Exceptional Material Properties Research Articles

Sample Preparation and Determination of Trace Elements in High-Entropy Alloys by Total Reflection X-Ray Fluorescence (TXRF)

High-entropy alloys (HEAs) have attracted significant attention in recent years owing to their exceptional material properties; however, trace impurities in these alloys can significantly affect their strength, toughness, and radiation resistance. This study employs total reflection X-ray fluorescence (TXRF) to determine the trace impurities in three common HEA powders prepared via suspension techniques. High-Z (Ca and Mn) and low-Z (Mg and Al) elements were quantified using the internal standard and calibration curve methods, respectively. The levels of high-Z elements are consistent with those determined using inductively coupled plasma – optical emission spectrometry (ICP-OES). Although the physical mechanisms exerted various effects on low-Z elements, qualitative and semi-quantitative analyses remained feasible, demonstrating the effectiveness of TXRF for impurities in HEAs. Additionally, the combination of suspension sample preparation and TXRF affords a nondestructive, rapid, and cost-effective methodology that requires minimal sample quantities. Consequently, TXRF is well suited for the rapid determination of impurities in HEAs.

(Invited) Zwitter Ion-Promoted Hybrid Sepiolite Membranes for Energy Applications

Functionalized natural clays exhibit significant potential as electrode materials, solid-state electrolytes and separators in energy storage and conversion devices. Features that evoke interest in clay minerals are their (1) porous structures and adsorption properties, (2) tunable surface areas, (3) remarkable thermal and mechanical stabilities, (4) abundant natural reserves, and (5) cost. By tweaking such features along with functionalization with desired molecules, they can be used as an ideal candidate for solid-state electrolyte and battery separators. Naturally occurring clays possess layered silicate structures with interchangeable, intercalated ions and tunable chemical properties. Among them, sepiolite, which is a hydrated magnesium silicate, is one of the most appealing clays having a high-aspect ratio. The blocks and channels in sepiolite with discontinuity in the external silica sheet expose a significant number of surface-silanol groups directly accessible to functionalize with organic and inorganic species. Moreover, its exceptionally high surface area and high cation exchange capacity (CEC) compared to other clays enables easy functionalization, thereby imparting exceptional mechanical durability and material properties that can be used for myriads of applications.In this work a sustainable, cost-effective, environmentally benign, carbon-neutral, and bio-friendly sepiolite clay composites have been developed using betaine and ionic liquid without the use of polymers, metals, or carbon-based precursors.Betaine-modified sepiolite clay composites have been synthesized to fabricate flexible and mechanically robust membranes. These membranes are characterized using powder X-ray diffraction, ATR-FTIR, XPS, surface area analyses, rheology, and imaging techniques (e.g., SEM). Morphological analyses reveal sepiolite possesses needle-shaped morphology in a highly aggregated state. The addition of betaine disaggregates such bundles, forming a 3D network with unique “clay anemone” structures. The XRD patterns are consistent with the literature reflecting no change in the d-spacing and corresponding 2θ value (d100 2θ = 7.4 ͦ) before and after betaine treatment. This provides strong evidence of modification limited to the external surface. ATR-FTIR spectra of the sepiolite-betaine composite membranes show the presence of 935, 1330,1391, and 1616 cm-1 frequencies that correspond to C-N-C, N-C-H, C-N and C=Ostretching respectively. This suggests the successful functionalization of sepiolite clay by betaine through an intercalation mechanism. Further, the electrochemical properties of betaine-modified sepiolite membranes are investigated by electrochemical impedance spectroscopy (EIS) measurements to study the ion dynamics of the hybrid membranes. The room temperature ionic conductivities of these membranes are measured using lithium perchlorate (LiClO4) in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solvent (1:1). The concentration of LiClO4 is varied to monitor the change in ionic conductivity and ease of ion transfer through the membranes. The highest ionic conductivity is observed in 0.1M LiClO4 concentration which is superior to the ionic conductivity of sepiolite or hybrid materials with carbon-based precursors, metal ions, quantum dots, or polymers. Viscoelastic properties of the sepiolite slurries with varying concentrations of betaine are also studied to investigate the interaction mechanism between the sepiolite-betaine system and correlate the impact of these interactions on the structure and ionic conductivity of the hybrid sepiolite membranes. Contrary, the IL-sepiolite membranes exhibit superior ionic conductivity compared to betaine-sepiolite membranes, which gives a distinct advantage in the physicochemical and electrochemical properties. The composites are synthesized with varying concentrations of ionic liquid-to-clay ratios and pressed into pellets for conductivity measurements. The highest ionic conductivity of 1 x 10-2 S/cm is achieved by modifying the clay with 10 wt. % IL specimens. This helps to improve the ionic conductivity of the IL-clays. The XRD spectra of sepiolite-IL composites show almost no change in the 2 theta values and peak intensities compared to the pristine sepiolite, confirming the crystalline structure of the sepiolite clay is intact after functionalization with IL. The ATR-FTIR confirms the IL-sepiolite modification with the appearance of a new band at 1345 cm-1 that is attributed to -CH stretching frequencyfrom the alkyl chains of IL present in the clay structures.We have developed a new approach using earth-abundant silicate-based materials to synthesize hybrid zwitterion-modified sepiolite clay membranes. Such materials are not only flexible and mechanically durable, but they also exhibit enhanced ionic conductivity and show exceptional thermal and chemical durability at temperatures above 300 °C and with most aggressive organic solvents, making them a superior candidate for an ergonomic and eco-friendly membrane-based separator for energy devices and gas absorption. Current work is in progress to understand the fundamentals underlying the unique structure-property relationship of hybrid sepiolite, zwitterion-silicate interactions, and conductivity variance with sepiolite architectures, thereby exploiting newer and better properties for application in catalysis, flexible electronics, and biomedical fields. Figure 1

Electrodeposition of FeNiCoCrMn high-entropy alloys on copper foam for enhanced hydrogen evolution reaction——influence of additives and deposition potential

High-entropy alloys (HEAs) have been paid attention for their exceptional material properties. FeNiCoCrMn HEAs electrocatalysts were synthesized on copper foam by electrodeposition. The effects of deposition potential and additives on the surface morphology and crystal structure of the catalysts were investigated, and their hydrogen evolution reaction (HER) performance in 1.0 M KOH solution was studied. The high deposition potential enhanced nucleation, leading to intricate structural formations, while CTAB and citrate additives notably altered the surface texture of the catalysts, affecting HER activity. Notably, Fe0.19Ni0.24Co0.29Cr0.18Mn0.1 electrocatalyst with a low Tafel slope of 84.7 mV dec−1 showed good HER activity, only required the overpotential of 191 mV to achieve a current density of 10 mA cm−2.

Chemical and Solvent‐Based Recycling of High‐Performance Epoxy Thermoset Utilizing Imine‐Containing Secondary Amine Hardener

AbstractEpoxy thermosets are indispensable in various industrial applications due to their exceptional material properties. However, their limited recyclability poses a significant challenge for sustainability. To address this issue, integrating recyclable imine moieties into epoxy systems has emerged as a promising strategy. Despite recent advancements, challenges persist concerning the hydrolytic stability of imine‐based epoxy thermosets and the formation of irregular oligomeric structures upon depolymerization. In this study, these shortcomings are solved by designing a liquid imine monomer with secondary amine functionalities, which is subsequently reacted with commercially available epoxy monomers to produce high‐performance epoxy thermosets. Remarkably, the developed imine‐based epoxy system shows no sign of hydrolysis even under high‐temperature aqueous conditions, underscoring its potential for various industrial applications. Only the treatment with aqueous HCl results in the selective formation of exclusively well‐defined molecules, in high isolated yields after depolymerization. Crosslinking these building blocks once again yields recycled polymers with properties identical to pristine material. Moreover, it is discovered that, despite the crosslinked nature of the epoxy thermoset, the complete dissolution of the intact polymer in dichloromethane allowed for simple solvent‐based recycling. Through design on the molecular level, the recycling of imine‐based epoxy polymers is achieved via chemical and solvent‐based techniques.

Enhancing the Strength and Ductility Synergy of Lightweight Ti-Rich Medium-Entropy Alloys through Ni Microalloying.

Medium-entropy alloys (MEAs) have attracted considerable attention in recent decades due to their exceptional material properties and design flexibility. In this study, lightweight and non-equiatomic MEAs with low density (~5 g/cm3), high strength (yield strength: 1200 MPa), and high ductility (plastic deformation: ≧10%) were explored. We fine-tuned a previously developed Ti-rich MEA by microalloying it with small amounts of Ni (reducing the atomic radius and increasing the elastic modulus) through solid solution strengthening to achieve a series of MEAs with enhanced mechanical properties. Among the prepared MEAs, Ti65Ni1 and Ti65Ni3 exhibited optimal properties in terms of the balance between strength and ductility. Furthermore, the Ti65Ni3 MEA was subjected to thermo-mechanical treatment (TMT) followed by cold rolling 70% (CR70) and cold rolling 85% (CR85). Subsequently, the processed samples were rapidly annealed at 743 °C, 770 °C, 817 °C, and 889 °C at a heating rate of 15 °C/s. X-ray diffraction analysis revealed that the MEA could retain its single-body-centered cubic solid solution structure after TMT. Additionally, the tensile testing results revealed that increasing the annealing temperature led to a decrease in yield strength and an increase in ductility. Notably, the Ti65Ni3 MEA sample that was subjected to CR70 and CR85 processing and annealed for 30 s exhibited high yield strength (>1250 MPa) and ductility (>13%). In particular, the Ti65Ni3 MEA subjected to CR85 exhibited a specific yield strength of 264 MPa·cm3/g, specific tensile strength of 300 MPa·cm3/g, and ductility of >13%.

Enhancing the Consistency and Performance of Graphene-Based Devices via Al Intermediate-Layer-Assisted Transfer and Patterning.

Graphene has garnered widespread attention, and its use is being explored for various electronic devices due to its exceptional material properties. However, the use of polymers (PMMA, photoresists, etc.) during graphene transfer and patterning processes inevitably leaves residues on graphene surface, which can decrease the performance and yield of graphene-based devices. This paper proposes a new transfer and patterning process that utilizes an Al intermediate layer to separate graphene from polymers. Through DFT calculations, the binding energy of graphene-Al was found to be only -0.48 eV, much lower than that of PMMA and photoresist with graphene, making it easier to remove Al from graphene. Subsequently, this was confirmed through XPS analysis. A morphological characterization demonstrated that the graphene patterns prepared using the Al intermediate layer process exhibited higher surface quality, with significantly reduced roughness. It is noteworthy that the devices obtained with the proposed method exhibited a notable enhancement in both consistency and sensitivity during electrical testing (increase of 67.14% in temperature sensitivity). The low-cost and pollution-free graphene-processing method proposed in this study will facilitate the further commercialization of graphene-based devices.

Carbon nanowall-based gas sensors for carbon dioxide gas detection

Carbon nanowalls (CNWs) have attracted significant attention for gas sensing applications due to their exceptional material properties such as large specific surface area, electric conductivity, nano- and/or micro-porous structure, and high charge carrier mobility. In this work, CNW films were synthesized and used to fabricate gas sensors for carbon dioxide (CO2) gas sensing. The CNW films were synthesized using an inductively-coupled plasma (ICP) plasma-enhanced chemical vapor deposition (PECVD) method and their structural and morphological properties were characterized using Raman spectroscopy and electron microscopy. The obtained CNW films were used to fabricate gas sensors employing interdigitated gold (Au) microelectrodes. The gas sensors were fabricated using both direct synthesis of CNW films on interdigitated Au microelectrodes on quartz and also transferring presynthesized CNW films onto interdigitated Au microelectrodes on glass. The CO2 gas-sensing properties of fabricated devices were investigated for different concentrations of CO2 gas and temperature-ranges. The sensitivities of fabricated devices were found to have a linear dependence on the concentration of CO2 gas and increase with temperature. It was revealed that devices, in which CNW films have a maze-like structure, perform better compared to the ones that have a petal-like structure. A sensitivity value of 1.18% was obtained at 500 ppm CO2 concentration and 100 °C device temperature. The CNW-based gas sensors have the potential for the development of easy-to-manufacture and efficient gas sensors for toxic gas monitoring.

Point-of-care devices engaging green graphene: an eco-conscious and sustainable paradigm.

The healthcare landscape has experienced a profound and irreversible transformation, primarily driven by the emergence of nanomaterial-assisted point-of-care (POC) devices. The inclusion of nanomaterials in POC devices has revolutionized healthcare by enabling rapid, on-site diagnostics with minimal infrastructure requirements. Among the materials poised to lead this technological revolution, green graphene emerges as a compelling contender. It possesses a unique combination of exceptional material properties and environmentally conscious attributes. These attributes include its substantial surface area, unparalleled electrical conductivity, and inherent biocompatibility. This article embarks on an exploration of POC devices incorporating green graphene. It meticulously dissects the intricacies of their design, performance characteristics, and diverse applications. Throughout the exposition, the transformative impact of green graphene on the advancement of POC diagnostics takes centre stage. It underscores the material's potential to drive sustainable and effective healthcare solutions, marking a significant milestone in the evolution of healthcare technology.

High-Performance α-Diimine Nickel Complexes for Facile Access of PE Elastomers with Exceptional Material Properties

High-Performance α-Diimine Nickel Complexes for Facile Access of PE Elastomers with Exceptional Material Properties

2D Materials Beyond Post-AI Era: Smart Fibers, Soft Robotics, and Single Atom Catalysts.

Recent consecutive discoveries of various 2D materials have triggered significant scientific and technological interests owing to their exceptional material properties, originally stemming from 2D confined geometry. Ever-expanding library of 2D materials can provide ideal solutions to critical challenges facing in current technological trend of the fourth industrial revolution. Moreover, chemical modification of 2D materials to customize their physical/chemical properties can satisfy the broad spectrum of different specific requirements across diverse application areas. This review focuses on three particular emerging application areas of 2D materials: smart fibers, soft robotics, and single atom catalysts (SACs),which hold immense potentials for academic and technological advancements in the post-artificial intelligence (AI) era. Smart fibers showcase unconventional functionalities including healthcare/environmental monitoring, energy storage/harvesting, and antipathogenic protection in the forms of wearable fibers and textiles. Soft robotics aligns with future trend to overcome longstanding limitations of hard-material based mechanics by introducing soft actuators and sensors. SACs are widely useful in energy storage/conversion and environmental management, principally contributing to low carbon footprint for sustainable post-AIera. Significance and unique values of 2D materials in these emerging applications are highlighted, where the research group has devoted research efforts for more than a decade.

Damage mechanism and mechanical properties of carbon nanotubes induced by He2+ ion irradiation: Molecular dynamics simulations and experiments

Carbon nanotubes (CNTs) are expected to play a pivotal role in future space device applications owing to their exceptional material properties. To ensure the reliability and safety of CNTs in such applications, meticulous assessment and understanding of their structural integrity under ions irradiation is imperative. In this study, the mechanisms of damage to 1–5 wall CNTs caused by the irradiation of He2+ ions in the 1–100 keV energy range were investigated by conducting molecular dynamics (MD) simulations. The mechanisms of damage induced by He2+ ion irradiation exhibited notable distinctions between single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). SWCNTs easily conducted the kinetic energy of the He2+ irradiation out of the CNTs with cascade collisions, thereby reducing the damage they incurred, whereas the interlayer structure of the MWCNTs resulted in the irradiation energy being confined inside the tubes, leading to an increase in defects. The MD simulations revealed the irradiation swelling phenomenon of the MWCNTs in relation to the kinetic energy of irradiation and the cumulative fluence and indicated that swelling occurred simultaneously inward and outward along the radial direction of the CNTs. Irradiation-induced swelling was observed in experiments involving vertical array carbon nanotubes (VACNTs) irradiated with 540 keV He2+ ions. The results from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization, along with the Raman analysis, indicate that the damage observed in CNTs due to He2+ ion irradiation closely resembles the findings obtained through MD simulations. Both experimental and MD simulation studies demonstrated that increasing the dosage of He2+ ion irradiation increased the CNT defects, causing a transition from the ordered graphite structure to amorphous C. Additionally, the compressive mechanical properties and surface adhesion mechanics of the irradiated VACNTs were examined by performing nanoindentation experiments. The tensile mechanical properties of the irradiated CNTs were evaluated using MD simulations. The combined results indicated that high-energy, high-fluence ion irradiation degraded the mechanical properties of the CNTs. This study comprehensively investigated the mechanisms of damage to CNTs under He2+ ion irradiation and the subsequent impacts on the mechanical properties of the CNTs. The findings of this research provide essential insights for comprehending the irradiation responses of CNTs and for designing composite CNT materials with enhanced radiation resistance.

Chitin nanofibers prepared by enzymatic hydrolysis: Characterization and application for Pickering emulsions

Chitin nanofibers (ChNFs) have a wide range of applications in numerous fields owing to their exceptional material properties and biological functionality. This research focused on producing ChNFs with diameters of 20–70 nm using chitinase and ultrasound from crayfish shells. The impact of enzymatic duration on ChNF yield and performance was investigated. Results revealed ChNFs forming a high aspect ratio network structure. Chitinase hydrolysis enhanced ChNF dispersion and yield while improving crystallinity and thermal stability without significantly altering their chemical structure. Enzymatically modified ChNF suspensions also exhibited stable rheological properties. Moreover, ChNFs showed good emulsification and emulsion stability in Pickering emulsion. The mechanism may be the effective adsorption of ChNFs at the oil-water interface, and the formation of a ChNF network in the continuous phase that prevents droplet coalescence. This study highlights that the potential of chitinase and ultrasound for the production of ChNFs and the utilization of crayfish shell waste.

Online micro defects detection for ductile cast iron pipes based on twin light photometric stereo

Ductile cast iron pipes (DCIPs) are widely utilized in water and gas supply due to their exceptional mechanical and material properties. Quality control during production is paramount for optimal performance, with surface defect detection being of utmost importance. Currently, production sites primarily rely on manual visual inspection, which presents several challenges, including high labor intensity, low efficiency, and subjectivity in defect judgment. 2D detection algorithms based on single images struggle to effectively detect small defects such as pores, pinholes, and scratches, resulting in high missed detection rates and vulnerability to interference from oil and water stains. To address these issues, this paper proposes a symmetrical twin-light photometric stereo (TLPS) detection algorithm based on photometric stereo theory, and image correction algorithm for mitigating the effects of ambient light. A visual inspection prototype system was designed and successfully implemented at a production site. The system comprises eight visual inspection units, each equipped with a high-speed line scan camera and two bar light sources for image acquisition of moving DCIP. Under the Lambertian model and parallel light source assumption, the gradient expression in the texture direction of the DCIP surface is derived based on light source symmetry. Production experiment results demonstrate that the gradient map obtained through the proposed TLPS effectively enhances defect contrast and accurately detects and locates micro defects such as pores, pinholes, and scratches on cast pipe surfaces. This verifies the effectiveness of the TLPS algorithm, addresses the shortcomings of traditional 2D detection algorithms, and lays the foundation for subsequent online detection of DCIP surface defects.

Shortwave infrared surface plasmons in multilayered two-dimensional Ti3C2T x MXenes

MXene, an ultra-thin two-dimensional conductive material, has attracted considerable interest in various fields due to its exceptional material properties. In particular, Ti3C2Tx MXene exhibits distinct optical properties, enabling it to support surface plasmons in the shortwave infrared (SWIR) region. However, it is challenging to enhance the field confinement of MXene surface plasmons in a single-interface structure due to the substantial intrinsic absorption of Ti3C2Tx MXene. Herein, we explore various multilayer structures capable of supporting high field confinement of Ti3C2Tx MXene plasmons, including insulator–MXene–insulator (IMI), MXene–insulator–MXene (MIM), and insulator–MXene–insulator–MXene (IMIM) configurations. We observe that the field confinement of MXene plasmons improves as the thickness of either the MXene or insulator layers decreases, which is attributed to the strong coupling between plasmons at the multilayer interfaces. Furthermore, the IMIM structure demonstrates the most substantial enhancement in field confinement. In an IMIM structure with a 1.3 nm-thick MXene monolayer and a 1.0 nm thick SiO2 layer, the wavelength and effective field size of the plasmon at a frequency of 150 THz (λ 0 = 2.0 μm) are calculated to be 24.61 nm and 1.50 nm, respectively. These values demonstrate a reduction by factors of 55 and 596, respectively, compared to those obtained in a single SiO2–MXene interface structure. Multilayer-based MXene plasmons provide a solution for enhancing the field confinement of MXene plasmons in the SWIR region, and we expect them to play a crucial role in a variety of 2D material-based SWIR plasmonic applications.

Hydrogel-Based Flexible Electronics.

Flexible electronics is an emerging field of research involving multiple disciplines, which include but not limited to physics, chemistry, materials science, electronic engineering, and biology. However, the broad applications of flexible electronics are still restricted due to several limitations, including high Young's modulus, poor biocompatibility, and poor responsiveness. Innovative materials aiming for overcoming these drawbacks and boost its practical application is highly desirable. Hydrogel is a class of 3D crosslinked hydrated polymer networks, and its exceptional material properties render it as a promising candidate for the next generation of flexible electronics. Here, the latest methods of synthesizing advanced functional hydrogels and the state-of-art applications of hydrogel-based flexible electronics in various fields are reviewed. More importantly, the correlation between properties of the hydrogel and device performance is discussed here, to have better understanding of the development of flexible electronics by using environmentally responsive hydrogels. Last, perspectives on the current challenges and future directions in the development of hydrogel-based multifunctional flexible electronics are provided.

Scalable, Highly Pure, and Diameter-Sorted Boron Nitride Nanotube by Aqueous Polymer Two-Phase Extraction.

Boron nitride nanotube (BNNT) has attracted recent attention owing to its exceptional material properties; yet, practical implementation in real-life applications has been elusive, mainly due to the purity issues associated with its large-scale synthesis. Although different purification methods have been discussed so far, there lacks a scalable solution method in the community. In this work, a simple, high-throughput, and scalable purification of BNNT is reported via modification of an established sorting technique, aqueous polymer two-phase extraction. A complete partition mapping of the boron nitridespecies is established, which enables the segregation of the highly pure BNNT with a major impurity removal efficiency of > 98%. A successful scaling up of the process is illustrated and provides solid evidence of its diameter sorting behavior. Last, towards its macroscopic assemblies, a liquid crystal of the purified BNNT is demonstrated. The effort toward large-scale solution purification of BNNT is believed to contribute significantly to the macroscopic realization of its exceptional properties in the near future.

Formation of buried 2D Aluminium Gallium Nitride structures with enhanced piezoelectric modulus by xenon ion implantation

Two-Dimensional (2D) III-V nitrides are anticipated to exhibit exceptional material properties with wide-ranging technological significance. We report, ion beam synthesis of buried 2D Aluminium Gallium Nitride structures with enhanced piezoelectric modulus. We propose three criteria for the formation of 2D AlGaN layers by ion implantation. The 2D layers were synthesized by Xe implantation into epitaxially grown, strain-free Al0.5Ga0.5N thin films and their presence was confirmed by scanning transmission electron microscopy. Alternating planar and buckled 2D III-Nitride layers in conjunction with a rapid change of polarity of the buckled layer confirms the weak interaction between the individual layers. Rutherford backscattering, in conjunction with piezoelectric force microscopy was used to identify the optimum Xe dose to induce maximum enhancement of piezoelectric modulus. Our results are supported by X-ray diffraction to quantify the macroscopic strain of the implanted film and Monte-Carlo simulations of ion-solid interactions. Fabrication of this material on a large scale may lead to highly efficient energy harvesters, communication devices, power devices and photocatalytic water splitting technologies.

High-Quality Dry Etching of LiNbO3 Assisted by Proton Substitution through H2-Plasma Surface Treatment.

The exceptional material properties of Lithium Niobate (LiNbO3) make it an excellent material platform for a wide range of RF, MEMS, phononic and photonic applications; however, nano-micro scale device concepts require high fidelity processing of LN films. Here, we reported a highly optimized processing methodology that achieves a deep etch with nearly vertical and smooth sidewalls. We demonstrated that Ti/Al/Cr stack works perfectly as a hard mask material during long plasma dry etching, where periodically pausing the etching and chemical cleaning between cycles were leveraged to avoid thermal effects and byproduct redeposition. To improve mask quality on X- and Y-cut substrates, a H2-plasma treatment was implemented to relieve surface tension by modifying the top surface atoms. Structures with etch depths as deep as 3.4 µm were obtained in our process across a range of crystallographic orientations with a smooth sidewall and perfect verticality on several crystallographic facets.

Surface oxidation mechanism of CoCrFeNi high entropy alloy

High-entropy alloys (HEAs) are becoming increasingly important in advanced manufacturing applications due to their exceptional material properties, including oxidation resistance at and within extreme conditions. In this study, a combined experimental and theoretical approach is used to elucidate surface/near-surface details of structural, energetic, and chemical/electronic properties of CoCrFeNi, a quaternary fcc HEA, upon exposure to oxygen. Employing Density functional theory (DFT) calculation and DFT-driven Molecular Dynamics (DFT-MD), as well as photoelectron spectroscopy, we show strong evidence that, at the oxygen coverages used, oxidation is limited to the near-surface region of this random HEA and that the propensity of oxidation of Cr >> Fe ≈ Co >> Ni atoms, identified by an enhanced hybridization of the O 2p with the Cr 3d, and lesser extent to Fe and Co. Moreover, comparing to the O interaction strength in pure metal surfaces, there is weakening of Cr-O binding due to the presence of Co and Ni while Co-O binding is stronger. Ni-O does not seem to be affected, but being this the weakest interaction, O binds to Cr, Fe, and Co and little is left to bind with Ni.

Silicon Carbide Technology for Advanced Human Healthcare Applications.

Silicon carbide (SiC) is a highly robust semiconductor material that has the potential to revolutionize implantable medical devices for human healthcare, such as biosensors and neuro-implants, to enable advanced biomedical therapeutic applications for humans. SiC is both bio and hemocompatible, and is already commercially used for long-term human in vivo applications ranging from heart stent coatings and dental implants to short-term diagnostic applications involving neural implants and sensors. One challenge facing the medical community today is the lack of biocompatible materials which are inherently smart or, in other words, capable of electronic functionality. Such devices are currently implemented using silicon technology, which either has to be hermetically sealed so it does not directly interact with biological tissue or has a short lifetime due to instabilities in vivo. Long-term, permanently implanted devices such as glucose sensors, neural interfaces, smart bone and organ implants, etc., require a more robust material that does not degrade over time and is not recognized and rejected as a foreign object by the inflammatory response. SiC has displayed these exceptional material properties, which opens up a whole new host of applications and allows for the development of many advanced biomedical devices never before possible for long-term use in vivo. This paper is a review of the state-of-the art and discusses cutting-edge device applications where SiC medical devices are poised to translate to the commercial marketplace.