Surface Energy Research Articles

Pyrene‐Based Self‐Assembled Monolayer with Improved Surface Coverage and Energy Level Alignment for Perovskite Solar Cells

AbstractRecently, the efficiency of p‐i‐n perovskite solar cells drastically increased, a pivotal factor being the incorporation of self‐assembled monolayers (SAMs) as a hole‐transporting layer (HTL). SAMs offer many advantages over conventional HTLs, including minimal material requirements, low cost, and facile processing. Current research is mainly focused on the development of carbazole‐derived SAMs. However, the versatility of organic chemistry allows for the design of SAMs with alternative organic cores that may possess specific benefits. In this study, three novel SAMs are incorporated in p‐i‐n perovskite solar cells, each based on an aromatic core commonly used in organic semiconductors. The novel SAMs vary in their energy level alignment with the perovskite active layer. Optimal alignment is achieved with a pyrene‐based SAM (4PAPyr), resulting in solar cells that outperform the commercially available 2PACz. Moreover, due to improved surface coverage, the use of 4PAPyr leads to a significantly higher number of working solar cell devices when compared to 2PACz, which is of particular interest with regard to upscaling. After device optimization, a power conversion efficiency of 22.2% is achieved with 4PAPyr. This research underlines the importance of diversifying SAMs to unlock further advancements in perovskite solar cell efficiency and scalability.

Investigating the Role of TiC Precipitation in Dynamic Recrystallization Behavior of a Novel Ship Steel

This study examines the single‐pass thermal compression behavior of Ti‐bearing ship plate steel across a temperature range of 850–1150 °C and strain rates from 0.01 to 7 s−1, employing the Gleeble‐2000D thermomechanical simulator. It delves into the evolution of TiC precipitation and dynamic recrystallization (DRX), along with the austenite decomposition transformation during hot compression and subsequent cooling. Active dynamic recrystallization commences at deformation temperatures above 1050 °C, facilitated by the diminished pinning pressure of TiC carbides. This leads to the development of fine DRX austenite grains, influenced by an increase in strain rates and a decrease in temperature. Simultaneously, the fraction of TiC dispersions decreases as the deformation temperature increases, yet they maintain a consistent size of 5–10 nm. The refined particle size is attributed to their low interfacial energy with the austenite matrix, determined by the first principle to be 0.21 J m−2. Due to the severe deformation and numerous dispersions, specimens subjected to a thermal deformation regime at 850 °C and a strain rate of 7 s−1 present a peak in hardness, reaching a maximum of 324 HV. The Ti microalloying approach offers pivotal insights into improving the rollability and mechanical characteristics of ship plate steel.

Fabrication of slanted gratings with high refractive index starting from master nanoimprint mold

Recently, nanoimprinting has attracted a new round of attention in the industry due to the boom in demand for augmented reality/virtual reality (AR/VR), metalens and microlens, and even semiconductors. Slanted gratings have great application prospects in AR/VR displays because of their high efficiency in light coupling. UV-Nanoimprint lithography (UV-NIL) has been identified as one of the most feasible routes for mass manufacture of high refractive index (RI) slanted gratings. This paper presents a fabrication of high RI slanted gratings based on UV-NIL. A comprehensive study on the optical principles of slanted gratings is conducted, followed by simulation-based optimization of the grating parameters. The key element for applying nanoimprint to fabricate slanted gratings is the master mold, which is acquired by a tilted angle etching of metal gratings as an etching mask on silicon wafers with F-based plasma. The influence of experimental parameters, such as the etching power and etching mask thickness on the morphology of the slanted gratings on the master mold are investigated. The working mold was simply duplicated from the master mold by UV-NIL with a low surface energy working mold material. The high RI slanted gratings were achieved by imprinting a UV-curable resin with high RI. Finally, experimental verification was performed to assess the optical performance of the slanted gratings.

Wetting phenomena of droplets and gas bubbles: Contact angle hysteresis based on varying liquid-solid and solid-gas interfacial tensions.

Wetting phenomena have been widely observed in our daily lives, such as dew on lotus leaf, and applied in technical applications, e.g., ink-jet printing. In contrast to constant liquid-solid and solid-gas interfacial tensions in Young's law, we here focus on the wetting phenomena by considering varying fluid-solid interfacial tensions. We analyze the energy landscape, the map of Young's contact angle, the number and corresponding contact angle of local energy minima, and the contact angle hysteresis for a liquid droplet on a solid substrate in a gas phase. In addition, a gas bubble on a solid substrate in a liquid phase has been scrutinized from the aspect of surface energy minimization. The wetting effect has been regarded, where the liquid and gas species penetrate into the solid phase on the microscopic scale [F. Wang and B. Nestler, Phys. Rev. Lett. 132, 126202 (2024)]. We assume the liquid-solid and the solid-gas interfacial tensions to be a function dependent on the volume fraction of the liquid and the gas species and investigate the impact of the size ratio of the droplet to the solid surface that is overlooked in existing theories on the wetting phenomena. Our finding sheds light on the microscopic origin of the contact angle hysteresis and the droplet size effect on the wetting phenomena.

The use of interphacial energies to estimate the spreading coefficients of organic liquids by the solid polymer surface of polytetrafluoroethylene

In the article, using equations previously obtained by the author, calculations were made of the interfacial energies of a solid polymer – polytetrafluoroethylene in contact with organic liquids and their vapors. Based on the calculation results, the spreading coefficients in the studied systems were calculated. Since Young’s derivation of the equation for the cosine of the contact angle, many researchers have attempted to determine the surface energy of solids, which would, in turn, make it possible to determine the interfacial energy at the solid-melt (liquid) interface. However, on the way to solving this problem there were obstacles associated with various processes that accompany phenomena occurring on the surface of a solid body in the presence of a liquid (melt) of another body on its surface. This is not the place to list all types of processes. They are well known to specialists in the field of surface phenomena. Here are just a few of them that affect the surface properties of bodies: chemical reactions, mutual dissolution of components of solid and liquid phases, deformation of solid phases, etc. In the case of contact of the polymer with organic liquids, such obstacles do not exist. Also, since it is impossible to dwell on all publications devoted to the determination of the surface energy of solids, the article discusses specific works on determining the interfacial energy at contact angles close to or equal to zero. Since the question of the behavior of interfacial energy at a contact angle equal to zero is of fundamental importance, and there are conflicting opinions in the literature on this matter, giving the correct answer to this question is an urgent task. Using examples of calculations of interfacial energies of homologous series of organic liquids on a solid surface of polytetrafluoroethylene, we have shown that only at zero contact angle the interfacial energy is zero. In this article, using interfacial energy values, we are the first to calculate the spreading coefficients of organic liquids over the surface of a solid polymer, which, in our opinion, is also an urgent task.

Uncertainty of DFT Calculated Mechanical and Structural Properties of Solids due to Incompatibility of Pseudopotentials and Exchange-Correlation Functionals.

The demand for pseudopotentials constructed for a given exchange-correlation (XC) functional far exceeds the supply, necessitating the use of those commonly available. The number of XC functionals currently available is in the hundreds, if not thousands, and the majority of pseudopotentials have been generated for LDA and PBE. The objective of this study is to identify the error in the determination of the mechanical and structural properties (lattice constant, cohesive energy, surface energy, elastic constants, and bulk modulus) of crystals calculated by DFT with such inconsistency. Additionally, this study aims to estimate the performance of popular XC functionals (LDA, PBE, PBEsol, and SCAN) for these calculations in a consistent manner.

Modeling of the perovskite nickelate SmNiO3 nucleation from amorphous thin films: A Volmer's thermodynamical approach

We present a thermodynamical model based on Volmer's nucleation theory adapted to the case of the perovskite nickelate SmNiO3 crystallization (SNO) from an amorphous (aSNO) thin film. This amorphous phase is synthesized via reactive magnetron sputtering and then subsequently annealed in air at temperatures between 725 and 925 K to crystallize it. This model allows to predict the theoretical nucleation rate of the crystallized perovskite phase according to the annealing temperature, the type of the nucleation (homogeneous and heterogeneous mechanisms) and to estimate some physical and thermodynamical data related to this transformation. A theoretical evaluation of the nucleation rate shows that the optimum temperature for crystallization is close to 800 K for which the nucleation rate can reach 1021 m-3.s-1 if considering both homogeneous and heterogeneous nucleation mechanisms. As the annealing temperature moves away from 800 K, the theoretical nucleation rate drops drastically, as observed experimentally by X-ray Diffraction (XRD) when we annealed 200 nm thick aSNO films. The good agreement between the presented model and the experimental crystallization results allows us to numerically evaluate some physical parameters not yet reported to date in the literature for SNO perovskites such as the surface energy between the amorphous and the crystallized SNO phases, the strain energy when the crystallization occurs and the enthalpy associated with crystallization.

Initial Stages of Electrocrystallization of Coatings with Tin and Tin-Copper and Tin-Copper-Ultradisperse Diamond Alloys

The need of modern microelectronics in the development of technological processes for the formation of nanostructured layers puts forward the necessity of understanding the mechanisms of nucleation and growth of deposits. The article considers the features of the initial stages of electrocrystallization of coatings with tin and tin-copper and tin-copper-ultradisperse diamond alloys. The kinetic regularities of electrode processes were studied by the voltammetry method. Based on the experimental data, the nucleation parameters (nucleation energy, effective interphase surface energy, radius and volume of the nucleus) were calculated. SEM images were obtained and the features of the roughness of the coating surfaces after deposition for 10, 20, 30 and 60 s were studied. It was found that co-deposition of tin-copper alloys and tin-copper-ultradisperse diamond particles increases the value of the limiting current from 2.8 · 10–2 to 5.0 · 10–2 A/cm2. With an increase in electrocrystallization over-voltage, the rate of nucleation increases and their size decreases, while fine-grained and dense deposits are formed. With an increase in the deposition duration, crystallites grow and gradually coalesce with each other, the value of the equivalent diameter of the grain coatings increases, respectively, for: Sn – from 1 ⋅ 10–6 to 4 ⋅ 10–6 m, Sn-Cu – from 0.3 ⋅ 10–6 to 1.3 ⋅ 10–6 m, Sn-Cu-ultradispersed diamond – from 0.9 ⋅ 10–6 to 1.4 ⋅ 10–6 m. The established patterns make it possible to control the structure of the coatings and obtain deposits with specified properties. The presented results may be of interest to specialists involved in the formation of solderable galvanic coatings.

Configurational Isomerization‐Induced Orientation Switching: Non‐Fused Ring Dipodal Phosphonic Acids as Hole‐Extraction Layers for Efficient Organic Solar Cells

AbstractPhosphonic acid (PA) self‐assembled molecules have recently emerged as efficient hole‐extraction layers (HELs) for organic solar cells (OSCs). However, the structural effects of PAs on their self‐assembly behaviors on indium tin oxide (ITO) and thus photovoltaic performance remain obscure. Herein, we present a novel class of PAs, namely “non‐fused ring dipodal phosphonic acids” (NFR‐DPAs), featuring simple and malleable non‐fused ring backbones and dipodal phosphonic acid anchoring groups. The efficacy of configurational isomerism in modulating the photoelectronic properties and switching molecular orientation of PAs atop electrodes results in distinct substrate surface energy and electronic characteristics. The NFR‐DPA with linear (C2h symmetry) and brominated backbone exhibits favorable face‐on orientation and enhanced work function modification capability compared to its angular (C2v symmetry) and non‐brominated counterparts. This makes it versatile HELs in mitigating interfacial resistance for energy barrier‐free hole collection, and affording optimal active layer morphology, which results in an impressive efficiency of 19.11 % with a low voltage loss of 0.52 V for binary OSC devices and an excellent efficiency of 19.66 % for ternary OSC devices. This study presents a new dimension to design PA‐based HELs for high‐performance OSCs.

Hot embossed micropatterned slippery Al 5083 alloys in stagnant and laminar saltwater

Slippery AA 5083 alloy surfaces were fabricated by using ground (mean roughness-Ra = 45±2 µm), polished (Ra = 9±3 µm) and hot embossed micro-patterned specimens, and coating them with silicone oils of varying viscosities (1000−100000 cSt). The surface energy of aluminium alloy (AA) 5083 was estimated to be 850±210 mJ·m−2 using Schultz model. The ground/polished specimens were coated with 12±1 µm and 24±0.3 µm thick oil. They showcased slippery character, wherein apparent water static contact angles (SCAs) of 94±1° to 104±1°, slide-off angles (SAs) of 4±0° to 21±2° and contact angle hysteresis (CAH) of <10° were observed. Also, CAH and SAs revealed an increasing trend with an increase in the oil viscosity, irrespective of the coating thickness or the substrate roughness. In addition, the water droplets bounced-off the oil coated (24 µm thick) surfaces up to Weber no. (We) of 3.91. Furthermore, micro-patterned specimens were fabricated by hot embossing at 300 °C, 17+1 MPa, 5 min and comprise of hexagonally arranged pillars and holes with 6.5−7.1 µm diameter and 9.5−13.6 µm pitch. A key finding is that micro-pillars offered the highest tolerance to shear drainage of oil under saltwater (3.5 wt% NaCl) for up to 7 days, in both stagnant and flowing laminar (Reynolds no.‐Re =247) conditions, as compared to micro-holes and unpatterned surfaces. Interestingly, the slippery properties of oil coated unpatterned AA5083 have retained after 7 days of submersion, showing SCAs ≥ 97±3° and SAs ≤ 14°, despite the negative spreading coefficient of oil on AA5083 under water. Such slippery durable micro-pillared and micro-holed AA5083 surfaces could be highly beneficial for mitigating biological corrosion of ship hulls in marine environments.

Photocurable Thiol-Ene/Nanocellulose Elastomeric Composites for Bioinspired and Fluorine-Free Superhydrophobic Surfaces.

Artificially prepared superhydrophobic surfaces toward a self-cleaning "lotus effect" and anticontamination performance have become critically important in the past few years. However, most approaches to create the required topology with a hierarchical roughness comprise several manufacturing steps of varying practicality. Moreover, the desired low surface energy is in most cases achieved with fluorinated moieties that are currently criticized due to biological and environmental hazards. In this work, rapidly photocuring but weak thiol-ene resins were reinforced with cellulose nanofibrils (CNFs) to replicate lotus leaves via one-step UV nanoimprint lithography. The CNFs were surface-modified using countercation exchange of carboxyl groups and grafting of thiol and methacrylate functionalities. The formulation methodology resulted in free-flowing, shear-thinning composite resins without surfactants or dispersants. The rheological and photo-cross-linking behavior of the resins, the thermal stability, the mechanical performance, and the hydrophobicity of the cured composites were characterized. Notably, the surface modifications increased the as received fibril diameter (1.9 ± 0.6 nm) by 1.6-2.3 nm and raised the fibril-resin compatibility. The resins underwent rapid polymerization and the high thermal stability of thiol-enes was retained. The methacrylated nanofibrils (10 vol %) significantly strengthened the rubbery network, outperforming the neat thiol-ene polymer in terms of hardness (3.4×), reduced modulus (5.8×), and wear resistance (>100×). Moreover, the surface of lotus-texturized composites was superhydrophobic with a water contact angle of 155°, higher than that of the neat polymer (147°), and was self-cleaning. These CNF composite resins are compatible with fast-cure processes such as 3D printing and roll-to-roll processing, are exempt of fluorine or any other hydrophobization treatment, and are extremely wear-resistant.

Characterizing heatwaves based on land surface energy budget

Heat extremes pose pronounced threats to social-ecological systems and are projected to become more intense, frequent, and longer. However, the mechanisms driving heatwaves vary across heatwave types and are not yet fully understood. Here we decompose perturbations in the surface energy budget to categorize global heatwave-days into four distinct types: sunny–humid (38%), sunny-dry (26%), advective (18%), and adiabatic (18%). Notably, sunny-dry heatwave-days decrease net ecosystem carbon uptake by 0.09 gC m−2 day−1 over harvested areas, while advective heatwave-days increase the thermal stress index by 6.20 K in populated regions. In addition, from 2000 to 2020, sunny-dry heatwaves have shown the most widespread increase compared to 1979 to 1999, with 67% of terrestrial areas experiencing a doubling in their occurrence. Our findings highlight the importance of classifying heatwave-days based on their underlying mechanisms, as this can enhance our understanding of heatwaves and improve strategies for heat adaptation.

Deciphering Doping Effects in a V-Doped Ni Catalyst for Hydrogen Electrooxidation.

The improved performance of soluble metal-doped Ni catalysts is perplexed by the evolvable surface structures in the alkaline electrolytes for hydrogen oxidation reaction (HOR). Herein, V-doped Ni nanoparticles, as a proof of concept, were carefully evaluated to explore the intrinsic function of the enthetic V-species in assisting the HOR kinetic improvement. As expected, it exhibits a mass-normalized kinetic current density of 50.34 mA mgNi-1, more than 12 times that of the Ni counterpart without the introduction of V. Systematic investigations prove that the surface V-species, including the V-oxides and the doped V atoms at the outmost layer, would be dissolved into the electrolytes during the alkaline HOR process. The remaining V-dopants inside the nanoparticles would rationally weaken the hydroxyl binding energy (OHBE) of the Ni-based surfaces, thereby accelerating the formation of water molecules. We also uncover that Ni is located at the overstrong branch of the OHBE-described volcano plot through theoretical calculations and alkali-metal cation probe experiments, and weakening the OHBE by internal V-doping can leave the activity to the volcanic apex.

Adsorption and evolution of N2 molecules over ZnO monolayer: a combined DFT and kinetic Monte-Carlo insight

A large surface area, wide band gap, and unique bonding property between Zn and O atoms make the hexagonal ZnO monolayer attractive as a gas sensor. In the present work, the adsorption and evolution of nitrogen (N2) molecules over a ZnO monolayer have been studied using two different theoretical methods: van der Waals density functional theory (vdW-DFT) and kinetic Monte-Carlo (kMC) simulation. The adsorption and diffusion (hopping over the surface) energy of a N2 gas molecule has been calculated considering the different sites over the ZnO substrate using the revPBE-vdW functional. Bader charge, electron localization function analysis, density of states and band structure plotting have been used to understand the adsorption mechanism. Lateral repulsive interaction between two N2 molecules limits the maximum packing number of gas molecules within one hexagonal ring. The output of the vdW-DFT calculation has been fed to the kMC code to predict the rate of adsorption, desorption, and diffusion, along with the overall surface coverage at different temperatures and pressures. Finally, the change in the N2 adsorption energy has been predicted with the increase of the ZnO layer number.

Emulsification and interfacial characteristics of different surfactants enhances heavy oil recovery: experimental evaluation and molecular dynamics simulation study

The high viscosity and poor fluidity of heavy oil challenge its extraction, leading to the widespread use of surfactant emulsification to reduce viscosity and enhance recovery. This study evaluated three surfactants—sodium dodecyl sulfate (SDS), sodium oleate (SO), and APG0810—for their suitability and effectiveness in the X reservoir. The solution properties of these surfactants were analyzed and their micro-mechanisms investigated using MD calculations. The effects of surfactant concentration and additives on emulsification and viscosity reduction were elucidated. Ultimately, a system for emulsification and viscosity reduction was selected for physical simulation research. The experimental findings show that SO reduces interfacial tension from 52.4 mN/m to 0.0027 mN/m, transforming lipophilic surfaces into hydrophilic. MD analyses reveal SO’s optimal interfacial properties, with the lowest interfacial energy of −6423.4 kcal/mol, maximum interfacial thickness of 2.56 nm, and minimal diffusion coefficient of 0.4087 Å2/ps at the oil-water interface. These findings align with experimental results, confirming SO’s superior interfacial properties. Combining 0.3% SO with 0.5% n-pentanol results in a 98% viscosity reduction. The emulsion shows excellent stability, with no water separation in the first 30 min and only 8.3% after 2 h. Physical simulation results show that in high(low) permeability core displacement experiments, system flooding and subsequent water flooding can increase recovery rates by 15.39%(36.91%), indicating the system’s potential for enhancing oil recovery in Reservoir X. The findings suggest that the implementation of this system not only boosts the crude oil recovery rate but also carries economic significance in the industry.

Transition state of matter in the fluctuation model of crystal growth

Two mechanisms of the effect of the transition state of building particles (activated complexes according to S. Arrhenius) on the crystal growth rate within the framework of the fluctuation model of dislocation crystal growth are discussed. Transition state clusters adsorbed on the surface of the growing face perform the function of an impurity that lowers the surface energy of the crystal at the time moments between free energy fluctuations. Thus, the transition state of the crystallizing substance by the first mechanism affects the relaxation rate of the secondary adsorption of impurities and shortens the time period of attachment of building particles to the crystal face. Other clusters formed in solution reduce the number of free particles and under conditions of low concentration of the building substance are able to decrease the crystallization rate. Nevertheless, in a natural multicomponent crystallization environment, at low concentrations of building material, significant thermal effect of crystallization and small deviations from equilibrium, the role of the transition state in crystal growth is generally insignificant.

Transparent, Flexible, Responsive Switching "Delayed" Amphiphilic Coatings Designed on the Basis of the Full-Cycle Antifouling Strategy.

Marine fouling on the surface of ships and equipment not only creates problems of enhanced resistance to navigation and increased energy consumption but also leads to unclear vision and inaccurate data collection. Antifouling coatings to resist fouling are effective, but it is difficult to achieve long-lasting fouling protection with a single interface state. Switching the status of the interface by intelligent response is a reasonable way to achieve full-cycle efficient antifouling. In this study, the hydrophobic and active antifouling interface in the initial state was achieved by adopting the fluorine-containing group and the natural extract (citronellol) as the antifouling active site. The switching of the interface relies on silanes, which respond to the generation of zwitterions in a seawater environment. Eventually, the interface switched from the hydrophobic state to the amphiphilic state with delayed formation, which achieved continued antifouling. Based on the full-cycle antifouling concept, the combination of low surface energy and antifouling active ingredients in the initial state sustainably switched surfaces in the midterm (free radicals generated during the hydrolysis process), and amphiphilic interfaces formed by "delays" produced an antifouling effect from the initial stage to the subsequent stage. The excellent antifouling activity (bacterial and diatom attachment inhibition by over 90% and significantly reduced mussel adhesion force), optical transparency, and flexibility of these coatings indicate the potential for the application of antifouling coatings prepared from hyperbranched silicone-based resins; they can also be used for data extraction sensors, underwater probes, marine photovoltaics, and other areas where transparency is required.

Determination of surface free energy and acido-basicity of MXene materials measured by inverse gas chromatography at infinite dilution

Since the seminal report of Ti3C2Tx in 2011, MXene has emerged as a subject of considerable interest among researchers, finding diverse applications spanning energy storage, catalysis, and coatings. Despite extensive studies on the physicochemical properties of MXene, a comprehensive understanding of its surface energetics, free from environmental influences or external substitutes, remains lacking. This study aims to fill this gap by employing the inverse gas chromatography (IGC) technique at infinite dilution to delineate the London dispersive and specific components, alongside the Lewis acid-base characters, of surface free energy in MXene materials, including MAX phase and MXene. Our findings reveal that the London dispersive surface energy values of MAX phase and MXene range from 59.3 to 80.2 mJ m−2 and 107.8–119.9 mJ m−2, respectively, across temperature ranges of 303–333 K and 393–423 K. The observed augmentation in surface energy for MXene is attributed to a higher density of non-polar surface groups and an enlarged interlayer spacing. Additionally, our analysis indicates significantly higher acceptor (KA) and donor (KD) parameters for MXene (0.97 and 1.97, respectively) compared to MAX phase (0.41 and 0.63, respectively), suggesting a preference for the Lewis acid-base character in both materials, with MXene exhibiting a more pronounced tendency. These findings offer crucial insights into the fundamental surface energetic characteristics underlying multiple physicochemical properties of MXene. This understanding facilitates the informed design of interface engineering strategies, advancing the exploration and advancement of MXene-based technologies across a broad spectrum of applications.

A Novel Method for Rapid and High-Performance SERS Substrate Fabrication by Combination of Cold Plasma and Laser Treatment.

In this paper, we report a simple yet efficient method for rapid and high-performance SERS substrate fabrication by a combination of cold plasma and laser treatment. Our analysis reveals that cold plasma pre-treatment significantly reduced surface roughness, transforming 200 nm spikes into an almost perfectly uniform surface, while enhancing the substrate's surface energy by lowering the water contact angle from 59° to 0°, all achieved within just 30 s of 0.9-mW plasma treatment, while 15-min green-laser treatment facilitated more uniform deposition of AuNPs across the entire treated area, effectively creating the SERS substrates. The combined treatments result in enhancement of the Raman intensity (11 times) and consistency over the whole area of the SERS substrates, and their reusability (up to 10 times). The fabricated SERS substrates exhibit a significant enhancement factor of approximately 3 × 10⁸ with R6G, allowing detection down to a concentration of 10-12 M. We demonstrate the application of these SERS substrates by detecting amoxicillin-an antibiotic used worldwide to treat a diversity of bacterial infections-in a dynamic expanded linear range of seven orders (from 10-3 to 10-9 M) with high reliability (R2 = 0.98), and a detection limit of 9 × 10-10 M. Our approach to high-performance SERS substrate fabrication holds potential for further expansion to other metallic NPs like Ag, or magnetic NPs (Fe3O4).

Mechanisms of hardness enhancement in CrB2 thin films with varying VB2 concentrations

Transition metal borides are well-known for their high hardness, excellent wear resistance, chemical inertness, and electrical conductivity, making them promising for a wide range of applications. Understanding the interconnections between material structure, composition, and mechanical properties is essential for designing and synthesizing effective coatings. This study systematically investigates the structural and mechanical properties of CrB₂ thin films with varying concentrations of VB₂ (0–10 wt%), focusing on structure, hardness, elastic behavior and deformation characteristics mechanisms through atomic force microscopy and nanoindentation measurements. The results show that increasing VB₂ content leads to the formation of island cluster structures, which significantly strengthens atomic bonds and, in turn, enhances the hardness of the thin films. As particle size decreases, the higher proportion of surface atoms and increased surface energy have a more pronounced effect on the mechanical properties. In particular, the addition of VB₂ up to 10 wt% in CrB₂ thin films results in a marked improvement in superhard properties. 26 % increase in hardness value is also influenced directly by the changes in Young's modulus and Poisson's ratio that depend on the VB₂ concentration.