Search

The paper presents a new approach, based on controlled oxidation of nanoscale metallic multilayers, to produce strong and hard oxide/metal nanocomposite coatings with high strength and good thermal stability. The approach is demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale metallic multilayers and investigating the evolution of their microstructure and mechanical properties by combining analytical transmission electron microscopy, nano-mechanical tests and finite element models. As-deposited multilayers were annealed at 350 °C in air for times ranging between 1 and 336 h. The elastic modulus increased by ∼20% and the hardness by ∼42% after 15 h of annealing. Longer annealing times did not lead to changes in hardness, although the elastic modulus increased up to 35% after 336 h. The hcp Zr layers were rapidly transformed into monoclinic ZrO 2 (in the first 15 h), while the Nb layers were progressively oxidised, from top surface down towards the substrate, to form an amorphous oxide phase at a much lower rate. The sequential oxidation of Zr and Nb layers was key for the oxidation to take place without rupture of the multi-layered structure and without coating spallation, as the plastic deformation of the metallic Nb layers allowed for the partial relieve of the residual stresses developed as a result of the volumetric expansion of the Zr layers upon oxidation. Moreover, the development of residual stresses induced further changes in mechanical properties in relation to the annealing time, as revealed by finite element simulations. [ABSTRACT FROM AUTHOR]

Along this work, the feasibility of using repetitive-impact tests with a cube-corner tip and low loads for obtaining quantitative fracture toughness values will be shown. It will be displayed that the impacts are able to produce a cracking similar to the pattern developed for the classical fracture toughness tests in structural ceramics. Moreover, it will be shown how it is possible to identify the crack geometry evolution from Palmqvist crack to half-penny crack with each new impact being able to study the proper evolution of fracture toughness in terms of different indentation models and as a function of the strain rate, ε ˙ . Fracture toughness values of Al 2 O 3 descend from ∼6.10 M P a m ( ε ˙ = 10 3 s − 1 ), to ∼3.52 M P a m ( ε ˙ = 10 − 3 s − 1 ). These values correspond to those found in the literature for α-Al 2 O 3 demonstrating that the use of repetitive-nano-impact tests provides good reproducibility, high accuracy for reliable fracture toughness testing. [ABSTRACT FROM AUTHOR]

This study investigates the effects of He bubbles on structural and mechanical properties of sputter-deposited Cu/W multilayers. A multilayer with a periodicity of 10 nm was deposited and subjected to helium ion irradiation with two different fluences. He bubbles formed mostly in Cu layers and their distribution was affected by He concentration and radiation damage. According to SRIM calculations, in low He concentration regions bubbles formed mostly along interfaces, while more homogeneously distributed bubbles were found in Cu layers and along columnar grain boundaries in higher He concentration regions. We suggest that the capability of interfaces to annihilate point defects is weakened by the He bubbles shielding effect. Nanoindentation tests revealed a hardness decrease amounting to ∼0.5 and ∼1 GPa for low and high fluences, respectively. The observed softening effect is attributed to He storage-induced changes in residual stresses and columnar grain boundary/interfacial sliding facilitated by He bubbles. [ABSTRACT FROM AUTHOR]

• Fe 2 AlB 2 samples were exposed to varying He fluences, energy, and temperatures. • Room temperature (RT) irradiation triggers notable changes: a-lattice expands 0.3 %, and c-lattice contracts 0.07 %. • An embedded amorphous layer formed after irradiation at RT. • No cracks are formed after irradiation, making Fe 2 AlB 2 more promising for nuclear application compared to Ti 3 SiC 2 and Ti 2 AlC. Layered carbides and borides, blending ceramic and metallic characteristics, present compelling prospects for future nuclear reactor applications due to their complex nanolaminate crystal structure. To explore the behavior of Fe 2 AlB 2 under different conditions, helium irradiation is conducted across saturation fluences and under different annealing and irradiation temperatures. Room temperature (RT) irradiation causes some changes: a-lattice expands 0.3 %, c-lattice contracts 0.07 %, and an embedded amorphous layer into the matrix is formed. 400 °C annealing keeps an amorphous structure whereas 800 °C annealing fully recrystallizes with bubble growth. Increasing the irradiation temperature to 400 °C with the same fluence, smaller bubbles form without an amorphous layer, indicating defect recombination depends on helium attachment to vacancies. Under irradiation at 700 °C, faceted bubbles develop exclusively within Fe 2 AlB 2 , with no such bubbles in Al 2 O 3. These faceted bubbles align themselves along (110) planes. Simultaneously, irradiation prompts tangled dislocations within the damaged layer, fostering the congregation of polygonal bubbles along grain boundaries (GBs) and creating denuded areas at GBs. Fe 2 AlB 2 demonstrates remarkable oxidation resistance under high-temperature irradiation, maintaining surface stability without the cracks seen in ion-irradiated Ti 3 SiC 2 and Ti 2 AlC at RT. Fe 2 AlB 2 shows promise for use in reactors operating at temperatures above 500 °C due to its resilience to irradiation. Further investigation is warranted for its application in reactors operating in environments exceeding this threshold temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

There are very few studies of PEEK wearing against DLC. In this study, DLC and Zr-DLC coatings were deposited by magnetron sputtering onto Ti alloy substrates. Coated and un-coated Ti alloy samples were tribologically tested in multidirectional pin-on-disk equipment against UHMWPE and PEEK. CoCr alloy was also tested as control. Each of the materials was tested for 2 million cycles (Mc) in bovine serum lubricant (37 °C). Gravimetrical weight loss and changes in surface profile were similar when tested against UHMWPE. However, Zr-DLC samples delaminated after 1.2 Mc. When tested against PEEK, both coated samples delaminated, despite that the coatings maintained their structural integrity. The synergetic effect of stress-induced corrosion through biological fluid and high cyclic shear stress may have caused interface fatigue and subsequent delamination of both coatings. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of Zr as alloying element to carbon films, particularly in respect to film structure and mechanical properties. The films were deposited by magnetron sputtering in reactive (Ar + CH 4 ) and non-reactive (Ar) atmosphere with different Zr contents (from 0 to 14 at.%) in order to achieve a nanocomposite based films. With an increase of Zr content a broad peak was observed in X-ray diffraction spectra suggesting the presence of nanocrystalline (nc) ZrC phase for the coatings with Zr content higher than 4 at.%. The application of Scherrer formula yielded a grain sizes with a dimension of 1.0–2.2 nm. These results were supported by X-ray photoelectron spectroscopy showing typical charge transfer at Zr C nanograins and carbon matrix interface. The nc-ZrC phase was also observed by transmission electron microscopy. The hardness of the coatings was approximately independent of Zr content. However, the Young modulus increased linearly. The residual stress of the coatings was strongly improved by the presence of nc-ZrC phase embedded in the a-C matrix. Finally, the incorporation of H into the matrix led to denser and harder films. [ABSTRACT FROM AUTHOR]

Amorphous carbon-based coatings (DLC) exhibit excellent mechanical and tribological properties such as high hardness, high elastic modulus, low friction and low wear. Reduced friction is often related to the formation of a low-friction tribolayer, which is formed during sliding and transferred to the counterpart. Here, we investigate the sliding of hydrogenated and non-hydrogenated DLC coatings alloyed with zirconium; pure DLC films are used as reference. The coatings were deposited by magnetron sputtering in Ar (non-hydrogenated) and Ar/methane atmosphere (hydrogenated) onto steel substrates and silicon wafers. The total thickness of the coatings was around 1.5 μm including a complex Ti/TiN/TiCN adhesion-improving interlayer with a thickness of 450 nm. All deposited coatings were amorphous, Zr/C ratio was approx. 0.05. The hardness was in the range of 9–13 GPa. Tribological tests were carried out in humid air at room temperature, at 100 °C and in nitrogen environment using pin-on-disk. Intermittent tribological test analysis has been performed to understand running-in behaviour. The worn surfaces and wear debris were analysed by Raman spectroscopy. Coatings alloyed with Zr showed lower friction and wear at room temperature compared to pure DLC. In general, Zr-doped hydrogenated coating outperformed the non-hydrogenated one when tested in an inert nitrogen atmosphere or at elevated temperature (100 °C), exhibiting almost super-low friction (μ = 0.03 in the steady-state regime) due to the formation of a homogenous, thick and stable tribolayer. [ABSTRACT FROM AUTHOR]

Cr–Al–N coatings with Zr alloying (Zr contents from 0 to 29.5 at.%) were deposited by d.c. reactive magnetron sputtering. The chemical composition and the morphology of as-deposited coatings were characterized, and the phase structure, mechanical properties and wear resistance of the coatings before and after thermal annealing were analyzed and evaluated. With the increase of Zr content, both Cr and N contents decrease whereas Al shows a growing trend. Low Zr (<26.9 at.%) coatings are stoichiometric and present a fcc NaCl-type B1 structure with columnar morphology, while high Zr (≥26.9 at.%) coatings are in N deficiency and have low crystallinity degree. The alloying of low contents of Zr improves the coating hardness and H / E ratio; however, for low ordered coatings these properties decrease significantly. After thermal annealing, fcc structure is kept in low Zr films whereas the crystalline degree is improved in the high Zr ones and their mechanical properties were slightly improved. Two coatings were selected for further testing, representatives of low (CrAlZr5N) and high (CrAlZr27N) Zr contents. The onset oxidation temperature is ∼900 °C and 600 °C for CrAlZr5N and CrAlZr27N coatings, respectively. Mainly Cr 2 O 3 is formed on low Zr coatings whereas mixed oxides of ZrO 2 and Cr 2 O 3 are detected on CrAlZr27N sample after thermal exposure. In all tribological tests, low Zr coating presents lower wear rate than the CrAlZr27N coating. In general, the addition of very high Zr contents (>20 at.%) with N deficiency markedly weakens the mechanical properties and the oxidation resistance of Cr–Al–Zr–N coatings. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h -BN) nanosheets, spherical W nanoparticles, and their combinations were utilized as lubricant additives to synthetic PAO6 oil. The addition of W NPs led to a decrease in the coefficient of friction and wear rate. Molecular dynamics (MD) simulations and in situ TEM mechanical tests showed that the positive effect of adding spherical W NPs can be attributed to their rolling and sliding in the tribological contact zone. Adding BN nanosheets to PAO6 also improved the tribological performance of friction pairs: MD simulations suggest that the exfoliation and sliding of BN layers under tribological contact can contribute to the reduction of friction and wear. Moreover, a synergistic effect from the simultaneous addition of W and BN nanoparticles was observed: the CoF and wear reached minimum values among all tested suspensions. The formation of W/BN core/shell structures by wrapping of W nanoparticles by h -BN sheets provided superior macroscale lubricity. • h -BN nanosheets and spherical W nanoparticles are studied as additives to PAO6 oil. • Adding W and BN NPs leads to a decrease in the friction coefficient and wear rate. • Exfoliation and sliding of h -BN NPs contribute to friction and wear reduction. • W NPs can withstand a high applied load and slide or rotate in the direction of applied load. • Formation of W/BN core/shell structures provides superior macroscale lubricity. [ABSTRACT FROM AUTHOR]

Sputter-deposited Zr/Nb nanoscale metallic multilayers with a periodicity of 27 (thin) and 96 nm (thick) were subjected to Cu+implantation with low and high fluences and then studied using various experimental techniques in combination with DFT calculations. After Cu+ implantation, the thinner multilayer exhibited a tensile strain along c-axis in Nb layers and a compressive strain in Zr layers, while the thicker multilayer showed a compressive strain in both layers. The strain is higher in the thin multilayer and increases for higher fluences. We developed a mathematical method for the fundamental understanding of the deformation mechanisms in metallic multilayers subjected to radiation damage. In the model, the cumulative strain within a layer is described as the combination of two contributions coming from the interfacial region and the inner region of the layers. The semi-analytical model predicts that the interfacial strain is dominant and extends over a certain region around the interface. Predictions are well supported by ab-initio calculations which show that in the vicinity of the interface and in the Zr side, vacancies and interstitials (low energy barriers) exhibit high mobility compared to the Nb side, thus resulting in a high recombination rate. As a consequence, less strain occurs in the Zr side of the interface compared to the Nb side. The density and distribution of various types of defects along the ion profile (low and high damaged regions) are obtained by combining DFT results and the predictions of the model. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The microstructure evolution of hydrogen-implanted 6H-SiC at different temperatures and fluences is investigated by using various experimental techniques. In H-implanted samples with relatively low fluence at RT, dense blister cavities are observed after annealing at 1100 °C, while no visible blister cavities appear after annealing at 1100 °C in the sample implanted at RT with high fluence. The absence of blister cavities is due to the loss of elastic energy during the crystalline-to-amorphous transition. With a further increase of implantation temperature to 450 and 900 °C, amorphization did not occur and H-containing microcracks grew laterally below the surface. Thus, blisters appeared on the surface of the samples implanted at 900 °C even without annealing. The results are compared to the microstructural evolution of He-implanted 6H-SiC which was explored in our previous work. The behavior of hydrogen and helium ions in 6H-SiC lattice was rather different. For He implantation, regardless of the fluence and implantation temperature, blisters did not form. The mechanism of migration and coalescence of nanoscale bubbles that are responsible for blistering were studied via density functional theory calculations, which well-supported the presented results. We found that both mechanisms (migration and coalescence) are energetically cheaper in the case of H compared to He. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The microstructural phenomena occurring in 6H–SiC subjected to different irradiation conditions and annealing temperatures were investigated to assess the suitability of 6H–SiC as a structural material for nuclear applications. To this aim, a single crystal of 6H–SiC was subjected to He+ irradiation at 300 keV with different fluences and at temperatures ranging from 25 to 750 °C. Rutherford backscattering/channeling (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were combined to shed light on the microstructural changes induced by irradiation and subsequent annealing (750 to 1500 °C). At room temperature, amorphization starts to occur at a fluence of 2.5 × 1016 cm−2 (0.66 dpa). On the contrary, amorphization was prevented at high irradiation temperatures and fluences. Furthermore, a thin and highly strained region located around the maximum He concentration (Rp) formed. This region results from the accumulation of interstitial atoms which are driven toward the highly damaged region under the actions of a strain gradient and high temperature. Regardless of the fluence and irradiation temperature, the material stores elastic energy, which leads to the trapping of He in dissimilar defect geometries. For irradiation temperatures below 750 °C, helium was accumulated in bubbles which coarsened after annealing. On the other hand, for an irradiation temperature of 750 °C, helium was trapped in platelets (even for medium fluence), which evolved into a homogeneous dense array of cavities during annealing. DFT calculations show that the bubbles are under high pressure and contribute to developing the overall tensile strain in the single crystal 6H–SiC. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Microstructure of radiation-induced Iron phases were investigated in a Fe + He irradiated 6H-SiC. • The irradiation process resulted in the formation of an amorphous layer containing an embedded band of helium bubbles located at the peak damage concentration. • After annealing, the amorphous layer recrystallized into a polycrystalline 6H-SiC. • formation of cubic FeSi compounds and small bcc-Fe precipitates located at the 6H-SiC grain boundaries. • MD annealing simulations reveal the formation of stable bcc Fe at high temperatures. Microstructure of radiation-induced Iron phases were investigated in a 6H-SiC subjected to Iron and Helium bombardment with a damage level of 8 dpa. The microstructural evolution before and after annealing was investigated by combining transmission electron microscopy (TEM, STEM-EDS), automated crystal phase and orientation imaging (ACOM-TEM), secondary ion mass spectroscopy (SIMS), and atomic scale simulations. The irradiation amorphized the entire damaged layer which contains an embedded band of He bubbles located at peak damage concentration. After annealing, the amorphous layer recrystallized into a polycrystalline 6H-SiC where the Fe profile significantly changed to form Fe-rich clusters. ACOM-TEM reveals the formation of large cubic FeSi clusters and small bcc-Fe precipitates located at the 6H-SiC grain boundaries. The type and size distribution of the precipitates greatly depend on the Fe profile. Fe-Si compounds form around the Fe peak concentration, while, bcc Fe precipitates tend to be more homogeneously distributed. Density functional theory (DFT) calculations demonstrate that the formation of Fe dimers and trimers in the 1st nearest neighbor is energetically favorable. A combined Monte Carlo/Classical molecular dynamic (MMC/MD) technique reveals that the Fe atoms prefer to form large clusters in accordance with experimental results. MD annealing simulations reveal the formation of stable bcc Fe at high temperatures. The phase transition starts at the cluster-matrix interface around 620 K and the cluster is fully transformed at 700 K. [Display omitted] [ABSTRACT FROM AUTHOR]

The study explored the microstructure evolution of 6H-SiC that underwent sequential iron and helium ion irradiation with energies of 2.5 MeV and 500 keV, respectively, at room temperature, followed by annealing at 1500°C for two hours. Following irradiation, the entire damaged layer underwent amorphization. However, during subsequent annealing, epitaxial recrystallization took place, resulting in the formation of defected polycrystalline 6H-SiC characterized by the presence of Fe-rich clusters, cavities, and stacking faults. Fe-rich cavities were found to predominantly form at the edges of the stacking faults, as revealed by XTEM. The interaction of microstructural defects is further investigated via first-principles calculations. The periphery of the stacking faults has been identified as the primary location for the emergence of vacancy clusters, serving as favorable sites for the accumulation of point defects, including Fe atoms. This behavior can be attributed to the combined effects of mechanical and electronic energy relaxation mechanisms. Mechanically, the presence of stacking faults allows for the release of elastic energy that had been stored at the boundary. Electronically, the energy relaxation arises from the saturation of C- and Si-dangling bonds. Both of these processes contribute to the observed behavior, highlighting the intricate interplay between mechanical and electronic factors in the system. The low point defect migration energy barriers in the vicinity of the stacking faults promise high recombination, which can limit cavity growth and enhance radiation resistance. The study not only offers valuable insights into the mechanism of cavity/stacking faults interaction, contributing to a better understanding of radiation damage in 6H-SiC but also demonstrates that 6H-SiC material containing stacking faults could serve as a viable alternative to 3C-SiC for nuclear application. [Display omitted] [ABSTRACT FROM AUTHOR]

Ideal biomaterials to fabricate orthopedic implants, especially for load-bearing joint replacements, should include only non-toxic elements with good biocompatibility, high corrosion resistance and surface bioactivity, together with a good combination of mechanical properties. Based on these criteria, a manufacturing approach based on sputtering techniques can be ideal to develop coatings free of toxic elements tailored for advanced applications on pure titanium or titanium alloys used in biomedical applications. In this work, the ternary Ti-Nb-Zr system was used to develop non-toxic β-rich Ti coatings with several complex microstructures by careful control of Nb and Zr concentration and deposition parameters, such as bias voltage. Depending on the alloy chemistry and processing, the coating included variable amounts of α- , α″- and β-phases of Ti with different morphologies and crystallographic texture. Mechanical properties of every coating is largely determined by the micro-structure present, which is directly related to bias voltage used during sputtering process. Thus, hardness values change as a function of the compressive residual stresses magnitude and Young's modulus decreased from 63 GPa, at 0 V, to 47 GPa, at −63 V, being this value close to human bone (~30 GPa). After that, Young's modulus progressively increases to 89 GPa, at −148 V. On the other hand, bioactivity of the coating is practically doubled when compared to Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

Zr/Nb 6 multilayers of 6 nm periodicity, with well-composition-modulated structures, were prepared by magnetron sputtering. Their microstructure and scratch properties were investigated using HAADF-STEM, XRD, AFM, and triboindenter. The Zr/Nb interfaces have various orientations along the growth direction. The hardness (H) and reduced elastic modulus (E) are measured as 6.6 GPa, and 176.3 GPa, respectively, resulting in a high ratio of H/E, compared to other multilayer systems such as Ta/Co and Ag/Cu, which indicates superior tribological performance. The coefficient of friction (COF) was 0.27, and the elastic recovery was observed along the scratch path. Extensive large molecular dynamics simulations (MD) were conducted to investigate the impact of different Zr/Nb interface orientations on the friction/wear behavior of Zr/Nb 6 multilayers. The primary cause of plastic deformation of the Nb layer was dislocations and BCC twinning, while Zr layers deform via dislocations and intrinsic stacking faults. The Zr/Nb 6 exhibited better tribological properties, such as lower COF, higher scratch hardness, and improved wear resistance compared to their single-crystal counterparts. The Pitsch-Schrader interface showed the lowest COF value, whereas Rong–Dunlop and Zhang-Killy orientations exhibited better wear resistance. The interface structure was analyzed, and its blocking strength was discussed. These findings contribute to understanding the relationship between Zr/Nb interface and wear performance and tailoring them to achieve desired properties for specific applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Ti 1 − x Al x N coatings with NaCl-type structure have been widely used in advanced machining and other high temperature applications due to their excellent mechanical, thermal and tribological properties. Here, we investigated the influence of Cr additions on the structure, mechanical properties and oxidation resistance, including the oxide scale characterization, of multilayered TiAlN/CrAlN coatings deposited by magnetron sputtering. The properties of Cr rich coatings were compared to a TiAlN film deposited as reference. XRD diffraction analysis revealed that all coatings showed an fcc NaCl-type structure. However, for the TiAlN monolayer Ti and Al are forming a solid solution whilst, for Cr rich coatings, a multilayer structure alternating TiAlN and CrAlN layers, also forming solid solutions, was grown as a result of the geometry of the targets distribution inside the deposition chamber in combination with a slow rotation of the sample holder and a sufficiently high deposition rate. TGA measurements showed that Cr additions increased the oxidation performance of the coatings. For Ti 0.47 Al 0.46 N, dual oxide layers occur when tested at 800 °C, being the porous inner one of TiO 2 and the outer a compact and continuous layer of Al-oxide which protects the coating from the oxidation. At 900 °C the oxidation resistance of this film degraded due to the fast Ti ions diffusion to the surface which impedes the formation of the continuous and protective Al oxide layer. Cr rich coatings showed different oxides scales depending on their chemical composition. For Ti 0.30 Al 0.46 Cr 0.26 N and Ti 0.28 Al 0.34 Cr 0.42 N, a Ti-O rich layer is formed on the top of a protective Al-Cr-O layer when the samples were tested at 900 °C and 1000 °C, being the oxide layers thicker for the higher temperature. Concerning the coating with the highest Cr content (Ti 0.28 Al 0.31 Cr 0.51 N), a compact and continuous Cr(Al) 2 O 3 oxide layer was formed at 900 and 1000 °C with residual TiO 2 islands on the top, contributing for a significant enhancement of the oxidation resistance. [ABSTRACT FROM AUTHOR]

High-entropy coatings (HECs) are of a great interest for the protection of structural steels and alloys used in the costal and offshore areas. Here, thick, dense, and uniform Fe-Cr-Ni-Co-(Cu) coatings with a crack-free surface have been successfully deposited on AISI 420S steel by vacuum electro-spark deposition using CrNiCo and CrNiCoCu electrodes. The coatings consist of columnar grains (approximately 300 nm in diameter) and subgrains (10–50 nm thick) of an fcc phase and spherical inclusions of mixed SiO 2 + (Cr,Ti) 2 O 3 oxide, 30–50 nm in size. Although Cu is an element prone to segregation, the experimental results show that Cu does not form its own phase and is in the metal solid solution. Molecular dynamics simulation shows that Cu has a slight tendency to self-clustering and form Cu-rich clusters in FeCrNiCo-Cu HECs. However, several regions enriched in Cu are observed in the FeCrNiCo-Cu samples. FeCrNiCo coatings tested in artificial seawater and the Black Sea exhibited enhanced corrosion resistance. In tribocorrosion tests, FeCrNiCo-(Cu) coatings performed better than steel substrate due to faster recovery of a passive film. The addition of Cu has a positive effect on the antibacterial activity of FeCrNiCo coatings against Gram-positive B. cereus Arc30 and B. cereus F strains. [Display omitted] • High-entropy FeCrNiCo-(Cu) coatings prepared by vacuum electrospark deposition • Single-phase fcc structure with columnar subgrain morphology and oxide inclusions • Superior corrosion and tribocorrosion resistance in seawater • Cu doping led to enhanced antibacterial activity against B. cereus strains. • Molecular dynamics simulation results correspond to experimental data. [ABSTRACT FROM AUTHOR]

In this work it was studied the possible use of thin films, composed of Au nanoparticles (NPs) embedded in a TiO 2 matrix, in biological applications, by evaluating their interaction with a well-known protein, Bovine Serum Albumin (BSA), as well as with microbial cells ( Candida albicans ). The films were produced by one-step reactive DC magnetron sputtering followed by heat-treatment. The samples revealed a composition of 8.3 at.% of Au and a stoichiometric TiO 2 matrix. The annealing promoted grain size increase of the Au NPs from 3 nm (at 300 °C) to 7 nm (at 500 °C) and a progressive crystallization of the TiO 2 matrix to anatase. A broad localized surface plasmon resonance (LSPR) absorption band (λ = 580–720 nm) was clearly observed in the sample annealed at 500 °C, being less intense at 300 °C. The biological tests indicated that the BSA adhesion is dependent on surface nanostructure morphology, which in turn depends on the annealing temperature that changed the roughness and wettability of the films. The Au:TiO 2 thin films also induced a significant change of the microbial cell membrane integrity, and ultimately the cell viability, which in turn affected the adhesion on its surface. The microstructural changes (structure, grain size and surface morphology) of the Au:TiO 2 films promoted by heat-treatment shaped the amount of BSA adhered and affected cell viability. [ABSTRACT FROM AUTHOR]

SiC is considered a perspective material in advanced nuclear systems as well as for electronic or spintronic applications, which require an ion implantation process. In this regard, two sets of 6H-SiC samples were implanted with i) 2.5 MeV Fe ions and ii) 2.5 MeV Fe ions and co-implanted 500 keV He ions at room temperature and then annealed at 1500 °C for 2 h. The microstructure evolution and Fe diffusion behavior before and after annealing were characterized and analyzed. After annealing, Fe concentration is enhanced close to the surface in the Fe-implanted sample, whereas in the co-implanted system, Fe atoms are redistributed into two distinct, spatially separated regions (close to the surface, and around the He-induced defects). The reason behind this finding is explained from an energetic point of view by using ab initio simulations. Technologically, the pre-existing cavities can be used to control the Fe diffusion. [Display omitted] [ABSTRACT FROM AUTHOR]

The ternary aluminium oxynitride (AlN x O y ) system offers the possibility to obtain a wide range of properties by tailoring the ratio between pure Al, AlN x and AlO y and therefore opening a significant number of possible applications. In this work the thermal behaviour of AlN x O y thin films was analysed by modulated infrared radiometry (MIRR), taking as reference the binary AlO y and AlN x systems. MIRR is a non-contact and non-destructive thermal wave measurement technique based on the excitation, propagation and detection of temperature oscillations of very small amplitudes. The intended change of the partial pressure of the reactive gas (N 2 and/or O 2 ) influenced the target condition and hence the deposition characteristics which, altogether, affected the composition and microstructure of the films. Based on the MIRR measurements and their qualitative and quantitative interpretation, some correlations between the thermal transport properties of the films and their chemical/physical properties have been found. Furthermore, the potential of such technique applied in this oxynitride system, which present a wide range of different physical responses, is also discussed. The experimental results obtained are consistent with those reported in previous works and show a high potential to fulfil the demands needed for the possible applications of the systems studied. They are clearly indicative of an adequate thermal response if this particular thin film system is aimed to be applied in small sensor devices or in electrodes for biosignal acquisition, such as those for electroencephalography or electromyography as it is the case of the main research area that is being developed in the group. [ABSTRACT FROM AUTHOR]

The effects of Ni–Ti(–Cu) interlayers on the mechanical and tribological behaviour of W–S–C/Ni–Ti(–Cu) and W:DLC/Ni–Ti(–Cu) bilayer coatings have been investigated. The mechanical properties of the bilayers, measured at different depths by nanoindentation, exhibited a clear dependence on the combination between different Ni–Ti(–Cu) interlayers and top layers. The tribological performance of the bilayers was evaluated by pin-on-disk under different load conditions. The use of Ni–Ti(–Cu) interlayers improved the adhesion of the top layers and the resistance against surface damage such as delamination and cracking. Transmission electron microscopy analyses performed in the wear tracks of W–S–C/Ni–Ti and W:DLC/Ni–Ti bilayers tested with high load revealed that the formation of stabilised martensite was limited when a much harder top functional layer was employed. [ABSTRACT FROM AUTHOR]

Nanostructured metallic multilayers systems continue to garner interest because of their promising mechanical properties, exploitable in the field of materials engineering. These novel materials show high yield strengths, anomalous Young’s modulus values and even superior radiation tolerance for layer thicknesses up to a few tens of nanometers. However, there are still many unknowns related to the deformation mechanisms operating at the nanoscale because of deformation mechanisms, in this nanoscale, depend directly on the layer thickness and the combination of different or similar crystal structures in the interface. The objective of this work is to produce Zr/Nb multilayers and investigate the dependence of deformation mechanisms when the layer thickness is reduced. Nanoindentation hardness as a function of periodicity, λ, has been measured for Zr/Nb multilayers. It has been found that for decreasing h the yield strength values, σ 2.7 , do not increase. For λ =60 nm and λ =30 nm, σ 2.7 values are almost constant: 1.97 and 1.93 GPa, respectively, whereas for λ =10 nm, the yield strength shows a decrease to 1.79 GPa. The mismatch between σ 2.7 and σ CLS values for any core cut-off, α, condition (0.2 and 1) and for any η ratio (η= h Zr /h Nb ), indicates that the strain mechanism based on CLS did not occur for any period studied; therefore, the strain mechanism based on IBS is suggested, in accord with the activation of a pyramidal slip system { 11 2 ¯ 2 } 〈 1 ¯ 1 ¯ 23〉, along Zr layer, even for thickness up to 30 nm. Thereby, dislocation loop glide is not confined to an isolated layer, changing the plastic behaviour of the nano-multilayer. [ABSTRACT FROM AUTHOR]

Based on our previous knowledge on Cu/Nb nanoscale metallic multilayers (NMMs), Cu/W NMMs show a good potential for applications as heat skins in plasma experiments and armors, and it could be expected that the substitution of Nb by W would increase the strength, particularly at high temperatures. To check this hypothesis, Cu/W NMMs with individual layer thicknesses ranging between 5 and 30 nm were deposited by physical vapor deposition, and their mechanical properties were measured by nanoindentation. The results showed that, contrary to Cu/Nb NMMs, the hardness was independent of the layer thickness and decreased rapidly with temperature, especially above 200 °C. This behavior was attributed to the growth morphology of the W layers as well as the jagged Cu/W interface, both a consequence of the low W adatom mobility during deposition. Therefore, future efforts on the development of Cu/W multilayers should concentrate on optimization of the W deposition parameters via substrate heating and/or ion assisted deposition to increase the W adatom mobility during deposition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanical and structural properties of ion (C, Si, or Cu) irradiated Zr/Nb NMMs are highly dependent on thickness and damage. • Thin (Zr/Nb27) multilayer is 11% harder than the thick (Zr/Nb96) one. • Irradiation hardening in Zr/Nb27 is minuscule (maximum 8 %) while a significant hardening is observed in Zr/Nb96 (maximum 24%). • In Zr/Nb multilayer, the higher the interface density, the higher the strain. In this work, the radiation responses of Zr/Nb nanostructured metallic multilayers (NMMs) are studied. The nanostructures with different layer thicknesses were deposited on Si (1 1 1) substrate by using magnetron sputtering and were subjected to heavy-ion irradiation at room temperature with different fluences. Nanoindentation, XRD, DFT, SIMS, and Variable Energy Positron Annihilation Spectroscopy (VEPAS) techniques were used to study the type and distribution of defects, and strain within the material as well as the changes in the hardness of the structures as a function of damage. Our results suggest that the strain and the irradiation hardening are layer thickness- and damage-dependent while they are independent of the type of irradiated ions. The magnitude of hardening decreases with decreasing individual layer thickness indicating that the number of interfaces has a direct effect on the radiation tolerance enhancement. For thin layers with a periodicity of 27 nm (Zr/Nb 27), a transition from hardening to softening occurs at high fluence, and a saturation point is reached in thick layers with a periodicity of 96 nm (Zr/Nb 96). The as-deposited thin multilayers presented a significantly higher atomic-scale disorder which increases with ion irradiation compared to the thick multilayers. VEPAS reveals the vacancy defects before and after irradiation that contribute to the presented strain. Based on the findings, thin nanostructured Zr/Nb multilayered structures possess excellent radiation resistance due to the high density of interfaces that act as sinks for radiation-induced point defects. [ABSTRACT FROM AUTHOR]

Tailoring interfaces is a powerful way of reducing the accumulation of radiation defects. Understanding strain evolution induced by ion bombardment in nuclear materials with high interface density is crucial for next-generation reactors since induced defects are responsible for volumetric swelling and catastrophic failure. X-ray and selected-area diffraction patterns (SADPs) measurements reveal, after Cu implantation, that a relatively high out-of-plane strain is created in thin Zr/Nb 6 multilayers, while thick Zr/Nb 96 is barely distorted. The absence of layer deformation in Zr/Nb 96 is explained by local TEM strain mapping showing the presence of two oppositely distorted regions (inner and interface-affected regions) within one layer producing only a small overall strain, whereas the whole individual layers of Zr/Nb 6 are affected by the interface manifesting high strain. Using MD simulations, the types of defects responsible for layer distortion are identified. The opposite distortion within the layer is attributed to the inequality of the defect flux from the inner to interface-affected region due to the difference in migration energy barriers of the point defects. Moreover, the interface sink efficiency (defect annihilation) is determined for Zr/Nb as an illustration which provides a strategy for designing new derivate structures of multilayers with high radiation damage resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

Sliding of the WSC coated ceramics (ball-on-disc configuration) was investigated under vacuum condition at multiple loads (2–18 N), and each experiment was followed by detailed Raman and SEM analysis of both the wear track and the wear scar (on the ball). Main finding is that under low loads (up to 8 N), wear is polishing, carbon structure becomes more ordered and the number of WS 2 monolayer increases. Above 8 N, wear transitions into an abrasive regime interrupting the aforementioned processes increasing both friction and wear. Furthermore, roles of the coating components were differentiated: WS component is responsible for the low friction, whereas the carbon part is responsible for excellent wear properties. • W-S-C coatings where deposited onto lightweight ceramic substrates. • Tribological properties were evaluated for multiple loads under vacuum conditions. • Characterisation of coatings and produced wear tracks was performed by Raman and SEM microscopy. • Ab-inition simulations of the WS 2 Raman spectra were performed in support of the experimental data. • Low friction is attributed to the TMD part of the coating, while the good wear properties are attributed to carbon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Super hardness and toughness of VSiN are achieved with Si content at 5.5 at.% Si. • With Si content, highly textured columnar grains, refined columnar grains, nanocomposite structure are formed. • DFT revealed that the ternary VSiN coatings become more ductile as the calculated Cauchy pressures (P C) raise, while the Pugh's ratios (G/B) decrease. • Transfer of electrons to the Si-N bond from the neighboring V-N bonds causes Friedel oscillations and multiplication of the slip system. Microstructural evolution and deformation mechanisms of magnetron sputtered V-Si-N coatings with various Si contents are investigated by transmission electron microscopy, X-ray absorption spectroscopy, and ab initio calculations. A small amount of Si atoms was dissolved into the cubic VN lattice, locally reducing the neighboring V-N p-d hybridization near the Si site. The Si content was found to impact the architecture of coating significantly. With increasing Si content, the microstructure evolved through three different architectures: (i) highly textured columnar grains, (ii) refined columnar grains, and (iii) nanocomposite structures where elongated grains were bounded by vein-like boundaries. Enhanced damage tolerance was observed in the nanocomposite structure, where multiple toughening mechanisms become active. Ab initio calculations revealed that the incorporation of Si monolayer in the (1 1 1)-oriented VN resulted in the formation of weaker Si-N bonds compared to V-N bonds, which allowed a selective response to strain and shear deformations by assisting the activation of the slip systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Blister formation in He-H co-implanted InP is dependent on He and H fluence ratio. • The blisters are formed at LF, peaked at MF, and disappeares at HF. • At LF ions are stored in microcracks and bubbles, at HF they reside in bubbles. • The bubbles are stable, the Ostwald ripening and the coalescence are not active. The blistering efficiency in He-H-ions co-implanted and annealed InP has been found to peak and vanish in a narrow range of ion fluence ratio (Φ H /Φ He = 1. 5–3. 5) with a fixed He fluence of 2 × 1016 He+/cm2. The blisters are formed at low fluence (Φ H /Φ He = 1. 5), peaked in the middle (Φ H /Φ He = 2. 5), and disappeared at the high fluence ratio (Φ H /Φ He = 3. 5). To get a fundamental understanding of blister formation in nanoscale, the defect profiles were studied by various experimental techniques combined with FEM and ab-initio simulations. Cross-section TEM images showed that at a low fluence ratio, He and H are stored in microcracks and bubbles whereas, at a high fluence ratio, the ions are trapped only inside bubbles. These atomic processes that occur during and after co-implantation and annealing are presented together with detailed scenarios in an attempt to explain our results. Based on DFT simulations, the de-trapping of He atoms from the small clusters is energetically cheaper compared to the migration of He from the large clusters formed at high fluence. Moreover, at a high fluence ratio, the presence of large clusters inhibits the He diffusion to the small clusters (precursor of blisters) by capturing migrating He atoms. [ABSTRACT FROM AUTHOR]

• Si-Ta-C-(N) consists of fcc Ta(C,N) grains and amorphous a-Si and a-SiC(N) phases. • Ion implantation improved thermal shock resistance of the coatings. • Si-Ta-C-(N) coatings are resistant to oxidation at 800 °C. • The formation of TaSiO x fibers results in a low coefficient of friction, 0.23, at 800 °C. • Excellent wear resistance was achieved due to high ductility of the N-doped coatings. Challenges related to the application of wear resistant coatings at high temperatures require the development of novel materials with an exceptional combination of mechanical, chemical and tribological properties. The present paper is focused on understanding of relationships between structure, composition and high-temperature performance of the Si-Ta-C-(N) coatings. The coatings were produced using combined magnetron sputtering (MS) and ion implantation (CMSII) technique. It was found that ion implanted coatings demonstrated better thermal shock resistance compared to MS Si-Ta-C-(N) coatings. The Si-Ta-C-(N) coatings revealed a nanocomposite structure consisting of 2–3 nm fcc TaC(N) grains and amorphous a-Si and a-SiC(N) phases. The composition and structure of amorphous matrix and nanocrystallites strongly affected tribological performance of the Si-Ta-C-(N) coatings. The N-doped coatings exhibited exceptionally good tribological performance due to a higher ductility of N-rich amorphous a-SiCN and a-SiN x matrix, and fcc Ta(C,N)-based crystallites compared with the a-Si + a-SiC, and fcc TaC-based phases in N-free coating. The Si-Ta-C-(N) coatings easily withstood oxidation annealing at 800 °C due to the formation of a 200 nm protective TaSiO x amorphous layer. Oxidation annealings revealed that under thin protective TaSiO x layer crystalline components of coatings did not change when Si and C from the amorphous matrix started to diffuse towards the substrate at 800 °C but even after redistribution of elements and formation of oxide scale the coatings demonstrated reasonably high hardness – 13–16 GPa. Triboactivated formation of TaSiO x fibers which could slide/roll against the same TaSiO x tribolayer during high-temperature tribotests resulted in low coefficient of friction values (0.23 at 800 °C) and absence of wear. [ABSTRACT FROM AUTHOR]

The manufacturing of future implants based on NiTi shape memory alloys, like stents, orthodontic archwires, intracranial aneurysms..., clips aims to eliminate the cytotoxicity and allergic problems associated with the release of nickel ions. In this context, the design of β-rich Ti-22Nb-10Zr (mass.%) coating by magnetron sputtering, with a non-linear elastic behavior and tunable mechanical properties, offers a novel approach for the development of a new biocompatible implants with self-adjusting mechanical properties. The XRD and TEM analyses reveal that microstructure consisting of hexagonal close-packed (α-phase), prevalent body-centered cubic (β-phase) and orthorhombic (α″-phase) nanograins, which can be tuned during the deposition by a single parameter – applied bias voltage as a result of the activation of a stress-induced martensitic transformation (β → α″). We found that the minimum stress value to trigger the SIM transformation must be higher than 712 MPa (bias −63 V). The application of higher bias voltage values alters the main deformation mechanism, from a combination of reversible SIM transformation and mechanical twinning to dislocation slip, causing the compressive residual stresses to decrease from 712 to 120 MPa, the hardness increases from 2,1 to 4,1 GPa, and the coating stops showing low Young's modulus (<50 GPa) and non-linear elastic behavior. Unlabelled Image • A coating with a non-linear elastic behavior were deposited by magnetron sputtering. • The activation of a stress-induced martensitic transformation was studied. • Different deformation mechanisms are tuneable depending on the bias voltage used. • The hardness and Young's modulus are manipulated with increasing bias voltage. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) devices play a key role in solar-to-electricity energy conversion at small and large scales; unfortunately, their efficiency heavily depends on optimal weather and environmental conditions. The optimal scenario would be to extend the capabilities of PV devices so that they are also able to harvest energy from environmental sources other than light. An optimal solution is represented by hybrid photovoltaic-triboelectric (PV-TENG) devices which have both photovoltaic and triboelectric capabilities for electric power generation. Two-dimensional transition metal dichalcogenides (TMDs) are highly promising candidates for such PV-TENG devices, thanks to the easy tunability of their electrical, optical, mechanical, and chemical properties. In this respect, we here propose a quantum mechanical study to identify suitable TMD-based chemical compositions with optimal photovoltaic and triboelectric generation properties. Among the considered materials, we identify MoTe 2 /WS 2 , MoS 2 /WSe 2 , WS 2 /TiO 2 , WS 2 /IrO 2 , and MoS 2 /WTe 2 as the most promising bilayer compositions; under operative conditions, the band gap varies in the range 0.51-1.61 eV, ensuring the photovoltaic activity, while the relative motion of the layers may produce an electromotive force between 1.21 and 3.21 V (triboelectric generation) with a TMD/TMD interface area equal to about 200 Å 2 . The results constitute theoretical guidelines on how to check if specific chemical compositions of TMD bilayers are optimal for a combined photovoltaic and triboelectric power generation. Thanks to its generality, the presented approach can be promptly extended to van der Waals heterostructures other than those here considered and implemented in automated workflows for the search of novel low-dimensional materials with target PV and TENG response.

Efficient and affordable batteries require the design of novel organic electrode materials to overcome the drawbacks of the traditionally used inorganic materials, and the computational screening of potential candidates is a very efficient way to identify prospective solutions and minimize experimental testing. Here we present a DFT high-throughput computational screening where 86 million molecules contained in the PUBCHEM database have been analyzed and classified according to their estimated electrochemical features. The 5445 top-performing candidates were identified, and among them, 2306 are expected to have a one-electron reduction potential higher than 4 V versus (Li/Li + ). Analogously, one-electron energy densities higher than 800 Whkg -1 have been predicted for 626 molecules. Explicit calculations performed for certain materials show that at least 69 candidates with a two-electron energy density higher than 1300 Whkg -1 . Successful molecules were sorted into several families, some of them already commonly used electrode materials, and others still experimentally untested. Most of them are small systems containing conjugated CO, NN, or NC functional groups. Our selected molecules form a valuable starting point for experimentalists exploring new materials for organic electrodes., (© 2023 The Authors. Journal of Computational Chemistry published by Wiley Periodicals LLC.)

The interaction between protoporphyrin molecules (donor) and Si nanocrystals (acceptor) up to 2.5 nm for varying distances and orientations is studied by DFT, semi-empirical and TDDFT methods. Simulations show an effect on electronic structure, indicative of electron charge transfer in parallel orientation and small distances and nonelectron energy transfer for different orientations and larger distances. An absorption-emission spectral overlap is observed. The calculations of coupling and energy transfer rates show a distance dependence typical of fluorescence resonance energy transfer (FRET) in the long range, while in the short and ultra-short range the distance dependence indicates electron transfer in addition to FRET. The Si NCs with the smallest size yield larger couplings than the larger nanocrystals. The PPIX/Si NC coupling was enhanced by adding a plasmon nanoparticle as a bridge in the donor-acceptor system. Results using Au nanoparticles show increased energy transfer rates up to 10 4 and lower distance dependence., (© 2023 Wiley Periodicals LLC.)

van der Waals (vdW) homo/heterostructures are ideal systems for studying interfacial tribological properties such as structural superlubricity. Previous studies concentrated on the mechanism of translational motion in vdW interfaces. However, detailed mechanisms and general properties of the rotational motion are barely explored. Here, we combine experiments and simulations to reveal the twisting dynamics of the MoS 2 /graphite heterostructure. Unlike the translational friction falling into the superlubricity regime with no twist angle dependence, the dynamic rotational resistances highly depend on twist angles. Our results show that the periodic rotational resistance force originates from structural potential energy changes during the twisting. The structural potential energy of MoS 2 /graphite heterostructure increases monotonically from 0° to 30° twist angles, and the estimated relative energy barrier is (1.43 ± 0.36) × 10 -3 J/m 2 . The formation of Moiré superstructures in the graphene layer is the key to controlling the structural potential energy of the MoS 2 /graphene heterostructure. Our results suggest that in twisting 2D heterostructures, even if the interface sliding friction is negligible, the evolving potential energy change results in a nonvanishing rotational resistance force. The structural change of the heterostructure can be an additional pathway for energy dissipation in the rotational motion, further enhancing the rotational friction force.

Molybdenum disulfide (MoS 2 ) is a solid lubricant used in various forms, such as a dry lubricant by itself or as a component of a more complex coating. In both these forms, the effect of oxygen contamination on the sliding properties of the MoS 2 coatings is traditionally considered detrimental, resulting in expensive technological processes to produce pure MoS 2 . Here, it is shown that the high oxygen content does not necessarily hinder the solid lubricant properties and may even result in a lower friction and wear when compared to pure MoS 2 . Mo-S-O coatings were fabricated by unbalanced magnetron sputtering and tribologically tested under vacuum conditions. Oxygen caused amorphization of the as-deposited coatings but did not prevent the triboactivated formation of an ultra-thin crystalline MoS 2 tribolayer with the incorporated oxygen. Such an imperfect tribolayer was found to reduce the coefficient of friction to 0.02, a value lower than that of pure MoS 2 . Moreover, owing to the higher density and hardness of oxygen-containing films, the wear rate was also found to be lower. Molecular dynamics simulations performed using a newly developed Mo-S-O force field confirmed that such an imperfect tribolayer can mitigate friction in a manner comparable to that of MoS 2 .

Two-dimensional (2D) materials and transition metal dichalcogenides (TMD) in particular are at the forefront of nanotechnology. To tailor their properties for engineering applications, alloying strategies-used successfully for bulk metals in the last century-need to be extended to this novel class of materials. Here we present a systematic analysis of the phase behavior of substitutional 2D alloys in the TMD family on both the metal and the chalcogenide site. The phase behavior is quantified in terms of a metastability metric and benchmarked against systematic computational screening of configurational energy landscapes from First-Principles. The resulting Pettifor maps can be used to identify broad trends across chemical spaces and as starting point for setting up rational search strategies in phase space, thus allowing for targeted computational analysis of properties on likely thermodynamically stable compounds. The results presented here also constitute a useful guideline for synthesis of binary metal 2D TMDs alloys via a range of synthesis techniques., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The fabrication process for the uniform large-scale MoS 2 , WS 2 transition-metal dichalcogenides (TMDCs) monolayers, and their heterostructures has been developed by van der Waals epitaxy (VdWE) through the reaction of MoCl 5 or WCl 6 precursors and the reactive gas H 2 S to form MoS 2 or WS 2 monolayers, respectively. The heterostructures of MoS 2 /WS 2 or WS 2 /MoS 2 can be easily achieved by changing the precursor from WCl 6 to MoCl 5 once the WS 2 monolayer has been fabricated or switching the precursor from MoCl 5 to WCl 6 after the MoS 2 monolayer has been deposited on the substrate. These VdWE-grown MoS 2 , WS 2 monolayers, and their heterostructures have been successfully deposited on Si wafers with 300 nm SiO 2 coating (300 nm SiO 2 /Si), quartz glass, fused silica, and sapphire substrates using the protocol that we have developed. We have characterized these TMDCs materials with a range of tools/techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), micro-Raman analysis, photoluminescence (PL), atomic force microscopy (AFM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and selected-area electron diffraction (SAED). The band alignment and large-scale uniformity of MoS 2 /WS 2 heterostructures have also been evaluated with PL spectroscopy. This process and resulting large-scale MoS 2 , WS 2 monolayers, and their heterostructures have demonstrated promising solutions for the applications in next-generation nanoelectronics, nanophotonics, and quantum technology.

We present a new reactive force field (ReaxFF) parameter set for simulations of Mo-S structures. We compare our parameterization to the state-of-the-art ones in their performance against density functional theory (DFT) benchmarks and MoS 2 crystallization simulations. Our new force field matches DFT data significantly better than any previously published force fields and provides a realistic layered MoS 2 structure in crystallization simulations. It significantly improves the state-of-the-art force fields, which tend to crystallize in the experimentally unknown rock-salt MoS structure. Therefore, our new force field is a good candidate for further development and inclusion of other practically relevant elements, such as O, C, N, and H, which can be used to study the formation and tribological or catalytical properties of molybdenum disulfide., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Nanolayered metallic alloys are promising materials for nuclear applications thanks to their resistance to radiation damage. Here, we investigate the effect of ion (C, Si, and Cu) irradiation at room temperature with different fluences into sputtered Zr/Nb metallic multilayer films with periods 27 nm (thin) and 96 nm (thick). After irradiation, while a high strain in the entire thin nanoscale metallic multilayer (NMM) is observed, a quite small strain in the entire thick NMM is established. This difference is further analyzed by a semianalytical model, and the reasons behind it are revealed, which are also validated by local strain mapping. Both methods show that within a thick layer, two opposite distortions occur, making the overall strain small, whereas in a thin layer, all the atomic planes are affected by the interface and are subjected to only a single type of distortion (Nb─tension and Zr─compression). In both thin and thick NMMs, with increasing damage, the strain around the interface increases, resulting in a release of the elastic energy at the interface (decrease in the lattice mismatch), and the radiation-induced transition of the Zr/Nb interfaces from incoherent to partially coherent occurs. Density functional theory simulations decipher that the inequality of point defect diffusion flux from the inner to the interface-affected region is responsible for the presence of opposite distortions within a layer. Technologically, based on this work, we estimated that Zr/Nb55 with thicknesses around Zr = 24 nm and Nb = 31 nm is the most promising multilayer system with the high radiation damage resistance and minimum swelling for nuclear applications.

Two-dimensional heterostructures are excellent platforms to realize twist-angle-independent ultra-low friction due to their weak interlayer van der Waals interactions and natural lattice mismatch. However, for finite-size interfaces, the effect of domain edges on the friction process remains unclear. Here we report the superlubricity phenomenon and the edge-pinning effect at MoS 2 /graphite and MoS 2 /hexagonal boron nitride van der Waals heterostructure interfaces. We found that the friction coefficients of these heterostructures are below 10 -6 . Molecular dynamics simulations corroborate the experiments, which highlights the contribution of edges and interface steps to friction forces. Our experiments and simulations provide more information on the sliding mechanism of finite low-dimensional structures, which is vital to understand the friction process of laminar solid lubricants., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Although singlet fission presents deep advantages or the generation of solar energy, the list of efficient singlet fission sensitizers is still very short, encouraging the theoreticians to focus their efforts on selecting and designing new candidates. Here, it is presented a computational protocol for the efficient screening of databases to select those species matching the energy requirements for singlet fission. Hence, out of the initial 29,123 species, 254 molecules (0.87%) were found to match singlet fission energy conditions. The consideration of practical concerns such as availability or stability reduced the number to just 24 (0.08%), among which the aminoanthraquinone derivatives are found particularly promising. The proposed protocol correct the deficiencies of the preceding ones, reaching DFT accuracy and minimizing the risk of getting false negatives especially at the early stages of the screening. In addition, this protocol can be used in future high-throughput investigations using datasets composed of millions of species., (© 2021 Wiley Periodicals LLC.)

The stability of nanostructured metal alloys is currently being extensively investigated, and several mathematical models have been developed to describe the thermodynamics of these systems. However, model capability in terms of thermal stability predictions strongly relies on grain boundary-related parameters that are difficult to measure or estimate accurately. To overcome this limitation, a novel theoretical approach is proposed and adopted in this work to identify W-based nanocrystalline alloys which are potentially able to show thermodynamic stability. A comparison between model outcomes and experimental findings is reported for two selected alloys, namely W-Ag and W-Al. Experimental results clearly highlight that W-Ag mixtures retain a segregated structure on relatively coarse length scales even after prolonged mechanical treatments. Moreover, annealing at moderate temperatures readily induces demixing of the constituent elements. In contrast, homogeneous nanostructured W-Al solid solutions are obtained by ball milling of elemental powders. These alloys show enhanced thermal stability with respect to pure W even at high homologous temperatures. Experimental evidences agree with model predictions for both the investigated systems.

In dry sliding, the coefficient of friction depends on the material pair and contact conditions. If the material and operating conditions remain unchanged, the coefficient of friction is constant. Obviously, we can tune friction by surface treatments, but it is a nonreversible process. Here, we report active control of friction forces on TiO 2 thin films under UV light. It is reversible and stable and can be tuned/controlled with the light wavelength. The analysis of atomic force microscopy signals by wavelet spectrograms reveals different mechanisms acting in the darkness and under UV. Ab initio simulations on UV light-exposed TiO 2 show a lower atomic orbital overlapping on the surface, which leads to a friction reduction of up to 60%. We suggest that photocontrol of friction is due to the modification of atomic orbital interactions from both surfaces at the sliding interface.

Solid lubricants have received substantial attention due to their excellent frictional properties. Among others, molybdenum disulfide (MoS 2 ) is one of the most studied lubricants. Humidity results in a deterioration of the frictional properties of MoS 2 . The actual mechanism at the nanoscale is still under debate, although there are indications that chemical reactions are not likely to occur in defect-free structures. In this study, we performed nonequilibrium molecular dynamics simulations to study the frictional properties of multilayer MoS 2 during sliding in the presence of water. Moreover, we also investigated the effect of sliding speed and normal load. We confirmed earlier results that a thin layer of water organizes as a solidified, ice-like network of hydrogen bonds as a result of being confined in a two-dimensional fashion between MoS 2 . Moreover, we found that there exists an energy-driven, rotational dependence of the water network atop/beneath MoS 2 . This orientational anisotropy is directly related to the dissipative character of MoS 2 during sliding. Finally, three distinct frictional regimes were identified, two for a thin layer of water and one for bulk water. In the case of a thin layer and low coverage, water represents a solid-like contaminant, causing high energy dissipation. For a thin layer and high coverage, water starts to act as a solid-like lubricant, reducing dissipation during sliding. Finally, a regime where water acts as a liquid lubricant, characterized by a clear velocity dependence was found., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Claerbout, Nicolini and Polcar.)

Transition metal dichalcogenide (TMD)-based coatings are known for their low friction performance, which is attributed to the formation of a tribolayer consisting almost exclusively of pure well-ordered TMD. However, the formation of such a tribolayer and its wear track coverage is still unknown. In this study, we employed surface mapping and nanotribological techniques to study the properties of the wear tracks of composite W-S-C coatings. Our analysis revealed that the as-deposited coating consisted of two phases, with significantly different nanoscale frictional properties. We attributed the phases to nanocrystalline WS 2 (low friction) and amorphous solution of carbon and WS 2 (high friction). The two phases wear at different rates, especially at lower loads, where we observed faster depletion of nanocrystalline WS 2 . In the wear track, sparse flat WS 2 flakes were identified, suggesting that the recrystallization of the WS 2 phase occurs only at the spots where the contact pressure is the highest.

In the present work, modified embedded atom potential and large-scale molecular dynamics' simulations were used to explore the effect of grain boundary (GB) segregated foreign interstitials on the deformation behavior of nanocrystalline (nc) iron. As a case study, carbon and nitrogen (about 2.5 at.%) were added to (nc) iron. The tensile test results showed that, at the onset of plasticity, grain boundary sliding mediated was dominated, whereas both dislocations and twinning were prevailing deformation mechanisms at high strain. Adding C/N into GBs reduces the free excess volume and consequently increases resistance to GB sliding. In agreement with experiments, the flow stress increased due to the presence of carbon or nitrogen and carbon had the stronger impact. Additionally, the simulation results revealed that GB reduction and suppressing GBs' dislocation were the primary cause for GB strengthening. Moreover, we also found that the stress required for both intragranular dislocation and twinning nucleation were strongly dependent on the solute type.