Paper & Patents

Janus MXenes, a new category of two-dimensional (2D) materials, show promising potential for advances in optoelectronics, spintronics, and nanoelectronics. Our theoretical investigations not only provide interesting insights but also highlight the promise of Janus MCrCT2 (M = Ti, Mo; T = O, F, OH) MXenes for future spintronic applications and highlight the need for their synthesis. Electronic structure analysis shows different metallic and semimetallic properties: MoCrCF2 exhibits metallic property, TiCrC(OH)2 and MoCrCO2 exhibit near semimetallicity with spin polarization values of 61 and 86%, respectively, while TiCrCO2 and TiCrCF2 are completely half-metallic with 100% spin polarization at the Fermi level. All studied Janus MXenes exhibit intrinsic ferromagnetism, which is mainly attributed to the chromium (Cr) atoms, as shown by the spin density difference plots. Among them, the TiCrCO2 monolayer stands out with the highest exchange constant and ferromagnetic transition temperature (Tc). Notably, the O-terminated Janus MXenes exhibit weak perpendicular magnetic anisotropy, in contrast to the in-plane anisotropy observed for F and OH-terminated MXenes, making them particularly interesting for future spintronic applications, which we further demonstrate with micromagnetic simulation which reveal distinct current-induced switching behaviors in these Janus MXenes with different surface terminations.

This study investigates the catalytic degradation of ground-level ozone on low-index stoichiometric and reduced CeO2 surfaces using first-principles calculations. The presence of oxygen vacancies on the surface enhances the interaction between ozone and the catalyst by serving as active sites for adsorption and decomposition. Our results suggest that the {111} surface has superior ozone decomposition performance due to unstable oxygen species resulting from reactions with catalysts. However, when water is present, it competes with ozone molecules for these active sites, resulting a reduced catalytic activity or water poisoning. A possible solution could be heat treatment that reduces the vacancy concentration, thereby increasing the available adsorption sites for ozone molecules while minimizing competitive adsorption by water molecules. These results suggest that controlling moisture content during operation is crucial for the efficient use of CeO2-based catalysts in industrial applications to reduce ground-level ozone pollution.

Despite having favorable energetics and tunable optoelectronic properties, utilization of BaTiO3 (BTO) for photocatalytic reactions is limited by its absorption only in the ultraviolet region. To address this challenge, BTO is doped with iridium (Ir) to induce visible light absorption. The visible light-induced photocatalytic H2 generation efficiency is enhanced by 2 orders of magnitude on selective conversion of the Ir valence state from Ir 4+ to Ir 3+. To understand such intriguing behavior, valence state-dependent changes in the optoelectronic, structural, and surface properties and electronic band structure are comprehensively investigated. The effect of electron occupancy change between Ir 4+ (t 2g 5 e g 0) and Ir 3+ (t 2g 6 e g 0) and their energetic positions within the band gap is found to significantly influence H 2 generation. Besides this, converting Ir 4+ to Ir 3+ enhanced the photocathodic current and lowered the onset potential. Results aid in designing photocatalysts to efficiently use low-energy photons for enhancing solar H2 production in these emerging BTO-based photocatalysts. Collectively, the observations made in this work highlight the promising application of Ir 3+ :BTO in z-scheme photocatalysis.

Monolayer silicene is a front runner in the two-dimensional (2D)-Xene family, which also comprises germanene, stanene, and phosphorene, to name a few, due to its compatibility with current silicon fabrication technology. Here, we investigate the utility of 2D-Xenes for straintronics using the ab initio density functional theory (DFT) coupled with quantum transport based on the Landauer formalism. With a rigorous band structure analysis, we show the effect of strain on the K-point and calculate the directional piezoresistances for the buckled Xenes as per their critical strain limit. Further, we compare the relevant gauge factors (GFs) and their sinusoidal dependencies on the transport angle akin to those of silicene and graphene. The strain-insensitive transport angles corresponding to the zero gauge factors for silicene and germanene are 81 and 34° for armchair (AC) and zigzag (ZZ) strains, respectively. As the strain limit is increased to 10% in stanene, there are notable changes in the fundamental parameters, which entail a change in the critical angle along the armchair (69°) and zigzag (34°) directions. The small values of gauge factors can be attributed to their stable Dirac cones and strain-independent valley degeneracies. We also explore conductance modulation, which is quantized in nature and exhibits a variation pattern similar to that of other transport parameters against applied strain. Based on the obtained results, we propose the buckled Xenes as an interconnect in flexible electronics and that they are promising candidates for various applications in straintronics.

The role of 2D transition metal carbides, also known as MXenes, as active catalyst supports in Co-based oxygen evolution reaction (OER) catalysts was elucidated through a combination of experimental and computation electrochemistry. Through facile seeding of commericial Co nanoparticles on three different MXene supports (Ti3C2Tx, Mo2Ti2C3Tx, Mo2CTx), Co@MXene catalysts were prepared and their electrochemical properties examined for alkaline OER electrocatalysts. The OER activity enhancement of Co was significantly improved for Mo2CTx and Mo2Ti2C3Tx supports, but marginal on the Ti3C2Tx in rotating disk electrode and membrane electrode assembly tests. The Co@Mo2CTx exhibited the highest anion exchange water electrolysis performance of 2.11 A cm−2 at 1.8 V with over 700 h of stable performance, exceeding previous benchmarks for non-platinum group (non-PGM) metal OER catalysts. The superior performance was attributed to the strong chemical interaction of Co nanoparticle with the Mo2CTx MXene support. Insights into the electrochemical and chemical oxidation according to MXene type as related to cell durability, as well the effect of electrical conductivity and inherent boosting of electrocatalytic activity of Mo-based MXenes elucidated through density functional theory (DFT) calculations helped explain the performance and durability enhancement of Mo-based MXene supports over Ti3C2Tx supports.

Material science literature is a rich source of factual information about various categories of entities (like materials and compositions) and various relations between these entities, such as conductivity, voltage, etc. Automatically extracting this information to generate a material science knowledge base is a challenging task. In this paper, we propose MatSciRE (Material Science Relation Extractor), a Pointer Network-based encoder–decoder framework, to jointly extract entities and relations from material science articles as a triplet (entity1, relation, entity2). Specifically, we target the battery materials and identify five relations to work on — conductivity, coulombic efficiency, capacity, voltage, and energy. Our proposed approach achieved a much better F1-score (0.771) than a previous attempt using ChemDataExtractor (0.716). The overall graphical framework of MatSciRE is shown in Fig. 1. The material information is extracted from material science literature in the form of entity–relation triplets using MatSciRE.

MXenes are a promising class of two-dimensional transition metal carbides, nitrides, and carbonitrides, widely utilized in diverse fields such as energy storage, electromagnetic shielding, electrocatalysis, and sensing applications. Their potential in chemical sensing is particularly noteworthy, where optimizing surface chemistry for strong interaction with target analytes and increasing surface area for efficient gas adsorption are crucial factors. In this study, a versatile and general self-assembly method for fabricating nanometer-scale thin films of surface-functionalized MXene, enabling high-performance gas sensors is developed. By dropping MXene dispersed in organic solvents onto nonsolvents, rapid formation of nanometer-scale films is achieved. This method allows easy adjustment of film properties by using different solvent-nonsolvent combinations, leading to improved optoelectronic properties compared to conventional techniques. The surface-functionalized MXenes using ADOPA ligands greatly enhance the gas response and long-term environmental stability compared to pristine MXenes. Computational methods are also employed to gain insights into the molecular interactions and changes in electronic structure that contribute to the enhanced sensing properties. Furthermore, the environmental stability of MXene sensors is largely enhanced after surface functionalization, which can be attributed to increased surface hydrophobicity. Overall, this innovative technique opens up opportunities for tailoring MXene thin films for specific applications.

Skyrmions are localized swirling noncoplanar spin textures offering a promising revolution in future spintronic applications. These topologically nontrivial spin textures lead to an additional contribution to the Hall effect, called the topological Hall effect. Here, we investigate the origin of the topological Hall effect—a trademark of skyrmions—in a centrosymmetric shape memory Heusler alloy (SMHA) Mn2NiGa. The magnetization measurement unveils the presence of austenite to martensite transition in the studied system. The topological Hall effect (THE) in the present system is examined experimentally and theoretically. The presence of a large THE in the austenite (cubic) phase of the system strongly suggests that the observed THE in Mn2NiGa cannot be attributed to the antiskyrmions stabilized by D2d symmetry as reported earlier. To comprehend the underlying mechanism behind the origin of THE, we have performed micromagnetic simulations for a range of magnetic field with a small value of DMI (local DMI) to consider the possible impact of earlier reported atomic disorder in the centrosymmetric SMHA Mn2NiGa. The results showed the stabilization of Néel-type skyrmions, which can be assigned to the expected local symmetry breaking at the interface of disorder originated ferromagnetic nanoclusters and ferrimagnetic lattice of the system. A theoretical calculation of topological Hall resistivity by utilizing micromagnetic simulations is performed, which is of the same order as the experimentally obtained values in the both martensite and austenite phases.

The realization of the spin Hall effect has opened new frontiers for the design of efficient memory storage devices facilitated by the conversion of charge currents to spin currents. Here, using the Kubo formula, we calculate the intrinsic spin Hall conductivity (SHC) of orthorhombic tin selenide (o-SnSe) under the influence of isotropic compressive strain in the ab-plane. As the strain is gradually increased, we obtain a substantial hybridization between the pz orbitals of Sn and Se atoms of an electron pocket from the lowest conduction band and the topmost valence band, respectively. This hybridization process greatly enhances the SHC at the Fermi level and charge-to-spin conversion efficiency, the latter of which is superior to that of popular transition metals such as Ta and Pt. This makes strained o-SnSe an attractive candidate for use in spintronic devices.

This Perspective provides an overview of recent developments in the field of 3d transition metal (TM) catalysts for different reactions, including oxygen-based reactions such as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The spin moments of 3d TMs can be exploited to influence chemical reactions, and recent advances in this area, including the theory of chemisorption based on spin-dependent d-band centers and magnetic field effects, are discussed. The Perspective also explores the use of scaling relationships and surface magnetic moments in catalyst design as well as the effect of magnetism on chemisorption and vice versa. In addition, recent studies on the influence of a magnetic field on the ORR and the OER are presented, demonstrating the potential of ferromagnetic catalysts to enhance these reactions through spin polarization.