Charge Transfer Gap Tuning via Structural Distortion in Monolayer 1T-NbSe2.

The Mott state in 1T-TaS2 is predicted to host quantum spin liquids (QSLs). However, its insulating mechanism is controversial due to complications from interlayer coupling. Here, we study the charge transfer state in monolayer 1T-NbSe2, an electronic analogue to TaS2 exempt from interlayer coupling, using spectroscopic imaging scanning tunneling microscopy and first-principles calculations. Monolayer NbSe2 surprisingly displays two types of star of David (SD) motifs with different charge transfer gap sizes, which are interconvertible via temperature variation. In addition, bilayer 1T-NbSe2 shows a Mott collapse by interlayer coupling. Our calculation unveils that the two types of SDs possess distinct structural distortions, altering the effective Coulomb energies of the central Nb orbital. Our calculation suggests that the charge transfer gap, the same parameter for determining the QSL regime, is tunable with strain. This finding offers a general strategy for manipulating the charge transfer state in related systems, which may be tuned into the potential QSL regime.

Graphether: a reversible and high-capacity anode material for sodium-ion batteries with ultrafast directional Na-ion diffusion.

Sodium-ion batteries (SIBs) have been attracting great attention as the most promising alternative to lithium-ion batteries (LIBs) for large-scale energy storage. However, the absence of suitable anode materials is the main bottleneck for the commercial application of SIBs. Herein, the adsorption and diffusion behaviors of Na on graphether are predicted by first-principles density functional calculations. Our results show that Na atoms can be adsorbed on graphether forming a uniform and stable coverage on both sides. Even at low intercalated Na concentrations, the semiconducting graphether can be changed to a metallic state, ensuring good electrical conductivity. Due to the structural anisotropy of graphether, the Na+ ions show a remarkable one-dimensional diffusion with an ultralow energy barrier of 0.04 eV, suggesting ultrafast charge/discharge characteristics. The graphether monolayer has a high theoretical specific capacity of 670 mA h g-1, which is much higher than commercial graphite anode materials. Furthermore, the average voltage is 1.58 V, comparable with that of commercial TiO2 anode materials for LIBs (1.5 V). During the charge/discharge process, graphether could mostly preserve the structural integrity upon the adsorption of Na even at the maximum concentration, suggesting its good reversibility. All these results show that graphether is a promising anode material for high-performance SIBs.

Bacterial community structure in geothermal springs on the northern edge of Qinghai-Tibet plateau.

Introduction: In order to reveal the composition of the subsurface hydrothermal bacterial community in the zones of magmatic tectonics and their response to heat storage environments. Methods: In this study, we performed hydrochemical analysis and regional sequencing of the 16S rRNA microbial V4-V5 region in 7 Pleistocene and Lower Neogene hot water samples from the Gonghe basin. Results: Two geothermal hot spring reservoirs in the study area were found to be alkaline reducing environments with a mean temperature of 24.83°C and 69.28°C, respectively, and the major type of hydrochemistry was SO4-Cl·Na. The composition and structure of microorganisms in both types of geologic thermal storage were primarily controlled by temperature, reducing environment intensity, and hydrogeochemical processes. Only 195 ASVs were shared across different temperature environments, and the dominant bacterial genera in recent samples from temperate hot springs were Thermus and Hydrogenobacter, with both genera being typical of thermophiles. The correlation analysis showed that the overall level of relative abundance of the subsurface hot spring relied on a high temperature and a slightly alkaline reducing environment. Nearly all of the top 4 species in the abundance level (53.99% of total abundance) were positively correlated with temperature and pH, whereas they were negatively correlated with ORP (oxidation-reduction potential), nitrate, and bromine ions. Discussion: In general, the composition of bacteria in the groundwater in the study area was sensitive to the response of the thermal storage environment and also showed a relationship with geochemical processes, such as gypsum dissolution, mineral oxidation, etc.

Theoretical prediction of silicether: a two-dimensional hyperconjugated disilicon monoxide nanosheet.

The gapless feature and air instability greatly hinder the applications of silicene in nanoelectronics. We theoretically design an oxidized derivative of silicene (named silicether) assembled by disilyl ether molecules. Silicether has an indirect band gap of 1.89 eV with a photoresponse in the ultraviolet-visible region. In addition to excellent thermodynamic stability, it is inert towards oxygen molecules. The material shows the hyperconjugation effect, leading to high performances of in-plane stiffness (107.8 N m-1) and electron mobility (6.4 × 103 cm2 V-1 s-1). Moreover, the uniaxial tensile strain can trigger an indirect-direct-indirect band gap transition. We identify Ag(100) as a potential substrate for the adsorption and dehydrogenation of disilyl ether. The moderate reaction barriers of dehydrogenation may provide a good possibility of bottom-up growth of silicether. All these outstanding properties make silicether a promising candidate for silicon-based nanoelectronic devices.

Graphether: a two-dimensional oxocarbon as a direct wide-band-gap semiconductor with high mechanical and electrical performances.

Although many graphene derivatives have sizable band gaps, their electrical or mechanical properties are significantly degraded due to the low degree of π-conjugation. Besides the π-π conjugation, there exist hyperconjugative interactions arising from the delocalization of σ electrons. Inspired by the structural characteristics of a hyperconjugated molecule, dimethyl ether, we design a two-dimensional oxocarbon (named graphether) by the assembly of dimethyl ether molecules. Our first-principles calculations reveal the following findings: (1) monolayer graphether possesses excellent dynamic and thermal stabilities as demonstrated by its favourable cohesive energy, the absence of soft phonon modes, and high melting point. (2) It has a direct wide-band-gap energy of 2.39 eV, indicating its potential applications in ultraviolet optoelectronic devices. Interestingly, the direct band gap feature is rather robust against the external strains (-10% to 10%) and stacking configurations. (3) Due to the hyperconjugative effect, graphether has the high intrinsic electron mobility. More importantly, its in-plane stiffness (459.8 N m-1) is even larger than that of graphene. (4) The Pt(100) surface exhibits high catalytic activity for the dehydrogenation of dimethyl ether. The electrostatic repulsion serves as a driving force for the rotation and coalescence of two dehydrogenated precursors, which is favourable for the bottom-up growth of graphether. (5) Replacement of the C-C bond with an isoelectronic B-N bond can generate a stable Pmn21-BNO monolayer. Compared with monolayer hexagonal boron nitride, Pmn21-BNO has a moderate direct band gap energy (3.32 eV) and better mechanical property along the armchair direction.

A Multi-Branch 3D Convolutional Neural Network for EEG-Based Motor Imagery Classification.

One of the challenges in motor imagery (MI) classification tasks is finding an easy-handled electroencephalogram (EEG) representation method which can preserve not only temporal features but also spatial ones. To fully utilize the features on various dimensions of EEG, a novel MI classification framework is first introduced in this paper, including a new 3D representation of EEG, a multi-branch 3D convolutional neural network (3D CNN) and the corresponding classification strategy. The 3D representation is generated by transforming EEG signals into a sequence of 2D array which preserves spatial distribution of sampling electrodes. The multi-branch 3D CNN and classification strategy are designed accordingly for the 3D representation. Experimental evaluation reveals that the proposed framework reaches state-of-the-art classification kappa value level and significantly outperforms other algorithms by 50% decrease in standard deviation of different subjects, which shows good performance and excellent robustness on different subjects. The framework also shows great performance with only nine sampling electrodes, which can significantly enhance its practicality. Moreover, the multi-branch structure exhibits its low latency and a strong ability in mitigating overfitting issues which often occur in MI classification because of the small training dataset.

Removal of hexavalent chromium from water by modified sponge iron particles and insights into mechanism.

Sponge iron particles modified with expanded graphite and Cu were used to purify solutions contaminated with aqueous Cr(VI). A removal mechanism that involved physical adsorption and a redox reaction is proposed. The reaction, which consisted of rapid adsorption, a desorption stage, and an adsorption-desorption equilibrium stage, corresponded to a first-order kinetic model. The properties of the adsorption materials before and after use were investigated by X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, energy-dispersive X-ray fluorescence spectroscopy, and surface area measurements. Changes in the surface properties, e.g., attachment of material to the surface and filling of pores with Cr, were clearly observed. The Langmuir model best described Cr(VI) adsorption on the sponge iron and its modified particles. Removal efficiencies of 98.7, 98.8, and 100% were achieved in 7 h at a Cr(VI) dosage of 10 mg/L. Sponge iron particles are therefore potential adsorbents and after modification give good removal of Cr(VI) ions from contaminated water.

Atomic Vacancies Control of Pd-Based Catalysts for Enhanced Electrochemical Performance.

Structure-engineered Pd-based catalysts at the atomic level can effectively improve the catalytic performance for oxygen or small organic molecules electrocatalysis, comparable to or even superior to that of commercial Pt/C. Here, PdCuCo anisotropic structure (AS) electrocatalysts are synthesized with abundant vacancy defects on the exterior surface, which is unambiguously verified by aberration-corrected transmission electron microscopy. The PdCuCo-AS with vacancy (v-PdCuCo-AS) shows excellent electrochemical activity toward oxygen reduction (ORR) and oxidation of alcohols. The mass activity of the v-PdCuCo-AS is 0.18 A mg-1 at 0.9 V versus reversible hydrogen electrode (RHE), which is 15.55 times larger than that of the commercial Pd/C catalyst in acidic electrolyte. According to the theoretical calculations, this significant improvement can be understood as a result of the promoted charge transfer by polarized electronic structures of the v-PdCuCo-AS in the processes of ORR. The synergistic effect of the correlated defects and the compressive strain caused by the doping Co and Cu atoms effectively improve the electrocatalysis activity for the ORR in acidic/alkaline electrolyte on the v-PdCuCo-AS stems. This approach provides a strategy to design other AS structures for improving their electrochemical performance.

[IS6110-restriction fragment length polymorphism based DNA fingerprinting in molecular epidemiology of tuberculosis].

OBJECTIVE: To identify the IS6110-restriction fragment length polymorphism (RFLP) DNA fingerprinting patterns of some clinical isolates of Mycobacterium tuberculosis (MTB) isolated from Ningxia, Beijing and Shanghai in recent years, and to observe their epidemiological characteristics. METHODS: Chromosomal DNA of MTB was digested with endonuclease PvuII, then electrophoresed on agarose gel plate and transferred capillarilly to a nylon filter and hybridized with 245 bp fragment of IS6110 which labeled using random primer fluorescein labeling kit. The RFLP patterns of Southern hybridization were inspected autofluorographically and the chromosomal DNAs of MTB were thereby typed. RESULTS: Most of 103 isolates of MTB shared 8 approximately 21 copies. Some of them were clustered. Strains isolated from Ningxia and Beijing had similar DNA fingerprinting patterns. One zero copy strain and one single copy strain were found among isolates from Shanghai. CONCLUSIONS: IS6110-RFLP based typing is feasible for MTB molecular epidemiological study in China. Most of isolates of MTB show analyzable patterns. Isolates of MTB from Ningxia and Beijing have close genomic relation.