Transition Layer Research Articles

Simulations of Infrared Reflectivity and Transmission Phonon Spectra for Undoped and Doped GeC/Si (001).

Exploring the phonon characteristics of novel group-IV binary XC (X = Si, Ge, Sn) carbides and their polymorphs has recently gained considerable scientific/technological interest as promising alternatives to Si for high-temperature, high-power, optoelectronic, gas-sensing, and photovoltaic applications. Historically, the effects of phonons on materials were considered to be a hindrance. However, modern research has confirmed that the coupling of phonons in solids initiates excitations, causing several impacts on their thermal, dielectric, and electronic properties. These studies have motivated many scientists to design low-dimensional heterostructures and investigate their lattice dynamical properties. Proper simulation/characterization of phonons in XC materials and ultrathin epilayers has been challenging. Achieving the high crystalline quality of heteroepitaxial multilayer films on different substrates with flat surfaces, intra-wafer, and wafer-to-wafer uniformity is not only inspiring but crucial for their use as functional components to boost the performance of different nano-optoelectronic devices. Despite many efforts in growing strained zinc-blende (zb) GeC/Si (001) epifilms, no IR measurements exist to monitor the effects of surface roughness on spectral interference fringes. Here, we emphasize the importance of infrared reflectivity Rω and transmission Tω spectroscopy at near normal θi = 0 and oblique θi ≠ 0 incidence (Berreman effect) for comprehending the phonon characteristics of both undoped and doped GeC/Si (001) epilayers. Methodical simulations of Rω and Tω revealing atypical fringe contrasts in ultrathin GeC/Si are linked to the conducting transition layer and/or surface roughness. This research provided strong perspectives that the Berreman effect can complement Raman scattering spectroscopy for allowing the identification of longitudinal optical ωLO phonons, transverse optical ωTO phonons, and LO-phonon-plasmon coupled ωLPP+ modes, respectively.

Investigation on the machining mechanism of silicon modified by Au ion irradiation in elliptical vibration diamond cutting

Single-crystal silicon (Si) has important applications in semiconductor, infrared optics, and photovoltaic industries. However, Si is difficult to be machined precisely due to its hard and brittle characteristics. Ion irradiation is proposed as an advanced technology to reduce the hardness and brittleness for a covalent crystal, which is beneficial for the ductile machining process. In the present research, the simulation and experimental investigation of Si with Au ion irradiation were carried out firstly. As following, the grooving experiment is carried out by elliptical vibration cutting (EVC). the machining performance is compared with ordinary cutting (OC) and the material removal mechanism is elaborated. The critical depth of cut for brittle-to-ductile transition is nearly 7 times higher by EVC compared to OC. Initial verification of material modification was conducted by Raman spectra and cutting microgrooves. Finally, the ion irradiation damage mechanism and amorphous Si (a-Si)/crystalline Si (c-Si) machining deformation mechanism were analyzed in detail by transmission electron microscopy. The irradiated sample contains an amorphous layer of 1050 nm, a transition layer containing dislocations and nanocrystals, and a fully crystalline layer. During machining a-Si/c-Si interface, the machining defects in the amorphous layer will first absorb the energy and ensure that the crystalline layer does not produce subsurface damage. In summary, ion-irradiated Si can be achieved in the amorphous region at any depth position and the substrate ductile machining without subsurface damage generation by EVC.

Revealing the degradation pathways of layered Li-rich oxide cathodes.

Layered lithium-rich transition metal oxides are promising cathode candidates for high-energy-density lithium batteries due to the redox contributions from transition metal cations and oxygen anions. However, their practical application is hindered by gradual capacity fading and voltage decay. Although oxygen loss and phase transformation are recognized as primary factors, the structural deterioration, chemical rearrangement, kinetic and thermodynamic effects remain unclear. Here we integrate analysis of morphological, structural and oxidation state evolution from individual atoms to secondary particles. By performing nanoscale to microscale characterizations, distinct structural change pathways associated with intraparticle heterogeneous reactions are identified. The high level of oxygen defects formed throughout the particle by slow electrochemical activation triggers progressive phase transformation and the formation of nanovoids. Ultrafast lithium (de)intercalation leads to oxygen-distortion-dominated lattice displacement, transition metal ion dissolution and lithium site variation. These inhomogeneous and irreversible structural changes are responsible for the low initial Coulombic efficiency, and ongoing particle cracking and expansion in the subsequent cycles.

Microstructure, interfacial reaction behavior, and mechanical properties of Ti3AlC2 reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti3AlC2 at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated. The results show that the addition of 3.0 wt.% Ti3AlC2 refines the average grain size of α(Al) in the composite by 50.1% compared to Al6061 alloy. Morphological analyses indicate that an in-situ Al3Ti transition layer of ~180 nm in thickness is generated around the edge of Ti3AlC2 at 720 °C, forming a well-bonded Al−Al3Ti interface. At this processing temperature, the ultimate tensile strength of Al6061−3.0 wt.%Ti3AlC2 composite is 199.2 MPa, an improvement of 41.5% over the Al6061 matrix. Mechanism analyses further elucidate that 720 °C is favourable for forming the nano-sized transition layer at the Ti3AlC2 edges. And, the thermal mismatch strengthening plays a dominant role in this state, with a strengthening contribution of about 74.8%.

Inner Transition Layer in Solutions of the Discrete Painlevé II Equation

Inner Transition Layer in Solutions of the Discrete Painlevé II Equation

Development of electrode and electrolyte materials for solid-state batteries based on Li1.3Al0.3Ti1.7(PO4)3

The dependence of the electrochemical characteristics of a layered cathode material containing LiNi0.5Mn0.3Co0.2O2 on the method for applying a protective layer of nanoparticles of the lithium-conducting material Li1.3Al0.3Ti1.7(PO4)3 with a NASICON structure to its surface has been studied. The surface modification has been found to improve the capacity retention in prolonged charge/discharge cycling (up to 15%) and to allow fast charge/discharge processes. The possibility of using a composite electrolyte consisting of a porous ceramic matrix of aluminum-substituted lithium titanium phosphate Li1.3Al0.3Ti1.7(PO4)3 with a transition layer of liquid electrolyte LP-71 has been shown. The use of a thick composite solid electrolyte results in a slight reduction (∼5–7 mAh g−1) in initial capacity compared to laboratory cells with the widely used Celgard 2400 separator impregnated with liquid electrolyte. Laboratory cells assembled with a composite electrolyte showed higher stability during charge/discharge cycling: after 80 deep charge/discharge cycles, the capacity reduction was ∼12% for cells with a composite electrolyte, while for the reference cell it was ∼23%.

Gradient coating increases the temperature resistance of ceramic fiber fabric

Ceramic fiber fabric embrittlement at 1200 °C, resulting in poor tensile strength. In order to improve the tensile strength of ceramic fiber fabric after high temperature heat treatment. In this study, gradient coating is sprayed on the surface of ceramic fiber fabric by adjusting the composition of two kinds of slurry. The structure and property of ceramic fiber fabric with different coating are thoroughly investigated. The pore size of Al2O3-SiC porous transition layer is less than 1 μm, which limits the infiltration of the high-emission coating into the ceramic fiber fabric. A weak bond is formed between the ceramic fiber fabric and the porous transition layer, which induces the crack deflection. The flexibility of ceramic fiber fabric after heat treatment is significantly improved. After being heated by butane flame at 1200 °C for 20 min, the tensile strength of fiber fabric with gradient coating is double that of raw ceramic fiber fabric. The silicone cross-links to form a network, which improves the bonding strength of the gradient coating. Due to the high emissivity and low thermal conductivity of the gradient coating, the temperature of the ceramic fiber fabric is below 900 °C when heated by the butane flame.

In-Situ Turbulence and Particulate Measurements in Support of the BOLT II Flight Experiment

The results of a measurement campaign to characterize the freestream atmospheric turbulence intensity and particulate concentrations experienced by the Boundary Layer Transition (BOLT) II flight experiment are described. These measurements were obtained using custom high-altitude balloon-borne payloads using a modified commercial optical particle counter and a high-bandwidth coldwire thermometer and hotwire anemometer, designed for low cost and light weight, with telemetered data so that physical payload recovery is not necessary. Sixteen flights were carried out over a 10-day campaign, with viable data returned from 14 flights, including four centered on the BOLT II launch with 1-h cadence. Turbulence and particulate measurements are shown vs altitude for all 14 data sets, along with statistics derived from the measurements, quantifying the BOLT II atmospheric environment for use in assessing the impact of these freestream disturbances on the hypersonic-vehicle boundary layer.

Enhancing acid corrosion resistance in alkaline-activated materials with water treatment residue and blast-furnace slag

This study investigates the acid corrosion resistance of an alkaline-activated material (AAM) composed of ground granulated blast-furnace slag (GGBFS) and water treatment residue (WTR) as precursors. WTR, a byproduct of the drinking water treatment process rich in aluminium and silicon, proves to be a suitable precursor for AAM after cost-effective pre-treatment involving calcination and grinding. As its low-Ca content and aluminosilicate nature of the treated WTR, the AAM incorporating WTR exhibits significant potential for improving acid resistance. This is attributed to the formation of less acid-reactive N-A-S-H gels than C-A-S-H gels in high-Ca AAMs, indicating its applicability in concrete sewage pipes where microbiologically generated acid corrosion is prevalent. In the paper, a comprehensive analysis, including mechanical performance, ion leaching behaviour, and microstructural characteristics, was conducted on mortar samples containing varying WTR/GGBFS ratios before and after exposure to sulfuric acid. Incorporating WTR up to 40 % effectively reduced acid-induced strength loss compared to neat-GGBFS AAM. The obtained results reveal that high-Ca AAMs facilitate gypsum formation during acid attack, leading to mechanical degradation. The inclusion of WTR induces a Si-rich transition layer between the corroded and intact matrix, mitigating sulfate diffusion. The release of aluminium from WTR promotes secondary precipitation of aluminosilicate, beneficially increasing the thickness of the transition layer. This thicker transition layer in the higher WTR samples is advantageous in reducing the likelihood of cracks and reducing the sulfate transportation into the intact matrix.

A new method for joining Incoloy825/X65 composite plate by laser and CMT welding

Incoloy825/X65 composite plate had good application in the submarine transporting pipelines due to combination of the high resistance to Cl− corrosion and preferred mechanical properties. But the enrollment of Fe into Ni layer deteriorated the corrosion resistance in welding the transition layer of composite plate. In view of this, the paper respectively adopted the laser welding on the Ni layer without filler metal and then the swing arc CMT welding with steel filler metal as a transition in order to inhibit the Fe into Ni layer. The results showed the laser welding bead on Ni layer with uniform and fine γ microstructure ensured the better corrosion resistance. The CMT welding controlled the dilution rate under 6 % through optimizing the welding speed and swing frequency of arc. Finally, the tensile strength of transition weld was up to 500 MPa surpassing the base metal of 490 MPa. The clad bead with charge transfer resistance of 756 kΩ·cm2 satisfied general submarine pipeline anti-corrosion requirement.

Sulfur vacancy riched pure 2H phase VS2 for efficient electrocatalytic hydrogen evolution

Vanadium disulfide (VS2), a typical metallic layered transition metal chalcogenide (TMC), has been widely concerned for its high electrical conductivity and reactivity in electrochemical energy storage and conversion applications. The 2H phase VS2 is expected to exhibit high electrocatalytic activity and be more stable for hydrogen evolution reaction (HER) than the 1T phase structure. But at present, there still lacks a facile method to prepare pure 2H phase VS2. Herein, we successfully prepared pure 2H–VS2 through a simple one-step low-temperature hydrothermal method. We have investigated the effect of the hydrothermal reaction conditions (including the proportion of raw materials and hydrothermal reaction temperatures) on the phase composition and microstructure. Under the optimal condition of 140°C-24 h with a vanadium sulfur ratio of 1:5, a nano-flower-like 2H–VS2 material with high crystallinity and rich sulfur vacancy defects was obtained. Leveraging these structural advantages, as a demonstration, the product exhibits excellent electrocatalytic HER activity (with η10 of 181 mV, Tafel slope of 52 mV dec−1, and J0 of 67.9 × 10−3 mA cm−2) and stability (it can continuously produce hydrogen for 20 h at a current density of 50 mA cm−2 with ultra-small increased potential of less than 5 mV). This work provides a new way for constructing atomic vacancy defects in layered TMCs for efficient electrocatalysis and is also expected to promote the research of the basic properties of high phase purity TMCs.

Electrodeposition transition layer induced Cu/PPr hybrids

The high-performance metal-plastic hybrids have been widely applied in lightweight manufacturing. In this work, microstructures were prepared on the copper plate (Cu) surface using an electrodeposition process. Afterward, this microstructure was used to join with the pentatricopeptide repeats (PPr) to obtain Cu/PPr hybrids. The effect of electrodeposition process parameters on surface morphology was explored. The polyacrylic acid (PAA) content had the most significant effect on the surface morphology, and an increase in PAA content resulted in a shift from a lamellar to a granular structure. When the PAA content was 5 g/L, electrodeposition time was 300 s and the current density was 25 mA/cm2, the transition layer on the Cu surface was optimized, the roughness reached 164 nm, and the contact angle decreased to 2.41°. Meanwhile, the effect of molding temperature on the strength of the hybrids was explored, and the joining strength of the hybrids reached a maximum of 13.45 MPa when the temperature was 270 °C, which is 73.5 % of the strength of the PPr matrix. Further elevation of the molding temperature failed in the transition layer due to oxidation. The joining strength of the hybrids relies solely on the mechanical interlocking ability of the interface. The Cu/PPr hybrids provide design ideas for the practical production of copper-plastic composite pipes.

Design, fabrication, and hydrogen blocking performance of alumina/zirconia functional gradient coatings

When electrophoretic deposition (EPD) is employed for fabricating alumina (Al2O3)-based hydrogen barrier coatings, it becomes customary to enhance the adhesion strength by subjecting the deposited coating to high-temperature annealing. In this study, a functionally-graded Al2O3/ZrO2 coating was designed by using the thermal stress module of Ansys software. The influence of different gradient composition distribution indices, number of layers, and layer thickness on the distribution of thermal stress was systematically investigated by simulation. Based on simulation results, the gradient parameters of the functionally-graded coating were determined as follows: a transition layer with three layers, each with a thickness of 0.13 mm; the first layer consisted of Al2O3 to ZrO2 ratio of 1:3, the second layer with a ratio of 1:1, and the third layer with a ratio of 3:1. Subsequently, the process parameters for EPD of Al2O3 coating were optimized via experimental exploration. Under conditions of deposition time of 120 s, deposition voltage of 60 V, Al2O3 concentration of 8 g L−1 in the electrophoretic solution, and magnesium chloride hexahydrate concentration of 0.6 g L−1, the as-fabricated Al2O3 coating exhibited optimal hydrogen barrier performance. Finally, different proportions of ZrO2 were sequentially incorporated into the prepared Al2O3 coating to form functionally-graded materials (FGM). Thermal cycling experiments showed that the Al2O3 coating with added ZrO2 exhibited better stability at high temperatures. Regarding hydrogen barrier performance, the functionally-graded coating outperformed the non-functionally-graded coating.

Electric-magnetic dual-gradient structure design of thin MXene/Fe3O4 films for absorption-dominated electromagnetic interference shielding

The challenge of achieving high-performance electromagnetic interference (EMI) shielding films, which focuses on electromagnetic waves absorption while maintaining thin thickness, is a crucial endeavor in contemporary electronic device advancement. In this study, we have successfully engineered hybrid films based on MXene nanosheets and Fe3O4 nanoparticles, featuring intricate electric–magnetic dual-gradient structures. Through the collaborative influence of a unique dual-gradient structure equipped with transition and reflection layers, these hybrid films demonstrate favorable impedance matching, abundant loss mechanisms (Ohmic loss, interfacial polarization and magnetic loss), and an “absorb-reflect-reabsorb” process to achieve absorption-dominated EMI shielding capability. Compared with the single conductive gradient structure, the dual-gradient structure effectively enhances the absorption intensity per unit thickness, and thus reduces the thickness of the film. The optimized film demonstrates a remarkable EMI shielding effectiveness (SE) of 49.98 dB alongside an enhanced absorption coefficient (A) of 0.51 with a thickness of only 180 μm. The thin films with a dual-gradient structure hold promise for crafting absorption-dominated electromagnetic shielding materials, highlighting the potential for advanced electromagnetic protection solutions.

A mechanical TiAl/TiAlN multinanolayer coating model based on microstructural analysis and nanoindentation

A finite element model reproducing the mechanical behaviour during nanoindentation tests on Ti0.67Al0.33/Ti0.54Al0.46N multilayer coatings was developed. Coatings with two different nanoperiods (10 and 50 nm) were deposited by radio-frequency magnetron sputtering from a single sintered titanium/aluminium target using the reactive gas pulsing process. X-ray diffraction and transmission electron microscopy confirmed the multilayer stacking of the coatings. The finite element models of coatings with these two stacking periods were built considering successive hypotheses: equal thicknesses for metal and nitride nanolayers stacked without transition layer, equal thicknesses stacking with a transition layer between each metal and nitride nanolayer and finally imbalanced thicknesses stacking with a transition layer. The elastic and plastic properties of the stacked nanolayers were determined on thick monolithic coatings of metal and nitride using indentation testing and the finite element model updating method respectively. The elastic-plastic properties of the interface were introduced in the multilayer model as a rule of mixtures of the metal and nitride properties using two hypotheses: parallel or serial. For 50 nm-period film, the interface has a negligible effect on the overall indentation response. On the other hand, for the 10 nm period, the imbalanced stacking model with precise knowledge of the transition layer thickness obtained by N K-edge electron energy loss spectroscopy is required to reproduce the experimental indentation curve. Compared to classical analytical models accounting for hardness, not only the hardnesses but also the indentation moduli appear to be well predicted and evaluated in this work.

Microstructure characterization and high-temperature wear mechanism of high-entropy alloy matrix composite coating fabricated by laser cladding

The development of diecasting technology requires hot die steels with high-temperature resistance. In this study, a high-entropy alloy (HEA) was combined with ceramic particles to generate a CoCrFeNiMo0.2Nb0.2/WC composite coating via laser cladding. The coating consisted of a face-centered cubic (FCC) matrix with unmelted WC particles, eutectics and nanoscale (Mo)NbC phases. With the strong lattice distortion caused by the sequestration of W atoms, a nanoscale amorphous layer existed between the Laves and HEA matrix phases. A transition layer with the same structure as the Laves phase was facilitated between the WC particles and the HEA matrix. Due to the hard phases in the HEA matrix and their interfaces, the composite coating with a high proportion of WC exhibited excellent wear resistance under high-temperature dry friction conditions. When the WC was 60 wt%, a minimum wear rate reached to 0.74 × 10−5 mm3/(N·m) at 600 ℃ and 1.46 × 10−5 mm3/(N·m) at 800 ℃. The destruction pattern of the composite coating at 600 ∼ 800 °C was due to the interaction of the adhesive, oxidative and abrasive wear. The composite coatings fabricated in this study provide a route to enhance the high-temperature wear resistance of die-casting molds.

Underwater carbonation of alkali-activated slag pastes

Carbonation of alkali-activated slag (AAS) materials has been primarily concerned in atmospheres with gaseous CO2. This study, by contrast, highlights that AAS pastes would also be carbonated under tap water immersion. Calcite is the main CO2-bear phase in both sodium hydroxide- and sodium silicate-activated AAS pastes, and the paste pre-cured for a longer curing period shows more severe carbonation. Additionally, calcium carbonate can densify the deteriorated microstructure of sodium hydroxide-activated paste caused by long-term leaching. The indentation modulus of pastes subjected to tap water immersion is higher than those under deionized water immersion. The uptake of CO32- by hydrotalcite (Ht) and gels is also detected, resulting in the formation of Ht-CO3 and decalcification of gels. Due to the synergistic effect of leaching and carbonation, a characteristic layered distribution of pastes close to the exposure front is observed, comprising the carbonated layer, transitional (carbonated + leached) layer, and leached layer, progressing from the outermost to the inner regions. Eventually, the kinetics of underwater carbonation, as well as the discrepancy between dry and underwater carbonation, is revealed.

Changes of epidermal proteins immunolocalization in the corneous layer from embryonic to definitive avian beak

The process of keratinization and cornification in the developing beak has been studied through immunofluorescence and immunogold electron microscopy in chick and zebrafinch embryos. After the curved beak anlagen appears at the tip of the maxillar bone, 5–8 layers of embryonic epidermis are generated from the basal layer of the epidermis. These cells are weakly immunoabeled for IFKs (Intermediate Filament Keratins) and more intensely for scaffoldin, a protein of the EDC (Epidermal Differentiation Complex) involved in the soft keratinization of the embryonic epidermis. Immunolabeling for CBPs (Corneous Beta Proteins) is visible in the transitional embryonic layers that are temporarily generated between the embryonic and definitive beak epidermis. The electron microscope reveals that intermediate layers contain immunolabeled periderm granules for scaffoldin mixed with bundles of corneous material immunolabeled for CBPs. Intense CBPs labeling occurs in the compacting corneous bundles of beta-keratinocytes in the definitive beak while scaffolding labeling disappears. The embryonic epidermis is sloughed before hatching. Sox (Sulfhydryl Oxidase) immunolabeling reveals that the enzyme is almost absent in embryonic layers but is present in transitional and definitive beta-keratinocytes. This indicates the formation of cross-linked disulfide bonds in the definitive corneous layer of the beak. Some calcium precipitation, suggested from von Kossa staining, occurs in the corneous layers only on the 18th day of development in the chick, in preparation for hatching.

Influence of mixed dimples on aerodynamic performance of high-load compressor cascade

In this study, the effect of mixed dimples on the aerodynamic performance of a high-load compressor cascade, named National Advisory Committee for Aeronautics 65-K48, at different attack angles was numerically and experimentally investigated. Mixed dimples with four columns and eight rows were arranged at 10% to 32% of the chord length of the half-blade height. The performance parameters of the cascade outlet section and vortex structure inside the cascade were exploited. The results reveal that the boundary layer is disturbed, and the boundary layer transition occurs ahead of time, induced by the mixed dimples. The anti-separation ability of the fluid was enhanced, and the separation bubbles on the suction surface were eliminated. Meanwhile, the lateral secondary flow was inhibited, and the intensities of the passage and concentrated shedding vortices were consequently reduced. Compared with the prototype cascade, the total pressure loss of the dimpled cascade at all attack angles was reduced. The total pressure loss can be reduced by nearly 20% at –9°.

Microstructure and mechanical properties of Mg/Al laminated composite: The effect of transition layer thickness

This study successfully prepared Mg/Al laminated composites with various thicknesses of pure Cu transition layer via extrusion, overcoming the challenge of forming of Mg/Al composite plates through stacked extrusion technology. The effects of varying Cu layer thicknesses on the microstructure, mechanical properties, and fracture behaviors were systematically investigated. Microstructure analysis showed an uneven Cu layer distribution at the interface of the composite plate, characterized by alternating thicker and thinner layers, which stemmed from the low fluidity of pure Cu during extrusion. Although the thicker Cu layer significantly inhibited the diffusion of Mg and Al elements, there was still a significant enrichment of Mg-Al intermetallic compounds (IMCs) in the thinner Cu layer. There hard and brittle IMCs caused cracking during the deformation process. Increasing Cu layer thickness did not significantly affect the microstructure but contributed to the decrease of strength owing to increased stress concentration. Moreover, the thicker Cu layer exacerbated its uneven distribution and Mg-Al IMCs enrichment at the interface, resulting in a pattern of first decreasing and then increasing elongation and shear strength of the laminated composite.