Jiuxiang Dai

Nature Communications, Published online: 11 January 2022; doi:10.1038/s41467-021-27916-y

Partly Covered PProDOT-Me₂ on MoS₂ Nanosheets Counter Electrode

In article number 2100945, M. A. Khalifa, K. Sheng, Z. Wang, J. Zheng, and C. Xu develop a partly covered PProDOT-Me₂ on MoS₂ nanosheets counter electrode for self-powered electrochromic device. The device can be applied to smart windows to reduce heat insulation and produce electrical energy that can charge many electronic devices. The electrochromic device can be dark blue under sunlight and transparent at night.

npj 2D Materials and Applications, Published online: 10 January 2022; doi:10.1038/s41699-021-00282-5

A Fe/Mn dual single-atom catalyst with an excellent bifunctional activity is prepared as the cathode for a flexible low-temperature Zn-air battery (ZAB). Profiting from the combined Fe/Mn dual-site effect as well as the porous 2D nanosheet structure, the ZAB could operate efficiently at the ultra-low temperature of −40 °C.

Abstract

Herein, a novel dual single-atom catalyst comprising adjacent Fe-N₄ and Mn-N₄ sites on 2D ultrathin N-doped carbon nanosheets with porous structure (FeMn-DSAC) was constructed as the cathode for a flexible low-temperature Zn-air battery (ZAB). FeMn-DSAC exhibits remarkable bifunctional activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Control experiments and density functional theory calculations reveal that the catalytic activity arises from the cooperative effect of the Fe/Mn dual-sites aiding *OOH dissociation as well as the porous 2D nanosheet structure promoting active sits exposure and mass transfer during the reaction process. The excellent bifunctional activity of FeMn-DSAC enables the ZAB to operate efficiently at ultra-low temperature of −40 °C, delivering 30 mW cm⁻² peak power density and retaining up to 86 % specific capacity from the room temperature counterpart.

Author(s): Qiao Jin et al.

Heterointerfaces have led to the discovery of novel electronic and magnetic states because of their strongly entangled electronic degrees of freedom. Single-phase chromium compounds always exhibit antiferromagnetism following the prediction of the Goodenough-Kanamori rules. So far, exchange coupling...

[Phys. Rev. Lett. 128, 017202] Published Fri Jan 07, 2022

A fully vacuum-processed photomultiplication-type organic photodetector for near-infrared (NIR) sensing with high and bias-independent specific detectivity is achieved by efficient trap-assisted electron injection. More than 100% external quantum efficiency is exhibited at only −1 V. For the NIR light, an impressive specific detectivity ≈10¹³ Jones can almost be voltage-independent up to −10 V, indicating their potential in state-of-the-art readout electronics.

Abstract

Highly responsive organic photodetectors allow a plethora of applications in fields like imaging, health, security monitoring, etc. Photomultiplication-type organic photodetectors (PM-OPDs) are a desirable option due to their internal amplification mechanism. However, for such devices, significant gain and low dark currents are often mutually excluded since large operation voltages often induce high shot noise. Here, a fully vacuum-processed PM-OPD is demonstrated using trap-assisted electron injection in BDP-OMe:C₆₀ material system. By applying only −1 V, compared with the self-powered working condition, the responsivity is increased by one order of magnitude, resulting in an outstanding specific detectivity of ≈10¹³ Jones. Remarkably, the superior detectivity in the near-infrared region is stable and almost voltage-independent up to −10 V. Compared with two photovoltaic-type photodetectors, these PM-OPDs exhibit the great potential to be easily integrated with state-of-the-art readout electronics in terms of their high responsivity, fast response speed, and bias-independent specific detectivity. The employed vacuum fabrication process and the easy-to-adapt PM-OPD concept enable seamless upscaling of production, paving the way to a commercially relevant photodetector technology.

Orientated growth of Te with a thickness down to 5 nm is realized on the three-fold symmetric substrates (WSe₂, WS₂, MoSe₂, and MoS₂). This method is extended to the growth of SeTe alloys, providing flexibility for band engineering. Finally, growth of single-crystal-textured Te film is demonstrated on the low-symmetric surface of WTe₂.

Abstract

Tellurium, as an elemental van der Waals semiconductor, has intriguing anisotropic physical properties owing to its inherent 1D crystal structure. To exploit the anisotropic and thickness-dependent behavior, it is important to realize orientated growth of ultrathin tellurium. Here, van der Waals epitaxial growth of Te on the surface of 2D transition metal dichalcogenides is systematically investigated. Orientated growth of Te with a thickness down to 5 nm is realized on three-fold symmetric substrates (WSe₂, WS₂, MoSe₂, and MoS₂), where the atomic chains of Te are aligned with the armchair directions of substrates. 1D/2D moiré superlattices are observed for the Te/WSe₂ heterostructure. This method is extended to the growth of SeTe alloys, providing flexibility for band engineering. Finally, growth of textured Te film is demonstrated on the lower-symmetry surface of WTe₂.

WS_2x Se_2−2x spiral nanosheets demonstrate quadratically enhanced strong layer-dependent second-harmonic generation effects. The atomic scanning tunneling microscopy images and scanning tunneling spectroscopy maps at the WS/WSe interfaces demonstrate electron scattering at the alloy interfaces at deeper energy levels, providing a detailed nanoscale interpretation of the S/Se-ratio-dependent lifetimes inferred from pump–probe spectroscopy measurements.

Abstract

Electronic properties at the interfaces between different-composition domains of 2D-alloys are key for their optical, electronic, and optoelectronic applications. Understanding the interfacial electronic structures and carrier dynamics is essential for designing and fabricating devices that use these alloys. Here, WS_2x Se_2−2x spiral nanosheets are prepared using the physical vapor deposition method, and the nonlinear optical and electronic properties, as well as the carrier dynamics at the interfaces between the WS and WSe domains, are studied. Second-harmonic generation tests demonstrate that these nanosheets exhibit a very strong layer-dependent nonlinear optical effect. Atomic-resolution scanning tunneling microscopy (STM) and spectroscopy (STS) measurements reveal that S and Se atoms are non-uniformly distributed, forming WS domains, WSe domains, and defect-related areas. Atomic STM images and STS maps reveal enhanced local density of states by electron scattering at the WS/WSe interfaces, providing a detailed nanoscale interpretation of the S/Se-ratio-dependent lifetimes observed in pump–probe spectroscopy measurements. This work provides valuable interfacial characterization of 2D-alloy materials, using state-of-the-art methods with high temporal and spatial resolutions. The obtained insights are likely to be useful for prospective applications.

A class of ultrathin 2D copper chalcogenides with intrinsic memristive properties is synthesized via van der Waals epitaxy. The fabricated memristors exhibit relatively small switching voltage, fast switching speed, high switching uniformity, and wide operating temperature range, as well as stable retention and switching characteristics, indicating their tangible applications in future electronics.

Abstract

Copper chalcogenides represent a class of materials with unique crystal structures, high electrical conductivity, and earth abundance, and are recognized as promising candidates for next-generation green electronics. However, their 2D structures and the corresponding electronic properties have rarely been touched. Herein, a series of ultrathin copper chalcogenide nanosheets with thicknesses down to two unit cells are successfully synthesized, including layered Cu₂Te, as well as nonlayered CuSe and Cu₉S₅, via van der Waals epitaxy, and their nonvolatile memristive behavior is investigated for the first time. Benefiting from the highly active Cu ions with low migration barriers, the memristors based on ultrathin 2D copper chalcogenide crystals exhibit relatively small switching voltage (≈0.4 V), fast switching speed, high switching uniformity, and wide operating temperature range (from 80 to 420 K), as well as stable retention and good cyclic endurance. These results demonstrate their tangible applications in future low-power, cryogenic, and high temperature harsh electronics.

2D superlattices comprising monolayer FeP nanoframes are designed and synthesized through a space-confined topochemical transformation approach, using carbon-coated Fe₃O₄ nanocube superlattices as a precursor. The resulting 2D FeP nanoframe superlattices possess a number of unique features unavailable in conventional nanocrystal superlattices, which make them particularly promising as highly efficient and durable electrocatalysts in hydrogen evolution reaction process.

Abstract

Self-assembled nanocrystal superlattices represent an emergent class of designer materials with potentially programmable functionalities. The ability to construct hierarchically structured nanocrystal superlattices with tailored geometry and porosity is critical for extending their applications. Here, 2D superlattices comprising monolayer FeP nanoframes are synthesized through a space-confined topochemical transformation approach induced by the Kirkendall effect, using carbon-coated Fe₃O₄ nanocube superlattices as a precursor. The particle shape and the close-packed nature of Fe₃O₄ nanocubes as well as the interconnected carbon layer network contribute to the topochemical transformation process. The resulting 2D FeP nanoframe superlattices possess several unique and advantageous structural features that are unavailable in conventional 3D nanocrystal superlattices, which make them particularly attractive for catalytic applications. As a proof of concept, such 2D FeP nanoframe superlattices are harnessed as highly efficient and durable electrocatalysts for the hydrogen evolution reaction, the performance of which is superior to that of most FeP-based catalysts reported previously. This topochemical transformation approach is scalable and general, representing a new route of designing hierarchical superlattices with highly open features that cannot be accessible by traditional self-assembly methods.

The very recent advances in controlled production of two-dimension transition metal carbides and nitrides (MXenes) crystals by chemical vapor deposition, included several kinds of MXenes crystals and MXenes heterostructures.

Abstract

As a novel family of 2D materials, MXenes have drawn intensive interests owing to its fascinating property profile. The ability to grow high-quality MXenes in a controllable way would in turn further promote the development of fabrication techniques and expand wide advanced applications. Then 2D MXenes crystals are highly desirable and many approaches have been explored to realize the mass production. Chemical vapor deposition (CVD) provides compelling benefits over other alternatives in controllability, uniformity and scalability. In this review, the recent advances in growth of MXenes crystals by CVD method will comprehensively present. Several typical kinds of MXenes crystals are demonstrated to be fabricated with a precise control in terms of size, morphology and thickness. Further, a series of MXenes heterostructures are constructed including vertical and lateral spatial orientations. Then, the properties and applications of MXenes crystals are exhibited, of which superconductivity and electrochemical catalysts will be mainly emphasized. Finally, the authors put forward views on the future development in the synthesis of MXenes. With continuous efforts devoted, a bright future of MXenes crystals prepared by CVD is expected.

Robust spin-dependent transport is demonstrated well beyond room temperature in heterostructures of graphene and the antiferromagnetic oxide chromia. The spin-dependent transport is attributed to the symmetry-breaking action of chromia, and persists at zero magnetic field and despite the absence of any ferromagnetic elements in the devices. These results represent an important advance for practical spintronics based on graphene.

Abstract

Evidence of robust spin-dependent transport in monolayer graphene, deposited on the (0001) surface of the antiferromagnetic (AFM)/magneto-electric oxide chromia (Cr₂O₃), is provided. Measurements performed in the non-local spin-Hall geometry reveal a robust signal that is present at zero external magnetic field and which is significantly larger than any possible ohmic contribution. The spin-related signal persists well beyond the Néel temperature (≈307 K) that defines the transition between the AFM and paramagnetic states, remaining visible at the highest studied temperature of close to 450 K. This robust character is consistent with prior theoretical studies of the graphene/Cr₂O₃ system, predicting that the lifting of sub-lattice symmetry in the graphene shall induce an effective spin–orbit term of ≈40 meV. Overall, the results indicate that graphene-on-chromia heterostructures are a highly promising framework for the implementation of spintronic devices, capable of operation well beyond room temperature.