Hexagonal Nitride Research Articles

Hexagonal ε-Iron Nitrides Occurring at Low Nitrogen Contents: Interplay between Nitrogen Content and Magnetism

Hexagonal ε-Iron Nitrides Occurring at Low Nitrogen Contents: Interplay between Nitrogen Content and Magnetism

Advancing high thermal conductivity: novel theories, innovative materials, and applications in thermal management technologies.

Effective thermal management is crucial for the performance and stability of modern electronics, emphasizing the demand for high thermal conductivity (κ). This review summarizes the latest development in highκ, discussing the emerging theories, innovative materials and practical applications for interfacial heat dissipation. Unique phononic thermal transport behaviors are discussed, including four phonon-phonon scattering, hydrodynamic phonons, surface phonon-polaritons, and more. The review also highlights innovative materials with highκ, such as two-dimensional pentagonal structures, boron carbon nitrogen structures, hexagonal boron arsenide andθ-phase tantalum nitride. In addition, the potential of polymer composites reinforced with highκfillers and surface engineering for advanced electronic applications are also discussed. By integrating these theoretical approaches and material innovations, this review offers comprehensive strategies for enhancing thermal management in modern electronic devices.

Structures and ammonia synthesis activity of hexagonal ruthenium iron nitride phases

A series of ruthenium iron nitride phases with Ru:Fe ratios of ca. 1:3 were synthesized by ammonolysis. When the ammonolysis temperature was above 500°C, the obtained RuxFe3Ny materials had a ε-Fe3N (P6322) structure, while two similar phases were present when the ammonolysis was lower than 500°C. Powder neutron diffraction identified one phase as relating to the ε-Fe3N structure, while the other had a disordered NiAs-type (P63/mmc) structure. These ternary metal nitrides show ammonia synthesis activity at low temperature (200°C-300°C) and ambient pressure, which can be related to the loss of lattice nitrogen. Steady state catalytic performance at 400°C is associated with ruthenium-iron alloy. Additionally, density functional theory calculations were performed using an approximate model for the disordered hexagonal phase, revealing that this phase is more stable than a cubic anti-perovskite phase which has been previously investigated computationally, and corroborating the experimental findings of the present work.

Synthesis, Crystal Structure, Stability, and Mechanical Properties of the Hexagonal Tungsten Nitride WN1−δ

Synthesis, Crystal Structure, Stability, and Mechanical Properties of the Hexagonal Tungsten Nitride WN_1−δ

Single-metal-adatom catalysts for the synthesis of 2D carbon nitride metal-coordinated networks

Metal-coordinated networks have been found to be excellent catalyst for environmental purposes, such as green hydrogen generation or photo-degradation of pollutants. Recently, its traditional three-dimensional structure has been extended to two dimensions. However, the synthesis and stability of these networks in their 2D form remains a challenge. We have designed, characterized and synthesized, using a bottom-up approach, a 2D metal-coordinated network combining melamine molecules and thermally generated native copper adatoms on a Cu(110) substrate at 600 K. As a result, we have obtained a 2D hexagonal carbon nitride Cu-coordinated network. We demonstrate that the underlying mechanism of its formation involves partial dehydrogenation and subsequent metalation of amino groups. We prove the crucial role of copper adatoms in the formation, serving as heterogeneous metal-site catalysts, as well as in the further stabilization of the network. The obtained metal-coordinated network is indeed a single atom catalyst with high potential in technological applications.

Ionic copolymer-modified hexagonal carbon nitride tube as a high-performance catalyst for regioselective synthesis of hexahydroquinoline frameworks

The conventional structure of carbon nitride materials presents limitations, especially in the catalysis field, attributed to a restricted number of active sites and a low surface area. To address these challenges, we developed a unique design for a mesoporous carbon nitride tube (CNT), which was constructed by incorporating the ionic imidazole-epichlorohydrin copolymer ([IMEP][Cl]) as a template in the fabrication process. The self-assembly behavior of [IMEP][Cl] influences the formation of the melamine-cyanuric acid aggregate (as precursors) through electrostatic forces and polarity, potentially resulting in the creation of a thin-wall CNT with unique pore morphology. Synthesized three-dimensional hollow CNT demonstrated key factors of a high-performance catalyst in terms of high thermal stability (up to 550 °C), good specific surface area (108 m²/g), and significant recoverability (seven runs without a significant decrease in reaction yield). The CNT architecture was employed as a heterogeneous catalyst, and its catalytic efficiency was investigated in the regioselective synthesis of hexahydroquinoline ring systems. Based on the obtained results, CNT shows super-fast synthesis (5 min) of different pharmaceutical quinoline frameworks with exceptional yields (94–98 %) under ultrasound agitations. For the first time, an effective synthesis method is introduced for constructing hollow carbon nitride tubes, utilizing an ionic polymer (produced via chemical crosslinking rather than radical chain polymerization) as a template. This work offers a new viewpoint on improving the catalytic capability of traditional graphitic carbon nitrides through the utilization of ionic copolymers, presenting potential advancements for various technological applications.

Tunable spatial and angular spin splitting of reflected vortex-beam off hyperbolic metasurface

This paper investigated the spin splitting of the reflected beam with a vortex beam irradiating on a hyperbolic metasurface. This metasurface structure is the periodically rectangular-groove array on the surface of a hyperbolic crystal with the optical axis normal to its surface, where the array is a sub-wavelength biaxially hyperbolic grating with its periodical direction situated in the surface plane. Based on the hexagonal nitride boron crystal, we theoretically and numerically analyzed the spatial and angular spin splittings of the reflected beam, containing those produced by the transverse and longitudinal shifts. We found that the spatial shifts or spin splitting can be obtained in the first-order approximation of beam deflection, but the angular shifts can be described in the second-order approximation so that it enormously varies with the beam waist. Due to the hyperbolic anisotropy of the metasurface and the intrinsic orbital angular momentum in the incident beam, the expressions of spatial and angular shifts are effectively modified, and a unique double reflection effect occurs on the surface. Near certain reflective intensity distribution singularities, extremely asymmetrical spin splitting can be observed. These shifts and spin splitting can be tuned by varying the orientation of the incident plane and the angle of incidence.

Orbital hybridization and defective states of vacancy defects in AlN

Intrinsic atomic defects pose a great effect in wide-bandgap semiconductors owing to the high tendency of forming in-gap defective states. Utilizing density-functional theory, the atomic vacancy defects of Al and N vacancies in hexagonal wurtzite aluminum nitride (AlN) are investigated. We find that the most energetically favorable form of vacancies is predicted to be negatively trivalent charged Al vacancy (VAl−3) in n-type AlN and positively monovalent charged N vacancy (VN+1) in p-type AlN, respectively. N vacancy generally has a low formation energy and could be either an acceptor or a donor: Under p-type conduction, it is a deep donor with a positively monovalent charge of +1, acting as a compensating center for holes; Under n-type conduction, it is a deep acceptor carrying charge of −3, acting as a compensating center for electrons. For the Al vacancy, it tends to be a shallow acceptor in p-type AlN but a high formation energy or a deep acceptor in n-type AlN with low formation energy, most possibly at a negatively trivalent charged state. Our orbital hybridization analysis shows that these vacancies can be facilely generated which are rooted in the antibonding coupling Al3 s-N2p states in valence band. The above finding is independent of the chemical potential of nitrogen and aluminum and holds true under both nitrogen rich and poor conditions. Our work provides a guide to experimental works by providing the energetics and atomic-scale mechanism of doping nature of atomic vacancies in AlN.

Efficient Rhodamine B dye uptake onto MgZrO3@g-C3N4 nanostructures: Fabrication and adsorption mechanism

Pristine graphitic carbon nitride (g-C3N4) was synthesized by calcination of urea under elevated temperature. A blend of g-C3N4 nanosheets and nanosized ZrO2 and MgO precursors were used to prepare MgZrO3@g-C3N4 hybrid nanocomposite (MZCN) then it was assessed for the adsorption of Rhodamine B (RhB) dye from aqueous solution. The X-ray diffraction analysis revealed the development of the monoclinic ZrO2, cubic MgO, and hexagonal graphitic carbon nitride phases. The energy diffraction X-rays (EDX), photoelectron electron, and Fourier transformed infrared (FT-IR) spectroscopy analyses collectively validated the formation of the presumed composite. An improved porosity with a surface area 35.86 m2.g−1 and pore volume 0.087 cm3.g−1 were determined by N2 adsorption setup. The adsorption kinetics fitted well with the pseudo-first-order model (R2 > 0.99), which designated an adsorption process influenced by physisorption. The kinetics models investigations revealed a film diffusion control of the adsorption process. The adsorption equilibrium matched perfectly with the Langmuir isotherm model (R2 > 0.99) marking a maximum adsorption capacity of 370.8 mg g−1, demonstrating outstanding monolayer adsorption process. In addition, the Freundlich constant (n = 1.76) value is falling in the range 1–10 suggested a favorable adsorption of RhB onto the composite surface. The mechanistic enquiry suggested van der Waal, hydrogen bonds and π–π electron–donor interactions between the electron-rich RhB and the functional groups in the adsorbent’s molecule. This work stipulates that MgZrO3@g-C3N4 holds promise as efficient adsorbent for organic dyes from contaminated wastewater.

High harmonic generation in monolayer indium nitride

In our work, we theoretically investigate high harmonic generation (HHG) in monolayer hexagonal indium nitride (h-InN) based on the semiconductor Bloch equation under strong laser fields. Compared with h-BN, there is no multiplateau in h-InN. This is because the intraband mechanism dominates the total HHG, and the harmonic generated by the intraband current is about three orders of magnitude higher than that generated by the interband polarization. We find that the higher order part of the HHG is mainly supplied by the interband current, which can be analyzed on the basis of the transition dipole moments between the energy bands. In addition, we found that the HHG of h-InN is sensitive to the external strains due to the modified band dispersion in the electronic structures. This study provides a useful reference for understanding the microscopic mechanism of laser-solid interaction.

Mechanical Characterization of Emerging 2D Materials for Electronics: Review

The rapid growth in the field of electronics has created the need for studying new materials that offer improved qualities. Among these options, materials which exist in two dimensions (referred to as 2D materials) emerged as the most popular choices because of their unique mechanical and electrical properties. The present study provides a thorough review of the mechanical properties of new two-dimensional (2D) materials, with a particular focus on their potential utility throughout the electronics sector. In this research, It provide a comprehensive examination of the mechanical properties of multiple two-dimensional (2D) materials, such as graphene, which transition-metals dichalcogenides (TMDs), and hexagonal nitride of boron (h-BN), under different conditions that mimic the operational environment of electronic systems. The elastic moduli, strength, and flexibility of the components are evaluated by the utilization of sophisticated characterization methods such as atomic force microscopy (AFM), and nanoindentation. Also, this study examines the impact of environmental factors, specifically temperature and humidity, on the characteristics mentioned earlier. Results illustrate that the 2D materials exhibit remarkable mechanical properties, distinguished by both strength and flexibility, leaving them well-suited for applications in flexible electronic devices and high-performance nanodevices.

Hexagonal crystalline nanofillers reinforced composite carbon nanofibers with optimized crystal structure and improved mechanical properties

The mechanical properties of carbon nanofibers (CNFs) are always restricted by their disorganized crystal structures. Herein, this paper utilizes two typical hexagonal crystalline flake materials, nanoscale flake graphite (NG) and hexagonal nitride boron (BN), as nanofillers to optimize the crystal domains of CNFs and achieves enhancement in fiber strength, modulus and toughness. For this purpose, in situ polymerization technique is developed for the rapid and uniform mixing of nanofillers with polyacrylonitrile (PAN) precursors of CNFs. The nanofillers are exfoliated in this process and wrapped with PAN to prevent potential agglomeration. The obtained core-shell nanocomposites can be produced into composite CNFs via electrospinning, stabilization and carbonization. Based on the attraction effect, the dispersed nanofillers can organize PAN molecular chains into oriented crystalline fibrils in as-spun nanofibers and accelerate their transformation to more ladder structures in stabilized nanofibers. On this basis, NG is shown to act as the templating and nucleating agent to promote the formation, growth and compact stacking of graphitic planes in CNFs. BN also improves fiber crystallinity, while its limited templating effect leads to looser and finer crystal domains. As a result, NG-doped CNFs have significantly improved strength and modulus, and BN-doped CNFs possess simultaneously enhanced strength and toughness.

Plasma-enhanced atomic layer deposition of molybdenum carbide and carbonitride films using bis(isopropylcyclopentadienyl)molybdenum(IV) dihydride and an H2/N2/Ar plasma

Molybdenum carbide (MoC) and molybdenum carbonitride (MoCN) films were successfully deposited by plasma-enhanced atomic layer deposition (PEALD) using bis(isopropylcyclopentadienyl)molybdenum(IV) dihydride [(iPrCp)2MoH2] as the Mo precursor at temperatures of 200−400 °C. To obtain the MoC and MoCN films, 4%H2/96%Ar (H2/Ar) and 4%H2/96%N2 (H2/N2) plasmas were selectively used as co-reactants, respectively. PEALD MoC and MoCN exhibited atomic layer deposition temperature windows of 200−400 and 250−300 °C with growth per cycle of 0.012 and 0.047 nm/cycle, respectively. X-ray photoelectron spectroscopy revealed that the 300 °C-grown MoC film prepared using an H2/Ar plasma contained Mo–C bonds and an atomic composition of MoC0.77. In contrast, the 300 °C-grown MoCN film prepared using an H2/N2 plasma exhibited Mo–C and Mo–N bonds, with an atomic composition of MoC0.31N0.23. The atomic composition of the PEALD MoCN films varied depending on the deposition temperature; at 200 °C, the carbon-rich MoC0.52N0.16 film was obtained, whereas the MoC0.23N0.23 film with a carbon-to-nitrogen ratio of 1 was grown at a higher temperature of 400 °C. The 300 °C-grown MoC film was crystallized into a cubic δ-MoC phase, whereas the PEALD MoCN film showed diffraction peaks corresponding to the hexagonal MoC and molybdenum nitride (MoN) structures. The as-deposited PEALD MoC and MoCN films at 300 °C exhibited resistivities of 600 and 3038 μΩ cm, respectively, and post-deposition annealing at 700−800 °C resulted in significantly low resistivities of 37−203 μΩ cm due to the formation of metallic Mo films.

Crystal Structure and Magnetic Properties of Hexagonal FeCo Nitrides Prepared Using Ammonia Gas Nitrification

Single-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϵ</i> -(FeCo) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i> N compound particles with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = 2.25 to 2.48 were synthesized using ammonia gas nitrification. The mass magnetization <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> at 10 K under a magnetic field of 9 T was 77 A <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">·</i> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /kg, and Curie temperature <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> was 100 K for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = 2.48. These values decreased with increasing nitrogen content. Compared with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϵ</i> -Fe <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i> N, (FeCo) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i> N had significantly lower <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> values, even at comparable nitrogen content. M¨ossbauer spectroscopy suggests that the magnetic moment of Co decreases with increasing nitrogen content and disappears at approximately <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = 2.35, even at the lowest measurement temperature of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> = 3 K. Griffiths phase-like magnetic behavior was observed in the temperature dependence of magnetic susceptibility. The experimental results indicate that the Fe–Fe interaction may change from ferromagnetic to antiferromagnetic at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = 2.25 when the nitrogen content is low.

Photoinduced Rippling of Two-Dimensional Hexagonal Nitride Monolayers.

Inducing structural changes and deformation using noninvasive methods, such as ultrafast laser technology, is an attractive route to multiple optomechanical and optoelectronic applications. Here, we show how photon excitation could accumulate in-plane stress and induce long-wavelength ripples in two-dimensional (2D) materials. Numerical results based on first-principles calculations and a continuum model predict that long-range nanoscale rippling could emerge under photon excitation in hexagonal nitride single atomic sheets. The photosoftened transverse acoustic mode dominates the out-of-plane distortion of the sheet, and the resultant rippling pattern strongly depends on the boundary condition. We reveal that the wavelength and height of the ripple scale as I-1/3 and I1/6, respectively, where I is the incident light energy flux. Our findings based on multiscale theory and simulations elucidate the interplay between carrier excitation, phonon dispersion, and long-range mechanical deformations, which could find potential usage in flexible electronics and electromechanical devices.

Crystal‐Phase Controlled Epitaxial Growth of NbNx Superconductors on Wide‐Bandgap AlN Semiconductors (Adv. Mater. Interfaces 31/2022)

Superconductor/Semiconductor Hybrid Devices In article number 2201244, Atsushi Kobayashi and colleagues report a high quality superconductor/semiconductor junction using hexagonal nitride crystals. They developed a technique to match the crystal systems of a niobium nitride superconductor and an aluminum nitride wide-bandgap semiconductor. This technique paves the way for the realization of nitride-based superconductor/semiconductor hybrid devices.

Effect of Nitrogen Doping on the Structure and Mechanical Properties of the Fe40Mn40Cr10Co10 High-Entropy Alloy

The structure and mechanical properties of as-cast and thermomechanicaly processed (cold rolling followed by annealing at 700 °C and 900 °C) Fe40Mn40Cr10Co10 (at.%) high-entropy alloys doped with different amounts (0, 0.5, and 2.0 at.%) of N were examined. The as-cast Fe40Mn40Cr10Co10 alloy (N0) contained σ-phase particles at the boundaries of the fcc grains. The addition of 0.5 (N0.5) and 2.0 (N2) at.% of nitrogen suppressed the formation of the σ-phase due to which the alloys consisted of only the fcc phase. Annealing after rolling resulted in the development of static recrystallization and precipitation of additional phases: the σ-phase was found in the N0 and N0.5 alloys, and hexagonal M2N nitrides were found in the N2 alloy. The strength of the as-cast alloys at room temperature increased with increasing nitrogen concentration due to interstitial solid solution strengthening. Cold rolling and subsequent annealing resulted in considerable strengthening of the program alloys. The strength of the alloys increased with the N content and decreased with increasing annealing temperature. The best combination of mechanical properties at room temperature was attained in the N2 alloy after annealing at 700 °C, and at 77 K, was demonstrated by the N0.5 alloy after annealing at 900 °C.

Electronic structure of hexagonal REN (RE = Sc, Y, and Lu) materials

Structural properties and band structures of bulk and monolayer hexagonal (BN-type) rare earth nitrides have been studied from first principles. The bulk materials are expected to exhibit bigger lattice parameters than those of monolayers. The band structures and band gaps of 3D and 2D systems also differ from each other. Band gaps of ScN and YN bulk materials are rather pressure resistant, whereas the band gaps of all monolayers may be well tuned by strain. The monolayer rare earth nitrides exhibit splittings of valence bands in the K point in the Brillouin zone, driven by spin–orbit coupling, which are similar to those present in transition metal dichalcogenides. The 2D rare earth nitrides may be interesting candidate materials for some applications in optoelectronics and spintronics.

Topochemical Synthesis of Ca3CrN3H Involving a Rotational Structural Transformation for Catalytic Ammonia Synthesis

Topochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties. With these reactions, the overall crystal structure of the host material is generally maintained. Here we report a topochemical synthesis of a hexagonal nitride hydride, h-Ca3CrN3H, by heating an orthorhombic nitride, o-Ca3CrN3, under hydrogen at 673 K, accompanied by a rotational structural transformation. The hydrogen intercalation modifies the Ca-N rock-salt-like atomic packing in o-Ca3CrN3 to a face-sharing octahedral chain in h-Ca3CrN3H, mimicking a 'hinged tessellation' movement. In addition, the h-Ca3CrN3H exhibited stable ammonia synthesis activity when used as a catalyst.

Topochemical Synthesis of Ca3CrN3H Involving a Rotational Structural Transformation for Catalytic Ammonia Synthesis

AbstractTopochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties. With these reactions, the overall crystal structure of the host material is generally maintained. Here we report a topochemical synthesis of a hexagonal nitride hydride, h‐Ca3CrN3H, by heating an orthorhombic nitride, o‐Ca3CrN3, under hydrogen at 673 K, accompanied by a rotational structural transformation. The hydrogen intercalation modifies the Ca−N rock‐salt‐like atomic packing in o‐Ca3CrN3 to a face‐sharing octahedral chain in h‐Ca3CrN3H, mimicking a “hinged tessellation” movement. In addition, the h‐Ca3CrN3H exhibited stable ammonia synthesis activity when used as a catalyst.