Nitridation Of Si Research Articles

Si3N4 preparation from photovoltaic kerf loss silicon waste by copper collaborative nitriding method

In this work, Si3N4 powders were prepared by collaborative direct nitriding method from photovoltaic kerf loss silicon waste. The catalytic effect of copper (Cu) on the direct nitriding reaction of photovoltaic Si waste and the morphologies of the nitriding products were investigated. The quantitative analysis of XRD results and thermogravimetric results demonstrate that Cu significantly reduces the initial nitriding temperature, and Cu has a positive effect on the nitriding of silicon waste. At 1300 °C, the sample without Cu had almost no nitriding reaction, while the total conversion rate of kerf loss waste Si was 100 %, and the yield of (α+β) Si3N4 was up to 79.2 % with 8 wt% Cu additive. The thermodynamic analysis of the Si-O-N-Cu and nitriding process was carried out by FactSage software. Moreover, the morphologies of the nitride products were observed by SEM. The addition of copper promoted the generation of Si3N4 nanorods, and the number and diameter of α-Si3N4 nanorods increased with the increase in copper content. Three reaction mechanisms of Si nitridation were discussed. This work provides a feasible method to reuse and recycle the kerf lost silicon waste.

Effect of Ti-Si-Fe alloy on the nitriding behavior of Si powder

Adding Ti-Si-Fe alloy to Si powder reduced the complete nitriding temperature of Si from 1450 °C to 1300 °C, greatly reducing the nitriding temperature of Si powder and the formation temperature of Si3N4 whiskers. At low temperature, Fe in Ti-Si-Fe alloy damaged the SiO2 film on the surface of Si and produced SiO (g), which was conducive for the indirect and direct nitridation of Si. The density functional theory (DFT) calculation results showed that the energy levels of SiO (g) molecules adsorbed by Fe broadened and moved towards lower energy levels, resulting in a decrease in the bonding strength and an increase in reaction activity of SiO (g) molecules. It was beneficial for the indirect nitridation reaction of 3SiO (g)+2N2 (g)=Si3N4 (s)+3/2O2 (g), and promoted the formation of α-Si3N4 whisker. The liquid phase formed by increasing temperature and Ti-Si-Fe alloy addition promoted the direct nitridation of Si. The activation energy of TiSi2 and Ti-Si-Fe alloy nitridation was 78.42 (KJ/mol) and 14.97 (KJ/mol), respectively. The nitridation of Ti-Si-Fe alloy was easier, and the pores and cracks generated by Ti5Si3 and TiSi2 step-by-step nitridation at low temperature in Ti-Si-Fe alloy provided pore channels for N2 transport and sufficient nitrogen for Si nitridation.

Influence of ZrB2 on Si3N4 ceramics prepared by Si nitridation and hot‐pressing process

AbstractThis work investigated the effect of ZrB2 content on phase composition, relative density, microstructure, and mechanical performance of Si3N4 ceramics prepared by Si nitridation and hot‐pressing method. Si3N4 ceramics were fabricated using Si powder by nitridation and hot‐pressing process. Results showed that the addition of ZrB2 enhanced the transformation of α‐Si3N4 into β‐Si3N4 phase during nitridation, resulting in a greater fraction of β‐Si3N4 (above 90 wt.%) phase in Si3N4 ceramics with ZrB2 after hot‐pressing. In contrast, ceramics without ZrB2 had a lower ratio of β‐Si3N4 (40.4 wt.%). The use of 2.5 vol.% ZrB2 yielded a significant bimodal microstructure and increased fracture toughness to 5.0 ± 0.2 MPa·m1/2, but decreased Vickers hardness to 16.4 ± 0.5 GPa. However, increasing the ZrB2 content to 5 vol.% and 10 vol.% led to a massive formation of equiaxed coarse β‐Si3N4 grains and a significant decrease in Vickers hardness and fracture toughness.

Effects of thermal vacuum nitridation of Si(100) surface via NH3 exposure

• Si(100) is nitrided with NH 3 at 400 °C without plasma to form SiN x . • The nitridation method decreases defect densities at HfO 2 /Si(100) interface. • The nitridation method decreases leakage current through HfO 2 /SiO 2 /Si. Low temperature treatments to control the Si-interface properties become more and more relevant to the broad Si-based electronics and photonics technology when the back-end-of-line processing is developed and the integration of hybrid materials on the Si platform increases. In this work we have investigated effects of NH 3 nitridation of three different Si surfaces in ultrahigh-vacuum (UHV) chamber at 400 °C : (i) nitridation of well-defined Si(100) (2 × 1)+(1 × 2) cleaned by the high-temperature flash heating, (ii) nitridation of the Radio Corporation of America (RCA)-cleaned H-terminated Si(100) with the final HF dip, and (iii) nitridation of the RCA-treated (without the final HF dip) Si(100) which includes so-called wet-chemical oxide of SiO 2 . X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy/spectroscopy measurements show that nitrogen incorporates into subsurface layers of clean Si and into the SiO 2 chemical-oxide layer, when the materials are exposed to NH 3 background in UHV chamber without a plasma source at 400 °C or even at room temperature. XPS results indicate that the nitridation does not remove oxygen from the SiO 2 chemical oxide. The nitridation of SiO 2 is also found to increase the density of electron levels at 3 to 4 eV above the Fermi level. Electrical measurements of atomic-layer deposited HfO 2 /Si(100) capacitors with and without the nitridation support that the method has potential to decrease amount of interface defects and to control interface properties.

Formation of Aligned α-Si3N4 Microfibers by Plasma Nitridation of Si (110) Substrate Coated with SiO2

Plasma nitridation of an amorphous SiO2 layer on Si (110) substrate can form well-aligned α-Si3N4 crystallites in fibrous morphology. Nitriding is performed at a temperature in the range of 800–1000 °C by using microwave plasma with a gas mixture of N2 and H2. Raman spectroscopy shows the characteristics of an α-Si3N4 phase without other crystalline nitrides. As shown by scanning electron microscopy, the formed α-Si3N4 microfibers on the Si substrate can be in a dense and straight array nearly along with Si <11¯0>, and can have a length over 2 mm with a diameter in the range of 5–10 μm. Structural characterization of scanning transmission electron microscopy in cross section view reveals that the elongated α-Si3N4 crystallites are formed on the surface of the nitrided SiO2/Si (110) substrate without any interlayers between Si3N4 and Si, and the longitudinal direction of α-Si3N4 appears mainly along <112¯0>, which is approximately parallel to Si <11¯0>.

Electromagnetic wave-transparent porous silicon nitride ceramic prepared by gel-casting combined with in-situ nitridation reaction

To achieve the balance between mechanical properties and electromagnetic wave-transparent properties of porous silicon nitride (Si3N4), the key is to form an interlocking microstructure constituted by columnar β-Si3N4 crystals. This structure can be realized by liquid-phase sintering. However, grain boundaries which affect high temperature properties and volume shrinkage during sintering are inevitable. We proposed a strategy to realize this structure by gel-casting of β-Si3N4 whisker (Si3N4w) and Si powder followed by in-situ nitridation of Si. To achieve chemically-stable slurry containing micro-sized Si with low viscosity, a novel formulation was developed. Two key structural parameters of the interlocking Si3N4w network, i.e., density of the Si3N4w skeleton and inter-whisker bonding mode, were adjusted by composition of raw materials and nitridation temperature. The flexural strength, dielectric constant and loss of the porous ceramics are 44.9 MPa, 2.7 and 2 × 10−3, when the volume fraction of Si3N4w/Si is 5 and the nitriding temperature is 1400 °C.

Synthesis of monophase two‐dimensional α‐Si3N4 nanoplatelets via an ionothermal route

AbstractMonophase α‐Si3N4 was prepared by a salt melt strategy using Si as a starting material. The results showed that molten salt enhanced the conversion of Si to monophase α‐Si3N4, and some as‐synthesized α‐Si3N4 nanoparticles had a hexagonal platelet morphology. The α‐Si3N4 hexagonal nanoplatelets had an average lateral dimension of about 170 nm and a thickness of about 5.2 nm. The nitridation of Si in molten salt was investigated by a thermal quenching method, and the silicon halide intermediate products were detected by X‐ray photoelectron spectroscopy. Silicon halides possessing higher reactive activity facilitated the nitridation of Si and nucleation of α‐Si3N4. Furthermore, the lattice mismatch between α‐Si3N4 and the salts was calculated, suggesting that the lateral growth of α‐Si3N4 nanoplatelets had been guided by the salt crystal structure. Based on the results, the relevant formation mechanism of α‐Si3N4 nanoplatelets was proposed.

Post deposition nitridation of Si in W/Si soft X-ray multilayer systems

Partial nitridation of W/Si multilayer systems with a nm period was investigated in an attempt to reduce optically unfavorable tungsten silicide formation in the systems. Nitridation was applied directly after the deposition of every Si layer by exposing the Si surfaces to reactive nitrogen species from an ion source. As a result the formation of substantially sharper interfaces and a reduction in the silicide formation were observed in the systems. However, the passivation treatment caused a pronounced reduction in the X-ray reflectivity at 0.84 nm wavelength because of deep nitrogen penetration in the Si layers. This reduced the optical contrast between the reflector and spacer layer, which compensated the effect of the improved interface profile.

The high temperature reaction of ammonia with carbon and SiC–C ceramics

This contribution aimed at developing a treatment under ammonia in order to eliminate free carbon from the surface of SiC-based fine ceramics like fibers or coatings. The reaction of NH3 with graphitic and non-graphitic carbon was first investigated through kinetic measurements, in situ gas phase analysis and physicochemical investigations of the solid. The carbon etching rate is controlled by heterogeneous reactions involving active sites arising from bulk structural defects and the formation of HCN. A selection of SiC-based fibers and coatings with various carbon contents and (micro)structures was treated in ammonia in favorable conditions. The analyses of the tested SiC–C specimens revealed a reduction of the free carbon content and, simultaneously, a nitridation of the initial Si–C–(O) continuum over a reaction layer. The growth rate, composition and the volume change of this layer vary with the initial microstructure. The ammonia treatment is able to restore the adhesion of carbon-contaminated surfaces.

A comparative study on nitridation mechanism and microstructural development of porous reaction bonded silicon nitride in the presence of CaO, MgO and Al2O3

ABSTRACT During the in-situ nitridation of Si in the presence of CaO, MgO and Al2O3 formation of reaction bonded silicon nitride ceramics (RBSN) having various microstructures indicated the possibility of different nitridation mechanisms operating. Experimental evidence suggested that, whereas the morphology of pores was controlled by nitridation of Si(g) in CaO-RBSN and SiO(g) in Al2O3-RBSN, a combination of these two reactions occurred during the nitridation of the MgO-RBSN. By inhibiting the growth of whiskers and maximizing the α/β ratio, the CaO addition led to the formation of matte grains creating clean spherical cavities with d < 40 µm and flexural strength of 0.8 MPa. In contrast, when using Al2O3 additions, a microstructure with a very low α/β ratio, fine inter-particle pores and 2.4 MPa flexural strength, reinforced with interlocking whiskers, was produced. The highest porosity (85%) and the lowest strength (0.3 MPa) occurred in the MgO-RBSN, which was composed of both matte grains and fine whiskers. Local supersaturation and low content of β-nuclei led to the formation of anisotropic β-grains with a bimodal microstructure in heat-treated CaO-RBSN while a unimodal microstructure was observed in heat-treated MgO-RBSN. No porosity loss or β-grain growth occurred in the heat-treated Al2O3-RBSN.

Preparation, structure and mechanical properties of Sialon ceramics by transition metal-catalyzed nitriding reaction

Sialon ceramics were prepared by the nitridation of Si, Al and Al2O3 powders with the transition metals (Fe, Co, Ni) catalysts. The phase composition, microstructure and mechanical properties of specimens were studied. Compared with the catalyst-free specimen, the addition of Fe, Co and Ni greatly promoted the nitridation process of Sialon ceramics and improved the weight gain rate and mechanical properties of specimens. With the increased content of catalysts, the apparent porosity of the products decreased first and then increased, contrary to flexural strength and compressive strength. The specimen with 2.5 wt% Fe had the highest flexural strength 145.8 MPa, and it exhibited the highest compressive strength of 594.6 MPa when Co content was 2.5 wt%, whereas they were 71.9 and 78.7 MPa, respectively, when without catalyst.

In Situ Catalytic Synthesis of Si3N4 Nanowhiskers Reinforced SiC Refractories and Their High-Temperature Properties

Silicon nitride (Si3N4)–bonded silicon carbide (SiC) refractory (Si3N4-SiC) is one of the most important nonoxide refractories, but its mechanical properties still suffer from the residual Si. Herein, we report that the nitridation of Si and properties of Si3N4-SiC refractories can be improved by in-situ formed CoOx catalysts. The room-temperature modulus of rupture (MOR), high-temperature MOR, thermal shock resistance, and oxidation resistance of as-prepared Si3N4(w)-SiC refractories with catalysts were investigated. The results showed that CoOx catalysts enhanced the nitridation of Si powders and promoted the formation of Si3N4 whiskers. The high-temperature MOR at 1573 K of as-prepared refractories was improved by 30%, compared with samples without catalysts. Moreover, the thermal shock resistance and oxidation resistance of the former was remarkably higher than that of the latter. The improvement was attributed to in-situ formation of Si3N4 whiskers network structure in the samples due to the catalytic effects of CoOx catalysts.

Combustion synthesis of well‐dispersed rod‐like β‐Si3N4 crystals by the addition of carbon

AbstractThe well‐dispersed rod‐like β‐Si3N4 crystals have been prepared by combustion synthesis with the addition of carbon. The added carbon helps to separate Si particles and remove the SiO2 oxide layer, and thus reduces the agglomeration of β‐Si3N4 crystals. By adding carbon, the reaction temperature and the width of β‐Si3N4 crystals are decreased, but the aspect ratio of β‐Si3N4 crystals is increased. The well‐dispersed β‐Si3N4 crystals with an average width of 0.84 μm and aspect ratio of 2.3 are produced by adding 2 wt% carbon. When 5 wt% carbon is added, the reaction temperature is too low and the nitridation of Si becomes incomplete, and at the same time much SiC occurs in the product.

In situ nitriding reaction formation of β-Sialon with fibers using transition metal catalysts

β-Sialon powder containing nanofibers was synthesized at 1300–1450 °C for 5 h in nitrogen by using transition metals (Fe, Co and Ni) as catalysts. Such synthesis conditions obviously reduced the nitriding temperature (~100 °C) of β-Sialon and increased the degree of nitridation. Observations from the weight gain rates of specimens relative to the content of catalysts suggest that the nitridation process was accelerated sharply via the addition of 0–2.5 wt% metallic catalysts. In addition, the amount of nanofibers of β-Sialon found in the specimens increased with the amount of transition metals, which was governed by the VLS formation mechanism with the help of transition metals. It could be concluded that transition metals not only greatly accelerated the nitridation of Si but also facilitated the formation of β-Sialon nanofibers in the specimens, as the formed metal-containing liquid greatly enhanced the amount of vapor generation.

Growth of Catalyst-Free Hexagonal Pyramid-Like InN Nanocolumns on Nitrided Si(111) Substrates via Radio-Frequency Metal–Organic Molecular Beam Epitaxy

Hexagonal pyramid-like InN nanocolumns were grown on Si(111) substrates via radio-frequency (RF) metal–organic molecular beam epitaxy (MOMBE) together with a substrate nitridation process. The metal–organic precursor served as a group-III source for the growth of InN nanocolumns. The nitridation of Si(111) under flowing N2 RF plasma and the MOMBE growth of InN nanocolumns on the nitrided Si(111) substrates were investigated along with the effects of growth temperature on the structural, optical, and chemical properties of the InN nanocolumns. Based on X-ray diffraction analysis, highly &lt;0001&gt;-oriented, hexagonal InN nanocolumns were grown on the nitride Si(111) substrates. To evaluate the alignment of arrays, the deviation angles of the InN nanocolumns were measured using scanning electron microscopy. Transmission electron microscopy analysis indicated that the InN nanocolumns were single-phase wurtzite crystals having preferred orientations along the c-axis. Raman spectroscopy confirmed the hexagonal structures of the deposited InN nanocolumns.

(SiC-Si3N4)w/SiBCN composite ceramics with tunable electromagnetic properties

In this study, composite ceramics with tunable electromagnetic properties were developed based on SiC-Si3N4 hybrids. First, SiC-Si3N4 whisker preforms with various SiC whisker (SiCw) concentrations were prepared by the nitridation of Si in SiCw-Si powder compacts. The in-situ-grown Si3N4 whiskers (Si3N4w) were dispersed uniformly in the voids inside the interconnected network formed by SiCw. The whisker reinforcements effectively toughened the SiBCN matrix through interface debonding, crack deflection and whisker pullout mechanisms. The electromagnetic properties of the composite ceramics can be tuned by adjusting the composition of (SiC-Si3N4)w preforms. The composite ceramic with 31.9 vol% SiCw exhibited the broadest effective absorption bandwidth (EAB) of 2.9 GHz in X band. Furthermore, a multilayer radar absorbing structure (RAS) composed of ceramic composites with gradient electromagnetic parameters was constructed to further improve the absorption properties. By adjusting the structure of the RAS, the resulting EAB of the RAS covered the entire X band.

Effects of ultrathin AlN prelayers on the spontaneous growth of GaN nanowires by plasma assisted molecular beam epitaxy

The effects of ultrathin AlN prelayers, with nominal thicknesses between 0 and 1.5 nm, on the spontaneous growth of GaN nanowires (NWs) on Si (1 1 1) substrates were investigated. The morphological and structural characteristics of GaN NWs were analyzed by electron microscopy and X-ray diffraction techniques. The results quantify how the AlN prelayer thickness affects GaN NWs. The increase of AlN thickness gradually limits nitridation of the substrate surface and accelerates 3D GaN nucleation. The formation of amorphous SixNy by Si nitridation is completely avoided for 1.5 nm of AlN that fully covers the Si surface. The dependence of the height, diameter and density of GaN NWs on the AlN thickness was also determined. The 1.5 nm AlN provided the optimum condition for GaN NW nucleation and growth; the NWs exhibited a large homogeneous height with almost no parasitic GaN formation between them. High resolution transmission electron microscopy showed the full relaxation of misfit strain of AlN on Si (1 1 1) and of GaN NWs on AlN. In-situ reflection high energy electron diffraction during AlN nucleation revealed the immediate relaxation of the AlN prelayer before GaN NW nucleation. Formation of β-Si3N4 before AlN nucleation was also observed.

Effect of Cr2O3 additive on the nitridation of Si powder

The effect of Cr2O3 additive on nitridation of Si powder was studied at 1200 °C, 1300 °C and 1350 °C. At 1200 °C for 2 h, only Cr2N and CrSi2 peaks were found except Si in sample with 8 wt% Cr2O3. At 1300 °C, no visible Si3N4 peak was detected by XRD in pure Si sample, but in Cr2O3 added samples and with increasing of Cr2O3 additive the intensity of Si was reduced. At 1350 °C, Si peaks weakened in pure Si sample and Si powder was completely nitrided with Cr2O3 additive. The results showed that Cr2O3 additive improved the nitridation degree by the transformation between Cr2O3 and Cr2N and increasing the nitridation temperature promoted the nitridation of Si.

Catalytic Preparation of Si3N4-Bonded SiC Refractories and Their High-Temperature Properties

Effects of Cr2O3 nanoparticles (NPs) on the catalytic nitridation of Si powders were investigated, and the results showed that the Cr2O3 NP catalysts enhanced the nitridation of Si powders and promoted the formation of Si3N4 whiskers. The complete conversion of Si was achieved at [1473 K (1200 °C)] for 3 hours with the addition of 3 wt pct Cr2O3 NPs. First-principle calculations suggested that the electron transfer from Cr2O3 to N2 molecules facilitates the Si nitridation. Moreover, Si3N4-bonded SiC refractories were also prepared using in-situ formed Cr2O3 NPs as catalysts, and the hot modulus of rupture at [1673 K (1400 °C)] of as-prepared refractories was about three times higher than that of samples without catalysts; the corrosion resistance against molten cryolite of the former was remarkably lower than that of the latter. The improvement was attributed to the catalytic effects of Cr2O3 NPs for in-situ formation of a fund of Si3N4 whiskers, which formed a network structure in the samples.

Combustion synthesis of α-Si3N4 with the addition of NH4Cl

This paper reports combustion synthesis of α-Si3N4 with the addition of NH4Cl. The effect of NH4Cl on the phase composition of the products is investigated, and the reaction mechanism in the nitridation of Si with the participation of NH4Cl is discussed. The content of α-Si3N4 in the products increases with increasing content of NH4Cl in the starting compositions, and reaches 93% when 10 wt% NH4Cl is added. It is proposed that the addition of NH4Cl promotes the nitridation of Si by gaseous reaction and improves the formation of α-Si3N4. In the reaction, NH4Cl decomposes into HCl and NH3, and HCl reacts with Si to form SiCl4, which is later nitridized into Si3N4. In the nitridation of Si, HCl acts as a catalyst and a carrier to transfer Si atoms from solid and liquid Si particles into gas phase. The contribution of NH3 to the nitridation of Si is limited, and most N atoms required for the synthesis of Si3N4 are provided by N2.