Interpretation of Fringes Produced by Time‐Averaged Projection Moiré

Abstract: New exact formulas describing the observed shift of projected moiré grating lines on a surface of an object are derived for the paraxial model. These formulas enable to construct more accurate explicit relationship among the amplitude of oscillation, the pitch of the projected grating and the order of the fringe. Analytical derivations and numerical illustrations are used throughout the text to explain the process of formation of double‐exposure and time‐averaged projection moiré fringes.     

Investigation of Residual Stress in 2D Plane Weave Aramid Fibre Composite Plates Using Moiré Interferometry and Hole‐Drilling Technique

Residual stress (RS) is crucial to the fabrications of woven composite plates and difficult to measure experimentally because of the complex structures of these plates. This study aims to investigate the RS in 2D plane weave aramid fiber composite plates using hole‐drilling technique coupled with moiré interferometry. A two‐step drilling method is proposed to solve the problems caused by the ‘peel up’ phenomenon, which facilitates the analyses of the obtained moiré patterns. The holes are deliberately selected at the intersection points of the symmetry axes of warp and weft yarns to obtain symmetrically released displacement fields. Moreover, finite element method calibration is conducted to measure RS using a model created based on the real structure of the woven composite. Based on the error analysis in numerical simulations, the less sensitive points are proposed for the RS calculation. The results show that the RS components of each specimen are compressive along the aramid yarns and tensile perpendicular to them. In addition, investigating of the influence of drilling depths on RS shows that RS decreases along the hole‐depth direction. Findings of this study are helpful for the manufacture and quality evaluation of woven aramid fibre composites.     

Moiré Interferometry Assessement of Residual Stress Variation in Depth on a Shot Peened Surface

Abstract: The main goal of this work was the development of experimental techniques to measure in depth non‐uniform residual stresses, as alternative to the more conventional hole‐drilling method with strain gauges. The proposed experimental methodology is based on moiré interferometry. This high resolution field technique allows in‐plane displacement assessment without contact. Grating replication techniques were also developed to record high quality diffraction gratings onto the specimen’s surface. A laser interferometry setup was implemented to generate the master grating (virtual). The stress relaxation was promoted by blind hole‐drilling and the obtained fringe patterns were video recorded. Image processing techniques were applied to assess the in‐plane strain full‐field. A finite elements code (FEM), ANSYS^®, was used to simulate the stress relaxation process and to calculate the hole‐drilling calibration constants.     

Application of Moiré Interferometry to Study Residual Deformation in Lap‐Welded Steel Plates

Abstract: Moiré interferometry combined with hole‐drilling is an effective method for measuring welding residual deformation. In this study, two lap‐welded rectangular steel plates with different overlap widths were manufactured, and cross‐gratings with a frequency of 1200 lines per mm were replicated on test areas of the welds. Sixteen through holes were drilled in the plates to release residual stress, while Moiré interferometry, integrated with a phase‐shifting technique, was used to determine the corresponding surface residual deformation. The distribution characteristics of the residual displacements around the drilled holes were investigated using the experimental data as basis. The relationship between the residual displacement located in the plates and the distance to the weld lines is also presented in this paper. Furthermore, the magnitude and direction of the residual strain both near the holes and within the plates were analysed. The experimental data and detailed analysis in this paper can serve as some reference for research on the residual strain of welds.     

Orientation‐Dependent Strain Relaxation and Chemical Functionalization of Graphene on a Cu(111) Foil

Epitaxial graphene grown on single crystal Cu(111) foils by chemical vapor deposition is found to be free of wrinkles and under biaxial compressive strain. The compressive strain in the epitaxial regions (0.25–0.40%) is higher than regions where the graphene is not epitaxial with the underlying surface (0.20–0.25%). This orientation‐dependent strain relaxation is through the loss of local adhesion and the generation of graphene wrinkles. Density functional theory calculations suggest a large frictional force between the epitaxial graphene and the Cu(111) substrate, and this is therefore an energy barrier to the formation of wrinkles in the graphene. Enhanced chemical reactivity is found in epitaxial graphene on Cu(111) foils as compared to graphene on polycrystalline Cu foils for certain chemical reactions. A higher compressive strain possibly favors lowering the formation energy and/or the energy gap between the initial and transition states, either of which can lead to an increase in chemical reactivity.     

An in situ STM study of cobalt electrodeposition on Au(111) in BMIBF4 ionic liquid

The initial stage of Co electrodeposition on Au(111) from CoCl₂ and Co(BF₄)₂ in a room-temperature ionic liquid of BMIBF₄ is investigated by in situ STM. Preferential nucleation of Co at structure imperfections of the reconstructed Au(111) surface is observed for deposition from CoCl₂ at a surprisingly negative potential (?2.05?V vs. Pt wire). Monoatomic-height Co clusters of 2–3?nm in diameter are formed, which develop into Co islands with size confinement of 3–4?nm after prolonged deposition. The large driving force required for Co deposition from CoCl₂ is attributed to the molecular type of the salt in the ionic liquid together with the tip shielding effect. This is proved by the pronounced difference of Co deposition from Co(BF₄)₂, which takes place at a much less negative potential and proceeds in a 3D progressive nucleation and growth mode without preference in nucleation sites. Surface alloying accompanies the island formation, which is confirmed by pit generation upon stripping of the Co islands. The results are discussed in comparison with features of Co deposition in UHV and in aqueous solutions.     

Out‐of‐Plane Magnetic Patterning Based on Indentation‐Induced Nanocrystallization of a Metallic Glass

Periodic arrays of micrometer‐sized ferromagnetic structures with perpendicular magnetic anisotropy are prepared by nanoindentation at the surface of a Fe_67.7B₂₀Cr₁₂Nb_0.3 glassy ribbon initially showing in‐plane magnetic anisotropy. The indented regions exhibit enhanced coercivity and saturation magnetization with respect to the surrounding nondeformed matrix. These effects are due to a mechanically driven selective nanocrystallization of the metallic glass, induced by nanoindentation, even without the need for thermal annealing. In addition, while the amorphous matrix becomes paramagnetic above 325 K, the crystallized regions (consisting of α‐Fe) remain ferromagnetic upon heating to high temperatures. The local change in the magnetic anisotropy direction is ascribed to a certain degree of crystallographic texture, together with the inverse magnetostriction effect caused by the compressive indentation stresses.     

Surface Engineering of MoS2 via Laser‐Induced Exfoliation in Protic Solvents

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS₂) is considered a promising nonprecious candidate to substitute Pt‐based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one‐step exfoliation of bulk 2H‐MoS₂ to ultrastable few‐layer MoS₂ nanosheets. Such prepared MoS₂ nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H‐to‐1T phase transition under laser irradiation. MoS₂ exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm^?2 and Tafel slope of 54 mV dec^?1.     

Adlayer‐Free Large‐Area Single Crystal Graphene Grown on a Cu(111) Foil

To date, thousands of publications have reported chemical vapor deposition growth of “single layer” graphene, but none of them has described truly single layer graphene over large area because a fraction of the area has adlayers. It is found that the amount of subsurface carbon (leading to additional nuclei) in Cu foils directly correlates with the extent of adlayer growth. Annealing in hydrogen gas atmosphere depletes the subsurface carbon in the Cu foil. Adlayer‐free single crystal and polycrystalline single layer graphene films are grown on Cu(111) and polycrystalline Cu foils containing no subsurface carbon, respectively. This single crystal graphene contains parallel, centimeter‐long ≈100 nm wide “folds,” separated by 20 to 50 µm, while folds (and wrinkles) are distributed quasi‐randomly in the polycrystalline graphene film. High‐performance field‐effect transistors are readily fabricated in the large regions between adjacent parallel folds in the adlayer‐free single crystal graphene film.     

Assembling of redox proteins on Au(111) surfaces: A scanning probe microscopy investigation for application in bio-nanodevices

The morphology and conductive properties of azurin molecules, chemically attached to sulfhydryl terminated alkanethiol monolayer assembled on Au(111) surface, are mapped at single molecule level and compared with those observed for the same molecule immobilised on bare Au(111). High-resolution Tapping Mode Atomic Force Microscopy shows that the protein molecules immobilised on modified gold, better reproduces the crystallographic height of the protein, than that immobilised on bare gold. Such a height recovering is also found in the Scanning Tunnelling Microscopy images. Consistently, a good tunnelling conduction of azurins on the modified gold electrode is demonstrated by Tunnelling Spectroscopy. Cyclic voltammetry measurements show, in addition, that the redox activity of azurin molecules covalently immobilised on sulfhydryl functionalised Au(111) surface is retained. These results are discussed in connection with possible use of this linker in the assembling of nano-hybrid systems.     

Strain and carrier-induced coexistence of topologically insulating and superconducting phase in iodized Si(111) films

The importance of silicon in modern electronic devices has led to considerable interest in exploring the unconventional electronic properties of Si-based materials for future applications in spintronics and quantum computing. Here, using density functional theory, we present the results of a systematic study of the effect of strain on Si(111) thin films whose surfaces are functionalized with iodine. Films with an odd number of layers under biaxial strain are found to undergo a phase transition from a normal insulator to a topological insulator and ultimately to a metal. The spin-orbit coupling-induced topologically nontrivial band gap at the Γ point is found to be as large as 0.50 eV, which not only surpasses that of other Si-based topological materials, it is also large enough for practical realization of quantum spin Hall states at room temperature. No such nontrivial states are found in films with an even number of layers. Mechanisms for such a strain-induced transition are illustrated by a tight-binding model composed of s, p_x, and p_y orbitals. Equally important, we predict that iodized silicene, when stretched and hole-doped, would be a phonon-mediated superconductor with a critical temperature of 9.2 K. This coexistence of a topological insulator and a superconducting phase in a single material is unusual; it has the potential for applications in electronic circuits and for the realization of Majorana fermions in quantum computations.

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Temperature‐Related Morphological Evolution of MoS2 Domains on Graphene and Electron Transfer within Heterostructures

Other than the well‐known sulfurization of molybdate compound to synthesize molybdenum disulfide (MoS₂) layers, the dynamic process in the whole crystalline growth from nuclei to triangular domains has been rarely experimentally explored. Here, a competing sulfur‐capture principle jointly with strict epitaxial mechanism is first proposed for the initial topography evolution and the final intrinsic highly oriented growth of triangular MoS₂ domains with Mo or S terminations on the graphene (Gr) template. Additionally, potential distributions on MoS₂ domains and bare Gr are presented to be different due to the charge transfer within heterostructures. The findings offer the mechanism of templated growth of 2D transition metal dichalcogenides, and provide general principles in syntheses of vertical 2D heterostructures that can be applied to electronics.