Efficient Modulation of Schottky to Ohmic Contact in MoSi2N4/M3C2 (M = Zn, Cd, Hg) van der Waals Heterostructures.

A strong Fermi level pinning (FLP) effect can induce a large Schottky barrier in metal/semiconductor contacts; reducing the Schottky barrier height (SBH) to form an Ohmic contact (OhC) is a critical problem in designing high-performance electronic devices. Herein, we report the interfacial electronic features and efficient modulation of the Schottky contact (ShC) to OhC for MoSi2N4/M3C2 (M = Zn, Cd, Hg) van der Waals heterostructures (vdWHs). We find that the MoSi2N4/M3C2 vdWHs can form a p-type ShC with small SBH with the calculated pinning factor S ≈ 0.8 for MoSi2N4/M3C2 contacts. These results indicate that the FLP effect can be effectively suppressed in MoSi2N4 contact with M3C2. Moreover, the interfacial properties and SBH of MoSi2N4/Zn3C2 vdWHs can be effectively modulated by a perpendicular electric field and biaxial strain. In particular, an efficient OhC can be achieved in MoSi2N4/Zn3C2 vdWHs by applying a positive electric field of 0.5 V/Å and strain of ±8%.

Tunable Interfacial Electronic and Photoexcited Carrier Dynamics of an S-Scheme MoSi2N4/SnS2 Heterojunction.

Exploring and designing an efficient S-scheme heterojunction photocatalyst for water splitting are crucial. Herein, we report the interfacial electronics, photoexcited carrier dynamics, and photocatalytic performance for water splitting of the MoSi2N4/SnS2 van der Waals heterojunction under the modulation of an electric field and biaxial strain. Our results show that the MoSi2N4/SnS2 heterojunction has a direct band gap of 0.41 eV and obeys the S-scheme charge transfer mechanism. Further calculations of the photoexcited carrier dynamics demonstrate that the interfacial carrier recombination time is 7.22 ps, which is shorter than the electron (hole) transfer time of 39.5 ps (566 ps). Moreover, under the effect of a positive electric field and tensile strain, the S-scheme MoSi2N4/SnS2 heterojunction exhibits excellent visible-light absorption, satisfactory band-edge potentials, tunable interfacial charge transfer, and spontaneous hydrogen evolution reaction activity. The calculated STH efficiency indicates that a tensile strain of 2% is the most effective means of improving the photocatalytic performance of the S-scheme MoSi2N4/SnS2 heterojunction.

Theoretical study of CDW phases for bulk NbX2 (X = S and Se).

In most two-dimensional transition metal chalcogenides, the superconducting phase coexists with the charge density wave (CDW) phase. There exists at least one case, i.e. bulk 2H-NbS2, that does not conform to this picture. Scientists have shown great interest in trying to experimentally find the CDW phase of bulk NbS2 since 1975. Is there any theoretically more stable thermodynamic state than its higher-temperature metal phase, especially in the case of charge injection? Theoretically more stable CDW bulk configurations (TC for 2H-NbS2 and TTs for 2H-NbSe2) with partial pseudo energy gaps were predicted through the harmonic phonon softening theory and first-principles calculations. The ratios of larger to smaller pseudo gaps around K-H segment in the Brillouin zone for CDW phases are basically equal to those of superconductivity phases for bulk 2H-NbX2 (X = S and Se). The CDW phase should coexist with its superconductor state below the critical temperature rather than the metal phase for bulk 2H-NbS2. The presence of CDW phase should be more easily observed experimentally when the injected charge reaches 0.5e/Nb18S36 for bulk 2H-NbS2. Our calculations of density of state (DOS) indicated that, during Nb atoms contracting to form the CDW phases with symmetry breaking in the in-plane direction, dominant conductive carriers are always of p-type for bulk 2H-NbS2 while the alternation of carrier type from p-type to n-type occurs for bulk 2H-NbSe2. The Fermi level continuously drops and then the M-L segment of the out-of-plane energy band emerges from the Fermi surface, which corresponds to the reversal of p-n type sign. Lifshitz transition of pocket-vanishing types occurs in the out-of-plane direction without symmetry breaking during the geometrical structural phase transition for bulk 2H-NbSe2. Our calculations have theoretically addressed the long-standing coexistence issue of CDW and superconducting phases.

Key phonon modes to determine the phase transition of two dimensional Janus transition metal dichalcogenides: a DFT and tight-binding study.

Phase stability and the phase transition of Janus transition metal chalcogenides (TMDs) have become interesting issues that have not been fully resolved since their successful synthesis. By fitting the results from first principles calculations, a tight-binding dynamics matrix of the 1T' phase is constructed and the eigenvectors are also obtained. We propose a method to project the atomic motion causing the phase transition from 2H to 1T' onto these eigenvectors, and identify four key phonon modes which are the major factors to trigger phase transition. Temperature excitation is used to excite the key modes and the free energy criterion is used to determine the phase stability. The relatively large enthalpy difference between the 2H and 1T' phases favours the 2H one as the stable phase at low temperature. While the 1T' phase has a quick increase in vibrational free energy with rising temperature, especially for 1T' Janus TMDs which have a quicker increase in the total free energy than that of 1T' non-Janus TMDs, making them show a lower phase transition temperature. Our work will deepen our understanding of the phase transition behavior of 2D Janus TMDs, and the tight-binding dynamics matrix and the method to obtain the key modes will be a useful tool for further study of the phase transitions of 2D Janus TMDs and other related materials.

A strain induced polar metal phase in a ferromagnetic Fe3GeTe2 monolayer.

The electronic structure and magnetic properties of the ferromagnetic Fe3GeTe2 monolayer have been extensively studied in recent years. Experimentally, external strain can be produced inevitably during the growth on the substrate. However, the impact of strain on the structural, electronic, and magnetic properties remains largely underexplored. Herein, by using density functional theory, we systematically investigate the crystalline configuration and electronic structure of the Fe3GeTe2 monolayer in the presence of external strain. We find that a moderate compressive strain could break the structural vertical symmetry, leading to a sizable out-of-plane dipole moment, while the ferromagnetism can be retained. Surprisingly, strain-induced polarization in the off-center Fe and Ge atoms barely contributes to the energy states at the Fermi level. The efficient decoupling of the conductivity and polarization in the strained Fe3GeTe2 monolayer results in an extremely rare phase with the coexistence of polarization, metallicity, and ferromagnetism, i.e., magnetic polar metals for potential applications in magnetoelectricity and spintronics.

Excellent removal performance of 4,4'-biphenyldicarboxaldehyde m-phenylenediamine Schiff base magnetic polymer towards phenanthrene and 9-phenanthrol: Experimental, modeling and DFT calculations studies.

Phenanthrene (PTH) and 9-phenanthrol (9-PTH) exhibited severe health threats and ecological hazards, for this reason, exploring a high-efficient removing strategy for PTH and 9-PTH could be considered of great urgency. Herein the 4,4'-biphenyldicarboxaldehyde m-phenylenediamine Schiff base magnetic polymer (magnetic BIPH-PHEN) was successfully fabricated via Schiff base polycondensation reaction and the subsequently one-pot embedded method. The mutual aromatic nucleus of BIPH-PHEN polymer and PTH/9-PTH could form π-π interaction, thus improving the capture ability, the embedded Fe3O4 nanoparticles provided the possibility for rapid separation. The physical and chemical properties of the magnetic BIPH-PHEN were systematically characterized. The removal rate of magnetic BIPH-PHEN towards PTH and 9-PTH was 85.65 % and 98.52 %, respectively (PTH or 9-PTH: 8 mg/L; Adsorbent: 0.2 g/L). The DFT calculations including energy calculations and electrostatic potential distribution analyzed the different bonding modes and proposed the most possible bonding modes in the adsorbent/adsorbate system. Moreover, the LUMO and HOMO orbits combined with energy gaps analysis proved the existence and specific types of the π-π interaction. The monolayer adsorption occurred on the homogeneous magnetic BIPH-PHEN surface, simultaneously the chemisorption was dominant. This work not only proposed new sights on assembling magnetic Schiff base polymer for removing polycyclic aromatic hydrocarbons, but also provided a deeper understanding of intramolecular interactions.

A theoretical study on pseudo Mott phase transition of vanadium dioxide.

The structural phase transition (SPT) and metal-insulator phase transition (MIT) always occur simultaneously upon heating from the low-temperature insulator M1 phase to the high-temperature metal R phase in vanadium dioxide, and it is still unclear which one of Mott correlation and Peierls distortion plays a decisive role in the thermally induced phase transition (PT) since 1959. Our density functional theory (DFT)-based calculations revealed that the intermediate phase in the PT, the so-called monoclinic metal phase, is a zero indirect band gap semimetal (P21/c space group) with a pseudo gap (199 meV). From the M1 phase to the monoclinic metal phase, the band gap decreases gradually to zero, and the bonding lengths between vanadium-vanadium atoms remain nearly constant. The SPT and MIT from the intermediate structure to the R phase occur simultaneously with a sudden change of bonding lengths between vanadium-vanadium atoms, in which electrons can jump down rather than jump up to the conduction band minimum (CBM) from the valence band maximum (VBM) under thermal fluctuation in order to lower the total energy of the system to push forward the occurrence of PT. The electron jumping does not require additional energy from Coulomb repulsion between electrons even though it is always present. This SPT is a typical Peierls PT or a pseudo Mott PT rather than an actual Mott PT in the each of the two stages. Our conclusions provide a new understanding of SPT and MIT in vanadium dioxide that has been debated for more than 80 years.

Comprehensive bioinformatics analysis confirms RBMS3 as the central candidate biological target for ovarian cancer.

Ovarian cancer (OC) is one of the most lethal malignancies in the female reproductive system. To find genes related to cancer progression targeting specific biological factors for targeted therapy, bioinformatics technology has been widely used. To screen the prognostic gene markers of OC by bioinformatics and explore their potential molecular biological mechanisms. Two data sets related to OC, GSE54388, and GSE119056, were rooted in the open comprehensive gene expression database (GEO). To correct the background of the data, standardize and screen differentially expressed genes (DEGs) using the R software limma package. The selected DEGs were enriched by Gene Ontology (GO) and through DAVID online database. Kyoto Encyclopedia of Genes and Genomes (KEGG) signal pathway analysis and protein-protein interaction network (PPI-network) map were constructed by STRING online database and Cytoscape software. Combined with the TCGA database, univariate and multivariate COX regression were used to screen prognostic genes. QRT-PCR was used to verify DEGs in clinical tissue samples. Eventually, the function of RBMS3 on the viability, migration, invasion, and apoptosis of OC cells was tested through functional experiments in vitro. 352 common DEGs were screened from GSE54388 and GSE119056 data sets. Survival analysis showed that MEIS2, TSTA3, CNTN1, RBMS3, and TRA2A were considered to be connected with the prognosis of OC. We discover that the expression level of RBMS3 was positively connected with the overall survival (OS) rate of sufferers with OC. The level of RBMS3 in OC tissues was markedly lower than that in neighboring structures and the outcomes of the GEPIA database were consistent with those of the qRT-PCR experiment. Through gene transfection technology it was found that overexpression of RBMS3 in OC cells substantially suppressed the vitality, migration, and invasion of OC cells and raised the rates of apoptosis in the OC cells. In this experiment, we distinguish 5 genes that may participate in the prognosis of OC and showed the key genes and pathways related to OC. It is speculated that RBMS3, a tumor suppressor gene, can be applied as a potential biological marker for the treatment of OC, gene expression summary, and prognosis.

Water-in-Oil Emulsion Gels Stabilized by a Low-Molecular Weight Organogelator Derived from Dehydroabietic Acid.

High concentrations of surfactants or gelators are usually necessary to prepare emulsions gels with unusual physicochemical properties. This situation may be improved by innovating the aggregate morphology in systems. Herein, a rosin-based molecule is designed and synthesized using dehydroabietic acid as the starting material (denoted as R-Lys-R). The molecule acts as an effective organogelator and can gelate several hydrocarbon compounds with a minimum gelation concentration of 0.2% (w/v). Analysis using atomic force microscopy (AFM) and circular dichroism (CD) reveals that in n-decane, R-Lys-R forms left-handed helical fibers with a cross-sectional diameter of approximately 15 nm. The directional hydrogen bonding of the amide group is helpful to the formation of aggregates. At concentrations of R-Lys-R above 2%, water-in-oil emulsions are transformed into emulsion gels owing to the aptitude of R-Lys-R in gelating the oil phase. The concentrations of the emulsifier can be adjusted to obtain emulsion gels with different formulations. This work reveals the potential of rosin derivatives for the formation of small molecular weight organogels and provides a novel method for the utilization of natural resources in soft materials and home care products.

Helicid Improves Lipopolysaccharide-Induced Apoptosis of C6 Cells by Regulating SH2D5 DNA Methylation via the CytC/Caspase9/Caspase3 Signaling Pathway.

DNA methylation is reportedly associated with stress responses and depression. Treatment with antidepressants can regulate DNA methylation and, subsequently, gene expression in the hippocampus. Hence, DNA methylation is a potential target for treatment of depression. Screening of high-throughput data of a rat model of chronic unpredictable mild stress revealed relatively low expression of SH2 domain-containing 5 (SH2D5). SH2D5 can be overexpressed by treatment with helicid. Therefore, in order to further explore the role of SH2D5 in depression and whether helicid mediates the DNA methylation of SH2D5 as a potential antidepressant role, SH2D5 was overexpressed in C6 cells as a lipopolysaccharides (LPS)-induced model of depression. The expression levels of Bax, Bcl-2, Bad, and Daxx, and changes to the CytC/caspase9/caspase3 signal pathway were detected by qRT-PCR and Western blot analyses. After treatment with helicid or silencing of SH2D5, the above indices were detected. The results showed that helicid regulated the CytC/caspase9/caspase3 signaling pathway and improved the apoptosis indices of C6 cells through the overexpression of SH2D5. Interestingly, silencing of SH2D5 reversed the effects of helicid on the above indices. Then, in order to study the underlying mechanism, the cells were administered to helicid or 5-aza-2'-deoxycytidine (5-AzaD) and expression of SH2D5 was detected by qRT-PCR and Western blot analyses, while to assess the DNA methylation level of SH2D5 using bisulfite sequencing/PCR. The results showed that SH2D5 was hypermethylated with low expression in LPS-induced C6 cells, which was reversed by helicid and 5-AzaD. These results suggest that helicid may affect the CytC/caspase9/caspase3 apoptosis signaling pathway and improve the apoptosis indices by mediating DNA methylation of SH2D5.

High-efficiency adsorption of phenanthrene by Fe3O4-SiO2-dimethoxydiphenylsilane nanocomposite: Experimental and theoretical study.

Phenanthrene (PHE), as one of representative polycyclic aromatic hydrocarbons (PAHs) can cause serious adverse effects on human health, developing effective adsorbents to alleviate PHE contamination is in urgent demand. A novel Fe3O4-SiO2-Dimethoxydiphenylsilane (Fe3O4-SiO2-2DMDPS) nanocomposite was fabricated from encapsulation and grafting process. Magnetic Fe3O4 nanoparticles were served as preliminary matrix material, SiO2 was used to link the magnetic oxide and provide hydroxyl groups for proceeding the silane coupling reaction subsequently, and the aromatic rings in DMDPS could provide active sites for PHE adsorption via π-π interaction. SEM-EDS, TEM, BET, VSM, XRD, FTIR, Raman, Zeta potential, and XPS techniques were used to characterize magnetic nanocomposite. The prepared Fe3O4-SiO2-2DMDPS exhibited an excellent adsorption performance towards PHE, it could maintain 75.97% adsorption capacity after four regeneration cycles. Homogeneous adsorption acted crucial role in the whole adsorption process and film diffusion was the rate-controlling procedure. Theoretical calculations put forward the most favorable bonding modes between Fe3O4-SiO2-2DMDPS and PHE molecules, confirmed the π-π interaction was valid and it usually existed in the form of parallel-displaced. This work might aid us to develop effective modification strategy for Fe3O4 nanoparticles and expand its application in the PAHs removing field.

Helicid Reverses the Effect of Overexpressing NCALD, Which Blocks the sGC/cGMP/PKG Signaling Pathway in the CUMS-Induced Rat Model.

Background: Increasing evidence has shown that apoptosis in the hippocampus is closely related to depressive-like behavior. We previously reported that helicid had good antidepressant activities, which manifested as the alleviation of depression-like behaviors and the reversal of the high expression of neurocalcin delta (NCALD) in chronic unpredictable mild stress (CUMS) rats. The aim of this study was, therefore, to characterize the antidepressant-like effects and underlying mechanism of helicid on CUMS rats by silencing NCALD and using rescue experiments. Methods: We developed the CUMS rat model using CUMS stimulation from week 0 to week 6. The rats were treated with helicid, or NCALD silenced, then we overexpressed NCALD using adeno-associated virus. We also measured the protein levels of sGCα1, sGCß1, PKG1/2, and cleaved caspase-3 in hippocampal tissues using western blotting and measured cGMP using an ELISA. Results: Treating CUMS rats by silencing NCALD or by the administration of helicid improved the depressive-like behavior. The levels of proteins, including sGC, PKG, cleaved caspase-3, and cGMP, in hippocampus all decreased. NCALD overexpression reversed these decreases and reversed the alleviation of depression-like behaviors in CUMS rats. Limitation. We only detected the antidepressant effects of helicid in the hippocampus; therefore, other parts of brain should also be studied. Conclusions: Inhibition of NCALD, as well as helicid administration, alleviated antidepressant-like behavior by regulating the expressions of apoptotic cytokines and the sGC/cGMP/PKG signaling pathway. Overexpressing NCALD reversed the amelioration effects of silenced NCALD and helicid administration.

A theoretical study of the electrochemical reduction of CO2 on cerium dioxide supported palladium single atoms and nanoparticles.

Pd/CeO2 catalysts show superior catalytic performance owing to their optimal cycling activity and stability. In this study, single-atom Pd and eight-atom Pd nanoparticle clusters were supported on the surface of CeO2(110) to investigate the effect of loaded-metal size on the catalytic performance of the Pd-CeO2 system for CO2 reduction. We investigated the CO2 reduction reaction (CRR) that produces C1 products (CO, HCOOH, CH3OH, and CH4) on Pd8/CeO2 and Pd/CeO2 by density functional theory. The structures, CO2 adsorption configurations, and CO2 reduction mechanisms of these two electrocatalysts were systematically studied. Subsequently, different reduction pathways on Pd8/CeO2 and Pd/CeO2 were investigated to identify the optimal reaction pathway for further assessment. The results showed that both of these catalysts are more selective towards the production of CH3OH than CH4. Moreover, compared to Pd/CeO2 and Pd4/CeO2 (from a previously reported study) the production of CH3OH via the CRR on Pd8/CeO2 exhibited the lowest limiting potential. These results demonstrate the superiority of Pd8/CeO2 as an electrocatalyst for the electrochemical reduction of CO2 to CH3OH.

A theoretical study on the role of ammonium ions in the double-layered V2O5 electrode.

Double-layered V2O5 and its analogues have received increasing attention as a proper cathode for Mg2+, Na+, Li+ ion batteries, even for ammonium ion batteries. Our theoretical research focuses on the effects of NH4+ ions on the structural stability and the ion diffusion properties of double-layered V2O5. The elastic constant calculations indicate the NH4+ and water contents have a dramatic influence on the stability of the electrode. When the ratio of H2O and ammonia ions decreases to (NH4)0.125V2O5·0.125H2O, double-layered bronze will transform into other phases. The predicted specific capacity for the redox process from (NH4)0.5V2O5·0.5H2O to (NH4)0.125V2O5·0.125H2O is 54.6 mA h g-1, which agrees with the experimental value of 55.6 mA h g-1. From the diffusion barrier calculations, it is found that the H2O molecules can shield the polarization of NH4+ and lower the diffusion barrier of NH4+ ions. Furthermore, the migrations of common charge carriers in NH4+ pre-intercalated V2O5 have also been studied, which implies that Li+, Zn2+, Na+, Mg2+ ions may move easily in the electrode with energy barriers lower than 525 meV. Our findings match well with the reported experimental results. A special structure of Mg6NH4V8O20 with a much higher Mg ion concentration has been reported. Our findings show that the theoretical specific density of Mg batteries based on NH4+ pre-intercalated V2O5 can be improved to 431 mA h g-1, which is 2.5 times larger than the reported values. This work highlights the effects of the ratio of NH4+ and H2O on double-layered V2O5 and provides insights into designing vanadium oxide based fast-diffusion multivalent ion conductors, which are suitable for battery applications.

Long-term study of heavy metal pollution in the northern Hangzhou Bay of China: temporal and spatial distribution, contamination evaluation, and potential ecological risk.

Coastal ecosystem is vulnerable to heavy metal contamination. The northern Hangzhou Bay is under intensifying impact of anthropogenic activities. To reveal the heavy metal pollution status in the coastal environment of the Hangzhou Bay, a long-term investigation into the heavy metal contamination during 2011 to 2016 was initiated. Seawater and sediment samples of 25 locations depending on the sewage outlet locations in the northern Hangzhou Bay were collected to analyze the concentrations and temporal and spatial distribution of Cu, Pb, Zn, Cd, Hg, and As. Pollution condition, ecological risk, and potential sources were additionally analyzed. Results show that the annual mean concentrations of Cu, Pb, Zn, Cd, Hg, and As were 2.13-4.59, 0.212-1.480, 7.81-20.34, 0.054-0.279, 0.026-0.090, and 1.08-2.57 µg/L in the seawater, and were 16.34-28.35, 16.25-26.33, 67.32-97.61, 0.084-0.185, 0.029-0.061, and 6.09-14.08 µg/L in the sediments. A decreasing trend in Cu, Pb, Zn, Cd, and Hg concentrations and an increasing trend in As of the seawater were observed. However, in the sediment, the heavy metals demonstrated a rising trend, except for Hg. The single-factor pollution index showed an increasing trend in Cd and As in the seawater, depicting an enhanced pollution of Cd and As, while in the sediments, Cu, Pb, and As were in pollution-free level (average Geo-accumulation index (Igeo) values below 0) in general, and only occasional slight pollution occurred in individual years, e.g., As with 0.403 in 2016. The mean Igeo values of Cd ranged from - 0.865 to 0.274 during 2011 to 2016, indicating that the pollution level of Cd was slight, but is likely to increase in the forthcoming years. The level of heavy metal contamination in sediments was low in 2011 (5.853) and 2012 (5.172), and moderate during 2013 to 2016 (in the range of 6.107 to 7.598), while the degree of potential ecological risk was low in the study period, except moderate in 2013 (125.107). The highest contamination degree and potential ecological risk appeared in 2013 (Cd = 7.598; RI = 125.107), while Cd and Hg contributed over 75% of the ecological risk. Overall, the results show low pollution level and low potential ecological risk in the northern Hangzhou Bay; however, more attention should be paid to the potential ecological risk due to Hg and Cd. Graphical abstract Spatial distribution of the heavy metal levels in the sediment of the coastal environment of the northern Hangzhou Bay on a long-term basis.

High spin polarization in formamidinium transition metal iodides: first principles prediction of novel half-metals and spin gapless semiconductors.

The electronic structure and magnetic properties of ten formamidinium transition metal iodides in the ground state and under strain have been studied. These formamidinium transition metal iodides have a stable cubic perovskite structure. In the ground state, FAVI3 is a spin gapless semiconductor, and FAScI3, FATiI3, FACrI3, FAFeI3, FACoI3 and FANiI3 are ferromagnetic half-metals. They all have 100% spin polarization and integer total magnetic moment. Under the action of strain, the high spin polarization of some formamidinium transition metal iodides can still be well maintained, and several novel spin gapless semiconductors such as FATiI3, FAFeI3 and FACoI3 have been discovered. Magnetic studies show that these formamidinium transition metal iodides with half-metal, semiconductor and spin-gapless semiconductor properties have integral total magnetic moments under strain ranging from -10.0% to 10.0%. These newly discovered half-metallic ferromagnetic materials and spin gapless semiconductors have broad application prospects in the field of spintronics due to their high spin polarization.

Half-metal state of a Ti2C monolayer by asymmetric surface decoration.

Searching for two-dimensional (2D) ferromagnetic materials is one of the key steps in 2D spintronics. 2D metal carbide/nitride materials (MXene) are widely regarded as promising candidates for this kind of material. However, when the surfaces are saturated with some functional groups during the preparation, the ground states of most of the MXenes transit from ferromagnetic (FM) to antiferromagnetic (AFM) or non-magnetic (NM) states. In this article, we propose a new method to avoid this problem by adopting asymmetric decoration of the MXene surface, which can make MXenes ferromagnetic ground states. Based on hybrid density functional theory calculations, our results show asymmetrical adsorption of negative ions or metal atoms makes the Ti atoms have different valence states, such as one sublayer Ti4+ and another Ti+, which prefer FM ground states. This research will deepen our understanding of the magnetic properties of 2D materials and contribute to the design of new 2D ferromagnetic materials.

Structure-property relationship of nitramino oxetane polymers: a computational study on the effect of pendant chains.

A comprehensive study of the effect of the structure of pendant chains on the energetic and mechanical properties of nitramino oxetane polymers has been conducted. Enthalpy of formation (EOF), density, glass transition temperature, and elastic moduli were calculated via quantum mechanics and molecular dynamic simulations. It is shown in this study that -CH2 groups are unfavorable for EOFs, densities, and elastic moduli of the polymers, whereas -NCH3NO2 groups are favorable for these parameters. The glass transition temperature (T g) shows non-monotonic features with increasing -CH2 groups; it reaches a minimum value when the pendant chains consist of 1 or 2 -CH2 groups. Moreover, the location of the pendant chains can strongly affect T g of the polymers. Our study suggests that the asymmetric structure, distantly located pendant chains and appropriate length of the pendant chains can effectively reduce T g of the polymers with negligible compromise to other properties.

Rhombohedral Lanthanum Manganite: A New Class of Dirac Half-Metal with Promising Potential in Spintronics.

Dirac half-metals have drawn great scientific interests in spintronics because of their outstanding physical properties such as the large spin polarization and massless Dirac fermions. By using first-principles calculations, we investigate the perovskite-type lanthanum manganite (LaMnO3) as a novel Dirac half-metal. Specifically, LaMnO3 displays multiple linear band crossings in the spin-up direction, while it has a large band gap (∼5 eV) in the spin-down orientation. The intriguing linear band dispersions guarantee the ultrafast electron transport and the significant band differences between spin up and down directions promise the realization of 100% spin-polarized current and the extremely low energy consumption. Such a spin-polarized Dirac material is rare among perovskite-type compounds. By adopting the mean-field theory, the estimated Curie temperature Tc is 438.4 K. Importantly, the LaMnO3 crystal has been experimentally realized 2 decades ago, which facilitates the future experimental validation. With the novel spin-polarized electronic properties and the high possibility of experimental fabrication, LaMnO3 is ideal for the spintronic application.

Modulating the magnetic properties of MoS2 monolayers by group VIII doping and vacancy engineering.

In this work, density functional theory is adopted to study the electronic and magnetic properties of MoS2 monolayers combined with a single S vacancy defect and a group VIII (G8) atom dopant, in which the dopant is incorporated via Mo substitution. The calculated results show that the magnetic properties of monolayer MoS2 can be tuned by changing the distribution of the G8 atom and S vacancy. The S vacancy tends to decrease the net magnetic moment of the doped system when these two defects are in their closest configuration. By adjusting the distance between the dopant and the S vacancy, the doped MoS2 monolayer may show a variable net magnetic moment. In particular, all of the Ni-doped MoS2 monolayers show zero magnetic moment with or without an S vacancy. The mean-field approximation is used to estimate the Curie temperature (T C). Our results show that Fe, Co, Ru, Rh, Os and Ir-doped MoS2 monolayers are potential candidates for ferromagnetism above room temperature. The density of states calculations provide further explanations as to the magnetic behavior of these doped systems. These results provide a new route for the potential application of atomically thin dilute magnetic semiconductors in spintronic devices by employing monolayer MoS2.