Moiré superlattices arising from growth induced by screw dislocations in layered materials

Moiré superlattices(MSLs) are modulated structures produced from homogeneous or heterogeneous two-dimensional layers stacked with a twist angle and/or lattice mismatch. Enriching the methods for fabricating MSL and realizing the unique emergent properties are key challenges in its investigation. Here we recommend that the spiral dislocation driven growth is another optional method for the preparation of high quality MSL samples. The spiral structure stabilizes the constant out-of-plane lattice distance, causing the variations in electronic and optical properties. Taking SnS_(2) MSL as an example, we find prominent properties including large band gap reduction(~ 0.4 e V) and enhanced optical activity. Firstprinciples calculations reveal that these unusual properties can be ascribed to the locally enhanced interlayer interaction associated with the Moiré potential modulation. We believe that the spiral dislocation driven growth would be a powerful method to expand the MSL family and broaden their scope of application.

Peak structure in the interlayer conductance of Moirésuperlattices

We investigate the peak structure in the interlayer conductance of Moirésuperlattices using a tunneling theory wedeveloped previously.The theoretical results predict that,due to the resonance of two different partial waves,the doublepeakstructure can appear in the curve of the interlayer conductance versus twist angle.Furthermore,we study the influencesof the model parameters,i.e.,the chemical potential of electrodes,the thickness of Moirésuperlattice,and the strength ofinterface potential,on the peak structure of the interlayer conductance.In particular,the parameter dependence of the peakstructure is concluded via a phase diagram,and the physical meanings of the phase diagram is formulized.Finally,thepotential applications of the present work is discussed.

Theory and verification of moiréfringes for x-ray three-phase grating interferometer

Dual-phase and three-phase grating x-ray interference is a promising new technique for grating-based x-ray differential phase contrast imaging.Dual-phase grating interferometers have been relatively completely studied and discussed.In this paper,the corresponding imaging fringe formula of the three-phase grating interferometer is provided.At the same time,the similarities and differences between the three-phase grating interferometer and the dual-phase grating interferometer are investigated and verified,and that the three-phase grating interferometer can produce large-period moiréfringes without using the analyzing grating is demonstrated experimentally.Finally,a simple method of designing three-phase grating and multi-grating imaging systems from geometric optics based on the thin-lens theory of gratings is presented.These theoretical formulas and experimental results provide optimization tools for designing three-phase grating interferometer systems.

Ultra-precision alignment technique based on modified Moiré signals

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.

基于Talbot-Moiré效应长焦测焦仪的设计及校准技术研究

为了满足100m^3km特长焦距参量的测试校准需求,采用Talbot-Moiré条纹技术法,设计了一套长焦测焦仪.针对影响仪器测量不确定度的系统参量,分别设计了校准方法,并对仪器测量不确定度评定结果进行了实验比对验证.结果表明,校准后仪器测量不确定度评定为6.4%;校准后的长焦测焦仪测量结果与刀口仪测量结果满足测量不确定度比对公式;对比结果最大为0.64,小于1;长焦测焦仪测量不确定度评定合理.该研究验证了长焦测焦仪系统参量校准方法的可行性.

Moire光纤光栅的原理及应用

Moire光纤光栅是近几年出现的新型光纤器件 ,有其特有的性质 ,被广泛用于波分复用系统( WDM)中的多带通滤波、色散补偿以及通道选择等方面。文中系统介绍了 Moire光纤光栅的原理和工作特性 ,同时介绍了最新的研究动态。

An electron moir■ method for a common SEM

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.

NANO-MOIRE METHOD

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.

平面有限变形与转动的Moiré几何学

本文论证有限变形理论中的拖带坐标系描述法和近年来发展的实验应变分析的Moiré方法,在数学基础上是同一.因此从Moiré几何学进一步肯定文[12]提出几何场论的重要实用意义。

基于啁啾Moire光纤布拉格光栅的波分复用/解复用器件的理论分析(英文)

对基于啁啾Moire光纤布拉格光栅的波分复用/解复用器件进行了理论分析。用传输矩阵法计算了Moire光栅的透射谱特性,可知其透射谱具有多个通带及好的通道隔离度。通过调整光栅参数可获得通道间隔满足国际电信联盟标准的Moire光栅。

啁啾Moire光栅波分复用/解复用器件的理论分析

根据耦合模理论 ,用传输矩阵法计算了啁啾Moire光栅的透射谱特性 ,分析表明其透射谱具有多个通带及好的通道隔离度

Recent progress on fabrication and flat-band physics in 2D transition metal dichalcogenides moiré superlattices

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.

物理光学方法分析Moire偏折法

本文在物理光学领域里,严格分析了 Moire 偏折法的测试原理和特性,获得了一些关于 Moire 偏折法的新的和严格的结论。实验证实了本文的结论。

Review of phonons in moiré superlattices

Moirépatterns in physics are interference fringes produced when a periodic template is stacked on another similar one with different displacement and twist angles.The phonon in two-dimensional(2D)material affected by moirépatterns in the lattice shows various novel physical phenomena,such as frequency shift,different linewidth,and mediation to the superconductivity.This review gives a brief overview of phonons in 2D moirésuperlattice.First,we introduce the theory of the moiréphonon modes based on a continuum approach using the elastic theory and discuss the effect of the moirépattern on phonons in 2D materials such as graphene and MoS_(2).Then,we discuss the electron-phonon coupling(EPC)modulated by moirépatterns,which can be detected by the spectroscopy methods.Furthermore,the phonon-mediated unconventional superconductivity in 2D moirésuperlattice is introduced.The theory of phonon-mediated superconductivity in moirésuperlattice sets up a general framework,which promises to predict the response of superconductivity to various perturbations,such as disorder,magnetic field,and electric displacement field.

计算机模拟Moire条纹现象

利用计算机图像技术产生周期性条纹方法模拟光栅叠加实现Moire条纹现象.考察Moire条纹的空间放大作用,研究一块光栅相对另一块平移时产生的Moire条纹移动过程,计算Moire条纹在平移过程中探测器的输出变化关系.

哺乳类动物臼齿的Moire等高线研究

哺乳类动物的臼齿形态与食性的关系十分密切,而对于齿型的判别一直依赖于直观的经验观察,缺乏实验资料。本文根据对刺猬、犬蝠、松鼠、裼家鼠、黑熊、豹、熊猴、现代人、水鹿以及猪的下颌第2臼齿齿啮合面及其外侧面的Moire等高线特征,提出了对哺乳类动物齿型进行初步对比和分类的建议。

DETERMINING CRITICAL TIME OF ROCK DYNAMIC FRACTURE BY DYNAMIC MOIRE METHOD

An effective Dynamic Moire method was presented to determine the critical time of crack instable propagation in rock dynamic fracture. Two pieces of grating were installed near the notch of Short Rod specimen to form the Moire fringes, then the COD versus time could be monitored from the movement of the Moire fringes, and finally the critical time could be determined from the velocity of COD. This method was also compared with another one.It could be concluded that the critical time determined by Dynamic Moire method corresponds with that of the Transmitted Wave method at the loading rates from 103 to 104 MPa·m(1/2)·S(-1).

基于Talbot效应和moire条纹的CCD精细拼接理论研究

在空间探测等领域,要想得到像元尺寸小、像元数多且价格便宜的CCD器件是比较困难的.目前解决的方法主要采用两片或多片CCD通过拼接来实现,故而在拼接时,错位量的准确移动直接影响着拼接后的整体效果.本文只用一块光栅和DⅡ-180°直角棱镜相结合并利用Talbot效应和moire条纹来进行CCD精细拼接.拼接精度可达到单个像元尺寸的1/20.

Moire偏转技术(MD)检测相位物体的研究

本文给出了Moire偏转技术检测相位物体的基本原理,分析了该技术的灵敏度,提出了一种消除测量光路系统误差的有效方法,并给出了实验结果。

EXPERIMENTAL STUDIES ON J-DOMINANCE IN HETEROGENEOUS WELDED JOINTS BY MOIRE INTERFEROMETRY

Moire interferometry method is introduced to study the feasibilities of J integral as a plastic singularity parameter at the tip of the notch in the welded joints. The results show that J dominance in most studied cases is not validated in v and u displacement fields. Therefore, it can be concluded that J-integral as controlling parameter used to estimate the safety of welded structures is not always valid.