Metal Nitrides Research Articles

Vibrational Property Tuning of MXenes Revealed by Sublattice N Reactivity in Polar and Nonpolar Solvents.

MXenes, a family of two-dimensional (2D) materials based on transition metal carbides and nitrides, have desirable properties, such as high conductivity, high surface area, and tunable surface groups, for electrocatalysis. Nitride MXenes, in particular, have shown excellent electrocatalytic performance for the nitrogen and oxygen reduction reactions, but a fundamental understanding of how their structures evolve during electrocatalysis remains unknown. Equally important and yet unknown is the effect of the reactivity of the lattice nitrogen on the vibrational behavior of nitride MXenes and the resulting implications in electrocatalysis. Here, we investigate the reactivity of lattice nitrogen and the vibrational properties of titanium nitride MXenes in relevant electrocatalytic solvents using confocal Raman spectroscopy. We found that the vibrational modes of titanium nitride MXenes are attenuated in polar solvents, which is revealed through the alteration of the Raman scattering in solvents. Contrary to polar solvents, the vibrational modes remain unchanged in nonpolar solvents like hydrocarbons due to the inactivity of the lattice nitrogen. We found that this behavior is unique to nitrides because the Raman characteristics of carbides and sulfides are unaffected by the solvent types. However, the inclusion of nitrogen into the carbide structure does exhibit Raman-solvent behavior similar to that of nitrides, suggesting that replacing carbon with nitrogen affects MXene-light interactions. We demonstrated a proof-of-concept utilizing lattice nitrogen reactivity to enhance the electrocatalytic nitrogen reduction reaction for ammonia production. In summary, we elucidate the vibrational properties of nitride MXenes in solvents and demonstrate the tunability of MXene vibrational properties via lattice atom substitution, which in turn can be exploited to advance the applications of MXenes in electrocatalysis.

New Ultra‐High Cycle Stable Accordion‐Like High Entropy MXene with Improving Energy Storage Performance of Supercapacitors

Abstract2D transition metal carbides, nitrides, and carbonitrides (MXenes) are widely used in energy‐related fields, however, the instability of MXenes limits their application in supercapacitors. Currently, one of the main scientific challenges is how to modify MXenes to enhance their electrochemical performance. Compared to mono‐transition‐metal MXenes (MTMs), the large surface combined with multiple transition metals makes high entropy MXenes (HE‐MXenes) more appealing in energy storage. Here, a HE‐MAX phase, (TiVNbMoW)3AlC2, and a corresponding accordion‐like HE‐MXene are successfully synthesized by selective removal of Al from the HE‐MAX in aqueous hydrofluoric acid (HF). The addition of W allows the high‐entropy MAX (HE‐MAX) to reach greater lattice distortion than (TiVNbMo)3AlC2. It also successfully resolves the problem of inadequate configurational entropy in the M layer and expands the range of M layer. The accordion‐like HE‐MXene with open microstructure and high crystallinity provides multi‐channels for rapid ionic charge diffusion during interlayer ion insertion/extraction. Owing to these designs, the capacity retention rate is 98.7% after 10 000 cycles at 5 A g−1, demonstrating high stability throughout the charge–discharge cycling both in acidic and alkaline. The synthesis of HE‐MXene enriches the selection for energy applications and greatly increases the compositional variety of the MXene family.

Unique dual superlyophobic covalent organic frameworks (COF-TpBD) intercalated MXene composite membrane for efficient oil-water separation

The development of composite membranes utilizing transition metal carbides and nitrides, exemplified by Ti3C2Tx (MXene), has proven efficacious in the treatment of oily wastewater. However, challenges arise from the prolonged and convoluted transport paths within MXene interlayer nanochannels, significantly impeding mass transfer and diminishing membrane permeability. This investigation incorporated porous covalent organic frameworks (COFs) as intercalating agents into two-dimensional (2D) MXene-based membranes to expand the interlayer nanochannels. The resulting MXene@COF-TpBD functional layer polyethersulfone (PES) composite membrane exhibited a distinctive dual superoleophobic surface, concurrently manifesting underwater superoleophobicity and underoil superhydrophobicity (underwater oil contact angle > 150°, underoil water contact angle > 150°). The membranes exhibited excellent water flux (up to 4092.7 L·m-2·h-1·bar-1), efficient oil-water emulsion separation (up to 1908.4 L·m-2·h-1·bar-1, rejection rates >99.78%), noteworthy fouling resistance and structural stability, outperforming most of existing similar membranes. Furthermore, supported by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the incorporation of COF-TpBD improved the antifouling characteristics of the composite membrane. This work presents innovative insights into the improvement of 2D MXene membranes and the use of COF-TpBD for the specific remediation of oily wastewater.

Recent advances and strategies of metal nitrides for accelerating polysulfide redox and regulating Li plating

Recent advances and strategies of metal nitrides for accelerating polysulfide redox and regulating Li plating

Representative modeling of biocompatible MXene nanocomposites for next-generation biomedical technologies and healthcare.

MXenes are a class of 2D transition metal carbides and nitrides (Mn+1XnT) that have attracted significant interest owing to their remarkable potential in various fields. The unique combination of their excellent electromagnetic, optical, mechanical, and physical properties have extended their applications to the biological realm as well. In particular, their ultra-thin layered structure holds specific promise for diverse biomedical applications. This comprehensive review explores the synthesis methods of MXene composites, alongside the biological and medical design strategies that have been employed for their surface engineering. This review delves into the interplay between these strategies and the resulting properties, biological activities, and unique effects at the nano-bio-interface. Furthermore, the latest advancements in MXene-based biomaterials and medicine are systematically summarized. Further discussion on MXene composites designed for various applications, including biosensors, antimicrobial agents, bioimaging, tissue engineering, and regenerative medicine, are also provided. Finally, with a focus on translating research results into real-world applications, this review addresses the current challenges and exciting future prospects of MXene composite-based biomaterials.

In Situ Formation of Ripplocations in Hybrid Organic-Inorganic MXenes.

Inorganic-organic hybrid MXenes (h-MXenes) are a family of 2D transition metal carbides and nitrides functionalized with alkylimido and alkylamido surface groups. Using cryogenic and room temperature scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS), it is shown that ripplocations, a form of a fundamental defect in 2D and layered structures, are abundant in this family of materials. Furthermore, detailed studies of electron probe sample interactions, focusing on structural deformations caused by the electron beam are presented. The findings indicate that at cryogenic temperatures (≈100K) and below a specific dose threshold, the structure of h-MXenes remains largely intact. However, exceeding this threshold leads to electron beam-induced deformation through ripplocations. Interestingly, the deformation behavior, required dose, and resultant structure are highly dependent on temperature. At 100K, it is demonstrated that the electron beam can induce ripplocations in situ with a high degree of precision.

Epitaxial growth of transition metal nitrides by reactive sputtering

Implementing transition metal nitride (TM-nitride) layers by epitaxy into group-III nitride semiconductor layer structures may solve substantial persisting problems for electronic and optoelectronic device configurations and subsequently enable new device classes in the favorable nitride semiconductor family. As a prominent example, the integration of the group-III-transition metal nitride AlScN enabled an improved performance of GaN based transistor structures due to stronger polarization fields as has been recently demonstrated. For other transition metal nitrides (TMNs) and their alloys with group-III nitrides a range of other interesting properties is expected to enable novel devices and applications. We investigated the compatibility of TM-nitride layers with the growth of GaN-based structures on silicon substrates. As we show TiN layers are compatible and particularly suited as highly conducting, metallic-like buffer layer enabling true vertical conduction without elaborate backside processing. Also, we demonstrate epitaxial growth of alloys based on ScN and AlN as well as of HfN layers on Si(111) substrates by reactive sputtering using high purity gases and targets. Particularly, we analyzed the crystal structure and the quality of Sc-rich AlxSc1-xN. For HfN layers, we find a unique impact on the growth polarity of MOVPE-grown GaN layers on Si(111) which changes to N-polar growth. This represents a simple and technologically scalable approach for N-polar GaN-based layers on Si substrates.

Unlocking the Potential of Ti3C2Tx MXene: Present Trends and Future Developments of Gas Sensing

In recent years, the need for future developments in sensor technology has arisen out of the changing landscape, such as pollution monitoring, industrial safety, and healthcare. MXenes, a 2D class of transition metal carbides, nitrides, and carbonitrides, have emerged as a particularly promising group in part due to their exceptionally high conductivity, large area, and tunable surface chemistry. Proposed future research directions, including material modification and novel sensor designs, are presented to maximize Ti3C2Tx MXene-based sensors for various gas sensing applications. While recent progress in Ti3C2Tx MXene-based gas sensors is reviewed, we consolidate their material properties, fabrication strategy, and sensing mechanisms. Further, the significant progress on the synthesis and applications of Ti3C2Tx MXene-based gas sensors, as well as the innovative technologies developed, will be discussed in detail. Interestingly, the high sensitivity, selectivity, and quick response times identified in recent studies are discussed, with specificity and composite formation highlighted to have a significant influence on sensor performance. In addition, this review highlights the limitations witnessed in real-life implementability, including stability, the possibility of achieving reproducible results, and interaction with currently available technologies. Prospects for further work are considered, emphasizing increased production scale, new techniques for synthesis, and new application areas for Ti3C2Tx MXenes, including electronic nose and environmental sensing. Contemplating the existing works, further directions and the development framework for Ti3C2Tx MXene-based gas sensors are discussed.

Computational prediction of novel two-dimensional tungsten nitride superconductors

Transition metal nitrides are well-known 3D superconductor materials. However, there is a lack of knowledge related to their two-dimensional (2D) counterparts, which have several potential technological applications. In this work, we predict, using an evolutionary algorithm coupled with a first-principles approach, a set of novel 2D superconductive structures based on tungsten nitride. Through a systematic process including energetic and dynamical analysis, three thermodynamically stable compositions along with metastable compounds were studied in the following stoichiometries: W4N2, W2N2, and W2N3. Their superconductive temperature (Tc) values, estimated by means of the Eliashberg superconductive theory and the McMillan equation, range from 2.3 to 21.6 K, where the highestTcvalue corresponds to a W2N3metastable hexagonal system. A systematic analysis of the structural, electronic, vibrational and electron-phonon (e-ph) properties, allowed us to recognize the variables that modulate theTcin theses systems. The superconductive behavior is strongly affected by changes in the nitrogen density of states at Fermi level, the e-ph coupling constant and the lattice symmetry. The present results aim to encourage further theoretical and experimental efforts over non fully explored superconductors in two dimensions.

Stability of Expanded Austenite During Annealing in Vacuum

In situ X-ray diffraction has been used to investigate the stability of expanded austenite during annealing in vacuum for the austenitic stainless steel 316Ti, the super-austenitic stainless steel 904L, and the duplex steel 318LN. Expanded austenite has been formed using plasma immersion ion nitriding before. Time-of-flight secondary ion mass spectrometry before and after annealing yielded complementary information regarding nitrogen depth profiles and CrN precipitation using cluster analysis. The decay of expanded austenite during annealing was found to be thermally activated with an activation energy of 1.8 ± 0.3 eV, starting within five minutes at 550 °C and taking more than two hours below 450 °C. The decay occurs simultaneously throughout the whole nitrogen-containing zone—and not at the surface as during nitriding. Nitrogen diffusion occurring in parallel slightly complicates the data analysis. Further transmission electron microscopy investigations are necessary to understand the microstructure after annealing in vacuum. The limit for operating hard and wear-resistant expanded austenite layers at elevated temperatures of up to 350 °C is given, however, by nitrogen diffusion and not the decay into CrN.

Spin Chains with Highly Quantum Character through Strong Covalency in Ca3CrN3.

The insulating transition metal nitride Ca3CrN3 consists of sheets of triangular [CrN3]6- units with C2v symmetry that are connected via quasi-1D zigzag chains. Due to strong covalency between Cr and N, Cr3+ ions are unusually low-spin, and S = 1/2. Magnetic susceptibility measurements reveal dominant quasi-1D spin correlations with very large nearest-neighbor antiferromagnetic exchange J = 340 K and yet no sign of magnetic order down to T = 0.1 K. Density functional theory calculations are used to model the local electronic structure and the magnetic interactions, supporting the low-spin assignment of Cr3+ that is driven by strong π donation from the nitride ligands. The surprising failure of interchain exchange to drive long-range magnetic order is accounted for by the complex connectivity of the spin chain pairs that further frustrates order. Our combined results establish Ca3CrN3 as a nearly ideal manifestation of a quantum spin chain whose dynamics remain unquenched down to extraordinarily low temperatures despite strong near-neighbor exchange coupling.

A brief review on the progress of MXene-based catalysts for electro- and photochemical water splitting for hydrogen generation.

The development and generation of affordable and highly efficient energy, particularly hydrogen, are one of the best approaches to address the challenges posed by the depletion of non-renewable energy sources. Hydrogen energy, as a green and ecosystem-friendly source with zero carbon emission, can be generated through various methods, including water splitting (HER/OER) via either photo- or electrocatalytic reactions. To implement these reactions effectively in practical applications, it is highly desirable to develop extremely efficient and cost-effective catalytic materials that are comparable to contemporary catalysts. MXenes, a family of newly discovered 2D transition metal carbides, nitrides, or carbonitrides with surface termination groups, such as -OH, -O, and -F, have emerged as promising materials and substrates for photo- and electrocatalytic applications due to their unique characteristics. These include excellent conductivity provided by the transition metals, hydrophilic nature imparted by the surface termination groups, high mechanical stability, fast electronic transmission and extremely high surface area-to-volume ratios. In this review, we provide detailed insights into the synthesis, properties, and catalytic applications of MXenes. We systematically outline the photo- and electrocatalytic water splitting reactions carried out by various MXene-based heterostructures, supported by experimental data. A thorough deliberation on the structure-activity associations of reported catalysts and a basic understanding of the electrocatalytic applications of MXenes are also included. Furthermore, we offer an insight into the upcoming tasks, challenges, prospects and new research strategies for MXenes in water splitting applications. A noteworthy recognition of the design and optimization of extremely efficient MXene-based catalysts in water splitting applications is therefore offered in this review.

The Future of MXenes: Exploring Oxidative Degradation Pathways and Coping with Surface/Edge Passivation Approach.

The MXene, which is usually transition metal carbide, nitride, and carbonitride, is one of the emerging family of 2D materials, exhibiting considerable potential across various research areas. Despite theoretical versatility, practical application of MXene is prohibited due to its spontaneous oxidative degradation. This review meticulously discusses the factors influencing the oxidation of MXenes, considering both thermodynamic and kinetic point of view. The potential mechanisms of oxidation are systematically introduced, based on experimental and theoretical models. Typically, the surfaces and edges of MXenes are susceptible to oxidation, as the surface terminal groups are easily attacked by oxygen and water molecules, ultimately leading to structural deformation. To retard oxidative degradation, ligand mediated surface/edge passivation is suggested as a promising strategy. In this regard, detailed passivation strategies for MXenes are systematically explained based on the types of chemistry at the MXene-ligand interface-covalent bonding, electrostatic interactions, and hydrogen bonding-and the type of stabilizing moieties-organic, inorganic, biomolecules, and polymers. The retardation of oxidation is discussed in relation with the interaction type and passivating moiety. This review aims to catalyze future research to identify efficient and cost-effective ligands for the surface engineering of MXenes, enhancing their oxidation stability.

2D MXenes: Synthesis, Properties, and Applications in Silicon-Based Optoelectronic Devices.

MXenes, a rapidly emerging class of 2D transition metal carbides, nitrides, and carbonitrides, have attracted significant attention for their outstanding properties, including high electrical conductivity, tunable work function, and solution processability. These characteristics have made MXenes highly versatile and widely adopted in the next generation of optoelectronic devices, such as perovskite and organic solar cells. However, their integration into silicon-based optoelectronic devices remains relatively underexplored, despite silicon's dominance in the semiconductor industry. In this review, a timely summary of the recent progress in utilizing Ti-based MXenes, particularly Ti3C2Tx, in silicon-based optoelectronic devices is provided. The composition, synthesis methods, and key properties of MXenes that contribute to their potential for enhanced device performance are focused on. Furthermore, the latest advancements in MXene applications in silicon-based solar cells and photodetectors are discussed from fundamental and applied perspectives. Finally, the key challenges and future opportunities for the integration of MXenes in silicon-based optoelectronic devices are outlined.

Diverse Behaviors of N2 on Mo Centers Bearing POCOP-Pincer Ligands and the Role of π-Electron Configuration in Regulating the Pathway of N2 Activation.

Activation of N2 through transition-metal complexes has emerged as a powerful strategy for N2 fixation under mild conditions. Dissociative route and associative route are considered as two major routes for N2 transformation on transition-metal complexes. Homolysis of N2 between two metal fragments is the crucial step of the dissociative route and has been proven to be an efficient approach to the terminal metal nitride, which is the key intermediate for both routes. Hence, the conditions for N2 cleavage have attracted much interest and discussion. Herein, we investigated the reactivity of N2 when coordinated on Mo centers bearing POCOP-pincer ligands and isolated and characterized many novel N2-related intermediates such as [(POCOPCy)MoI]2(μ-N2) (2Cy), (POCOPCy)Mo(N)(μ-N)MoI (5Cy), {[(POCOPCy)Mo(N2)2]2(μ-N2)}[Na(crypt-222)] (6Cy-crypt), and [(POCOPCy)Mo(N2)2(μ-N2)Mo(N)]Na (8Cy). The influences of the oxidation state of the metal centers, π electrons, reaction conditions, etc., on the N2-reactivity were also studied both experimentally and theoretically. Accordingly, some fundamental understanding of the regulation of N2 activation pathways was proposed: an N2-bridged Mo dimer without ligand trans to the bridging N2 is a preferred structure for N2 cleavage; having adequate electrons to be transferred into the σ-σ*-σ related orbital in the {MoNNMo} manifold is the key; and heating or electron excitation is advantageous to the dissociative route.

Downscaling of Non-Van der Waals Semimetallic W5N6 with Resistivity Preservation.

The bulk phase of transition metal nitrides (TMNs) has long been a subject of extensive investigation due to their utility as coating materials, electrocatalysts, and diffusion barriers, attributed to their high conductivity and refractory properties. Downscaling TMNs into two-dimensional (2D) forms would provide valuable members to the existing 2D materials repertoire, with potential enhancements across various applications. Moreover, calculations have anticipated the emergence of uncommon physical phenomena in TMNs at the 2D limit. In this study, we use the atomic substitution approach to synthesize 2D W5N6 with tunable thicknesses from tens of nanometers down to 2.9 nm. The obtained flakes exhibit high crystallinity and smooth surfaces. Electrical measurements on 15 samples show an average electrical conductivity of 161.1 S/cm, which persists while thickness decreases from 45.6 to 2.9 nm. The observed weak gate-tuning effect suggests the semimetallic nature of the synthesized 2D W5N6. Further investigation of the conversion mechanism elucidates the crucial role of chalcogen vacancies in the precursor for initiating the reaction and strain in propagating the conversion. Our work introduces a desired semimetallic crystal to the 2D material library with mechanistic insights for future design of the synthesis.

Preparation and Lithium Storage Properties of MOF‐Derived Bimetallic Sulfide ZnxInyS/MXene Composites

Nanostructured metal sulfides (MSs) are considered promising anode materials for Li‐ion batteries (LIBs) due to their high specific capacity and abundant raw material resources. However, the practical application of these materials faces challenges such as poor conductivity and volume expansion. To address these issues and enhance the performance of LIBs, it is crucial to tackle the structural design problem associated with ZnxInyS anode material. The utilization of metal sulfides derived from metal‐organic frameworks (MOFs) not only improves conductivity but also mitigates the issue of volume expansion in metal sulfides. Furthermore, connecting the metal sulfides derived from MOF to various conductive substrates can further enhance their conductivity. Two‐dimensional transition metal carbides and nitrides (MXenes), a novel type of 2D material with plentiful functional groups and chemical properties, offer great potential. In this study, we have strategically constructed ZnxInyS/MXene heterostructures by combining the advantages of 2D Ti3C2TX nanosheets and bimetallic MOF structures. The results demonstrate that due to the synergistic effect between MXene and heterostructure, a significant number of lattice defects and ample buffer space are provided, resulting in excellent lithium storage performance and fast ion diffusion kinetics for the electrode.

Ferroelectricity with concomitant Coulomb screening in van der Waals heterostructures.

Interfacial ferroelectricity emerges in non-centrosymmetric heterostructures consisting of non-polar van der Waals (vdW) layers. Ferroelectricity with concomitant Coulomb screening can switch topological currents or superconductivity and simulate synaptic response. So far, it has only been realized in bilayer graphene moiré superlattices, posing stringent requirements to constituent materials and twist angles. Here we report ferroelectricity with concomitant Coulomb screening in different vdW heterostructures free of moiré interfaces containing monolayer graphene, boron nitride (BN) and transition metal chalcogenide layers. We observe a ferroelectric hysteretic response in a BN/monolayer graphene/BN, as well as in BN/WSe2/monolayer graphene/WSe2/BN heterostructure, but also when replacing the stacking fault-containing BN with multilayer twisted MoS2, a prototypical sliding ferroelectric. Our control experiments exclude alternative mechanisms, such that we conclude that ferroelectricity originates from stacking faults in the BN flakes. Hysteretic switching occurs when a conductive ferroelectric screens the gating field electrically and controls the monolayer graphene through its polarization field. Our results relax some of the material and design constraints for device applications based on sliding ferroelectricity and should enable memory device or the combination with diverse vdW materials with superconducting, topological or magnetic properties.

A review on MXene (Ti3C2Tx) composites with varied sizes of carbon for supercapacitor applications

MXenes belongs to a family of two‐dimensional (2D) layered transition metal carbides or nitrides which shows outstanding potential for various energy storage applications because of their high‐specific surface area, phenomenal electrical conductivity, outstanding hydrophilicity, and variable terminations. Of these different types of MXenes, the most widely studied member is Ti3C2Tx especially in supercapacitors (SCs). However, due to the problem of stacking and oxidation in MXene sheets, significant loss of electrochemically active sites happens. To overcome these issues, incorporation of carbon materials is carried out into MXenes for enhancing its electrochemical performance. This review aims to introduce various common strategies employed in synthesizing Ti3C2Tx, followed by a brief overview of latest developments in fabricating Ti3C2Tx/carbon electrode materials for SCs. The composition of Ti3C2Tx/carbon are summarized based on different dimensions of carbons, such as 0D carbon dots, 1D carbon nanotubes and fibers, 2D graphene, and 3D carbon materials (activated carbon, polymer‐derived carbon, etc.). Further, this review also aims in highlighting several insights on fabrication of novel MXenes/carbon composites as electrodes for application in SCs.

Microstructure and Mechanical Behavior of Magnetron Co-Sputtering MoTaN Coatings

In recent years, there have been important developments in the refractory metal nitride coatings used for versatile applications, such as MoN, TaN, NbN, etc. Engineered approaches, including the deposition method, microstructure control, structural design, and the addition of functional elements, are put into practice for the promotion of coating characteristics. This study focuses on the microstructure and mechanical properties of ternary molybdenum tantalum nitride, MoTaN, coatings. MoTaN was deposited using a reactive radio frequency (r.f.) magnetron co-sputtering system with Mo/Ta target input power modulation control. The effects of composition and microstructure variations on its mechanical properties, including its hardness, elastic modulus, and wear behavior, were investigated. In general, the MoTaN coatings exhibited a columnar polycrystalline microstructure with MoN(111), Mo2N(111), Mo2N(200), TaN(200), and TaN(220) phases and orientations based on X-ray diffraction analysis. The addition of Ta triggered the transition of the primary orientation of Mo2N(111) into Mo2N(200). Transmission electron microscopy was utilized to analyze the transformation of the multiphase structure and changes in the grain size in terms of the Ta addition. According to nanoindentation and wear resistance analyses, superior hardness, elastic modulus, H/E, H3/E2, and wear-resistance values were identified for the MoTaN coatings with 6.8 to 10.4 at.% Ta, and a maximum hardness of 18.0 GPa was found for the MoTaN coating deposited at an input power of Mo/Ta = 150/100 W/W. An optimized hardness of 18.0 GPa and an elastic modulus of 220.7 GPa were obtained. The adjustment of the input power during deposition played a critical role in determining the overall performance of the MoTaN co-sputtering coatings. The MoTaN coating with optimized mechanical properties is attributed to its multiphase microstructure and fine columnar grain size of less than 30 nm.