Exciton Localization Modulated by Ultradeep Moiré Potential in Twisted Bilayer γ-Graphdiyne.

Twisted moiré superlattice is featured with its moiré potential energy, the depth of which renders an effective approach to strengthening the exciton-exciton interaction and exciton localization toward high-performance quantum photonic devices. However, it remains as a long-standing challenge to further push the limit of moiré potential depth. Herein, owing to the pz orbital induced band edge states enabled by the unique sp-C in bilayer γ-graphdiyne (GDY), an ultradeep moiré potential of ∼289 meV is yielded. After being twisted into the hole-to-hole layer stacking configuration, the interlayer coupling is substantially intensified to augment the lattice potential of bilayer GDY up to 475%. The presence of lateral constrained moiré potential shifts the spatial distribution of electrons and holes in excitons from the regular alternating mode to their respective separated and localized mode. According to the well-established wave function distribution of electrons contained in excitons, the AA-stacked site is identified to serve for exciton localization. This work extends the materials systems available for moiré superlattice design further to serial carbon allotropes featured with benzene ring-alkyne chain coupling, unlocking tremendous potential for twistronic-based quantum device applications.

Periodically Interrupting Bonding Behavior to Reformat Delocalized Electronic States of Graphdiyne for Improved Electrocatalytic Hydrogen Evolution.

π electron configuration plays a pivotal role in metal-free carbon catalysts, and its delocalization degree overwhelmingly dominates catalytic activity. However, precise and targeted regulation of inherent π electrons still remain challenging. Here, one chemical-bond-targeted physical clipping strategy is proposed and effectively adopted in the cutting-edge carbon material system of graphdiyne (GDY) as a concept-of-proof. The delocalized electrons are expected to be periodically reformatted for substantially enhancing π electron delocalization. Via theoretical screening and well-designed experiments, periodical interruption of Csp-Csp2 bonds in GDY can render sp-C sites with decent activity, ultimately yielding top-ranking electrocatalytic performance without intentionally introducing external decoration. The as-proposed concept endows a universal prescription to push the limit of delocalization degree, thus shedding novel light on the rational design of decent metal-free catalysts.

A new mark shearing technique for strain measurement using digital image correlation method.

The digital image correlation (DIC) method is a noncontact, full-field surface deformation measuring method, which is widely used in experimental mechanics. Although the DIC method has a high precision in displacement measurement, its precision in strain determination is a bit low. In this paper, a new mark shearing technique is proposed to improve the accuracy of the strain measurement of the DIC method. A wedge mirror is used to introduce a shearing distance of the marks, which are made on the specimen to calculate the strain. The measurement principle of the mark shearing technique is described in detail. From the analysis, it can be concluded that this method is suitable for both large-scaled and small-scaled specimens, and thus has a wider adaptability than the common DIC method. Using this method, the maximum gauge length is 80 mm, and the accuracy of strain measurement can reach 4 microm strains. A tensile experiment with aluminum sample was conducted, and the successful results demonstrated the feasibility of this method.

Artificial submicron or nanometer speckle fabricating technique and electron microscope speckle photography.

In this article, a novel artificial submicro- or nanometer speckle fabricating technique is proposed by taking advantage of submicro or nanometer particles. In the technique, submicron or nanometer particles were adhered to an object surface by using ultrasonic dispersing technique. The particles on the object surface can be regarded as submicro or nanometer speckle by using a scanning electronic microscope at a special magnification. In addition, an electron microscope speckle photography (EMSP) method is developed to measure in-plane submicron or nanometer deformation of the object coated with the artificial submicro or nanometer speckles. The principle of artificial submicro or nanometer speckle fabricating technique and the EMSP method are discussed in detail in this article. Some typical applications of this method are offered. The experimental results verified that the artificial submicro or nanometer speckle fabricating technique and EMSP method is feasible.

Steps of Al/Si nanocluster studied by scanning tunneling microscope Moiré method.

The surface stress around the steps of Al/Si (111)-7x7 artificial nanocluster array has been studied by the scanning tunneling microscope (STM) Moiré method. The distributions of sigma(ij)(epsilon(ij)) near the selected step edge are precisely quantified by Moiré pattern. Observation by STM reveals the details of stress distribution that varies around steps and other defects of the surface. The experimental results show that the intrinsic surface stress tensors are quite different in the upper and lower terraces near a step, which provides indirect evidence that the exchange incorporation occurs for Al atoms on the Si (111) surface. The study also provides valuable data regarding control of the growth mode of artificial nanostructures by manipulating the growth conditions and kinetics.