Moire Research Articles

Nanoscale plasmonic wires with maximal figure of merits as a superior flexible transparent conducting electrode for RGB colors

Based on incredibly increasing applications in modern optoelectronic devices, the demand for securing a superior conductive transparent electrode (TCE) candidate becomes significant and urgent. However, boosting both transmittance and conductance simultaneously is an intrinsic limitation. In this work, we present silver nanoscale plasmonic wires (Ag NPWs) to function as TCEs in the visible light region by lowering their corresponding plasma frequencies. By carefully designing geometric dimensions of the Ag NPWs, we also optimize the performance for red, green, and blue colors, respectively. The demonstrated figure of merits for RGB colors appeared respectively 443.29, 459.46, and 133.78 in simulation and 302.75, 344.11, and 348.02 in experiments. Evidently, our Ag NPWs offer much greater FoMs beyond conventional TCEs that are most frequently comprised of indium tin oxide and show further advantages of flexibility and less Moire effect for the applications of flexible and high-resolution optoelectronic devices.

SiamTrans: Zero-Shot Multi-Frame Image Restoration with Pre-trained Siamese Transformers

We propose a novel zero-shot multi-frame image restoration method for removing unwanted obstruction elements (such as rains, snow, and moire patterns) that vary in successive frames. It has three stages: transformer pre-training, zero-shot restoration, and hard patch refinement. Using the pre-trained transformers, our model is able to tell the motion difference between the true image information and the obstructing elements. For zero-shot image restoration, we design a novel model, termed SiamTrans, which is constructed by Siamese transformers, encoders, and decoders. Each transformer has a temporal attention layer and several self-attention layers, to capture both temporal and spatial information of multiple frames. Only self-supervisedly pre-trained on the denoising task, SiamTrans is tested on three different low-level vision tasks (deraining, demoireing, and desnowing). Compared with related methods, SiamTrans achieves the best performances, even outperforming those with supervised learning.

Assessment of changes in the sagittal plane of the spine in girls with adolescent idiopathic scoliosis using the moire method.

The gold standard in the clinical assessment of the extent of scoliosis is the Cobb method but the analysis also covers the changes that occur within the spine and trunk in relation to the transverse and sagittal planes. The study aimed to estimate changes in the sagittal plane of the spine in girls with right-sided thoracic adolescent idiopathic scoliosis. The study involved 29 girls with scoliosis (13.6 ± 0.6 years) and 36 healthy girls as the comparison group. The tests included an interview, clinical examination (with the use of Adam's test and the Cobb angle), and examination of shape of the spine surface with the use of the photogrammetric method and the projection moire effect. Lower values of the thoracic kyphosis parameters were found in the scoliosis group. Significant differences were noted for the parameters of the lumbosacral section α (p= 0.02), thoracolumbar section β (p< 0.001), the upper thoracic section γ (p< 0.001), thoracolumbar and upper thoracic section β+γ (p< 0.001) and the total size of α+β+γ (p< 0.001) curvatures. The study showed that with an increase in the angular value of the thoracic curvature, the thoracic kyphosis decreased.

Application of Moire Profilometry in Three-Dimensional Profile Reconstruction of Key Parts in Railway.

Moire profilometry (MP) is one of the three-dimensional (3D) topography measurement methods of structured light, which has the advantages of single frame reconstruction, high speed, no contact and high precision, and is suitable for dynamic measurement scenes. In this article, the digital MP is applied to the wheel tread measurement, the virtual grating is generated by computer to project to the object surface, the moire fringe pattern of the object is obtained by filtering, and finally the continuous phase pattern is obtained by phase unwrapping. The 3D shape reconstruction of the wheel tread is realized, and a new method of wheel tread detection is provided. At the same time, in this paper, the results of using different filters are compared, and the significance of the frequency domain filtering to MP is proved. It is necessary to choose a suitable filtering method according to different environmental conditions. At present, digital MP can be used in industrial static detection, and it can be extended to the dynamic detection of rolling wheels in the future, so as to improve the detection efficiency and realize the automatic detection of trains.

Moiré patterns and carbon nanotube sorting

Moiré patterns (MPs), arising from the superposition of two lattices with close periods, are tightly related to the physicochemical properties of bilayer nanostructures. Here, we develop the theory of complex MPs emerging in twisted bilayer graphene and planar nets of double-walled nanotubes at significant relative twist and/or deformation of layers. The proposed theory clarifies the physicochemical regularities arising at sorting of single-walled carbon nanotubes (SWCNTs) by organic molecules, which self-assemble in regular coatings on both the tubes and planar graphene. We introduce and consider an outer tubular virtual lattice that is a parent structure for the deposited coating and due to this fact, its existence is crucial for the coating formation. As we show, such outer lattices exist only for successfully sorted SWCNTs and the superposition between the outer lattice and SWCNT forms a specific long-period MP. We explain known experimental results of SWCNT sorting by molecules of flavin group, poly(9,9-dioctylfluorene-2,7-diyl), and poly [(m-phenylenevinylene)-alt-(p-phenylenevinylene)]. Also, our approach points out other organic molecules and polymers suitable for effective carbon nanotube sorting.

Image Demoireing via U-Net for Detection of Display Defects

Mura defects, which occur during display manufacturing, degrade the quality of the display. Therefore, Mura detection is critical. When the camera is focused on the display for accurately detecting Mura defects, a moire pattern occurs in a captured image because of the frequency difference between the subpixels of the display and the color filter array of the camera. Typical image data handled with existing demoireing methods do not have Mura defects and include synthetic moire images. Therefore, we created a dataset to detect Mura defects that include real moire patterns, classified into two categories: weak and strong. We propose a new demoireing framework to remove the moire patterns in the captured image, thereby accurately detecting Mura defects. We also propose inserting ArUco markers for accurate alignment and automation, conducting multiple experiments with U-Net. Based on the captured data, the proposed U-Net, which combines a frequency loss and data augmentation, improves the performance by 6.41 dB higher for the weak moire pattern and 4.14dB higher for the strong moire pattern than state-of-the-art networks in terms of peak signal-to-noise ratio.

Spoof Trace Disentanglement for Generic Face Anti-Spoofing.

Prior studies show that the key to face anti-spoofing lies in the subtle image patterns, termed "spoof trace," e.g., color distortion, 3D mask edge, and Moiré pattern. Spoof detection rooted on those spoof traces can improve not only the model's generalization but also the interpretability. Yet, it is a challenging task due to the diversity of spoof attacks and the lack of ground truth for spoof traces. In this work, we propose a novel adversarial learning framework to explicitly estimate the spoof related patterns for face anti-spoofing. Inspired by the physical process, spoof faces are disentangled into spoof traces and the live counterparts in two steps: additive step and inpainting step. This two-step modeling can effectively narrow down the searching space for adversarial learning of spoof trace. Based on the trace modeling, the disentangled spoof traces can be utilized to reversely construct new spoof faces, which is used as data augmentation to effectively tackle long-tail spoof types. In addition, we apply frequency-based image decomposition in both the input and disentangled traces to better reflect the low-level vision cues. Our approach demonstrates superior spoof detection performance on 3 testing scenarios: known attacks, unknown attacks, and open-set attacks. Meanwhile, it provides a visually-convincing estimation of the spoof traces. Source code and pre-trained models will be publicly available upon publication.

Unravelling the electromechanical coupling in a graphene/bulk h-BN heterostructure.

The stacking heterostructure of graphene on bulk h-BN produces a moiré pattern with topographic corrugation. The corrugation of the moiré pattern expectantly induces a considerable curvature and a flexoelectric response, which calls for a detailed study. In this work, we used lateral force microscopy, a scanning technique to locally observe the moiré pattern and topographic corrugation. The curvature and flexoelectric potentials are derived from the measured topographic corrugation, revealing a huge curvature of ∼107 m-1 and a flexoelectric potential of ∼10 mV in the hexagonal domain wall region (∼3-4 nm) of the moiré pattern. In addition, the domain walls of the moiré pattern also generate a clear electromechanical and frictional response, arising from the corrugation-induced flexoelectric response. In summary, the results of this work provide insights into the understanding of the flexoelectricity in the graphene/bulk h-BN and its associated electromechanical coupling behavior in the moiré pattern of a van der Waals stacking heterostructure.

Faces behind bars: illusory eye movements induced by gratings

I describe a novel illusion in which perceived eye movements are induced by moving a vertical grating across a single image of a forward-looking face. By varying properties of the grating, a wide range of illusory eye movements can be generated including nystagmus, a ‘swirling’ motion of the eyes, and vertical scanning/blinking. I suggest that the phenomenon is closely related to the footsteps illusion, but reveals the role that object shape and grating spatial frequency together play in determining the direction of illusory motion that observers perceive. I also discuss the relationship between the current illusion, the footsteps illusion, and Moire pattern animations.

Freeform Electronic and Photonic Landscapes in Hexagonal Boron Nitride.

Atomically smooth hexagonal boron nitride (hBN) flakes have revolutionized two-dimensional (2D) optoelectronics. They provide the key substrate, encapsulant, and gate dielectric for 2D electronics while offering hyperbolic dispersion and quantum emission for photonics. The shape, thickness, and profile of these hBN flakes affect device functionality. However, researchers are restricted to simple, flat flakes, limiting next-generation devices. If arbitrary structures were possible, enhanced control over the flow of photons, electrons, and excitons could be exploited. Here, we demonstrate freeform hBN landscapes by combining thermal scanning-probe lithography and reactive-ion etching to produce previously unattainable flake structures with surprising fidelity. We fabricate photonic microelements (phase plates, grating couplers, and lenses) and show their straightforward integration, constructing a high-quality optical microcavity. We then decrease the length scale to introduce Fourier surfaces for electrons, creating sophisticated Moiré patterns for strain and band-structure engineering. These capabilities generate opportunities for 2D polaritonics, twistronics, quantum materials, and deep-ultraviolet devices.

Moire profilometry through simultaneous dual fringe projection for accurate phase demodulation: a comparative study.

In optical metrology, fringe projection and moire techniques have been widely used to measure the topography of objects. We can combine the advantages of the two techniques by applying a configuration of simultaneous dual projection in the fringe projection technique, which generates a superimposed fringe pattern containing a moire pattern that is phase modulated according to the topography. In this work, we present an analytic and comparative study of three methods to demodulate the phase of the moire pattern: the spatial, spatial-temporal, and temporal methods. Those methods consist of two steps: first, the moire pattern is extracted from the superimposed fringe pattern; next, the phase of the moire pattern is demodulated. The analytical results show that the resulting phase map has double phase sensitivity compared to that of the classical fringe projection technique. Experimental and numeric results prove the feasibility of this technique.

Rotational Friction Correlated with Moiré Patterns in Strained Bilayer Graphene: Implications for Nanoscale Lubrication

Energy conservation of graphene nanodevices requires frictional dissipation management for their high surface area to volume rates, and rotational motion besides sliding scenarios appear frequently. Here, the rotational friction between graphene layers is investigated by molecular dynamics simulations with a validated graphene-spring model. It shows that the interlayer frictional torque drops an order of magnitude and approaches superlubricity with the emergence of Moiré patterns (MPs). Further analysis reveals that the incommensurate interface of MPs tunes the local energy, which cancels each other out with relative rotation, resulting in ultralow interlayer energy barriers. Accordingly, for bilayer systems with biaxially stretched substrates, a significant torque reduction can be achieved when the size of MPs matches that of the graphene flake. This study would provide new insight into the lubrication of rotatable nanomechanical systems.

Resonant Coupling of a Moiré Exciton to a Phonon in a WSe2/MoSe2 Heterobilayer.

Moiré patterns with an angular mismatch in van der Waals heterostructures are a fascinating platform to engineer optically generated excitonic properties. The moiré pattern can give rise to spatially ordered exciton ensembles, which offer the possibility for coherent quantum emitters and quantum simulation of many-body physics. The intriguing moiré exciton properties are affected by their dynamics and exciton-phonon interaction. Here, we report the moiré exciton and phonon interaction in a twisted WSe2/MoSe2 heterobilayer. By tuning the excitation energy, we realized the selective excitation of the moiré exciton at phonon resonances and the otherwise negligible small absorption. Furthermore, we revealed the relaxation of moiré exciton ensembles between different potential minima via the resonant phonon scattering process. Our findings highlight resonant coupling of a moiré exciton to a phonon and could pave a new way for the exploration of novel quantum phenomena of the moiré exciton.

Magnetic proximity effect in two-dimensional van der Waals heterostructure

The evolution of low-dimensional materials has frequently revolutionized new intriguing physical standards and suggests a unique approach to scientifically design a novel device. However, scaling down of spin-electronic devices entails in-depth knowledge and precise control on engineering interfacial structures, which unveils the exciting opportunity. To reveal exotic quantum phases, atomically thin two-dimensional van der Waals material, embraces control and tuning of various physical states by coupling with peripheral perturbation such as pressure, photon, gating, Moire pattern and proximity effect. Herein, we discuss the physical property of a pristine material which can be converted via proximity effects to attain intrinsic spin-dependent properties from its adjacent material like magnetic, topological or spin–orbit phenomena. Realizing magnetic proximity effect in atomically thin vdW heterostructure not only balance the traditional techniques of designing quality spin interface by doping, defects or surface modification, but also can overcome their restrictions for modelling and fabricate novel spin-related devices in nanoscale phases. The proximitized van der Waals heterostructure systems unveil properties, which cannot be realized in any integral component of considered heterostructure system. These proximitized van der Waals material provide an ideal platform for exploring new physical phenomena, which delivers a broader framework for employing novel materials and investigate nanoscale phases in spintronics and valleytronics.

Simulation of moire pattern based on transmittance calculation of LCD metal mesh touch panel

AbstractIn this paper, a precise and effective computational method for moire patterns' simulation and prediction of liquid crystal display (LCD) metal mesh touch panel based on the transmittance calculation of LCD's sub‐pixel is proposed. Firstly, we analyze the actual physical model and build our simulation model. Secondly, we explain the form reason of moire phenomenon and establish the transmittance calculation formula. Finally, we demonstrate the accuracy and validation of our simulation approach by practical experiment. The experimental results show that the simulation matching rate is about 88.2%, and the simulated graphs are extremely similar to the actual moire pattern. We can evaluate the moire degree with our new method; this research is significant to touch panel's production.

Subatomic Distortion of Surface Monolayer Lattice Visualized by Moiré Pattern.

Mapping of the local lattice distortion is required to understand the details of the chemical and physical properties of thin films. However, the resolution by the direct microscopic methods was insufficient to detect the local distortion. Here, we have demonstrated that the local distortion of a monatomic film on a substrate is estimated with high resolution using the moiré pattern of the topographic scanning tunneling microscopy image. The analysis focused on the apparently low centers of the moiré pattern of the hexagonal iron nitride monolayer on the Cu(111) substrate. The local distortion was visualized by estimating the displacement of the experimentally detected center position from the ideal position that is extracted from the adjacent center positions. The map of the local distortion revealed that the subsurface impurities are preferentially located on the largely distorted areas. This approach is widely applicable to other thin films on the substrates.

Moiré magic three years on

Moiré magic three years on

Electron-hole asymmetry and band gaps of commensurate double moire patterns in twisted bilayer graphene on hexagonal boron nitride

Spontaneous orbital magnetism observed in twisted bilayer graphene (tBG) on nearly aligned hexagonal boron nitride (BN) substrate builds on top of the electronic structure resulting from combined G/G and G/BN double moire interfaces. Here we show that tBG/BN commensurate double moire patterns can be classified into two types, each favoring the narrowing of either the conduction or valence bands on average, and obtain the evolution of the bands as a function of the interlayer sliding vectors and electric fields. Finite valley Chern numbers $\pm 1$ are found in a wide range of parameter space when the moire bands are isolated through gaps, while the local density of states associated to the flat bands are weakly affected by the BN substrate invariably concentrating around the AA-stacked regions of tBG. We illustrate the impact of the BN substrate for a particularly pronounced electron-hole asymmetric band structure by calculating the optical conductivities of twisted bilayer graphene near the magic angle as a function of carrier density. The band structures corresponding to other $N$-multiple commensurate moire period ratios indicate it is possible to achieve narrow width $W \lesssim 30$ meV isolated folded band bundles for tBG angles $\theta \lesssim 1^{\circ}$.

Intrinsic Defects in MoS2 Grown by Pulsed Laser Deposition: From Monolayers to Bilayers.

Pulsed laser deposition (PLD) can be considered a powerful method for the growth of two-dimensional (2D) transition-metal dichalcogenides (TMDs) into van der Waals heterostructures. However, despite significant progress, the defects in 2D TMDs grown by PLD remain largely unknown and yet to be explored. Here, we combine atomic resolution images and first-principles calculations to reveal the atomic structure of defects, grains, and grain boundaries in mono- and bilayer MoS2 grown by PLD. We find that sulfur vacancies and MoS antisites are the predominant point defects in 2D MoS2. We predict that the aforementioned point defects are thermodynamically favorable under a Mo-rich/S-poor environment. The MoS2 monolayers are polycrystalline and feature nanometer size grains connected by a high density of grain boundaries. In particular, the coalescence of nanometer grains results in the formation of 180° mirror twin boundaries consisting of distinct 4- and 8-membered rings. We show that PLD synthesis of bilayer MoS2 results in various structural symmetries, including AA' and AB, but also turbostratic with characteristic moiré patterns. Moreover, we report on the experimental demonstration of an electron beam-driven transition between the AB and AA' stacking orientations in bilayer MoS2. These results provide a detailed insight into the atomic structure of monolayer MoS2 and the role of the grain boundaries on the growth of bilayer MoS2, which has importance for future applications in optoelectronics.

Анализ современного состояния и перспективы развития методов контроля натяжения радиоотражающего сетеполотна на развертываемый каркас крупногабаритной зеркальной антенны

The article considers the problems of developing an operating automated method for monitoring the force and uniformity of tension of a radio-reflecting mesh on the deployable frame of large mirror antennas. Based on the performed analysis of known control methods they are classified as contact mechanical methods and non-contact optical ones. It is shown that only optical monitoring methods provide automated control of the tension force of the radio-reflecting mesh on the frame. Among the known optical methods for monitoring, only the moire band method allows creating an immediate picture of the uniformity of the tension of the radio-reflecting mesh over the entire surface under consideration. The method is based on the revealed relationship of moire patterns with the uniformity and tension force of the radio-reflecting mesh. The advantages of the described method are shown; the main advantage is the possibility of installing a radio-reflecting mesh on the deployable frame of the large mirror antenna in real time. Due to its versatility, the proposed method can be used in any other structures where the element being tested is a grid, regardless of the material from which it is made.