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Palladium diselenide (PdSe2), as a member of two-dimensional dichalcogenides, has a puckered pentagonal structure and tends to exhibit distinct physical properties due to the various polymorphic phases. In contrast to conventionally orthorhombic PdSe2 (O-PdSe2), the fabrication of continuous metastable monoclinic PdSe2 (M-PdSe2) remains a challenge. Here, we report the polymorphic integration of orthorhombic and monoclinic PdSe2 crystals by concisely controlled selenization engineering under Se-sufficient and Se-deficient growth conditions. Thus, the hybrid O-PdSe2/M-PdSe2 (O/M-PdSe2) nanostructures were fabricated for the first time. We found that the O/M-PdSe2 nanostructures may be used as the broadband photodetector with a relatively high responsivity of 211.4 mA W–1, laying the foundation for the expansion of high-performance photoexcited gas sensors operating at room temperature. The O/M-PdSe2 sensor exhibited extremely fast response and recovery times (132/84 s) toward 10 ppm NO2 gas under 405 nm light illumination compared to the dark condition. In addition, according to the optical absorption spectra and ultraviolet photoemission spectroscopy analyses, the energy band alignment at the O/M-PdSe2 interface was determined, and the detailed gas-sensing mechanism was also proposed on this basis. This work realizes the continuous fabrication of the hybrid O/M-PdSe2 nanostructures with promisingly combined photoelectric and gas-electric properties, which may promote the development of high-performance multifunctional nanoelectronic devices to meet the global challenges of energy shortage and environmental protection. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2), a transition metal dichalcogenide (TMD), is conventionally regarded as a promising room-temperature sensing material due to its unique physical and chemical properties. However, the gas sensors based on pure MoS2 films do not seem to achieve the expectation. In this study, we fabricated the unique structure of dispersed Co and Zn atoms doped on the MoS2/graphite (Co–Zn/MG) composite and investigated the gas-sensing properties. We find that the sensor based on the Co–Zn/MG composite shows high responses toward NO2 gas (Ra/Rg = ∼1.3 at 50 ppb and ∼5.5 at 5 ppm) at room temperature, which is significantly higher than that of the pristine MoS2 sensor in our work. In addition, the Co–Zn/MG sensor has a low limit of detection of 6.2 ppb, fast response–recovery time (118/383 s toward 1 ppm NO2), and long-term stability. Compared with other gases, including NO, NH3, H2, CO, and ethanol, the sensor exhibits good selectivity toward NO2 due to its lower activation energy. Furthermore, the enhanced gas-sensing mechanism can be attributed to the modulation of Schottky barrier height, enriched oxygen adsorption, and catalysis. This work may open a new avenue to achieve NO2 sensors with absolutely competitive performance at room temperature. [ABSTRACT FROM AUTHOR]

The fabrication of van der Waals (vdWs) heterostructures mainly extends to two-dimensional (2D) materials. Nevertheless, the current processes for obtaining high-quality 2D films are mainly exfoliated from their bulk counterparts or by high-temperature chemical vapor deposition (CVD), which limits industrial production and is often accompanied by defects. Herein, we first fabricated the type-II p-PdSe 2 /n-InSe vdWs heterostructure using the ultra-high vacuum laser molecular beam epitaxy (LMBE) technique combined with the vertical 2D stacking strategy, which is reproducible and suitable for high-volume manufacturing. This work found that the introduction of 365 nm UV light illumination can significantly improve the electrical transport properties and NO 2 sensing performance of the PdSe 2 /InSe heterojunction-based device at room temperature (RT). The detailed studies confirm that the sensor based on the PdSe 2 /InSe heterojunction delivers the comparable sensitivity ( R a / R g = ∼2.6 at 10 ppm), a low limit of detection of 52 ppb, and excellent selectivity for NO 2 gas under UV light illumination, indicating great potential for NO 2 detection. Notably, the sensor possesses fast response and full recovery properties (275/1078 s) compared to the results in the dark. Furthermore, the mechanism of enhanced gas sensitivity was proposed based on the energy band alignment of the PdSe 2 /InSe heterojunction with the assistance of investigating the surface potential variations. This work may pave the way for the development of high-performance, room-temperature gas sensors based on 2D vdWs heterostructures through the LMBE technique.