region. The wear testing revealed that the gradation also resulted in a remarkable enhancement of the wear properties of the piston head.

Characterization of tungsten–nickel simultaneous Ohmic contacts to p- and n-type 4H-SiC

Ohmic contacts to p- and n-type 4H-SiC using refractory alloyed W:Ni thin films were investigated. Transfer length measurement test structures to p-type 4H-SiC (NA = 3 × 1020 cm−3) revealed Ohmic contacts with specific contact resistances, ρc, of ∼10−5 Ω cm2 after 0.5 h annealing in argon at temperatures of 1000 °C, 1100 °C, 1150 °C, and 1200 °C. Contacts fabricated on n-type 4H-SiC (ND = 2 × 1019 cm−3) by similar methods were shown to have similar specific contact resistance values after annealing, demonstrating simultaneous Ohmic contact formation for W:Ni alloys on 4H-SiC. The lowest ρc values were (7.3 ± 0.9) × 10−6 Ω cm2 for p-SiC and (6.8 ± 3.1) × 10−6 Ω cm2 for n-SiC after annealing at 1150 °C. X-ray diffraction shows a cubic tungsten–nickel–carbide phase in the Ohmic contacts after annealing as well as WC after higher temperatures. Auger electron spectroscopy depth profiles support the presence of metal carbide regions above a nickel and silicon-rich region near the interface. X-ray energy dispersive spectroscopy mapping showed tungsten-rich and nickel-rich regions after annealing at 1100 °C and above. W:Ni alloys show promise as simultaneous Ohmic contacts to p- and n-SiC, offering low and comparable ρc values along with the formation of WxNiyC.

Corrosion Behaviour of the Anodised A356 Aluminium Alloy Produced by the Rheo-High Pressure Die Casting Process

<span><p>Semi-solid metal forming of aluminium alloys has demonstrated the capability to produce near net shaped high integrity components. Anodising of these components for aesthetic and/or improved corrosion resistance is specified by some designers or users of this technology. The corrosion behaviour of fully anodised and partially anodised A356 aluminium alloy plates produced using the CSIR Rheo-High Pressure Die Casting (CSIR-RHPDC) process was investigated using immersion testing in a 3.5% NaCl solution with pH = 7. Optical microscope equipped with image analysis software and scanning electron microscope (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) were used to evaluate the behaviour of the corroded samples. The fully anodised sample showed that the anodised surface displayed some surface degradation. This degradation was more severe on the anodised surface with surface liquid segregation (SLS), but provided sufficient protection to prevent corrosion of the base metal. The partially anodised sample showed severe corrosion of the based metal with the corrosion concentrated in the silicon rich eutectic and SLS regions.</p> <span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3"> </span>

ON SILICON GROUP ELEMENTS EJECTED BY SUPERNOVAE TYPE IA

There is compelling evidence that the peak brightness of a Type Ia supernova is affected by the electron fraction Ye at the time of the explosion. The electron fraction is set by the aboriginal composition of the white dwarf and the reactions that occur during the pre explosive convective burning. To date, determining the makeup of the white dwarf progenitor has relied on indirect proxies, such as the average metallicity of the host stellar population. In this paper, we present analytical calculations supporting the idea that the electron fraction of the progenitor systematically influences the nucleosynthesis of silicon group ejecta in Type Ia supernovae. In particular, we suggest the abundances generated in quasi nuclear statistical equilibrium are preserved during the subsequent freezeout. This allows one to potential recovery of Ye at explosion from the abundances recovered from an observed spectra. We show that measurement of 28Si, 32S, 40Ca, and 54Fe abundances can be used to construct Ye in the silicon rich regions of the supernovae. If these four abundances are determined exactly, they are sufficient to recover Ye to 6 percent. This is because these isotopes dominate the composition of silicon-rich material and iron rich material in quasi nuclear statistical equilibrium. Analytical analysis shows that the 28Si abundance is insensitive to Ye, the 32S abundance has a nearly linear trend with Ye, and the 40Ca abundance has a nearly quadratic trend with Ye. We verify these trends with post-processing of 1D models and show that these trends are reflected in model synthetic spectra.

Influence of high-dose nitrogen implantation on the positive charge density of the buried oxide of silicon-on-insulator wafers

The influence of nitrogen implantation on the properties of silicon-on-insulator buried oxide using separation by oxygen implantation was studied. Nitrogen ions were implanted into the buried oxide layer with a high-dose of 1016 cm-2. The experimental results showed that the positive charge density of the nitrogen-implanted buried oxide was obviously increased, compared with the control sampes without nitrogen implantation. It was also found that the post-implantation annealing caused an additional increase of the positive charge density in the nitrogen implanted samples. However, annealing time displayed a small effect on the positive charge density of the nitrogen implanted buried oxide, compared with the significant increase induced by nitrogen implantation. Moreover, the capacitance-voltage results showed that the positive charge density of the unannealed sample with nitrogen implanted is approximately equal to that of the sample annealed at 1100 ℃ for 2.5 h in N2 ambient, despite an additional increase brought with annealing, and the buried oxide of the sample after 0.5 h annealing has a maximum value of positive charge density. According to the simulating results, the nitrogen implantation resulted in a heavy damage to the buried oxide, a lot of silicon and oxygen vacancies were introduced in the buried oxide during implantation. However, the Fourier transform infrared spectroscopy of the samples indicates that implantation induced defects can be basically eliminated after an annealing at 1100 ℃ for 0.5 h. The increase of the positive charge density of the nitrogen implanted buried oxide is ascribed to the accumulation of implanted nitrogen near the interface of buried oxide and silicon, which caused the break of weak Si-Si bonds and the production of positive silicon ions in the silicon-rich region of the buried oxide near the interface, and this conclusion is supported by the results of secondary ion mass spectrometry.

Annealing effects on PECVD-grown Si rich aSiNx thin films

Abstract We report on the effect of the annealing temperature (range 600–1100 °C) on amorphous silicon-rich nitride films deposited by PECVD at 300 °C. The evolution of Raman spectra, room temperature photoluminescence, and optical absorption has been investigated on samples with different stoichiometry. Evidence of partial phase separation, with silicon-rich and nitrogen-rich regions, in the as-grown material has been inferred, with the thermal treatments inducing further reorganization of the two phases. Nucleation of silicon nanocrystals has been detected only after the highest temperature treatment on the sample with larger silicon content.

Silicone‐polyacrylate chemical compatibilization with organosilanes

AbstractSilicone‐polyacrylate polymer blends were prepared using methacryloxy‐propyl‐trimethoxysilane (MAPTMS) as a compatibilizing agent (chemical linker). Energy dispersive X‐ray spectroscopy elemental mapping showed silicon and carbon rich regions corresponding to poly(dimethyl‐siloxane) (PDMS) and poly(methyl methacrylate) PMMA domains. Infrared spectroscopy confirmed that covalent bonds are formed between PMMA and the organosilane, MAPTMS. The organosilane addition decreased the water‐to‐blend contact angles and tended to increase the modulus of elasticity and tensile strength of the resulting PDMS‐PMMA blends. Cytotoxicity was not detectable for any samples. Silicone‐based materials are currently used as prosthetic materials to replace damaged tissues; the methodology described here can be readily adapted to this application with improved performance. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Etching behavior of Pb ion from PbO-B2O3-SiO2 glasses in HNO3 solution

Quantitative studies on the dissolution of Pb in an acid solution were conducted to understand the etching mechanism in PbO-SiO2-B2O3 glasses. In this study, the etching was done on bulk glasses of a PbO-SiO2-B2O3 system with a HNO3 solution at 40 °C, and the surface structure of the glasses and ion dissolution behavior were analyzed using X-ray photoelectron spectroscopy (XPS), Raman spectrophotometer, and inductive coupled plasma spectrometry, respectively. The results showed that Pb (1.5–5.5 %) and B (0.8–3 %) ions are the major components etched. Small amounts of Si, Al, Ti, and Zr were detected in the etching solution. The analysis of O1s in the XPS peaks showed that the ratio of non-bridging oxygen (NBO) to bridging oxygen (BO) changed from 1:2.7 to 1:0.6 after leaching with the HNO3 solution. The Si-O-Pb and Si-O-Si bindings on the glass surface appeared to be a silicon-rich region where Si-O binding occurs after etching.

Structure study of multi-component borosilicate glasses from high-Q neutron diffraction measurement and RMC modeling

A neutron diffraction structure study has been performed on multi-component borosilicate glasses with compositions (65−x)SiO2·xB2O3·25Na2O·5BaO·5ZrO2, x=5–15mol%. The structure factor has been measured up to a rather high momentum transfer value of 30Å−1, which made high r-space resolution available for real space analyses. Reverse Monte Carlo simulation was applied to calculate the partial atomic pair correlation functions, nearest neighbor atomic distances and coordination number distributions. The Si–O network consists of tetrahedral SiO4 units with characteristic first neighbor distances at rSi–O=1.60Å and rSi–Si=3.0Å. The boron environment contains two well-resolved B–O distances at 1.40 and 1.60Å and both 3- and 4-fold coordinated B atoms are present. A chemically mixed network structure is proposed including [4]B–O–[4]Si and [3]B–O–[4]Si chain segments. The O–O and Na–O distributions suggest partial segregation of silicon and boron rich regions. The highly effective ability of Zr to stabilize glassy and hydrolytic properties of sodium-borosilicate materials is interpreted by the network-forming role of Zr ions.

Network structure of multi-component sodium borosilicate glasses by neutron diffraction

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 − x)SiO 2. · xB 2O 3 · 25Na 2O · 5BaO · 5ZrO 2, x = 5–15 mol%. The maximum momentum transfer of the experimental structure factor was 30 Å −1, which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si–O and Si–Si distributions are similar for all glassy samples, suggesting that the Si–O network consisting of tetrahedral SiO 4 units is highly stable even in the multi-component glasses. The B–O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 Å and 1.60 Å, the latter equals the Si–O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O–O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO 3 units, and the silicon rich network is formed by a mixed continuous network of [4]Si–O–Si [4] with several different [4]B–O–Si [4] and [3]B–O–Si [4] linkages.

Development of anodic coatings on aluminium under sparking conditions in silicate electrolyte

Spark anodizing of aluminium at 5 A dm −2 in sodium metasilicate/potassium hydroxide electrolytes is studied, with particular emphasis on the mechanism of coating growth, using transmission electron microscopy and surface analytical techniques, with coatings typically 10 μm, or more, thick. Two-layered coatings develop by deposition of an outer layer based on amorphous silica, associated with low levels of alkali-metal species, at the coating surface and growth of an inner, mainly alumina-based, layer, with an amorphous region next to the metal/coating interface. Formation of crystalline phases in the inner layer, mainly γ-Al 2O 3, with some α-Al 2O 3 and occasional δ-Al 2O, is assisted by local heating, and possibly also by ionic migration processes, arising from the rapid coating growth at sites of breakdown. Due to local access of electrolyte species in channels created by breakdown events, the silicon content in the inner coating regions varies widely, ranging from negligible levels to about 10 at.%. Silica deposition at the coating surface and formation of Al 2SiO 5 and Al 6Si 2O 13 phases is promoted by increased time of anodizing and concentration of metasilicate in the electrolyte. However, at sufficiently high concentration of metasilicate and pH, when more extreme voltage fluctuations accompany breakdown, the two-layered nature of coatings is replaced by a mixture of aluminium-rich and silicon-rich regions throughout the coating thickness.

Comparison of the plastic deformation and failure of A359/SiC and 6061-T6/Al2O3 metal matrix composites under dynamic tension

Abstract A comparison is presented of the dynamic plastic deformation and tensile failure of two metal-matrix composites (one with a cast alloy matrix and the other with a wrought alloy matrix). The two composites are ceramic particle reinforced aluminum alloys: F3S.20S (A359 aluminum alloy reinforced by 20% SiC particles) and W6A20A (6061-T6 aluminum alloy reinforced by 20% Al2O3 particles). The corresponding unreinforced matrix alloys were also examined. The effects of strain rate on the tensile responses of these composites were determined using the tension Kolsky bar. The microstructures and fracture surfaces of the specimens of each composite were examined using SEM and optical microscopy. The experimental results show that the flow stresses of both composites are higher than that of their matrix alloys, whereas the composite fracture strains are lower. The fracture strains of the W6A20A composite and the 6061-T6 monolithic matrix alloy were much higher than those of the F3S20S composite and the A359 monolithic matrix alloy. Both the W6A20A composite and 6061-T6 monolithic matrix alloy behaved in a ductile manner with necking prior to fracture, while both the F3S.20S composite and A359 monolithic matrix alloy behaved in a brittle manner with no necking prior to fracture. Microscopic examination revealed tensile failure of the A359 matrix alloy and its composite to be controlled by the microcracking of Si network, which formed in the interdendritic silicon rich region, whereas failure of the 6061-T6 based composite is controlled by cracking of reinforcement particles.

Non-Fermi liquid-like behavior around the critical concentration in CeCoGe 3− xSi x ( x≃1.2)

Kondo effect and quantum critical behavior in the pseudoternary system of CeCoGe 3− x Si x ( x≃1.2) have been studied down to about 0.1 K. The antiferromagnetism is suppressed near x=1.2 by the enhanced Kondo effect and an intermediate-valence regime with a very high Kondo temperature of the order of 900 K is followed further on in the silicon-rich region. Non-Fermi liquid-like behavior around the critical concentration, the ln T -dependence of C/ T in the intermediate temperature ranges and the T-linear electrical resistivity have been investigated in some detail.

Microstructure of SiO x :H Films prepared by plasma enhanced chemical vapor deposition

The micro-Raman spectroscopy and infrared (IR) spectroscopy have been performed for the study of the microstructure of amorphous hydrogenated oxidized silicon (alpha-SiOx,:H) films prepared by Plasma Enhanced Chemical Vapor Deposition technique. It is found that a-SiOx:H consists of two phases: an amorphous silicon-rich phase and an oxygen-rich phase mainly comprised of HSi-SiO2 and HSi-O-3. The Raman scattering; results exhibit that the frequency of TO-like mode of amorphous silicon red-shifts with decreasing size of silicon-rich region. This is related to the quantum confinement effects, similar to the nanocrystalline silicon.

Optoelectronic and structural properties of amorphous silicon–carbon alloys deposited by low-power electron-cyclotron resonance plasma-enhanced chemical-vapor deposition

The optoelectronic and structural properties of hydrogenated amorphous silicon-carbon alloys (a-SiC:H) are studied over the entire compositional range of carbon content. The films are prepared using low-power electron-cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition. The carbon content was varied by using different methane (or ethylene-)-to-silane gas phase ratios and by introducing the methane (or ethylene) either remotely into the plasma stream or directly through the ECR source, together with the excitation gas (hydrogen). Regardless of the deposition conditions and source gases used, the optical, structural and transport properties of the a-SiC:H alloys followed simple universal dependencies related to changes in the density of states associated with their structural disorder. The deep defect density from photothermal deflection spectroscopy, the ESR spin density, the steady state and the transient photoluminescence, the dark and photoconductivity, the temperature of the hydrogen evolution peaks and the bonding from infrared spectroscopy are correlated to the Urbach tail energy, the B factor of the Tauc plot and E04 (defined as the energy at which the absorption coefficient is equal to 104 cm−1). Silicon-rich and carbon-rich regions with very different properties, corresponding approximately to carbon fractions below and above 0.5, respectively, can be distinguished. The properties of the ECR a-SiC:H alloys are compared with those of alloys deposited by rf glow discharge.

New phases in the Yb–Au–Si and Ca–Au–Si systems

Abstract The YbAu2–x Si x and CaAu2–x Si x systems were studied by X-ray techniques in the range 0.7 ≤ x ≤ 1.3. The YbAuSi compound forms peritectically at 1478 K and is stable till 1168 K in its high-temperature form (EuAuGe type); below 1168 K the SrAgGe type occurs. No equiatomic compound exists in the Ca–Au–Si system. In the gold- and silicon-rich regions the two systems show similar structural behaviour: the gold-rich phases belong to the CeCu2 or the EuAuGe type, while the silicon-rich phases crystallize in the A1B2 type. The magnetic susceptibility at room temperature indicates the divalency of ytterbium in YbAuSi.