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van der Waals (vdW) magnets are receiving ever-growing attention nowadays due to their significance in both fundamental research on low-dimensional magnetism and potential applications in spintronic devices. The high crystalline quality of vdW magnets is the key to maintaining intrinsic magnetic and electronic properties, especially when exfoliated down to the two-dimensional limit. Here, ultrahigh-quality air-stable vdW CrSBr crystals are synthesized using the direct solid-vapor synthesis method. The high single crystallinity and spatial homogeneity have been thoroughly evidenced at length scales from submm to atomic resolution by X-ray diffraction, second harmonic generation, and scanning transmission electron microscopy. More importantly, specific heat measurements of ultrahigh-quality CrSBr crystals show three thermodynamic anomalies at 185, 156, and 132 K, revealing a stage-by-stage development of the magnetic order upon cooling, which is also corroborated with the magnetization and transport results. Our ultrahigh-quality CrSBr can further be exfoliated down to monolayers and bilayers easily, providing the building blocks of heterostructures for spintronic and magneto-optoelectronic applications.

Here, we introduce polymer of intrinsic microporosity 1 (PIM-1) to design single-layer and multilayered all-inorganic antireflective coatings (ARCs) with excellent mechanical properties. Using PIM-1 as a template in sequential infiltration synthesis (SIS), we can fabricate highly uniform, mechanically stable conformal coatings of AlO

Anisotropic porous boron carbide (B4C) structures were successfully produced, for the first time, using the magnetic field-assisted freeze casting method. The effect of the magnetic field on the structure and mechanical strength of the formed porous B4C was compared for two different magnetic field directions that were either aligned with ice growth (vertical), or perpendicular to the ice growth direction (horizontal). It was shown that applying even a weak horizontal magnetic field of 0.1–0.3 T noticeably affected the alignment of mineral bridges between lamellar walls. Both the porosity and the channel widths decreased with increasing horizontal magnetic field strength. In the case of a vertical magnetic field, a larger strength of 0.4 T was required for highly aligned lamellar walls and larger channel widths. Compression strength tests indicated that the application of magnetic fields led to more homogeneously aligned channels, which resulted in increased compression strength in the longitudinal (parallel to the ice growth) direction. Applying a vertical magnetic field of 0.4 T with a cooling rate of 2 °C/min during the freezing step of the magnetic field-assisted freeze-casting method was found to result in the best conditions for producing highly anisotropic structures with large channel widths and fewer mineral bridges, which led to an increase in the mechanical strength.

Minimizing the wear of the surfaces exposed to mechanical shear stresses is a critical challenge for maximizing the lifespan of rotary mechanical parts. In this study, we have discovered the anti-wear capability of a series of metal nitride-copper nanocomposite coatings tested in a liquid hydrocarbon environment. The results indicate substantial reduction of the wear in comparison to the uncoated steel substrate. Analysis of the wear tracks indicates the formation of carbon-based protective films directly at the sliding interface during the tribological tests. Raman spectroscopy mapping of the wear track suggests the amorphous carbon (a-C) nature of the formed tribofilm. Further analysis of the tribocatalytic activity of the best coating candidate, MoN-Cu, as a function of load (0.25–1 N) and temperature (25 °C and 50 °C) was performed in three alkane solutions, decane, dodecane, and hexadecane. Results indicated that elevated temperature and high contact pressure lead to different tribological characteristics of the coating tested in different environments. The elemental energy dispersive x-ray spectroscopy analysis and Raman analysis revealed formation of the amorphous carbon film that facilitates easy shearing at the contact interface thus enabling more stable friction behavior and lower wear of the tribocatalytic coating. These findings provide new insights into the tribocatalysis mechanism that enables the formation of zero-wear coatings.

Expanding the low-friction temperature range of molybdenum disulfide-based coatings has been a topic of intense research interest. This paper introduces a coating concept, enabling achieving macroscale superlubricity, or near-zero friction, when exposed to open-air and high-temperature sliding conditions. This low-friction composite coating with a thickness of approximately 150–250 nm was accomplished by uniformly burnishing hydrothermally synthesized lamellate magnesium silicate hydroxide with an average diameter of 50 nm and an average thickness of 10 nm, molybdenum disulfide, and antimony trioxide powders onto a copper substrate. The tribological experiments performed in an open-air environment revealed that with the increase of testing temperature up to 200 °C or above (up to 300 or 400 °C), the coefficient of friction of the composite coating rapidly decreases and finally reaches the superlubricity state (the coefficient of friction is lower than 0.01). This intriguing superlubricity performance is attributed to the synergistic characteristics of lubricating antimony trioxide, molybdenum disulfide, and magnesium silicate hydroxide phases, enabling easy shearing of the film at high-temperature conditions. The results offer an approach for designing a solid lubricant solution for tribological applications.

Al/Al2O3 metal matrix composites (MMCs) were produced by metal infiltration of porous ceramic preforms. The porous ceramic preforms were fabricated using the magnetic field-assisted freeze-casting method, resulting in vertically aligned porous channels. Preforms were prepared by freezing an Al2O3/Fe3O4-containing slurry within an applied magnetic field. Vertical alignment of the channels was facilitated by the magnetic response of the Fe3O4 in the slurry during the freezing process. After freezing and sublimation, the ceramic preforms were sintered and then infiltrated with molten A356 Al-based alloy. The mechanical properties of the resulting Al2O3/A356 MMCs were compared to those of bulk Al2O3, bulk Al-based alloy (A356), and porous Al2O3 preforms using micro-indentation testing. The indentation hardness and elastic moduli values of Al2O3/A356 MMCs showed good agreement with the predicted theoretical calculations. This study provides a new approach for the design of MMCs with controlled composition and improved mechanical characteristics.

The adaptation of systems to external influences is of broad interest. We study the influence of microwave signals of different shapes on the magnetoacoustic wave system with a giant nonlinearity in canted antiferromagnet FeBO3 at room temperature, which is close to its phase transition to the paramagnetic state. The classical nonlinear system obeys external deterministic signals; the modulation response describes the shape of these signals. In response to a noisy spectrum, the system shows self-organization, and mode competition selects one excited mode while suppressing others. With an increase in the power of the external signal, another self-organization is observed in the form of a narrow peak at the frequency of the fundamental minimum. This represents the first observation of the macroscopic quantum statistical phenomenon, Bose-Einstein condensation of magnetoacoustic wave quanta in a wave system with a high level of thermal fluctuations. The resulting picture of adaptation can analogously be transferred to many other adaptive wave systems, including large scale adaptive wave systems in the natural environment.

The human body involves a large number of systems subjected to contact stresses and thus experiencing wear and degradation. The limited efficacy of existing solutions constantly puts a significant financial burden on the healthcare system, more importantly, patients are suffering due to the complications following a partial or total system failure. More effective strategies are highly dependent on the availability of advanced functional materials demonstrating excellent tribological response and good biocompatibility. In this article, we review the recent progress in implementing two-dimensional (2D) materials into bio-applications involving tribological contacts. We further summarize the current challenges for future progress in the field.

The mitigation of CMAS (calcium–magnesium–aluminum–silicon oxide) infiltration is a major requirement for the stability of thermal barrier coatings. In this study, yttria-stabilized zirconia (YSZ)–Al2O3–SiC, YSZ–Al2O3–Ta2O5, and YSZ–Al2O3–Nb2O5 self-healing composites produced by uniaxially pressing powders were investigated as an alternative to YSZ. CMAS infiltration in these materials was tested at 1250 °C for 10 h. Comparing the depth of CMAS infiltration using scanning electron microscope (SEM) in tandem with electron-dispersive X-ray spectroscopy (EDS), all self-healing materials were found to perform better than the reference materials. While standard YSZ shows massive CMAS infiltration, SEM micrographs and EDS maps revealed a 33-fold improvement in CMAS resistance for the YSZ–Al2O3–Nb2O5 system, which exhibited the best performance among the selected self-repairing materials. X-ray diffraction and high-resolution SEM micrographs taken 10 μm below the surface revealed that CMAS only infiltrated pores in the topmost region of the samples. Both YSZ–Al2O3–Ta2O5 and YSZ–Al2O3–Nb2O5 systems showed no signs of chemical reaction with CMAS.

Magnetic field-assisted freeze-casting of porous alumina structures is reported. Different freeze-casting parameters were investigated and include the composition of the original slurry (Fe3O4 and PVA content) and the control of temperature during the free casting process. The optimum content of the additives in the slurry were 3 and 6 wt% for PVA and Fe3O4, respectively. These conditions provided the most unidirectional porous structures throughout the length of the sample. The sintering temperature was maintained at 1500 °C for 3 h. The application of a vertical magnetic field (parallel to ice growth direction) with using a cooling rate mode technique was found to enhance the homogeneity of the porous structure across the sample. The current study suggests that magnetic field-assisted freeze-casting is a viable method to create highly anisotropic porous ceramic structures.

Bioresorbable metals are quickly advancing in the field of regenerative medicine for their promises of tissue restoration without adverse consequences from their lifelong presence. Zn has recently risen to the top of bioresorbable metals with great potential as a medical implant. However, cell adhesion and colonization on the Zn substrate surface remains challenging, which could damper interfacial tissue-implant integration. Inspired by the fact that surface topography can regulate cell function and fate, we hypothesize that topography on bioresorbable Zn can dictate material biocompatibility, cell differentiation, and immunomodulation. To verify this, surface-engineered Zn plates with nano-, submicro-, and microtopographies were systematically investigated. The microscale topography exhibited increased adhesion, pronounced self-renewal, and enhanced osteogenic differentiation of bone cells as well as less macrophage inflammatory polarization, reduced platelet adhesion, and better hemocompatibility. Thus, surface topography could be a viable strategy to enhance bioresorbable Zn's biocompatibility and integration with surrounding tissues while reducing inflammation.

Here, we present a new combined freeze-casting and laser processing method for the design of yttria-stabilized zirconia (YSZ) based thermal-barrier coatings. YSZ ceramics with unidirectionally-aligned pore channels were created using the freeze-casting method. After sintering, top view and cross-sectional scanning electron microscopy (SEM) revealed the structural features of the preform, which exhibits a 74 ± 2% volume fraction of porosity and an average pore channel size of 30 ± 3 μm. The measured thermal conductivity of this porous structure was 0.27 ± 0.02 W/(m K), which is eight times lower than that of reported values for dense YSZ. Though high porosity is beneficial both from a structural and thermal response perspective, the open porosity could potentially be an issue from an application stand-point when evaluating the resistance of materials to calcium–magnesium–aluminum–silicon oxide (CMAS) attack. CMAS attack, which can originate from deposits of molten sand, ash, and dust, is one of the major causes of thermal barrier coating failure. Therefore, the surface of the porous samples was modified using a laser process to create a barrier to CMAS infiltration. SEM micrographs aided in determining the optimum laser parameters required to fully seal the surface using a laser treatment. The performance of the original porous and surface-modified YSZ was compared by conducting CMAS infiltration studies. Laser modification was shown to be a viable technique to significantly reduce CMAS infiltration in porous thermal barrier coatings.

Robust and efficient approaches for the synthesis of materials with structure, porosity, and composition controlled at the nanoscale are highly important for a wide range of applications. Polymer templates are promising platforms to achieve such control. The self-assembly process of polymers provides access to diverse structures that can serve as templates for the deposition of inorganic materials. By infiltrating metal precursors from gas or liquid phases, using sequential infiltration synthesis (SIS) or swelling-based infiltration (SBI), respectively, into the polymer templates, one can create finely-tuned texturing of the surface films and bulk materials. In this review, we outline the specifics and dynamics of the polymer infiltration process and characterize the structure and properties of the synthesized materials. Finally, we highlight recent progress in implementing polymer infiltration-based nanoporous ceramics for many applications, including sensors, antireflective coatings, oil-absorbing foams, nanolithographic patterns, and catalytic materials.

Molecular hydrogen recently attracted lots of attention in biomedical community because of its abilities to modulate signal transduction, protein phosphorylation, and gene expression that enable its anti-inflammatory, anti-allergy, and anti-apoptotic activities. However, controllable and local delivery of hydrogen molecules to tissues still remains challenging. Here, we propose a new method of delivering molecular hydrogen directly to human skin cells by designing a hydrogen-generating patch that releases hydrogen in surrounding environment as a product of chemical reaction of aluminum and carbon hydroxide in presence of water. We show that in the presence of molecular hydrogen the cells viability, expression of collagen, and migration efficiency of cells increase, thus suggesting that hydrogen can be used to promote better and faster healing of skin issues such as wounds and bruises.

Under the high-contact-pressure and shear conditions of tribological interfaces lubricated by gaseous, liquid, and solid forms of carbon precursors, a variety of highly favorable tribocatalytic processes may take place and result in the

Here, we report a swelling-assisted sequential infiltration synthesis (SIS) approach for the design of highly porous zinc oxide (ZnO) films by infiltration of block copolymer templates such as polystyrene-block-polyvinyl pyridine with inorganic precursors followed by UV ozone-assisted removal of the polymer template. We show that porous ZnO coatings with the thickness in the range between 140 and 420 nm can be obtained using only five cycles of SIS. The pores in ZnO fabricated via swelling-assisted SIS are highly accessible, and up to 98% of pores are available for solvent penetration. The XPS data indicate that the surface of nanoporous ZnO films is terminated with -OH groups. Density functional theory calculations show a lower energy barrier for ethanol-induced release of the oxygen restricted depletion layer in the case of the presence of -OH groups at the ZnO surface, and hence, it can lead to higher sensitivity in sensing of ethanol. We monitored the response of ZnO porous coatings with different thicknesses and porosities to ethanol vapors using combined mass-based and chemiresistive approaches at room temperature and 90 °C. The porous ZnO conformal coatings reveal a promising sensitivity toward detection of ethanol at low temperatures. Our results suggest the excellent potential of the SIS approach for the design of conformal ZnO coatings with controlled porosity, thickness, and composition that can be adapted for sensing applications.

Activating a self-healing process is a viable approach for preventing the failure of ceramics experiencing mechanically-induced crack propagation. Previously, it was demonstrated that niobium oxide (Nb2O5) exhibits self-healing properties activated by the formation of Nb-Ag-O ternary oxide when heated above 945 °C in presence of silver. In this study, we explore the mechanism of lowering the high-temperature healing requirement by assisting the process of crack repair with a normal load and shear stresses. Specifically, we propose to use tribologically-induced local heating as a mechanism to enhance the self-healing ability of Nb2O5. During a pin-on-disk test, whereby a niobium oxide flat was sliding against a silver-coated ball, a sudden lowering of the coefficient of friction was observed at elevated temperatures (~600 °C). The better performance of the coating was associated with a surface reconstruction process initiated inside the wear track. Extensive characterization analysis of the wear track using energy-dispersive x-ray spectroscopy, Raman spectroscopy, and x-ray diffraction confirmed the presence of an Nb-Ag-O ternary oxide phase inside the wear track formed at elevated temperature. The formation of an Nb-Ag-O ternary oxide at a much lower than thermodynamically-required temperature suggests that the self-healing process can be initiated directly during mechanically induced stresses. Such a process is a new recipe for improving wear and crack resistance characteristics of ceramic components and may be tuned to provide the desired frictional response.

Polymer templates play an essential role in the robust infiltration-based synthesis of functional multicomponent heterostructures with controlled structure, porosity, and composition. Such heterostructures are be used as hybrid organic&ndash, inorganic composites or as all-inorganic systems once the polymer templates are removed. Using iron oxide/alumina heterostructures formed by two-step infiltration of polystyrene-block-polyvinyl pyridine block copolymer with iron and aluminum precursors from the solution and vapor-phases, respectively, we show that the phase and morphology of iron oxide nanoparticles dramatically depend on the approach used to remove the polymer. We demonstrate that thermal and plasma oxidative treatments result in iron oxide nanoparticles with either solid or hollow morphologies, respectively, that lead to different magnetic properties of the resulting materials. Our study extends the boundaries of structure manipulations in multicomponent heterostructures synthesized using polymer infiltration synthesis, and hence their properties.

We report the synthesis and physical properties studies of quasi-one-dimensional (quais-1D) iron chalcogenide ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{4}$ which shares the ${\mathrm{FeSe}}_{4}$ tetrahedra building motif commonly seen in the iron chalcogenide superconductors. A high-quality polycrystalline sample was achieved by solid-state reaction method and characterized by x-ray diffraction, electrical resistivity, magnetic susceptibility, and neutron diffraction measurements. ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{4}$ is a narrow gap semiconductor that magnetically orders at $\ensuremath{\sim}310$ K. Both neutron powder diffraction results and isothermal $M\ensuremath{-}H$ loops suggest a canted antiferromagnetic structure where Fe sublattices are antiferromagnetically ordered along the $c$-axis quasi-1D chain direction, resulting in a net ferromagnetic moment in the perpendicular direction along the $a$ axis with tilted angle of $18.{7}^{\ensuremath{\circ}}$ towards the $b$ axis.

Nanocrystalline Fe5Si3 structures embedded within the top 50 nm of Si substrate have been synthesized via low-energy (50 keV) Fe− ion implantation and subsequent thermal annealing in vacuum at 500 °C for 1 h. Prior to the ion irradiation, the distribution of the implanted ions and sputtering of the implanted and target atoms were modeled using both static and dynamic ion solid interaction simulation codes in order to determine the desired ion implantation experimental parameters. The simulation showed that for a 50 keV Fe ion beam, the concentration of the Fe reaches a saturation value of 48% at a fluence ~ 2 × 1017 ions/cm2, while distributed within the top 60 nm from the surface of the Si substrate. Depth profile utilizing X-ray photoelectron spectroscopy spectra along with Ar-ion etching shows the presence of Fe ions buried under the surface of Si. X-ray diffraction pattern confirms the presence of crystalline Fe5Si3 in Si. In the vibrating sample magnetometer analysis, the synthesized Fe5Si3 nanocrystal structures show superparamagnetic behavior with very low magnetization at room temperature.

Hybrid dual-phase coatings composed of an A356 aluminum alloy modified by plasma electrolytic oxidation (PEO) and burnished with graphite-MoS2-Sb2O3 chameleon solid lubricant powders have been produced. The PEO layer provides high hardness and load support while the solid lubricant powders reduce friction. These hybrid coatings were tribotested against steel and silicon nitride counterparts in air from 25 °C to 300 °C and using variable contact loads. The open porosity and surface roughness of the PEO layers were reduced considerably by the burnishing process. Polishing of the PEO surfaces prior to burnishing significantly reduced the resulting coefficient of friction (COF) of the hybrid coating. In-situ Raman spectroscopy revealed the chemical stability of the dual phase coatings at temperatures up to 300 °C with no signs of oxidation or reduction of the chameleon components. COF values ranged from 0.2 at room temperature down to 0.02 at 300 °C. The observed low friction values were attributed to the synergism between PEO and chameleon layers that promote defect healing and adaptive behavior of the coating. Top view scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) confirmed that the thermo-mechanical stimulus caused the chameleon coating to fill the voids in the PEO layer. In-situ Raman spectroscopy revealed that the lubricating phases, i.e. MoS2 and graphite, were protected from oxidation by the porous PEO structure. These lubricious phases formed a transfer film in the wear tracks and the counterpart bodies as a result of the contact pressure (up to 1.4 GPa) and thermal energy, which led to an order of magnitude reduction in the COF at high temperatures. The low shear strength of MoS2 and graphite and the good adhesion and integration of the chameleon coating with the PEO sublayer due to high contact pressures during sliding were responsible for the ultra-low friction behavior of the composite coating.