Damaged Layer Research Articles

PFOS and F–53B disrupted inner cell mass development in mouse preimplantation embryo

Perfluorooctane sulfonic acid (PFOS) is a perfluoroalkyl and polyfluoroalkyl substance (PFAS) widely used in daily life. As its toxicity was confirmed, it has been gradually substituted by F–53B (chlorinated polyfluoroalkyl sulfonates, Cl-PFESAs) in China. PFOS exposure during prenatal development may hinder the development of preimplantation embryos, as indicated by recent epidemiological research and in vivo assays. However, the embryotoxicity data for F–53B are scarce. Furthermore, knowledge about the toxicity of F–53B and PFOS exposure to internal follicular fluid concentrations on early preimplantation embryo development remains limited. In this study, internal exposure concentrations of PFOS (10 nM) and F–53B (2 nM) in human follicular fluid were chosen to study the effects of PFAS on early mouse preimplantation embryo development. We found that both PFOS and F–53B treated zygotes exhibited higher ROS activity in 8-cell embryos but not in 2-cell stage embryos. PFOS and F–53B significantly affected the proportion and aggregation of the inner cell mass (ICM) in the blastocyst, but not the total cell number. Mouse embryonic stem cells (mESCs, isolated from the ICM) and embryoid body (EB) assays were employed to assess the toxicity of PFOS and F–53B on the development and differentiation of embryonic pluripotent cells. These results suggested that mESCs exhibited more DNA damage and abnormal germ layer differentiation after brief exposure to PFOS or F–53B. Finally, RNA-sequencing revealed that PFOS and F–53B exposure affected mESCs biosynthetic processes and chromatin-nucleosome assembly. Our results indicate that F–53B has potential risks as an alternative to PFOS, which disrupts ICM development and differentiation.

Development of a Real-Time Boron Concentration Monitoring Technique for Plasma Doping Implantation

Plasma doping (PLAD) technology is widely used in the semiconductor industry. One of the problems associated with PLAD is precise dosage control and monitoring during the doping process. Excessive boron doping into the n-type poly gate will affect the p-MOSFET threshold voltage. In this study, we develop a novel method for the real-time monitoring of the boron concentration as it penetrates into an oxide film. We attempted to determine whether the real-time monitoring of the boron concentration can be replaced by measuring the thickness of the damaged layer remaining after plasma doping and a cleaning process, since the thickness of the damaged layer can be measured relatively easily in real time by means of ellipsometry. It is found that as the plasma doping energy is increased, the boron concentration increases linearly, with a strong correlation (R2 = 0.98) between the plasma doping energy and the boron concentration. Moreover, there is a close relationship between the plasma doping energy and the thickness of the damaged layer. As the doping energy is increased, the thickness of the damaged layer also increases linearly. We also find a close correlation (R2 = 0.92) between the change in the thickness of the damaged layer and the p-MOSFET threshold voltage. In summary, there are very good correlations between the plasma doping energy and the concentration of boron, the doping energy and the thickness of the damaged layer, and the thickness of the damaged layer and the threshold voltage. It is proven that the concentration of boron penetrating into the oxide layer can be monitored by measuring the thickness of the damaged layer in real time.

Study of subsurface damage during nano-grinding of B3-GaN using molecular dynamics simulations

The mechanism of subsurface damage formation during zinc blende gallium nitride (B3-GaN) nano-grinding was investigated using molecular dynamics (MD). The effects of grinding depth and abrasive radius on the grinding force, temperature, potential energy, phase transition, dislocations, the average coefficient of friction (COF), material removal rate (MRR) and subsurface damage were systematically investigated. The results show that dislocations, amorphization and wurtzite (B4) phase transitions are the primary defects present in the subsurface damage layer. Dislocation nucleation and proliferation are the main mechanisms aggravating the subsurface damage, and the 1/2<110> perfect dislocation along the <110> slip direction predominates in the dislocation. Grinding forces, temperature, potential energy, amorphous atoms, B4 phase atoms and dislocations increase with increasing grinding depth, exacerbating the subsurface damage of B3-GaN. As the abrasive radius increases, the amorphous atoms increase and then decrease, with the B4 phase atoms gradually reducing. The rest of the above parameters increase gradually, exacerbating the subsurface damage of B3-GaN. Furthermore, a smaller grinding depth and abrasive radius result in better machining accuracy, but decrease MRR. A technical reference for the ultra-precise and low-damage processing of B3-GaN can be provided by this study.

A new method for machining RB-SiC with high efficiency and quality: Laser assisted ultrasonic grinding

Reaction Bonded Silicon carbide (RB-SiC) ceramic is preferred material for space mirrors in aerospace field. However, the high hardness, brittleness and inhomogeneous structure bring great challenges for high quality and efficient machining. In this study, laser ablation assisted ultrasonic grinding (LAAUG) process was proposed. The high efficiency of laser ablation and high quality of ultrasonic grinding were effectively combined. Laser pre-ablation experiments were carried out firstly, and then thermal damage layer was removed through ultrasonic grinding. The results show that RB-SiC ceramics transform into relatively loose and homogeneous ablation products (SiO2 and recrystallized SiC) by laser irradiation. Moreover, it is accompanied by cracks development. Compared with conventional grinding, the maximum reduction of grinding force and surface roughness is 34 % and 13.8 %, respectively. Abrasive grain wear is significantly restrained and the percentage of plasticity removal is improved. This study indicates that LAAUG is feasible and efficient method for machining RB-SiC ceramics.

Influence of vacuum annealing on mechanical characteristics of focused ion beam fabricated silicon nanowires

This paper describes the influence of vacuum annealing on the mechanical characteristics of silicon (Si) nanowires (NWs) fabricated using focused ion beam (FIB) technologies. Two types of Si NWs having a cross-sectional one-side length or diameter ranging from 19 to 447 nm are prepared using the direct milling and Ga ion doping functions of FIB. The Si NWs prepared are annealed at 400–700 °C in high vacuum for 10 min, followed by quasi-static uniaxial tensile testing using a microelectromechanical system based tensile test system in a scanning electron microscope. All the Si NWs fracture in a brittle manner. Young's modulus of submicrometer-sized Si NWs shows both annealing and specimen size influences in the range from 120 to 170 GPa, whereas that of nano-sized Si NWs shows only annealing influence in the range from 60 to 110 GPa. Tensile strength scatters greatly, ranging from 1.0 to 7.2 GPa, which increases with increasing the NW size. A transmission electron microscope and an atomic force microscope suggest that, by annealing, recrystallization happens in the damaged layer introduced by FIB milling and the NW surface morphology changes due to its recrystallization and gallium (Ga) ion evaporation. Fracture origin is discussed through the comparison between surface roughness and crack length estimated by the Griffith theory of brittle fracture.

Micro/nano mechanical properties differences of shallow irradiation damage layer revealed by a combined experimental and MD study

Micropillar compression and nanoindentation techniques are both adopted to measure the mechanical properties in multi-energy He ion-irradiated Ni-based samples to study their relationship, and a distinct variation is observed. TEM characterization of the microstructure evolution and calculations based on the DBH model indicate that irradiation defects are not responsible for the observed variation. Subsequently, a comparative analysis of these two methods is simulated and their mechanisms are investigated using MD. Several factors, including activation of various slip systems, plastic area, and surface absorption, account for the differences observed in indentation and pillar compression tests, leading to the distinct evolution of internal initial dislocation lines, which significantly contribute to additional hardening in indentation tests.

Effect of graphene on the surface nanomechanical behavior and subsurface layer of GaN damage during nanogrinding using molecular dynamics simulation

Molecular dynamics simulations were used to investigate the surface nanomechanical behavior and subsurface layer damage of gallium nitride (GaN)/graphene composites when subjected to nanogrinding with diamond abrasive. The effects of graphene on GaN were analyzed based on parameters such as atomic displacement, forces, crystal structure, subsurface damage, atomic stress, and temperature. The simulation results indicate that graphene has a noteworthy impact on the surface morphology, such as the pile-up atoms on the workpiece surface and the elastic recovery on the machined surface. In addition, the addition of graphene can reduce the atomic temperature, stress, and normal and tangential forces. In terms of subsurface damage formation, graphene can suppress lattice damage and amorphization of GaN during nanogrinding. The addition of graphene can significantly reduce the dislocation length and the phase transition from wurtzite to a five-fold coordination hexagonal structure. Overall, the addition of graphene can improve the deformation mechanism on the GaN surfaces. This study provides technical references for the design of GaN with improved friction and wear resistance.

An approximate formula for the Rayleigh wave velocity in the machined surface with residual stress

The present paper is concerned with the Rayleigh wave propagation in the machined surface with a thin damaged layer with residual stress. We assume that the layer and the half-space are bonded perfectly to each other. Biot’s theory of small deformations influenced by initial stress forms the basis for this study. With the help of the effective boundary condition method, a third-order approximate secular equation of Rayleigh waves is established for the case that the layer and half-space are both orthotropic. In addition, an explicit third-order approximate formula for the Rayleigh wave velocity is derived from the secular equation. By considering a sample of silicon wafer by fine grinding with fine abrasive grains, the accuracy of the approximate formula has been verified. This study is meant to serve as the mathematical foundation for non-destructive testing of residual stress in the practical applications.

Novel green chemical mechanical polishing for an aluminum alloy and mechanisms interpreted by molecular dynamics simulations and measurements

Aluminum (Al) alloy is a kind of soft-plastic metal, and traditional chemical mechanical polishing (CMP) is easy to produce scratches on the polished surface and embed of abrasives, resulting in the degradation of devices. In addition, conventional CMP generally employs toxic and corrosive slurries, leading to the pollution of environment. To address these challenges, a novel green CMP was developed for Al alloy, consisting of ceria, silica, sodium carbonate, hydrogen peroxide, glycine and deionized water. After CMP, surface roughness Sa is 0.258 nm under an area of 100 × 100 μm2, which is the lowest surface roughness reported previously in such a big measurement area for Al alloy. Transmission electron microscopy confirms that the thickness of damaged layer is merely 4.6 nm. X-ray photoelectron microscopy and Fourier transform infrared spectroscopy reveal that composite abrasives are conducive for the generation of Al-O, Al-O-Si and Ce-Al bonds on the polished surface. Molecular dynamics simulations elucidate that the subsurface damage is mainly caused by exerted loading of abrasives on amorphous layer, as well as vacancy induced through the annihilation of dislocations profoundly. These outcomes provide a new avenue to manufacture atomic surfaces of soft-plastic metals for latent applications in devices.

Investigation of defect characterization, formation mechanism, and effect in distributed feedback lasers

InP, which exhibits attractive physical characteristics, such as high electron mobility, high conductivity, and high bandgap width, has always been fanatically pursued in high frequency and high speed devices in recent years. However, the inherent high density defects hinder the quality of the epitaxial layer and, even worse, impede the device’s life. Here, we found a kind of defect in the distributed feedback laser layers on an InP based substrate. A focused ion beam was employed in order to dissect the defect. The formation process was characterized using a transmission electron microscope and a high-resolution transmission electron microscope. Closer analysis reveals that defects form a subsurface damage layer between the substrate and the epitaxial layer. The subsurface damage layer already has a potentially destructive lattice, including lots of dislocations and lattice distortions, which leads to anisotropy in the interface layer. As the epitaxial film thickness increases, so does this strain relax, and dislocations form.

Study on the mechanism of chemical mechanical polishing on high-quality surface of single crystal diamond

Due to the ultra-high hardness and excellent chemical inertness of single crystal diamond (SCD), achieving a high-quality surface of SCD by chemical mechanical polishing (CMP) is challenging. To obtain a high-quality surface of SCD, we developed a novel slurry containing a mixed oxidant of hydrogen peroxide (H2O2) and potassium ferrate (K2FeO4). The surface micro-morphology, profile, roughness, and damage layer characteristics of SCD were characterized by a 3D surface optical profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Simultaneously, the reasons for the formation of high-quality surface of SCD were investigated. The results demonstrated that the polished SCD surface was smooth and scratch-free with an average Ra of 0.681 ± 0.023 nm over six areas of 868 × 868 μm2 and a damage layer thickness of 0.6 nm. Furthermore, the state of the chemical bonds of elements on the SCD surface was surveyed by X-ray photoelectron spectroscopy (XPS), and the polishing mechanism was deduced as follows: hydroxyl radicals were adsorbed on the SCD surface to oxidize and formed COH and CO bonds, while the damage due to lattice distortion resulted in the breakage of the CC bond to achieve carbon atom removal.

Study of the Relationship between Changes in the Structural, Optical, and Strength Properties of AlN Ceramics Subjected to Irradiation with Heavy Xe23+ Ions.

The purpose of this study is to comprehensively analyze the influence of different fluences of irradiation with Xe23+ heavy ions on alterations in the structural, optical, and strength properties of AlN ceramics and to establish a connection between structural distortions and alterations in the optical and mechanical properties of the ceramics. X-ray diffraction, UV-Vis and Raman spectroscopy, and indentation and single-compression methods were used as research methods. During the study, it was demonstrated that at low irradiation fluences, the main role in the changes in the properties of the AlN ceramics is played by effects related to changes in their optical properties and a fundamental absorption edge shift, which characterizes changes in the electronic properties of the ceramics (changes in the distribution of electron density). A study of the variations in the optical properties of the examined samples in relation to the irradiation fluence showed that when the fluence surpasses 5 × 1011 ion/cm2, an extra-spectral absorption band emerges within the range of 3.38-3.40 eV. This band is distinctive for the creation of vacancy ON-VAl complexes within the damaged layer's structure. The presence of these complexes signifies structural deformations and the accumulation of defective inclusions within the damaged layer. An analysis of changes in the parameters of the crystal lattice showed that structural distortions in the damaged layer are due to the accumulation of tensile residual mechanical stresses, an increase in the concentration of which leads to the swelling and destruction of the damaged layer. Some correlations between the mechanical properties of ceramics and the irradiation fluence indicate the ceramics' remarkable resistance to radiation-induced brittleness and weakening. These effects become apparent only when structural damage accumulates, resulting in the swelling of the crystal lattice exceeding 2.5-3%.

Discussion on the water absorption depth of gangue-based concrete and its relationship with the damage layer thickness

Capillary water absorption is one of the key factors in evaluating the durability of concrete structures. In this paper, solid waste-coal gangue was used as raw material, and activated gangue powder (ACGP) was used to prepare gangue-based concrete (GBC) by partially replacing cement. The capillary water absorption performance of GBC under the action of freeze-thaw cycles was investigated by freeze-thaw cycle test as well as capillary water absorption test. The relationship between water absorption depth and water content was established. The interrelationship between the water absorption depth and the damage layer thickness was analyzed. The test results indicated that the frost resistance of concrete was enhanced after incorporating ACGP. The capillary water absorption performance of GBC was weaker than that of ordinary concrete, with less water content and lower sorptivity, and the effect was most apparent when the dosage of ACGP was 20%. The water absorption depth gradually grew with the number of freeze-thaw cycles and the water absorption time. There was a significant linear correlation between the water content and the water absorption depth, which provided a new insight into the prediction of the hardly measurable water absorption depth from the easily accessible water content. The water absorption depth was significantly higher than the damage layer thickness, and the difference between them was broadened after the incorporation of ACGP. Besides, an approximate linear relationship between the water absorption depth and the damage layer thickness was pointed out.

Radiation damage evolution in High Entropy Alloys (HEAs) caused by 3–5 MeV Au and 5 MeV Cu ions in a broad range of dpa in connection to mechanical properties and internal morphology

High Entropy Alloys (HEAs) are prospective materials for nuclear fusion reactors and were irradiated in this study at a broad range of energetic ion fluences. Different ion masses (Cu and Au ions) and energies (3 and 5 MeV) were selected to investigate dpa (displacement per atom) development, radiation defect accumulation based on prevailing collision processes (Au ions) and ionization processes (Cu ions) in various HEAs. The studied HEAs differ in terms of elemental composition, internal morphology (grain structure) and other modifiers. Dpa values of 1 to ∼66 were achieved at Cu and Au ion fluences from 4 × 1014 to 1.3 × 1016 ions.cm−2 at room temperature, which generated varying levels of lattice damage. Theoretical simulations were performed to estimate the energy stopping and dpa depth distribution using SRIM code and compared with Au-concentration depth profiles determined by Rutherford backscattering spectrometry for Au-ions with 3 MeV ion energy. The prevailing energy losses of ions via ionization processes for Cu-5 MeV ions were found to increase the damage through lattice strain and probable lattice distortion, although the main defect introduction is expected to occur via collisions during nuclear stopping. Structural modification and defect accumulation were investigated by positron annihilation spectroscopy (PAS), which revealed a broader damaged layer with defects, where HEA-Nb (NbCrFeMnNi) exhibited the least damage accumulation from chosen alloys with no strong relation to the Au-5 MeV ion implantation fluence, whereas strong defect accumulation was recorded in the Au-ion implanted Eurofer97 used for comparison and HEA-Co (CoCrFeMnNi). PAS analysis also allowed defect sizes to be determined as an additional structural characteristic. The observed trends were also confirmed by thermal property analysis, with a worsening of thermal effusivity recorded after the irradiation in HEA-Co and Eurofer97. The worsening of the thermal properties was confirmed by the layer thickness, where the layer identified by PAS was found to be broader than the SRIM theoretical predictions. Nanoindentation measurements confirmed less pronounced radiation hardening of HEA-Nb relative to that observed in HEA-Co and Eurofer97. Transmission Electron Microscopy (TEM) analysis revealed layer thicknesses in reasonable agreement with the dpa depth profiles. The thermal effusivity decreased in the surface-irradiated layer in all investigated samples, the least influenced material was HEA-Nb.

Acceleration of wound healing By PVA-PEG-MgO nanocomposite hydrogel with human epidermal growth factor

This study focuses on development of a nanocomposite hydrogel for wound healing purposes. Poly-vinyl alcohol and poly-ethylene glycol-4000 were used to fabricate the hydrogel, physically crosslinking through freeze-thaw method, and magnesium oxide nanoparticles were incoprorated onto them. Notably, the integration of these nanoparticles induced significant changes in the hydrogel's properties, leading to marked improvements in its swelling ratio, water content, and tensile strength. This, in conjunction with their intrinsic moisture retention ability and enhanced antibacterial efficacy, makes these hydrogel nanocomposites as highly promising candidates for wound healing applications. Also, the minimal leaching of nanoparticles from these films reduced the risk of metal accumulation on wounds. To evaluate their performance in wound contraction, assessments were conducted using a live Wister rat model. It was observed that both bare and unloaded hydrogels promoted cell proliferation, and addition of human epidermal growth factor exponentially accelerated the process.The hydrogel films demonstrated biocompatibility and stimulated cell growth. Various parameters, including wound size contraction, angiogenesis, and reconstruction of the damaged epithelial layer, were examined using microscopic methods to assess the rate of wound healing.

Surface/subsurface formation mechanism of tungsten during ultrasonic elliptical vibration cutting

The ultrasonic elliptical vibration cutting (UEVC) has been proved to be a valid method to improve surface quality and reduce subsurface damage of tungsten. However, it is still a huge challenge to elucidate the surface/subsurface formation mechanism of tungsten during UEVC. Hence, molecular dynamics simulations were employed to reveal the formation mechanism of surface/subsurface during UEVC of tungsten from the atomic level, and the effects of ultrasonic amplitude and frequency on the surface/subsurface formation were explored. The results showed that compared with general cutting (GC), the improved surface quality was attributed to the smaller actual cutting depth and more amorphous tungsten in chips caused by cyclic loading-unloading during UEVC. Moreover, the reversing friction direction facilitated the formation of surface chips during UEVC as well. The thermal-activated dislocations caused by high transient cutting temperature could result in the wide distribution of subsurface dislocations, and the dislocations were usually expanded by the way of crystal plane slip to suppress generation of long slip plane, which could reduce the subsurface damage of tungsten during UEVC. In comparison with ultrasonic amplitude in cutting depth direction, elevated ultrasonic amplitude in cutting speed direction or ultrasonic frequency could reduce depth of subsurface damage layer, surface roughness, and dislocation density, which derived from the small transient cutting force and stress as well as high strain rate. This study provides a new insight into the surface/subsurface formation mechanism of tungsten during UEVC, which can offer a theoretical basis on the selection of ultrasonic parameters for achieving high surface/subsurface quality for tungsten and other materials machined by UEVC.

Effect of annealing on focused ion beam induced surface damages in silicon analyzed by micro-Raman spectroscopy

In this paper, we describe Raman spectroscopic study for evaluating the influence of vacuum annealing on the surface modification of the focused ion beam (FIB) induced damaged layer on a single crystalline Si (c-Si) substrate. The damaged layer consisting of amorphous silicon (a-Si) with implanted Ga ions is formed after irradiating FIB onto the c-Si surface. After vacuum annealing at 700 °C for 10 s, the Raman spectrum peak of poly crystalline Si (p-Si) appears. With increasing annealing time, the spectral parameters, peak shift, peak intensity, and full width at half maximum (FWHM), for p-Si and c-Si change. Through the comparison between the phase fraction of a-Si, p-Si, and c-Si in the FIB damaged layer and the mechanical properties of the FIB-processed Si nanowires obtained in the quasistatic tensile testing, a recovery of the damaged layer by annealing is discussed.

Macro and micro-nano machining mechanism for ultrasonic vibration assisted chemical mechanical polishing of sapphire

Ultrasonic vibration assisted chemical mechanical polishing (UV-CMP) has been proven to achieve better sapphire polishing performance. However, its polishing mechanism is still ambiguous. Few studies about pads and slurries have been reported in the field of sapphire UV-CMP. Thus the effects of the pad material and structure, abrasive material and size, and slurry pH on UV-CMP were explored in this paper. The influences of each factor on the material removal rate and surface roughness were analyzed and compared. Transmission electron microscopy images reveal the types of subsurface damage including amorphous layers, dislocations, residual stresses, stacking faults and lattice distortions. The sapphire subsurface damage layer after UV-CMP (123 nm) is much thinner and more uniform than that after CMP (199 nm). The chemical products during sapphire UV-CMP are softer than those in sapphire CMP. And the chemical compounds are detected on the sapphire surface by X-ray photoelectron spectroscopy. This article deeply explores the machining mechanism of sapphire UV-CMP and provides the important theoretical and practical guidance for sapphire ultra-precision polishing.

Angstrom surface on copper induced by novel green chemical mechanical polishing using ceria and silica composite abrasives

Toxic and corrosive slurries are widely employed in traditional chemical mechanical polishing (CMP), leading to the pollution to the environment. Consequently, it is a challenge to acquire angstrom surface using green CMP. To solve this challenge, a novel green CMP was developed for copper (Cu), including only four ingredients. Ceria and silica are used as composite abrasives. Tartaric acid was applied to adjust the pH value of the developed green slurry to 6.5. After CMP, surface roughness Ra is 0.1 nm measured by atomic force microscopy and surface profilometer respectively, with measurement areas of 5 × 5 μm2 and 50 × 50 μm2, correspondingly. So far, this is the lowest surface roughness reported in such a large measurement area. Transmission electron microscopy confirms that the thickness of damaged layer after CMP varies from 0.4 to 2 nm. CMP mechanism is elucidated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Firstly, the Cu surface was oxidized by hydrogen peroxide, then solved via hydrogen ions, and finally chelated with hydroxyl groups of tartaric acid. These findings provide a novel approach and new insights to achieve angstrom level surface, for the potential use in high-performance devices of Cu.

The tensile properties and repair behavior of glass fiber reinforced polymer using resin pre-coating technology

Resin pre-coating technology is widely used in all aspects of composite materials, especially in the repair of composite materials. The pre-coating is formed by combining acetone with the resin, which is diffused and cured by the epoxy adhesive at the same time. It acts as an interlock to prevent the interface from debonding and to fill in the damaged cracks. The capillary action of acetone allows the resin to permeate the cracks in the fiber damage layers, thus filling the cracks and completing the repair. The pre-coating solutions of 10 wt%, 20 wt%, 25 wt%, 35 wt%, and 45 wt% resin were applied to damaged areas respectively, and cured at 60°C for 7 days. The crack filling effect was observed by scanning electronic microscopy (SEM). At the same concentration, the effect of prolonged repair time was also studied. The other two repair times were 14 days and 30 days respectively. In addition, the tensile properties of the materials before and after repair were tested and compared. The results showed that 25 wt% resin pre-coating had the best repair performance after 7 days, with a repair rate of 27%, which was 22% higher than the conventional repair without resin pre-coating. However, the repair effect became more obvious after the extension of repair time, and the repair effect of 25 wt% resin pre-coating reached 44% after 30 days curing. Therefore, it was found that the resin can fully penetrate the cracks in the damaged area with resin pre-coating technology, and 25 wt% resin pre-coating solution is the best choice.