Modified Surface Layer Research Articles

Characterization of Quasi-Static/Dynamic Contact Mechanical Properties of Mo Surface-Modified TC4

By using the double glow plasma surface alloying technique, a Mo surface-modified layer is prepared on Ti6Al4V(TC4). The element concentration and microstructure are characterized with a glow-discharge optical emission spectroscope and a scanning electron microscope. The results indicate that the Mo modified layer is compact in structure and gradation in composition, which consists of a pure Mo deposition layer and a thick Mo diffusion layer. Nanoindentation test results indicate that the surface hardness of TC4 is significantly improved after surface modification. Therefore, the initial part of the Mo diffusion layer has higher hardness than the Mo deposition layer. The impact tests for 10,000 cycles at different loads demonstrate that impact load 100 N only causes small plastic deformation, while impact loads 300 N and 500 N could result in cracks. Combining nanoindentation test with finite element reverse analysis, plastic parameters of the Mo modified layer are quantitatively determined. By using the impact test and finite element forward analysis, the dynamic contact mechanical properties of Mo surface-modified TC4 are characterized. When the impact cycles are fixed, ring cracks firstly occur and then radial cracks occur with the impact load increase on the graded layer. The ring cracks are mainly caused by impact stretch fatigue and corresponding cyclic stress is between 3.53 and 2.62 GPa. The radial cracks are mainly related to the tension-compression fatigue and corresponding cyclic stress is between 3.92 and −0.97 GPa.

Low-infrared-emissivity Al@SiO2/EPDM composite coating compatible with low dielectric loss and antistatic property

Low infrared emissivity coatings have been widely used in many fields. At present, there are few researches on coatings that are compatible with low infrared emissivity and high radar wave transmittance. In this paper, floating aluminum (Al) powdercoated with SiO2 was prepared using tetraethyl orthosilicate (TEOS) as raw material by sol-gel method. The composite coating was prepared using modified Al powder and antistatic carbonaceous fiber (CF) as filler, EPDM as binder. The surface morphology, infrared absorption properties of the modified Al powder and the infrared emissivity, surface resistivity, electromagnetic properties and mechanical properties of the composite coating were analyzed. The results show that with the increase of TEOS addition amount, more SiO2 was covered to the surface of floating Al powder. By adjusting the thickness of the surface modification layer of floating Al powder,the dielectric constant (ε) and dielectric loss tangent values (tanδ) of the composite coating were significantly reduced. When the addition amount of TEOS is 1 g for Al@SiO2, the ε and tanδ can be significantly reduced, and the infrared emissivity was less than 0.6, the tensile strength (σb) and elongation rate at break (e) decreased slightly. This suggests that the composite coating has low infrared emissivity compatible with high radar wave transmittance was obtained, which is expected to be applied to the surface of aircraft radome.

Diketopyrrolopyrrole-based conjugated polymers containing planar benzo[c]cinnoline and tetraazapyrene structures for high-performance and long-term stable triboelectric nanogenerators

A promising strategy to simultaneously improve the performance and stability of a triboelectric nanogenerator is demonstrated by using DPP-based conjugated polymers containing planar BZC and TAP structures as the surface modification layer.

Temperature-time characteristics of hardened and modified surface layers of parts

The role of the temperature-time characteristics of the surface layers of the part hardened and modified with copper in determining their performance properties is shown. Regularities of changes in the temperature-time characteristics of technological residual stresses depending on the state of the surface layer of parts are studied. It is proved that at the maximum value of the initial value of the temperature-time characteristic of the hardened modified layer of the part, the friction coefficient for given conditions and friction modes has the smallest value.

Achieving a dendrite-free lithium metal anode through lithiophilic surface modification with sodium diethyldithiocarbamate

Sodium diethyldithiocarbamate (DDTC) monolayer self-assembly on Cu foil can be used to construct a lithiophilic surface modification layer, which can help to achieve a robust and stable SEI and guide homogeneous and dendrite-free Li deposition.

The structure and mechanical properties of Cr-based Cr-Ti alloy films

Previous studies have dealt with Cr and its alloy films that exhibit promising characteristics as surface modification layers for antiwear, anticorrosive, and decorative applications. However, the effect of Ti alloying on the structure and mechanical properties of Cr films has not been studied. This work aimed to the structure and mechanical properties of Cr-Ti alloy films in the Cr-rich side. To this end, pure Cr, Cr-6 at.% Ti, Cr-11 at.% Ti, Cr-16 at.% Ti, and Cr-21 at.% Ti alloy films were prepared by magnetron sputtering, and the structure and mechanical properties of the films were evaluated. The results indicated that all the films exhibited a Cr-based growth with body-centered cubic structure, and increasing the Ti content decreased the (110) orientation growth of Cr basis. Ti alloying increased the hardness of the films, while leaded to a monotonic decrease in the modulus of the films. The first-principles method was employed to demonstrate that the reduced modulus was determined by the Ti alloying degree, rather than the orientation evolution of the films. The analysis of H/E value suggested that the wear resistance of the films was improved by Ti alloying. The mechanical properties of present Cr-Ti alloy films, and other Cr-based alloy films or metallic glasses in publications were compared and discussed. We proposed that Ti alloying is a considerable way to explore advanced mechanical properties of Cr-based alloy films.

Atomic layer etching of SiO2 with self-limiting behavior on the surface modification step using sequential exposure of HF and NH3

Thermal atomic layer etching (ALE) for SiO2 films with self-limiting behavior on the surface modification step was developed using sequential exposure to HF and NH3 gases followed by infrared (IR) annealing. X-ray photoelectron spectroscopy analysis showed that an (NH4)2SiF6-based surface-modified layer was formed on the SiO2 surface after gas exposures and that this layer was removed using IR annealing. The etch per cycle (EPC) of the ALE process saturated at 0.9 nm/cycle as the gas exposure times increased. With this self-limiting behavior, SiO2 was etched with high selectivity to poly-Si and Si3N4. The dependence of the EPC on the partial pressures of HF and NH3 was found to be in good agreement with the Langmuir adsorption model. This indicated that the HF and NH­3 molecules were in equilibrium between adsorption and desorption during the exposure, which resulted in the self-limiting formation of the modified layer. In addition to the process with an HF gas flow, it was demonstrated that an H2/SF6 plasma can replace the HF gas exposure step to supply the SiO2 surfaces with HF molecules. The EPC saturated at 2.7 nm/cycle, while no measurable thickness change was observed for poly-Si and Si3N4 films.

Applications of 2D MXenes for Electrochemical Energy Conversion and Storage

As newly emerged 2D layered transition metal carbides or carbonitrides, MXenes have attracted growing attention in energy conversion and storage applications due to their exceptional high electronic conductivity, ample functional groups (e.g., -OH, -F, -O), desirable hydrophilicity, and superior dispersibility in aqueous solutions. The significant advantages of MXenes enable them to be intriguing structural units to engineer advanced MXene-based nanocomposites for electrochemical storage devices with remarkable performances. Herein, this review summarizes the current advances of MXene-based materials for energy storage (e.g., supercapacitors, lithium ion batteries, and zinc ion storage devices), in which the fabrication routes and the special functions of MXenes for electrode materials, conductive matrix, surface modification, heteroatom doping, crumpling, and protective layer to prevent dendrite growth are highlighted. Additionally, given that MXene are versatile for self-assembling into specific configuration with geometric flexibility, great efforts about methodologies (e.g., vacuum filtration, mask-assisted filtration, screen printing, extrusion printing technique, and directly writing) of patterned MXene-based composite film or MXene-based conductive ink for fabricating more types of energy storage device were also discussed. Finally, the existing challenges and prospects of MXene-based materials and growing trend for further energy storage devices are also presented.

Evaluation of tribotechnical properties of modified surfaces after plasma electrolytic treatment

The article considers the study of the effect of plasma electrolytic processing on the tribotechnical characteristics of medium-carbon steel. Friction tests were carried out in dry friction mode. Electron microscope and profilometer were used to study the friction tracks. For a comprehensive assessment of the quality of the modified surface layer, the Kragelsky-Kombalov complex parameter was calculated. It was found that plasma electrolytic treatment leads to a decrease in the coefficient of friction and weight wear in comparison with hardened and untreated steel. It has been determined that the mechanism of wear of samples after plasma electrolytic treatment is fatigue wear at boundary friction and plastic contact.

Research study of the elastic-strength and tribological characteristics of the surface after laser processing of the slurry coatings

The research paper examines the results of applying the proposed method of the laser processing of the composite slurry coating on the steel samples` surface such as 12Kh2N4A-Sh. An increase in the elastic-strength and tribological characteristics` surface occurs as a result of the imposition of several physicochemical processes in the laser-impact zone on the applied composite slurry coating with an epoxy element as the base material with the laser thermal hardening, the diffusion influence on the atomic boron along grain boundaries, carbonization and the formation of a modified surface layer. The conducted research shows the gradient structure of the surface layers. The coating composition varies in the studied samples, however, for all experimental samples, the elastic-strength and tribological characteristics are higher than the corresponding characteristics of the standard steel sample as 12Kh2N4A-Sh, which has undergone the cementation process. The calculated values of the resistance indicators of the elastic and plastic deformation are confirmed by the conducted tribological tests. It is given the higher efficiency of the laser processing method of the slurry coating and it is concluded the prospects of the proposed method.

Multifunctional Electrolyte Additive Stabilizes Electrode-Electrolyte Interface Layers for High-Voltage Lithium Metal Batteries.

A lithium metal anode and high nickel ternary cathode are considered viable candidates for high energy density lithium metal batteries (LMBs). However, unstable electrode-electrolyte interfaces and structure degradation of high nickel ternary cathode materials lead to serious capacity decay, consequently hindering their practical applications in LMBs. Herein, we introduced N,O-bis(trimethylsilyl) trifluoro acetamide (BTA) as a multifunctional additive for removing trace water and hydrofluoric acid (HF) from the electrolyte and inhibiting corrosive HF from disrupting the electrode-electrolyte interface layers. Furthermore, the BTA additive containing multiple functional groups (C-F, Si-O, Si-N, and C═N) promotes the formation of LiF-rich, Si- and N-containing solid electrolyte interfacial films on a lithium metal anode and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode surfaces, thereby improving the electrode-electrolytes interfacial stability and mitigating the capacity decay caused by structural degradation of the layered cathode. Using the BTA additive had tremendous benefits through modification of both anode and cathode surface layers. This was demonstrated using a Li||NMC811 metal battery with the BTA electrolyte, which exhibits remarkable cycling and rate performances (122.9 mA h g-1 at 10 C) and delivers a discharge capacity of 162 mA h g-1 after 100 cycles at 45 °C. Likewise, this study establishes a cost-effective approach of using a single additive to improve the electrochemical performance of LMBs.

Role of mixed conducting Pr0.1Gd0.1Ce0.8O1.9-δ barrier layer on the promotion of SOFC performance

The cathode activity in a solid oxide fuel cell can be promoted by introducing various catalysts to reduce its polarization resistance towards oxygen reduction, and thus improve cell performance. In this work, the La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode surface is modified by the infiltration of Pr6O11 and the power density at 0.8 V and 750 °C is improved by 21%. Moreover, by replacing the traditional barrier layer Gd0.2Ce0.8O1.9 with mixed conducting Pr0.1Gd0.1Ce0.8O1.9 (PGCO), the power density increases by 38%. The ohmic resistance is dramatically reduced by applying the PGCO interlayer. The distribution of relaxation time was used to analyze the mechanism for which the polarization resistance was decreased, attributing to the mixed conduction nature in PrOx. An increase of power density, ∼0.358 W/cm2 (71%) at 0.8 V, is achieved with the implementation of both surface modification and buffer layer engineering.

Surface Modification of a Nickel-Free Austenitic Stainless Steel by Low-Temperature Nitriding

Low-temperature nitriding allows to improve surface hardening of austenitic stainless steels, maintaining or even increasing their corrosion resistance. The treatment conditions to be used in order to avoid the precipitation of large amounts of nitrides are strictly related to alloy composition. When nickel is substituted by manganese as an austenite forming element, the production of nitride-free modified surface layers becomes a challenge, since manganese is a nitride forming element while nickel is not. In this study, the effects of nitriding conditions on the characteristics of the modified surface layers obtained on an austenitic stainless steel having a high manganese content and a negligible nickel one, a so-called nickel-free austenitic stainless steel, were investigated. Microstructure, phase composition, surface microhardness, and corrosion behavior in 5% NaCl were evaluated. The obtained results suggest that the precipitation of a large volume fraction of nitrides can be avoided using treatment temperatures lower than those usually employed for nickel-containing austenitic stainless steels. Nitriding at 360 and 380 °C for duration up to 5 h allows to produce modified surface layers, consisting mainly of the so-called expanded austenite or γN, which increase surface hardness in comparison with the untreated steel. Using selected conditions, corrosion resistance can also be significantly improved.

Study of the structure and properties of a high-entropy ceramic composite material

The article describes the technology development of layered surface compositions, including a high-entropy layer of a material with high-temperature memory effect of TiNiZrHfCoCu and a high-temperature ceramic layer based on zirconium dioxide ZrO2 stabilized by Y2O3. The authors also studied the structure, functional and mechanical properties of the abovementioned compositions. The proposed technology was implemented on a patented multifunctional technological complex for the formation of composite layered materials on the surface of steel products in a single technological cycle. On the basis of complex X-ray diffraction and electron microscopic studies, the structural parameters of the constituent layers of the surface composition were determined with subsequent thermal and thermomechanical treatment. The tests for ‘friction-wear’ and mechanical multi-cycle fatigue of the constituent layers of the surface composition showed a decrease in wear intensity and an increase in cyclic durability compared to the steel base. The comparison of wear intensity and cyclic durability of the surface-modified layers of the layered composition TiNiZrHfCoCu-ZrO2(Y2O3) with the composite materials obtained and studied by the authors earlier allowed the recommendation of the surface composition ‘high-entropy alloy TiNiZrHfCoCu-high-temperature ceramics’ for products of various purposes.

Nano Silica application for inducing rice resistance and the possibility for Ytterbium Rare Earth Elements green mining

There is a growing interest and recognition of Silicon (Si) in plants to increase growth, productivity, and plant resistance. This research examines the role of Nano Silica to increase yield and resistance. This study set out to assess the effect of hydrophilic fumed Nano Silica application with the frequency of 1×, 2×, 3×, and 4× applications respectively with three replications using RCBD as well as SEM-EDX and XRF analysis. Nano Silica frequencies showed a distinctive decrease of damage intensity at the 3× and 4× applications. The rice husk increases of metal-like surface appearance as more Nano Silica frequency was applied. It is proposed that Nano Si induced plant resistance through the modification of surface layer and stronger plant tolerance against environmental stress. The most unexpected observation to emerge was the Ytterbium (Yb) concentration known as a Rare Earth Elements at the 3× and 4× Nano Si applications. This indicates that Nano Silica application provides insights and opportunities to Nano Si application on Rice for the purpose of acquiring Ytterbium from farmland. Nano Silica can play an important role as a new method in addressing the Ytterbium green mining.

Dislocation-related conductivity in Au(In)/Cd1–xZnxTe(x = 0, 0.1) Schottky contacts

Dislocation-related conductivity is studied in Schottky contacts Au(In)/Cd1-xZnxTe (x = 0, 0.1) prepared on the surface of single crystals modified by multiple irradiation with a ruby laser and mechanical polishing. The contacts were examined by measuring the DC current as a function of the applied bias and temperature as well as the photoelectric response. It is shown that both methods of surface modification result in p-to-n conversion of the conductivity type of the surface layer. The charge transfer in contacts is explained by the formation of dislocation networks buried under the surface. A model of two potential barriers is proposed for the interpretation of the photovoltaic response in contacts. Their existence is associated with compressive strains in the modified surface layer caused by dislocations, which leads to an increase in the band gap and the formation of a heterostructure.

Activation energy of silicon diffusion in gallium oxide: Roles of the mediating defects charge states and phase modification

Silicon (Si) is an efficient n-type dopant in gallium oxide (Ga2O3)—an ultra-wide bandgap semiconductor promising in a number of applications. However, in spite of the technological importance for device fabrication, the activation energy for Si diffusion in Ga2O3 is missing in the literature. In the present work, we do such measurements in ion implanted monoclinic β-Ga2O3 samples employing anneals in air ambient, also admitting the influence of potential ion beam induced phase modifications on diffusion. Importantly, we show that Si diffusion in β-Ga2O3 fits with the concentration dependent diffusion model, involving neutral and single negatively charged point defects to mediate the process; so that we assumed gallium vacancies in the corresponding charge states to assist Si diffusion in β-Ga2O3 with activation energies of 3.2 ± 0.3 and 5.4 ± 0.4 eV, respectively. Moreover, we also found that a preexisting phase modified surface layer efficiently suppressed Si diffusion in β-Ga2O3 for temperatures up to 1000 °C.

Multi-cycle of AISI 5135 steel modification by irradiation of the “film (Si (0.2 μm) + Nb (0.2 μm))/(AISI 5135 steel) substrate” system with an intense pulsed electron beam

Steel AISI 5135 surface layer modification carried out by high-cycle high-speed melting of the “film (Si + Nb)/(steel AISI 5135) substrate” system with an intense pulsed electron beam with an impact area of several square centimeters, have been implemented in a single vacuum cycle on the “COMPLEX” setup. The regime of the system “film (Si (0.2 μm) + Nb (0.2 μm))/(steel AISI 5135) substrate” irradiation with an intense pulsed electron beam (20 J/cm2, 200 μs, 3 pulses, 3 cycles) which makes it possible to form a surface layer with high thermal stability have been revealed. This layer is characterized by high hardness, more than 3 times higher than the hardness of AISI 5135 steel in the original (ferrite-pearlite structure) and wear resistance, more than 90 times higher than the wear resistance of the initial AISI 5135 steel. It is shown that the high strength and tribological properties of steel are due to the formation of the hardening phase particles (niobium silicide of Nb5Si3 composition).

Fatigue fracture of surface-modified layers in 18CrNiMo7-6 carburized steel

A modified layer of a certain thickness is produced on the surface of 18CrNiMo7-6 alloy steel after carburizing and quenching that greatly affects the microstructure and fatigue properties of the material. In this work, the fatigue performance of each layer was studied. The fatigue fracture and tensile fracture were compared under different depths of the modified layer. The fatigue fractures of the modified layer for different stresses were analyzed. As the depth of the modified layer increased, the slope of the S–N curve gradually decreased. As the depth of the modified layer increased, the fracture mode changed from brittle fracture to brittle-ductile mixed fracture, the shear lip became thicker, and the dimple became larger. There was no flat area in the tensile fracture. At the same depth of the modified layer, a smaller stress amplitude, led to a larger proportion of the crack propagation area.

(Tutorial) Thermal Atomic Layer Etching

Thermal atomic layer etching (ALE) can be performed using sequential self-limiting reactions that yield controlled etching at the atomic level. Thermal ALE is the opposite of atomic layer deposition (ALD). The sequential reactions during thermal ALE are based on surface modification followed by volatile release of the modified surface layer. Surface modification typically results from fluorination. Volatile release can be accomplished using metal precursors that undergo ligand-exchange reactions with the fluorinated surface layer. This tutorial will first concentrate on thermal Al2O3 ALE as a model system. The tutorial will then survey the thermal ALE of other materials and selectivity in thermal ALE.Thermal Al2O3 ALE is a model system that illustrates the basics of thermal ALE. The surface modification reaction in thermal Al2O3 ALE results from the fluorination of Al2O3 to AlF3 using HF. Al2O3 fluorination by HF is a self-limiting process that forms a thin stable AlF3 layer on the Al2O3 surface with a thickness of several Angstroms. The AlF3 layer can then be removed by ligand-exchange reactions. During the ligand-exchange reactions, a molecular precursor transfers a ligand to the AlF3 layer and the AlF3 layer transfers a F atom to the molecular precursor. This ligand-exchange breaks the strong F bridge-bonding in the AlF3 layer. A typical molecular precursor for ligand-exchange is Al(CH3)3 (trimethylaluminum, TMA).The ligand-exchange reaction with TMA adds CH3 ligands to the AlF3 layer. In addition, the TMA molecular precursor forms AlF(CH3)2 (dimethylaluminum fluoride (DMAF)) after ligand-exchange. The DMAF ligand-exchange product is volatile at the etching temperatures. Progressive ligand-exchange reactions between TMA and the AlF3 layer continue to break F bridge-bonding and eventually form volatile DMAF etch products. DMAF is monitored as the etch product by mass spectrometry investigations. However, these studies reveal that dimers of DMAF with itself (DMAF/DMAF) and dimers of DMAF with TMA (DMAF/TMA) have the largest signal intensities.Thermal Al2O3 ALE using HF and TMA as the reactants occurs with a temperature-dependent etch rate that varies from 0.14 Å/cycle at 250°C to 0.75 Å/cycle at 325°C. The etch rate can also be dependent on the HF pressure because thicker fluoride layers are formed on Al2O3 at higher HF pressure. There is also competition between thermal Al2O3 ALE and AlF3 ALD. At lower temperatures, the TMA and HF reactants can produce AlF3 ALD instead of Al2O3 ALE. The presence of HF coverage on the surface at lower temperatures is believed to lead to AlF3 ALD.In addition to thermal Al2O3 ALE, a variety of other metal oxides and metal oxides, including HfO2, ZrO2, Ga2O3, VO2, AlN and GaN, can be etched using sequential fluorination and ligand-exchange reactions. Various fluorination reactants can be employed such as HF, SF4 and XeF2. A wide range of molecular precursors are also effective for ligand-exchange such as AlCl(CH3)2, Sn(acac)2, TiCl4, SiCl4 and BCl3. In addition, a variety of other materials, such as ZnO, Si, SiO2, Si3N4, TiO2 and WO3 can be etched using conversion reactions that first convert the surface of the original material to a new surface layer that has a pathway for etching. Thermal ALE pathways are also available for etching elemental metals, such as Ni and Co, using chlorination and ligand-addition reactions.Thermal ALE yields isotropic etching that will be valuable for advanced semiconductor fabrication. Isotropic thermal ALE will be necessary to provide lateral etching in three-dimensional structures such as nanowire or nanosheet transistors. The ligand-exchange reactions during thermal ALE are also extremely selective depending on the stability and volatility of the etch products. This selectivity can be tuned by using different molecular precursors for ligand-exchange. The selectivity during ligand-exchange can provide new pathways for area-selective etching.