Silicon Metal Research Articles

From SiO2 to Alkoxysilanes for the Synthesis of Useful Chemicals.

The transformation of silica (SiO2) to useful chemicals is difficult to explore because of the strength of the Si–O bond and thermodynamic stability of the SiO2 structure. The direct formation of alkoxysilanes from SiO2 has been explored as an alternative to the carbothermal reduction (1900 °C) of SiO2 to metallic silicon (Simet) followed by treatment with alcohols. The base-catalyzed depolymerization of SiO2 with diols and monoalcohols afforded cyclic silicon alkoxides and tetraalkoxysilanes, respectively. SiO2 can also be converted to alkoxysilanes in the presence of organic carbonates, such as dimethyl carbonate. Alkoxysilanes can be further converted to useful chemicals, such as carbamates, organic carbonates, and chlorosilanes. An interesting and highly efficient pathway to the direct conversion of SiO2 to alkoxysilanes has been discussed in detail along with the corresponding economic and environmental implications. The thermodynamic and kinetic aspects of SiO2 transformations in the presence of alcohols are also discussed.

Tunable plasmon–polarizmon resonance and hotspots in metal–silicon core–shell nanostructures

Metal nanostructures create near-field super hotspots under light irradiation with a range limited to a few nanometers. The intense field in the spot affords enhanced nonlinear optical processes, such as Raman spectroscopy. The intense field, however, can cause heavy distortion and thermal damage to the molecular specimen as well as heavy convolution with the metal electronic structure. In this work, we simulate concentric layered silicon–metal core–shell (and its inverse) nanostructures that may alleviate the disadvantages of the pure metal environment. Our results using Mie and finite-difference time-domain scattering studies show that, in addition to the super hotspot at the gold–silicon interface, there emerges a super hotspot at the silicon–vacuum interface, whose intensities anti-correlate and are tuned by tuning the silicon thickness. Moreover, the plasmonic resonance red shifts with the thickness of the silicon shell, reaching a terminal wavelength of ∼840 nm. These features are understood in terms of induced polarization charge at the silicon–metal and silicon–vacuum interfaces, which for high κ materials (13.32) can be significant. The metal–silicon system creates plasmon–polarizmon hotspots tunable in strength and wavelength content that can be designed to alleviate high field damage, useful for Raman scattering and photovoltaic applications. The integrated metal–silicon system also promises field enhancement of visible luminescence of silicon nanoparticles, useful for imaging and tracking applications.

Experimental study on improving silicon crystal discharge cutting efficiency based on laser irradiation method

The contact barrier formed between a metal and crystalline silicon during wire electrical discharge machining (wire-EDM) hinders improvements in the processing efficiency; thus, this paper proposes a workpiece pretreatment method that increases the doping concentration of the crystalline silicon surface. First, a silver layer was coated on a silicon surface by silk screen printing, then a laser marking machine was used to irradiate the coating surface. The mechanism of this method to form a heavily-doped layer was analyzed, and the current-voltage (I–V) characteristic curves under different pretreatment processes were compared. Finally, the influence of this method on the machining performance was studied by wire-EDM experiments. The results showed that the doping concentration of the silicon surface increased, and the contact resistance decreased. When the open voltage was 120 V, the cutting efficiency of the workpiece treated with laser irradiation and screen printing was 60% higher than that without pretreatment, and it was 28% higher than the workpiece with only the metal coating treatment; however, the treatment method had little effect on the kerf width or surface roughness. It is hoped that this work will provide useful guidance for improving the EDM efficiency of crystalline silicon.

Silicon Metal–Oxide–Semiconductor Transistor with a Dependent Pocket Contact and Two-Layer Polysilicon Gate

Silicon Metal–Oxide–Semiconductor Transistor with a Dependent Pocket Contact and Two-Layer Polysilicon Gate

Processing of waste slag of non-ferrous metallurgy for the purpose of its complex utilization as a secondary mineral raw material

This article provides an overview of the methods of processing slag from welting is given, different approaches and attempts of scientists from a number of countries aimed at processing such slags are considered. In the course of the review it was found that a huge number of the following methods and methods of processing from waelz slag, there is not a single option that has sufficient complexity of processing, and that at the moment are in the dumps toxins from waelz never found its use as a secondary raw material. The elemental chemical composition of the slag from welting, which is represented by compounds of calcium, silicon, iron, aluminum, carbon and heavy nonferrous metals in the form of zinc and lead, is determined. Thus, it is established that for many years, the slags from waelz that have not found their application and are in the dump at the moment continue to have a polluting effect on the environment. Ill. 1. Ref. 63.

Highly elastic and low resistance deformable current collectors for safe and high-performance silicon and metallic lithium anodes

Silicon and lithium metal are promising anode materials toward high energy densities Li (ion) batteries. However, silicon and lithium generally have dramatic volume change during lithiation/delithiation cycles. With the repeated expansion/shrinkage, the internal stress fluctuations and electrode pulverization can cause high interfacial resistance and the failure of electrodes. Herein, a novel strategy is proposed to engineer the current collector by using a polydopamine-assisted electroless metallization process to prepare an elastic deformable current collector covered with a high electrical conductivity Cu nano-network surface. The deformable current collectors can not only stabilize the interfacial stress as an artificial-spring, but also improve the electrical conductivity of anodes without any binders and conductive agents. Featured with outstanding deformable structure, the well-designed current collector achieves a low surface resistance of 0.06 Ω/sq and excellent electrochemical performance when applied in the commercial Si anode batteries, solid-state batteries, and ionic liquid electrolyte batteries at room-temperature.

Demonstration of Multi-layered Macaroni Filler for Back-Biasing-Assisted Erasing Configuration in 3D V-NAND

Controlling the erase speed of a NAND flash is one of the challenges in memory technology. As the planar NAND flash has evolved to the vertically integrated gate-all-around (GAA), the number of stacks of word-lines (WL) was increased for better packing density. However, potential transfer through the silicon substrate or metal bit-line (BL) is insufficient with the increased number of stacks. Hence, we propose a novel V-NAND structure including multi-layered macaroni filler. The proposed macaroni filler is composed of a dielectric outer layer and a metallic core layer. The metallic core layer makes back-biasing is possible in V-NAND. As a result, erase speed can be improved without large modification of fabrication process or device layout.

In situ synthesis of cobalt silicide particle reinforcing and coloring Si3N4 ceramics

AbstractIn this paper, silicon nitride (Si3N4) ceramics with black color and high toughness were fabricated by gas pressure sintering and characterized by X‐ray diffraction, Raman, scanning electron microscopy, EDS, and transmission electron microscopy. The in situ formed cobalt silicide was confirmed to contribute to the black color through the introduction of CoO. Due to the addition of CoO, the growth of β‐Si3N4 grains is promoted, forming elongated grains, and eventually forms the self‐reinforcing microstructure. However, with adding excessive CoO, interfacial debonding is found between cobalt silicide and Si3N4 matrix and a decrease in strength was resulted. The optimum composition is 1 mol% CoO in Si3N4, with the fracture toughness of 9.9 ± 0.3 MPa m1/2, flexural strength of 826.1 ± 46.0 MPa, and a much darker black color. The mechanism of color formation is discussed where the black color derives mainly from the metallic silicon and additionally the porosity.

Influence of process parameters, hot metal silicon content and slag properties on steel dephosphorization

During the process of dephosphorization, the main solid phases formed in slag are dicalcium silicate (2CaO.SiO2), tricalcium silicate (3CaO.SiO2) and tricalcium phosphate (3CaO.P2O5). The last one is the main responsible for phosphorous removal. The present paper aims to study the influence of temperature, chemical composition, slag properties (viscosity, liquid amount, activities of CaO and FeO) and hot metal silicon (Si) content in the efficiency of steel dephosphorization. Different industrial heats with different slags, hot metal and steel compositions, were selected to be analyzed. The mentioned slag properties and phases were determined by computational thermodynamics using the software FactSage and the results of these analyzes was related to the dephosphorization efficiency from the slags respective heats. Based on these simulations, the parameter Dephosphorization Factor (FDeP = aCaO + aFeO + (Nliquid – Nsolid) ∗ KDeP) was used to measure the slags efficiency in hot metal dephosphorization and several analyzes were made by correlation observation. The results show that CaO activity is the most important parameter on the dephosphorization, whereas hot metal with higher Si content presents less efficiency in dephosphorization, due to the higher SiO2 formation, which increase the amount of solid phases, in addition to decrease in basicity and CaO activity. It was found that FDeP presents a high correlation (R2) with the dephosphorization efficiency and can be used to predict which slag will be the most efficient. The temperature, in the analyzed range, does not seem to be a directly relevant factor in the DeP efficiency.

How economic indicators impact the EU internal demand for critical raw materials

To be able to better predict future demand for critical raw materials, to better negotiate trade agreements or to better stimulate the extraction of such raw materials, we investigate how economic indicators (raw material average annual price, EU GDP at purchasing power parity, cumulative EU inflation, and EU population) impact the EU internal demand for 11 raw materials in the period from 1994 to 2012.The results show that none of the critical raw materials has an identical trend in the development of internal EU demand with any economic indicator. There is a strong correlation between some of the factors studied and the internal EU demand for magnesite, tungsten, silicon (metal), chromium, and cobalt. The results also show that for most critical raw materials the correlation between the price of a critical raw material and its internal EU demand is lower than between other economic indicators and internal EU demand for certain critical raw material. This finding is consistent with economic theory indicating that the price is not a determinant of demand, but influences the quantity demanded. The demand curve shifts due to other factors and it can be observed in our findings on silicon (metal) element. The correlation between silicon (metal) demand and economic indicators such as cumulative EU inflation, the EU population and EU GDP are very high suggesting that this element is the most appropriate critical raw material to predict its internal EU demand. Using Spearman's rank correlation coefficient, the research results show that correlation between EU internal demand for critical raw materials and its economic indicators is positively affected by the volatility of this demand but negatively affected by its average value during reference period. The results may also be important with regard to recycling activities and identifying investment needs to alleviate Europe's reliance on imports of raw materials.

Engineering local strain for single-atom nuclear acoustic resonance in silicon

Mechanical strain plays a key role in the physics and operation of nanoscale semiconductor systems, including quantum dots and single-dopant devices. Here, we describe the design of a nanoelectronic device, where a single nuclear spin is coherently controlled via nuclear acoustic resonance (NAR) through the local application of dynamical strain. The strain drives spin transitions by modulating the nuclear quadrupole interaction. We adopt an AlN piezoelectric actuator compatible with standard silicon metal–oxide–semiconductor processing and optimize the device layout to maximize the NAR drive. We predict NAR Rabi frequencies of order 200 Hz for a single 123Sb nucleus in a wide region of the device. Spin transitions driven directly by electric fields are suppressed in the center of the device, allowing the observation of pure NAR. Using electric field gradient-elastic tensors calculated by the density-functional theory, we extend our predictions to other high-spin group-V donors in silicon and to the isoelectronic 73Ge atom.

A hybrid dynamic model for the prediction of molten iron and slag quality indices of a large-scale blast furnace

The stable, economically optimal, and environmental-friendly operation of blast furnaces is still a challenge. Blast furnaces consume huge amounts of energy and are among the biggest sources of CO2 in the metal industry. The operation of industrial blast furnaces is challenging because of their sheer size, multi-phase and multi-scale physics and chemistry, slow dynamics with response times of 8 hours and more, and the lack of direct measurements of most of the important inner variables. Model-based schemes are prime candidates for providing the missing information and improving the operation. However, only recently, such schemes have been applied successfully, and there is still a lot of room for improvements. The spatial extension, the lack of precise mechanistic knowledge about the chemical and physical phenomena, and the presence of unmeasured disturbances make the application of first-principle models to process operations extremely challenging. In this work, a hybrid dynamic model is developed for the prediction of the hot metal silicon content and the slag basicity in the blast furnace process. These two variables are the key indicators of the internal process conditions, and the ultimate goal of our work is to control them by a model-based scheme. The core relationships between the process variables are imposed by a first-principles-based steady-state model, and a parallel data-based model represents the process dynamics and compensates for the deficiencies of the mechanistic model. Validation results for real plant measurements of a world-scale blast furnace show that the hybrid model is more accurate than the rigorous model and a stand-alone data-based model in long-term predictions of the dynamic behavior of the process.

Optimized Hole Injection, Diffusion, and Consumption for Efficient Metal-Assisted Chemical Etching Depending on the Silicon Doping Type and Metal Catalyst Area

Even though metal-assisted chemical etching (MACE) has been widely used for silicon (Si) nano/micromachining due to its low cost and high applicability, it is still difficult to fabricate elaborate Si nano/microstructures for high-value applications. In particular, further studies about effective factors in the MACE process with systematic approaches are highly required to obtain explicitly controlled MACE products. In this study, how the Si doping type and gold (Au) catalyst area influence MACE products in terms of the hole behavior during MACE is investigated. The type-dependent etching rate of MACE, amount of reaction products, and lateral etching/porosity of the MACE product are characterized with hole injection, diffusion, and consumption scenarios, respectively. Moreover, it is demonstrated that the dependence of the etching rate of MACE and stability/porosity of the MACE product on the Au catalyst area can be understood from the point of view of hole injection per interfacial contact plane area of the Au catalysts. As a result, elaborately controlled Si nano/microstructures can be obtained through an effective and accurate MACE process due to the optimized hole behavior. These findings could increase the accessibility and commercial availability of MACE products in many fields.

Dual ensemble online modeling for dynamic estimation of hot metal silicon content in blast furnace system

Hot metal silicon content (HMSC) is usually utilized to measure the quality of hot metal and reflect the thermal status of blast furnace (BF) system. However, most state-of-the-arts ignore the time-varying behavior of BF ironmaking process, which are impractical. Accordingly, a novel dual ensemble online sequential extreme learning machine (DE-OS-ELM) is proposed to establish the online estimation model of HMSC, which can update the data-driven model with the latest operation data. Specifically, an online learning method with recursive modification is first proposed based on OS-ELM (referred to as RM-OS-ELM) to address the modeling with uncertainty. To heel, a dynamic forgetting factor is presented for the dynamic tracking capability enhancement and convergence acceleration. Furthermore, a final updating rule for sequential implementation is constructed by combining the output weights of OS-ELM and RM-OS-ELM based on their corresponding contributions on modeling. Considering the modeling accuracy and curve trend consistency, multiobjective parameter optimization model is also implemented to achieve the satisfactory performance. By taking the proposed DE-OS-ELM, the estimation model of HMSC is established using industrial data. Comprehensive experiments demonstrate that DE-OS-ELM-based HMSC estimation model is more feasible and practical.

Broadband polarization-insensitive Jerusalem-shaped metasurface absorber based on phase-change material for the visible region

In this paper, a broadband metasurface absorber using phase change material covering the visible region (500 THz to 740 THz) is numerically investigated. The top metallic layer comprises an array of Jerusalem shaped structures periodic in the x-y direction placed above the Ge2Sb2Te5 (GST) layer. The GST layer is followed by a thick metallic layer and silicon dioxide (SiO2). The intermediate dielectric layer in between two metallic layers is made of phase change material. The tri-layer structure is placed above the SiO2 with average absorption is achieved with an efficiency of 92.86% using the amorphous GST (a-GST) phase in the dielectric layer. The average absorption of a-GST is more in the crystalline GST (c-GST) phase in the proposed absorber. The change in the absorption peaks are observed using GST material in the terahertz region. The proposed broadband Jerusalem-shaped metasurface absorber is polarization insensitive due to its symmetrical structure.

Anchoring of SiC and Fe3Si nanocrystallines in carbon nanofibers inducing interfacial polarization to promote microwave attenuation ability

Carbon-based nanomaterials are widely employed for microwave absorption. However, reasonable methods to enhance microwave absorption capacity remain worth exploring. Herein, carbon nanofibers (CNFs) modified by silicon carbide and metal silicide (SiC/Fe3Si/C) were fabricated through electrospinning and high-temperature pyrolysis processes, and their phase composition, micro-morphology, micro-structure, and magnetic characteristics evaluated. The composite nanofibers (SiC/Fe3Si/CNFs) exhibited excellent microwave absorption, with minimum reflection loss (RLmin) values of −41.6 dB at 12.8 GHz and a matching thickness of 4.5 mm. Further, the maximum effective absorption bandwidth (EAB, RL<−10 dB) of the as-synthesized sample is 11.5 GHz with a matching thickness of 5 mm. These novel carbide and intermetallic compounds loaded CNFs are remarkable candidates for lightweight, tunable, and efficient microwave absorbers.

Excellent low-temperature electrochemical cycling of an anode consisting of Si nanoparticles seeded in Sn nanowires for lithium-ion batteries

Lithium-alloys such as metallic silicon (Si) and tin (Sn) with a high theoretical capacity are currently regarded as the most promising anode materials for the next generation of Lithium-ion batteries. Here, an anode consisting of Si nanoparticles (SiNPs) seeded in Sn nanowires (SnNWs) was synthesized via a facile solid-vapor reaction. Its electrochemical performance, particularly below room temperature (RT) was investigated in detail. The structured anode bestowed lithiation of SiNPs into the network of conducting SnNWs, resulting in significantly improved cycling performance, even at 0 and -20 °C. It demonstrated not only a high and stable capacity of ∼1500 mAh/g (0.2 C) at RT but also an excellent capacity of ∼1300 mAh/g at 0 °C and ∼600 mAh/g at −20 °C. The improved low-temperature cycling performance of the structured anode is attributed to its high lithium-ion chemical diffusion coefficient, low increase of charge transfer impedance, and high lithium intercalation kinetics.

Effect of Modified Silica Fume Using MPTMS for the Enhanced EPDM Foam Insulation.

Silica fume (SF) is a by-product from the production of silicon metal, which has a relatively high silica concentration. The surface modified silica fume (mSF) is treated with (3-mercaptopropyl) trimethoxysilane (MPTMS) as filler in ethylene propylene diene monomer (EPDM) foam. The FTIR spectra of mSF clearly indicated that MPTMS can be successfully bonded to the SF surface. The reinforcing efficiency of mSF-filled EPDM foam insulation indicated that the mechanical properties such as hardness, tensile strength, modulus, and compression set enhanced higher than in case of SF and calcium carbonate. While the cure characteristics such as the maximum torque (MH), the minimum torque (ML) and the differential torque (MH-ML) are increasing in proportion to increasing filler contents, mainly with mSF. For the cure behavior, the mSF-filled EPDM foam insulation showed the fastest cure time (tc90) and scorch time (ts2) due to reduced accelerator adsorption. Whereas, the calcium carbonate-filled EPDM foam insulation increased the cure time (tc90) and scorch time (ts2), therefore, it also prevents compound scorching. The results indicated that the mSF with MPTMS can be used as an alternative filler for EPDM foam insulation.

Nano-Gaps Fabricated by Thermal Evaporation and Stripping Techniques.

The fabrication of inexpensive nano-gaps is vitally important for the research and application of nanochannel-based devices. This study presents a low-cost and simple method for the fabrication of nano-gaps using thermal evaporation and stripping techniques. The structural morphology of metal films deposited on the convex structures of photoresist by sputtering and thermal evaporation was studied. The effect of angles of thermal evaporation on the width of nano-gaps was investigated. The characteristics of metal film deposited on the convex structures of photoresist and spaces between these convex structures after stripping were investigated, and the adhesive force between the metal film and silicon substrate was also analyzed. Finally, a metal film of Cu was deposited on the convex structures of photoresist by thermal evaporation. After stripping, nano-gaps with a width of 187 nm were fabricated. The method proposed in this paper can be employed to mass-produce two-dimensional nanochannels based devices at low cost.

Microstructure beneath screen-printed silver contacts and its correlation to metallization-induced recombination parameters

In this work, we present an approach to model metallization-induced recombination losses j 0,met of screen-printed fire-through metallization pastes, which are used e.g. for the contacts on the front side of passivated emitter and rear cells (PERC). Modelling is based on the local phosphorus emitter doping profile and the local microstructure of the interface between metal contact and silicon surface, which is characterized during a quantitative microstructural analysis using the scanning electron microscope (SEM). By comparing the modelled j 0,met to measured j 0,met results determined at the same position of both, the microstructural analysis and emitter doping profile, we find that in most cases recombination is dominated by the etch back of the emitter by the glass frit rather than by penetration of crystallites into the doped region. However, for crystallites protruding deep into the emitter or rather up to the junction, recombination at the crystallites becomes significant as well. Our modelled results yield indications that the etch depth into the emitter doping profile by the glass frit contained in the metallization paste, is sensitive to the emitter doping profile itself. • Metallization-induced recombination is dominated by the etch back of the emitter doping profile • Etch back of the emitter doping profile is sensitive to doping profile itself • Plating useful to enhance contrast for microstructure analysis