Manipulation of wavefront lies at the core of next-generation information technologies. Compared to metal and dielectric metasurfaces, atomic 2D materials exhibit excellent prospects toward fulfilling ultra-thin thickness requirements in flat optics in wavefront shaping, with thickness much smaller than those of traditional bulky devices. However, phase manipulation by light propagating through atomic 2D materials is suppressed due to its sub-nanometer thickness. Here, an approach is reported to realize reflection phase singularities by establishing a zero-reflection point in a monolayer MoS 2 -based multilayer system, which broadens topological study beyond polarization singularity. This is achieved through the creation of a multilayer Fabry-Perot-type interference, and a pronounced phase change in the reflected light is realized due to the high absorption of monolayer MoS 2 in the studied wavelength range. As an application, a rapid, sensitive, and label-free detection of SARS-CoV-2 (2019-nCov) antigen is demonstrated with a detection limit of 10 −12 M L −1 (62 pg ml −1 ) by using monolayer MoS 2 based optical biosensor. In addition to offering a comprehensive study in phase singularity, efficient wavefront engineering based on the reflective system using materials is presented with atomic thickness which may greatly simplify optical architecture in flat optics, and promote its development toward compactness and integrated functions.
The construction of ultra-close 2D atomic-thickness Van der Waals heterojunctions with high-speed charge transfer still faces challenges. Here, we synthesized single-layer ZnIn 2 S 4 and g-C 3 N 4 , and introduced silver single atoms to regulate Van der Waals heterojunctions at the atomic level to optimize charge transfer and catalytic activity. At the atomic scale, the impact of detailed structural differences between the two characteristic surfaces of ZnIn 2 S 4 ([Zn-S 4 ] and [In-S 4 ]) on catalytic performance has been first proposed. Experiments combined with the DFT study demonstrate that single atom Ag not only acts as a charge transfer bridge but also regulates the energy band and intrinsic catalytic activity. Benefiting from the enhanced electron delocalization, the synthesized catalyst ZIS/Ag@CN exhibits excellent photocatalytic performance, with a hydrogen production rate of 5.50 mmol·g −1 ·h −1 , which is much higher than the reported Ag-based single-atom catalysts so far. This work provides a new understanding of atomic-level heterojunction interface regulation and modification.
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