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New Moiré Effect Discovered in Tungsten Ditelluride Bilayers
A captivating and intricate phenomenon known as the moiré effect can be observed when light interacts with slightly misaligned periodic structures. This visual effect not only captivates observers with its aesthetic appeal but also plays a significant role in determining the characteristics of various materials.
Recently, researchers from the Institute of Industrial Science at The University of Tokyo, as detailed in the journal ACS Nano, unveiled a novel moiré pattern within tungsten ditelluride bilayers. This newly identified pattern consists of a series of one-dimensional bands, marking a significant departure from previously documented patterns.
The formation of moiré patterns in nanomaterials is contingent upon the relative orientation of atomic layers. By manipulating the angle of these lattices, researchers can create diverse patterns. Typically, these twist angles are minimal—often just a few degrees—since larger angles tend to produce smaller characteristic patterns. However, in this study, the researchers ventured into the realm of larger twist angles, leading to unexpected results.
Yijin Zhang, a co-author on the research, noted, “The resulting pattern manifests as parallel stripes. Unlike standard interference patterns, which resemble two-dimensional grids of light spots, these one-dimensional bands are unlike any previously recognized configurations.”
The unique crystal structure of tungsten ditelluride, which comprises distorted quadrilaterals rather than an organized honeycomb lattice, contributes to this distinct phenomenon.
Tomoki Machida, the lead author, elaborated, “A less ordered lattice system introduces greater flexibility regarding the twist angle. This allowed us to rigorously investigate the emerging patterns as we significantly altered the angle.”
Employing theoretical modeling alongside transmission electron microscopy experiments, the research team pinpointed that these one-dimensional bands emerge precisely at twist angles of 61.767º and 58.264º. Even a minor adjustment of just a tenth of a degree resets the interference pattern to the conventional bright spots.
Zhang emphasized the implications of this finding, stating, “Moiré patterns influence the optoelectronic characteristics of materials. This discovery potentially paves the way for engineering substances with distinct anisotropic properties. For instance, we may engineer nanomaterials capable of selectively conducting heat or electricity in a specific orientation.”
Looking forward, the researchers speculate that other materials might exhibit similar one-dimensional patterns at elevated twist angles. They are actively searching for these occurrences while also developing methodologies to apply their findings to explore one-dimensional phenomena. As this research progresses, more intriguing interference patterns are anticipated to emerge, expanding our understanding of material properties.
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