Physics

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We propose an interacting non-Hermitian model described by a two-mode quadratic Hamiltonian along with an interaction term to locate and analyse the presence of an exceptional point in the system. Each mode is guided by a Swanson-like quadratic Hamiltonian and a suitable choice is made for the interaction term. The parity-time symmetric transformation is adopted in the standard way relevant for a coupled system. © Copyright © 2022 EPLA.

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Exceptional point in a coupled Swanson system

Ultra-thin diamond membranes, diamanes, are one of the most intriguing quasi-2D films, combining unique mechanical, electronic and optical properties. At present, diamanes have been obtained from bi- or few-layer graphene in AA- and AB-stacking by full hydrogenation or fluorination. Here, we study the thermal conductivity of diamanes obtained from bi-layer graphene with twist angle (Formula presented.) between layers forming a Moiré pattern. The combination of DFT calculations and machine learning interatomic potentials makes it possible to perform calculations of the lattice thermal conductivity of such diamanes with twist angles (Formula presented.) of 13.2 (Formula presented.), 21.8 (Formula presented.) and 27.8 (Formula presented.) using the solution of the phonon Boltzmann transport equation. Obtained results show that Moiré diamanes exhibit a wide variety of thermal properties depending on the twist angle, namely a sharp decrease in thermal conductivity from high for “untwisted” diamanes to ultra-low values when the twist angle tends to 30 (Formula presented.), especially for hydrogenated Moiré diamanes. This effect is associated with high anharmonicity and scattering of phonons related to a strong symmetry breaking of the atomic structure of Moiré diamanes compared with untwisted ones. © 2022 by the authors.

Membranes

Ultra-Low Thermal Conductivity of Moiré Diamanes

Alteration of transport properties of any material, especially metal oxides, by doping suitable impurities is not straightforward as it may introduce multiple defects like oxygen vacancies (Vo) in the system. It plays a decisive role in controlling the resistive switching (RS) performance of metal oxide-based memory devices. Therefore, a judicious choice of dopants and their atomic concentrations is crucial for achieving an optimum Voconfiguration. Here, we show that the rational designing of RS memory devices with cationic dopants (Ta), in particular, Au/Ti1-xTaxO2-δ/Pt devices, is promising for the upcoming non-volatile memory technology. Indeed, a current window of ∼104is realized at an ultralow voltage as low as 0.25 V with significant retention (∼104s) and endurance (∼105cycles) of the device by considering 1.11 at % Ta doping. The obtained device parameters are compared with those in the available literature to establish its excellent performance. Furthermore, using detailed experimental analyses and density functional theory (DFT)-based first-principles calculations, we comprehend that the meticulous presence of Voconfigurations and the columnar-like dendritic structures is crucial for achieving ultralow-voltage bipolar RS characteristics. In fact, the dopant-mediated Vointeractions are found to be responsible for the enhancement in local current conduction, as evidenced from the DFT-simulated electron localization function plots, and these, in turn, augment the device performance. Overall, the present study on cationic-dopant-controlled defect engineering could pave a neoteric direction for future energy-efficient oxide memristors. © 2022 American Chemical Society. All rights reserved.

ACS Applied Materials and Interfaces

Aliovalent Ta-Doping-Engineered Oxygen Vacancy Configurations for Ultralow-Voltage Resistive Memory Devices: A DFT-Supported Experimental Study

Ultrasmall MoS2 nanocrystals have unique optoelectronic and catalytic properties that have acquired significant attraction in many areas. We propose here a simple and economical method for synthesizing the luminescent nanocrystals MoS2 using the hydrothermal technique. In addition, the synthesized MoS2 nanocrystals display photoluminescence that is tunable according to size. MoS2 nanocrystals have many advantages, such as stable dispersion, low toxicity and luminescent characteristics, offering their encouraging applicability in biomedical disciplines. In this study, human lung cancer epithelial cells (A549) are used to assess fluorescence imaging of MoS2 nanocrystals. MTT assay, trypan blue assay, flow cytometry and fluorescence imaging results have shown that MoS2 nanocrystals can selectively target and destroy lung cancer cells, especially drug-resistant cells (A549). © 2022 Sahoo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

PLoS ONE

Cost-effective synthesis of 2D molybdenum disulfide (MoS2) nanocrystals: An exploration of the influence on cellular uptake, cytotoxicity, and bio-imaging

In this review article, we provide an overview of skyrmion dynamics in the transport behavior of skyrmions based on the existing theoretical and experimental works in addition to the device applications. Swirling spin textures, namely, skyrmions are expected to play extremely important role in future energy efficient spintronic devices. We emphasize specifically on the electrical control of the skyrmion dynamics from the fundamental to application point of view. To begin with, we discuss the role of antisymmetric exchange interaction, namely, the Dzyaloshinskii-Moriya interaction which has its origin in spin-orbit coupling and symmetry breaking at the interface in stabilizing the skyrmion. In-depth understanding of the role of in-plane and out of plane spin torque in governing the skyrmion dynamics is discussed. Importantly, the skyrmion Hall effect, voltage control of skyrmion dynamics, and various important experimental techniques for generating and detecting skyrmion have been elaborated. Given the delicate physics involved with the manipulation and detection of skyrmion, the crucial understanding of the experimental results and theory from the perspective of electrical transport are discussed. Finally, the application of skyrmions in various devices e.g., magnetic memory, transistors and logic gates along with challenges involved are summarized briefly. © 2022 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited.

ECS Journal of Solid State Science and Technology

Review—Magnetic Skyrmions in Chiral Ferromagnets: Electrical Transport Properties and Device Applications

Large collections of molecules (chemical libraries) are nowadays routinely screened in the process of designing drugs for specific ailments. Chemical and structural similarities between these molecules can be quantified using molecular descriptors, and these similarities can in turn be used to represent any chemical library as an undirected network called a chemical space network (CSN). Here we study different CSNs using conventional graph measures as well as random matrix theory (RMT). For the conventional graph measures, we focus on the average degree, average path length, graph diameter, degree assortativity, transitivity, average clustering coefficient and modularity. For the RMT analyses, we examine the eigenvalue spectra of adjacency matrices constructed from the molecular similarities for different CSNs, and examine their local fluctuation properties, contrasting them with the predictions of RMT. Changes in the conventional graph measures and RMT statistics with the network structure are examined for three different chemical libraries by varying the edge density (fraction of the actual to the maximum possible number of edges) of the networks. It is found that the assortativity among the conventional graph measures, and long-range fluctuation statistics of RMT in eigenvalue space respond to the changes in global network structure as well as the chemical space. We expect that this investigation of the network characteristics of different kinds of chemical libraries will provide guidance in the design of high-throughput screening libraries for different drug design applications. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.

Journal of Mathematical Chemistry

Investigation of chemical space networks using graph measures and random matrix theory

We investigate the (1 + 1)-dimensional position-dependent mass Dirac equation within the confines of so(2, 1) potential algebra by utilizing the character of a spatial varying Fermi velocity. We examine the combined effects of the two when the Dirac equation is equipped with an external pseudoscalar potential. Solutions of the three cases induced by so(2, 1) are explored by profitably making use of a point canonical transformation. © 2022 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

so(2, 1) algebra, local Fermi velocity, and position-dependent mass Dirac equation

This work reports a detailed and systematic theoretical study of the anisotropic thermoelectric properties of bulk Germanium Sulfide (GeS) in its orthorhombic Pnma phase. Density functional theory (DFT), employing the generalized gradient approximation (GGA), has been used to examine the structural and electronic band structure properties of bulk GeS. Electronic transport properties have been studied by solving semiclassical Boltzmann transport equations. A machine-learning approach has been used to estimate the temperature-dependent lattice part of thermal conductivity. The study reveals that GeS has a direct band gap of 1.20 eV. Lattice thermal conductivity is lowest along crystallographic a-direction, with a minimum of ∼0.98 Wm −1 K −1 at 700 K. We have obtained the maximum figure of merit (ZT) ∼ 0.73 at 700 K and the efficiency ∼7.86% in a working temperature range of 300 K-700 K for pristine GeS along crystallographic a-direction. © 2022 IOP Publishing Ltd.

Physica Scripta

A study of anisotropic thermoelectric properties of bulk Germanium Sulfide in its Pnma phase: a combined first-principles and machine-learning approach

Vanadium Diselenide (VSe2) is a prominent candidate in the 2D transition metal dichalcogenides family for energy storage applications. Herein, we report the experimental and theoretical investigations on the effect of cobalt doping in 1T-VSe2. The energy storage performance in terms of specific capacitance, stability and energy and power density is studied. It is observed that 3% Co doped VSe2 exhibits better energy storage performance as compared to other concentrations, with a specific capacitance of 1/4193 F g-1 in a two-electrode symmetric configuration. First-principles Density Functional Theory based simulations support the experimental findings by suggesting an enhanced quantum capacitance value after the Co doping in the 1T-VSe2. By making use of the advantages of the specific electrode materials, a solid state asymmetric supercapacitor (SASC) is also assembled with MoS2 as the negative electrode. The assembled Co-VSe2//MoS2 SASC device shows excellent energy storage performance with a maximum energy density of 33.36 Wh kg-1 and a maximum power density of 5148 W kg-1 with a cyclic stability of 90% after 5000 galvano static charge discharge cycles. © 2022 IOP Publishing Ltd.

Nanotechnology

Effect of cobalt doping on the enhanced energy storage performance of 2D vanadium diselenide: Experimental and theoretical investigations

Castor oil (CO) and cocoa butter (CB) were studied as potential hydrophobic and plasticizer additives for pectin biopolymer films. The optimum concentration of CO and CB additives and drying temperature were determined by using a 23 (two-level, three-factor) statistical factorial design of experiments. The CO and CB integrated pectin films displayed remarkably lower moisture and oxygen transmission rates relative to the control pectin films. Furthermore, the hydrophobicity, ductility (elongation at break) and flexibility (low elastic modulus) of the CO and CB added films are significantly higher than that of the control pectin films. The modified films retained 90% of their weight at a temperature of 200 °C, indicating their excellent thermal stability. A very low glass transition temperature of 2 ± 2 °C and a melting point of ~ 150 °C of the films designates their stability under processing and storage conditions. Scanning electron microscopy analysis confirmed the formation of homogeneous films without any micro-cracks or agglomerations. Detailed statistical analysis shows that the optimal conditions for producing improved pectin films: the concentration of CO (15% w/w of pectin) and CB (10% w/w of pectin) and film drying temperature (T = 35–52 °C). A coating of film forming solution comprising optimum amounts of pectin, CO and CB was able to delay the ripening of a banana by 4 days and of capsicum by 15 days at atmospheric conditions. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.