Silicon Nitride Crystals Research Articles

Feature Fusion Deep Learning Model for Defects Prediction in Crystal Structures

Detection of defective crystal structures can help in refute such defective structures to decrease industrial defects. In our research, we are concerned with Silicon nitride crystals. There are four types of crystal structure classes, namely no-defect structures, pristine crystal structures, defective random displacement crystal structures, and defective 25% vacancies crystal structures. This paper proposes a deep learning model to detect the four types of crystal structures with high accuracy and precision. The proposed model consists of both classification and regression models with a new loss function definition. After training both models, the features extracted are fused and utilized as an input to a perceptron classifier to identify the four types of crystal structures. A novel dense neural network (DNN) is proposed with a multitasking tactic. The developed multitask tactic is validated using a dataset of 16,000 crystal structures, with 30% highly defective crystals. Crystal structure images are captured under cobalt blue light. The multitask DNN model achieves an accuracy and precision of 97% and 96% respectively. Also, the average area under the curve (AUC) is 0.96 on average, which outperforms existing detection methods for crystal structures. The experiments depict the computational time comparison of a single training epoch of our model versus state-of-the-art models. the training computational time is performed using crystal structures diffraction image database of twelve image batches. It can be realized that the prediction computational time of our multitasking model is the least time of 21 s.

Relation between crystal structure and lattice oxygen content of sintered reaction‐bonded silicon nitride

AbstractWhen reaction‐bonded silicon nitride containing MgO/Y2O3 additives is sintered at three different temperatures to form sintered reaction‐bonded silicon nitride (SRBSN), the thermal conductivity increases with sintering temperature. The β‐Si3N4 (silicon nitride) crystals of SRBSN ceramics were synthesized and characterized to investigate the relation between the crystal structure and the lattice oxygen content. The hot‐gas extraction measurement result and the crystal structure obtained using Rietveld analysis suggested that the unit cell size of the β‐Si3N4 crystal increases with the decrease in the lattice oxygen content. This result is reasonable considering that the lattice oxygen with the smaller covalent radius substitutes nitrogen with the larger one in the β‐Si3N4 crystals. The lattice oxygen content decreased with increasing sintering temperature which also correlated with increase in thermal conductivity. Moreover, it is noteworthy from the viewpoint that it may be possible to apply the lattice constant analysis for the nondestructive and simple measurement of the lattice oxygen content that deteriorates the thermal conductivity of the β‐Si3N4 ceramics.

Synthesis the composites Si3N4-TiN by hot pressing

The Si3N4-TiN composites were obtained by hot pressing at 1600–1800 °C in a nitrogen atmosphere from mixtures of powders of silicon nitride and metallic titanium. The influence of particle morphology, Ti content in the initial charge and synthesis conditions on the microstructure, phase composition, mechanical strength of the samples of ceramic composites Si3N4-TiN was studied. It was established that in the process of sintering, complete nitriding of titanium occurs with the formation of a non-stoichiometric nitride of composition TiN0.9. Samples of composites Si3N4-TiN, obtained from a mixture containing 5-30 % Ti, have a density of 3.02-3.41 g/cm3, water absorption 0.01-0.14 %, open porosity 0.03-0.44 % and flexural strength from 250 to 584 MPa. It is shown that ceramics Si3N4-TiN with a sintering additive of calcium aluminates is characterized by a dense intergrowth of silicon nitride crystals, which provides an increase in the strength of the samples.

Strain-Tunable Quantum Integrated Photonics.

Semiconductor quantum dots are crucial parts of the photonic quantum technology toolbox because they show excellent single-photon emission properties in addition to their potential as solid-state qubits. Recently, there has been an increasing effort to deterministically integrate single semiconductor quantum dots into complex photonic circuits. Despite rapid progress in the field, it remains challenging to manipulate the optical properties of waveguide-integrated quantum emitters in a deterministic, reversible, and nonintrusive manner. Here we demonstrate a new class of hybrid quantum photonic circuits combining III–V semiconductors, silicon nitride, and piezoelectric crystals. Using a combination of bottom-up, top-down, and nanomanipulation techniques, we realize strain tuning of a selected, waveguide-integrated, quantum emitter and a planar integrated optical resonator. Our findings are an important step toward realizing reconfigurable quantum-integrated photonics, with full control over the quantum sources and the photonic circuit.

Preparation of silicon-carbide nanopowder and compositions based on it using SHS azide technology

Combustion of the “silicon-sodium azide-ammonium hexafluorosilicate-carbon-aluminum” powder mixture in the nitrogen medium is investigated. Conditions of the self-propagating high-temperature synthesis (SHS) of the composition of the silicon carbide nanopowder with whisker silicon nitride crystals and flux, which can be used as a modifier of cast aluminum alloys and a reinforcing phase in dispersion-hardened alumomatrix composites, are determined.

Reversible nanovalves in inorganic materials

This article describes recent developments in the design, fabrication and investigation of reversible nanovalves prepared in inorganic nanoporous materials such as glass, silicon nitride, mesoporous silica, anodized alumina and silica colloidal crystals. Their surfaces have been modified with pH-, temperature- and light-responsive molecules, as well as molecules that can undergo redox reactions and bind small molecules. This surface modification allows reversibly opening and closing of the nanovalves to the transport of ions based on electrostatic interactions, and to the transport of molecules based on mechanically gating the nanopores.

Thermal conductivity of high-temperature Si–B–C–N thin films

In this study, thermal transport was investigated for ceramic films with different silicon, boron, carbon, and nitrogen (Si–B–C–N) compositions. In order to investigate the effect of morphology on thermal barrier properties, the microstructure of these materials was varied from amorphous to nanocrystalline. Thermal conductivity trends of several ceramic thin films were characterized with a time-domain thermoreflectance (TDTR) technique. Samples containing two different Si–B–C–N chemical compositions were created by reactive magnetron sputtering and then subjected to annealing at temperatures up to 1400°C. The room temperature thermal conductivity of the samples prepared via a 50% Ar/50% N2 gas mixture remained constant near 1.3Wm−1K−1, while samples prepared via a 75% Ar/25% N2 gas mixture exhibited an increase in the thermal conductivity of 2.2Wm−1K−1 (or higher). X-ray diffraction data demonstrated that the former samples were amorphous, while the latter samples formed silicon nitride (Si3N4) crystals. The experiments reveal which Si–B–C–N film composition remains stable in the amorphous state at high temperatures, thereby retaining lower thermal transport properties. These material aspects are ideal for thermal barrier applications such as non-oxide based ceramic coatings for high-temperature protective systems of aircrafts, as well as surfaces of cutting tools and optical devices.

Effect of thickness and composition on the structure and ordering in La-doped intergranular films between Si 3N 4 crystals

Molecular dynamics simulations were used to determine the effect of the composition and thickness on the atomistic structure of La–Si–O–N intergranular films (IGFs) between prism and misaligned high-index silicon nitride crystals. Results showed that ordered La adsorption onto the prism-terminated surface is not affected by the orientation of the opposing crystal, although the extent of the ordering away from the interface is affected by IGF thickness. La adsorption at ordered sites 1 and 2 on the prism surface occurred for almost all of the compositions in both 1.8 and 0.6 nm thick IGFs and at sites farther from the prism interface in the thicker IGF, similar to adsorption in triple points. La adsorption on the prism surface occurred at sites precisely the same as seen in high-angle annular dark field scanning transmission electron microscopy studies. Saturation of available sites is affected by the thickness of the IGF, which governs the number of La ions (and N ions) in the IGF, with lower site filling in the thinner IGF. There are clear energy differences for La in the interior of the IGF vs. the interface based on composition and IGF thickness, with the thicker IGF showing greater variation in driving forces for segregation or La incorporation into the IGF. Fracture is affected by both composition and thickness and occurs in the glassy IGF and not in the ordered interfacial regions, consistent with experimentally observed intergranular fracture for La-doped silicon nitride. Segregation of La to the interface affects N distribution within the interior of the IGF, which affects strength.

Effect of Compact Density on the Combustion Synthesizing Silicon Nitride Crystals

This paper presents the results of synthesizing β-Si3N4 crystals with Y2O3 as additives by combustion synthesis. The effect of compact density on the final morphology was investigated. The results reveal that with the increasing of the compact density, the amount of rod-like crystals decreased. The growth mechanism of the β-Si3N4 crystals under the high temperature and high pressure is discussed.

Molecular Dynamics Simulations of the Locations of La Ions in La–Si–O–N Intergranular Films in Silicon Nitride

Molecular dynamics computer simulations were used to determine the locations and energies of La ions in silicate intergranular films (IGFs) between basal and prism‐oriented silicon nitride crystals as a function of composition. La segregation to the interfaces occurs at each surface with no nitrogen present in the IGF, but segregates preferentially to the prism surface with nitrogen in the IGF. La adsorption onto the prism surface occurs in the simulations at the two sites observed previously in studies using high‐angle annular dark field scanning transmission electron microscopy. The binding energies of La at the two sites differ with no nitrogen in the IGF, and both are more strongly bonded than for La in the interior of the IGF. However, with nitrogen in the IGF, the binding energies are less different between the two prism surface sites and the interior of the IGF, indicating a decreased driving force for segregation. The simulations provide evidence justifying the preferential segregation of La ions to the prism surface and also indicate that a variation in the local composition would cause some IGFs to show segregation of all La to the interface, leaving little La within the glassy IGF, while other IGFs may show more La remaining in the glassy IGF.

Anisotropic Ostwald Ripening in Silicon Nitride: On the Reaction-Controlled Kinetics

A model for anisotropic Ostwald ripening was developed using a chemical potential (weighted mean curvature) difference as a driving force for mass-transport. Based on this model, grain growth simulations of silicon nitride during the phase transformation and Ostwald ripening were performed. Comparison with experimental results during the phase transformation suggests that grain growth be controlled by interfacial reaction. Simulations of Ostwald ripening predict that the growth exponent be 3 for the reaction-controlled case, and increases up to 5 as the growth kinetics shifts from reaction-controlled to diffusion-controlled. It was reported that the mean aspect ratio of silicon nitride crystals increased during the phase transformation, and decreased during Ostwald ripening. These behaviors were successfully simulated by this model. The concave depression at the tip of silicon nitride crystal that was experimentally observed. Simulations by the Ostwald ripening model demonstrated that it could be developed when the liquid phase was super-saturated, and further that the tip shape was a function of the liquid concentration.

Molecular dynamics simulations of La2O3-doped silicate intergranular films in Si3N4

Molecular dynamics (MD) computer simulations are used to evaluate the effect of composition of the IGF on the location and energetics of La ions in silicon oxy-nitride intergranular films (IGFs) between basal and prism oriented silicon nitride crystals. Results of the simulations show La adsorption at the four sites on the prism oriented nitride surface that are the same as those observed with HAADF-STEM. In addition, the simulations also show the effect of composition on this behavior, in which La segregation to at least the two closest surface sites on the prism surface is observed at almost all compositions, whereas La segregation to the basal interface is significantly affected by composition. With increasing La content, La site-filling increases on both prism and basal interfaces. Because of Lanthanum's role as a network modifier in a pure silica glass, IGFs with no N and low La content show complete segregation of La to the crystal surfaces. Increasing N content in the IGF reduces this La segregation to the interfaces, allowing for more La in the interior IGF. This is consistent with the change in binding energy of the La ions in the interior IGF in comparison to that at the interfaces, reducing the driving force for segregation. Because the additive rare earth ‘poisons’ the surface to which it adsorbs from further growth, the change in segregation is important in the development of microstructure in the ceramic. Importantly, increasing N content in the IGF causes preferential La depletion from the basal surface, with no such significant depletion of La on the prism surface, providing a mechanism for the anisotropic grain growth observed in this system.

Molecular Dynamics Simulations of the Effect of the Composition of the Intergranular Film on Fracture in Si3N4

Molecular dynamics computer simulations were used to study the fracture behavior of silica, multicomponent silicate, and oxynitride intergranular films (IGFs) between silicon nitride crystals as a function of composition, film thickness, and crystallographic orientation. The maximum fracture strength is higher in the IGF between prism surfaces than between basal surfaces. This is caused by the preferential segregation of specific species to the basal surfaces in contrast to the prism surfaces, effectively modifying the composition within the glassy portion of the IGF, with a subsequent effect on strength. The ordering observed in the thinner IGFs causes an increase in strength in the linear portions of the stress/strain curves, effectively increasing fracture stress. The simulations show that the force/atom in the 1 nm SiO2 IGF in the direction of tensile strain is more similar to that in β‐cristobalite than to v‐SiO2, whereas such data in the 2 nm SiO2 IGF is more similar to v‐SiO2. Simulations of the multicomponent silicate IGFs show the expected effect of lowering fracture strength with increasing modifier content in the silicate IGF, similar to that of bulk glasses. Similar to experimental studies, a decrease in strength is observed in silicon oxynitride IGFs with increasing oxygen concentration.

Effect of Thickness of the Intergranular Film on Fracture in Si3N4

Molecular dynamics computer simulations were used to study the fracture behavior of silica intergranular films (IGFs) between silicon nitride crystals as a function of film thickness. Results showed a significant increase in fracture stress with decreasing IGF thickness. IGFs that are 2 nm thick fracture similarly to bulk silica glass, while the 1 nm IGF fractured at a much higher value. The simulations show bond rupture and rearrangement of siloxane rings that coalescence to form larger rings, or “voids.” The delineating difference in the systems is the significantly larger concentration of six‐membered rings in the 1 nm IGF in comparison to the 2 nm IGF or bulk silica glass. The Si–O bond is more stable in six‐membered rings than other ring sizes. Rupture is more catastrophic in the 1 nm IGF than the other systems where stress decays more slowly with strain.

Mechanism of growth of silicon nitride crystals in combustion of ferrosilicon in nitrogen

The process of nitride formation in burning of iron-silicon melt in gaseous nitrogen was investigated. It was found that silicon nitride is synthesized at temperatures (2100°C) which are much higher than the temperature of appearance of the liquid phase (1206°C). Silicon is in the liquid state during synthesis in the form of an iron-silicon melt and a gaseous melt. The electron-microscopic studies showed that silicon nitride crystals grow according to two mechanisms: vapor-liquid-crystal and crystallization from iron-silicon melt. The ratio of the contributions of these mechanisms to structural formation of silicon nitride is determined by the conditions of synthesis.

Morphology of Silicon Nitride Grown from a Liquid Phase

To explain the recent experimental observation of liquid-grown silicon nitride (Si{sub 3}N{sub 4}) crystals with a concave depression in the center of the (0001) end face, the authors propose a new growth mechanism and develop an analytical solution for the steady state. The model allows for atoms that diffuse via the liquid to the side surface but demands that the majority of these atoms be transported to the end caps to feed axial growth. The analysis shows that, for a large radius crystal, the redistribution of atoms by surface diffusion on the end caps requires a long relaxation time; hence, a nonequilibrium shape results. For an isolated Si{sub 3}N{sub 4} crystal growing in a liquid environment, the shape of the end cap is largely determined by the ratio of the supersaturation to the equilibrium surface potential, which is inversely proportional to the crystal radius. A large shape distortion is predicted to occur during the growth stage for large-radiation crystals and during the coarsening stage for a population of crystals with a large size distribution. This mechanism ceases to operate when the liquid flux to the side surface is blocked, as in silicon nitride ceramics, but is otherwise insensitive to factorsmore » such as radial growth kinetics and liquid diffusivity.« less

Molecular Dynamics Simulations of Calcium Silicate Intergranular Films between Silicon Nitride Crystals

Molecular dynamics simulations were used to study the structure of calcium silicate intergranular films (IGFs) formed between the basal planes of silicon nitride crystals. A multibody potential was used to describe the interactions between ions. Samples with different film thickness and CaO contents were studied. Epitaxial adsorption of Si and O atoms from the intergranular films onto N and Si, respectively, in the crystal surface was observed. This epitaxial order induced a structural order into the nominally amorphous IGF that decreased as a function of distance from the IGF/crystal interface. A higher concentration of strained siloxane bonds was observed at the IGF/crystal interface in comparison to the amorphous interior of the IGF. While Ca ions were observed to segregate to the IGF/crystal interface in simulations of calcium silicate glass IGFs between alumina crystals, no segregation of calcium to the first adsorbed layer on the nitride was found in these simulations using silicon nitride crystals. Planar alignment of Ca ions parallel to the IGF/crystal interface occurred with either the largest concentrations of CaO or with the thinnest IGFs studied here. This alignment creates localized nonbridging oxygen that would affect the stability of the IGF/crystal system.

522 プリズマティック転位モデルによるセラミックス微小押込試験結果の逆問題的解釈

Nano-indentation test on polycrystalline silicon nitride and single crystals of silicon carbide is done to examine the indentation size effect (ISE). The hardness is evaluated by using the Oliver-Pharr scheme. The experimental results are analyzed on a dislocation mechanism model based on the punching of prismatic dislocation loops to accommodate the volume of plastic penetration at the indentation. The parameters of the model are determined numerically by solving the inverse problem, using the parameters obtained from loading-unloading curve. The theoretical results show that the profile of plastic core zone do not evolve in a self-similar manner with decreasing load. The ratio of plastic work for punching dislocation with respect to total work decrease with decreasing load.

Growth competition between crystalline silicon carbon nitrides and silicon nitrides deposited on Si wafer by MPCVD

The Si–C–N films were synthesized on Si wafer by microwave plasma chemical vapor deposition with CH 4, N 2, 0.0–8.3 vol.% H 2 and the additional Si chips, as the sources. The growth competition on Si wafer between crystalline ternary Si–C–N and binary silicon nitrides was examined. Based merely on the results of ESCA, XRD and SEM analyses on the film surface, it might often give false impression of forming ternary silicon carbon nitride crystalline films, as reported in the literature, though their volume fractions of H 2 were from 35 to 77%. One of the possible reasons for a false impression is due to the fact that carbon often settles on the deposited films during cooling period. The further examinations on the cross-section of the films by TEM+EDS+ED, and on the film surface by FTIR and Raman spectroscopy clarify that the films essentially consist of ∼2 μm binary silicon nitride crystals on top of ∼100 nm ternary Si–C–N crystallites. This is in agreement with the ESCA depth profile examinations and the substrate scratching experiment by Si 3N 4 powders, which greatly enhance nucleation rate of binary silicon nitride crystals. Under a higher temperature and a longer deposition time, growth competition between crystalline Si–C–N and silicon nitrides will generally result in forming a film covered with silicon nitrides. The crystal structure of the silicon nitrides on the films is much close to α-Si 3N 4 than β-Si 3N 4 and tetragonal Si 3N 4 type structures, but silicon content is higher.

The control of morphology in silicon nitride powder prepared from rice husk

Abstract α-Silicon nitride powder of high purity has been prepared by nitriding pyrolysed rice husk at temperatures between 1260 and 1450°C under 95% nitrogen-5% hydrogen. Hydrogen addition is beneficial in accelerating the rate of nitride formation. The addition of iron (III) oxide and nickel (II) oxide to the rice husk promotes the competitive formation of silicon carbide at temperature as low as 1300°C. Other transition metal oxides are without catalytic effect on the nitridation reaction, though vanadium (V) oxide favours formation of β-phase silicon nitride. The silicon nitride particle morphology is determined in part by the particle dimension of the milled rice husk. Silicon nitride crystals of hexagonal symmetry are obtained from starting powder of dimension ≤ 53 μm, whereas greater particle dimensions, and lower packing densities, yield silicon nitride of a whiskery morphology. Addition of pre-formed silicon nitride powder results in the formation of fine, equiaxed, silicon nitride particles.