Surface Phase Research Articles

Exact Equations for the Back and Effective Focal Lengths of a Plano-Concave Thick Lens

In this work, we present the exact equations for the back and effective focal lengths of a plano-concave thick lens. These equations are derived through a detailed ray-tracing approach, calculating the meridional ray’s path parallel to the optical axis while taking into account lens thickness, refractive index, and surface curvature. Our analysis bridges the gap between paraxial approximations and exact ray behavior, highlighting how traditional models (e.g., thin-lens equations) can be extended to thick lenses. Additionally, we review recent advancements in negative refraction and surface phase manipulation techniques to demonstrate how our equations compare to modern numerical methods and metacoating-enhanced designs. This work provides a comprehensive and exact framework for understanding the optical properties of plano-concave thick lenses, offering new insights into their application in precision optics.

Tracking Water Dissociation on RuO2(110) Using Atomic Force Microscopy and First-Principles Simulations.

The interaction between interfacial water and transition metal oxides is a primary enabling step for the oxygen evolution reaction (OER). RuO2 is a prototypical OER electrocatalyst whose ability to activate interfacial water molecules is essential to its OER activity. We image the dissociation of surface water into OH* and O* on RuO2(110), where * denotes adsorbed species, using atomic force microscopy. Starting from the surface-bound water molecules, which form a one-dimensional network along the rows of Ru surface sites, increasing the oxidative potential strips hydrogen away and transforms the water molecules into OH* and O*. This oxidative step changes the pattern of the adsorbates from one- to two-dimensional. First-principles calculations with interfacial polarization, capacitive charging, and adsorbate interactions attribute this evolution to the cooperative dehydrogenation of adsorbed water and OH* on RuO2. We use these results to map the surface phase diagram of RuO2(110) and provide a quantitative interpretation of its cyclic voltammetry. Our result provides the visualization of the water dissociation on a conductive oxide surface, a critical step in the OER, and demonstrates that the water activation is a collective phenomenon at RuO2(110) electrodes.

Influence of platinum content on semiconductor and electrochemical properties of materials based on titanium suboxides

The effect of platinum content on the surface morphology, phase composition and electrochemical properties of materials based on titanium suboxides was investigated. Titanium suboxides are formed at the stage of coating reduction under cathodic polarization, which allows the formation of a porous developed surface for electrodeposition of catalytic platinum layers. The main allotropic modification of TiOx in the studied composite materials is anatase, which contains particles of elemental titanium and platinum. The investigated materials are highly doped semiconductors with a high concentration of charge carriers. With an increase in the platinum content, an extreme dependence of the potential of flat zones is observed, which is associated with the formation of a composite material. The electrocatalytic activity was studied in the reactions of oxygen and hydrogen evolution. The overvoltage of oxygen production on platinum-containing materials is much lower than on the TiOx electrode. The slope of the linear dependence of the potential on the current density decreases with an increase in platinum content. The Tafel slope for the studied materials in the hydrogen evolution reaction was 160 mVdec–1 for coatings containing 0.25 mgcm–2 Pt; whereas it was equal to 42 and 43 mVdec–1 for electrodes with 0.5 and 2 mgcm–2 Pt, respectively.

Enhancing Chemomechanical Stability and High-Rate Performance of Nickel-Rich Cathodes for Lithium-Ion Batteries through Three-in-One Modification

Ni-rich cathode, recognized for high specific capacities and cost-effectiveness, are deemed promising candidates for high-energy Li-ion batteries. However, these cathodes display notable structural instability and experience severe strain propagation during rapid charging and extended cycling under high voltage, hindering their widespread commercialization. To tackle this chemo-mechanical instability without compromising energy and power density, we propose an efficient modification strategy involving hexavalent metal cation-induced three-in-one modification to reconstruct the nanoscale surface phase. This strategy includes uniform W-doping, integration of cation-mixed phases, and Li2WO4 nanolayers on the surface of Ni-rich cathode microspheres. W-doping strengthen the bond to oxygen, thereby enhancing structural stability and suppressing oxygen loss linked to a layered-to-rock salt phase transition during deep delithiation process. Additionally, establishing a cation-mixing domain with an optimal thickness on the cathode surface enhances Li⁺ diffusivity and alleviates particle structural degradation. Moreover, Li2WO4 nanolayers reduce electrolyte side reactions and act as a damping medium against cycling stresses. Importantly, detailed investigations into structural changes before and after modification at varying current rates were conducted to better comprehend the rate-dependent degradation mechanism. These findings yield valuable mechanistic insights into the high-rate utilization of a viable Ni-rich cathode, ensuring prolonged service life in electric vehicles.

Overlooked Role of Electrostatic Interactions in HER Kinetics on MXenes: Beyond the Conventional Descriptor ΔG ∼ 0 to Identify the Real Active Site.

Understanding the atomic-level mechanism of the hydrogen evolution reaction (HER) on MXene materials is crucial for developing affordable HER catalysts, while their complex surface terminations present a substantial challenge. Herein, employing constant-potential grand canonical density functional theory calculations, we elucidate the reaction kinetics of the HER on MXenes with various surface terminations by taking experimentally reported Mo2C as a prototype. We observe a contradictory scenario on Mo2C MXene when using conventional thermodynamic descriptor ΔGH* (hydrogen binding energy). Both competing surface phases that emerge close to the equilibrium potential meet the ΔGH* ∼ 0 criterion, while they exhibit distinctly different reaction kinetics. Contrary to previous studies that identified surface *O species as active sites, our research reveals that these *O sites are kinetically inert for producing H2 but are easily reduced to H2O. Consequently, the surface Mo atoms, exposed from the rapid reduction of the surface *O species, serve as the actual active sites catalyzing the HER via the Volmer-Heyrovsky mechanism, as confirmed by experimental studies. Our findings highlight the overlooked role of electrostatic repulsion in HER kinetics, a factor not captured by thermodynamic descriptor ΔGH*. This work provides new insights into the HER mechanism and emphasizes the importance of kinetic investigations for a comprehensive understanding of the HER.

From Synthesis to Energy Storage, The Microchemistry of MXene and MBene

AbstractMXene and MBene, with diverse and adjustable surface and bulk structures, show many unique chemical properties and are applied in various energy storage technologies, and the latest developments for them are reviewed respectively. However, the current reports on the synthesis of the two materials and the application of related devices are still separate and limited to the macro details. In this review, the microscopic chemistry of synthesis strategies for MXene and MBene and the differences in synthesis strategies caused by the structure differences between them are elucidated. Later, the impact of synthesis strategies on their overall morphologies and subsequent material property differences are discussed, and key considerations in the field of energy storage are described. Next, it is elaborated on how the surface and bulk phases of MXene and MBene utilize these properties to participate in electrochemical reactions individually or synergistically. Unlike previous reviews, MXene and MBene are incorporated into a unified framework from a microscopic perspective for discussion, and the relationship of synthesis‐structure/properties‐function is elucidated. Finally, the “skipping strategy” and “joint devices” as the next‐generation design concepts of MXene in the synthesis and application fields, and the development template for MBene materials are proposed.

The effect of coating chitosan from cuttlefish bone (Sepia Sp.) on the surface of orthodontic mini-screw

IntroductionPeri-implantitis is a significant complication resulting from the failure of orthodontic mini-screws. Recent strategies to address this issue include the application of natural antibacterial coatings to prevent bacterial colonization. Notably, cuttlefish (Sepia sp.) bones are rich in chitosan, which is recognized for its antibacterial effectiveness and biocompatibility. ObjectivesTo evaluate the effects of a chitosan coating derived from cuttlefish bone (Sepia sp.) on mini-screws against Aggregatibacter actinomycetemcomitans bacteria frequently linked to peri‑implantitis. Materials and MethodsThe surface functional groups, phase composition, and crystal morphology of chitosan were analyzed using conventional analytic techniques alongside energy-dispersive X-ray analysis. These prepared were tested for antibacterial activity against A. actinomycetemcomitans by disk diffusion assay; minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) were determined. Stainless steel mini-screws were coated with chitosan, and their surfaces were characterized using scanning electron microscopy (SEM). ResultsThe investigation revealed that chitosan exhibited a MIC value of 8 ppm against A. actinomycetemcomitans with MBCs recorded at 16 ppm. Zones of inhibition varied based on concentration; notably, concentrations at 0.4 %, 0.6 %, and 0.8 % produced zones averaging 16.17 ± 1.64 mm collectively while increasing to a mean zone size of 20.99 ± 3.63 mm at the highest tested concentration (0.8 %). SEM analyses further confirmed the successful adhesion of the chitosan compound onto immersed mini-screw surfaces. ConclusionThe prepared chitosan from cuttlefish bone (Sepia sp.) has antibacterial activity against the bacteria A. actinomycetemcomitans in vitro and can successfully coat SS mini-screws to enhance their efficiency.

Evolution of the surface phase transitions in IrTe2

The phase transitions in IrTe2 have been extensively studied but the symmetry at each phase is yet to be settled. Employing second harmonic generation (SHG) measurements over a temperature range of 4 –300 K, we probe the evolution of the symmetry of IrTe2. Our results indicate shifts in two distinct transition temperatures (Ts1 and Ts2 with Ts1 > Ts2) through thermal cycling, providing an explanation for the variations of reported values in literature. The SHG polarimetry measurements identify symmetries in different temperature ranges, confirming the trigonal symmetry above Ts1, the triclinic symmetry between Ts1 and Ts2, and the coexistence of multiple stripe phases below Ts2. The most striking feature is the reemergence of a trigonal phase as reflected by six-fold symmetry below ~ 10 K which is likely responsible for phenomena observed at low temperatures.

Structure and Properties of Thin Films Prepared on Flexible Substrates from SnCl4-Derived Solutions

Thin transparent films of SnO2 were obtained from aqueous–alcohol solutions of SnCl4 on a flexible polyethylene terephthalate (PET) substrate by spray pyrolysis at 100 °C. The influence of the addition of aqueous ammonia to the film-forming solution on the different properties has been studied. Properties studied include surface morphology, phase composition and transparency of the formed films and the crystallization processes and band gap of the film material. It was found that the addition of aqueous ammonia causes the formation of skeletal crystals (NH4)2[SnCl6] with a perovskite structure in the film structure. The resulting films are promising for use in the technology of manufacturing flexible solar cells.

Numerical analysis on the fate and transport of TiO2 nanoparticles in fractured porous media: Addressing intrinsic heterogeneities in sorptive mass transfer

The aggregation and slow migration of nanoparticles in aqueous media have caused serious concerns about their fate and impacts in the subsurface environment. Anthropogenic release and distribution of TiO2 nanoparticles (TNP) have immense potential for surface adsorption, occlusion, impregnation, bioaccumulation, and phase partition into various environmental compartments, and the actual risks in their interactions are still unknown. In an attempt to realize the extent of source zone migration of TNP in a fracture-skin-matrix (F-S-M) medium, a numerical model is developed and analyzed for sensitivity of certain features of the flow field. In addition, the sorptive mass transfer is simulated under four characteristic scenarios with varying assumptions pertaining to the intrinsic heterogeneities. The simulation results highlight the non-selective regulatory role of the skin in providing temporary interfacial space for reversible adsorption between the fracture and the matrix as well as in retarding the desorption rate. A preferential detachment of TNP is observed to be favored by the enhanced properties of skin due to the similarity in diffusion and dispersion coefficients. Out of the four scenarios, the two-site model and two-step model simulated the dynamic pore-filling features of adsorption pertaining to the heterogeneities in TNP and F-S-M characteristics. The results demonstrate that the proposed numerical could fairly detect the transition between local equilibrium and dynamic adsorption-desorption cycles that would eventually determine the mass transfer limitations and the extent of elution of TNP along the flow.

Optimizing secure multimedia communication in embedded systems a parallel convolutional neural network approach to RIS and D2D resource allocation

With the rapid development of Internet of Things (IoT) services, technologies that leverage multimedia computer communication for information sharing in embedded systems have become a research focus. To address the challenges of low spectral efficiency and poor network flexibility in multimedia computer communications, this paper proposes a resource allocation scheme based on parallel Convolutional Neural Network (CNN). The scheme optimizes the base station beamforming vector and the Reconfigurable Intelligent Surface (RIS) phase shifts to maximize the secure transmission rate for cellular users (CUs), while ensuring normal and secure communication for device-to-device (D2D) users. First, to mitigate interference caused by D2D users reusing CU spectrum resources, the RIS phase shifts and beamforming vectors are optimized to suppress interference and enhance system secrecy rates. Second, to maximize the CU secrecy rate, the paper proposes a parallel CNN-based resource allocation model that considers base station transmission power, RIS reflection coefficients, and D2D communication rate constraints, incorporating multi-scale residual modules in the convolutional layers of the model. Simulation results demonstrate that the proposed CNN-based resource allocation scheme significantly improves the secrecy rate of embedded system communications, ensuring secure multimedia computing, and outperforms traditional methods.

First-principles thermodynamical modeling of molecular reactions on α-U(001) and α-UH3(001) surfaces and their influence on hydrogen activation

Density functional theory calculations coupled with thermodynamic analysis have been performed to investigate the reactions of hydrogen and impurity gases including O2, CO2, CO, N2 on α-U(001) and α-UH3(001) surfaces. Binding strength of adsorbates on α-UH3 is calculated to be weaker than α-U, suggesting enhanced poisoning-resistant properties of U-hydride compared to its metallic state. Surface phase diagrams of U under binary H2-O2, H2-N2 and H2-CO gaseous environments show that while N and C elements prefer to stay in their hydrogenated states on the hydride surface, isolated O atoms favorably interact with both α-U(001) and α-UH3(001), indicating the heavily poisoning effect of impurities containing oxygen. Global optimization of partially oxidized α-U(001) slabs induces surface geometry reconstruction and the activity of oxidized surfaces toward hydrogen adsorption can be linearly correlated with local electronic and atomic properties of the adsorption site.

Optical anisotropy and surface phases of cholesterol derivative monolayer at air–water interface

Cholesterol and its derivatives play crucial roles in regulating processes of biological membranes. Langmuir monolayer can mimic a bio-membrane which can be used to investigate the molecular interaction governing the important physical phenomena. The cholesterol derivative exhibiting mesophases (CHLC molecules) was synthesized and spread at the air–water (A/W) interface to investigate the surface behavior. The monolayer exhibited a variety of surface phases such as gas, liquid expanded (LE), low density liquid like (L1) and liquid condensed (L2) phases. Treating the CHLC molecules to be rod-like, the average tilt of the molecules with respect to the surface normal in these phases are found to be different. The tilt angle decreases systematically from LE to L2 phase. The optical anisotropy of the ultrathin Langmuir-Blodgett (LB) films of CHLC molecules in these phases was measured using the surface plasmon resonance (SPR) spectroscopy. The high tilted molecules in the ultrathin LB film displayed a high value of optical anisotropy. The ultrathin film of CHLC molecules at different interfaces was investigated using Brewster angle microscopy, X-ray reflectivity (XRR), SPR spectroscopy and atomic force microscopy. This study is useful for the systems where the physical phenomena are governed by tilt of the molecules.

Influences of Sr(OH)2 on the Structure and Corrosion Resistance of Micro‐Arc Oxidation Coatings Formed on TC4 Titanium Alloy

ABSTRACTIn order to improve the comprehensive properties of TC4 titanium alloy, micro‐arc oxidation (MAO) coating is prepared on the surface of a TC4 substrate in a basic electrolyte with varying concentrations of Sr(OH)2. The surface morphology, phase composition, element distribution, and corrosion resistance of MAO coatings are analyzed by scanning electron microscopy, X‐ray diffraction, an energy‐dispersive spectrometer, the electrochemical test, and the erosion–corrosion test. The results show that the voltage of the MAO process increases and then decreases; the surface morphology and density of the coatings are greatly improved after doping Sr(OH)2. When the concentration of Sr(OH)2 is 0.6 g L−1, the thickness, hardness, and adhesion strength of the coating reach the maximum values of 37.04 μm, 836.2 HV, and 21.8 N, respectively. At this time, the wear resistance and corrosion resistance are the best, and the friction coefficient and the corrosion rate are the lowest: 0.3352 and 1.04 × 10−10 mm a−1, respectively.

Self-generated B-MAX phase composites: The effect of sintering temperature on surface morphology and phase composition

The use of metal-based MAX phase composites is widespread in the production of high-temperature structural materials, anticorrosive materials and electrode materials. Herein, novel B-Ti3AlC2 and B-Ti4AlN3 composites were prepared using the hot-pressing method at varying sintering temperatures ranging from 950 °C to 1325 °C. This study also explores the effect of sintering temperature on the surface morphology and phase composition of both B-MAX phase composites. The morphological and crystal phase composition of MAX phase composites were investigated through SEM coupled with EDS, FE-SEM, AFM, and XRD test analysis. The results revealed that higher sintering temperatures increase the clear formation of MAX phases and composites as compared to lower temperatures. The findings also expose that the in-situ formation of B-MAX composites significantly changes the structure, contributing to transforming the overall performance and making it suitable for high-stress applications like electronics, aerospace, and cutting tools.

Effects of preservatives on the activities of salivary enzymes

ObjectivesTo investigate the effects of common preservatives used in oral health care products on the enzymatic activities of lysozyme, peroxidase, and α-amylase in-solution and on-hydroxyapatite surface phases. DesignThe preservatives used in this study were sodium benzoate, methylparaben, propylparaben, and benzalkonium chloride. Hen egg-white lysozyme, bovine lactoperoxidase, and α-amylase from Bacillus sp. served as sources of purified enzymes. Human unstimulated whole saliva was used as a source of salivary enzymes. Hydroxyapatite beads were used as the surface phase. The preservatives were incubated with purified enzymes or saliva samples in-solution or on-hydroxyapatite surface phases, respectively. Enzymatic activities of lysozyme, peroxidase, and α-amylase were measured by hydrolysis of fluorescein-labelled Micrococcus lysodeikticus, oxidation of fluorogenic 2′,7′-dichlorofluorescin, and hydrolysis of fluorogenic starch, respectively. ResultsThe effects of the preservatives on the enzymatic activities of lysozyme and peroxidase were more distinct in the saliva samples than purified substances, and in the in-solution phase than on-hydroxyapatite surface phase, and the opposite was true for α-amylase. The most significant result was apparent decrease in peroxidase activities caused by the parabens in the in-solution phase (P<0.05). Sodium benzoate and parabens inhibited lysozyme activity in the in-solution phase, but differently for the purified and salivary lysozymes. Parabens and benzalkonium chloride inhibited the enzymatic activity of α-amylase from Bacillus sp., not saliva samples, only on-hydroxyapatite surface (P<0.05). ConclusionsEach preservative affected the enzymatic activities of lysozyme, peroxidase, and α-amylase differently. Based on the effects on salivary enzymes, sodium benzoate or benzalkonium chloride was recommended as preservatives rather than parabens.

The effect of roughness and top layer in solid particle impingement erosion of multilayer nanostructured nitride PVD coatings

The effect of the surface roughness of the coating and the composition of the upper layer on the solid particle erosion of multilayer nanostructured coatings applied via cathodic arc evaporation (CAEPVD) method was investigated. CrN/TiN nanostructured multilayer coating (TiN as the upper layer) and TiN/CrN nanostructured multilayer coating (CrN as the upper layer) were applied on 410 stainless steel through the CAEPVD method with the following architecture. 1) a bottom layer of Cr and CrN deposited on the substrate, 2) nanolayers of TiN and CrN deposited on the bottom layer alternately and 3) an upper layer of CrN or TiN deposited on the nanolayers. After applying the coating, half of the samples were polished to obtain smooth surfaces, while the other half remained unpolished, resulting in rough surfaces. Surface morphology, phases identification, adhesion, mechanical, and erosion behavior of the coatings were characterized using SEM, XRD, Rockwell adhesion measurements, nanoindentation test, and solid particle impingement, respectively. The nano-scale indentation results demonstrated that the hardness, Young's modulus, H/E, and H3/E2 of the CrN/TiN coating were 5.57, 1.42, 3.86, and 85.39 times larger than those of the substrate. For the TiN/CrN coating, the values were 4.04, 1.13, 3.53 and 51.68 times greater than those of the substrate. The results of the erosion test showed that the erosion mass loss for the CrN/TiN and TiN/CrN coatings decreased up to 73% and 67%, respectively. Additionally, surface smoothing improved erosion resistance by 40% for both coatings. This shows that the smoothed CrN/TiN nanostructured multilayer coating is an excellent candidate for increasing the erosion resistance due to the higher ratios of H/E and H3/E2 and smoother surface.

Surface-modified composites of metal–organic framework and wood-derived carbon for high-performance supercapacitors

The renewable nature, high carbon content, and unique hierarchical structure of wood-derived carbon make it an optimal self-supporting electrode for energy storage. However, the limitations in specific surface area and electrical conductivity defects pose challenges to achieving satisfactory charge storage in wood-derived carbon electrodes. Therefore, exploring diverse and effective surface strategies is crucial for enhancing the electrochemical energy storage performance. Herein, a decoration technique for enhancing aesthetic appeal involves applying a metal–organic framework (Ni/Co-MOF) containing nickel and cobalt onto the inner walls of wood tracheids. The sequential modification steps include carbonization, oxidation activation, and acid-etching. The Ni/NiO/CoO-CW-4 electrode, made by acid-etching carbonized wood (CW) doped with nickel, nickel oxide, and cobalt oxide for 4 h, has excellent surface area and pore size distribution, high graphitization degree, and exceptional conductivity. Furthermore, surface modification optimizes the surface chemistry and phase composition, resulting in a 0.8 mm thick Ni/NiO/CoO-CW-4 electrode with an exceptionally high areal capacitance of 16.76 F cm−2 at 5 mA cm−2. Meanwhile, the fabricated solid-state supercapacitor achieves an impressive energy density of 0.67 mWh cm−2 (8.38 mWh cm−3) at 2.5 mW cm−2 (31.25 mW cm−3), surpassing representative modified wood-based carbon electrodes by approximately 2–7 times. Additionally, the supercapacitor demonstrates exceptional stability, maintaining 96.21 % of capacitance even over 10,000 cycles. The parameters presented here demonstrate a significant improvement compared to those typically observed in most modified wood-derived carbon-based supercapacitors, effectively addressing common issues of low energy density and suboptimal cycling performance with wood carbon composites.

Hydrothermal preparation of magnesium alloy surface composite coatings and its performance research

Magnesium alloys have great potential for industrial and aerospace applications due to their low density and high strength. Aiming at its defects of poor corrosion resistance and susceptibility to galvanic coupling corrosion in metal coatings, a composite coating was prepared on the surface of AZ91D magnesium alloy by the hydrothermal method. Scanning electron microscope, x-ray diffraction, and x-ray photoelectron spectroscopy were used to characterize the surface micromorphology, phase composition, and elemental valence and evaluate the adhesion of the coating to the substrate by the ASTM D3359-09 test standard. Electrochemical experiments were done in a 3.5% NaCl solution. The results show that there are nanoscale dense granular structures on the surface of the samples, and the main components of the coatings are Mg(OH)2, Al2O3, and MgSiO3. ASTM grade 4B is between coating and substrate. The corrosion rate of the best sample was reduced by a factor of 238.96 compared to the substrate, and the corrosion current density was reduced by two orders of magnitude. The corrosion rate and corrosion current of the samples after repeated friction did not change much compared with those before friction, which proved that the composite coating had better corrosion resistance and friction stability.

Improving the tribological and corrosion behavior of Ni[sbnd]B coating with low boron content from optimized lead-free bath on aluminum alloys

This study focuses on producing environmentally friendly, lead-free nickel‑boron (NiB) coatings as an alternative to hard chromium coatings. Using the electroless method, the NiB coatings were fabricated from a lead-free bath, and the effects of varying B and Ni concentrations on the coatings' chemical composition, surface morphology, hardness, corrosion resistance, and wear performance were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze surface morphology and phase composition. Corrosion performance was evaluated using potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS), while wear behavior was tested at sliding speeds of 20, 30, and 40 cm/s. The study highlights the critical role of sliding speed on wear mechanisms, friction coefficient, wear rate, and surface morphology. The analyses revealed that the optimal NiB coating, containing 34 g/L Ni and 3 g/L B, exhibited the highest hardness, the lowest corrosion rate, and the highest wear rate performance. The values obtained from these analyses were 891 HV for hardness, 8.87 × 10−6 mpy for corrosion rate, and 2.21 × 10−4 mm3/N·m for wear rate. The use of analysis of variance (ANOVA) identified key factors influencing these properties. The findings suggest that optimizing boron and nickel concentrations significantly enhances NiB coatings' corrosion resistance and wear performance, making them suitable for industrial applications.