Ferroelectric Domain and Switching Dynamics in Curved In2Se3: First Principle and Deep Learning Molecular Dynamics Simulations

Complex strain status can exist in 2D materials during their synthesis process, resulting in significant impacts on the physical and chemical properties. Despite their prevalence in experiments, their influence on the material properties and the corresponding mechanism are often understudied due to the lack of effective simulation methods. In this work, we investigated the effects of bending, rippling, and bubbling on the ferroelectric domains in In2Se3 monolayer by density functional theory (DFT) and deep learning molecular dynamics (DLMD) simulations. The analysis of the tube model shows that bending deformation imparts asymmetry into the system, and the polarization direction tends to orient towards the tensile side, which has a lower energy state than the opposite polarization direction. The energy barrier for polarization switching can be reduced by compressive strain according DFT results. The dynamics of the polarization switching is investigated by the DLMD simulations. The influence of curvature and temperature on the switching time follows the Arrhenius-style function. For the complex strain status in the rippling and bubbling model, the lifetime of the local transient polarization is analyzed by the autocorrelation function, and the size of the stable polarization domain is identified. Local curvature and temperature can influence the local polarization dynamics following the proposed Arrhenius-style equation. Through cross-scale simulations, this study demonstrates the capability of deep-learning potentials in simulating polarization for ferroelectric materials. It further reveals the potential to manipulate local polarization in ferroelectric materials through strain engineering

2D ferroelectric devices : Working principles and research progress

Two-dimensional (2D) ferroelectric materials are promising for use in high-performance nanoelectronic devices due to the non-volatility, high storage density, low energy cost and short response time originating from their bistable and switchable polarization states. In this mini review, we first discuss the mechanism and operation principles of ferroelectric devices to facilitate understanding of these novel nanoelectronics and then summarize the latest research progress of electronic devices based on 2D ferroelectrics. Finally, the perspectives for future research and development directions in various fields are provided. We expect this will provide an overview regarding the application of 2D ferroelectrics in electronic appliances.</p

Bimetallic conjugated metal-organic frameworks as bifunctional electrocatalysts for overall water splitting

Stable, high-efficiency, and highly active electrocatalysts are critical for the conversion of renewable energy through overall water splitting. Our first-principles calculations identify two-dimensional conjugated metal-organic frameworks (2D c-MOFs) with dual metal sites as promising candidates for this process. Among them, PcCo-O8-Rh stands out as the best catalyst, with Rh serving as the active site for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), resulting in a low ηHER/ηOER of −0.19/0.25 V. Our findings suggest that the HER/OER activity of PcTM-O8-TM′ can be optimized through tensile strain, as it is related to the absorption strength of intermediates and the d-band center (ϵd) of the TM atom. This study presents a new family of 2D c-MOFs as high-performance bifunctional electrocatalysts for overall water splitting, paving the way towards sustainable energy conversion.</p

Complex anthropogenic interaction on vegetation greening in the Chinese Loess Plateau

Vegetation greening steered by land use management in the Chinese Loess Plateau has been widely reported, however studies that quantitatively assessing and explicitly linking the anthropogenic forcing on vegetation greening and browning are scarce. Here in this study, we calculate the increment and rate of change of fractional vegetation cover (FVC) from 1998 to 2018 in the Loess Plateau, and compare the results with changing rainfall, soil types, and Gross Domestic Product (GDP), to detail a systematic assessment of the role of the climate-vegetation-human nexus. We have observed that nearly 80% of the study area has undergone greening, and no-ticed that rainfall was not the main driver of rapid vegetation change, instead of human land use management such as, irrigation along the Yellow River, snowmelt-runoff irrigation, and irrigation from reservoirs formed by check dams contributed the most for the increased FVC in the Chinese Loess Plateau. Concurrently, rapid vegeta-tion browning is almost fully driven by urban expansion. Our findings show that GDP growth promotes both browning and greening, indicative of sustainable development in the Loess plateau region. These contrasting trends reveal that the relationship between human activities and greening is very complex. (c) 2021 Elsevier B.V. All rights reserved

Density Functional Theory Studies on Magnetic Manipulation in NiI2Layers

Effective manipulation of magnetic states is fundamentally important to modern data storage and electronic devices that underpin the information age. Controlling magnetism via electric fields instead of magnetic fields has long been envisioned as a revolutionary technology to achieve higher energy efficiency and ultimate device miniaturization. The electric field paradigms, however, face major challenges of volatility, high energy cost, and low storage density. In this work, from density functional theory simulations, we developed effective approaches to achieve magnetic control in bilayer NiI2 via electrostatic doping and polarization field of the ferroelectric heterostructure. The interlayer antiferromagnetic (AFM) to ferromagnetic (FM) transition has been observed in bilayer NiI2 when the critical electron doping concentration reaches 0.625% due to the magnetic exchange competition between antiferromagnetic and ferromagnetic couplings. The critical concentration of magnetic transition can be reduced or increased depending on the polarization direction when it is placed on the ferroelectric substrate of Sc2CO2 as a result of polarization-induced interfacial electron transfer. Owing to the antiferromagnetic-to-ferromagnetic (AFM–FM) transition, the reversal of ferroelectric polarization modulates the electronic properties dramatically due to the strong interfacial magnetoelectric effect. The magnetic and electronic manipulation from electrostatic doping and polarization provides feasible approaches for next-generation electronics and spintronics.</p

Density Functional Theory Calculations of the Stacking-Dependent Optoelectronic Properties of 2D GeSe/SnS Heterobilayers : Implications for Photovoltaics

Manipulation of interlayer interaction in nanoscale can effectively modulate the electronic and optical properties of layered materials, which can find photovoltaic applications when it is coupled with the in-plane or out-of-plan polarization. Here, based on in-plane ferroelectric 2D GeSe/SnS heterobilayer, we found that the optoelectronic properties can be well modulated by the interlayer stacking patterns from the density functional theory (DFT) simulations, where the ferroelectric ground states, electronic bandgaps and optical adsorptions are highly dependent on the relative interlayer configurations. Comparing with the homogeneous counterparts, the modulations are more significant due to the presence of vertical polarization. As a result, the power conversion efficiency of the heterobilayer increases from 13.4% to 22.8% by interlayer sliding. These findings provide feasible strategies to optimize the photovoltaic performance of 2D nanomaterial-based solar cells. </p

Ferroelectric Domain and Switching Dynamics in Curved In2Se3: First-Principles and Deep Learning Molecular Dynamics Simulations

Despite its prevalence in experiments, the influence of complex strain on material properties remains understudied due to the lack of effective simulation methods. Here, the effects of bending, rippling, and bubbling on the ferroelectric domains are investigated in an In2Se3 monolayer by density functional theory and deep learning molecular dynamics simulations. Since the ferroelectric switching barrier can be increased (decreased) by tensile (compressive) strain, automatic polarization reversal occurs in α-In2Se3 with a strain gradient when it is subjected to bending, rippling, or bubbling deformations to create localized ferroelectric domains with varying sizes. The switching dynamics depends on the magnitude of curvature and temperature, following an Arrhenius-style relationship. This study not only provides a promising solution for cross-scale studies using deep learning but also reveals the potential to manipulate local polarization in ferroelectric materials through strain engineering.</p

Degree of joint risk factor control and hazard of mortality in diabetes patients: a matched cohort study in UK Biobank

Abstract Background Diabetes patients are at higher risk for mortality than the general population; however, little is known about whether the excess mortality risk associated with diabetes could be mitigated or nullified via controlling for risk factors. Methods We included 18,535 diabetes patients and 91,745 matched individuals without diabetes without baseline cancer or cardiovascular disease (CVD), followed up from 2006 to 2021. The main exposure was the number of optimized risk factors including glycated hemoglobin < 53 mmol/mole, systolic blood pressure < 140 mmHg and diastolic blood pressure < 90 mmHg, no albuminuria, non-current smoking and low-density lipoprotein cholesterol (LDL-C) < 2.5 mmol/L. We used Cox proportional hazards models to explore the association of the degree of risk factor control with all-cause mortality, cancer mortality, CVD mortality and other mortality. Results Each additional risk factor control was associated with a 16, 10, 21 and 15% lower risk of all-cause mortality, cancer mortality, CVD mortality and other mortality, respectively. Optimal risk factors control (controlling 5 risk factors) was associated with a 50% (HR 0.50, 95% CI 0.41–0.62), 74% (HR 0.26, 95% CI 0.16–0.43) and 38% (HR 0.62, 95% CI 0.44–0.87) lower risk of all-cause mortality, CVD mortality and other mortality, respectively. Diabetes patients with 4, 3 and 5 or more controlled risk factors, respectively, showed no excess risk of all-cause mortality, cancer mortality and CVD mortality compared to matched non-diabetes patients. Conclusions The results from this study indicate that optimal risk factor control may eliminate diabetes-related excess risk of all-cause mortality, CVD mortality and other mortality

Magnetic skyrmions and their manipulations in a 2D multiferroic CuCrP2Te6 monolayer

Magnetic skyrmions and their effective manipulations are promising for the design of next-generation information storage and processing devices, due to their topologically protected chiral spin textures and low energy cost. They, therefore, have attracted significant interest from the communities of condensed matter physics and materials science. Herein, based on density functional theory (DFT) calculations and micromagnetic simulations, we report the spontaneous 2 nm-diameter magnetic skyrmions in the monolayer CuCrP2Te6 originating from the synergistic effect of broken inversion symmetry and strong Dzyaloshinskii-Moriya interactions (DMIs). The creation and annihilation of magnetic skyrmions can be achieved via the ferroelectric to anti-ferroelectric (FE-to-AFE) transition, due to the variation of the magnetic parameter D2/|KJ|. Moreover, we also found that the DMIs and Heisenberg isotropic exchange can be manipulated by bi-axial strain, to effectively enhance skyrmion stability. Our findings provide feasible approaches to manipulate the skyrmions, which can be used for the design of next-generation information storage devices.</p