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Broadband photodetectors based on narrow bandgap 2D materials have garnered considerable interest for application in the field of optoelectronic devices. However, their large dark current hinders device performance. In this work, a PtSe2/MoS2 heterojunction was fabricated for a broadband photodetector operating within the range of visible to near-infrared. The device exhibited suppressed dark currents with a high rectification ratio of 104. The built-in electric field of the heterojunction promoted carrier separation effectively, and the device achieved excellent photoelectric performance with responsivities of 1.7 × 103, 27.52, and 21 mA/W at 635, 785, and 1550 nm wavelengths, respectively. Moreover, the specific detectivities (D*) were 2.2 × 1013 Jones (635 nm), 3.55 × 1011 Jones (785 nm), and 2.72 × 108 Jones (1550 nm). The device demonstrated a rise/fall time of 131/241 µs under 1550 nm laser illumination. Visible and near-infrared imaging detection was also demonstrated based on the heterojunction device at room temperature. This work sheds light on the remarkable potential of PtSe2/MoS2 heterojunctions in the domain of high-performance broadband photodetectors. [ABSTRACT FROM AUTHOR]

Birefringence is at the heart of photonic applications. Layered van der Waals materials inherently support considerable out-of-plane birefringence. However, funnelling light into their small nanoscale area parallel to its out-of-plane optical axis remains challenging. Thus far, the lack of large in-plane birefringence has been a major roadblock hindering their applications. Here, we introduce the presence of broadband, low-loss, giant birefringence in a biaxial van der Waals materials Ta2NiS5, spanning an ultrawide-band from visible to mid-infrared wavelengths of 0.3–16 μm. The in-plane birefringence Δn ≈ 2 and 0.5 in the visible and mid-infrared ranges is one of the highest among van der Waals materials known to date. Meanwhile, the real-space propagating waveguide modes in Ta2NiS5 show strong in-plane anisotropy with a long propagation length (>20 μm) in the mid-infrared range. Our work may promote next-generation broadband and ultracompact integrated photonics based on van der Waals materials. van der Waals materials are usually characterized by a significant out-of-plane optical anisotropy, but in-plane birefringence is also necessary for photonics applications. Here, the authors report the presence of broadband optical anisotropy in a layered material, Ta2NiS5, showing in-plane birefringence of ~2 and ~0.5 in the visible and mid-infrared range, respectively. [ABSTRACT FROM AUTHOR]

Single- and bi-atom catalysts (SACs and BACs) exhibit great potential in catalyzing electrochemical nitrogen reduction reaction (NRR) due to their unusual coordination-environment effect of active centers, which unfortunately remains elusive so far. Herein, by applying a descriptor ψ based on the valence-electron number and electronegativity of the catalytic centers, we have systematically studied NRR on SACs and BACs with diverse coordination environments. Our results quantify the elemental type and number of metal atoms and their neighbors at the active centers on the adsorption properties and reactivity of atomic catalysts. This uncovers the pronounced differences and similarities between SACs, homonuclear BACs, and heteronuclear BACs as well as the unique role of N dopant. With these findings, we have also predicted that Ir-N4-SAC and TiMn-N6-BAC as promising candidates for further experimental studies. Therefore, our findings can serve as useful guidelines for developing high-performance catalysts for NRR. [ABSTRACT FROM AUTHOR]