Top Layer Research Articles

Multifunctional hydrogel to achieve cartilage-mimetic properties

It remains challenging for conventional materials to achieve cartilage-mimetic structures and properties. In this work, a sandwich hydrogel was reported to overcome this issue. Due to the introduction of soy lecithin (SL) at the top layer, the friction coefficient was 0.02. On account of the multiple linkages from polyvinyl alcohol (PVA), chitosan (CS), and grape seed protein (GSP) in the intermediate layer, the compressive strength was 42 MPa. Owing to the existence of GSP and tannic acid (TA) in the bottom layer, the hydrogel exhibited excellent adhesion onto various materials. Meanwhile, the volume and mechanical performances were almost constant after soaking in simulated synovial fluid for a week. Furthermore, the abundant phenols of GSP empowered remarkable antioxidant capacity. Because of biocompatible materials, the cell viability was 100 %. All of these merits make it an ideal substitute for cartilage.

Insight into layer formation during friction surfacing: Relationship between deposition behavior and microstructure

Friction surfacing (FS) is a solid state layer deposition technique with a simple setup, presenting advantages compared to fusion-based approaches. Previous investigations showed microstructural gradients along layer width and thickness. The current study provides new insight into the FS layer formation for aluminum and its relation with the microstructure evolution. Special consumable studs containing two different aluminum alloys were used to visualize the different materials in the resulting deposit. The investigation was performed at different process parameters, revealing some fundamental material flow characteristics. The layer center presents inner stud material, where advancing side and top are formed by outer stud material. The bottom and retreating side present a mixture of inner and outer stud material. The part of the layer that is formed by the outer material, presumably undergoes higher strain rates during deposition, presenting finer grains. The top of FS layers shows a pronounced texture, i.e. shear texture components, compared to the other parts with random texture. This phenomenon can be related to the shearing of the stud material between already deposited material below and the stud at its rear edge. Overall, the FS layer formation characteristics revealed in this study are directly related to local microstructural properties.

Janus-structured graphene scaffold for bottom-up lithium deposition: A progressive gradient approach

Graphene-based materials have been explored as hosts for Li metal anodes, but their high interfacial activity and short diffusion distances frequently result in dendrite formation on the surface. Herein, we utilize the adjustable conductivity and Li affinity of graphene oxide (GO) to develop a Janus structure comprising a top GO layer and a bottom reduced graphene oxide (rGO) layer. The progressive conductivity and lithiophilicity gradient structure of GO/rGO enables a bottom-up Li deposition mode, rendering an average Coulombic efficiency of 99.1 % over 350 cycles at 1 mA cm−2 and 1 mAh cm−2. Full cells equipped with a LiFePO4 cathode maintain a capacity retention of 85 % after 350 cycles at 1 C. This innovative approach provides fresh insights into the development of graphene-based hosts, offering significant potential for future Li metal battery applications.

A tough Janus poly(vinyl alcohol)-based hydrogel for wound closure and anti postoperative adhesion

Traditional adhesive hydrogels perform well in tissue adhesion but they fail to prevent postoperative tissue adhesion. To address this challenge, a biodegradable Janus adhesive hydrogel (J-AH) was designed and fabricated by the assembly of three different functional layers including anti-adhesive layer, reinforceable layer, and wet tissue adhesive layer. Each layer of J-AH serves a specific function: the top zwitterionic polymeric anti-adhesive layer shows superior resistance to cell/protein and tissue adhesion; the middle poly(vinyl alcohol)/tannic acid reinforceable matrix layer endows the hydrogel with good mechanical toughness of ∼2.700 MJ/m3; the bottom poly(acrylic acid)/polyethyleneimine adhesive layer imparts tough adhesion (∼382.93 J/m2 of interfacial toughness) to wet tissues. In the rat liver and femoral injury models, J-AH could firmly adhere to the bleeding tissues to seal the wounds and exhibit impressive hemostatic efficiency. Moreover, in the in vivo adhesion/anti-adhesion assay of J-AH between the defected cecum and peritoneal walls, the top anti-adhesive layer can effectively inhibit undesired postoperative abdominal adhesion and inflammatory reaction. Therefore, this research may present a new strategy for the design of advanced bio-absorbable Janus adhesive hydrogels with multi-functions including tissue adhesion, anti-postoperative adhesion and biodegradation. Statement of significanceDespite many adhesive hydrogels with tough tissue adhesion capability have been reported, their proclivity for undesired postoperative adhesion remains a serious problem. The postoperative adhesion may lead to major complications and even endanger the lives of patients. The injectable hydrogels can cover the irregular wound and suppress the formation of postoperative adhesion. However, due to the lack of adhesive properties with tissue, it is difficult for the hydrogels to maintain on the wound surface, resulting in poor anti-postoperative adhesion effect. Herein, we design a Janus adhesive hydrogel (J-AH). J-AH integrates together robust wet tissue adhesion and anti-postoperative adhesion. Therefore, this research may present a new strategy for the design of advanced bio-absorbable Janus adhesive hydrogels.

Higher Seed Rates Enlarge the Effects of Wide-Belt Sowing on Root Length Density, Thereby Improving Nitrogen Uptake and Use Efficiencies in Winter Wheat.

The optimized sowing method and appropriate seed rate can improve wheat N use efficiency. However, the interactive effect of the sowing method and seed rate on N use efficiency, particularly N uptake and root length density, are unclear. A field experiment was conducted for two growing seasons in southern Shanxi province, China, using a split-plot design with the sowing method as the main plot (wide-belt sowing, WBS, and conventional narrow-drill sowing, NDS) and seed rate as the sub-plot (100-700 m-2). Our results showed that WBS had a significant and positive effect on N use efficiency (yield per unit of available N from the fertilizer and soil, by 4.7-15.4%), and the relatively higher seed rates (>300 or 400 m-2) enlarged the effects. The N use efficiency increases under WBS were mainly attributed to the increases in N uptake before anthesis, resulting from the promoted nodal roots per plant and per unit area, and root length density in the top layer(s). WBS promoted N translocation and the N harvest index, resulting in equivalent grain protein concentration and processing quality compared to NDS. Thus, adopting higher seed rates (>300 m-2) combined with WBS is recommended for achieving greater N efficiencies while maintaining the grain protein concentration and processing quality of winter wheat.

Using a Carbon Quantum Dot Suspension as a New Solvent for Clear Hydrophobic Surface Coating on Hydrophilic PVA Films.

Polyvinyl alcohol (PVA) is a popular material used in the packaging industry. However, it is vulnerable to moisture, which can affect its performance and durability. Introducing hydrophobic substances, such as tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS), on the top layer of PVA can help maintain the excellent properties of PVA under high-humidity conditions. The low compatibility of hydrophobic materials with the hydrophilic layers allows them to aggregate more easily. To overcome these issues, we focused on the effects of particle size when increasing the coating suspension's dispersibility. A carbon quantum dot (CQD) suspension is an appropriate novel solvent for hydrophobic TEOS/HDTMS coating suspensions because its particles are small and light and exhibit good dispersibility. The CQD suspension formed a smooth hydrophobic coating on the TEOS/HDTMS materials. Furthermore, the uniformly coated PVA with the CQD suspension exhibited a water contact angle of 110°. The water droplets remained intact without being absorbed, confirming the effectiveness of the surface coating facilitated by CQDs. These results suggested that CQDs improved the dispersibility and enhanced the coating quality of TEOS/HDTMS on PVA. Enhancing the hydrophobicity of PVA is ideal for applications in packaging and other fields.

In situ observations of supercooled liquid water clouds over Dome C, Antarctica, by balloon-borne sondes

Abstract. Clouds in Antarctica are key elements that affect radiative forcing and thus Antarctic climate evolution. Although the vast majority of clouds are composed of ice crystals, a non-negligible fraction constitutes supercooled liquid water (SLW; water held in liquid form below 0 °C). Numerical weather prediction models have great difficulty in forecasting SLW clouds over Antarctica, favouring ice at the expense of liquid water and therefore incorrectly estimating the cloud radiative forcing. Remote-sensing observations of SLW clouds have been carried out for several years at Concordia Station (75° S, 123° E; 3233 m above mean sea level), combining active lidar measurements (SLW cloud detection) and passive HAMSTRAD microwave measurements (liquid water path, LWP). The present project aimed at in situ observations of SLW clouds using sondes developed by the company Anasphere, specifically designed for SLW content (SLWC) measurements. These SLWC sondes were coupled to standard meteorological pressure–temperature–humidity sondes from Vaisala and released under meteorological balloons. During the 2021–2022 summer campaign, 15 launches were made, of which 7 were scientifically exploitable above a height of 400 m above ground level, a threshold height imposed by the time the SLWC sonde takes to stabilize after launch. The three main outcomes from our analyses are as follows: (a) the first in situ observations so far of SLW clouds in Antarctica with SLWC sondes; (b) on average, the consistency of SLW cloud heights as observed by in situ sondes and remote-sensing lidar; and (c) the liquid water path (vertically integrated SLWC) deduced by the sondes being generally equal to or greater than the LWP remotely sensed by HAMSTRAD. In general, the SLW clouds were observed in a layer close to saturation (U > 80 %) or saturated (U ∼ 100 %–105 %) just below or at the lowermost part of the entrainment zone, or capping inversion zone, which exists at the top of the planetary boundary layer and is characterized by an inflection point in the potential temperature vertical profile. Our results are consistent with the theoretical view that SLW clouds form and remain at the top of the planetary boundary layer.

Innovative K-band slot antenna array for radar applications

This article introduces a novel microstrip slot antenna array (SAA) configuration for radar applications. The proposed antenna is specifically designed for operation in the K-band, spanning from 23 to 24.3 GHz. The antenna structure comprises two substrates: the feed network and ground plane are on the bottom substrate, and the radiating slots are on the top layer of the first substrate. The incorporation of a unique grid feed configuration, featuring 50 Ohm center excitation for the first time, improves the feed mechanism of the microstrip SAA. This innovation contributes to achieving a compact size and high gain. To enhance the side lobe level, the design incorporates a substrate-integrated waveguide-backed cavity, which significantly reduces surface waves. The SAA consists of 25 radiating elements with a gain of 14 dBi. In the elevation and azimuth planes, the half-power beamwidths are measured at 12.1° and 69.1°, respectively. The proposed antenna array’s measured impedance bandwidth ranges from 23.15 to 24.75 GHz, guaranteeing a reflection coefficient (S11) of less than − 10 dB. The suggested antenna's applicability for automotive multi-input multi-output radar has been validated.

Towards ZnO-Based Near-Infra-Red Radiation Detectors: Performance Improvement via Si Nanoclusters Embedment

Si nanoparticles embedded in a ZnO matrix were produced by a sequential deposition of ZnO/Si/ZnO layers, by radio frequency sputtering. Sample growth temperatures of 25 °C, 300 °C, and 500 °C were used to deposit ZnO/Si/ZnO layers on soda lime glass and p-type silicon substrates; ZnO layers were deposited by reactive radio-frequency sputtering employing a mixture of Ar/O2, with a ratio of 66/33, as working atmosphere. The type of substrate and the growth temperature affect the first ZnO layer roughness, promoting the formation of silicon nanoparticles, matrix characteristics, and as consequence, spectral response. The roughness of the initial ZnO layer is transferred to the top layer of ZnO, and it can be tailored between 65 and 370 Å, depending on the sample growth temperature. Transmission electron microscopy show that substrate temperature mainly affects the density of silicon nanoparticles rather than their size. ZnO/Si/ZnO films deposited on p-type silicon substrate were processed and photosensors were obtained, showing a selective response in the 950 to 1150 nm wavelength range, making them suitable candidates for near infrared detectors.

Simulation of rapid sand filters to understand and design sequential iron and manganese removal using reactive transport modelling

Iron (Fe2+), manganese (Mn2+), and ammonium (NH4+) oxidation processes were studied in three single media and three dual media full-scale rapid sand filters (RSFs) using reactive transport modelling (RTM) in PHREEQC and parameter estimation using PEST. Here, we present the insights gained into the spatial distribution of Fe and Mn mineral coatings in RSFs and its influence on the oxidation sequence and rates. Fe2+ and Mn2+ oxidation predominantly occurred simultaneously in the RSFs, contrary to the expected sequential oxidation based on Gibbs free energy calculations. During backwashing, RSF grains become fully mixed, which initiates heterogeneous Mn2+ oxidation on Mn-coated grains that end up in the top layer. The resulting grains have a mixed Fe/Mn mineral coating, which is limiting heterogeneous Mn2+ oxidation due to the limited Mn mineral surface available. Mixed coatings did not seem to affect Fe2+ oxidation rates, instead oxidation rates were increasing at lower pH. We found that RSFs can be designed to spatially separate Fe2+ and Mn2+ oxidation, which results in optimal conditions for Mn2+ oxidation. The RSF needs to consist of two layers with varying density to inhibit mixing and complete Fe2+ oxidation should occur in the top layer. The developed RTM can be used to estimate the depth at which Fe2+ oxidation is complete, and thus the ideal intersection depth of the two layers. A novel perspective is provided on how mineral coating distribution in single and dual media filters influence removal rates and the sequence of oxidation, which contributes to the design of more efficient groundwater filters.

Response to "Comment on 'Anomalous reflection from a two-layered marine sediment' " [J. Acoust. Soc. Am. 156, 1524-1527 (2024)

In their Comment, the authors conclude that acoustic glint is not present in the reflection coefficient of a two-layer sediment in which the top layer is an Airy medium. They conclude, not that the original, inverse-square analysis of the glint is incorrect, but rather that the presence of glint is very sensitive to the detailed shape of the sound speed profile in the top layer.

Rolling contact fatigue property of gradient rare earth addition M50 bearing steel with surface nano-grains and its inhibited martensite decay

A gradient nanostructured surface layer of ∼600 μm in thickness was prepared on M50 steel with rare earth additions by a surface mechanical rolling treatment. The initial microstructure was refined into nanosized grains (∼29 nm in diameter) in the top surface layer, causing a significant increase of surface hardness. Meanwhile, the grain size increases, and the microhardness decreases gradually to the matrix values with increasing depth. Rolling contact fatigue tests showed that the fatigue lives are significantly increased by the gradient nanostructured surface layer. Analysis of failure mechanism revealed that both softening in the near surface layer and hardening in the subsurface occur under rolling contact testing. And surface spalling is the predominant failure mode, of which the cracks initiate from primary carbides in the top surface layer owing to surface softening. In gradient nanostructured samples, the nano-grains inhibit carbon migration by impeding dislocation movement in the near surface layer, so that martensite decay is suppressed. Consequently, the crack initiation is inhibited, and the fatigue property is enhanced.

Poly(aniline/aminophenol)-wrapped graphene nanoplates loaded with gabapentin inhibitor as a filler in poly(aniline/vinylalcohol/aminophenol)/acrylic coating to endow corrosion/wear durability by triple protection mechanism

A coating with excellent tribological behavior and corrosion durability was synthesized by chemical/electrochemical method from the composition of polyaniline (PANI), polyaminophenol (PAP), polyvinylalcohol (PVA), and reinforced with PANI/PAP/Gabapentin-functionalized Graphene nanoplates. Acrylic (AC) covered the composite coating as a top layer. According to the evaluations, G@PANI/PAP/GP-reinforced coating has 5 times more corrosion resistance than unreinforced one (on the 1st and 30th days). Not only has the corrosion resistance of PANI/PVA/PAP contained G@PANI/PAP/GP not decreased over time, but it has increased by ∼20 %. The defect density of passive film under (PANI/PVA/PAP)/Acrylic coating containing G@PANI/PAP/GP is 10 times less than that of the (PANI/PVA/PAP)/Acrylic coating. G@PANI/PAP/GP decreased the friction coefficient and wear rate of PANI composite coating over time by ∼47 % and 84 %. Furthermore, the simultaneous presence of graphene and gabapentin has increased the lubrication (Rsk = -0.24 µm) and adhesion (13 %) of the coating. It is how a polyaniline-based composite coating with three mechanisms of passivation, corrosion barrier, and inhibition protects the 304 SS over time.

Investigating the friction stir additively manufactured AA2024 build and the influence of material flow in enhancing the inter-surface bonding

Friction Stir Additive Manufacturing (FSAM) is a solid-state joining process that operates below the material’s melting point, avoiding the drawbacks of fusion-based methods. In FSAM, inter-surface bonding is crucial for the build strength and is influenced by material flow at the interface. This study examines the influence of flat-faced (square) and smooth (threaded conical) pins, along with rotational speed, on the material flow, using Al-clad as a tracer. It also analyses the microstructure, micro-texture, mechanical properties of the builds, and the role of the forging force in FSAM. Defect-free builds were achieved with a forging force above 7000N. The threaded conical pin caused upward migration of Al-clad, while the square pin led to fragmentation and distribution, offering excellent inter-surface bonding. Refined grain structures (~5µm) were observed in the top layers. The highest tensile strengths were 392MPa in the weld direction (80% build efficiency) with the threaded conical pin, and 358MPa in the build direction (75% build efficiency) with the square pin. Strong γ-fiber in ODFs indicates better ductility, with up to 60% improvement in elongation. The current research shall guide the selection of appropriate process parameters and, in turn, reduce trial-and-error during manufacturing aluminum alloys through friction stir additive manufacturing.

SAMPO-P: A prototypical scale low-temperature experiment on two-layer melt pool heat transfer in LWR lower head

To better understand the thermal behavior of a two-layer melt pool with a high Rayleigh number—a pattern observed in the RASPLAV study, which indicates a significant risk to pressure vessel integrity and the success of in-vessel retention (IVR) strategies—this paper reports experimental findings from a 2D, full-scale (1:1 ratio) Prototypical Stratified Melt pool (SAMPO-P). A series of experimental tests were carried out with varying heating powers and top layer heights, achieving a Rayleigh number of 3.77×1015, comparable to that found in light water reactors (LWR). Water was used to simulate the bottom layer, while n-octanol represented the top layer. Internal decay heat was modeled in the bottom layer using electric heating rods. After analyzing the main heat transfer parameters from the experiment, this paper derived several useful heat transfer correlations. The normalized temperature and heat flux distributions remained consistent across different power levels, and the normalized heat flux in the bottom layer aligned well with existing experimental correlations. In the bottom layer, the downward heat transfer coefficient was lower compared to other single-layer correlations, likely due to increased upward heat transfer.

High sensitivity and high figure of merit graphene mid-infrared multi-band tunable metamaterial perfect absorber

In the research of this paper, we have devised a mid-infrared band metamaterial perfect absorber made of graphene material. The absorber is composed of a traditional three-layer structure of MPA. The top layer is a graphene layer with a specific structure, with SiO2 as the dielectric layer and the gold film as the substrate. In the wavelength range of 5500 – 13000 nm, the graphene layer generates seven absorption peaks and shows ultra-high absorption efficiency. The respective absorption rates are 91.17%, 99.41%, 99.01%, 95.69%, 94.16%, 96.89%, and 95.01%. By verifying the absorption spectra and the principle of effective impedance matching, analyze the electric field distribution image of the xoy plane based on the principle of surface plasmon resonance, we have proved that it conforms to the classical physical theory and expounded the reason why the absorption peaks were formed. The comparison of different graphene patterns has confirmed the superiority of this structure. By changing the relaxation time and Fermi level of graphene, the tunability of the absorber structure has been verified. Changing the incident angle has proved its insensitivity to the polarization angle (0° - 50°). Finally, by calculating and comparing the figure of merit (FOM) and the sensitivity (S), it is shown that this structure has significant sensitivity and excellent application ability and value. We firmly believe that our absorber can be well applied in high-sensitivity sensors, filters and detectors, and can contribute to fields such as photoelectric detection, optical communication and photoelectric sensing.

FamLink2 - A comprehensive tool for likelihood computations in pedigrees analyses involving linked DNA markers accounting for genotype uncertainties

There is an increasing demand for software that can handle an arbitrary number of linked markers in forensic genetics; primarily with application to inference of relationships and direct matching but also in applications such as ancestry inference and mixture interpretation. With the emergence of sequencing technologies, denser sets of SNP markers are generated and analyzed. Additionally, sequence data of low quality and quantity DNA generate uncertainty about the underlying true genotype. We provide an efficient implementation of a general model for pedigree likelihood computations with genetic marker data using a three-layered approach. The top and first layer is the population model where allele frequencies and population substructure are accounted for. The second layer is the inheritance model which efficiently handles linked markers using an IBD model. The third and bottom layer is the observational level where we model the likelihood of the true genotype given underlying reads as well as parameters for errors.We exemplify the utility of our implementation as well as provide validation according to guidelines established by the ISFG using a combination of two published SNP panels. We demonstrate that computations are feasible for panels encompassing 10,000 markers and we argue that, due to the properties of the underlying algorithm, extending the number of markers will result in a linear increase in computation time. In addition we study the impact of parameters used in our model and suggest some guidelines pertaining to their values. The results demonstrate that a probabilistic model for low coverage sequence read data is needed instead of relying on an a threshold based genotype and applying our general model for inference of relationships on a real case can be superior, i.e. higher information content, to other methods relying on either fixed genotypes with low quality sequence data or simple pair wise relationship tests.In summary, the implementation, FamLink2 (freely available at https://famlink.se), can jointly handle genetic linkage, genotype uncertainty and population substructure for an arbitrary pedigree with data for any number of individuals. Whereas the current study will focus on calculations disregarding mutations, FamLink2 has the ability to model mutations for certain built-in pedigrees.

Direct Writing of graphene/graphitic foam through picosecond pulsed laser-induced transformation of soluble polyimide suspension

We report the direct writing of graphene/graphitic foam with high electrical conductivity using laser-induced-transformation of polyimide (PI) resin films on glass surfaces. Raman spectroscopy of the treated surfaces indicated that average laser power irradiation between 900-1500 kW/cm2 transformed the PI film into a few layered graphene-dominated film, and the increase in irradiation power above 1500 kW/cm2 led to the formation of graphitic (multilayered graphene) material. The electrical conductivity of the transformed film was between 5800±750 S/m (lower power irradiation) and 1250±300 S/m (higher laser power irradiation). SEM imaging showed that the transformed material has a closed cell foam morphology enclosed between the smooth top and bottom layers. The results indicate that heat treatment of the polyimide suspension films, and subsequent ultra-short, pulsed laser irradiation resulted in a closed-cell graphene/graphitic foam with high electrical conductivity. The pore aspect ratio, density, and film conductivity are used to estimate the conductivity of the solid phases in the laser-treated films at different powers. Laser-induced transformation of the PI suspension into graphene/graphitic foam is conducive to additive manufacturing and may enable the direct printing of graphitic foam-based three-dimensional components.

Parametric Analysis of Indium Gallium Arsenide Wafer-based Thin Body (5 nm) Double-gate MOSFETs for Hybrid RF Applications.

The electrical behavior of a high-performance Indium Gallium Arsenide (In- GaAs) wafer-based n-type Double-Gate (DG) MOSFET with a gate length (LG1= LG2) of 2 nm was analyzed. The relationship of channel length, gate length, top and bottom gate oxide layer thickness, a gate oxide material, and the rectangular wafer with upgraded structural characteristics and the parameters, such as switch current ratio (ION/IOFF) and transconductance (Gm) was analyzed for hybrid RF applications. This work was carried out at 300 K utilizing a Non-Equilibrium Green Function (NEGF) mechanism for the proposed DG MOSFET architecture with La2O3 (EOT=1 nm) as gate dielectric oxide and source-drain device length (LSD) of 45 nm. It resulted in a maximum drain current (IDmax) of 4.52 mA, where the drain-source voltage (VDS) varied between 0 V and 0.5 V at the fixed gate to source voltage (VGS) = 0.5 V. The ON current(ION), leakage current (IOFF), and (ION/IOFF) switching current ratios of 1.56 mA, 8.49Í10-6 μA, and 18.3Í107 μA were obtained when the gate to source voltage (VGS) varied between 0 and 0.5 V at fixed drain-source voltage (VDS)=0.5V. The simulated result showed the values of maximum current density (Jmax), one and twodimensional electron density (N1D and N2D), electron mobility (μn), transconductance (Gm), and Subthreshold Slope (SS) are 52.4 μA/m2, 3.6Í107 cm-1, 11.36Í1012 cm-2, 1417 cm2V-1S-1, 3140 μS/μm, and 178 mV/dec, respectively. The Fermi-Dirac statistics were employed to limit the charge distribution of holes and electrons at a semiconductor-insulator interface. The flat-band voltage (VFB) of - 0.45 V for the fixed threshold voltage greatly impacted the breakdown voltage. The results were obtained by applying carriers to the channels with the (001) axis perpendicular to the gate oxide. The sub-band energy profile and electron density were well implemented and derived using the Non-Equilibrium Green's Function (NEGF) formalism. Further, a few advantages of the proposed heterostructure-based DG MOSFET structure over the other structures were observed. This proposed patent design, with a reduction in the leakage current characteristics, is mainly suitable for advanced Silicon-based solid-state CMOS devices, Microelectronics, Nanotechnologies, and future-generation device applications.

Microstructure characterization of plasma electrolytic oxidation coating on Hf-Nb-Ta-Zr high entropy alloy

The morphology, composition, and microstructure of plasma electrolytic oxidation (PEO) coating on Hf-Nb-Ta-Zr high entropy alloy (HEA) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, glow discharge optical emission spectroscopy (GDOES) and transmission electron microscopy (TEM). The formation mechanism of PEO coating was analyzed. It was found that a dense PEO coating of ~4 μm thick on the HEA surface was formed, which consisted of tetragonal and monoclinic ZrO2 phases, tetragonal and monoclinic HfO2 phases, Nb2O5 and Ta2O5 phases. The PEO coating from the alloy substrate to the surface contained five distinctive layers: amorphous barrier layer, nanocrystalline layer, columnar grain layer, amorphous outer layer, and top porous layer. Their formation was ascribed to the different cooling rates of the melt in the different depths of the discharge channel across the coating. Meanwhile, the formation of an amorphous barrier layer near the HEA substrate was also related to the mutual migration and diffusion of Hf4+, Nb5+, Ta5+, Zr4+, and O2− besides the rapid cooling of melt in the bottom of the discharge channel. The columnar grains of ~70 nm wide were mainly composed of the monoclinic ZrO2 and monoclinic HfO2 phases, but both the amorphous layers enrich the Ta and Nb elements. It was believed that the high-content Ta and Nb in the HEA enhanced the formation of the amorphous layers.