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The modulation of electrostatic potential and optoelectronic characteristics of Janus MoSSe/MX2 (M = Mo, X = S, Se) van der Waals (vdW) heterostructures with strain engineering were studied by first principles. Based on the effection of uniaxial strain, the electronic properties of heterostructures not only are induced to form direct band gap and indirect band gap and even semiconductor-metal transformation, but also lead to strong interface-built electric field and excellent optical adsorption properties in the range of IR-visible. This work reveals the photophysical properties of MoSSe/MX2 vdW heterostructures as well as shows their strong potential for applications in novel optoelectronic devices and photocatalysis. [ABSTRACT FROM AUTHOR]

Cobalt iron phosphide (Co–Fe–P), a metalloid-like material with zero band gap and high specific capacity, has received much attention in the field of supercapacitors, but the poor rate performance and cycling stability limit its commercial applications. Herein, we used cobalt-iron metal organic framework as the precursor (under the modulation of the polyvinylpyrrolidone (PVP), the morphology changes from three-dimensions to one-dimension), to synthesize the Co–Fe–P@NiCo-layered double hydroxide (LDH) core–shell nanostructure on conductive nickel foam (NF). Profiting of high conductivity of Co–Fe–P nanowires as the core and large surface area of NiCoLDH nanosheets as the shell, the fabricated Co–Fe–P@NiCoLDH/NF electrode exhibits outstanding electrochemical properties, such as high special capacity of 5.67 C cm−2 at a current density of 1 mA cm−2, remarkable rate capability (78.59% from 1 to 20 mA cm−2). Moreover, the asymmetric supercapacitor assembled by Co–Fe–P@NiCoLDH/NF and activated carbon/NF, also delivers excellent electrochemical performance with high energy density of 0.164 mW h cm−2 (30.4 mW h cm−3) and a superior cyclic life span of 91.67% over 5000 cyclic tests under 20 mA cm−2. This work proposes a unique route for the application of Co–Fe–P with elaborate structures, which may excite new significant findings in the energy storage field. [ABSTRACT FROM AUTHOR]

The electronic properties of one-dimensional superlattices which are alternately composed of graphene nanoribbon (GNR) and boron nitride nanoribbon (BNNR) with different unit ratio (GNR:BNNR) have been investigated by applying first-principles methods. The results show that the band gap of the superlattices is regulated in a wide range for both zigzag and armchair edges with increasing the BN proportion. With the increase of the BN proportion, the band gap increases either for zigzag edges superlattices or armchair edges superlattices. From analyzing the band structures, the local density of states, and the charge densities, the engineering mechanism is explored. Furthermore, the present results are coincidence with the conclusion of Kronig-Penney model. [ABSTRACT FROM AUTHOR]

van der Waals (vdW) heterojunctions enable arbitrary combinations of different layered semiconductors with unique band structures, offering distinctive band engineering for photonic and optoelectronic devices with new functionalities and superior performance. Here, an interlayer photoresponse of a few‐layer MoSe2/WSe2 vdW heterojunction is reported. With proper electrical gating and bias, the heterojunction exhibits high‐sensitivity photodetection with the operation wavelength extended up to the telecommunication band (i.e. 1550 nm). The photoresponsivity and normalized photocurrent‐to‐dark current ratio reach up to 127 mA W−1 and 1.9 × 104 mW−1, respectively. The results not only provide a promising solution to realize high‐performance vdW telecommunication band photodetectors, but also pave the way for using sub‐bandgap engineering of two‐dimensional layered materials for photonic and optoelectronic applications. van der Waals heterostructures are demonstrated as building blocks for photonics and optoelectronics. Herein, a sub‐bandgap photodetection at λ = 1550 nm based on a MoSe2/WSe2 heterojunction is demonstrated. The high responsivity as well as high normalized photocurrent‐to‐dark current ratio indicate that the heterojunction device has promising applications in future optoelectronic. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structures of the two-dimensional transition-metal dichalcogenide nanosheets under different out-of-plane pressure were investigated by using the first principle calculations. The band-gaps of all the nanosheets (thickness = 2, 4 and 6 layers) decrease with increasing pressure and finally close, indicating a semiconductor–metal transition. The critical pressure for the semiconductor–metal transition is larger for the thinner nanosheets, and the band-gap closes faster for the Mo-containing nanosheets than the W-containing ones. By taking bilayer MoS2 as an example, it was found that the physical mechanism of the band-gap variation relates to the charge accumulation and delocalization in the interlayer region. [Copyright &y& Elsevier]