Transition-metal embedded carbon nitride monolayers: high-temperature ferromagnetism and half-metallicity

Stacking Engineering of Heterojunctions in Half-Metallic Carbon Nitride for Efficient CO2 Photoreduction

Enhancing charge separation in semiconductor photocatalysts is a major challenge for efficient artificial photosynthesis. Herein, a compact heterojunction is designed by embedding half-metallic C(CN)3 (hm-CN) hydrothermally in BiOBr (BOB) as the backbone. The interface between hm-CN and BOB is seamless and formed by covalent bonding to facilitate the transmission of photoinduced electrons from BOB to hm-CN. The transient photocurrents and electrochemical impedance spectra reveal that the modified composite catalyst exhibits a larger electron transfer rate. The photocatalytic activity of hm-CN/BOB increases significantly as indicated by a CO yield that is about four times higher than that of individual components. Density-functional theory calculations verify that the heterojunction improves electron transport and decreases the reaction energy barrier, thus promoting the overall photocatalytic CO2 conversion efficiency. The half-metal nitride coupled semiconductor heterojunctions might have large potential in artificial photosynthesis and related applications.

A facile and green synthesis of Mn and P functionalized graphitic carbon nitride nanosheets for spintronics devices and enhanced photocatalytic performance under visible-light

Manganese and phosphorus co-doped, graphitic carbon nitride (g-C₃N₄) nanosheet (Mn/P-g-C₃N₄) is prepared by facile and green calcination process of melamine (C₃H₆N₆), manganese chloride tetrahydrate (MnCl₂·4H₂O), and ammonium dihydrogen phosphate ((NH₄)H₂PO₄). The Mn/P co-doping significantly enhances magnetic values compared to pristine-g-C₃N₄, phosphorus-doped g-C₃N₄ (P-g-C₃N₄), and manganese-doped g-C₃N₄ (Mn-g-C₃N₄). We find that Mn/P-g-C₃N₄ is a half-metallic ferromagnetic material having a magnetic moment and Curie temperature of 4.51 μ_B and ∼ 800 K, respectively. The ultraviolet-visible (UV-vis) absorption spectrum of Mn/P-g-C₃N₄ reveals superior absorption in broader wavelength compared to pristine-g-C₃N₄, P-g-C₃N₄, and Mn-g-C₃N₄. The methyl orange degradation efficiency of Mn/P-g-C₃N₄ photocatalyst is 94 %, which is three times more than that of pristine-g-C₃N₄ (29 %) and more significant than the P-g-C₃N₄ (46 %) and Mn-g-C₃N₄ (58 %). Furthermore, density functional theory (DFT) calculation explains the origin of high magnetic behavior, the boosted photocatalytic efficiency of Mn/P-g-C₃N₄, and the essential material properties like structure, bandgap, the density of states (DOS), and atomic level interaction. This work may be helpful for reasonably designing ferromagnetic material for spintronics devices and boosting visible-light (VL) photocatalytic performance for environmental remediation.

Structural, Electronic, and Magnetic Characteristics of Graphitic Carbon Nitride Nanoribbons and Their Applications in Spintronics

The development of quantum information and quantum computing technology requires special materials to design and manufacture nanosized spintronic devices. Possessing remarkable structural, electronic, and magnetic characteristics, graphitic carbon nitride (g-C₃N₄) can be a promising candidate as a building block of futuristic nanoelectronics and spintronic systems. Here, using first-principles calculations, we perform a comprehensive study on the structural stability as well as electronic and magnetic properties of triazine-based g-C₃N₄ nanoribbons (gt-CNRs). Our calculations show that gt-CNRs with different edge conformation exhibit distinct electronic and magnetic characteristics, which can be tuned by the edge H-passivation rate. By investigating gt-CNRs with various possible edge configurations and H-termination rates, we show that while the ferromagnetic (FM) ordering of gt-CNRs stays preserved for all of the studied configurations, half metallicity can only be achieved in nanoribbons with specific edge structure under full H-passivation rate. For spintronic application purposes, we also study spin-transport properties of half-metal gt-CNRs. By determining the suitable gt-CNR configuration, we show the possibility of developing a perfect gt-CNR-based spin filter with a spin filter efficiency (SFE) of 100%. Considering the above-mentioned notable electronic and magnetic characteristics as well as its high thermal stability, we show that gt-CNR would be a remarkable material to fabricate multifunctional spintronic devices.

Presence and absence of intrinsic magnetism in graphitic carbon nitrides designed through C-N-H building blocks

We use the first principle calculation to investigate the intrinsic magnetism of graphitic carbon nitrides (GCNs). By preserving three-fold symmetry, the GCN building blocks have been built out of different combinations between 6 components which are C atom, N atom, s-triazine, heptazine, heptazine with C atom at the center, and benzimidazole-like component. That results in 20 phases where 11 phases have been previously reported, and 9 phases are newly derived. The partial density of states and charge density have been analyzed through 20 phases to understand the origin of the presence and absence of intrinsic magnetism in GCNs. The intrinsic magnetism will be present not only because the GCNs comprising of radical components but also the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi$$\end{document}π-conjugated states are not the valence maximum to break the delocalization of unpaired electrons. The building blocks are also employed to study alloys between g-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {C}_3\hbox {N}_4$$\end{document}C3N4 and g-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {C}_4\hbox {N}_3$$\end{document}C4N3. The magnetization of the alloys has been found to be linearly dependent on a number of C atoms in the unit cell and some magnetic alloys are energetically favorable. Moreover, the intrinsic magnetism in GCNs can be promoted or demoted by passivating with a H atom depending on the passivated positions.

Theoretically evaluating two-dimensional tetragonal Si2Se2 and SiSe2 nanosheets as anode materials for alkali metal-ion batteries

In this work, based on first-principles calculations, we theoretically predict two kinds of two-dimensional tetragonal Si–Se compounds, Si2Se2 and SiSe2, as the anode materials for alkali metal-ion batteries.

High carrier separation efficiency for a defective g-C3N4 with polarization effect and defect engineering: mechanism, properties and prospects

Different types of defects in g-C3N4 induce polarization effect to promote the separation of charge carriers and improve the photocatalytic efficiency.

Spin Polarization-Induced Facile Dioxygen Activation in Boron-Doped Graphitic Carbon Nitride

Dioxygen (O₂) activation is a vital step in many oxidation reactions, and a graphitic carbon nitride (g-C₃N₄) sheet is known as a famous semiconductor catalytic material. Here, we report that the atomic boron (B)-doped g-C₃N₄ (B/g-C₃N₄) can be used as a highly efficient catalyst for O₂ activation. Our first-principles results show that O₂ can be easily chemisorbed at the B site and thus can be highly activated, featured by an elongated O-O bond (∼1.52 Å). Interestingly, the O-O cleavage is almost barrier free at room temperatures, independent of the doping concentration. It is revealed that the B atom can induce considerable spin polarization on B/g-C₃N₄, which accounts for O₂ activation. The doping concentration determines the coupling configuration of net-spin and thus the magnitude of the magnetism. However, the distribution of net-spin at the active site is independent of the doping concentration, giving rise to the doping concentration-independent catalytic capacity. The unique monolayer geometry and the existing multiple active sites may facilitate the adsorption and activation of O₂ from two sides, and the newly generated surface oxygen-containing groups can catalyze the oxidation coupling of methane to ethane. The present findings pave a new way to design g-C₃N₄-based metal-free catalysts for oxidation reactions.

Coexistence of intrinsic piezoelectricity and ferromagnetism induced by small biaxial strain in septuple-atomic-layer VSi2P4

The VSi₂P₄ spans a wide range of properties upon the increasing strain from ferromagnetic metal (FMM) to spin-gapless semiconductor (SGS) to ferromagnetic semiconductor (FMS) to SGS to ferromagnetic half-metal (FMHM).

Double-Exchange Magnetic Interactions in High-Temperature Ferromagnetic Iron Chalcogenide Monolayers

Smythite ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub><mml:mrow><mml:mi>F</mml:mi> <mml:mi>e</mml:mi></mml:mrow> <mml:mn>3</mml:mn></mml:msub> <mml:msub><mml:mi>S</mml:mi> <mml:mn>4</mml:mn></mml:msub> </mml:mrow> </mml:math> ) is an iron-based chalcogenide with a lamellar structure, different from the compositionally identical mineral greigite. Owing to their natural abundance, such transition metal chalcogenides are promising materials for low-cost spintronic-based devices. Herein, we discuss the charge transfer processes and complex magnetic ordering in a two-dimensional (2D) smythite lattice. We find that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>F</mml:mi> <mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn> <mml:mo>+</mml:mo></mml:mrow> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>F</mml:mi> <mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow> <mml:mrow><mml:mn>3</mml:mn> <mml:mo>+</mml:mo></mml:mrow> </mml:msup> </mml:mrow> </mml:math> redox couple and complex magnetic ordering are governing factors in the charge transfer processes. A very strong ferromagnetic in-lattice coupling is also observed, which is attributed to the presence of three Fe-centres. To describe the magnetic behaviour molecular and periodic approaches have been considered. We found a substantial increase in Curie temperature with applied mechanical stress due to opening of the double exchange interaction angle. We also observe an in-plane Jahn-Teller distortion, which is further confirmed by the spin-orbit counter plot. Our study thus provides an insight into the double exchange mechanism favoured by the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>F</mml:mi> <mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn> <mml:mo>+</mml:mo></mml:mrow> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>F</mml:mi> <mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow> <mml:mrow><mml:mn>3</mml:mn> <mml:mo>+</mml:mo></mml:mrow> </mml:msup> </mml:mrow> </mml:math> redox couple and results in a strong ferromagnetic ordering.

Band gap opening in stanene induced by patterned B-N doping

Stanene is a quantum spin Hall insulator and a promising material for electronic and optoelectronic devices. Density functional theory (DFT) calculations are performed to study the band gap opening in stanene by elemental mono-doping (B, N) and co-doping (B-N). Different patterned B-N co-doping is studied to change the electronic properties of stanene. A patterned B-N co-doping opens the band gap in stanene and its semiconducting nature persists under strain. Molecular dynamics (MD) simulations are performed to confirm the thermal stability of such a doped system. The stress-strain study indicates that such a doped system is as stable as pure stanene. Our work function calculations show that stanene and doped stanene have a lower work function than graphene and thus are promising materials for photocatalysts and electronic devices.

Ferromagnetism and Half-Metallicity in a High-Band-Gap Hexagonal Boron Nitride System

Metal-free half-metallicity is the subject of intense research in the field of spintronics devices. Using density functional theoretical calculations, atom-thin hexagonal boron nitride (h-BN)-based systems are studied for possible spintronics applications. Ferromagnetism is observed in patterned C-doped h-BN systems. Interestingly, such a patterned C-doped h-BN exhibits half-metallicity with a Curie temperature of approximately 324 K at a particular C-doping concentration. It shows half-metallicity more than metal-free systems studied to date. Thus, such a BN-based system can be used to achieve a 100 % spin-polarised current at the Fermi level. Furthermore, this C-doped system shows excellent dynamical, thermal, and mechanical properties. Therefore, a stable metal-free planar ferromagnetic half-metallic h-BN-based system is proposed for use in room-temperature spintronics devices.

High Curie temperature and half-metallicity in an atomically thin main group-based boron phosphide system: long range ferromagnetism

In this work, we have designed a main group-based novel ferromagnetic half-metallic material with a high Curie temperature for spintronics.

Metal Immiscibility Route to Synthesis of Ultrathin Carbides, Borides, and Nitrides

Ultrathin ceramic coatings are of high interest as protective coatings from aviation to biomedical applications. Here, a generic approach of making scalable ultrathin transition metal-carbide/boride/nitride using immiscibility of two metals is demonstrated. Ultrathin tantalum carbide, nitride, and boride are grown using chemical vapor deposition by heating a tantalum-copper bilayer with corresponding precursor (C₂ H₂ , B powder, and NH₃ ). The ultrathin crystals are found on the copper surface (opposite of the metal-metal junction). A detailed microscopy analysis followed by density functional theory based calculation demonstrates the migration mechanism, where Ta atoms prefer to stay in clusters in the Cu matrix. These ultrathin materials have good interface attachment with Cu, improving the scratch resistance and oxidation resistance of Cu. This metal-metal immiscibility system can be extended to other metals to synthesize metal carbide, boride, and nitride coatings.

Two-dimensional hexagonal CrN with promising magnetic and optical properties: A theoretical prediction

Half-metallic ferromagnetic materials with planar forms are promising for spintronics applications. A wide range of 2D lattices like graphene, h-BN, transition metal dichalcogenides, etc. are non-magnetic or weakly magnetic. Using first principles calculations, the existence of graphene-like hexagonal chromium nitride (h-CrN) with an almost flat atomically thin structure is predicted. We find that freestanding h-CrN has a 100% spin-polarized half-metallic nature with possible ferromagnetic ordering and a high rate of optical transparency. As a possible method for stabilization and synthesis, deposition of h-CrN on 2D MoSe₂ or on MoS₂ is proposed. The formation of composites retains the half-metallic properties and leads to the reduction of spin-down band gaps to 1.43 and 1.71 eV for energetically favorable h-CrN/MoSe₂ and h-CrN/MoS₂ configurations, respectively. Calculation of the dielectric functions of h-CrN, h-CrN/MoSe₂ and h-CrN/MoS₂ exhibit the high transparency of all three low-dimensional nanomaterials. The honeycomb CrN may be considered as a promising fundamental 2D material for a variety of potential applications of critical importance.

Stanene based gas sensors: effect of spin–orbit coupling

B@, N@, and B–N@stanene for NO₂ gas sensors.

Fe doped LaGaO3: good white light emitters

Photoluminescence emission spectra from Fe doped LaGaO₃. The luminescence due to ultra violet He–Cd laser is shown in the inset.

Cuboctahedral vs. octahedral platinum nanoclusters: insights into the shape-dependent catalytic activity for fuel cell applications

The shape of a catalyst plays an important role in any catalytic reaction.