The measurement field of view of the conventional transmission electron microscopy(TEM)nano-moiréand scanning transmission electron microscopy(STEM)nano-moirémethods is limited to the hundred-nanometer scale...The measurement field of view of the conventional transmission electron microscopy(TEM)nano-moiréand scanning transmission electron microscopy(STEM)nano-moirémethods is limited to the hundred-nanometer scale,unable to meet the deformation field measurement requirements of micrometer-scale materials such as transistors and micro-devices.This paper proposed a novel measurement method based on scanning secondary moire,which can realize cross-scale deformation field measurement from nanometers to micrometers and solve the problem of insufficient measurement accuracy when using only the TEM moire method.This method utilized the electron wave in the TEM passing through the atomic lattice of two layers of different materials to generate TEM moire.On this basis,the TEM was tuned to the STEM mode,and by adjusting parameters such as the amount of defocusing,magnification,scanning angle,etc.,the electron beam was focused on the position near the interface of the two layers of materials,and at the same time,the scanning line was made approximately parallel to the direction of one of the TEM moire fringes.The scanning secondary moire patterns were generated when the scanning spacing was close to the TEM moire spacing.Through this method,the deformation field,mechanical properties,and internal defects of crystals can be detected by a large field of view with high sensitivity and high efficiency.Compared to traditional methods,the advantages of scanning secondary moire method lie in significantly improving the measurement field of TEM moire and STEM moire methods,realizing the cross-scale visualization measurement from nanometers to micrometers,and possessing atomic-level displacement measurement sensitivity.It can also simplify and efficiently identify dislocations,offering a new method for large-area visualization observation of dislocation density in broad application prospects.展开更多
A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can ef...A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can effectively improve detecting sensitivity of signals and simplify the control system by using only one pair of laser-Moiré sensors.We present the mathematical model and simulation results of diffracting two gratings.The effect of various parameters on Moiré signals is studied theoretically and experimentally,and the results are found to be consistent.A computer controlled alignment device using one pair of Moiré sensors is designed.The device can achieve a fully automatic precision alignment by the modified Moiré signal.The experimental result shows that the alignment device can obtain the resolution of 5 nm and the positioning accuracy of ±0 5 μm.展开更多
In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticl...In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticle excitations including holons,doublons and interlayer exciton insulators.Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators.Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier.The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites.For the interlayer exciton insulator consisting of a holon and a carrier in different layers,we have also obtained its effective Bohr radius and energy splitting between the ground and the first-excited states.展开更多
Moiré superlattices have revolutionized the study of two-dimensional materials, enabling unprecedented control over their electronic, magnetic, optical, and mechanical properties. This review provides a comprehen...Moiré superlattices have revolutionized the study of two-dimensional materials, enabling unprecedented control over their electronic, magnetic, optical, and mechanical properties. This review provides a comprehensive analysis of the latest advancements in moiré physics, focusing on the formation of moiré superlattices due to rotational misalignment or lattice mismatch in two-dimensional materials. These superlattices induce flat band structures and strong correlation effects,leading to the emergence of exotic quantum phases, such as unconventional superconductivity, correlated insulating states,and fractional quantum anomalous Hall effects. The review also explores the underlying mechanisms of these phenomena and discusses the potential technological applications of moiré physics, offering insights into future research directions in this rapidly evolving field.展开更多
The exertion of a long-period potential on two-dimensional(2D)systems leads to band-structure downfolding and the formation of mini flat bands,thereby providing a route for band engineering and enabling the realizatio...The exertion of a long-period potential on two-dimensional(2D)systems leads to band-structure downfolding and the formation of mini flat bands,thereby providing a route for band engineering and enabling the realization of new physical phenomena through the tuning of electron–electron interactions.In this work,the effect of the moiré superlattice formed between the substrate and the bottom quintuple layer(QL)of 3-and 4-QL three-dimensional(3D)topological insulator Sb_(2)Te_(3) thin films on the top surface states is investigated.The scanning tunneling spectra reveal that the bulk-like bands exhibit potential variations consistent with the moirépattern.In contrast,the surface states display only minimal potential variations,resulting in the absence of mini-band formation in the top surface states.These surface states remain nearly unaffected,as confirmed by Landau-level spectroscopy and simulations.The results suggest distinct roles of the bottom-surface moirépotential on the bulk states and the top surface states in the weak coupling regime between the two surfaces.展开更多
Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots(QD) realized on semiconductor moiré superlattices with a deep moiré po...Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots(QD) realized on semiconductor moiré superlattices with a deep moiré potential. We diagonalize single QD with multiple electrons, and find degenerate ground states serving as local degrees of freedom(qudits) in the superlattice. With a deep moiré potential, the hopping and exchange interaction between nearby QDs become irrelevant,and the direct Coulomb interaction of the density–density type dominates. Therefore, nearby QDs must arrange the spatial densities to optimize the Coulomb energy. When the local Hilbert space has a two-fold orbital degeneracy, we find that a square superlattice realizes an anisotropic XY model, while a triangular superlattice realizes a generalized XY model with geometric frustration.展开更多
Two-dimensional(2D)moirésuperlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle.Here...Two-dimensional(2D)moirésuperlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle.Here,we report a metal-semiconductor phase transition in homojunction moirésuperlattices of NiS_(2) and PtTe_(2) with large twist angles based on high-throughput screening of 2D materials MX_(2)(M=Ni,Pd,Pt;X=S,Se,Te)via density functional theory(DFT)calculations.Firstly,the calculations for different stacking configurations(AA,AB and AC)reveal that AA stacking ones are stable for all the bilayer MX_(2).The metallic or semiconducting properties of these 2D materials remain invariable for different stacking without twisting except for NiS_(2) and PtTe_(2).For the twisted configurations,NiS_(2) transfers from metal to semiconductor when the twist angles are 21.79°,27.79°,32.20°and 60°.PtTe_(2) exhibits a similar transition at 60°.The phase transition is due to the weakened d-p orbital hybridization around the Fermi level as the interlayer distance increases in the twisted configurations.Further calculations of untwisted bilayers with increasing interlayer distance demonstrate that all the materials undergo metal-semiconductor phase transition with the increased interlayer distance because of the weakened d-p orbital hybridization.These findings provide fundamental insights into tuning the electronic properties of moirésuperlattices with large twist angles.展开更多
Two-dimensional(2D)van der Waals(vdW)moiré superlattices have attracted significant attention due to their novel physical properties and quantum phenomena.The realization of these fascinating properties,however h...Two-dimensional(2D)van der Waals(vdW)moiré superlattices have attracted significant attention due to their novel physical properties and quantum phenomena.The realization of these fascinating properties,however heavily depends on the quality of the measured moiré superlattices,emphasizing the importance of advanced fabrication techniques.This review provides an in-depth discussion of the methods for fabricating moiré superlattices.It begins with a brief overview of the structure,properties,and potential applications of moiré superlattices,followed by a detailed examination of fabrication techniques,focuses on different kinds of transfer techniques and growth methods,particularly chemical vapor deposition(CVD)method.Finally,it addresses current challenges in fabricating high-quality moiré superlattices and discusses potential directions for future advancements in this field.This review will enhance the understanding of moiré superlattice fabrication and contributing to the continued development of 2D twistronics.展开更多
Moirésystems have emerged as an ideal platform for exploring interaction effects and correlated states.However,most of the experimental systems are based on either triangular or honeycomb lattices.In this study,b...Moirésystems have emerged as an ideal platform for exploring interaction effects and correlated states.However,most of the experimental systems are based on either triangular or honeycomb lattices.In this study,based on the self-consistent Hartree–Fock calculation,we investigate the phase diagram of the kagomélattice in a recently discovered system with two degenerateΓvalley orbitals and strong spin–orbit coupling.By focusing on the filling factors of 1/2,1/3 and 2/3,we identify various symmetry-breaking states by adjusting the screening length and dielectric constant.At the half filling,we discover that the spin–orbit coupling induces Dzyaloshinskii–Moriya interaction and stabilizes a classical magnetic state with 120°ordering.Additionally,we observe a transition to a ferromagnetic state with out-of-plane ordering.In the case of 1/3 filling,the system is ferromagnetically ordered due to the lattice frustration.Furthermore,for 2/3 filling,the system exhibits a pinned droplet state and a 120°magnetic ordered state at weak and immediate coupling strengths,respectively.For the strong coupling case,when dealing with non-integer filling,the system is always charge ordered with sublattice polarization.Our study serves as a starting point for exploring the effects of correlation in moirékagomésystems.展开更多
Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafas...Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafast and coherent method of manipulating matter states,which,however,has not been demonstrated in moirématerials.Here,we report the valleyselective optical Stark effect of moiréexcitons in the WSe_(2)/WS_(2)superlattice by using transient reflection spectroscopy.Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiréexcitons,corresponding to pseudomagnetic fields as large as 34 T.Our results provide a route to coherently manipulate exotic states in moirésuperlattices.展开更多
In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. Howeve...In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. However, a special beam scanning control device is required to produce a grating and generate a moiré fringe pattern for the scanning electron microscope （SEM）. Because only a few SEMs used in the material science studies are equipped with this device, the use of the electron moiré method is limited. In this study, an electron moiré method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any observing mode. A real-time moiré pattern can also be generated in the SEM or an optical filtering system. Without the beam control device being a prerequisite, the electron moiré method can be more widely used. The experimental results from three different types of SEMs show that high quality gratings with uniform lines and less pitch error can be fabricated by this method, and moiré patterns can also be correctly generated.展开更多
Nano-moiré method presented in this paper is an experimental technique which allows direct measurement of nanoscopic mechanical parameters, such as displacement, strain and dislocation distribution. The basic ide...Nano-moiré method presented in this paper is an experimental technique which allows direct measurement of nanoscopic mechanical parameters, such as displacement, strain and dislocation distribution. The basic idea is the formation of moiré fringes when a HREM (high resolution electron microscopy) image of crystal material is superimposed with a unidirectional grating. Fourier filtering technique is used to increase the contrast of fringes and to multiple the fringes. This method has atom-size sensitivity and spatial resolution, and relatively large range. It provides a new experimental technique with very high sensitivity and spatial resolution for nanomechanics.展开更多
Moiré superlattices are formed when overlaying two materials with a slight mismatch in twist angle or lattice constant. They provide a novel platform for the study of strong electronic correlations and non-trivia...Moiré superlattices are formed when overlaying two materials with a slight mismatch in twist angle or lattice constant. They provide a novel platform for the study of strong electronic correlations and non-trivial band topology, where emergent phenomena such as correlated insulating states, unconventional superconductivity, and quantum anomalous Hall effect are discovered. In this review, we focus on the semiconducting transition metal dichalcogenides(TMDs) based moiré systems that host intriguing flat-band physics. We first review the exfoliation methods of two-dimensional materials and the fabrication technique of their moiré structures. Secondly, we overview the progress of the optically excited moiré excitons, which render the main discovery in the early experiments on TMD moiré systems. We then introduce the formation mechanism of flat bands and their potential in the quantum simulation of the Hubbard model with tunable doping, degeneracies, and correlation strength. Finally, we briefly discuss the challenges and future perspectives of this field.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12372178 and 12327801).
文摘The measurement field of view of the conventional transmission electron microscopy(TEM)nano-moiréand scanning transmission electron microscopy(STEM)nano-moirémethods is limited to the hundred-nanometer scale,unable to meet the deformation field measurement requirements of micrometer-scale materials such as transistors and micro-devices.This paper proposed a novel measurement method based on scanning secondary moire,which can realize cross-scale deformation field measurement from nanometers to micrometers and solve the problem of insufficient measurement accuracy when using only the TEM moire method.This method utilized the electron wave in the TEM passing through the atomic lattice of two layers of different materials to generate TEM moire.On this basis,the TEM was tuned to the STEM mode,and by adjusting parameters such as the amount of defocusing,magnification,scanning angle,etc.,the electron beam was focused on the position near the interface of the two layers of materials,and at the same time,the scanning line was made approximately parallel to the direction of one of the TEM moire fringes.The scanning secondary moire patterns were generated when the scanning spacing was close to the TEM moire spacing.Through this method,the deformation field,mechanical properties,and internal defects of crystals can be detected by a large field of view with high sensitivity and high efficiency.Compared to traditional methods,the advantages of scanning secondary moire method lie in significantly improving the measurement field of TEM moire and STEM moire methods,realizing the cross-scale visualization measurement from nanometers to micrometers,and possessing atomic-level displacement measurement sensitivity.It can also simplify and efficiently identify dislocations,offering a new method for large-area visualization observation of dislocation density in broad application prospects.
文摘A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can effectively improve detecting sensitivity of signals and simplify the control system by using only one pair of laser-Moiré sensors.We present the mathematical model and simulation results of diffracting two gratings.The effect of various parameters on Moiré signals is studied theoretically and experimentally,and the results are found to be consistent.A computer controlled alignment device using one pair of Moiré sensors is designed.The device can achieve a fully automatic precision alignment by the modified Moiré signal.The experimental result shows that the alignment device can obtain the resolution of 5 nm and the positioning accuracy of ±0 5 μm.
基金support by the National Natural Sci-ence Foundation of China(Grant No.12274477)the De-partment of Science and Technology of Guangdong Provincein China(Grant No.2019QN01X061)。
文摘In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticle excitations including holons,doublons and interlayer exciton insulators.Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators.Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier.The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites.For the interlayer exciton insulator consisting of a holon and a carrier in different layers,we have also obtained its effective Bohr radius and energy splitting between the ground and the first-excited states.
基金Project supported by the National Key R&D Program of China (Grant No. 2019YFA0307800)the National Natural Science Foundation of China (Grant No. 12074377)+2 种基金Fundamental Research Funds for the Central Universities,the International Partnership Program of Chinese Academy of Sciences (Grant No. 211211KYSB20210007)the China Postdoctoral Science Foundation (Grant No. 2024M753465)the Postdoctoral Fellowship Program (Grade C) of China Postdoctoral Science Foundation (Grant No. GZC20241893)。
文摘Moiré superlattices have revolutionized the study of two-dimensional materials, enabling unprecedented control over their electronic, magnetic, optical, and mechanical properties. This review provides a comprehensive analysis of the latest advancements in moiré physics, focusing on the formation of moiré superlattices due to rotational misalignment or lattice mismatch in two-dimensional materials. These superlattices induce flat band structures and strong correlation effects,leading to the emergence of exotic quantum phases, such as unconventional superconductivity, correlated insulating states,and fractional quantum anomalous Hall effects. The review also explores the underlying mechanisms of these phenomena and discusses the potential technological applications of moiré physics, offering insights into future research directions in this rapidly evolving field.
基金the supporting from the National Key R&D Program of China(Grant No.2022YFA1403102)the National Natural Science Foundation of China(Grant Nos.12474478,92065102,and 12574094)。
文摘The exertion of a long-period potential on two-dimensional(2D)systems leads to band-structure downfolding and the formation of mini flat bands,thereby providing a route for band engineering and enabling the realization of new physical phenomena through the tuning of electron–electron interactions.In this work,the effect of the moiré superlattice formed between the substrate and the bottom quintuple layer(QL)of 3-and 4-QL three-dimensional(3D)topological insulator Sb_(2)Te_(3) thin films on the top surface states is investigated.The scanning tunneling spectra reveal that the bulk-like bands exhibit potential variations consistent with the moirépattern.In contrast,the surface states display only minimal potential variations,resulting in the absence of mini-band formation in the top surface states.These surface states remain nearly unaffected,as confirmed by Landau-level spectroscopy and simulations.The results suggest distinct roles of the bottom-surface moirépotential on the bulk states and the top surface states in the weak coupling regime between the two surfaces.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12274005)the National Key Research and Development Program of China (Grant No. 2021YFA1401903)Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302403)。
文摘Moiré superlattices provide a new platform to engineer various many-body problems. In this work, we consider arrays of quantum dots(QD) realized on semiconductor moiré superlattices with a deep moiré potential. We diagonalize single QD with multiple electrons, and find degenerate ground states serving as local degrees of freedom(qudits) in the superlattice. With a deep moiré potential, the hopping and exchange interaction between nearby QDs become irrelevant,and the direct Coulomb interaction of the density–density type dominates. Therefore, nearby QDs must arrange the spatial densities to optimize the Coulomb energy. When the local Hilbert space has a two-fold orbital degeneracy, we find that a square superlattice realizes an anisotropic XY model, while a triangular superlattice realizes a generalized XY model with geometric frustration.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52472153,11704081,62488201)the National Key Research and Development Program of China(Grant No.2022YFA1204100)+2 种基金National Science and Technology Innovation Talent Cultivation Program(Grant No.2023BZRC016)Guangxi Natural Science Foundation(Grant No.2020GXNSFAA297182)the special fund for“Guangxi Bagui Scholars”。
文摘Two-dimensional(2D)moirésuperlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle.Here,we report a metal-semiconductor phase transition in homojunction moirésuperlattices of NiS_(2) and PtTe_(2) with large twist angles based on high-throughput screening of 2D materials MX_(2)(M=Ni,Pd,Pt;X=S,Se,Te)via density functional theory(DFT)calculations.Firstly,the calculations for different stacking configurations(AA,AB and AC)reveal that AA stacking ones are stable for all the bilayer MX_(2).The metallic or semiconducting properties of these 2D materials remain invariable for different stacking without twisting except for NiS_(2) and PtTe_(2).For the twisted configurations,NiS_(2) transfers from metal to semiconductor when the twist angles are 21.79°,27.79°,32.20°and 60°.PtTe_(2) exhibits a similar transition at 60°.The phase transition is due to the weakened d-p orbital hybridization around the Fermi level as the interlayer distance increases in the twisted configurations.Further calculations of untwisted bilayers with increasing interlayer distance demonstrate that all the materials undergo metal-semiconductor phase transition with the increased interlayer distance because of the weakened d-p orbital hybridization.These findings provide fundamental insights into tuning the electronic properties of moirésuperlattices with large twist angles.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52425203 and 12104218)the the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20240008 and BK20241252)+2 种基金the China National Postdoctoral Program for Innovative Talents(Grant No.BX2021120)the Xiaomi Foundation,the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20231093)Jiangsu Funding Program for Excellent Postdoctoral Talent(Grant No.2023ZB553).
文摘Two-dimensional(2D)van der Waals(vdW)moiré superlattices have attracted significant attention due to their novel physical properties and quantum phenomena.The realization of these fascinating properties,however heavily depends on the quality of the measured moiré superlattices,emphasizing the importance of advanced fabrication techniques.This review provides an in-depth discussion of the methods for fabricating moiré superlattices.It begins with a brief overview of the structure,properties,and potential applications of moiré superlattices,followed by a detailed examination of fabrication techniques,focuses on different kinds of transfer techniques and growth methods,particularly chemical vapor deposition(CVD)method.Finally,it addresses current challenges in fabricating high-quality moiré superlattices and discusses potential directions for future advancements in this field.This review will enhance the understanding of moiré superlattice fabrication and contributing to the continued development of 2D twistronics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12350404 and 12174066)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302600)+1 种基金the National Key Research and Development Program of China(Grant No.2019YFA0308404)the Science and Technology Commission of Shanghai Municipality(Grant Nos.23JC1400600 and 2019SHZDZX01)。
文摘Moirésystems have emerged as an ideal platform for exploring interaction effects and correlated states.However,most of the experimental systems are based on either triangular or honeycomb lattices.In this study,based on the self-consistent Hartree–Fock calculation,we investigate the phase diagram of the kagomélattice in a recently discovered system with two degenerateΓvalley orbitals and strong spin–orbit coupling.By focusing on the filling factors of 1/2,1/3 and 2/3,we identify various symmetry-breaking states by adjusting the screening length and dielectric constant.At the half filling,we discover that the spin–orbit coupling induces Dzyaloshinskii–Moriya interaction and stabilizes a classical magnetic state with 120°ordering.Additionally,we observe a transition to a ferromagnetic state with out-of-plane ordering.In the case of 1/3 filling,the system is ferromagnetically ordered due to the lattice frustration.Furthermore,for 2/3 filling,the system exhibits a pinned droplet state and a 120°magnetic ordered state at weak and immediate coupling strengths,respectively.For the strong coupling case,when dealing with non-integer filling,the system is always charge ordered with sublattice polarization.Our study serves as a starting point for exploring the effects of correlation in moirékagomésystems.
基金Project supported by the National Key R&D Program of China(Grant Nos.2022YFA1402400 and 2022YFA1405400)the National Natural Science Foundation of China(Grant Nos.11934011 and 12274365)+3 种基金Zhejiang Provincial Natural Science Foundation of China(Grant No.LR24A040001)Open project of Key Laboratory of Artificial Structures and Quantum Control(Ministry of Education)of Shanghai Jiao Tong Universitysupport from the JSPS KAKENHI(Grant Nos.20H00354 and 23H02052)World Premier International Research Center Initiative(WPI),MEXT,Japan。
文摘Semiconductor moirésuperlattices provide great platforms for exploring exotic collective excitations.Optical Stark effect,a shift of the electronic transition in the presence of a light field,provides an ultrafast and coherent method of manipulating matter states,which,however,has not been demonstrated in moirématerials.Here,we report the valleyselective optical Stark effect of moiréexcitons in the WSe_(2)/WS_(2)superlattice by using transient reflection spectroscopy.Prominent valley-selective energy shifts up to 7.8 meV have been observed for moiréexcitons,corresponding to pseudomagnetic fields as large as 34 T.Our results provide a route to coherently manipulate exotic states in moirésuperlattices.
基金The project supported by the National Natural Science Foundation of China (10662005)JSPS fellowship in Japan.
文摘In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. However, a special beam scanning control device is required to produce a grating and generate a moiré fringe pattern for the scanning electron microscope （SEM）. Because only a few SEMs used in the material science studies are equipped with this device, the use of the electron moiré method is limited. In this study, an electron moiré method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any observing mode. A real-time moiré pattern can also be generated in the SEM or an optical filtering system. Without the beam control device being a prerequisite, the electron moiré method can be more widely used. The experimental results from three different types of SEMs show that high quality gratings with uniform lines and less pitch error can be fabricated by this method, and moiré patterns can also be correctly generated.
基金The project supported by the National Natural Science Foundation of China
文摘Nano-moiré method presented in this paper is an experimental technique which allows direct measurement of nanoscopic mechanical parameters, such as displacement, strain and dislocation distribution. The basic idea is the formation of moiré fringes when a HREM (high resolution electron microscopy) image of crystal material is superimposed with a unidirectional grating. Fourier filtering technique is used to increase the contrast of fringes and to multiple the fringes. This method has atom-size sensitivity and spatial resolution, and relatively large range. It provides a new experimental technique with very high sensitivity and spatial resolution for nanomechanics.
基金supported by the National Natural Science Foundation of China(Grant Nos.62022089,12174439,11874405,52272135,62274010,61971035)the National Key Research and Development Program of China(Grant Nos.2019YFA0308000,2021YFA1401300,2021YFA1401800,2018YFA0704200,2021YFA1400100,2020YFA0308800)+2 种基金Chongqing Outstanding Youth Fund(Grant No.2021ZX0400005)Beijing Institute of Technology Science and Technology Innovation Program Innovative Talent Science and Technology Funding SpecialProgram(No.2022CX01022)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant Nos.XDB33000000)。
文摘Moiré superlattices are formed when overlaying two materials with a slight mismatch in twist angle or lattice constant. They provide a novel platform for the study of strong electronic correlations and non-trivial band topology, where emergent phenomena such as correlated insulating states, unconventional superconductivity, and quantum anomalous Hall effect are discovered. In this review, we focus on the semiconducting transition metal dichalcogenides(TMDs) based moiré systems that host intriguing flat-band physics. We first review the exfoliation methods of two-dimensional materials and the fabrication technique of their moiré structures. Secondly, we overview the progress of the optically excited moiré excitons, which render the main discovery in the early experiments on TMD moiré systems. We then introduce the formation mechanism of flat bands and their potential in the quantum simulation of the Hubbard model with tunable doping, degeneracies, and correlation strength. Finally, we briefly discuss the challenges and future perspectives of this field.
