Heat-treated Silicon Research Articles

Modeling of Dry Conditioned Sliding Wear And Friction Behavior of Heat-Treated Silicon Nitride Strengthened Al Metal Matrix Nanocomposites

In the presented work, the sliding wear under dry conditions and friction behaviour of Si3N4 reinforced high-strength Aluminum alloy (AA)7068 nanocomposites have been investigated under various loads, sliding velocity, and rubbing distances. The fabrication of nanocomposites has been done by using the stir casting technique with the advancement of ultrasonication. Scanning electron microscope (SEM), Elemental mapping, and energy dispersive spectroscopy (EDS) are used to analyze the microstructure of prepared nanocomposites and worn surfaces. The wear resistance improves with the incorporation of Si3N4 particles in Al 7068 alloy and further increases by increasing the weight % of reinforcement. The reinforcement is done by 0.5, 1, and 1.5 % Si3N4 by weight. ANOVA reveals that sliding distance is the most dominating factor in the wear loss of samples, and load became the most influential parameter in the coefficient of friction (COF). Microstructure reveals grain boundaries become discontinued after T6 heat treatment. AMNCs containing 1.5wt.% Si3N4 shows minimum wear loss compared to other nanocomposites and alloys.

Tensostimulated Effect in a Doped and Heat-Treated Silicon at an Oriented Deformation

Tensostimulated Effect in a Doped and Heat-Treated Silicon at an Oriented Deformation

An investigation of the wetting behavior of heat-treated silicon nitride particles with liquid silicon

Silicon nitride is commonly used as a coating material for the silica crucibles utilized for the growth of multicrystalline silicon by directional solidification. The coating material might introduce impurities into the silicon melt during the growth. To investigate the wetting and incorporation behavior of the silicon nitride particles, silicon nitride particles were put intentionally into silicon rods, which were then grown by the float zone technique. To ensure that the particles stay within the melt and are not pushed out of the molten zone, the particles must show good wetting. Superheating the silicon nitride powders up to 105 K over the melting point of silicon was a successful approach to ensure wetting and thus to investigate the incorporation behavior of the silicon nitride in photovoltaic silicon. The heat treated silicon nitride particles stayed within the melt zone during the float zone experiments and the distribution behavior of the particles could be studied. Incidentally, the results imply that to suppress incorporation of silicon nitride particles (as coating material) into molten silicon during directional solidification, superheating the melt must be avoided.

Yolk-shell Si/SiOx@Void@C composites as anode materials for lithium-ion batteries

Silicon (Si) has been considered as one of the most promising anode materials in lithium-ion battery. However, practical applications of Si are hindered by undesirable cycling stability resulting from poor electrical conductivity and huge volumetric change during cycling process. Here, we prepared a yolk-shell silicon/carbon composite by etching carbon-coated heat-treated silicon monoxide (SiO) precursor. The as-prepared Si/SiOx@Void@C composite of inner silicon/silicon oxides and outer carbon shell with voids between them (Si/SiOx@Void@C), shows impressive cycling stability (1020[Formula: see text]mAh[Formula: see text]g[Formula: see text] at 1[Formula: see text]A[Formula: see text]g[Formula: see text] over 200 cycles) and excellent rate performance (775[Formula: see text]mAh[Formula: see text]g[Formula: see text] at 6[Formula: see text]A[Formula: see text]g[Formula: see text]). The remarkable electrochemical performance is due to the enhanced electrical conductivity originated from the carbon shell and the volume buffer effect of the yolk-shell structure. A combination of the yolk-shell structure with Si/C composites is believed to be a promising way to improve the performance of Si-based materials in lithium-ion batteries.

Processing of heat-treated silicon carbide-reinforced aluminum alloy composites

ABSTRACTThe present study investigates the processing of heat-treated silicon carbide (SiC) particle-reinforced 6061 aluminum alloy (AA) composites. As-received SiC powders were heat treated at 1300ºC, 1400ºC, and 1500ºC in nitrogen atmosphere for 2 h, and the 6061 AA–SiC composites were developed by spark plasma sintering at 560ºC and 60 MPa for 5 min in argon atmosphere. The amorphous silicon nitride is found to form in SiC particles as a result of heating at 1400ºC. The microstructure of the composites exhibited uniform distribution of SiC or SiC/Si3N4 particles in 6061 AA matrix. Further, the heat-treated SiC-reinforced 6061AA composites exhibited improved mechanical properties. A typical combination of UTS of 240 MPa and elongation of 21% is obtained for the 6061 AA composites prepared using SiC powders heated at 1400ºC.

Purification of Silicon Using the Liquid Phase Migration Technique under Temperature Gradient

A new conceptual technique for solar grade silicon (SOG-Si) purification was proposed in the present work. Most impurity elements in metallurgical grade silicon (MG-Si) exist in the grain boundary phases and their contents inside of silicon grains are extremely small, which is resulted from significant segregation during the solidification. Thus, the excellent purification was expected by selective ejection of grain boundary phases from silicon matrix. Such phases can be melted above the eutectic temperature of the system to form impurity-enriched liquid phase. In order to achieve the selective ejection of the liquid phase, its migration in the silicon matrix was investigated by conducting the heat treatment of silicon under the temperature gradient in this paper.

Diffusion model of the formation of growth microdefects as applied to the description of defect formation in heat-treated silicon single crystals

The diffusion model of the formation of growth microdefects has been considered as applied to the description of defect formation in heat-treated silicon single crystals. It has been shown that, in the framework of the proposed kinetic model of defect formation, the formation and development of the defect structure during the growth of a crystal and its heat treatment can be considered within a unified context. The mathematical apparatus of the diffusion model can provide a basis for the development of a program package for the analysis and calculation of the formation of growth and postgrowth microdefects in dislocation-free silicon single crystals. It has been demonstrated that the diffusion model of the formation of growth and post-growth microdefects allows one to determine necessary conditions for the growth of a crystal and the regimes of its heat treatment for the preparation of a precisely defined defect structure.

Processing of vacuum heat-treated MgO-densified silicon nitride crucible for molten cast iron handling

Abstract Silicon nitride with 3% MgO powder mix is uniaxially and cold isostatically pressed to form a green Si 3 N 4 crucible. Liquid phase sintering was applied to the green Si 3 N 4 crucible at 1600 °C for 30 min under the nitrogen atmosphere. Intergranular Mg–Si–O–N glass remained between the silicon nitride grains which reacted with the molten metal during melting. This grain boundary glass was removed by vacuum heat treatment at 1575 °C for 5 h. The vacuum heat treated crucible was used to melt cast iron to examine reactions between the molten metal and Si 3 N 4 ceramic crucible. EDX spectra across the Si 3 N 4 –cast iron interface and XRD for silicon nitride sample after cast-iron melting side surface analysis were carried out. Optical microscopy and SEM image analysis were made to examine the interaction between Si 3 N 4 crucible and cast iron melt. Surprisingly, no reaction was observed between the vacuum heat treated crucible and melted cast iron.

Dislocation generation in heat-treated nitrogen-doped silicon wafers when applying external loads

The features of generation and motion of dislocations in nitrogen-doped dislocation-free silicon wafers after their multistage thermal treatments are investigated. It is established that doping with nitrogen leads to a substantial increase in stresses of the onset of plastic deformation from the external and internal heterogeneous sources in heat-treated wafers. The motion velocity of dislocations in nitrogen-doped silicon wafers is lower than in undoped wafers. The strengthening effect of nitrogen is apparently caused by its activating effect on the decomposition process of a supersaturated solid solution of oxygen during heat treatment.

Electron spin resonance study of the Si-B5 paramagnetic center in neutron-irradiated heat-treated silicon

A detailed electron spin resonance study has been performed on the Si-B5 paramagnetic defect (C 3v symmetry) in neutron-irradiated c-Si subjected to annealing in the range 200–350 °C. A rich and detailed 29Si hyperfine structure is newly resolved and fully angularly mapped. Computer simulations point toward the defect's unpaired electron as having its strongest interaction with one Si site, followed by interaction with two shells of two equivalent Si sites each, and two more shells of both three equivalent Si sites. Two previously proposed tri-interstitial models are discussed as possible candidates for the Si-B5. However in lack of extensive theoretical calculations, assignment of the Si-B5 to one of the tri-interstitial models remains undecided. In addition we also report on an unusual temperature behavior of the hf splittings as well as the principal g matrix values.

Atomic-scale observation of the grain-boundary structure of Yb-doped and heat-treated silicon nitride ceramics

The effect of secondary sintering additives and/or a post-sintering heat treatment on the semicrystalline atomic structure of the intergranular phase in silicon nitride ceramics is investigated. Three different Yb-doped Si3N4 ceramic compositions are examined using a scanning transmission electron microscope, whereby the intergranular atomic structure is directly imaged with Ångstrom resolution. The resulting high-resolution images show that the atomic arrangement of the Yb takes very periodic positions along the interface between the intergranular phase and the matrix grains, and that a postsintering 1250°C heat treatment, as well as a change of the secondary sintering additives (Al2O3 vs SiO2), does not alter the atomic positions of Yb. This result has implications for the understanding of how the mechanical properties of ceramics are influenced by the presence of the nanoscale intergranular phase, and for associated computational modeling of its precise role and atomic structure.

VO<sub>n</sub> (n≥3) Defects in Irradiated and Heat-Treated Silicon

Local vibrational mode (LVM) spectroscopy has been used to study the evolution of vacancy-oxygen-related defects (VOn) in the temperature range 300-700°C in carbon-lean Cz-Si samples irradiated with MeV electrons or neutrons. New experimental data confirming an attribution of the absorption bands at 910, 976 and 1105 cm-1 to the VO3 complex are obtained. In particular, a correlated generation of VO3 and the oxygen trimer is observed upon irradiation of Cz- Si crystals in the temperature range 300-400°C. Strong evidence for the assignment of the bands at 991 and 1014 cm-1 to a VO4 defect is presented. The lines are found to develop very efficiently in the VO2 containing materials enriched with the oxygen dimer. In such materials the formation of VO4 is enhanced due to occurrence of the reaction O2i+VO2 ⇒ VO4. Annealing of the VO3 and VO4 defects at T ≥ 550C °C is found to result in the appearance of new defects giving rise to a number of O-related LVM bands in the range 990-1110 cm-1. These bands are suggested to arise from VO5 and/or VO6 defects. Similar bands also appear upon the annihilation of oxygen-related thermal double donors at 650°C in Cz-Si crystals pre-annealed at 450°C.

"New Donors" in Czochralski Grown Silicon Annealed at T≥ 600°C under Compressive Stress

Effects of compressive stress on oxygen agglomeration processes in Czochralski grown silicon heat treated at T= 450OC, used as a reference temperature, and T= 600OC to 800OC are investigated in some detail. Compressive stresses of about P= 1 GPa lead to enhanced formation of Thermal Double Donors in materials annealed over a temperature range of T= 450OC – 600OC. It has been shown that the formation of thermal donors at T= 450OC under normal conditions and compressive stress is accompanied with loss of substitutional boron. In contrast, the concentration of the shallow acceptor states of substitutional boron in silicon annealed under stress at T≥ 600OC remains constant. An enhancement effect of thermal donor formation is gradually weakened at T≥ 700OC. The oxygen diffusivity sensitive to mechanical stress is believed to be responsible for the observed effects in heat-treated silicon.

Electron spin resonance study of paramagnetic centers in neutron-irradiated heat-treated silicon

Electron spin resonance (ESR) was used to study neutron-induced defects in silicon as functions of anneal temperature T{sub an}. For T{sub an} below 200 deg. C, the ESR response is dominated by the Si-P3 and Si-P6 spectra, as observed before. At T{sub an}=200 deg. C, a low symmetry center Si-H8, only once reported before, appears. Here, a hyperfine doublet, corresponding to interaction with one {sup 29}Si nucleus, is resolved. In the range T{sub an}{>=}250 deg. C, two other paramagnetic defects dominate. The first is the tetragonal center Si-B3: Mapping of the full angular dependence of known and newly resolved {sup 29}Si hyperfine structure enables conclusive identification as the tetra-interstitial (I{sub 4}) in the positive charged state, based on compliance of the data with former theoretical calculations. Second, we report the observation of an unidentified trigonal center, Si-B5, exhibiting two hyperfine (hf) doublets corresponding with hf interaction with four and six equivalent Si sites. The tri-interstitial I{sub 3} is proposed as a provisional defect model. The annealing behavior and symmetry of these defects provides evidence for linking these paramagnetic B3 and B5 centers to the X and W optical centers, respectively.

Annealing behavior of oxygen in-diffusion from SiO2 film to silicon substrate

Diffusion behavior of oxygen at (near) the Si∕SiO2 interface was investigated. We first oxidized the floating-zone-grown silicon substrates, and then annealed the SiO2-covered substrates in an argon ambient. We examined two different conditions for oxidation: wet and dry oxidation. By the secondary-ion-mass spectrometry, we measured the depth profiles of the oxygen in-diffusion of these heat-treated silicon substrates: We found that the energy of dissolution (in-diffusion) of an oxygen atom that dominates the oxygen concentration at the Si∕SiO2 interface depends on the oxidation condition: 2.0 and 1.7eV for wet and dry oxidation, respectively. We also found that the barrier heights for the oxygen diffusion in argon anneal were significantly different for different ambients adopted for the SiO2 formation: 3.3 and 1.8eV for wet and dry oxidation, respectively. These findings suggest that the microscopic behavior of the oxygen atoms at the Si∕SiO2 interface during the argon anneal depends on the ambient adopted for the SiO2 formation.

Diffuse x-ray scattering study of the formation of microdefects in heat-treated dislocation-free large-diameter silicon wafers

Diffuse x-ray scattering (DXS) is used to study the formation of microdefects (MDs) in heat-treated dislocation-free large-diameter silicon wafers with vacancies. The DXS method is shown to be efficient for investigating MDs in silicon single crystals. Specific defects, such as impurity clouds, are found to form in the silicon wafers during low-temperature annealing at 450°C. These defects are oxygen-rich regions in the solid solution with diffuse coherent interfaces. In the following stages of decomposition of the supersaturated solid solution, oxide precipitates form inside these regions and the impurity clouds disappear. As a result of the decomposition of the supersaturated solid solution of oxygen, interstitial MDs form in the silicon wafers during multistep heat treatment. These MDs lie in the {110} planes and have nonspherical displacement fields. The volume density and size of MDs forming in the silicon wafers at various stages of the decomposition are determined.

Specific features in the generation and motion of dislocations in heat-treated silicon wafers

The specific features in the generation and motion of dislocations in silicon single-crystal wafers after different heat treatments are investigated by the four-point bending technique. It is demonstrated that annealing of silicon single-crystal wafers at a temperature of 450°C leads to their substantial hardening as compared to the postgrowth state. The oxygen-containing precipitates and precipitate dislocation pileups formed in the silicon wafer bulk during multistage heat treatment are efficient heterogeneous nucleation sites of dislocations under the action of thermal or mechanical stresses. It is found that the multistage heat treatment of the silicon wafers under conditions providing the formation of an internal getter within their bulk results in considerable disordering of the wafer structure. The inference is made that the formation of the defect state in the crystal lattice of silicon and the strength characteristics of silicon wafers substantially depend on the temperature-time schedules of the low-temperature stage of multistage heat treatment.

Carbon-Oxygen-Related Complexes in Irradiated and Heat-Treated Silicon: IR Absorption Studies

Carbon-oxygen-related complexes in Si crystals enriched with either oxygen (O-16,O-18) or carbon (C-12, C-13) isotopes were investigated by Fourier Transform infrared absorption spectroscopy. The samples were irradiated with electrons at room temperature as well as at elevated temperatures (400-600 degreesC). The oxygen isotopic shifts of the local vibrational modes related to C3 and C4 centers were determined. Several new lines were found to appear after irradiation at elevated temperatures. Possible assignments of them are suggested.

Impact of Compressive Stress on the Formation of Thermal Donors in Heat-Treated Silicon

Impact of Compressive Stress on the Formation of Thermal Donors in Heat-Treated Silicon

A Study of the Conversion of the VO to the VO<sub>2</sub> Defect in Heat-Treated Silicon under Stress

A Study of the Conversion of the VO to the VO<sub>2</sub> Defect in Heat-Treated Silicon under Stress