SiC Clusters Research Articles

Combined silicon refining for boron removal and Si-Kerf recycling using K2O-CaO-SiO2 slags

It is crucial for the photovoltaic (PV) industry to establish a circular materials flow for more sustainable solar silicon production. In the present work, a series of K2O-SiO2 and K2O-CaO-SiO2 slags were examined for the combination of silicon purification and Si-kerf waste recycling. The study revealed that the predominant mass transfer mechanism and the variation in slag composition during refining are due to the silicothermic reduction of K2O. The boron removal degree reached levels above 80% in most of tests, with boron gasification as potassium metaborate confirmed as an important mechanism for boron removal, especially in slags with high K2O content. In the case of ternary slags, the results indicated that an increase in CaO enhances boron partitioning in slag phase and a high K2O content also led to boron accumulation in the slag phase due to rapid reaction kinetics in the early stage of refining. The distinct behaviours of calcium and postassium ions in the slag phase were revealed by molecular dynamics simulations. It was found that potassium ions preferentially modify bridging oxygen, while calcium ions contribute more to depolymerizing the tectosilicate network and generating more non-bridging oxygens, which may further aid in the boron stabilization in slag phase. The oxidation layer of Si-kerf was removed successfully and enabled the coalescence of the silicon nanoparticles into the Si melt. Additionally, the presence of SiC clusters in the slag phase was also observed, indicating effective removal of SiC and the feasibility of Si-kerf waste recycling.

Role of carbon in n-type bulk GaN crystals

In this work co-doping with silicon and carbon in gallium nitride grown by halide vapor phase epitaxy was performed. Native seeds of high structural quality with bowing radii of (0001) crystallographic planes higher than 15 m and threading dislocation density on the order of 5 × 104 cm−3 were used. The crystallized material was examined in terms of structural, optical, and electrical properties. For this purpose different characterization methods: X-ray diffraction, Raman spectroscopy, low-temperature photoluminescence, and Hall measurements, were applied. The physical properties of samples doped only with silicon and co-doped with carbon were analyzed and compared. However, during the crystallization process, due to high amount of Si and C, clusters of silicon carbide were unintentionally formed. The formation of these SiC clusters had an impact on the properties of the GaN crystals that were being studied. The research provides an initial insight into the complex studies of co-doping gallium nitride crystals. The results of this paper give us groundwork for more in-depth exploration of this topic.

New insight into efficient photocatalytic CO2 reduction without any sacrifice agent over the novel hierarchical structured SiOC whisker aerogel

Photoreduction of CO2 to valuable fuels provides a promising strategy for managing the global carbon balance using renewable solar energy, yet the design of active, cost-effective, highly selective, and stable CO2 reduction photocatalysts remains a big challenge. Herein, we report a novel SiOC aerogel photocatalyst synthesized by a simple one-step sol-gel process, combined with the supercritical drying technique and heat treatment processes. The resulting SiOC aerogel exhibits a large BET specific area with typical hierarchical structures, which is responsible for the enhanced photocatalytic activity. In addition, the formation mechanism of the SiOC whisker aerogel is revealed in this study. The optimized SiOC aerogel exhibits CH4 and CO evolution activity of 5.8 and 20.5 μmol/g under simulated sunlight irradiation, respectively, without any additional co-catalyst or sacrificial agent, which is 6.4 and 3.9 times higher than those of the pristine SiC aerogel. The density functional theory (DFT) calculation confirms that the resulting SiOC aerogel can effectively adsorb and activate CO2 and H2O molecules on the catalyst surface. The Gibbs free energy diagram further verifies the superior performance of the resulting SiOC aerogel over the pristine SiC and SiO2 cluster via the rate-determining step calculations. The high efficiency of CO2 reduction can be attributed to the structural merits and the electronic structures modulation, which greatly achieves fast separation and transfer of charge carriers. The work paves an insight into the rational design of photocatalysts toward simultaneously facilitating carrier separation and CO2 activation from aerogel-based porous materials.

Kinetic Monte Carlo simulation study of the early stages of epitaxial SiC (0001) growth

A kinetic Monte Carlo (kMC) simulation with a cluster-multiple labeling technique was carried out to study the dynamic behavior of Si-C clusters during the early stage of epitaxial growth. In the model, a crystal lattice was established to fix the physical location of atoms and interatomic bonding. Events, such as adatoms adsorption, diffusion on the planar surface, and attachment to and detachment from clusters of adatoms were considered in the model. The Si and C atoms were treated individually to achieve more elaborate information for dynamic behavior of the clusters in the crystal surface. Moreover, a cluster multiple labeling technique, also known as the Hoshen - Kopelman algorithm was used to identify Si-C clusters. Then the properties of the clusters were calculated and analyzed by the algorithm. The simulation results showed that the number of Si-C clusters gradually decreases with increasing substrate temperature and decreasing deposition rate, and that the average size of Si-C clusters at high temperatures is much larger than that at low temperatures. Furthermore, the Si:C ratio on the growing surface has a significant effect on the surface morphology. At Si-rich conditions, the cluster density is relatively high, and the cluster shape is not homogeneously distributed. While with the increase of C mole fraction, the cluster density gradually decreases and the cluster shape becomes more uniform. Therefore, a higher concentration of C in deposition flux is beneficial to the early stage of nucleation. These findings are consistent with predictions for the case of the epitaxial growth of SiC.

Microstructures and mechanical properties of reactive spark plasma-sintered ZrB2–SiC–MoSi2 composites

Ternary ZrB2–SiC–MoSi2 composites with different nominal volume fractions of SiC (10–25 vol%) and MoSi2 (5–20 vol%) were sintered by reactive spark plasma sintering (RSPS) at 1650 °C and 35 MPa from the starting powders of ZrB2, Si, Mo and activated charcoal. The densification behaviour, microstructures and mechanical properties were comprehensively investigated. SiC clusters and MoSi2 were formed by in-situ reactions and the improved sintering efficiency was attributed to the mass transfer by liquid Si. The formation of a core–shell (Zr, Mo)B2 solid solution was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). With the addition of the nominal MoSi2 content up to 15 vol%, the molar ratio of MoB2 in the solid solution shell increased owing to the increase of Mo; the densification and mechanical properties decreased owing to the softness of MoSi2, the cracks, and the large size of SiC clusters. The relative density, Vickers hardness, and fracture toughness of ZrB2–SiC–MoSi2 composites were significantly better than those of bulk ZrB2 owing to the combined effect of phase enhancement and solid solution strengthening.

Effects of cyclic closed-die forging on the microstructural evolution and mechanical properties of SiC/AZ91D nanocomposites

A two-step cyclic closed-die forging (CCDF), with the first step to enhance the formability and the second step to refine the matrix grain, was implemented on a solution-treated SiC/AZ91D nanocomposites. Results show that the initial coarse grain is refined from ∼105 μm to ∼27 μm after the implementation of CCDF at 400∘C, and further refined to ∼6.8 μm after another 6-pass of CCDF at 300∘C. Mg17Al12 precipitates are gradually crushed with the progress of CCDF and eventually evolve into small particles uniformly distributed within the matrix. SiC clusters are effectively dispersed into smaller clusters or single particle. Yield stress (YS) and ultimate tensile strength (UTS) of the SiC/AZ91D nanocomposites increase after 1 pass of CCDF at 300∘C, while the elongation to fracture decreases. With the progress of CCDF, YS, UTS and elongation to fracture exhibit a continual increase, reaching their maximum values of 196 MPa, 371 MPa and 9.2% after 6 passes of CCDF.

Effect of SiC Nanoparticles on AZ31 Magnesium Alloy.

Magnesium alloys are attractive for the production of lightweight parts in modern automobile and aerospace industries due to their advanced properties. Their mechanical properties are usually enhanced by the incorporation with reinforcement particles. In the current study, reinforced AZ31 magnesium alloy was fabricated through the addition of bulk Al and the incorporation of SiC nanoparticles using a stir casting process to obtain AZ31-SiC nanocomposites. Scanning electron microscope (SEM) investigations revealed the formation of Mg17Al12 lamellar intermetallic structures and SiC clusters in the nanocomposites. Energy dispersive spectroscopy (EDS) detected the uniform distribution of SiC nanoparticles in the AZ31-SiC nanocomposites. Enhancements in hardness and yield strength (YS) were detected in the fabricated nanocomposites. This behavior was referred to a joint strengthening mechanisms which showed matrix-reinforcement coefficient of thermal expansion (CTE) and elastic modulus mismatches, Orowan strengthening, and load transfer mechanism. The mechanical properties and wear resistance were gradually increased with an increase in SiC content in the nanocomposite. The maximum values were obtained from nanocomposites containing 1 wt% of SiC (AZ31-1SiC). AZ31-1SiC nanocomposite YS and hardness were improved by 27% and 30%, respectively, compared to AZ31 alloy. This nanocomposite also exhibited the highest wear resistance; its wear mass loss and depth of the worn surface decreased by 26% and 15%, respectively, compared to AZ31 alloy.

Mechanical properties of fusion welded ceramics in the SiC-ZrB2 and SiC-ZrB2-ZrC systems

Mechanical properties of welded SiC-ZrB2 and SiC-ZrB2-ZrC ceramics were measured up to 1700 °C. Commercial powders were hot pressed, machined into coupons, and preheated to 1600 °C before joining the ceramics using either tungsten inert gas welding or plasma arc welding. Toughness of the parent materials was 3–4 MPa*m1/2 which decreased after welding to 2–2.5 MPa*m1/2. Strength of the SiC-ZrB2-ZrC parent material was ~700 MPa at 25 °C, ~300 MPa at 1700 °C, and retained 40–60% of this strength once welded. Strength of the SiC-ZrB2 parent material was ~600 MPa at 25 °C and 1700 °C and retained 20–30% of this strength once welded. Griffith analysis indicated that the strength in the parent materials was controlled by the size of SiC clusters while strength of welds was controlled by the size of pores in fusion zones. Therefore, removal of pores in produced fusion zones should be investigated to improve strength of future ceramic welds.

SiC/Mn co-doped CaO pellets with enhanced optical and thermal properties for calcium looping thermochemical heat storage

To achieve high heat storage capacity, excellent mechanical, optical and thermal properties in calcium looping thermochemical heat storage, the novel SiC/Mn co-doped CaO pellets were fabricated by the extrusion-spheronization method. The heat storage performances of the novel CaO pellets were studied under harsh calcination (pure CO2, 950 °C) and pressurized carbonation (pure CO2, 13 bar, 800 °C) conditions in a dual fixed-bed reactor system. The additions of SiC and Mn enhance the cyclic stability of CaO pellets during the multiple heat storage cycles. When the mass ratio of CaO:SiC:MnO2 is 100:5:5, the co-doped CaO pellets exhibit an excellent heat storage performance. The effective conversion and heat storage density of the co-doped CaO pellets are 41.5% higher than those of original CaO pellets, respectively. Meanwhile, the co-doped CaO pellets possess a good optical absorption capacity and a high thermal conductivity, which are 17.6 and 3.2 times as high as those of original CaO pellets, respectively. In addition, the co-doped CaO pellets show much higher crushing strength and lower weight loss during the attrition test. The stronger interaction between SiC and CaO cluster mitigates the movement of CaO, which is determined by density functional theory simulation. The adsorption of CO2 onto the CaO surface is enhanced by the addition of Mn. Therefore, SiC/Mn co-doped CaO pellets used in the calcium looping thermochemical heat storage process appear promising.

Influence of Hot Extrusion on the Microstructure, Tensile and Wear Properties of Mg–5Sb–xSiC Hybrid Composites

The structure, hardness, tensile and wear behavior of Mg–5Sb–xSiC hybrid composites experimented where the amount of SiC particles were 1, 3, and 5 wt% SiCp before and after applying hot extrusion process. Micron size SiC particles were added to Mg–5Sb alloy via stir casting technique to form both Mg3Sb2 and SiC particles in the as-cast microstructures. Although SiC addition reduced the grain size of the Mg–5%Sb in-situ metal matrix composite (MMC), no improvement was observed on ultimate tensile strength (UTS) and the ductility (EL.%) in the as-cast state. The use of the extrusion process led to a remarkable fracturing of Mg3Sb2 intermetallic along the extrusion direction, grain refinement, and reduction in the size of SiC clusters. The optimal amount of SiC was found to be 3 wt%, which reduced the grain size from ~ 827 to ~ 4 µm and promoted the UTS amounts from 120 to 244 MPa for as-cast and hot extruded composites. Besides, the enhancement of yield strength of extruded MMCs was rationalized depending on the grain size compared to the as-cast condition. The fractography of the as-cast composites revealed more cleavage planes in contrast with hot extruded composites, which proved much more dimples. It was also found that the use of hard SiC particles in hybrid composite improved wear properties just in the extruded state. According to observations, in various sliding test conditions, the abrasive, oxidation and delamination are mostly operated in combination.

Atomic Structure and Cohesion Energy of Isolated SiC Clusters

Ab initio calculations of the atomic and electronic structure and cohesion energy of Si60C60 fullerene-like clusters have been performed. For the first time, a model of a two-layer cluster Si12C12@Si48C48 with mixed sp2/sp3 bonds has been built. Ab initio calculations were carried out in the framework of the theory of the electron density functional and the hybrid functional B3LYP. The stability and width of the energy gap of the clusters were estimated depending on their geometry. It is shown that the stability of the two-layer cluster Si12C12@Si48C48 exceeds the stability of other clusters with the same number of atoms, but is inferior to the structure of sphalerite to the SiC cluster. In the process of relaxation, a two-layer cluster has an outward shift of the surface layer.

Атомная структура и энергия когезии изолированных кластеров SiC

The first-principle calculations of the atomic and electronic structures and cohesion energy of fullerene-like Si60C60 clusters have been carried out. A model of two-layer fullerene-like Si12C12@Si48C48 cluster with mixed sp2/sp3 bonds has been built for the first time. Ab initio calculations are performed in terms of the electron density functional and the hybrid B3LYP functional theory. The stability and the energy gap width of the clusters are estimated in the dependence on its geometry. It is shown that cohesion energy of two-layer fullerene-like Si12C12@Si48C48 cluster exceeds the cohesion energy of the other fullerene-like clusters with the same number of atoms, but is inferior to the SiC cluster with sphalerite structure. The relaxation of two-layer cluster is shift on outward the surface layer occurs.

Low-Temperature Synthesis of α-SiC Nanocrystals

Thick SiCx films have been deposited on a c-Si surface by radiofrequency (rf) magnetron sputtering (150 W, 13.56 MHz, Ar flow 2.4 L/h, 0.4 Pa) of graphite and silicon targets. The X-ray diffraction study shows that fast annealing of the SiCx film deposited on the c-Si surface for 3 h leads to the low-temperature (970°C) formation of hexagonal structural phases α-SiC (6H-SiC and other) along with the cubic modification of silicon carbide β-SiC. The IR spectroscopy has shown the formation of SiC nanocrystal nuclei due to the energy action of the rf plasma ions on the upper layer of the SiC film during its growth. The data of X-ray reflectometry demonstrate a high density of the films up to 3.59 g/cm2 as a result of formation of dense C and SiC clusters in the layers under action of the rf plasma.

Impurity Effects on Nucleation and Growth of SiC Clusters and Layers on Si(100) and Si(111)

A kinetic Monte Carlo model of silicon carbide growth on silicon surface is proposed. Based on this model, the growth of silicon carbide clusters on silicon in the presence of a pre-deposited impurity of various types: attractive and repulsive, is studied. The density of silicon carbide clusters on silicon is calculated. Calculations of the dependencies of the silicon carbide clusters density on the impurity mobility are carried out. The process of redistribution of the species in the multi-component C|Ge|Si structure during annealing is studied in the framework of the kinetic approach. Concentration profiles of the structure components are determined.

Initial nucleation of amorphous Si–B–C–N ceramics derived from polymer-precursors

Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy (TEM) combined with spatially-resolved electron energy-loss spectroscopy (EELS) analysis. The ceramics were pyrolyzed at 1000 °C followed by further annealing in N2, and SiC nano-crystallites start to emerge at 1200 °C and dominate at 1500 °C. Observed by high-angle annular dark-field imaging, bright and dark clusters were revealed as universal nano-structured features in ceramic matrices before and after nucleation, and the growth of cluster size saturated before reaching 5 nm at 1400 °C. EELS analysis demonstrated the gradual development of bonding structures successively into SiC, graphetic BNCx and Si3N4 phases, as well as a constant presence of unexpected oxygen in the matrices. Furthermore, EELS profiling revealed the bright SiC clusters and less bright Si3N4-like clusters at 1200–1400 °C. Since the amorphous matrix has already phase separated into SiCN and carbon clusters, another phase separation of SiCN into SiC and Si3N4-like clusters might occur by annealing to accompany their nucleation and growth, albeit one crystallized and another remained in amorphous structure. Hinderance of the cluster growth and further crystallization was owing to the formation of BNCx layers that developed between SiC and Si3N4-like clusters as well as from the excessive oxygen to form the stable SiO2.

Низкотемпературный синтез нанокристаллов alpha-SiC

Abstract Thick SiC_ x films have been deposited on a c -Si surface by radiofrequency (rf) magnetron sputtering (150 W, 13.56 MHz, Ar flow 2.4 L/h, 0.4 Pa) of graphite and silicon targets. The X-ray diffraction study shows that fast annealing of the SiC_ x film deposited on the c -Si surface for 3 h leads to the low-temperature (970°C) formation of hexagonal structural phases α-SiC (6 H -SiC and other) along with the cubic modification of silicon carbide β-SiC. The IR spectroscopy has shown the formation of SiC nanocrystal nuclei due to the energy action of the rf plasma ions on the upper layer of the SiC film during its growth. The data of X-ray reflectometry demonstrate a high density of the films up to 3.59 g/cm^2 as a result of formation of dense C and SiC clusters in the layers under action of the rf plasma.

Characterization and Formation Mechanism of the Nanodiamond Synthesized by A High Energy Arc‐Plasma

A new fabrication strategy using thermal source of DC arc‐discharge plasma is developed in the synthesis of nanodiamond particles. In the fabrication process, a solid mixture of Ni/Si/graphite coarse powders is used as the raw materials, meanwhile the gaseous mixture of H2/Ar served as the preparation atmosphere. The well‐established arc‐discharge plasma is significant in operation under a low gaseous pressure and an acceptable energy condition, and would be potential to become a novel process for synthesis of nanodiamond particles in large scale. The initially formed SiC clusters and the solid solution of Ni(C) particles are crucial in serving as crystal nuclei of diamond and an in situ carbon source which can gradually be released with cooling, respectively. Structural characterizations by high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectra, and X‐ray diffraction (XRD) confirm the existence nanodiamond particles, they are typically spherical with 5–20 nm in size. The formation of such nanodiamond particles by the arc‐discharge thermal source is discussed in detail on the knowledge of binary phase diagram, constitution of raw materials, and nucleation/growth processes under the experimental conditions.

Effect of Nitrogen Doping and Temperature on Mechanical Durability of Silicon Carbide Thin Films

Amorphous silicon carbide (a-SiC) films are promising solution for functional coatings intended for harsh environment due to their superior combination of physical and chemical properties and high temperature stability. However, the structural applications are limited by its brittleness. The possible solution may be an introduction of nitrogen atoms into the SiC structure. The effect of structure and composition on tribo-mechanical properties of magnetron-sputtered a-SiCxNy thin films with various nitrogen content (0–40 at.%) and C/Si close to one deposited on silicon substrates were evaluated before and after exposure to high temperatures up to 1100 °C in air and vacuum. IR transmission spectroscopy revealed formation of multiple C-N bonds for the films with N content higher than 30 at.%. Improvement of the organization in the carbon phase with the increase of nitrogen content in the a-SiCN films was detected by Raman spectroscopy. Nanoindentation and scratch test point out on the beneficial effect of the nitrogen doping on the tribo-mechanical performance of a-SiCxNy coatings, especially for the annealed coatings. The improved fracture resistance of the SiCN films stems from the formation of triple C≡N bonds for the as deposited films and also by suppression of SiC clusters crystallization by incorporation of nitrogen atoms for annealed films. This together with higher susceptibility to oxidation of a-SiCN films impart them higher scratch and wear resistance in comparison to SiC films before as well as after the thermal exposure. The best tribo-mechanical performance in term of high hardness and sufficient level of ductility were observed for the a-Si0.32C0.32N0.36 film. The enhanced performance is preserved after the thermal exposure in air (up to 1100 °C) and vacuum (up to 900 °C) atmosphere. Annealing in oxidizing atmosphere has a beneficial effect in terms of tribological properties. Harder films with lower nitrogen content suffer from higher brittleness. FIB-SEM identified film-confined cracking as the initial failure event in SiC, while it was through-interface cracking for SiCN at higher loads. This points out on the higher fracture resistance of the SiCN films where higher strains are necessary for crack formation

Computational modeling of graphene nanopore for using in DNA sequencing devices

Graphene is a promising material for nanopore-sequencing DNA technology. In the current study, we have utilized molecular dynamic simulation in order to fabricate nanopores in the four divergent locations with different properties in a single-layer graphene nanosheet by using clusters bombardment. Ten different kinetic energies have been applied to three different diameters of SiC, Si and diamond clusters to fabricate nanopores. Image processing technology has also been applied to compute the exact area of regular and irregular drilled nanopores. The obtained results suggest that the desired size and qualities of nanopore can be achieved by controlling the type, diameter and the energy of the clusters. We have observed that the average area of nanopores increases by rising the kinetic energy in the most of cases. Moreover, the properties of the incident location can highly affect the area size and quality of the nanopores. The largest area size of the nanopores has been obtained when the incident location is placed in the center of the grains, while the smallest area of nanopores have been observed when the incident point is placed on the grain boundaries junction. Among all three types of clusters, the impact of the diamond cluster with diameter of 2 nm fabricates the most suitable nanopores. Therefore, we have used the diamond cluster to investigate the effect of straining the nanosheet on the topography of nanopores. We applied 3% and 5% of tensile and compressive strain to the graphene nanosheet. Under tensile strains we found that increasing the external tensile strain on the nanosheet fabricates larger nanopores with smoother edges. On the other hand, applying external compressive strains leads to nanopores with more irregular topography.

Fabrication of nanopores in polycrystalline boron-nitride nanosheet by using Si, SiC and diamond clusters bombardment

In this paper, molecular dynamic simulations have been performed to fabricate nanopores in a polycrystalline boron-nitride nanosheet applied to DNA sequencer devices by using Si clusters bombardment. Three different sizes of Si clusters with ten different kinetic energies and impacts at five different locations of the polycrystalline boron-nitride nanosheet have been simulated. Our results show that desired nanopores with expected size and topography can be created by controlling the kinetic energy and size of the cluster. The area size of nanopores also increase by rising the kinetic energy of the cluster. We have also observed that the existing grain boundary in the incident location highly affects the shape and size of the nanopores. Therefore, we subsequently applied an external tensile strain on the boron-nitride nanosheet and determined the effect of straining nanosheet on the area, quality and the shape of fabricated nanopores. We find that increasing the external tensile strain leads to a large increase in the area of nanopores, but the shape and quality of fabricated nanopores remains nearly unaffected, particularly compared to drilling nanopores in the unstrained nanosheet. In order to investigate the effect of the cluster type, two new type of clusters (SiC and diamond) have been used to generate nanopores. Our results reveal that SiC and diamond clusters bombardment lead to fabricate almost the same shape and quality of nanopores as well as the Si cluster. On the other hand, increasing the kinetic energy of the SiC and diamond cluster barely influences the area size of the nanopores. Among all clusters, the diamond cluster bombardment leads to fabricate the largest average area size of the nanopores.