Surface Layer Research Articles (Page 1)

The article proposes a model of friction of graphite, which is a stack of graphene sheets. The model is based on the thickness of the surface layer, which for graphite is 3 monolayers of graphene. Large internal stresses arise in the surface layer, leading to the occurrence of dislocations and nanocracks. The friction process can be described as a process of elastic-plastic deformation of the surface layer. For graphene, an important role in friction on graphite is played by the nanolayer, which is a quantum nanostructure. Graphene friction occurs in a stepwise manner, taking into account the Tamm states of the surface. It is shown that friction is accompanied by oscillatory and dissipative processes, the formation of a turbulent fragment, and self-organization in the form of Benard cells. A formula has been obtained that can serve as a criterion for selecting an antifriction coating made of graphene or its composites. The terahertz radiation we predicted in graphene refers to surface plasmon-polaritons (plasmons). The most promising approach to creating effective terahertz radiation detectors is the use of nanostructures as a sensitive element. These nanostructures include graphene and graphene-like materials. The proposed model opens a new approach for theoretical and experimental research of processes in nanotribology.

Thanks to JWST, a plethora of species in planet-forming disks around very low mass stars such as C2H2 C6H6 C4H2 CH3 etc. are being discovered. The column densities of these species retrieved from 0D slab models are very large (e.g. of the order of 10^20,cm^-2). This indicates a carbon-dominated chemistry in a gas with a high C/O ratio. The disk around 2MASS-J1605321-1993159 (M4.5) is one such source showing a molecular pseudo-continuum of C2H2 . Notably, two oxygen-bearing molecules, CO and CO2 are also detected in this source. We aim to take the next step beyond 0D slab models to interpret the spectrum. We examine whether 2D thermo-chemical disk models can produce the large inferred column densities of C2H2 in the inner regions of the disk and produce a pseudo-continuum in the mid-IR spectrum. We also seek to constrain whether the depletion of oxygen or the enrichment of carbon causes the high C/O ratio triggering a carbon-dominated chemistry. We utilised the radiative thermo-chemical disk model P RO D I M O to identify a disk structure that is capable of producing the observed molecular emission of species such as CO CO2 C2H2 and H2O simultaneously. The spectrum was generated using the fast line tracer FLiTs. We derived the gas temperature łangle T ̊angle, column density łangle log_ ̊m N̊angle, and the emitting area łangle r_ - r_ ̊angle for these molecules from the 2D disk model and compared them to the parameters retrieved originally from 0D slab models. We used the different effect that changing the O or C abundance has on CO and C2H2 respectively to discriminate between O depletion and C enhancement. We find that a disk structure characterised by the presence of a gap can best explain the observations. The inner disk is strongly depleted in dust, especially small grains ($<5,μm), and elemental oxygen, leading to a large C/O ratio. This is required to produce a molecular pseudo-continuum of C2H2 and at the same time a relatively weak CO emission. The P- and R-branch of C2H2 probe deeper layers of the disk whereas the Q-branch probes mostly the surface layers. The combined emission of CO and CO2 puts strong constraints on the gap's location (0.1-0.5,au) given a disk gas mass. We also report a new detection of the CO ν$= 2̊ightarrow1 transition in the JWST spectrum. Two-dimensional thermo-chemical disk models are able to produce the observed molecular pseudo-continuum of C2H2 . We find that the combination of different species emission in the JWST spectra can be used to discriminate between different scenarios such as O-depletion, C-enhancement or both, and offers the potential to extract spatial substructure at scales smaller than ∼,1,au.

Cyperus rotundus is one of the sedges that is widely considered to be the world’s worst weed and its control is troublesome due to a variety of factors. The objective of this research was to analyze the chemical composition as well as its morphology on leaves. It is important to know the barrier for absorption and translocation of foliar applied chemicals to control this weed effectively. Microscopic and SEM analysis revealed a thick epicuticular layer on the adaxial surface and thin layer on the abaxial surface, heterogenous wax coverage. While, GC-MS profiling identified major chemical constituents including pyrans, fatty acids, sesquiterpenes and nitrogenous compounds. Wax content ranged from 72.62 to 103.92 µg cm-2. that contributed to the formation of a nearly impermeable membrane in leaves that aids stress tolerance and act as a transport barrier for foliar applied chemicals. Formulation of glyphosate with appropriate surfactants, particularly CTAB at higher ratios (1:2) of herbicide-to-surfactant, significantly improved translocation to primary, secondary and tertiary tubers. The findings highlight the critical role of cuticular wax composition in herbicide resistance and demonstrate the potential of adjuvant selection and usage for optimal herbicide delivery as well as development of more effective weed control measures against C. rotundus and similar perennial weed species.

Abstract The realisation of the kilogram at PTB is based on the established x-ray crystal density method (XRCD). This method is based on a high-precision characterisation of spheres of isotope-enriched 28 Si. The crystal and material parameters are considered constant and do not need to be re-determined when the realisation of the kilogram is updated. Therefore, the re-determination is primarily based on new measurements of the volume and the mass of the surface layers of the 28 Si spheres. This paper presents new insights in the XRF analysis method used in the XRCD method by PTB and its effects on the volume and mass of 28 Si spheres used as primary mass standards, which provides a basis for participation in the key comparison CCM.M-K8.2024. In the key comparisons CCM.M-K8 from 2019, 2021 and 2024, the definition of the kilogram was realised using the AVO28-S8c and Si28kg01a spheres, as outlined in this document. When applying the new model for the spectral components of the XRF spectrum, realisation results of both spheres show an average mass increase of 13.5 µg.

In this work, it is proposed that the thermophysical properties of the composite material can be improved by modifying the binder with nanoscale additives. It is proved that the introduction of nanoparticles into oligomers at concentrations around 1% increases the thermal conductivity by 1.3–1.6 times. Macrosized particles were also used for comparison. It was found that this effect is achieved due to a decrease in thermal resistance at the interface in result of the formation of outer surface layers. Such modified binders are effective for creating various materials and coatings based on them with a wide range of characteristics.

Abstract. Understanding stratospheric intrusion (SI) is crucial for elucidating atmospheric complexities and improving strategies to mitigate surface ozone (O3) pollution. This study investigates a deep trough-induced SI event in China from 10 to 13 June 2013, based on ozonesondes from Beijing, Changchun, and Hong Kong, and validated O3 reanalysis products. Ozonesondes from Beijing indicated notable upper-level secondary O3 peaks (> 400 ppbv) since 11 June. Tropospheric sub-high O3 layers were observed in Changchun on 12 June (> 120 ppbv) and Hong Kong on 13 June (> 80 ppbv). Nationwide surface measurements recorded severe O3 pollution (> 100 ppbv) from western plateaus to eastern plains over China. Together, these observations suggest a widespread influence of stratospheric O3 intrusion. Further, the ozonesonde-validated EAC4 reanalysis reproduced the fine-scale SI structure (O3-rich “tongue”), in turn well explaining the secondary O3 peaks and sub-high O3 layers in ozonesonde observations. The O3-rich “tongue” swept through the Tibetan Plateau on 10 June, triggering extreme O3 pollution with a stratospheric contribution up to 30 ppbv (> 30 %). With the trough's eastward movement, the O3-rich “tongue” penetrated into the lower troposphere of eastern China, and then entrained into the surface layer, exacerbating surface O3 pollution occurred in eastern China on 13 June, with a stratospheric O3 contribution of 3–15 ppbv (2 %–10 %). This research underscores the importance of multi-site ozonesondes in understanding stratospheric O3 intrusions and the potential of the publicly available EAC4 reanalysis in multiyear SI analyses.

The long-term service of semi-rigid base asphalt pavements often leads to the formation of interlayer voids, a distress mode that is more severe than conventional debonding. This study employed a continuous-discrete coupled model to systematically investigate the influence of void width, void height, and material modulus on pavement mechanical behavior. The results indicate that increasing the void width markedly elevates interlayer shear stress and induces a transverse tensile stress zone at the bottom of the overlying layer, promoting simultaneous crack propagation in both transverse and upward directions. Conversely, as void height increases, the interlayer shear stress and the tensile stress zone diminish, allowing the pavement structure to settle into a new, relatively stable equilibrium state. Additionally, increasing the modulus of the lower surface layer effectively reduces both transverse tensile and shear stresses, thereby mitigating further void deterioration. These findings elucidate the complex mechanical responses induced by interlayer voids and offer theoretical guidance for improving structural design and prolonging the service life of asphalt pavements.

Road pavements are made of layers of various materials. In the case of a flexible pavement, it is a system of layers consisting of: a mineral - asphalt mixture (the upper part of the pavement), a sub - base made of an unbound mixture (the layer below the mineral - asphalt mixture) and lower layers of the pavement and the improved/unimproved subgrade. The load on the pavement causes stresses and strains in its layers. The values of strains and stresses determine its fatigue life. When designing a road pavement, the values of strains are calculated theoretically, e.g. using software based on constitutive models. The development of measurement technologies allows for an increasingly better assessment of the pavement behavior in real conditions. In particular, recent years have brought great progress in the use of fiber optic sensors to measure strains during the operation of the surface layers. The paper presents the results of tests of a flexible pavement using DOFS (Distributed Optical Fiber Sensors). The tests were carried out on a test section specially prepared for the needs of the research project.

The increasing demand for enhanced wear resistance and mechanical integrity in tooling applications has driven the development of advanced surface engineering strategies for high-alloy steels. Böhler K390 MICROCLEAN, a powder-metallurgical V–Cr–Mo–W cold work tool steel with high vanadium content, features a composite metal matrix–carbide microstructure, consisting of uniformly distributed coarse vanadium carbides and finer carbides (M7C3, M6C/MC) embedded in a ferritic matrix. This study investigated the effects of non-melting laser surface treatment (LST) applied to both as-received and bulk heat-treated K390 specimens. Microstructural characterization using SEM, EBSD, XRD, and EDX revealed the formation of a hardened surface layer comprising a structureless mixture of ultrafine-grained martensite and retained austenite, localized around vanadium carbides. Lattice parameter analysis and Williamson–Hall evaluation demonstrated increased carbon content, lattice distortion, and crystallite size reduction, contributing to high dislocation density (6.4 × 1014 to 2.6 × 1015 m−2) and enhanced hardness. Microhardness was increased by up to 160% compared to the initial state (reaching 835–887 HV20), and dry-sliding testing showed up to 3.94 times reduced volume loss and decreased friction coefficients. Wear occurred via the formation and delamination of thin oxide tribo-layers, which enhanced the wear behavior. The combined approach of bulk heat treatment followed by LST produced a graded microstructure with superior mechanical stability, offering clear advantages for extending tool life under severe contact loads in stamping and forming operations.

Abstract The use of leather in human history spans thousands of years, and the mass production of leather techniques also has a longstanding history over a century. The emergence of synthetic leather arose as a response to the market’s demand for an alternative due to a shortage of natural leather supply. However, the ongoing challenge of environmental pollution during the continuous development of synthetic leather to achieve comparable features to its natural counterparts has led the leather industry to deviate from its original goal of sustainability and environmentally friendliness, focused on “waste to worth” principle. Following the replacement of polyvinyl chloride (PVC) with polyurethane (PU) as the primary material for the surface layer in synthetic leather, waterborne polyurethane (WPU) and solvent-free polyurethane (SFPU) emerged as the principal environmentally friendly raw material for synthetic leather manufacturing. The free volume (FV) theory explains the relation between mass transfer in polymer films and increasing FV in polymer coatings, highlighting its benefit to water vapor permeability (WVP). The WVP of a synthetic leather is primarily influenced by the hydrophilicity and porous structure of the polymer coating, determined by the base fabrics and the raw polymer coating material. This paper reviews various methods for preparing porous structures to increase WVP of polymer films or coatings: chemical blowing, thermally expandable microspheres, laser drilling, hollow microspheres, surfactant-stabilized foam templates and Pickering aqueous foam templates. It also provides a concise outline of present issues and prospects in improving the breathability of synthetic leather derived from these approaches. Graphical Abstract

Silicon (Si) is typically found in low concentrations in weathered soils, and its application can benefit crop production. This study aimed to assess the dynamics of silicon in weathered soils of southern Brazil following the application of different silicon sources. The experiment followed a completely randomized design in a 4 × 5 factorial scheme, with four silicon sources (silicon oxide, potassium silicate, calcium–magnesium silicate, and Yoorin), five evaluation periods (1, 2, 3, 4, and 5 months after application), and five replicates. Silicon content was analyzed at three soil depths: 0-5, 5-10, and 10-15 cm. Data were subjected to analysis of variance and multivariate analysis. Among the sources evaluated, potassium silicate resulted in higher silicon accumulation in the surface layer, while calcium-magnesium silicate and Yoorin led to greater silicon levels in the deeper layers, indicating differences in solubility and mobility of the sources over time.

The Ni/Al2O3 interface bears the load transfer and energy dissipation, which determines the service performance of the composite materials. In this study, three distinct vacancy-defect-modified interface models (D1, D2, and D3, corresponding to vacancies in the first, second, and third layers of the Ni substrate surface, respectively) were constructed to systematically investigate the regulatory mechanism of vacancies on interfacial stability. The underlying mechanism of vacancy-enhanced interfacial stability was elucidated from both atomic-scale structural and electronic property perspectives. The results demonstrate that the D1, D2, and D3 structures increase the adhesion work of the interface by 2.0%, 6.7%, and 0.3%, respectively. This enhancement effect mainly stems from vacancy-induced atomic relaxation at the interface, which optimizes the equilibrium interfacial spacing and effectively releases residual strain energy. Further electronic structure analysis reveals a notable increase in charge density at the vacancy-modified interface (particularly in the D2 structure), indicating that vacancy defects promote charge transfer and redistribution by altering local electron distribution. More importantly, the bonding strength of the interface exhibits a positive correlation with electron orbital hybridization intensity, where stronger s-, p-, and d-orbit hybridization directly leads to a more stable interface. These findings provide atomic- and electronic-scale insights into the mechanistic role of vacancy defects in governing bonding at the Ni/Al2O3 interface.

Coatings based on the eutectic alloy Fe–TiB2–CrB2 were obtained by detonation spraying and subjected to pulsed plasma treatment. Comprehensive studies of the microstructure, phase composition, and mechanical and electrochemical properties of the coatings were carried out using SEM, TEM, and XRD methods. The initial coatings are characterized by a typical lamellar structure with interlamellar pores and defects. After pulsed plasma treatment, pronounced compaction of the surface layer, grain refinement, and sealing of interlamellar voids and cracks are observed. The thickness of the modified zone is about 15–30 μm, and the structure becomes fine-grained and more uniform. According to XRD and TEM data, the main boride phases (TiB2, CrB2) remain stable, while the intensity of γ-Fe decreases and weak Cr23C6 peaks appear, indicating phase stabilization and diffusion hardening. After treatment, the microhardness of the near-surface zone increases from ~14 GPa to 17–18 GPa, confirming the strengthening effect. Electrochemical tests showed an increase in corrosion resistance: the corrosion potential shifts to the positive side by approximately 0.15 V, and the corrosion current density decreases by almost two times. Thus, the use of pulsed plasma treatment significantly improves the density, phase stability, hardness, and corrosion resistance of Fe–TiB2–CrB2 detonation coatings, making this duplex approach promising for use in conditions of intense wear and exposure to aggressive environments.

Abstract The evening transition (ET) in the atmospheric surface layer marks the transition from a daytime convective boundary layer to a nocturnal stable layer around local sunset. Using data from multilevel turbulence towers on the east and west slopes of Granite Mountain during the MATERHORN campaign (September–November 2012), this study investigates atmospheric responses to the decay of solar forcing. To quantify slope ET dynamics and the influence of topographic shading, we compare the sunlit west slope with the earlier‐shaded east slope. Shading on the east side accelerates radiative cooling and advances ET onset relative to the still‐sunlit west side. A sigmoid fit to the 0.5–20‐m potential temperature difference captures a three‐phase evolution: slow cooling, rapid cooling, and a final slow cooling. We define ET onset at the sign reversal of the surface heat flux, marking weakly stable condition, and its ends at the initiation of downslope flows. Stability parameters (Monin–Obukhov parameter, gradient Richardson number, and flux Richardson number) consistently transition from unstable to weakly stable, with topographic shading accelerating and reshaping their evolution. Modeling of the cooling rates at 0.5 and 20 m shows vertical differences. After the heat flux reversal, near‐surface air cools exponentially, whereas potential temperature at 20 m decreases more slowly and nearly linearly. The ET time‐scale is well approximated by the e‐folding time of near‐surface exponential cooling. These results quantify the near‐surface thermal and flow transitions over slopes during ET and highlight the role of topographic shading in microclimate.

As a transition-metal oxide semiconductor with variable tungsten valence states and abundant oxygen vacancies, WO3-xhas attracted broad interest because its localized surface plasmon resonance performance can be tuned via controlling the concentration of oxygen vacancies. In this work, Cs-doped WO3-xnanosheets (Cs-WO3-x) were synthesized by solvothermal method. Subsequently, Cs-WO3-xwere further annealed in hydrogen and air atmosphere, respectively, forming a compact, highly crystalline surface layer (with thickness of ∼14 nm) on the surface while retaining abundant oxygen vacancy defects in the center region (denoted as a-Cs-WO3-x). As a proof-of-concept, the as-prepared nanosheets were employed as light harvesting materials in photocatalytic degradation of methyl orange (MO), a-Cs-WO3-xnanosheets demonstrate significantly improved degradation efficiency with respect to WO3-xand Cs-WO3-xcounterparts. The enhanced performance can be attributed to the hot-carrier transfer routes, which relies on not only direct electron transfer but also the more efficient plasmon-induced resonant energy transfer pathway. This work develops new pathway and provides important insights into the regulation of oxygen vacancies.

This article presents the results of a comprehensive study on the effect of electrolytic-plasma hardening (EPH) on the microstructure and mechanical properties of structural steel grade St4. This steel is widely used in heavy engineering and railway transport, where components operate under conditions of severe wear and variable loads, which highlights the relevance of developing effective strengthening methods. The experiments were carried out on specimens cut from a railway wheel rim, which makes the obtained results practically significant. The treatment was performed in an electrolyte consisting of 10% urea + 20% sodium carbonate + 70% water. The EPH regime included a voltage of 280 V, a current of 40 A, and a treatment duration of 9 seconds. This regime provided rapid heating of the surface layer to the austenitic state followed by instantaneous quenching in the electrolyte. Investigations carried out using scanning electron microscopy and metallographic analysis revealed that after EPH, the surface layer with a thickness of 1.0–1.5 mm consisted of a characteristic needle-shaped martensitic structure. Microhardness measurements confirmed a significant strengthening effect: the hardness increased fourfold from 200 HV to 800 HV. The substantial increase in hardness was accompanied by improved wear resistance and crack resistance, while maintaining the plastic properties of the material core. The obtained results demonstrate the high efficiency of EPH as an environmentally friendly and energy-saving local heat treatment method, which can be recommended to enhance the operational reliability and service life of critical components made of St4 structural steel.

Solid oxide electrolysis cells (SOECs) are among the most efficient energy-conversion devices for power-to-X applications in green energy technologies. Here, we report a high-level (5 mol%) Li- and Co-dual-doped gadolinium-doped ceria (GDC) electrolyte synthesized under an inert atmosphere, suitable for fabricating SOECs using conventional ferritic steel supports. The doped GDC exhibits uniform dopant incorporation and a single-phase cubic fluorite structure, achieving 98.18% relative density at 950 °C. Dilatometry and microstructural analyses reveal that Li-Co codoping significantly reduces sintering temperature and improves grain connectivity. Time-of-flight secondary ion mass spectrometry shows a Li,Co-rich surface layer whose thickness depends on sintering conditions, while Raman spectroscopy confirms the presence of a LiCoO2 phase and temperature-dependent oxygen-vacancy concentration. Electrochemical impedance spectroscopy demonstrates enhanced ionic conductivity, particularly for the sample sintered at 950 °C (denoted 5LC-4), which achieves increases of 269.5% at 450 °C and 138.85% at 750 °C compared with commercial GDC. The ionic conductivity reaches 2.17 × 10-2 S cm-1 with an activation energy of 0.32 eV. A symmetric five-layer SOEC integrating 5LC-GDC exhibits superior electrochemical performance to yttria-stabilized zirconia (YSZ) support, achieving a peak power density of 267.5 mW cm-2 at 850 °C.

ABSTRACT In relatively dry areas, due to lower soil moisture and less vegetation coverage, land surface microwave radiation comes from a certain depth of soil, while infrared skin temperature is only sensitive to the thin layer of the land surface. The inconsistencies in the detection depth of the microwave and infrared can lead to significant differences in retrieved emissivity between day and night. To improve the instantaneous microwave emissivity retrieval over barren areas, the land surface effective temperature calculation method was proposed based on AMSR2, which constructed the relationship between effective temperature and microwave brightness temperatures (TBs) in hours, approximating that monthly mean skin temperature equals monthly mean effective temperature and ignoring the change in emissivity over a month. The results showed that the effective temperature from 10.65 to 89 GHz had significantly smaller diurnal amplitude than skin temperature, and the lower the frequency, the smaller the amplitude. The effective temperature was then applied to the instantaneous emissivity inversion, and it was shown that this method remarkably reduced the emissivity difference between day and night, with the mean difference at the magnitude of 10^-3.

Mechanical characteristics of the neutral layer and skin surface flatness in rigid-filled press-bending forming of magnesium alloy panels

Bispecific T cell engager (BiTE) therapeutics that link T cells and tumor cells to induce tumor cell lysis have demonstrated great success in the clinic for the treatment of many cancers. However, T cell exhaustion in the tumor microenvironment leads to tumor cell escape and BiTE therapy resistance. Herein, we developed a drug-loaded bispecific T cell nanoengager (NanoBiTE) to overcome this obstacle. NanoBiTE is composed of a mesoporous silica nanoparticle encapsulating the adenosine A2A receptor antagonist PBF-509 as a core, with a lipid layer surface coating as a shell and modification with anti-CD19 and anti-CD3 antibodies for tumor and T cell binding, respectively. Like the traditional BiTE blinatumomab, NanoBiTE can engage T cells with CD19+ tumor cells to promote tumor cell lysis. However, unlike blinatumomab, which tends to induce T cell exhaustion, we showed that the release of PBF-509 from NanoBiTE suppressed the A2AR pathway and substantially improved tumor cell killing induced by NanoBiTE. Moreover, NanoBiTE treatment led to substantially reduced tumor burden in vivo in a humanized mouse model. Our results demonstrate that NanoBiTE is a safe and potent bispecific therapy that can also reduce T cell exhaustion for cancer immunotherapy.