The presence of ferroelectric polarization in 2D materials is extremely rare due to the effect of the surface depolarizing field. Here, we use first-principles calculations to show the largest ...out-of-plane polarization observed in a monolayer in functionalized MXenes (Sc2CO2). The switching of polarization in this new class of ferroelectric materials occurs through a previously unknown intermediate antiferroelectric structure, thus establishing three states for applications in low-dimensional nonvolatile memory. We show that the armchair domain interface acts as an 1D metallic nanowire separating two insulating domains. In the case of the van der Waals bilayer we observe, interestingly, the presence of an ultrathin 2D electron/hole gas (2DEG) on the top/bottom layers, respectively, due to the redistrubution of charge carriers. The 2DEG is nondegenerate due to spin–orbit coupling, thus paving the way for spin–orbitronic devices. The coexistence of ferroelectricity, antiferroelectricity, 2DEG, and spin–orbit splitting in this system suggests that such 2D polar materials possess high potential for device application in a multitude of fields ranging from nanoelectronics to photovoltaics.
Transition metal carbides (MXenes) with formula Mn+1CnTx (n = 2 and 3) have been emerging as a new family of two-dimensional (2D) materials that have great potential in electronic applications and ...CO2 conversion catalysts. It has been already found that the electronic and electrochemical properties of Ti3C2Tx MXenes can be tuned by replacing the two outer titanium layers with molybdenum layers. Similar to other 2D materials, intrinsic defects can be formed in the synthesized MXene flakes and the formation of defects can influence the performance of these materials. Herein, we systematically study the effect of the different types of structural defects on the structural stability, electronic behavior, and electrochemical properties of ordered Mo2TiC2Tx terminated with the specific surface functional groups of fluorine, oxygen, and hydroxide. The calculated defect formation energies imply that the formation of defects is dependent on the surface terminations, where the O-terminated MXenes demand more energy than the F- and OH-terminated MXenes. We found that defect formation is more feasible in the outer molybdenum layers than in the inner titanium layer. Our results predicted that the CO2 molecule adsorbs on the defective surfaces through a spontaneous and exothermic process that is critical to its capture, while the perfect surface weakly attracts the molecule through a nonspontaneous and endothermic process. Thus, our study predicts that the electronic and electrochemical properties of Mo2TiC2Tx can be tuned by forming specific defects and these MXenes could be promising materials for CO2 adsorption and conversion.
We have used computational methodology based on the density functional theory to describe both copper(I) and copper(II) oxides, followed by the investigation of a number of different low index CuO ...surfaces. Different magnetic orderings of all the surfaces were studied, and reconstructions of the polar surfaces are proposed. A detailed discussion on stabilities, electronic structure, and magnetic properties is presented. CuO(111) and CuO(111) were found to have the lowest surface energies, and their planes dominate in the calculated Wulff morphology of the CuO crystal. We next investigated the adsorption of CO2 on the three most exposed CuO surfaces, viz., (111), (111), and (011), by exploring various adsorption sites and configurations. We show that the CO2 molecule is activated on the CuO surfaces, with an adsorption energy of −93 kJ/mol on the (011) surface, showing exothermic adsorption, while (111) and (111) surfaces show comparatively weak adsorption. The activation of the CO2 molecule is characterized by large structural transformations and significant charge transfer, i.e., forming a negatively charged bent CO2 –δ species with elongated C–O bonds, which is further confirmed by vibrational analyses showing considerable red shift in the frequencies as a result of the activation.
In this paper, a new optimization algorithm called Spherical Search (SS) is proposed to solve the bound-constrained non-linear global optimization problems. The main operations of SS are the ...calculation of spherical boundary and generation of new trial solution on the surface of the spherical boundary. These operations are mathematically modeled with some more basic level operators: Initialization of solution, greedy selection and parameter adaptation, and are employed on the 30 black-box bound constrained global optimization problems. This study also analyzes the applicability of the proposed algorithm on a set of real-life optimization problems. Meanwhile, to show the robustness and proficiency of SS, the obtained results of the proposed algorithm are compared with the results of other well-known optimization algorithms and their advanced variants: Particle Swarm Optimization (PSO), Differential Evolution (DE), and Covariance Matrix Adapted Evolution Strategy (CMA-ES). The comparative analysis reveals that the performance of SS is quite competitive with respect to the other peer algorithms.
•In this work, a new optimization algorithm called spherical search (SS) is proposed.•SS shows a good balance between exploration and exploitation compared to PSO and DE.•SS fits to the contour of search-space similar to DE.•SS maintains high diversity during the optimization process compared to PSO and DE.•Efficacy of SS is showcased through extensive experiments.
The hydroxyl groups of naphthol and tautomerizable phenol derivatives have been substituted by O-, S-, N-, and C-centered nucleophiles under solvent-free reaction conditions. The products are ...generated in good to excellent yields. para-Toluenesulfonic acid exhibits the best catalytic activity compared to other Brønsted acids. Experimental observations suggest that the reaction proceeds through the intermediacy of the keto tautomer of naphthol. Nucleophilic addition to the carbonyl group followed by elimination of water generates the desired product. The present methodology provides access to substituted naphtho2,1-bfuran derivatives. The products generated using N-centered nucleophiles can be further transformed to important classes of organic molecules such as benzocarbazole and imidazole derivatives.
A metal and solvent free strategy to functionalize aryl methyl ethers through direct nucleophilic substitution of aryl C–OMe bond has been described. A wide range of O, S, N, and C-centered uncharged ...nucleophiles has been successfully employed. Using this protocol, functional derivatives of bisthiophene have been synthesized in a straightforward way. The reactions are highly atom-efficient and generate methanol as the only byproduct.
Increasing incidences of Chikungunya virus (CHIKV) infection and co-infections with Dengue/Zika virus have highlighted the urgency for CHIKV management. Failure in developing effective vaccines or ...specific antivirals has fuelled further research. This review discusses updated strategies of CHIKV inhibition and provides possible future directions. In addition, it analyzes advances in CHIKV lifecycle, drug-target development, and potential hits obtained by in silico and experimental methods. Molecules identified with anti-CHIKV properties using traditional/rational drug design and their potential to succeed in subsequent stages of drug development have also been discussed. Possibilities of repurposing existing drugs based on their in vitro findings have also been elucidated. Probable modes of interference of these compounds at various stages of infection, including entry and replication, have been highlighted. The use of host factors as targets to identify antivirals against CHIKV has been addressed. While most of the earlier antivirals were effective in the early phases of the CHIKV life cycle, this review is also focused on drug candidates that are effective at multiple stages of its life cycle. Since most of these antivirals require validation in preclinical and clinical models, the challenges regarding this have been discussed and will provide critical information for further research.
Phase change materials provide unique reconfigurable properties for photonic applications that mainly arise from their exotic characteristic to reversibly switch between the amorphous and crystalline ...nonvolatile phases. Optical pulse based reversible switching of nonvolatile phases is exploited in various nanophotonic devices. However, large area reversible switching is extremely challenging and has hindered its translation into a technologically significant terahertz spectral domain. Here, this limitation is circumvented by exploiting the semiconducting nature of germanium antimony telluride (GST) to achieve dynamic terahertz control at picosecond timescales. It is also shown that the ultrafast response can be actively altered by changing the crystallographic phase of GST. The ease of fabrication of phase change materials allows for the realization of a variable ultrafast terahertz modulator on a flexible platform. The rich properties of phase change materials combined with the diverse functionalities of metamaterials and all‐optical ultrafast control enables an ideal platform for design of efficient terahertz communication devices, terahertz neuromorphic photonics, and smart sensor systems.
All‐optical control of phase change material (PCM) integrated metamaterial allows for both multilevel nonvolatile and ultrafast volatile switching of terahertz resonances. At suprathreshold stimulus, phase change in the PCM allows for multilevel nonvolatile states. At sub‐threshold stimulus, the semiconducting nature of variable PCM phases provide unique ultrafast volatile states. Thus, optical reconfiguration of PCM metamaterial enables multifunctional terahertz wave manipulation.
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