Amorphous Si3N4 Research Articles

Atomistic Simulation of HF Etching Process of Amorphous Si3N4 Using Machine Learning Potential.

An atomistic understanding of dry-etching processes with reactive molecules is crucial for achieving geometric integrity in highly scaled semiconductor devices. Molecular dynamics (MD) simulations are instrumental, but the lack of reliable force fields hinders the widespread use of MD in etching simulations. In this work, we develop an accurate neural network potential (NNP) for simulating the etching process of amorphous Si3N4 with HF molecules. The surface reactions in diverse local environments are considered by incorporating several types of training sets: baseline structures, reaction-specific data, and general-purpose training sets. Furthermore, the NNP is refined through iterative comparisons with the density functional theory results. Using the trained NNP, we carry out etching simulations, which allow for detailed observation and analysis of key processes such as preferential sputtering, surface modification, etching yield, threshold energy, and the distribution of etching products. Additionally, we develop a simple continuum model, built from the MD simulation results, which effectively reproduces the surface composition obtained with MD simulations. By establishing a computational framework for atomistic etching simulation and scale bridging, this work will pave the way for more accurate and efficient design of etching processes in the semiconductor industry, enhancing device performance and manufacturing precision.

Application of neutron transmutation technology to control the physical properties of nanoparticles at the atomic scale

Purposeful control of the physical properties of materials at the nanoscale is significant throughout the application. The most effective way for this is to change or replace the lattice atoms that make up the nanomaterial. In nanomaterials, the efficiency of the doping process will be high if individual lattice atoms are replaced at the atomic level without affecting neighbouring atoms. Here we show that, with the application of neutron transmutation technology (NTT), it is possible to perform targeted changes in nanoparticles (NPs) at the atomic scale. Similar experiments were carried out on different classes of NPs to explore the possible manipulation of the properties of nanomaterials using neutrons. During the experiments, nanocrystalline 3C–SiC, BN, B4C, Si and amorphous Si3N4 and SiO2 particles were modified by NTT. The possibility of nuclear reactions and neutron transmutation (NT) were investigated on the individual atoms, which are formed nanoparticles. As a result of NT, the changes in the physical properties of the listed NPs were explained by various spectroscopic approaches. Simultaneously, additional neutron effects, defects and structural changes on the surface of NPs were studied with microscopic imaging.

Mechanical properties and biocompatibility of multilayer systems based on amorphous SiN:H/SiCN:H layers on Ti6Al7Nb titanium alloy

Surfaces of metallic implants that replace diseased joints are bound to degrade over time under constant mechanical wear and corrosion, caused by the presence of biological fluids. Production of wear particles and toxic metal ions that follows can undermine both implant stability and patient’s health. To counteract this process multiple surface modifications have been proposed in scientific literature, ranging from simple nitriding to protective layers (e.g.: DLC, CN:H) and multilayer systems. This work presents a combined approach to outlined issue, using multi-staged plasma deposition with SiCN:H layer as a key component, realized using the MW CVD (Microwave Chemical Vapour Deposition) system. The study covers chemical characterization by EDS and FTIR analysis and measurements of relevant functional parameters, such as hardness, Young’s modulus, coefficient of friction, specific wear rate and wettability. Additionally, biocompatibility of modified surfaces are tested on MG-63 cells using Alamar Blue assay, flow cytometry and alkaline phosphatase (ALP) assay. Chemical and microscopic studies revealed amorphous cauliflower-like microstructures that have proven to be hydrogenated SiCN/SiN structures. The obtained layers are turned out to be biocompatible (>70 % of cell survival rate), additionally layers based on amorphous SiCN:H boost ALP activity due to combination of their chemistry and mechanical properties.

Effect of arc deposition process on mechanical properties and microstructure of TiAlSiN gradient coatings

In order to successfully prepare a new advanced TiAlSiN gradient coating with Ti content gradually decreased but Al content gradually increased from the cemented carbide substrate to the outermost coating surface by arc ion plating, we deeply investigated the influence mechanisms of two important process parameters. These parameters include substrate bias voltage and arc current, which affect the mechanical properties and microstructure of the gradient coating. The results show that bias voltage and arc current directly affect the particle accumulation effect on the coating surface and the re-sputtering effect caused by high-energy ion bombardment, thus affecting the deposition efficiency of the coating and the formation of defects such as macro-particles and pits on the coating surface. The increase of bias voltage is conducive to the increase of the density of columnar crystals and nanocrystals. While the increase of arc current makes the coating with high Al content transform from columnar crystals to nanocrystals. The hardness and interfacial adhesion of the gradient coatings showed a tendency of firstly increasing and then decreasing with the increase of both bias voltage and arc current. When the bias voltage and arc current are -80 V and 160 A respectively, the coating has the best mechanical properties, its surface hardness reaches 36.94 GPa, and the interfacial adhesion exceeds 120 N. In addition, with the increase of bias voltage and arc current, particles are deposited on the surface of the coating with higher energy, which leads to the preferential orientation transition from (111) to (200) plane. The high hardness of TiAlSiN coating is mainly due to the formation of high Al content of fcc-TiAlN crystals and amorphous Si3N4 in the gradient-coated surface layer. The results have important theoretical and practical significance for developing new high-performance gradient coating tools.

Tackling residual tensile stress in AlN-on-Si nucleation layers via the controlled Si(111) surface nitridation

This work is devoted to the study of the influence of controlled Si(111) surface nitridation on the epitaxial growth of AlN-on-Si nucleation layers with reduced tensile stress on ordered crystalline silicon nitride phase. The Si(111) surface nitridation process was performed at low ammonia flux and substrate temperatures in the range of 700–900 °C and was studied using RHEED and STM techniques. A universal criterion, namely the stage of the nitridation process completion is introduced, taking into account the influence of substrate temperature, ammonia flux and nitridation time. The 100 nm AlN nucleation layer on silicon substrates grown by ammonia molecular beam epitaxy is studied using AFM, XRD, HR-TEM and Raman spectroscopy techniques. The Raman data show that reducing the nitridation temperature from 900 °C to 700 °C not only deteriorates the crystalline quality of the subsequent AlN nucleation layers, but also reduces the residual tensile stress by almost 30 %. In the present contribution, micro-Raman spectroscopy is used to determine the nature of the defects formed during the high temperature growth of the AlN nucleation layers and confirms them to be inversion domains. The HR-TEM technique was used to study the AlN/Si interface in AlN-on-Si nucleation layers grown on a nitridated silicon surface at 700 °C and 900 °C at the optimum stage of the nitridation process completion. HR-TEM images of AlN nucleation layers revealed regions with different AlN/Si(111) interfaces: 1) AlN/amorph-Si3N4/Si, 2) AlN/SiN(8 × 8)/Si, and 3) AlN/Si with a sharp interface boundary. Using fast Fourier transform image analysis, it is shown that the presence of amorphous Si3N4 phase inclusions in the AlN/Si interface boundary introduces tensile stresses in the AlN nucleation layer which can be reduced by lowering the nitridation temperature. The results obtained clearly show that one of the causes of cracks in III-nitride layers grown on silicon substrates is the formation of tensile AlN layers with a high content of the amorphous Si3N4 phase at the AlN/Si interface, which is characteristic of silicon nitridation at elevated temperatures (> 700 °C).

Study on the sand erosion resistance of ZrN and ZrAlSiN coatings

Brittle spalling is a crucial problem for hard ceramic coatings under high-angle sand erosion, especially for traditional binary nitride coatings such as ZrN. Here, we deposited the ZrAlSiN coating by co-doping Al and Si into the ZrN coating to improve the toughness and erosion resistance. ZrN coating was also prepared on Ti6Al4V substrates by magnetic filtration cathode vacuum arc technology (FCVA) under the same process for contrast. The microstructure, mechanical properties, and sand erosion resistance of ZrN and ZrAlSiN coatings were studied. The ZrAlSiN coating contains nanocrystalline ZrAlN and amorphous Si3N4. The results show that the ZrAlSiN coating exhibits the highest H, H/E, H3/E2, and Welastic/Wplastic among as-deposited coatings with the value of ~30.8Gpa, ~0.12, ~0.43Gpa, and 2.19, respectively. The erosion rate of the ZrAlSiN coating is about half that of the ZrN coating. The dopping of Si element is conducive to inhibition of the grain growth. The enhanced toughness while maintaining high hardness is one of the main reasons for the better anti-sand erosion performance of ZrAlSiN coatings. The research helps promote the application of ZrN-based coatings in the field of anti-sand erosion.

High‐Pressure Synthesis of Amorphous Si3N4 and SiBN‐Based Monoliths without Sintering Additives

Amorphous Si3N4 and SiBN monoliths without sintering additives are successfully prepared by high‐pressure–low‐temperature (HPLT) sintering using the single‐source‐precursor‐derived amorphous Si3N4 and SiBN powders as raw materials. The microstructural evolution and crystallization behavior of the as‐prepared samples are investigated using scanning electron and transmission electron microscopy and X‐ray powder diffraction, respectively. The results show that the incorporation of boron in the Si–N network enhances the crystallization temperature up to 1200 °C. The Vickers’ hardness of the HPLT‐sintered Si3N4 sample amounts ≈11.6 GPa whether prepared at 1000 or 1200 °C, while the maximum hardness of the SiBN sample is up to 16.3 GPa. The fracture toughness of amorphous Si3N4 and SiBN5 samples is almost identical (around 2.5 MPa m1/2) whether prepared at 1000 or 1200 °C, and SiBN2 and SiBN5 samples show an improved fracture toughness. In addition, the oxidation resistance of the as‐prepared samples is investigated at temperatures up to 1000 °C. A comparison between amorphous Si3N4 and SiBN monoliths demonstrates a positive effect of the presence of boron on their oxidation resistance.

Scalable Parallel Algorithm for Graph Neural Network Interatomic Potentials in Molecular Dynamics Simulations.

Message-passing graph neural network interatomic potentials (GNN-IPs), particularly those with equivariant representations such as NequIP, are attracting significant attention due to their data efficiency and high accuracy. However, parallelizing GNN-IPs poses challenges because multiple message-passing layers complicate data communication within the spatial decomposition method, which is preferred by many molecular dynamics (MD) packages. In this article, we propose an efficient parallelization scheme compatible with GNN-IPs and develop a package, SevenNet (Scalable EquiVariance-Enabled Neural NETwork), based on the NequIP architecture. For MD simulations, SevenNet interfaces with the LAMMPS package. Through benchmark tests on a 32-GPU cluster with examples of SiO2, SevenNet achieves over 80% parallel efficiency in weak-scaling scenarios and exhibits nearly ideal strong-scaling performance as long as GPUs are fully utilized. However, the strong-scaling performance significantly declines with suboptimal GPU utilization, particularly affecting parallel efficiency in cases involving lightweight models or simulations with small numbers of atoms. We also pretrain SevenNet with a vast data set from the Materials Project (dubbed "SevenNet-0") and assess its performance on generating amorphous Si3N4 containing more than 100,000 atoms. By developing scalable GNN-IPs, this work aims to bridge the gap between advanced machine-learning models and large-scale MD simulations, offering researchers a powerful tool to explore complex material systems with high accuracy and efficiency.

Synthesis of equiaxed Si3N4 from Si(NH)2 by adding seeds formed by in situ nitridation of silicon

High-quality Si3N4 powder is a prerequisite for the preparation of high-performance Si3N4 ceramics. In this paper, Si3N4 powders with regular morphology were successfully prepared by pyrolysis of Si(NH)2 using silicon as a nucleation inducing agent. The mechanism of the silicon in regulating the morphology and particle size of Si3N4 powders was investigated. The results show that when Si(NH)2 is pyrolyzed directly at 1500 °C under N2 atmosphere, the products are mainly whiskers accompanied by some particles with irregular shape. In the presence of silicon, the powder particles exhibit a regular hexagonal prismatic morphology. With the increase of silicon content, the whisker content decreases obviously, and the whisker disappears completely when the silicon content exceeds 10 %. Furthermore, the particle size of Si3N4 powder decreases with the increase of silicon content, and the particle size is the smallest when the silicon content is 15 wt%, which is about 802 nm. The nucleation and growth process of Si3N4 powder particles can be divided into three stages. Firstly, silicon reacts with N2 to form Si3N4 nuclei. Then, amorphous Si3N4 partially decomposes to form Si(g) and SiO(g) and grows on the formed Si3N4 nuclei as the temperature increased. Finally, undecomposed amorphous Si3N4 spontaneously nucleates and grows of the solid-phase diffusion mechanism. Ultimately, all the powders show equiaxial regular morphology. Preferential nitridation of silicon to form Si3N4 nuclei provides nucleation sites for vapor-phase products, which is the key to inhibiting whisker formation and regulating the particle size of Si3N4 powders.

Enhancing Thermoelectric Performance of n-Type Bi2Te2.7Se0.3 through Incorporation of Amorphous Si3N4 Nanoparticles.

Bi2Te3-based thermoelectric (TE) materials are the state-of-the-art compounds for commercial applications near room temperature. Nevertheless, the application of the n-type Bi2Te2.7Se0.3 (BTS) is restricted by the comparatively low figure of merit (ZT) and intrinsic embrittlement. Here, we show that through dispersion of amorphous Si3N4 (a-Si3N4) nanoparticles both 14% increase in power factor (at 300 K) and 48% decrease in lattice thermal conductivity are simultaneously realized. The increased power factor comes from enhanced thermopower and reduced electrical resistivity while the reduced lattice thermal conductivity originates mainly from scattering of middle- and low-frequency phonons at the incorporated a-Si3N4 nanoparticles. As a result, a large ZTmax = 1.19 (at 373 K) and an average ZTave ∼ 1.12 (300-473 K) with better mechanical properties are achieved for the BTS/0.25 wt % Si3N4 sample. Present results demonstrate that the incorporation of a-Si3N4 is a promising way to improve TE performance.

Influence of silicon content on high temperature tribology performance of TiAlCrSiN coatings

A series of TiAlCrSiXN coatings with various silicon contents were fabricated on Si(100) and 304 stainless steel substrates using a radiofrequency magnetron sputtering system, aiming to examine the effects of various Si content on wear behaviors at room temperature and 700 °C. The addition of silicon notably increased the coatings' hardness from 21 GPa to 29 GPa, attributed to significant compressive residual stress (−3.4 GPa) that inhibited dislocation movement. Room temperature wear tests revealed that wear rates varied between 0.6 and 3.7 (10−6mm3N−1 m−1) with increasing silicon content. The lowest wear rate is observed at a silicon content of 3.1 at.%, which is associated with an ideal residual stress of −1.2 GPa. This stress level played a crucial role in preventing crack propagation and delamination, thus enhancing wear protection. At 700 °C, the coatings' wear resistance was mainly governed by their oxidation resistance, with the most resistant coatings exhibiting wear rates from 1.6 to 4.4 (10−6mm3N−1 m−1). The silicon addition promoted the formation of an amorphous Si3N4 phase, serving as an oxygen diffusion barrier, thus enhancing resistance to oxidation at elevated temperatures. The findings suggest that TiAlCrSiN coatings offer a promising solution for advanced tribological applications, demonstrating improved performance at temperatures up to 700 °C.

Influence of underlayer roughness on the properties of Sc0.4Al0.6N thin films prepared via sputter deposition

Abstract A ScAlN thin film is one of the key materials of MEMS and high-frequency filters used in new-generation communication devices. Piezoelectricity can be improved by increasing Sc concentration. However, abnormal grains often appear at high Sc concentrations, degrading crystallinity and piezoelectricity. Herein, we demonstrated that underlayer roughness considerably affects the emergence of abnormal grains in a Sc0.4Al0.6N thin film formed via reactive DC sputtering. Dry etching with Ar plasma can effectively reduce the surface roughness of amorphous SiN and polycrystalline Si. Sc0.4Al0.6N thin films deposited on amorphous SiN and polycrystalline Si with sufficient flat surfaces exhibited a low density of abnormal grains, high crystallinity and piezoelectricity, and low loss tangent. Moreover, such high-quality thin films were obtained on a borophosphosilicate glass flattened using a reflow process without Ar etching. Therefore, underlayer roughness played an important role. The findings can help enable the large-scale production of highly doped ScAlN thin films.

Morphological and Dimensional Evolution of Nanosized Amorphous Silicon Nitride in α-Fe: Diffusional and Elastic Effects

We present a detailed analysis based on both experimental and 3D modelling approaches of the unique silicon nitride precipitation sequence observed in ferritic Fe-Si alloys upon nitriding. At 570 °C, Si3N4 silicon nitride was shown to form as an amorphous phase into α-Fe ferrite matrix, which is morphologically unstable over time. Precipitates nucleated with a spheroidal shape, then developed a cuboidal shape for intermediate sizes and octapod-like morphology for a longer time. Using transmission electron microscopy, we show that the transition between spheroid and cuboid morphology depended on particle size and resulted from competition between interfacial energy and elastic strain energy. The resulting morphology was then shown to be a cuboid shape whose faces were always parallel to the {100} planes of the α-Fe; the <100> directions of the matrix corresponded to the elastically soft directions. There was a critical size of around 45 nm for which the transition between the cuboid shape and the octapod-like morphology took place. This was characterised by a transformation of quasi-flat facets into concave ones and the development of lobes in the <111> directions of the bcc crystal. To better assess the kinetic effects of diffusion fields and internal stresses on the morphological instability observed, an original 3D model that explicitly coupled phase transformations and mechanical fields was developed and applied. The latter, validated on the basis of model cases, was shown to be able to describe the time-evolution of both chemical and mechanical fields and their interactions in diffusive mass transport. Using a model system, it was shown that the concentration field around the precipitates and the internal stresses played opposing roles in the cuboid to octapod-like morphological instability. This work gives some clarification regarding the morphological evolution of amorphous Si3N4 precipitates, an important point for controlling the mechanical properties of nitrogen steels.

Assessing the thermal conductivity of amorphous SiN by approach-to-equilibrium molecular dynamics.

First-principles molecular dynamics combined with the approach-to-equilibrium molecular dynamics methodology is employed to calculate the thermal conductivity of non-stoichiometric amorphous SiN. This is achieved by implementing thermal transients in five distinct models of different sizes along the direction of the heat transport. Such models have identical structural features and are representative of the same material, thereby allowing for a reliable analysis of thermal conductivity trends as a function of the relevant cell dimension. In line with the known physical law of heat propagation at short scale, the thermal conductivity increases in size with the direction of heat transport. The observed behavior is rationalized accounting for previous results on crystalline and amorphous materials, thus providing a unified description holding for a large class of materials and spanning a wide range of heat propagation lengths.

Atomic scale formation mechanism of the Amorphous-Nanocrystalline biphase structure in TiSiN Coating: Phase field crystal simulation and experimental characterization

TiSiN nanocomposite coatings have exceptional strength, toughness, and corrosion resistance due to their unique biphase amorphous/nanocrystalline structure with tiny TiN grains embedded in an amorphous Si3N4 phase. However, the unclear formation process makes microstructural control challenging. In this study the phase field crystal method has been employed to analyze the microstructure evolution in TiSiN coatings, uncovering a four-step formation mechanism for the amorphous-nanocrystalline structure. The initial stage results in appearance of concentration heterogeneities and the development of the triangular-like short-range order (Stage I). This stage is followed by the nucleation of nanocrystals in Ti-rich zones and the transformation of triangular short-range to the long-range order with a square symmetry (Stage II). Then, during coarsening stage, Ti-rich polycrystalline nanocrystals are formed (Stage Ⅲ) followed by the vacancy migration from the polycrystalline nanocrystals to amorphous phase and formation of monocrystalline Ti nanocrystals embedded in amorphous phase (Stage Ⅳ). The simulation results are compared qualitatively with aberration-corrected High-Resolution Scanning Transmission Electron Microscopy and High-Resolution Transmission Electron Microscopy images from our study.

Reactive spark plasma sintering of Si2N2O ceramic: Reaction process, microstructure, mechanical and dielectric properties

Dense Si2N2O ceramic was successfully prepared through the spark plasma sintering method at 1750 °C with nano-sized amorphous Si3N4 powder as raw material. The reaction sintering process, mechanical and dielectric properties of the Si2N2O ceramic were investigated in detail. The results revealed that the amorphous Si3N4 was initially crystallized to β-Si3N4, then oxidized to Si2N2O during the sintering process. With prolonging the dwell time, the grain orientation of Si2N2O gradually developed to the c-axis direction of the orthorhombic crystal. Meanwhile, the density of as-sintered ceramic was improved significantly, which greatly influenced the mechanical and dielectric properties of Si2N2O ceramic. In this work, the optimal dwell time of sintering process was 20 min, which is obviously shorter than the ordinary sintering methods. The Si2N2O ceramic fabricated at the above conditions exhibited the most favorable mechanical and dielectric properties with a bulk density of 2.80 ± 0.01 g cm−3, Vickers hardness of 13.1 ± 0.1 GPa, flexural strength of 214.1 ± 15.8 MPa, fracture toughness of 2.8 ± 0.3 MPa m1/2, and combined with low dielectric constant of around 3.5 to 4.5 at 8.2−12.4 GHz. Thus, the spark plasma sintering method is potentially regarded as a rapid way to prepare Si2N2O ceramic used as the structural and wave-transmitting functional material.

Stability of Interface Morphology and Thermal Boundary Conductance of Direct Wafer Bonded GaN|Si Heterojunction Interfaces Annealed at Growth and Annealing Temperatures

The properties of thin (~2 um) GaN templates on a silicon support substrate were studied to assess the stability of the direct wafer bonded GaN / Si interface. EVG® ComBond® equipment was used for bonding under high vacuum (~10-8 mtorr) at room temperature to remove unwanted native surface oxides [1,2]. For the bonded samples, the [1010] GaN edge was aligned parallel to the Si [110] edge. An X-ray diffraction reciprocal space map of the (004) Si and (0004) GaN revealed that there is a ~0.2° tilt between the GaN and Si layers and is simply due to the relative miscut between the two wafers. The treatment of the surfaces prior to bonding produces an amorphous region at the bonded interface that has been seen in many other bonded systems [3-5]. In the as-bonded sample, high resolution scanning transmission electron microscopy revealed a ~2 nm amorphous region on the Si side of the bonded interface, as confirmed by energy dispersive x-ray spectroscopy (EDX). Subsequent annealing was performed in an effort to recrystallize the amorphous interface. Previous work has shown that recrystallization between Si|Si wafer bonded samples occurred when annealed at 450 °C for 12 hours [3]. However, in the GaN|Si system, we found that the amorphous interface did not recrystallize when annealed under those conditions. Annealing at temperatures up to 450 °C and 120 hours showed only initial stages of interdiffusion and a stable interface. However, after annealing at 700 °C for 24 hours, high resolution EDX revealed the formation of amorphous SiN as well as the diffusion of gallium into silicon.Preliminary thermal results show that the thermal boundary conductance (TBC) of the as bonded sample is ~140 MW/(m2K). The TBC results of wafer bonded GaN|Si reported here is higher than previously reported TBC values of epitaxially grown interfaces such as GaN on Si [6], GaN on SiC [7], and GaN on diamond [8]. The TBC for the annealed interface is degraded by a factor of two compared to the as-bonded interface for the sample that was annealed at 700 °C for 24 hours. These results demonstrate that high TBC can be achieved through wafer bonding of GaN with materials such as silicon and that such interfaces are stable even up to device operation up to 300 °C. However, chemically rough interfaces formed due to high temperature annealing are detrimental to thermal transport across these interfaces. V. Dragoi, et al., ECS Trans., 86(5), 23 (2018)C. Flötgen, et al., ECS Trans., 64(5), 103 (2014)M.E. Liao, et al., ECS Trans., 86(5), 55 (2018)Y. Xu, et al., Ceramics International, 45, 6552 (2019)F. Mu, et al., Appl. Surf. Sci., 416, 1007 (2017)L. Yates, et al., ASME InterPACK (2015)J. Cho, et al., Phys. Rev. B, 89, 115301 (2014)H. Sun, et al., APL, 106(11), 111906 (2015) Figure 1

A study of microstructures and corrosion behavior of HVOF/PVD duplex coating against 10 vol% HCl solution

Injection mold for ABS+PVC mixture confront severe HCl severe corrosion, resulting in its short service lifetime. To overcome this problem, a duplex coating, consisting of an inner thick anti-corrosion NiCr-30Cr3C2(containing 30 wt% Cr3C2) interlayer and an outermost nano-composite TiSiN coating, was designed and provided by combination of High Velocity Oxygen Fuel (HVOF) and physical vapor deposition (PVD). The results show that the NiCr-30Cr3C2interlayer is composed of γ-NiCr and Cr3C2phases, with high-density defects (Pores, Cracks and Un/semi-melted zones), whereas the TiSiN coating consists of fcc nanocrystallines embedded amorphous Si3N4 matrix, also containing high-density micro-particles. The corrosion experiments against 10 vol% HCl solution at 65 °Cshow that the HVOF-PVD duplex coating displays a much superior corrosion resistance compared to single HVOF layer or PVD coating. Poor corrosion resistance of NiCr-30Cr3C2 layer is mainly due to the strong destruction of chlorine ions on the passivation films and its high-density defects which are prone to the infiltration of electrolyte, whereas poor anti-corrosion of TiSiN coating is attributed to the TiSiN-coating delamination caused by coupling effects of particle-induced pitting corrosion, interfacial corrosion and cracking. While the superior corrosion resistance of HVOF/PVD duplex coating is associated with the chemical inertness of TiSiN coating and the existence of the anti-corrosionNiCr-30Cr3C2interlayer which effectively inhibits interfacial corrosion and the generation of cracks. This indicates that the HVOF/PVD duplex coating may be as a good candidate for injection molds under HCl environments.

The new nanocapsule structure and cyclic tribological properties of Mo2N/Ag/Si3N4 nanocomposite film

Nanostructured films present versatile properties in the area of friction. This paper introduced a adaptive nanostructured film with multiple cycle service capability. Based on the concept of capsule sustained-release, a series of Mo2N/Ag/Si3N4 composite films with different Si contents were prepared. The results show that the films were mainly composed of fcc-Mo2N, fcc-Ag and Si3N4, presenting a “capsule structure” with the encapsulation of Mo2N/Ag by Si3N4. The crystalline Si3N4 wrap the Mo2N to form a co-extended growth structure, when the Si content is lower than 6.3 at. %. However, the coherent interface could be destroyed for the film with higher content of Si (>6.3 at. %), owing to the transforming to an amorphous phase of Si3N4. When annealed at 500 °C, the growth of Ag content on the surface is higher for film with 6.3 at. % Si than that of film with 11.4 at. % Si, indicating that the capsule structure with amorphous Si3N4 can hinder the diffusion of Ag. With the increase of Si content, the hardness of the film increases firstly and then decreases gradually. The maximum hardness value of 34.3 GPa can be obtained for the film with 6.3 at. % Si. The average friction coefficient of Mo2N/Ag/Si3N4 composite films with 6.3 and 11.4 at.% Si contents decreased from 0.48 to 0.33 and from 0.42 to 0.31 respectively with the increase of friction temperature from 200 °C to 700 °C under friction test. At the same temperature, the friction coefficient for film with 6.3 at.% Si is always lower than that of film with 11.4 at.% Si, but the wear rate is always slightly higher. The temperature-cycling friction times of nanocomposite films consisting of amorphous Si3N4 capsule structure with11.4 at.% Si is twice that of crystalline Si3N4 with 6.3 at % Si. The amorphous “capsule” structure can improve the multi-cycle serviceability of the film.

Tuning LSPR of Thermal Spike-Induced Shape-Engineered Au Nanoparticles Embedded in Si3N4 Thin-Film Matrix for SERS Applications.

While gold nanoparticles (Au NPs) are widely used as surface-enhanced Raman spectroscopy (SERS) substrates, their agglomeration and dynamic movement under laser irradiation result in the major drawback in SERS applications, viz., the repeatability of SERS signals. We tune the optical and structural properties of size- and shape-modified Au NPs embedded in a thin silicon nitride (Si3N4) matrix by intense electronic excitation with swift heavy ion (SHI) irradiation with the aim of overcoming this classical SERS disadvantage. We demonstrate the shape evolution of a single layer of Au NPs inserted between amorphous Si3N4 thin films under fluences of 120 MeV Au9+ ions ranging between 1 × 1011 and 1 × 1013 ions cm-2. This shape modification results in the gradual blue shift of the localized surface plasmon resonance (LSPR) dip until 1 × 1012 ions/cm2 and then a sudden diminishment at 1 × 1013 ions/cm2. Finite domain time difference (FDTD) simulations further justify our experimental optical spectra. The dynamical NP aggregation and dissolution, in addition to NP elongation and deformation at different fluences, are noted from 2D grazing incidence small-angle X-ray scattering (GISAXS) profiles, as well as cross-sectional transmission electron microscopy (X-TEM). The systematic shape evolution of metal NPs embedded in the insulating matrix is shown to be due to thermal spike-induced localized melting and a localized pressure hike upon SHI irradiation. Utilizing this specific control over the characteristics of Au NPs, viz., shape, size, interparticle gap, and corresponding optical response via SHI irradiation, we demonstrate their applications as very stable SERS substrates, where the separation between NPs and analyte does not alter under laser illumination. Thus, these irradiated SERS active substrates with controlled NP size and gap provide the optimal conditions for creating localized electromagnetic hotspots that amplify the SERS signals, which do not alter with time or laser exposure. We found that the film irradiated with 1 × 1011 exhibits the highest SERS intensity due to its optimal NP size distribution and shape. Thus, not only our study provides a SERS substrate for stable and repeatable signals but also the understanding depicted here opens new research avenues in designing SERS substrates, photovoltaics, optoelectronic devices, etc. with ion beam irradiation.