Substrate Surface Research Articles

Dynamic Surface Interactions Enable the Self-Assembly of Perfect Supramolecular Crystals.

Supramolecular crystals arise from noncovalent interactions between macromonomers and allow for the engineering of dynamic functional materials. For two-dimensional (2D) crystals, the substrate surface can induce the formation of new polymorphs not available in solution, adding a layer of complexity to the supramolecular self-assembly process. Despite extensive studies on the 2D self-assembly of supramolecular crystals, unknowns remain regarding substrate-monomer interactions and the effects on network self-assembly and defect repair. Here, we used a DNA-mica model system to modulate and understand the impact of substrate-monomer interactions on the crystalline order. We controlled the surface interactions by tuning the Mg2+ concentration, varying the divalent cation type, and adjusting the relative concentration of divalent and monovalent cations. The competition between monovalent and divalent cations yielded nearly defect-free crystals with minimal polygon defects. These findings highlight the critical role of surface interactions in achieving high crystalline order, which is essential for optimizing the efficiency and performance of supramolecular functional nanomaterials.

Ultrathin PVP/ZnMoO4@PE separator for high-safety sodium-ion batteries

In this work, an ultrathin (∼19 μm) PVP/ZnMoO4@PE separator is designed and achieved with much enhanced thermal performance for high-safety sodium-ion batteries (SIBs). The PVP/ZnMoO4@PE separator is prepared by coating the polyvinyl pyrrolidone (PVP)/ZnMoO4 ceramic slurry on one side of commercial polyethylene (PE) separator in an economically efficient way. It is found that the superior PVP binder would interact with ZnMoO4 nanoparticles and enhance the bonding strength of heat-resistant ZnMoO4 ceramic nanoparticles on the surface of PE substrate, which significantly improves the thermal performance of the optimized separator. The optimized PVP/ZnMoO4@PE separator shows high thermal stability with no shrinkage at 180 °C for 30 min. In addition, the PVP/ZnMoO4@PE separator shows improved wettability with electrolyte, larger porosity and better electrolyte storage capacity than bare PE separator, which are quite beneficial to ionic conductivity. Furthermore, the electrochemical results show that half-cell (hard carbon/sodium) assembled with the optimized PVP/ZnMoO4@PE separator shows better electrochemical performance that the half-cell assembled with commercial glass fiber separator (thickness of ∼ 455 μm), while bare PE separator does not work properly in SIBs. This study provides insight into the practical application of ultrathin and high-safety PVP/ZnMoO4@PE separator in commercial SIBs.

Impact of water vapor on the 2D MoS2 growth in metal-organic chemical vapor deposition

In the presented work, the method of metal–organic chemical vapor deposition (MOCVD) using Mo(CO)6 and H2S assisted by oxidative etching with water vapor, was employed for the synthesis of MoS2. This study was aimed at detailed investigation of the films' properties obtained via this method and identifying methods for elimination of such disadvantages as the carbon impurities and the small size of crystalline domains in the films. It was found that in the temperature range from 850 °C to 950 °C, the effect of water vapor on the morphology of MoS2 is significantly different. The study of the chemical states of molybdenum and sulfur made it possible to associate the size of the crystal domains formed with the efficiency of removing the oxidized states of Mo6+ and S6+. It is assumed that the increase in the domains’ size is due to rapid lateral growth, resulting from the complete removal of the oxidized states at the edges, as well as a decrease in the density of nucleation centers due to the etching of less stable seeds on the substrate surface.

Polymerizable deep eutectic solvent-gels synthesized in situ under molecular engineering control exhibit excellent adhesion, freeze resistance, as well as stretching and humidity sensing capabilities

Hydrogels generally do not adhere well to different substrates and freeze at sub-zero temperatures, limiting their application. In this study, the strategy of replacing water in hydrogels with deep eutectic solvents (DES) was used to address these challenges. Specifically, choline chloride (ChCl) as hydrogen bond acceptor, acrylic acid (AA) and itaconic acid (IA) as hydrogen bond donors and polymerizable monomers constitute PDES. Afterwards, PDES-gel (PG) was obtained by adding a thermal initiator to polymerize AA and IA in PDES. PG has the following characteristics, because PG is almost water-free, it has remarkable low-temperature tolerance without any phase change at −60 °C to 20 °C. Thanks to the carboxyl groups and chloride ions contained in PG, it can form non-covalent interactions such as hydrogen bonding and ionic interactions with different substrates, so PG can adhere to various substrate surfaces. Furthermore, the breaking elongation of the novelty PG was up to ca. 960 %, tensile strength ca. 1 MPa, outstanding transparency with an average light transmittance of about 95 % in the visible-light range. Ultimately, the novel PG exhibited certain capabilities for moisture detection and deformation sensing. The new PDES-gel material developed using PDES is expected to provide new ideas for the advancement of wearable devices.

Valence Band-Tunable NiFe Electrocatalyst Triggered by the Dynamic Mo Exudation and Re-Deposition for Superior High Current Density Oxygen Evolution Reaction.

Developing energy- and time-efficient strategies to derive high-performance non-precious electrocatalysts for anodic oxygen evolution reaction (OER), especially stably working at industrial-demanding current density, is still a big challenge. In this work, a concise molten salt erosion scenario was devised to rapidly modulate the smooth surface of the commercial NiMo foam substrate into the rough, electronically coupled, and hierarchically porous Ni/Fe/Mo(oxy)hydroxide catalyst layer assembled by the nanosphere array. This self-supported catalyst is super-hydrophilic for the alkaline electrolyte and distinguished by a balanced Mo leaching/surface-readsorption process to tune the metal d band center and electronic perturbation. The altered electronic environment with the favored OER intermediate adsorption behavior attains the outstanding OER activity in terms of a very small overpotential of 230.21 mV at 10 mA cm-2 and an ultra-long stability for 1179.45 h to sustain the initial commercial-level current density of ca. 1000 mA cm-2. This superb performance transcends most of the edge-cutting transition metal peers reported recently and can satisfy the standards of industrial applications. This industrial-compatible synthesis technology holds profound implications for hydrogen production via water splitting and other electrochemical applications.

Properties of boron layers deposited during boronisations in W7-X

Boronisation was first used for wall conditioning in W7-X during the OP 1.2b operational period, which was characterized by the use of the fine-grain graphite Test Divertor Unit (TDU) and inertial cooling only. After this period, deposited layers were observed on all inner surfaces. Deposited layers were analyzed on 21 inner wall tiles using ion beam analysis methods, the deposited layers consisted mostly of boron with additional carbon and oxygen. During the operational period OP2.1 with an actively water cooled divertor made of carbon fiber reinforced carbon, different materials were exposed during two individual boronisations using the multi-purpose manipulator. Deposited boronisation layers on the samples were analyzed using nuclear reaction analysis. The deposited layer thicknesses showed some variation depending on substrate material and surface roughness, but a systematic dependence on material and/or roughness was not observed. Under the typical boronisation conditions at W7-X, one A × h (Ampere times hour) of boronisation results in a boronisation layer with a thickness of about 30 ± 15 × 1015B-atoms/cm2 (about 3 ± 1.5 nm) at the position of the multi-purpose manipulator. The oxygen gettering capacity of the layers is up to 0.5 – 0.9O/B.

Preparation of Atomically Smooth SrTiO₃ Substrates

SrTiO3 has been used as a substrate to grow thin films of materials including high-temperature superconductors such as cuprates, ferromagnetic oxides such as manganites, and ferroelectric oxides such as BaTiO3. The use of SrTiO3 as a substrate for the deposition of manganite thin films provides an excellent template for observing unique effects observed only in ferromagnets, such as the anomalous and planar Hall effects. The as-received SrTiO3 substrates require a process that prepares atomically smooth surfaces for thin film deposition. This study focuses on using ultrasonic cleaning, water annealing, and thermal annealing in air to prepare SrTiO3 substrate surfaces and verifying their smoothness at the atomic scale using atomic force microscopy.

Self-Assembly of Cyclic-Bending Collagen Fibrils by Polyimide Films.

The cyclic-bending morphologies of the fibrils formed by the self-assembly of type I collagen (Col) are closely related to the mechanisms of various diseases. Therefore, studies that allow the self-assembly of Col molecules to form cyclic-bending fibrils in vitro are vitally important. In this study, we successfully achieved the cyclic-bending shapes (specifically, a regular hexagonal shape) of Col molecules by controlling the steric structures of polyimide (PI) molecular chains through the film formation process. Specifically, when a single layer of PI film was baked, the PI molecular chains within the film bent in the direction parallel to the substrate surface plane. Repeating the layering and baking processes resulted in 3D structures of the PI molecular chains, which were oriented in the direction perpendicular to the substrate surface plane. This three-dimensional bending would result from the PI molecular chain interactions between the upper and lower layers. When the Col molecules were reacted on these film surfaces, they recognized the structures of the PI molecular chains and self-assembled to form cyclic-bending Col fibrils. Especially, in PI films subjected to three cycles of layering and baking, hemicircular-shaped Col fibrils were observed to be regularly arrayed. Additionally, these regularly cyclic-bending fibrils were aligned in the uniaxial direction through a uniaxial rubbing treatment of the PI films. This successful research is significant both as a method for controlling the morphologies of Col fibrils and as a study that explores the biomedical implications of Col fibril cyclic-bending in the living body.

The Effect of Shot Blasting Abrasive Particles on the Microstructure of Thermal Barrier Coatings Containing Ni-Based Superalloy

Grit particles remaining on the substrate surface after grit blasting are generally considered to impair the thermal performance of thermal barrier coatings (TBCs). However, the specific mechanisms by which these particles degrade the multilayer structure of TBCs during thermal cycling have not yet been fully elucidated. In this study, the superalloy substrate was grit-blasted using various processing parameters, followed by the deposition of thermal barrier coatings (TBCs) consisting of a metallic bond coat (BC) and a ceramic top coat (TC). After thermal shock tests, local thinning or discontinuities in the thermally grown oxide (TGO) layer were observed in TBCs where large grit particles were embedded at the BC/substrate interface. Moreover, cracks originated at the concave positions of the TGO layer and propagated vertically towards BC; these cracks may be associated with additional stress imposed by the foreign grit particles during thermal cycling. At the BC/substrate interface, crack origins were observed in the vicinity of large grit particles (~50 μm).

ENHANCING MECHANICAL RELIABILITY OF SILVER SINTERED JOINTS WITH COPPER NANOWIRES IN HIGH-POWER ELECTRONIC DEVICES

Abstract This study investigated the mechanical reliability of silver-sintered die attachment under harsh operating conditions, and explored the advantages of adding copper nanowires to improve the bond's mechanical properties. Samples were prepared using a template-assisted electrochemical deposition process to coat the substrate surface with copper nanowires, and were subjected to thermal aging at various temperatures to assess their mechanical reliability. Results showed that the incorporation of copper nanowires in the substrate interface significantly reduced degradation in shear strength as a result of thermal aging, acting as mechanical reinforcement and improving the interfacial resilience against mechanical shear stress. The addition of copper nanowires also reduced the void formation in the thermal aging, resulting in a more robust and reliable bond. The study demonstrates the potential of using copper nanowires as a reinforcing agent to enhance the mechanical properties of silver-sintered die attachment, particularly for high-temperature applications.

Numerical Studies of Influencing Factors on the Homogeneity of the Powder Mixture during the Powder Spreading Process of Powder Bed Fusion–Laser Beam/Metal

Recent studies have focused on the alloying of nitrogen (N) in high‐alloy stainless steels by powder bed fusion–laser beam/metal (PBF‐LB/M). However, N‐induced pore formation remains a challenge. To overcome this, a combined PBF‐LB/M and hot isostatic pressing (HIP) process is developed. AISI 304L stainless steel powder was mixed with silicon nitride (Si3N4) powder and processed by PBF‐LB/M, allowing partial retention of Si3N4. This helps to maintain sufficient N content while reducing pore formation. The microstructure is then homogenised by HIP. A major challenge of this process is to maintain the homogeneity of the deposited powder mixture on the powder bed to ensure a consistent N content in the final products. This study combines experimental and numerical methods to address this issue: scanning electron microscopy is used to characterize the microstructure and map the local N content, while various numerical studies based on the discrete element method are carried out to investigate the effects of layer thickness, substrate surface roughness, and powder properties on the intermediate product. The numerical approach effectively predicts the N content distribution and homogeneity on the powder bed. The models are validated with experimental data and optimal process conditions for PBF‐LB/M are identified.

Effect of relative humidity on passive spore release from substrate surfaces

Fungal spores are abundant in ambient air and exposure to this type of bioaerosols are found to cause significant health and climatic effects. In this study, we investigated the influence of air relative humidity (RH) on the passive release of spores from solid substrates. Preliminary investigations into the effect of RH on fungal spore release indicated an increase in spore flux with reduced air RH. The change in spore emission flux occurred very quickly in response to a change in ambient RH. To verify the hypothesis of extremely rapid drying under lower RH, experiments were conducted using a quartz crystal microbalance with dissipation (QCM-D) to understand the timescales of spore moisture uptake and drying. The analysis of mass transfer of water to and from the spores indicated that the bulk of the transfer occurred within a minute of exposure to any RH. The effect of the ambient RH was explained using a mathematical model with the spotlight on the parameter, E, that represented the energy required to aerosolise one spore. This study demonstrates the application of QCM-D to study interaction between ambient aerosol particles and various vapor phase and gas phase environments. The study enhances the overall understanding and capability to characterise passive fungal spore release under varying humidity conditions in the natural environment.

On the Role of Substrate in Hydroxyapatite Coating Formation by Cold Spray

The deposition of agglomerated hydroxyapatite (HAp) powders by low-pressure cold spray has been a topic of interest in recent years. Key parameters influencing the deposition of HAp powders include particle morphology and impact kinetic energy. This work examines the deposition of HAp powders on various metal surfaces to assess the impact of substrate properties on the formation of HAp deposits via cold spray. The substrates studied here encompass metals with varying hardness and thermal conductivities, including Al6061, Inconel alloy 625, AISI 316 stainless steel, H13 tool steel, Ti6Al4V, and AZ31 alloy. Single-track experiments offer insights into the initial interactions between HAp particles and different substrate surfaces. In this study, the results indicate that the ductility of the substrate may enhance HAp particle deposition only at the first deposition stages where substrate/particle interaction is the most critical factor for deposition. Features on the substrate associated with the first deposition sprayed layer include localized substrate deformation and the formation of clusters of HAp agglomerates, which aid in HAp deposition. Furthermore, after multiple spraying passes on the various metallic surfaces, deposition efficiency was significantly reduced when the build-up process of HAp coatings shifted from ceramic/metal to ceramic/ceramic interactions. Overall, this study achieved agglomerated HAp deposits with high deposition efficiencies (30–60%) through single-track experiments and resulted in the preparation of HAp coatings on various substrates with thickness values ranging from 24 to 53 µm. These coatings exhibited bioactive behavior in simulated body fluid.

Adsorption and gas sensing properties of Cun, Agn and Rhn (n=1–3) clusters doped with WTe2 for transformer winding deformation fault gases

In order to solve the problem that the initial WTe2 has poor adsorption effect on transformer winding deformation fault gas, this paper uses density functional theory (DFT) to study the adsorption behavior of three target gases (CO, C2H2 and CO2) on the surface of WTe2 substrate doped with three metal clusters: Cun, Agn, and Rhn (n=1–3). By analyzing the adsorption distance, adsorption energy, DCD and DOS of the three systems, the effect of metal cluster doping on the adsorption of fault gas by WTe2 was revealed. The results show that metal cluster doping can effectively improve the conductivity of WTe2 substrate and make its band structure more compact. CO and C2H2 have good adsorption characteristics in the three doping systems, while CO2 can be effectively adsorbed by Rh cluster-doped WTe2. In addition, this article also uses work function and band gap to analyze the effect of gas adsorption on substrate conductivity, and discusses the practical application prospects of the three metal cluster doping systems from the perspectives of recovery time and sensitivity, and achieved good results. This paper provides theoretical guidance for exploring the application prospects of WTe2 substrate in transformer winding deformation fault diagnosis and gas detection.

Unsteady numerical simulations of aircraft icing based on the dynamic grid method

In this study, an unsteady numerical simulation method based on dynamic grids was established to solve unsteady aircraft icing processes. The dual-time step method was used to achieve the time advancement of the transient airflow and droplets fields. The droplets trajectory was calculated using the Euler method, which incorporates a supercooled large droplets model. The transient evolution of the water film and ice layer on the substrate surface was considered in the icing thermodynamic model. The accuracy of the unsteady method for ice-shape prediction was verified via comparison and analysis of numerical examples. Additionally, the rime and glaze ice formation processes were explored, and the coupling effects of ice horn growth and the air convective heat transfer coefficient, water collection coefficient, and water film flow on the substrate surface were studied. The ice shapes calculated by unsteady and quasi-steady methods were compared. The results indicated that the latter predicts a larger icing range than the former. Moreover, there may be more obvious distinctions between these two methods in predicting glaze ice.

Spontaneous continuous multiple jump of condensate droplets on superhydrophobic surface with hierarchical micro-nano structures

When two or more droplets coalesce on a superhydrophobic surface, the released surface energy will partially convert into kinetic energy, resulting in droplet jump from substrate surface. In this paper, a kind of superhydrophobic surface with hierarchical papillary micro-nano structures was fabricated to facilitate droplets coalescence-induced jump. The surface is easy to prepare without complex process. Different from single jump, a kind of spontaneous continuous multiple jump was observed on this kind of superhydrophobic surface. The influences of continuous multiple jump on condensation nucleation rate and water collection rate are investigated and a theoretical model is adopted to determine energy conversion efficiency of continuous multiple jump. The results find that continuous multiple jump makes large droplets to move spontaneously, and improves performance of superhydrophobic surface to maintain dropwise condensation even under a high subcooling. With condensing, the continuous multiple jump becomes more frequent. The average condensation nucleation rate is 303 % higher than those of surfaces without hierarchical micro-nano structures. The water collection rate on superhydrophobic surface is 2 times higher than those without hierarchical micro-nano structures. The energy conversion efficiency of continuous multiple jump is two times higher than that of single jump. This study provides a potential direction for heat transfer enhancement of condensation and self-cleaning.

Fluoride-incorporated apatite coating on resin-based composite via laser-assisted rapid pseudo-biomineralization

A thin-layer of fluoride-incorporated hydroxyapatite (FAp) is useful as an acid-resistant antibacterial mineralized coating to protect a tooth surface. Recently, we achieved rapid and area-specific FAp coating on the surfaces of human tooth substrates via precoating with a light-absorbing agent, indocyanine green, followed by laser irradiation in a fluoride-containing supersaturated calcium phosphate solution. In the present study, this FAp coating technique was applied to a substrate of resin-based composite (RBC), an artificial material with no biomineral component. Similar to the case of tooth substrates, a mineralized layer consisting of needle-like FAp crystals was formed on the RBC surface after laser irradiation for 3 min. The needle-like crystals increased in size with increasing laser power. In the absence of fluoride ions in the supersaturated solution, a layer consisting of plate-like octacalcium phosphate crystals was formed on the RBC surface. The present FAp coating technique was finally applied to an RBC-restored tooth substrate. Cross-sectional analyses revealed that the boundary region between the tooth and RBC was coated and sealed with a mineralized layer. The present FAp coating technique is potentially a new tool to seal the tooth–RBC boundary and reduce the risk of secondary caries associated with RBC restorations.

Optimizing the grasping behavior of a soft robot's gripper

AbstractIn this study, smart composite materials based on 4D printing technology were used to determine the grasping ability of four‐claw gripper of soft robot. First, fused deposition modeling (FDM) is used to prepare polylactic acid (PLA) strips on the surface of a rectangular bamboo substrate to create a single‐claw gripper for a smart composite soft robot, while using stimulus (heat) to deform and recover its original shape. Here, the authors first evaluate the deformation and recovery angle of the single‐claw gripper of the smart composite soft robot, as well as various processing parameters such as heating temperature and time. This study then used FDM to print PLA ribbons on cross‐shaped bamboo sheets to design the four‐claw gripper of soft robot and its gripper technology was actuation type. Then, the four‐claw gripper of soft robot was used to grab the table tennis ball to test its grasping ability. Finally, four processing parameters (width of claw, pitch of PLA ribbon, heating temperature, and heating time) were applied to determine the grasping ability of the four‐claw gripper of soft robot. The optimal processing parameters for the grasping ability of the four‐claw gripper of soft robot were width of claw of 20.2 mm, pitch of PLA ribbon of 1 mm, heating temperature of 200°C, and the heating time of 15 s. The authors also applied the operation window of two processing parameters to discuss the success of the grasping ability of the four‐claw gripper of soft robot. The innovation of this study is the use of PLA/bamboo composite materials as the four‐claw gripper of soft robot and these materials are cheap, easy to obtain, and can be recycled naturally. This study uses a simple thermal stimulus to enable the four‐claw gripper of soft robot to easily grasp irregular objects.Highlights The innovative composite material of polylactic acid and bamboo fabricated by 3D printing. Width of claw and heating temperature are the key factors on grasping ability. Operating window of grasping ability appears on four‐claw gripper of soft robot.

Substrate and potential-driven surface morphology of bifunctional Ni-Fe electrode for efficient alkaline water electrolysis

Nickel-iron (Ni-Fe) alloy electrodes are synthesized using chronoamperometry. The influence of substrate type (copper, stainless steel, and nickel) and deposition potential on the structural, morphological, and electrocatalytic characteristics are systematically investigated. X-ray diffraction (XRD) analysis revealed the formation of a face-centered cubic (FCC) Ni-Fe alloy. Electrodeposition at higher potential (−1.45 V) forms well-defined nanoflakes, whereas electrodeposition at lower potential (−1.00 V) results aggregated Ni-Fe particles. The Ni-Fe alloy electrodes having well-defined nanoflakes demonstrated superior electrocatalytic performance, exhibiting a overpotential of −168 mV vs. RHE for the hydrogen evolution reaction (HER) and 236 mV vs. RHE for the oxygen evolution reaction (OER), at current density of 10 mA/cm2. The enhanced electrocatalytic activity of the nanoflakes based Ni-Fe alloy is attributed due to their larger catalytic surface area, porous morphology and higher Fe concentration. The Ni-Fe alloy electrodes displayed bifunctional electrocatalytic behavior, making them highly suitable for both HER and OER processes.

Evaluation of Micro Hardness of Magnesium Alloy Coated with ZnO and Al2O3

Magnesium and its alloys have wide range of application in automobile and aircraft industries because of their excellent mechanical properties i.e. high strength to weight ratio, availability and good castability etc. However, some challenges occur in using magnesium in aquas service applications, due to its highly reactive nature and low tribological properties such as low wear and corrosion resistance. In this work an experimental study has been done on uncoated and ceramic coated AZ91 alloy to compare hardness and wear properties of both. The coating was applied on varying weight percentage of ZnO and Al2O3ceramic particles. The effect of presence of ceramic particles on the surface of substrate was studied using scanning electron microscope. Micro Vickers hardness test and wear tests were conducted on the samples, and it was found that coating of ceramic particles made the surface harder and wear resistant as compared to the uncoated Mg alloy. Contribution of Al2O3 particles plays an importantrole in increasing the hardness and wear resistance of coated surface. A decrease of 84% in coefficient of friction, increase in wear resistance by 99% and increase in micro hardness by 92% was reported for Al2O3 coated sample as compared to the uncoated surface.