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Group 4 transition metal nitride (TMN) nanoparticles (NPs) display strong plasmonic responses in the visible and near-infrared regimes, exhibit high melting points and significant chemical stability, and thus are potential earth-abundant alternatives to Au and Ag based plasmonic applications. However, a detailed understanding of the relationship between TMN NP physical properties and plasmonic response is required to maximize their utility. In this study, the localized surface plasmon resonance (LSPR) frequency, bandwidth, and extinction of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) NPs were examined as a function of the particle size, surface oxidation, and refractive index of the surrounding medium using finite element method (FEM). A linear redshift in the LSPR frequency and a linear increase in the associated full width at half maximum (FWHM) was observed with increasing the particle size, oxidation layer thickness, and medium refractive index. We show that the effect of surface oxidation on plasmonic properties of TMN NPs is strongly size-dependent with a significant LSPR redshift, intensity reduction, and broadening in small NPs compared with larger NPs. Furthermore, the performance and efficiency of HfN, ZrN, and TiN, as well as Au NPs for narrowband (photothermal therapy, PTT) and broadband (solar energy conversion) applications, was investigated in detail. The results indicate that narrowband and broadband photothermal performance of NPs strongly depend on the particle size, surface properties, and in case of narrowband absorption, excitation wavelength.

High-rank coals are generally more floatable than low rank or oxidized coals due to their higher hydrophobicity. Surface oxidation of coals due to the exposure to atmospheric oxygen renders the sur...

Indium gallium arsenide (InGaAs) is one of the candidate materials to overcome the physical limitation of Si due to its excellent electrical properties. The effect of surface oxidation on the etching characteristics of InGaAs surface in acidic solutions were investigated. InGaAs surfaces was etched in HCl/H2O2/H2O (CPM) and HNO3/H2O2/H2O (NPM), while there was no thickness change in diluted HCl or HNO3. The CPM-treated InGaAs surface had a lower etching rate than the NPM-treated one, while etching rate of oxidized layer was higher in diluted HCl than in HNO3. NaCl added in the NPM acts as an etching inhibitor for InGaAs and the etching rate was significantly suppressed. It is thought that Cl− anion inhibits the formation of hydroxyl radical (OH∙) or consumes OH∙ in acidic solution, inhibiting surface oxidation of InGaAs and suppressing its material loss.

Stretchable elastomers with superhydrophobic surfaces have potential applications in wearable electronics. However, various types of damage inevitably occur on these elastomers in actual application, resulting in the deterioration of the superhydrophobic properties. In this work, superhydrophobic elastomers (HB-imine-BZn-PDMS), was fabricated by employing a dual-layered structure. The bottom layer was a silicon elastomer (imine-BZn-PDMS) with an imine/coordination dual cross-linked structure and room temperature self-healing efficiency of 94%. The top layer was imine-BZn-PDMS/silica nanocomposites to provide superhydrophobic properties. The HB-imine-BZn-PDMS elastomer exhibited fast triple self-healing ability at room temperature toward surface oxidation/decomposition, ruptures, or pinholes, and high durability under abrasion and stretching. The dual dynamic bonds of imine-BZn-PDMS enabled fast recovery of superhydrophobicity in 20 min at room temperature via bond exchange, after generating pinholes across the elastomer. Following surface chemical damage, the HB-imine-BZn-PDMS elastomer also exhibited fast (40 min) room-temperature self-healing ability, which is superior to that of most current self-healing superhydrophobic materials.

This work investigated the behavior and mechanism of Cu2+ in marmatite biotic system and abiotic system. The leaching experiments show that the high cupric ions concentration (5 g/L) had obvious isolation both in biotic system and abiotic system in the early stage, the barrier effect gradually disappeared in biotic system. X-ray photoelectron spectroscopy and electrochemical methods indicate that isolation substances were formed on marmatite surface in the presence of high cupric ions concentration (5 g/L), which may be CuxSy. However, the isolation substances were eliminated in biotic system. Meanwhile, polysulfides and other substances were produced. The effect of these newly generated substances by bacteria on the surface oxidation of the marmatite remains to be explored.

The crystal quality of Cu2ZnSn(S,Se)4 (CZTSSe) thin film is crucially important to the high-performance CZTSSe solar cell. After the selenization, a bi-layer CZTSSe thin film consisting of a large-...

This research presented the surface oxidation of stainless steel grade 304 (S304) welded by a gas tungsten arc welding (GTAW) process. The welded S304 was inspected by visual and penetrant testing methods. The surface of the welded specimen was oxidized by the chromic solution to an obtained oxide film on S304 welded specimen. After that, the structural phase and crystallite size of the oxide film were investigated by X-ray diffractometer (XRD). The thickness of the obtained film was analyzed by an atomic force microscope (AFM). Furthermore, the effects of the oxide film on hardness and corrosion properties of specimen were analyzed by Vickers hardness tester and potentiostat instrument to study the correlation between the property of oxide film and the surface properties of the welded pipe S304 after oxidation.

The dependence of the friction and wear behavior of MAB-phase Fe2AlB2 against GCr15 steel counterpart on the sliding speed (0.8–6.4 m/s) and normal force (20–60 N) is investigated. The friction coefficient (0.3–0.7) decreases with increasing sliding speed and normal force, however, with some abnormalities for low sliding speeds of 0.8–1.6 m/s in the latter case. In contrast, overall increasing wear rates ((0.5–2.5) × 10-5 mm3/(N·m)) are observed, with significantly high values at 0.8 m/s and 40–60 N. Surface oxidation is identified due to the high temperature. At 0.8–1.6 m/s, the surface tongue patterns and material migration are both indicative of adhesive wear, with the contribution of fatigue wear becoming more significant for sliding speeds of over 3.2 m/s. At 6.4 m/s and 40 N, the wear changes from deformation-controlled by shallow spalling to fracture-controlled by deep failure.

Semiconductor-sensitized TiO2 thin films with long-term air stability are attractive for optoelectronic devices and applications. Herein, we demonstrate the potential of the TiO2 thin film (∼800 nm...

In paper laser thermal oxidation of austenitic stainless steels AISI 201, 304L of different surface mill finishes, the hot and cold rolled was investigated by the Ytterbium-doped fibre laser (λ=1070 nm) with an output power of 400W by varying scanning speed in the range 5÷20m/s in the air atmosphere. The influence of laser oxidation parameters on the surface colour was evaluated by colorimetric identification.

Fabrication of carbonaceous bulk bodies via colloidal aqueous routes has some problems. So it was intended to fabricate carbonaceous bodies through the gelcasting method. Effective parameters of this process (stability of graphite in water-based solutions studied in different solid loadings, pH values, and tween 80 additive) have been investigated. Also, other methods for modifying rheological behavior like surface oxidation and adding nano-silica particles have been considered. It has been seen that with the use of graphite as the carbon source in quantities equal to 45 and 50 wt%, proper suspension can be made and stability of the suspension improves with adding 2.5 wt% nano-silica particles and 6 wt% twin 80. For preparing these suspensions, the addition of nano-silica particles in the mentioned quantity is essential. Based on experiments, above-mentioned parameters cause higher mechanical strength in comparison with carbon lack bodies with identical parameters. Microscopically experiments show polymeric network constructed in raw bodies.

The paper discusses the application potential of quenching in high-pressure nitrogen with respect to mediumand high-alloy steels, as well as precipitation-hardening alloys. A procedure for predicting the structure and properties of steels and alloys after quenching is proposed. It is shown that gas quenching provides a high level of mechanical properties while maintaining the geometry of the precision products due to elimination of surface oxidation.

As global regulations of CO2 emissions and fuel consumption efficiency become more strict, the automotive powertrain system has become more compact with lower lubrication viscosity. With the current trends in powertrain system improvement, the operating conditions of powertrain components such as gears are becoming more severe. As a result, it is increasingly important to improve the strength and durability of the materials used for the powertrain system by optimizing alloy design and heat treatment. Much research and development has focused on improving components by heat treatment, and especially carburization. Also, many different alloy concepts, such as Fe-Cr-Mo or Fe-Cr-Ni systems have been proposed for automotive components. Among various approaches, Cr and Si , and solid solution hardening, are known to effectively increase hardenability. However, it has been reported in many works that the carburized case depth can also be reduced by increasing the Cr/Si content, due to oxide film formation. The mechanism of Cr/Si oxide film formation during carburization has not yet been clearly determined. In the present work, therefore, the mechanism of surface oxide film formation during carburization was examined. Also, the microstructure, composition and crystal structure of different oxides were examined and compared in detail.

Electrocatalytic water splitting (EWS) is a promising route to produce hydrogen in a sustainable and environment-benign manner. To realize the large-scale hydrogen production, it is paramount to develop desirable electrocatalysts with engineered structure, high catalytic activity, facile accessibility, low cost, and good durability. Of late, boride-based materials, especially transition-metal borides (TMBs), are emerging as promising candidates for the EWS process. However, so far, little attempt has been made to provide a comprehensive summary on these findings. Herein, this review provides the up-to-date status on upgrading the catalytic performance of TMB-based nanomaterials by regulating the internal and external characteristics. The conventional synthetic techniques are first presented for the preparation of TMB-based catalysts. Afterwards, the advanced strategies are summarized to enhance the catalytic performance of TMBs, including morphology control, component regulation, phase engineering, surface oxidation and hybridization. Then, the design principles of TMB-based electrocatalysts for high-performance EWS are outlined. Lastly, the current challenges and future directions in the development of TMB-based materials are proposed. This review article is expected to envisage insights into the TMBs-based water splitting and to provide strategies for design of the next-generation TMB-based electrocatalysts.

The presence of a liquid can prevent moving surfaces from coming into intimate contact. With smooth-surfaced rubber, it is possible to examine by optical interferometry the shape and thickness of liquid films between the surfaces. Furthermore, in water lubrication, if the acidity or alkalinity of the water is altered, laboratory friction measurements reveal the impact on its lubricity. Extensive testing shows that some rubber materials are more sensitive to water pH than others, and air aging has an influence on the results. In some circumstances the level of wet friction can decrease by two orders of magnitude—a surprising result by normal lubrication experience. These water pH results are described in some detail and mechanistic explanations are offered. The overall conclusion is that pH and the state of oxidation of a rubber surface can have a marked effect on its water-lubricated friction.

Searching for highly efficient and low cost electrocatalysts is an urgent challenge to provide high capacity and long cycle life Li–O2 batteries (LOBs). In this work, the highly efficient electrocatalytic properties of MoSi2 were first demonstrated using particles prepared by a solid–state reaction method. The surface was activated, playing a dominant role in the electrocatalytic performance. After acid etching to remove SiO2 impurities arising from the surface oxidation, MoSi2 exhibited excellent bifunctional electrocatalytic properties for LOBs. Mo6+ on the surface contributed to the initial low overpotentials of 0.45 V (3.2 V for the OER and 2.75 V for the ORR) and transformed into Mo4+ for a long cycle life. As a consequence, outstanding rate capabilities of 12 708 mA h g−1 at 100 mA g−1 and 10 794 mA h g−1 at 800 mA g−1, and excellent cycle durability of 215 and 90 cycles at a limited capacity of 1000 mA h g−1 at 200 and 500 mA g−1, respectively, were obtained for the MoSi2 cathode.

International audience; Adhesive wear extension in metal fretting contacts was previously related to the partial pressure of oxygen gas in a porous third body layer. Below a threshold value, the surface oxidation is no more possible and adhesive wear prevails in the inner part of the interface. The contact oxygenation concept (COC) allowing the prediction of the dioxygen partial pressure profile was recently simulated for a 2D surface analysis (i.e. 3D contact) using a numerical Advection-Dispersion-Reaction (ADR) approach. In this study, a simple explicit formulation is derived to capture COC response using a 1D surface analysis (i.e. 2D contact hypothesis).

International audience; Predictive toxicity and structure-activity relationships (SARs) are raising interest since the number of nanomaterials has become unmanageable to assess their toxicity with a classical case-bycase approach. Graphene-based materials (GBMs) are among the most promising nanomaterials of this decade and their application might lead to several innovations. However, their toxicity impact needs to be thoroughly assessed. In this regard, we conducted a study on 22 GBMs to investigate their potential SARs by performing a complete physicochemical characterization and in vitro toxicity assessment (on RAW264.7 cells). We used GBMs of variable lateral size (0.5-38 µm), specific surface area (SSA, 30-880 m²/g), and surface oxidation (2-17%). We observed that reduced graphene oxides (RGOs) were more reactive than graphene nanoplatelets (GNPs), potentially highlighting the role of GBM's surface chemistry and surface defects density in their biological impact. We also observed that for GNPs, a smaller lateral size caused higher cytotoxicity. Lastly, GBMs showing a SSA higher than 200 m²/g were found to induce a higher ROS production. Mechanistic explanations are proposed in the discussion. In conclusion, pairing a full physicochemical characterization with a standardized toxicity assessment of a large set of samples allowed us to clarify SARs and provide an additional step toward safe-by-design GBMs.

Dissociation and adsorption of water on ferroelectric oxide surfaces play important role in the processes of screening and switching dynamics of ferroelectric polarization, as well as in catalytic processes which can be additionally coupled with light, temperature or vibration stimuli. In this work, we present XPS study of ferroelectric BaTiO3 thin films and determine the entanglement between surface chemistry, polarization direction and stability, by observing changes upon time exposure to environmental conditions, heating in O2 atmosphere and irradiation in vacuum. We devote special attention to Ba 3d spectral region and identify two different oxidation states of O atoms in the compounds of Ba. While this second specie was generally attributed to Ba in surface compounds where it has different oxygen coordination than in the bulk, based on the XPS results of oxygen annealed thin films, we demonstrate that this so far neglected component, corresponds to barium peroxide (BaO2) and identify it as important active specie for the study of screening mechanisms closely related with catalytic activity present in this ferroelectric material. Finally, we report on chemically assisted polarization switching in thin films induced by heating in vacuum or exposure to X-Ray radiation due to the formation of positive surface electric field created by oxygen or electron vacancies, respectively., Financial support was obtained under projects from the Spanish Ministerio de Ciencia e Innovación (MICINN) under projects FIS2015-73932-JIN, PID2019-109931GB-I00 and PID2019-110907GB-I00. In addition, this work was partially funded by 2017-SGR-579 from the Generalitat de Catalunya. The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence Programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and ICMAB is supported by the Severo Ochoa Centres of Excellence Programme, funded by the Spanish Research Agency (AEI, grant no. CEX2019-000917-S). I. S. acknowledges support of the Secretaria d'Universitats i Recerca - Departament d'Empresa i Coneixement - Generalitat de Catalunya and the European Social Fund (ESF) (FI grant reference 2020 FI_B2 00157).

Phase-Change Memory technology is increasing in maturity and in interest for next generation of non-volatile memory applications. In order to take advantage of the properties of innovative phase-change layers such as Ge-rich GST alloys, the understanding of the phenomena behind the possible evolution of the layer in time and temperature becomes fundamental. In this work, we present in detail the protocol we have developed using pARXPS technique, to reliably measure the surficial oxidation thickness on Ge-rich GST alloys with different nitrogen doping level. A double oxidation kinetic was observed on these samples for the first time, as well as an influence by nitrogen doping, and analyzed in detail by complementarily using pARXPS and TEM-EDX techniques.

An increasingly utilized way for the production of propene is propane dehydrogenation. The reaction presents an alternative to conventional processes based on petroleum resources. In this work, we investigate theoretically how Cr2O3 catalyzes this reaction in oxidative and reducing environments. Although previous studies showed that the reduced catalyst is selective for the non-oxidative dehydrogenation of propane, real operating conditions are oxidative. Herein, we use multiscale modeling to investigate the difference between the oxidized and reduced catalyst and their performance. The complete reaction pathway for propane dehydrogenation, including C-C cracking, formation of side products (propyne, ethane, ethylene, acetylene, and methane), and catalyst coking on oxidized and reduced surfaces of α-Cr2O3(0001), is calculated using density functional theory with the Hubbard correction. Parameters describing adsorption, desorption, and surface reactions are used in a kinetic Monte Carlo simulation, which employed industrially relevant conditions (700-900 K, pressures up to 2 bar, and varying oxidants: N2O, O2, and none). We observe that over the reduced surface, propene and hydrogen form with high selectivity. When oxidants are used, the surface is oxidized, which changes the reaction mechanism and kinetics. During a much faster reaction, H2O forms as a coproduct in a Mars-van Krevelen cycle. Additionally, CO2 is also formed, which represents waste and adversely affects the selectivity. It is shown that the oxidized surface is much more active but prone to the formation of CO2, while the reduced surface is less active but highly selective toward propene. Moreover, the effect of the oxidant used is investigated, showing that N2O is preferred to O2 due to higher selectivity and less catalyst coking. We show that there exists an optimum degree of surface oxidation, where the yield of propene is maximized. The coke, which forms during the reaction, can be burnt away as CO2 with oxygen.

With the depletion of high-grade ores, beneficiation of valuable minerals from mineral processing tailings attracts attentions of mining companies and researchers. Recovery of valuable sulfide mine...

The role of acid treatment of Taunit carbon nanotubes in the formation of oxygen-containing functional groups on its surface as well as morphological and textural properties was studied. Acid treatment was carried out in an HNO3 solution or its mixture with H2SO4 under mild conditions (85 °C/1 h) with subsequent washing with distilled water or without washing. Properties of the initial and oxidized samples were investigated using elemental carbon, hydrogen, nitrogen, oxygen (CHNO) analysis, BET (Brunauer-Emmett-Teller) determination of surface area, X-ray diffraction, Raman and Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, and hydrogen temperature-programmed reduction. Treatment with HNO3 and HNO3/H2SO4 mixture was shown to be efficient for the formation of various oxygen-containing groups on the Taunit surface; therewith, the water washing step also contributed to functionalization of the surface. Depending on the oxidant, acid treatment increased graphite and oxygen content in the samples by a factor of 3‒4.5. Treatment with HNO3 without water washing exerted a weak effect on the graphite structure ordering, the concentration of aliphatic groups was high as compared to other oxidation conditions. Treatment of Taunit with the HNO3/H2SO4 mixture, on the contrary, increased the number of defects in graphite layers and decreased the concentration of aliphatic structures.

The grain-size dependence of wear resistance of WC-Co cemented carbides (with mean WC grain sizes of 2.2 μm, 1.6 μm, 0.8 μm and 0.4 μm, respectively) was investigated under different tribological conditions. The results showed that the grain size had opposite effects on wear resistance of the cemented carbides in dry sliding wear and microabrasion tests. In the former condition, with decrease of WC grain size hence the increase of hardness, plastic deformation, fracture, fragmentation and oxidation were all mitigated, leading to a drastic decrease in the wear rate. In the latter condition, pull-out of WC grains after Co removal dominated the wear, so that the hardness of cemented carbide was not a core factor. As a result, the wear resistance of the cemented carbide generally showed a decreasing trend with decrease of the grain size, except for a slight increase in the ultrafine-grained cemented carbide. Single-pass scratching of the cemented carbides under various loads indicated the same failure mechanism as that in the sliding wear tests. Furthermore, the reasons for severe surface oxidation of the coarse-grained cemented carbides were disclosed.

International audience; The surface chemistry of gold nanoparticles produced by the pulsed laser ablation in liquids method is investigated by X-ray photoelectron spectroscopy (XPS). The presence of surface oxide expected on these systems is investigated using synchrotron radiation in conditions close to their original state in solvent but free from substrate or solvent effects which could affect the interpretation of spectroscopic observations. For that purpose we performed the experiment on a controlled free-standing nanoparticle beam produced by combination of an atomizer and an aerodynamic lens system. These results are compared with those obtained by the standard situation of deposited nanoparticles on silicon substrate. An accurate analysis based on Bayesian statistics concludes that the existence of oxide in the free-standing conditions cannot be solely confirmed by the recorded core-level 4f spectra. If present, our data indicate an upper limit of 2.15 ± 0.68% of oxide. However, a higher credence to the hypothesis of its existence is brought by the structureless valence profile of the free-standing beam. Moreover, the cross-comparison with the deposited nanoparticles case clearly evidences an important misleading substrate effect. Experiment with free-standing nanoparticles is then demonstrated to be the right way to further investigate oxidation states on Au nanoparticles.

In this research, the effect of particle size on the surface oxidation and flotation behavior of galena in the lime system was studied. Coarse (−0.074 + 0.038 mm), intermediate (−0.038 + 0.025 mm) ...

This study investigated the tribological properties of Cu36Zr48Ag8Al8 BMG against Cu36Zr48Ag8Al8 BMG under H2SO4 corrosive conditions with different concentrations. Results show that Cu36Zr48Ag8Al8 BMG exhibits good tribological behaviors under H2SO4 conditions. Especially, when the material was soaked in 15 wt% H2SO4 solution, the friction coefficient and wear rate can be as low as 0.10 ± 0.01 and (0.28 ± 0.23) × 10−6 mm3 N−1m−1. It is mainly attributed to the existence of metal oxide films formed by surface oxidation and passivation actions as well as the fluid lubricating films formed by H2SO4 solution and dissolution reaction products ( A l 2 ( S O 4 ) 3 and CuS O 4 ) on the worn surfaces. These perfect properties promote Cu36Zr48Ag8Al8 BMG to have the promise to replace the stainless steel under H2SO4 corrosive condition.

Subseafloor microbial activities are central to Earth’s biogeochemical cycles. They control Earth’s surface oxidation and major aspects of ocean chemistry. They affect climate on long timescales and play major roles in forming and destroying economic resources. In this review, we evaluate present understanding of subseafloor microbes and their activities, identify research gaps, and recommend approaches to filling those gaps. Our synthesis suggests that chemical diffusion rates and reaction affinities play a primary role in controlling rates of subseafloor activities. Fundamental aspects of subseafloor communities, including features that enable their persistence at low catabolic rates for millions of years, remain unknown., Subseafloor microbial activities are central to global biogeochemical cycles, affecting Earth’s surface oxidation, ocean chemistry, and climate. Here the authors review present understanding of subseafloor microbes and their activities, identify research gaps, and recommend approaches to fill those gaps.

The rapid development of mechanical systems’ miniaturization has expanded the demand for higher precision and performance micro formed parts. For improving the forming height and quality of formed parts, and studying the influences of the stress annealing and imprinting times on the forming as well as surface roughness (Sa) of the formed parts, this paper proposed a composite process of imprinting times and stress annealing on warm laser shock imprinting (WLSI) to realize the precision forming of the aluminium foil. In this research, the WLSI experiments were carried out with the imprinting temperature, imprinting times, and stress annealing treatment as variables. Subsequently, the forming height, surface roughness, and surface oxidation of the formed parts were measured, the loading–displacement curve were monitored, the transient deformation process induced by WLSI was divided four stages (deformation stage, rebound stage, vibration stage, and stable stage), and the residual stress distribution of the formed parts were simulated and analyzed by ABAQUS. Finally, the influences of the above three factors on the formed parts were discussed and explicated, and these results showed that the imprinting times and stress annealing can improve effectively the forming effect of WLSI.

Graphene has been shown to be a promising barrier for thermal corrosion due to its low gas and liquid permeability; however, there have been contradictory reports in the literature regarding the mechanisms of oxidation of graphene-coated Cu. This work systematically investigates the effect of chemical vapor deposited graphene grain size, point defect density, and underlying Cu orientation on the thermal oxidation of the underlying Cu in air. For graphene with either small grain size (~0.04–0.4 μm2) or large point defect density (~800 μm−2), oxidizers have relatively unhindered access through these defects to corrode the underlying Cu, and the corrosion is relatively independent of Cu orientation. For graphene with low defect density, the rate of Cu oxidation depends on the Cu crystal orientation on which the graphene is synthesized. Graphene-coated Cu (110) is completely corroded in just 2 min of thermal oxidation at 250 °C, while no surface oxidation for graphene-coated Cu (111) is observed for the same conditions. Thus, corrosion of graphene that is synthesized to achieve large grain size (>~170 μm2) is limited by the weakest graphene/Cu orientation interaction, not the size of the graphene grains, as was previously assumed.

Growing uniform surface oxides is vital for fabricating 2D materials based electronic and optoelectronic devices. However, the surface transition metal oxides (TMOs) of air-exposure transitional metal dichalcogenides (TMDs), such as HfOx on HfSe2, are island-type, with poor TMOs/TMDs interface quality. Here, we report a controlled surface oxidation of atomically thin HfSe2 flakes via oxygen-plasma treatment, where a dense atomically flat HfOx film is produced. This HfOx film is found to be a good surface passivation layer to prevent the inner part from further oxidation in air, which is also promising as a high-K dielectric in HfSe2-based devices.

In this study, we report DFT + U analysis of Pd/C- and Pd/N-codoped TiO 2 to assess their thermal catalytic activities. Various sites were explored for the codoping of Pd/C and Pd/N in TiO 2 . The effect of codopants on the net oxygen activation were investigated. Two unique crystal planes (0 0 1) and (1 0 0) of TiO 2 were chosen for codoping. The energetics of substitution in Ti 1 - x Pd x O 2 - δ - y C y was energetically favoured with an energy change of −4.2 eV while it was energy intensive in Ti 1 - x Pd x O 2 - δ - 2 y N 2 y with an energy requirement of 16.7 eV. Net oxygen activation as high as 23.8% was achieved in Ti 1 - x Pd x O 2 - δ - y C y while 25.6% activation was observed in Ti 1 - x Pd x O 2 - δ - 2 y N 2 y . Surface reconstructions were examined via transfer of electrons from the codoped sites to the nearest neighbouring sites leading to the superior potential of Ti 1 - x Pd x O 2 - δ - y C y and Ti 1 - x Pd x O 2 - δ - 2 y N 2 y towards surface oxidation reactions over (0 0 1) and (1 0 0) surface planes when compared to their monosubstituted counterparts. Redox nature of reducible oxides like TiO 2 has been very well established to govern their catalytic activity for reactions like CO oxidation, N O x reduction and water-gas shift reaction. Improvement in lattice oxygen exchange capacity has been reported to improve the catalytic activity. Hence, we have used quantitative net oxygen activation as a probe into the thermal catalytic activity of Pd/C and Pd/N-codoped TiO 2 .

The Co-Al coating was deposited on Ni-based superalloy DZ125 by pack cementation. The lifetime and interdiffusion behavior of the Co-Al coating on the Ni-based superalloy at 1050 °C, 1075 °C and 1100 °C were investigated. Surface oxidation and interdiffusion between the coating and the substrate led to depletion of Al in the coating, and β-Ni(Co)Al was gradually degraded into γ and γ' phases. Oxidation activation energy of the coating was calculated through oxidation weight gain curves of different temperatures. The formula of the coating lifetime related to the coating thickness and the temperature was established by calculating intermediate parameters. The lifetime determined by the formula and experiment showed good agreement.

The propensity of high voltage pulse (HVP) towards mineral-enriched ore particles during treatment has been reported by researchers at the Julius Kruttschnitt Mineral Research Centre. However, the fundamentals of HVP selective breakage between particles remains unclear due to complex mechanical and electrical properties of the natural ores. An experimental study of HVP selective breakage was conducted using fabricated synthetic particles embedded with various metalliferous minerals of different conductivities/permittivities. HVP tests were performed by placing the mineralised and the barren synthetic particles in the pulse discharge zone, which were then treated with one pulse loading. Part 1 of this study presents evidence of metalliferous grain-induced breakage in a two-particle paired system, with barren particles remaining intact. High-resolution images of the mineralised fragments showed that the electrical breakdown channel exerted detrimental effects upon the integrity of all the metalliferous grains tested, resulting in complete disintegration and heavy surface oxidation of the metalliferous grains, rather than liberating the metalliferous grain along its boundaries as reported in the literature. In addition, the influence of metalliferous grain locality in a particle on HVP breakage selectivity is also investigated.

The mechanical behavior of X-750 in rough vacuum environment was explored and compared with the mechanical behavior in air at a large range of temperatures (from room temperature to 900°C) for both Heat-Treated and Non-Heat-Treated X750 alloy. In the intermediate range of temperatures where the Portevin Le Chatelier (PLC) effect is observed, the effect of testing in air versus rough vacuum did not yield statistically significant different PLC characteristics. At temperatures above 650°C for Heat Treated and 750°C for Non-Heat-Treated X-750, the samples tested under rough vacuum had higher yield stress values than the respective samples tested under air. The decrease in yield stress under air was attributed to an oxide scale induced surface softening effect and the loss of strengthening efficiency for the gamma prime precipitates. At higher temperatures in air, around 800°-900°C, sinusoidal stress serrations in the stress strain curves indicated the occurrence of dynamic recrystallization (DRX). The vacuum environment however removed all stress serrations attributed to DRX, indicating that the surface oxidation with the concomitant formation of a γ’ free zone underneath the oxide layer plays a role in the DRX presence.

New formulation is introduced to model surface oxidation of soot particles. In the new development, the surface is represented by an arbitrary number of reactive sites and their physically-founded transformations. The latter are combined and integrated with gas-phase and particle-dynamics models. The surface reaction model defines two state properties and establishes a structural relationship between them that guides evolution of the surface. This new model form for the surface-chemistry led to close reproduction of shock-initiated oxidation of soot: CO profiles in two experiments performed at substantially different temperatures, 1990 and 2780 K, as well as CO production rates over a wide range of temperatures, 1652–3130 K, all without employing the parameter-α empiricism of the previous model formulation.

In order to probe the hydroxyl (OHad) adsorption energy as one of the possible descriptors for hydrogen evolution reaction (HER) in alkaline media, we performed studies on polycrystalline copper (Cu(Poly)), a well-known poor catalyst for HER. By employing three different preparation methods for Cu(Poly), we were able to establish links between surface oxidation extent, oxophilicity, hydrophilicity and their catalytic activity for the HER. Ultimately, we propose that the formation of Cu(I)-OHad‐‐‐OH2 activated complex is essential for lowering the energy barrier for water dissociation, which leads to higher activity for the HER in alkaline media. Keywords: Hydrogen evolution reaction, Electrocatalysis, Surface science, Copper, Structure-function relationships

Here, two-dimensional (2D) C/TiO2 hybrids synthesized via oxidation of Ti3C2Tx MXenes are reported as an ideal electrorheological (ER) candidate in pursuit of high ER efficiency. The lamellar struc...

Although the power conversion efficiency of perovskite solar cells has exceeded 23%, the poor ambient stability of organic–inorganic halide perovskites poses a challenge for their commercialization. Comprehensive understanding of the underlying degradation mechanisms is a crucial step to seek approaches that can effectively suppress the degradation of perovskites. Herein, on the basis of extensive first-principles calculations, a three-step photo-oxidative degradation mechanism of MAPbI3 at the atomic level is revealed. We find that, in a dry ambient environment, the photo-generated superoxide anions (O2−) first lead to fast surface oxidation. However, further oxidation of the perovskite interior is hindered by the solid oxidation product. The fresh water produced in surface oxidation leads to the hydration of the inner perovskite and eventual breakage of the MAPbI3 lattice. We devise a practical strategy for protecting MAPbI3 from photo-induced decomposition by anchoring hydrophobic 2-(4-fluorophenyl)propan-2-amine on the surface of MAPbI3. The surface modification significantly retards the photo-induced decomposition.

Bismuth vanadate photoanode has shown great potential for photoelectrochemical (PEC) catalysis, but it needs to be further modified because of its relatively low charge-separation efficiency and poor stability. Herein, the bimetallic phosphide NiCoP decorated Mo–BiVO4 is fabricated through the electrodeposition and drop-casting method, which significantly improves the charge separation and surface oxidation reaction. Therefore, the fabricated NiCoP/Mo–BiVO4 photoanode exhibits a low onset potential of 0.21 V (vs. RHE) and high photocurrent of 3.21 mA cm−2 at 1.23 V (vs. RHE), which is 3.12 times higher than that of pure BiVO4. Importantly, the decoration of NiCoP significantly improve the stability of BiVO4 photoanode.

The geometric structure of 38-atom AgPd and AgCu nanoalloys is obtained by the genetic algorithm and density functional theory for all compositions and their surface phase stability diagrams are established to provide a clear image for the initial oxidation process. Ag surface segregation is confirmed for both AgPd and AgCu nanoalloys in vacuum. Pure Pd and Cu nanoparticles have lower surface phase stability than bulk metals to be oxidized and the alloying can improve the oxidation resistance. Segregated AgCu nanoalloys have higher phase stability than mixed AgCu in vacuum and have lower surface phase stability than mixed AgCu nanoalloys in an oxygen atmosphere. Unexpectedly, segregated AgPd nanoalloys have both higher phase stability in vacuum and higher surface phase stability in an oxygen atmosphere than that of mixed AgPd nanoalloys. The higher surface phase stability of segregated AgPd nanoalloy could be attributed to the slight elevation of Pd Milliken charge and negative shift of d-band center. Compared with the selective oxidation in conventional alloy oxidation models where the selective oxidation is related to alloy composition, the nanoalloy oxidation is proposed to correlate with surface segregation in AgPd and AgCu nanoalloys in this work, which promotes the development of the conventional alloy oxidation models in that the surface segregation is a precursor to the surface oxidation of nanoalloy and plays a critical role in the selective oxidation of nanoalloy.

The tribological performances of perfluoroalkylpolyethers (PFPE) with graphene (Gr), WS2, and the mixture of Gr and WS2 (Gr + WS2) before and after ultraviolet (UV), atomic oxygen (AO), and proton (Pr) irradiations were investigated. The composition and structure of PFPE, Gr, WS2, and Gr + WS2 were also analyzed to understand the effects of irradiation on the tribological behaviors of PFPE with additives. The results indicated that serious deterioration and degradation of PFPE took place and Gr was transformed to amorphous carbon after Pr irradiation, and surface oxidation of WS2 occurred under the irradiations of AO and Pr. Moreover, compared to PFPE and PFPE additized with Gr and WS2, PFPE with the addition of Gr + WS2 exhibited excellent friction and wear reduction before and after UV and AO irradiations. Graphical Abstract

Acenes and azaacenes lie at the core of molecular materials' applications due to their important optical and electronic features. A critical aspect is provided by their heteroatom multiplicity, which can strongly affect their properties. Here we report pyrazinacenes containing the dihydro-decaazapentacene and dihydro-octaazatetracene chromophores and compare their properties/functions as a model case at an oxidizing metal substrate. We find a distinguished, oxidation-state-dependent conformational adaptation and self-assembly behaviour and discuss the analogies and differences of planar benzo-substituted decaazapentacene and octaazatetracene forms. Our broad experimental and theoretical study reveals that decaazapentacene is stable against oxidation but unstable against reduction, which is in contrast to pentacene, its C-H only analogue. Decaazapentacenes studied here combine a planar molecular backbone with conformationally flexible substituents. They provide a rich model case to understand the properties of a redox-switchable pi-electronic system in solution and at interfaces. Pyrazinacenes represent an unusual class of redox-active chromophores. Acenes are a promising class of organic materials with distinctive electronic and optical properties. Here decaazapentacene and octaazatetracenes are prepared and their self-assembly behaviour at different oxidation states is analysed. Práce se zabývá studiem pyrazinacenů obsahujících dihydro-dekaazapentacenové a dihydro-oktaazatetracenové chromofory a porovnáním jejich vlastností při modelovém chování na oxidačním kovovém substrátu. Byla nalezena odlišná, na oxidačním stavu závislá konformační adaptace a samouspořádající se chování. Byly připraveny dekaazapentaceny a oktaazatetraceny a analyzováno jejich samoorganizující se chování v různých oxidačních stavech.

Electrochemical Surface Oxidation Enhanced Raman Scattering (EC-SOERS) is a new phenomenon that provokes the enhancement of the Raman signal during the oxidation of a metal surface. Studies carried out so far indicate that carbonyl and carboxyl group are necessary to observe this phenomenon with a delocated charge being an important factor. In this work, the enhancement factors of EC-SOERS for different molecules, which present highly delocated charge and a carboxyl group, have been assessed. The systematic study of the enhancement factors helps to shed more light on the interaction of the molecules with the electrochemically generated SOERS substrates, yielding key information about the properties and specific features of this intriguing phenomenon. For the first time, a systematic information about the enhancement factors of this phenomenon is obtained. Analytical enhancement factors higher than 105 are obtained., Ministerio de Economía, y Competitividad (Grant CTQ2017-83935-R-AEI/FEDERUE), Junta de Castilla y León (Grant BU297P18) and Ministerio de Ciencia, Innovación y Universidades (Grant RED2018-102412-T). J.V.P-R. thanks Junta de Castilla y León for his postdoctoral fellowship (Grant BU033-U16).

Point-of-use (POU) water treatment systems and devices play an essential role in limited access to sanitary safe water resources. The filtering materials applied in POU systems must effectively eliminate contaminants, be readily produced and stable, and avoid secondary contamination of the treated water. We report an innovative, 2D Ti3C2/Al2O3/Ag/Cu nanocomposite-modified filtration material with the application potential for POU water treatment. The material is characterized by improved filtration velocity relative to an unmodified reference material, effective elimination of microorganisms, and self-disinfecting potential, which afforded the collection of 99.6% of bacteria in the filter. The effect was obtained with nanocomposite levels as low as 1%. Surface oxidation of the modified material increased its antimicrobial efficiency. No secondary release of the nanocomposites into the filtrate was observed and confirmed the stability of the material and its suitability for practical application in water treatment.

Regarded as a promising candidate for absorber material in photovoltaic applications, $\mathrm{Ba}{\mathrm{Si}}_{2}$ confronts the challenge of high-quality material synthesis via low-cost processes. Here, we fabricated $\mathrm{Ba}{\mathrm{Si}}_{2}$ thin films through the industrially applicable sputtering technique with the face-to-face annealing (FTFA) approach. The employment of the FTFA approach leads to an improvement of the sputtered $\mathrm{Ba}{\mathrm{Si}}_{2}$ from perspectives of surface homogeneity and crystal quality. Various covers are applied in the FTFA, including $\mathrm{Ba}{\mathrm{Si}}_{2}$, glass, and Si, which causes alterations in the film's electrical and optical properties. These impacts of the FTFA method on sputtered $\mathrm{Ba}{\mathrm{Si}}_{2}$ films stem from two aspects, i.e., heat redistributions caused by the variation of thermal networks, and interfacial interactions within the confined space between the cover and the film. The FTFA approach provides a facile strategy for minimizing the impacts of $\mathrm{Ba}{\mathrm{Si}}_{2}$ surface oxidation during high-temperature processes. These results and findings can push forward the material development of $\mathrm{Ba}{\mathrm{Si}}_{2}$ and its photovoltaic applications.

Nanodiamonds (NDs) have the characteristics of both diamonds and nanomaterials. However, it is difficult to disperse NDs, and this is why there is less research regarding NDs in the field of aluminum matrix composites. In the present work, NDs were modified via surface oxidation, and ND/Al matrix composites were successfully prepared via mechanical ball milling and vacuum sintering. The effects of different volume fraction of NDs (1%, 3%, 5%, 7%) after surface oxidation on the ND/Al matrix composite were analyzed using a metallographic microscope, scanning electron microscope, infrared spectrometer, X-ray diffractometer, microhardness tester, and universal testing machine. The results show that the optimal temperature of surface oxidation treatment is 673 K, which effectively purifies the surface of ND and introduces appropriate C=O functional groups. NDs are uniformly distributed in the aluminum matrix, and no harmful Al4C3 phase is formed. With an increase in the volume fraction of NDs, the grain size of the matrix first decreases and then increases, and the ultimate compressive strength first increases and then decreases. The volume fraction of ND with better comprehensive performance is 3% and the yield strength increased by 19%.

Mechanical exfoliation yields high‐quality 2D materials but is challenging to scale up due to the small lateral size and low yield of the exfoliated crystals. Gold‐mediated exfoliation of macroscale monolayer MoS2 and related crystals addresses this problem. However, it remains unclear whether this method can be extended to other metals. Herein, mechanical exfoliation of MoS2 on a range of metallic substrates is studied. It is found that Au outperforms all the other metals in their ability to exfoliate macroscale monolayer MoS2. This is rationalized by gold's ability to resist oxidation, which is compromised on other metals and leads to a weakened binding with MoS2. An anomalously high monolayer yield found for Ag suggests that the large interfacial strain in the metal–MoS2 heterostructures measured by Raman spectroscopy also is a critical factor facilitating the exfoliation, while the relative differences in the metal–MoS2 binding play only a minor role. These results provide a new incentive for investigations of 2D material‐substrate combinations applicable where high‐quality 2D crystals of macroscopic dimensions are of importance.

Correlating the structure and composition of nanowires grown by the vapour-liquid-solid (VLS) mechanism with their electrical properties is essential for designing nanowire devices. In situ transmission electron microscopy (TEM) that can image while simultaneously measuring the current–voltage (I–V) characteristics of individual isolated nanowires is a unique tool for linking changes in structure with electronic transport. Here we grow and electrically connect silicon nanowires inside a TEM to perform in situ electrical measurements on individual nanowires both at high temperature and upon surface oxidation, as well as under ambient conditions. As-grown, the oxide-free nanowires have nonlinear I–V characteristics. We analyse the I–V measurements in terms of both bulk and injection limited transport models, finding Joule heating effects, bulk-limiting effects for thin nanowires and an injection-limiting effect for thick wires when high voltages are applied. When the nanowire surface is modified by in situ oxidation, drastic changes occur in the electronic properties. We investigate the relation between the observed geometry, changes in the surface structure and changes in electronic transport, obtaining information for individual nanowires that is inaccessible to other measuring techniques.