Band engineering of valleytronics WSe_(2)–MoS_(2)heterostructures via stacking form,magnetic moment and thickness

Spin-valley polarization and bandgap regulation are critical in the developing of quantum devices.Here,by employing the density functional theory,we investigate the effects of stacking form,thickness and magnetic moment in the electronic structures of WSe_(2)–MoS_(2)heterostructures.Calculations show that spin-valley polarization maintains in all situations.Increasing thickness of 2H-MoS_(2)not only tunes the bandgap but also changes the degeneracy of the conduction band minimums(CBM)at K/K_(1) points.Gradual increase of micro magnetic moment tunes the bandgap and raises the valence band maximums(VBM)atΓpoint.In addition,the regulation of band gap by the thickness of 2H-MoS_(2)and introduced magnetic moment depends on the stacking type.Results suggest that WSe_(2)–MoS_(2)heterostructure supports an ideal platform for valleytronics applications.Our methods also give new ways of optical absorption regulation in spin-valley devices.

Magnetic proximity effect in the two-dimensional ε-Fe_(2)O_(3)/NbSe_(2)heterojunction

Two-dimensional(2D)magnet/superconductor heterostructures can promote the design of artificial materials for exploring 2D physics and device applications by exotic proximity effects.However,plagued by the low Curie temperature and instability in air,it is hard to realize practical applications for the reported layered magnetic materials at present.In this paper,we developed a space-confined chemical vapor deposition method to synthesize ultrathin air-stable ε-Fe_(2)O_(3) nanosheets with Curie temperature above 350 K.The ε-Fe_(2)O_(3)/NbSe_(2) heterojunction was constructed to study the magnetic proximity effect on the superconductivity of the NbSe_(2) multilayer.The electrical transport results show that the subtle proximity effect can modulate the interfacial spin–orbit interaction while undegrading the superconducting critical parameters.Our work paves the way to construct 2D heterojunctions with ultrathin nonlayered materials and layered van der Waals(vdW)materials for exploring new physical phenomena.

Visualizing the Local Twist Angle Variation within and between Domains of Twisted Bilayer Graphene

Moirésuperlattices in twisted two-dimensional materials have emerged as ideal platforms for engineering quantum phenomena,which are highly sensitive to twist angles,including both the global value and the spatial inhomogeneity.However,only a few methods provide spatial-resolved information for characterizing local twist angle distribution.

Enhanced resonance frequency in Co2FeAl thin film with different thicknesses grown on flexible graphene substrate

The flexible materials exhibit more favorable properties than most rigid substrates in flexibility,weight saving,mechanical reliability,and excellent environmental toughness.Particularly,flexible graphene film with unique mechanical properties was extensively explored in high frequency devices.Herein,we report the characteristics of structure and magnetic properties at high frequency of Co2FeAl thin film with different thicknesses grown on flexible graphene substrate at room temperature.The exciting finding for the columnar structure of Co2FeAl thin film lays the foundation for excellent high frequency property of Co2FeAl/flexible graphene structure.In-plane magnetic anisotropy field varying with increasing thickness of Co2FeAl thin film can be obtained by measurement of ferromagnetic resonance,which can be ascribed to the enhancement of crystallinity and the increase of grain size.Meanwhile,the resonance frequency which can be achieved by the measurement of vector network analyzer with the microstrip method increases with increasing thickness of Co2FeAl thin film.Moreover,in our case with graphene film,the resonance magnetic field is quite stable though folded for twenty cycles,which demonstrates that good flexibility of graphene film and the stability of high frequency magnetic property of Co2FeAl thin film grown on flexible graphene substrate.These results are promising for the design of microwave devices and wireless communication equipment.

A New Mechanism Responsible for the Enhancement of Local Electric Field on the Surface of Emitting Carbon Nanotubes

Aligned carbon nanotube (CNRT) films exhibit excellent electron emission properties at very low fields. This has been attributed to the high aspect ratio of CNTs, I.e. Their emitting surface can have high local field due to geometrical enhancement. It is found that a new mechanism can be responsible for the enhancement of the local field on the emitting surface of CNTs. This results from the space charge in the vacuum gap, which is readily generated due to the high emission current density of CNTs. Details are given of both experimental and theoretical studies of this effect. The mechanism also accounts for the distinct nonlinearity in Fowler-Nordheim plots often observed with CNTs. The implication of the technical application of our findings is also included.

Measurement of Binding Force between Microtubule-Associated Protein and Microtubule

联系微导管的蛋白质(地图) 是在房间的重要蛋白质。Theycan 调整微导管的组织，动力学和功能。我们测量在微导管和一张新植物地图之间的有约束力的力量，即 AtMAP65-1，由双光的镊子。力量被获得是从数据统计和分析的 14.6 +/- 3.5pN。这力量大小是有用的从机械观点理解地图的功能和机制并且为另外的 biologicalmacro 分子的机械性质的未来大小放地基。

Analysis of Step Etching on SrTiO_(3) Substrates for the Step-Edge YBCO Josephson Junctions

A way to determine some important etching parameters in the step fabrication for highTc step-edge Josephson junctions is described based on an analysis of the dynamics of the etching process.The optimum thickness of the etch mask is defined with negligible recession of the mask edge during the etch.Under this condition,the equilibrium angle of the steps etched on the SrTiO_(3)(STO)substrate with an Nb mask has been calculated to be about 76°.With optimized mask thickness,its sharp sidewall and straight edge,high-quality steps on STO substrates with step height from 200-300 nm and step angle above 70°are made.Josephson junctions and dc-SQUIDs with high reproducibility and less parameter scatter are obtained on the step substrates.

Effects of Spherical Aberration on Optical Trapping Forces for Rayleigh Particles

The Trapping force on Rayleigh particles in an optical tweezers system with an oil immersion objective is calculated by an electromagnetic model.The results indicate that the stability of particles trapped will be affected by spherical aberration,which is caused by refractive difference between objective oil and water solution,when the specimen manipulated is suspended in a water solution.The trapping force and depth of potential well will decrease and the minimum of laser power for ensuring the stability of particles trapped will increase with the enhancing trapping depth.

Power Law Behavior of the Zero Bias Tunneling Conductance:the New Evidence for d-Wave Symmetry

We report temperature-dependent behavior of the zero bias tunneling conductance(ZBTC),derived from tun neling spectroscopies on as-grown Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)single crystals taken with evaporated Zn and Pb planar junctions.At Tc the measured ZBTC shows a kink which gives an in situ measure of the superconducting transition temperature(T_(c)).Below T_(c),the T^(2)dependence of the ZBTC has been observed repeatedly as a new evidence of the d-wave symmetry in Bi2212.

Berry Phases for Many-Spin Systems with Anisotropy Exchange Interaction in a Strong Magnetic Field

Au approximate instantaneous eigenstate is presented for the many-spin system possessing the anisotropy exchange interaction in a strong magnetic field by the perturbation method.Based on the instantaneous eigenstate,the Berry phase of this state is worked out.Furthermore,the effect of the anisotropy exchange interaction on the Berry phase of the state for the many-spin system is studied.

Magnetization Reversal Processes in Pt/Co Multilayers Studied by a Magnetic Force Microscope

We have studied the magnetic reversal process of the magnetron sputtered Pt/Co multilayers by using magnetic force microscope with in situ bias magnetic fields.In thin films magnetic reversal is usually dominated either by domain nucleation or by domain wall motion.In our experiments,a series of magnetic images in situ captured in the same area indicates that the magnetic reversal in Pt/Co multilayers is dominated by domain nucleation,in stead of domain wall motion.In addition,the local demagnetized curve was obtained by using the bearing analysis of the domains in the series of magnetic images.

A Novel Titania Membrane with Uniform Macropores

A procedure for fabricating novel TiO_(2) membrane materialwith sub-micrometre pores and large specific surface area from the template has been demonstrated. The morphology and structure of the membrane have been characterized by scanning electron microscopy. The results have indicated that the macroporous membraneconsists of uniform hollow spheres which are interconnected to each other by 'small windows'. Potential unique applications of this macroporous materialin the fields of catalysis, optics, sensors, etc, are suggested.

Accurate determination of anisotropic thermal conductivity for ultrathin composite film

Highly anisotropic thermal conductive materials are of significance in thermal management applications. However,accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance,severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide(MMT/r GO) composite film with a thickness range from 0.2 μm to2 μm. The in-plane thermal conductivity measurement is realized by one-dimensional(1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.

Optically Detected Magnetic Resonance of Diamond Nitrogen-Vacancy Centers under Megabar Pressures

Megabar pressures are of crucial importance for cutting-edge studies of condensed matter physics and geophysics.With the development of diamond anvil cell(DAC),laboratory studies of high pressure have entered the megabar era for decades.However,it is still challenging to implement in situ magnetic sensing under ultrahigh pressures.In this work,we demonstrate optically detected magnetic resonance and coherent quantum control of diamond nitrogen-vacancy(NV)center,a promising quantum sensor inside the DAC,up to 1.4 Mbar.The pressure dependence of optical and spin properties of NV centers in diamond are quantified,and the evolution of an external magnetic field has been successfully tracked at about 80 GPa.These results shed new light on our understanding of diamond NV centers and pave the way for quantum sensing under extreme conditions.

Highly flexible and excellent performance continuous carbon nanotube fibrous thermoelectric modules for diversified applications

A highly flexible and continuous fibrous thermoelectric(TE)module with high-performance has been fabricated based on an ultra-long single-walled carbon nanotube fiber,which effectively avoids the drawbacks of traditional inorganic TE based modules.The maximum output power density of a 1-cm long fibrous TE module with 8 p–n pairs can reach to 3436μW·cm^(-2),the power per unit weight to 2034μW·g^(-1),at a steady-state temperature difference of 50 K.The continuous fibrous TE module is used to detect temperature change of a single point,which exhibits a good responsiveness and excellent stability.Because of its adjustability in length,the flexible fibrous TE module can satisfy the transformation of the temperature difference between two distant heat sources into electrical energy.Based on the signal of the as-fabricated TE module,a multi-region recognizer has been designed and demonstrated.The highly flexible and continuous fibrous TE module with excellent performance shows a great potential in diversified applications of TE generation,temperature detection,and position identification.

Electronic states of domain walls in commensurate charge density wave ground state and mosaic phase in 1T-TaS_(2)

Domain walls(DWs)in the charge-density-wave(CDW)Mott insulator 1T-TaS_(2)have unique localized states,which play an important role in exploring the electronic properties of the material.However,the electronic states in DWs in 1TTaS_(2)have not been clearly understood,mostly due to the complex structures,phases,and interlayer stacking orders in the DW areas.Here,we explored the electronic states of DWs in the large-area CDW phase and mosaic phase of 1T-TaS_(2)by scanning tunneling spectroscopy.Due to the different densities of DWs,the electronic states of DWs show distinct features in these phases.In the large area CDW phase,both the domain and the DWs(DW1,DW2,DW4)have zero conductance at the Fermi level;while in the mosaic phase,they can be metallic or insulating depending on their environments.In areas with a high density of DWs,some electronic states were observed both on the DWs and within the domains,indicating delocalized states over the whole region.Our work contributes to further understanding of the interplay between CDW and electron correlations in 1T-TaS_(2).

Controlled crossover of electron transport in graphene nanoconstriction:From Coulomb blockade to electron interference

The ability to control transport behaviors in nanostructure is crucial for usage as a fundamental research platform as well as a practical device.In this study,we report a gate-controlled crossover of electron transport behaviors using graphene nanoconstrictions as a platform.The observed transport properties span from Coulomb blockade-dominated single electron transmission to electron-wave interference-dominated quantum behavior.Such drastic modulation is achieved by utilizing a single back gate on a graphene nanoconstriction structure,where the size of nanostructure in the constriction and coupling strength of it to the electrodes can be tuned electrically.Our results indicate that electrostatic field by gate voltage upon the confined nanostructure defines both the size of the nanoconstriction as well as its interaction to electrodes.Increasing gate voltage raises Fermi level to cross the energy profile in the nanoconstriction,resulting in decreased energy barriers which affect the size of nanoconstriction and transmissivity of electrons.The gate-tunable nanoconstriction device can therefore become a potential platform to study quantum critical behaviors and enrich electronic and spintronic devices.

Fabrication of honeycomb AuTe monolayer with Dirac nodal line fermions

Two-dimensional honeycomb lattices show great potential in the realization of Dirac nodal line fermions(DNLFs).Here,we successfully synthesized a gold telluride(AuTe)monolayer by direct tellurizing an Au(111)substrate.Low energy electron diffraction measurements reveal that it is(2×2)AuTe layer stacked onto(3×3)Au(111)substrate.Moreover,scanning tunneling microscopy images show that the AuTe layer has a honeycomb structure.Scanning transmission electron microscopy reveals that it is a single-atom layer.In addition,first-principles calculations demonstrate that the honeycomb AuTe monolayer exhibits Dirac nodal line features protected by mirror symmetry,which is validated by angle-resolved photoemission spectra.Our results establish that monolayer AuTe can be a good candidate to investigate 2D DNLFs and provides opportunities to realize high-speed low-dissipation devices.

A Reflected Terahertz-Emission Microscopy

新奇反映的兆兆赫排放显微镜学为改进 THz 成像的空间决定被建议并且发展。当直接依附一条鞠躬关系天线到薄产生晶体上时，反映的 THz 波浪能由一条光导的天线镇定、检测，并且空间决定被集中的泵横梁的直径决定。这样，检测决定能大部分被改进并且悦耳。这显微镜学的配置和特征详细被描述。

Optical properties of the direct-coupled Y-branch filters by using photonic crystal slabs

We fabricated a new type of two-dimensional photonic crystal slab filter. The resonant cavities were directly put into the waveguide arms. The optical transmissions of the filters were measured and the results show that the optimized two-channel filters give good intensity distribution at the output ports of the waveguide. A minimum wavelength spacing of 5 nm of the filter outputs is realized by accurately controlling the size of the resonant cavities.