AUTOMATIC ORDER-DETERMINATION OF TRANSIENT IN--PLANE DISPLACEMENT MOIRE PATTERNS

This paper presents a fringe-carrier method that eliminates sign ambiguity of transient moire fringes which can be used to automatically determine the relative orders. A fringe carrier is preset in the static state of the specimen and the dynamic in-plane displacements are recorded as the modulation to the frequency of the carrier fringes when the specimen is loaded by impact. According to a modulating criterion developed from the modulation degree, the fringes of the transient moire patterns keep monotonical in orders so that they can be automatically encoded in grey levels by a digital image system. The moire orders purely caused by dynamic loadings are evaluated by subtracting the grey-value of the unmodulated carrier image from that of the modulated carrier images encoded by their orders. With the subtracted moire orders the strain components can be obtained, and, correspondingly, the histograms of dynamic displacement moire images are shown with order variation by image-difference.

Moire Patterns of θ'Precipitates in Al-Cu Alloy

A θ＇precipitate in an Al-Cu alloy was imaged.Its Moire patterns shown by TEM were discussed.

A NEW METHOD FOR CONSTRUCTING DIGITAL-STRAIN-FIELD-IMAGES FROM MOIRE PATTERNS

A new method for constructing digital-strain-field-image from a moire pattern with the help of digital image processing technique is proposed in this paper. The digital-strain-field-image expresses the strain values directly by its grey levels. The digital-strain-field-image can be obtained by making a differentiation for the digital moire pattern and doing a simple division operation. This image not only gives the visual strain field distribution, but also gives the strain values of every point. This method is simple and applicable and has satisfactory accuracy.

Melting of electronic/excitonic crystals in 2D semiconductor moirépatterns:A perspective from the Lindemann criterion

Using the Lindemann criterion,we analyzed the quantum and thermal melting of electronic/excitonic crystals recently discovered in two-dimensional(2D)semiconductor moirépatterns.We show that the finite 2D screening of the atomically thin material can suppress(enhance)the inter-site Coulomb(dipolar)interaction strength,thus inhibits(facilitates)the formation of the electronic(excitonic)crystal.Meanwhile,a strong enough moiréconfinement is found to be essential for realizing the crystal phase with a wavelength near 10 nm or shorter.From the calculated Lindemann ratio which quantifies the fluctuation of the site displacement,we estimate that the crystal will melt into a liquid above a critical temperature ranging from several tens Kelvin to above 100 K(depending on the system parameters).

Separation of contact stress components by moire interferometry

A hybrid technique of combining moire measurement and analytical solution is developed to separate the normal and the tangential components of distributed contact stresses between two co-plane bodies. The moire interfe-rometry offers the displacement fields near the deformed contact zone, from which the tangential strains and boundary slopes of the deformed configurations can be evaluated. Those experimental results provide boundary conditions for the discrete integration of Flamant＇s solutions, to inversely compute the separated components of the contact stresses.

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.

Formation of graphene on Ru（0001） surface

We report on the formation of a graphene monolayer on a Ru（0001） surface by annealing the Ru（0001） crystal. The samples are characterized by scanning tunnelling microscopy （STM） and Auger electron spectroscopy （AES）. STM images show that the Moire pattern is caused by the graphene layer mismatched with the underlying Ru（0001） surface and has an N × N superlattice. It is further found that the graphene monolayer on a Ru（0001） surface is very stable at high temperatures. Our results provide a simple and convenient method to produce a graphene monolayer on the Ru（0001） surface, which is used as a template for fabricating functional nanostructures needed in future nano devices and catalysis.

Moire-pattern-modulated electronic structures in Sb_(2)Te_(3)/graphene heterostructure

Moire superlattice has recently been found in topological insulators,which can lead to periodic modulation on the electronic structure.In this work,we report the low-temperature scanning tunneling microscopy study of Sb_(2)Te_(3) films grown on graphitized 4H-SiC.We find that substrate temperature can strongly influence the rotation angles between Sb_(2)Te_(3) film and graphene substrate.Three kinds of moire patterns are observed at the first quintuple layer Sb_(2)Te_(3) film under different substrate temperatures.One shows complicated patterns with a rotation angle of nearly 0°relative to the substrate,another just exhibits simple 1 ×1 structure with a rotation angle of 30°.Other rotation angle like 8.2°is observed at higher substrate temperature as well,which is relatively rare.Comparison of the d//dV curves from Sb_(2)Te_(3) films with different moire patterns indicates that the superstructure can offer degrees of freedom in tailoring electronic structure.This work may stimulate the further study on the moire modulation to the electronic properties of topological insulators.

Some Aspects in Application of Microscopical and Microanalytical Techniques

This article considers collectively some of the most recent advances in the application of microscopicaland microanalytical techniques in materials science. including studies concerning rare metals. These comprise the highest resolution obtained with electron microscopy. observation of moire patterns in transmisionelectron microscopy (TEM), electro-dimpling before ion beam thinning as an effective step in the preparation of TEM samples, hydrogen problem in atom probe analysis, and a novel analysis technique-lasermicroprobe mass spectrometry (LAMMS).

INTRAGRANULAR VC AND M_(23)C_6 IN GH36 SUPERALLOY

The distinct images of intragranular VC were observed on TEM in superalloy GH36 underwent normal heat treatment and prolonged aging.The size of VC particles were meas- ured by means of Moire pattern,and the misfit between VC and austenite was also calculated. The M23C6 enveloped in VC shell was also observed in the prolonged-aged specimens.The coherent relation between intragranular M_(23)C_6 twins and austenite as well as its coherent in- terface were also studied.

具有转角石墨烯结构碳纳米材料的电子显微学表征

本文通过一步高温烧结石墨烯量子点制备了一种具有转角石墨烯结构的碳纳米材料,并利用球差矫正电子显微镜进行表征。该碳纳米材料中存在大量纳米尺度的孔隙和由几层小片层的石墨烯以随机旋转角堆垛形成的结构。通过HRTEM图像的快速傅立叶变换(FFT)分析来区分每个旋转角度的石墨烯层,并且多层石墨烯的堆叠还能引起更复杂的层状结构。纳米尺度的局域型转角堆叠结构、孔隙意味着其具有多种可能的带隙结构,使这种碳材料有可能作为转角石墨烯结构与性能关联的研究平台;并且此类碳材料在碱溶液处理后,表现出类似于Pt催化剂的催化特性和一种商业化的20%Pt/C催化剂的催化活性。

TEM observation of sintered permanent magnetic strontium ferrite

Sintered permanent magnetic strontium ferrites were studied using transmission electron microscopy to investigate the microstructure morphology and its correlation with the magnetic properties. The present study shows that the microstructure of sintered permanent magnetic strontium ferrites is an important parameter in determining their magnetic properties. The microstructure morphology in low-performance ferrite magnet is obviously different from high-performance one. The magnetic properties of sintered permanent strontium ferrite depend strongly on the orientation degree of strong magnetic crystals. The presence of ferric oxide phase in ferrite magnet can deteriorate the magnetic properties. Moreover, proper quantities of crystal defects are beneficial to high coercive force due to the fixing of magnetic domain.

Real-time and label-free biosensing using moiré pattern generated by bioresponsive hydrogel

Bioresponsive hydrogels are smart materials that respond to various external stimuli and exhibit great potential as biosensors owing to their capability of real-time and label-free detection.Here,we propose a sensing platform based on bioresponsive hydrogels,employing the concept of moiré patterns.Two sets of line patterns with different pitch sizes are prepared;a hydrogel grating whose pitch size changes according to external stimuli and a reference grating with constant pitch size.The volume changes of the hydrogel caused by external stimuli changes the pitch size of the hydrogel grating,and subsequently,the pitch sizes of the moiré patterns(moiré signal),whose values can be obtained in a real-time and label-free manner through customized moiré microscopy and signal processing.After confirming that the pH-induced swelling of hydrogel could be monitored using moiré patterns,we performed moiré pattern-based detection of specific proteins using protein-responsive hydrogel that underwent shrinking via interaction with target proteins.Brain-derived neurotrophic factor and platelet-derived growth factor were selected as the model proteins,and our proposed system successfully detected both proteins at nanomolar levels.In both cases,the pitch size change of hydrogel grating was monitored much more sensitively using moiré patterns than through direct measurements.The changes in the moiré signals caused by target proteins were detected in ex-vivo environments using a custom-made intraocular lens incorporating the hydrogel grating,demonstrating the capability of the proposed system to detect various markers in intraocular aqueous humor,when implanted in the eye.

Moirépatterns arising from bilayer graphone/graphene superlattice

Moirépatterns from two-dimensional(2D)graphene heterostructures assembled via van der Waals interactions have sparked considerable interests in physics with the purpose to tailor the electronic properties of graphene.Here we report for the first time the observation of moire patterns arising from a bilayer graphone/graphene superlattice produced through direct single-sided hydrogenation of a bilayer graphene on substrate.Compared to pristine graphene,the bilayer superlattice exhibits a rippled surface and two types of moire patterns are observed:triangular and linear moire patterns with the periodicities of 11 nm and 8-9 nm,respectively.These moire patterns are revealed from atomic force microscopy and further confirmed by following fast Fourier transform(FFT)analysis.Density functional theory(DFT)calculations are also performed and the optimized lattice constants of bilayer superlattice heterostructure are in line with our experimental analysis.These findings show that well-defined triangular and linear periodic potentials can be introduced into the graphene system through the single-sided hydrogenation and also open a route towards the tailoring of electronic properties of graphene by various moirépotentials.

Distinct moiré textures of in-plane electric polarizations for distinguishing moiré origins in homobilayers

In binary compound 2D insulators/semiconductors such as hexagonal boron nitride(h BN), the different electron affinities of atoms can give rise to out-of-plane electric polarizations across inversion asymmetric van der Waals interface of near 0° interlayer twisting. Here we show that at a general stacking order where sliding breaks 2π/3-rotational symmetry, the interfacial charge redistribution also leads to an in-plane electric polarization, with a magnitude comparable to that of the out-of-plane ones.The effect is demonstrated in h BN bilayers, as well as in biased graphene bilayers with gate-controlled interlayer charge redistributions. In long wavelength moiré patterns, the in-plane electric polarizations determined by the local interlayer stacking registries constitute topologically nontrivial spatial textures. We show that these textures can be used to distinguish moirépatterns of different origins from twisting, biaxial-and uniaxial-heterostrain, where vector fields of electric polarizations feature Bloch-type merons, Néel-type merons, and anti-merons, respectively. Combinations of twisting and heterostrain can further be exploited for engineering various electric polarization textures including 1D quasiperiodic lattices.

摩尔超晶格中电场可调的极化激元拓扑输运

在由不同的单层过渡金属硫族化合物堆叠形成的双层范德瓦尔斯异质结中,两层之间的微小转角可导致摩尔超晶格的出现,其基态光学性质由位于不同层的电子和空穴通过库仑吸引形成的层间激子主导.层间激子携带的静电偶极矩使得它可以通过静电势来操控其定向流动,同时层间激子也具有一定的光学跃迁偶极矩,它的大小和方向随层间激子在摩尔超晶格中的位置而变化.本文指出摩尔超晶格中的层间激子与二维平面光学微腔内光子模的杂化可产生两种具备不同拓扑性质的摩尔极化激元,可导致自旋/谷霍尔效应和偏振霍尔效应.通过调节两层间的电压改变层间激子与光学腔内光子模的失谐量,可选择特定种类的摩尔极化激元,这使得它的拓扑输运现象具备卓越的电场可调性.