Electronic properties of size-dependent MoTe2/WTe2 heterostructure

Lateral two-dimensional(2D) heterostructures have opened up unprecedented opportunities in modern electronic device and material science. In this work, electronic properties of size-dependent MoTe2/WTe2 lateral heterostructures(LHSs)are investigated through the first-principles density functional calculations. The constructed periodic multi-interfaces patterns can also be defined as superlattice structures. Consequently, the direct band gap character remains in all considered LHSs without any external modulation, while the gap size changes within little difference range with the building blocks increasing due to the perfect lattice matching. The location of the conduction band minimum(CBM) and the valence band maximum(VBM) will change from P-point to Γ-point when m plus n is a multiple of 3 for A-mn LHSs as a result of Brillouin zone folding. The bandgap located at high symmetry Γ-point is favourable to electron transition, which might be useful to optoelectronic device and could be achieved by band engineering. Type-II band alignment occurs in the MoTe2/WTe2 LHSs, for electrons and holes are separated on the opposite domains, which would reduce the recombination rate of the charge carriers and facilitate the quantum efficiency. Moreover, external biaxial strain leads to efficient bandgap engineering. MoTe2/WTe2 LHSs could serve as potential candidate materials for next-generation electronic devices.

Non-Stoichiometry Effects on the Extreme Magnetoresistance in Weyl Semimetal WTe2

Non-stoiehiometry effect on the extreme magnetoresistanee is systematically investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistanee is strongly dependent on the residual resistivity ratio （i.e., the degree of non-stoichiometry）, which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe2.

CW热敏电阻传感器与WTE温度电子调节器的应用

在科学实验和工业生产中,有很多物理量如温度、湿度、压力、流量、液位等需要自动检测以实现自动控制。不论是常规仪表检测还是日益广泛应用的微机自动检测,都必须将被测物理量的变化转化为电信号。在此担负转换重任的器件叫传感器。如温度传感器就是各行业乃至人们日常生活中使用最广的传感器之一。通常有热敏电阻、热电偶。

Evidence of Electron-Hole Imbalance in WTe2 from High-Resolution Angle-Resolved Photoemission Spectroscopy

WTe2 has attracted a great deal of attention because it exhibits extremely large and non-saturating magnetore- sistance. The underlying origin of such a giant magnetoresistance is still under debate. Utilizing laser-based angle-resolved photoemission spectroscopy with high energy and momentum resolutions, we reveal the complete electronic structure of WTe2. This makes it possible to determine accurately the electron and hole concentrations and their temperature dependence. We find that, with increasing the temperature, the overall electron concen- tration increases while the total hole concentration decreases. It indicates that the electron-hole compensation, if it exists, can only occur in a narrow temperature range,and in most of the temperature range there is an electron-hole imbalance. Our results are not consistent with the perfect electron-hole compensation picture that is commonly considered to be the cause of the unusual magnetoresistance in WTe2. We identify a fiat band near the Brillouin zone center that is close to the Fermi level and exhibits a pronounced temperature dependence. Such a fiat band can play an important role in dictating the transport properties of WTe2. Our results provide new insight on understanding the origin of the unusual magnetoresistance in WTe2.

Tunning the Band Gap of 1T’-WTe2 by Uniaxial Strain

The QSH edge channels can be used to connect dissipationless nanoelectronic devices, when the topological edge states and the bulk states have the perfectly spaced. But the monolayer 1T’-WTe2 bulk state is metallic nature, with edge channel lengths around 100 nm, which hinders its further study. By simulating the different terminational edge states, using the GGA-1/2 method to calculate, we found a stable terminational edge state. And under strain engineering, fixed the a-axis, the band gap gradually increases with the b-axis tensile. When the tensile to 2.9%, the band gap increases to 245 meV. It greatly improves the application of 1T’-WTe2. During the phase transition of the material from half-metal to insulator, the topology of edge states remains unchanged, showing strong robustness. Thus introducing strain can make 1T’-WTe2 a suitable material for fundamental research or topological electronic devices.

WTe2在室温下的红外纳米成像

本文用扫描散射近场光学显微镜(s-SNOM)在室温下研究了碲化钨(WTe 2)的近场光学响应,利用有限偶极模型计算了WTe 2样品与金刚石基底的近场散射信号比,发现观测结果并不能完全由块材所描述,从而推测出样品表面具有与块材无耦合作用的WTe 2纳米薄层,并对在样品边缘发现的很强的亮纹做出了可能的解释.这个工作为今后对拓扑材料的光学研究提供了参考.

Energy and materials recovery from post-recycling wastes:WTE

One of the most misunderstood technologies in some parts of the world and widely adopted technologies in others is the recovery of energy and materials by the controlled combustion of post-recycling wastes.This technology is commonly called waste-to-energy,or simply WTE.After all possible efforts for recycling or composting wastes,there remains a large post-recycling fraction that is either landfilled or used as fuel in WTE power plants that also recover metals and minerals.Several nations,e.g.,Switzerland,Japan,Sweden,Belgium,Denmark,and Germany,have succeeded in phasing out landfilling by processing all theãir post-recycling municipal solid wastes(MSW)in WTE power plants.This paper reviews the evolution and importance of WTE in the twenty-first century,with special focus on the world’s largest economies:the EU,US,and China.

Environmental standards and beneficial uses of waste-to-energy(WTE)residues in civil engineering applications

The waste-to-energy(WTE)technologies are now recovering energy and materials from over 300 million tonnes of municipal solid wastes worldwide.Extensive studies have investigated substituting natural construction materials with WTE residues to relieve the environmental cost of natural resource depletion.This study examined the beneficial uses of WTE residues in civil engineering applications and the corresponding environmental standards in Europe,the U.S.,and China.This review presents the opportunities and challenges for current technical approaches and the environmental standards to be met to stabilize WTE residues.The principal characteristics of WTE residues(bottom ash and fly ash)and the possible solutions for their beneficial use in developed and developing countries are summarized.The leaching procedures and environmental standards for pH,heavy metals,and polychlorinated dibenzo-p-dioxins/furans(PCDD/Fs)are compared.The current practice and engineering properties of materials using WTE residues,including mixtures with stone aggregate or sand,cement-based or hot-mix asphalt concrete(pavement),fill material in the embankments,substitute of Portland cement or clinker production,and ceramic-based materials(bricks and lightweight aggregate)are comprehensively reviewed.

Development of waste-to-energy through integrated sustainable waste management:the case of ABREN WtERT Brazil towards changing status quo in Brazil

In the context of circular economy,it is known that once waste is generated,it should be subject to proper treatment for recovering material or energy before being disposed.Many countries worldwide,especially developing countries such as Brazil,have been struggling to effectively apply sustainable waste management in municipalities and still rely on dumpsites and unsuitable landfills.Misinformation,a weak legal framework,lack of financial resources and poor infra-structure as well as pressure from organizations profiting from the expansion of landfills are some factors contributing to the preservation of the negative status quo:the“landfill culture”.Material recovery,i.e.,recycling and composting,is applied to less than 5%of Brazilian municipal waste,while 95%is disposed of in landfills or dumpsites.In this context,ABREN WtERT(Waste-to-Energy Research and Technology Council)Brazil was created in 2019 as the first permanent organization formed to promote the development of energy and material recovery from waste focused on the waste-to-energy(WTE)market.In this paper,the strategy proposed and implemented by the organization towards changing the status quo in Brazil through an integrated sustainable waste management approach is described.The proposed strategy integrates the concepts of Sustainability and Circular Economy for minimizing landfill disposal(avoiding methane emissions)and maximizing material/energy recovery.Among others,the approach focuses on changing the public opinion regarding thermal treatment facilities,mainly incinerators,which has been wrongly linked to pollution,excessive public expenditures and considered a harm to the recycling industry.The activities performed by ABREN include engaging public and private institutions,enhancing education,leading the publication of research and business studies,gathering industry members and academy experts,as well as creating strategic alliances with players around the globe.As a result,within a few years,major outcomes were achieved in Brazil,such as:(i)changes in the legal framework,(ii)launching of a specific public auction category for sponsoring electricity production from WTE facilities,and(iii)establishment of official targets for municipalities to decrease landfill disposal and increase recycling/biological treatment and energy recovery from thermal treatment.Among the national goals,it should be highlighted the target regarding the increase from zero to 994 MW of electricity production from municipal solid waste,which will require building dozens of new WTE facilities.Global outcomes are expected as well since Brazil is the seventh largest country of the globe and the most influential in Latin America.International and national business deals should thrive due to the need of operational skills and technology imports,and the avoidance of carbon emissions will positively reflect the world climate.In parallel,there is also potential for the academy to benefit from research projects and investments if the WTE national industry is to be developed in the long term.

离子液体插层导致的MoTe2,WTe2拓扑及超导性质的双重调控

使拓扑材料具有超导电性是实现拓扑超导的一个重要途径.Td相的MoTe2和WTe2不仅具有新颖的拓扑性质,其物理特性紧密依赖于层间耦合作用的强弱.本工作通过一种新颖的实验方法,在MoTe2和WTe2单晶样品中插入离子液体的有机阳离子,制备出层间距可调、性质稳定且超导增强的有机-无机复合样品.插层后的MoTe2样品属于三维弱拓扑绝缘体,超导转变温度从0.25 K大幅提高到了7 K;而插层后WTe2的超导转变温度提高到了具有量子自旋霍尔效应的单层WTe2的2.8倍(2.3 K).本工作通过插层离子液体的有机阳离子到MoTe2和WTe2样品中,实现对其拓扑及超导性质的双层调控,为后续研究拓扑超导、实现马约拉纳零模提供了新的机遇.另外,这一新方法具有普适性,可以广泛适用于各种层状材料,这将为在层状材料中探索和实现更多新颖物理性质提供便利.

Effects of defects on the electronic properties of WTe_2 armchair nanoribbons

We have investigated the electronic properties of WTe2 armchair nanoribbons with defects. WTe2 nanoribbons can be categorized depending on the edge structure in two types： armchair and zigzag. WTe2 in its bulk form has an indirect band gap but nanoribbons and nanosheets of WTe2 have direct band gaps. Interestingly, the zigzag nanoribbon is metallic while the armchair nanoribbons are semiconducting. Thus they can find applications in device fabrication. Therefore, it is very important to study the effect of defects on the electronic properties of the armchair nanoribbons as these defects can impair the device properties and characteristics. We have considered defects such as： vacancy, rough edge, wrap, ripple and twist in this work. We report the band gap variation with these defects. We have also studied the change in band gap and total energy with varying degrees of wrap, ripple and twist.

Passively Q-switched ytterbium-doped fiber laser using the evanescent field interaction with bulk-like WTe_2 particles

The potential of bulk-like WTe2 particles for the realization of a passive Q-switch operating at the 1 μm wavelength was investigated. The WTe2 particles were prepared using a simple mechanical exfoliation method together with Scotch tape. By attaching bulk-like WTe2 particles, which remained on the top of the sticky surface of a small segment of the Scotch tape, to the flat side of a side-polished fiber, a saturable absorber（SA） was readily implemented. A strong saturable absorption was then readily obtained through an evanescent field interaction with the WTe2 particles. The modulation depth of the prepared SA was measured as ~2.18% at 1.03 μm. By incorporating the proposed SA into an all-fiberized ytterbium-doped fiber ring cavity, stable Qswitched pulses were readily achieved.

Waste to energy(WTE)in China:from latecomer to front runner

This paper discusses the 2000-2018 evolution of energy and metals recovery from urban wastes in the European Union and China.As a result of the zero-landfilling directive,in twenty years the European Union tripled its recycling rate(11%-30%)and its composting rate(6%-17%),doubled its WTE rate(14%-28%)and more than halved its landfilling(64%-25%).At the beginning of this century,the rapidly growing cities of China were literally surrounded by landfills.Therefore,the national government instituted policies,such as a credit of US$30 per MWh of WTE(waste to energy)electricity that resulted in the construction,by 2020,of 510 WTE plants with an annual WTE capacity of 193 million tons.In comparison,the European Union(EU)WTE capacity is 96 million tons and the USA has remained static at about 27 million tons,i.e.,10%of its post-recycling MSW(municipal solid waste),with the other 90%being landfilled.In the first decade of this century,two WTE technologies,moving grate and circulating fluid bed were developed in China at about the same rate.However,since 2010,the moving grate technology has become dominant and the WTE plants are built functionally and esthetically comparable to and U.S.plants.

Formation mechanism of twin domain boundary in 2D materials: The case for WTe2

Our scanning tunneling microscopy (STM) study observes, for the first time, twin domain boundary (TDB) formations on the surface of WTe2 single crystal, which is glued by solidifying indium to Si substrate. In these TDB regions, a large inhomogeneous strain field, especially a critical shear strain of about 7%, is observed by geometric phase analysis. This observation does not obey the old believe that a small mechanical stress is sufficient to drive thermally-induced TDB formations in two-dimensional materials. To resolve the contradiction, we perform density functional theory calculations combined with elasticity theory analysis, which show that TDBs on WTe2 are entirely displacement-induced, for which a critical strain is necessary to overcome the onset barrier.

Carrier balance and linear magnetoresistance in type-II Weyl semimetal WTe2

Unsaturated magnetoresistance （MR） has been reported in type-II Weyl semimetal WTe2, manifested as a perfect compensation of opposite carriers. We report linear MR （LMR） in WTe2 crystals, the onset of which was identified by constructing the MR mobility spectra for weak fields. The LMR further increased and became dominant for fields stronger than 20 T, while the parabolic MR gradually decayed. The LMR was also observed in high-pressure conditions.

Quasiparticle interference and impurity resonances on WTe2

Using scanning tunneling microscopy/spectroscopy(STM/STS),we examine quasiparticle scattering and interference properties at the surface of WTe2.WTe2,layered transition metal dichalcogenide,is predicted to be a type-ll Weyl semimetal.The Weyl fermion states in WTe2 emerge as topologically protected touching points of electron and hole pockets,and Fermi arcs connecting them can be visible in the spectral function on the surface.To probe the properties of surface states,we have conducted low-temperature STM/STS(at 2.7 K)on the surfaces of WTe2 single crystals.We visualize the surface states of WTe2 with atomic scale resolution.Clear surface states emerging from the bulk electron pocket have been identified and their connection with the bulk electronic states shows good agreement with calculations.We show the interesting double resonance peaks in the local density of states appearing at localized impurities.The low-energy resonant peak occurs near the Weyl point above the Fermi energy and it may be mixed with the surface state of Weyl points,which makes it difficult to observe the topological nature of the Weyl semimetal WTe2.

基于频域抗混叠小波时间熵提取牵引器磁定位信息特征的研究

提出了一种依据牵引器接箍磁定位信息特征提取判断水平井套管接箍及射孔位置的新检测方法。利用Db4小波基函数对磁定位信息进行小波变换,阐述相邻尺度重构信号能量泄露和混叠的成因;以小波熵为理论基础,对基于小波时间熵(WTE)的小波频域抗混叠方法进行研究,采用概率统计法论证小波时间熵在小波频域抗混叠及特征提取方面的应用机理,并通过算例仿真验证该理论的正确性;以牵引器运行于模拟水平井所获得的磁定位信息为分析对象,利用小波时间熵算法提取套管射孔、接箍等信息特征并进行分析。理论分析及实验结果证明,对磁定位信号进行小波时间熵变换,能够降低由小波频域混叠现象导致的负面影响,对磁定位信息特征进行有效的提取和分类,并判定套管射孔及接箍位置。

国有土地上房屋被征收人的公平感知对征收补偿意愿的影响

研究目的:通过对国有土地上房屋被征收人的公平感知对征收决策的影响分析,尝试验证提高征收中的公平度并不一定会降低征收效率。研究方法:选取黄石市旧城改造区23个社区发放问卷,测量被征收人的公平感知和征收意愿、补偿意愿。运用结构方程模型对以上三者进行路径分析。研究结果:被征收人公平感知分为意图公平感知、过程公平感知、结果公平感知三维度,对被征收人的征收意愿具有正向影响,对被征收人的补偿意愿具有负向影响;被征收人的征收意愿在公平感知对补偿意愿的关系中起部分中介作用。研究结论:公平不一定与效率相对立,因此除了提高补偿价格之外,房屋征收政策制定还要注重征收目的的公益性和被征收人的知情权、参与权、选择权以及补偿的人际公平。