Paper & Patents

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.

In this study, we address the significant challenge of overcoming limitations in the catalytic efficiency for the oxygen evolution reaction (OER). The current linear scaling relationships hinder the optimization of the electrocatalytic performance. To tackle this issue, we investigate the potential of designing single-atom catalysts (SACs) on Mo2CO2 MXenes for electrochemical OER using first-principles modeling simulations. By employing the Electrochemical Step Symmetry Index (ESSI) method, we assess OER intermediates to fine-tune the activity and identify the optimal SAC for Mo2CO2 MXenes. Our findings reveal that both Ag and Cu exhibit effectiveness as single atoms for enhancing OER activity on Mo2CO2 MXenes. However, among the 21 chosen transition metals (TMs) in this study, Cu stands out as the best catalyst for tweaking the overpotential (ηOER). This is due to Cu’s lowest overpotential compared to other TMs, which makes it more favorable for the OER performance. On the other hand, Ag is closely aligned with ESSI = ηOER, making the tuning of its overpotential more challenging. Furthermore, we employ symbolic regression analysis to identify the significant factors that exhibit a correlation with the OER overpotential. By utilizing this approach, we derive mathematical formulas for the overpotential and identify key descriptors that affect the catalytic efficiency in the electrochemical OER on Mo2CO2 MXenes. This comprehensive investigation not only sheds light on the potential of MXenes in advanced electrocatalytic processes but also highlights the prospect of improved activity and selectivity in OER applications.

The two-dimensional compound group of MXenes, which exhibit unique optical, electrical, chemical, and mechanical properties, are an exceptional class of transition metal carbides and nitrides. In addition to traditional applications in Li-S, Li-ion batteries, conductive electrodes, hydrogen storage, and fuel cells, the low lattice thermal conductivity coupled with high electron mobility in the semiconducting oxygen-functionalized MXene Ti2CO2 has led to the recent interests in high-performance thermoelectric and nanoelectronic devices. Apart from the above dc- transport applications, it is crucial to also understand ac- transport across them, given the growing interest in applications surrounding wireless communications and transparent conductors. In this work, we investigate using our recently developed abinitio transport model, the real and imaginary components of electron mobility and conductivity to conclusively depict carrier transport beyond the room temperature for frequency ranges upto the terahertz range. We also contrast the carrier mobility and conductivity with respect to the Drude's model to depict its inaccuracies for a meaningful comparison with experiments. Our calculations show the effect of acoustic deformation potential scattering, piezoelectric scattering, and polar optical phonon scattering mechanisms. Without relying on experimental data, our model requires inputs calculated from first principles using density functional theory. Our results set the stage for providing abinitio based ac- transport calculations given the current research on MXenes for high-frequency applications.

A new method for analyzing magnetization dynamics in spin textures under the influence of fast electron injection from topological ferromagnetic sources such as Dirac half metals has been proposed. These electrons, traveling at a velocity v with a non-negligible value of $v/c$ (where c is the speed of light), generate a non-equilibrium magnetization density in the spin-texture region, which is related to an electric dipole moment via relativistic interactions. When this resulting dipole moment interacts with gauge fields in the spin-texture region, an effective field is created that produces spin torques. These torques, like spin-orbit torques that occur when electrons are injected from a heavy metal into a ferromagnet, can display both damping-like and anti-damping-like properties. Finally, we demonstrate that such an interaction between the dipole moment and the gauge field introduces an anomalous velocity that can contribute to transverse electrical conductivity in the spin texture in a way comparable to the topological Hall effect.