Progress on 2D topological insulators and potential applications in electronic devices

Two-dimensional topological insulators(2DTIs)have attracted increasing attention during the past few years.New 2DTIs with increasing larger spin-orbit coupling(SOC)gaps have been predicted by theoretical calculations and some of them have been synthesized experimentally.In this review,the 2DTIs,ranging from single element graphene-like materials to bi-elemental transition metal chalcogenides(TMDs)and to multi-elemental materials,with different thicknesses,structures,and phases,have been summarized and discussed.The topological properties(especially the quantum spin Hall effect and Dirac fermion feature)and potential applications have been summarized.This review also points out the challenge and opportunities for future 2DTI study,especially on the device applications based on the topological properties.

Whole-soil warming shifts species composition without affecting diversity,biomass and productivity of the plant community in an alpine meadow

The structure and function of plant communities in alpine meadow ecosystems are potentially susceptible to climate warming.Here,we utilized a unique field manipulation experiment in an alpine meadow on the Qinghai-Tibetan Plateau and investigated the responses of plant species diversity,composition,biomass,and net primary productivity(NPP)at both community and functional group levels to whole-soil-profile warming(3–4℃ across 0–100 cm)during 2018–2021.Plant species diversity,biomass and NPP(both above-and belowground)at the community level showed remarkable resistance to warming.However,plant community composition gradually shifted over time.Over the whole experimental warming period,aboveground biomass of legumes significantly decreased by 45%.Conversely,warming significantly stimulated aboveground biomass of forbs by 84%,likely because of better growth and competitive advantages from the warming-induced stimulation of soil water and other variables.However,warming showed minor effects on aboveground biomass of grasses and sedges.Overall,we emphasize that experimental warming may significantly affect plant community composition in a short term by triggering adjustments in plant interspecific competition or survival strategies,which may cause potential changes in plant productivity over a more extended period and lead to changes in carbon source-sink dynamics in the alpine meadow ecosystem.

Improving the band alignment at PtSe_(2)grain boundaries with selective adsorption of TCNQ

Grain boundaries in two-dimensional(2D)semiconductors generally induce distorted band alignment and interfacial charge,which impair their electronic properties for device applications.Here,we report the improvement of band alignment at the grain boundaries of PtSe_(2),a 2D semiconductor,with selective adsorption of a presentative organic acceptor,tetracyanoquinodimethane(TCNQ).TCNQ molecules show selective adsorption at the PtSe_(2)grain boundary with strong interfacial charge.The adsorption of TCNQ distinctly improves the band alignment at the PtSe_(2)grain boundaries.With the charge transfer between the grain boundary and TCNQ,the local charge is inhibited,and the band bending at the grain boundary is suppressed,as revealed by the scanning tunneling microscopy and spectroscopy(STM/S)results.Our finding provides an effective method for the advancement of the band alignment at the grain boundary by functional molecules,improving the electronic properties of 2D semiconductors for their future applications.

Controlled fabrication and microwave absorbing mechanism of hollow Fe3O4@C microspheres

Uniform core-shell SiO2@Fe_3O_4@C microspheres were prepared by a one-step hydrothermal method with SiO_2 microspheres as the template, and the hollow Fe_3O_4@C(HFC) microspheres were achieved via etching SiO_2 template. By changing the sizes of SiO_2 microspheres, a series of HFC microspheres with variable cavity sizes were obtained to study the relationship between cavity size and microwave absorbing(MA) performance for the first time. The morphology and structure of samples were characterized in detail. The results showed that the MA performance of HFC sample depended on its cavity size. In particular, the hollow structure was good for improving MA performance and could make MA move to the high-frequency region. More importantly, as the cavity size increases, the resonance frequency of HFC-i(i=1,2, 3, 4) samples moved to a low frequency, and the optimal matching thickness of HFC-i samples was increasing. Among all HFC-i samples, HFC-3 showed the most excellent MA performance,which could be mainly explained by the quarter-wavelength matching model, intrinsical magnetic and dielectric loss. Furthermore,the MA performance of HFC mixture blended by the equal mass fraction of HFC-2, HFC-3 and HFC-4 was the comprehensive results of three HFC-i samples. All the above suggested that the cavity size in HFC sample had a great influence on the MA performance.

Fabrication, adsorption and photocatalytic properties of ZnTi0.6Fe1.4O4/Carbon nanotubes composites

ZnTi_xFe_(2–x)O_4 and ZnTi_(0.6)Fe_(1.4)O_4/Carbon nanotubes(ZT_(0.6)F_(1.4)/CNTs) composites were prepared by chemical co-precipitation method. The composition, microstructure, magnetic property, adsorption and photocatalytic activity of the prepared samples were characterized by means of modern analytical techniques. The results indicated that ZT_(0.6)F_(1.4)/CNTs composites not only held the original special structure and excellent adsorption properties of CNTs, but also had suitable magnetic property and excellent photocatalytic activity. The removal rate of the samples on Rhodamine B(RhB) depended on the adsorption of CNTs and the photocatalytic degradation of ZT_(0.6)F_(1.4) in the composites. The maximum adsorption amount(q_m) of ZT_(0.6)F_(1.4)/CNTs with the mass ratios of ZT_(0.6)F_(1.4) to CNTs(mZ/C)=1 was up to 17.153 mg g^(–1) for RhB, its adsorption behavior was in accord with Langmuir model, and its photocatalytic degradation activity on RhB had a positive correlation with the content of ZT_(0.6)F_(1.4) in the sample. The experimental results indicate that the total removal rate of composite with mZ/C=1 on RhB was more than 95% and the composite had good decontamination capability on industrial dye wastewater. In addition, the samples can be recovered conveniently, activated easily and had good performance for recycling.

The ecological adaptability of cloned sheep to free-grazing in the Tengger Desert of Inner Mongolia,China

Since the birth of the first cloned sheep,somatic cell nuclear transfer technology has been successfully used to clone a variety of mammals.Cloned livestock have no apparent health risks,and the quality and safety of the cloned animal products are similar to non-cloned animals.The social behavior and environmental adaptability of postnatal cloned animals,especially when used for grassland farm production purposes,is unknown.In the present study,the cloned Dorper sheep equipped with GPS location devices were free-grazed in a harsh natural environment similar to conditions commonly experienced by Mongolian sheep.The main findings of this research were as follows.(1)Under free-grazing conditions,the cloned sheep showed excellent climatic and ecological adaptability.In extreme temperature conditions ranging from–30 to 40°C,the cloned sheep maintained acceptable body condition and behaved as other sheep.(2)The cloned sheep quickly adapted from a herd feeding strategy to the harsh environment and quickly exhibited a grazing regimen as other free-grazing sheep.(3)The cloned sheep exhibited free-grazing patterns and social behavior as other sheep.(4)The cloned sheep in the harsh environment thrived and produced healthy lambs.Overall,the cloned Dorper sheep exhibited excellent ecological adaptation,which is an important consideration for breeding meat sheep by cloning.The Dorper sheep readily adapted to the free-grazing conditions on the Mongolian plateau grassland,which attests to their ability to withstand harsh environmental conditions.