Jiuxiang Dai

This work studies the growth, characterization, and device integration of 5-atom wide armchair graphene nanoribbons (5-AGNRs). 5-AGNRs are synthesized under ultrahigh vacuum conditions from Br- and I-substituted precursors. The authors show that I-substituted precursors and optimized initial precursor coverage quintupled the average 5-AGNR length. This significant length increase allows to integrate 5-AGNRs into field-effect transistors, showing switching behavior at room temperature.

Abstract

The electronic, optical, and magnetic properties of graphene nanoribbons (GNRs) can be engineered by controlling their edge structure and width with atomic precision through bottom-up fabrication based on molecular precursors. This approach offers a unique platform for all-carbon electronic devices but requires careful optimization of the growth conditions to match structural requirements for successful device integration, with GNR length being the most critical parameter. In this work, the growth, characterization, and device integration of 5-atom wide armchair GNRs (5-AGNRs) are studied, which are expected to have an optimal bandgap as active material in switching devices. 5-AGNRs are obtained via on-surface synthesis under ultrahigh vacuum conditions from Br- and I-substituted precursors. It is shown that the use of I-substituted precursors and the optimization of the initial precursor coverage quintupled the average 5-AGNR length. This significant length increase allowed the integration of 5-AGNRs into devices and the realization of the first field-effect transistor based on narrow bandgap AGNRs that shows switching behavior at room temperature. The study highlights that the optimized growth protocols can successfully bridge between the sub-nanometer scale, where atomic precision is needed to control the electronic properties, and the scale of tens of nanometers relevant for successful device integration of GNRs.

Sn doped MoSe₂ nanosheets are grown on graphene substrate uniformly in the vertical direction (Sn-MoSe₂@GN), which could introduce abundant defects and expose ample active sites to store Na-ions. When tested at a raised discharge cut-off voltage of 0.2 V for sodium ion batteries, the 9.6% Sn-MoSe₂@GN anode displays high specific capacity and superior cyclic stability.

Abstract

MoSe₂, as a typical 2D material, possesses tremendous potential in Na-ion batteries (SIBs) owing to larger interlayer distance, more favorable band gap structure, and higher theoretical specific capacity than other analogs. Nevertheless, the low intrinsic electronic conductivity and irreversible conversion of discharged products of Mo/Na₂Se to MoSe₂ seriously hamper its electrochemical performance. Herein, through a facile hydrothermal method combined with calcination process, Sn-doped MoSe₂ nanosheets grown on graphene substrate in the vertical direction are fabricated. Benefiting from the improved electronic conductivity contributed by the abundant defects and expanded interlamellar spacing of MoSe₂ originated from Sn doping, combined with a smart strategy of raising discharge cut-off voltage to 0.2 V during the actual performance testing for SIBs, the as-fabricated anode material delivers superior Na-ions storage performance in terms of electrons/ions transfer, reversible sodium storage as well as cycle stability. An ultra-stable reversible specific capacity of 268.5 mAh g^–1 at 1 A g^–1 can be maintained after 1600 cycles. Moreover, the great sodium storage property in the SIB full-cell system of the as-obtained nanocomposite illustrates practical potential. Density functional theory calculation and in situ/ex situ measurements are employed to further reveal the storage mechanism and process of Na-ions.

Author(s): Shihao Zhang, Xin Lu, and Jianpeng Liu

The correlated insulator (CI) states and the recently discovered density wave (DW) states in magic-angle twisted bilayer graphene (TBG) have stimulated intense research interest. However, to date, the nature of these “featureless” correlated states with zero Chern numbers are still elusive and lack …

[Phys. Rev. Lett. 128, 247402] Published Fri Jun 17, 2022

A feasible and general method that allows the controllable synthesis of higher-metal nitride nanosheets using amine-functionalized transition metal dichalcogenides (TMDs) nanosheets as precursors is reported. The solar water generation devices of higher-metal nitrides exhibit high-efficiency water evaporation. This study provides a series of advanced higher-metal nitrides with high-performance photothermal conversion efficiency for solar-driven steam evaporation.

Abstract

Higher-metal (HM) nitrides are a fascinating family of materials being increasingly researched due to their unique physical and chemical properties. However, few focus on investigating their application in a solar steam generation because the controllable and large-scale synthesis of these materials remains a significant challenge. Herein, it is reported that higher-metal molybdenum nitride nanosheets (HM-Mo₅N₆) can be produced at the gram-scale using amine-functionalized MoS₂ as precursor. The first-principles calculation confirms amine-functionalized MoS₂ nanosheet effectively lengthens the bonds of MoS leading to a lower bond binding energy, promoting the formation of MoN bonds and production of HM-Mo₅N₆. Using this strategy, other HM nitride nanosheets, such as W₂N₃, Ta₃N₅, and Nb₄N₅, can also be synthesized. Specifically, under one simulated sunlight irradiation (1 kW m^-2), the HM-Mo₅N₆ nanosheets are heated to 80 °C within only ≈24 s (0.4 min), which is around 78 s faster than the MoS₂ samples (102 s/1.7 min). More importantly, HM-Mo₅N₆ nanosheets exhibit excellent solar evaporation rate (2.48 kg m^-2 h^-1) and efficiency (114.6%), which are 1.5 times higher than the solar devices of MoS₂/MF.

The authors report a facile “topological-atom-extraction” synthesis protocol to design in-plane In₂O₃/HZIS (ZnIn₂S₄) heterostructure featuring zero-distance contact between In₂O₃ and HZIS, which renders remarkable charge redistribution on the thin in-plane heterostructure and creates local electric field confined within a thin layer. These characteristics are crucial for efficient charge-carrier separation in an S-scheme photocatalytic system and for providing long-lifetime carriers to the HZIS.

Abstract

Exploitation of atomic-level principles to optimize the charge transfer on ultrathin 2D heterostructures is an emerging frontier in relieving the energy and environmental crisis. Herein, a facile “topological-atom-extraction” protocol is disclosed, i.e., selective extraction of Zn from ultrathin half-unit-cell ZnIn₂S₄ (HZIS) can embed thin In₂O₃ domain into 1.60 nm thick HZIS layer to create an atomically thin in-plane In₂O₃/HZIS heterostructure. Thanks to the optimal distance and capability of charge separation, the in-plane In₂O₃/HZIS heterostructure is among the best ZnIn₂S₄-based CO₂ reduction reaction (CRR) photocatalysts, and indeed demonstrates a significant increase (from 6.8- to 128-fold) in CO production rate compared with those of out-plane ZIS@In₂O₃ and out-plane In₂O₃-HZIS_calcined heterostructures. Density Functional Theory simulation reveals that whereas the out-plane heterostructure has a much smaller ∆q of 0.2–0.25 e, the in-plane heterostructure with “zero distance contact” has an optimal ∆q of 1.05 e between In₂O₃ and HZIS that induces remarkable charge redistribution on the in-plane heterojunction interface and creates local electric field confined within the ultrathin layer. The charge redistribution efficiently directs the charge-carrier separation in S-scheme photocatalytic system and endows long-lifetime carrier to CRR active HZIS. The findings demonstrate the strong versatility of engineering atomic-level heterojunctions for efficient catalysts design.

Energy Harvesting

In article number 2200184, Yong Soo Cho and co-workers successfully apply an interdigitated electrode for a centimeter-scale monolayer MoS₂ film having preferred domain structure, without a complicated etching or e-beam lithography process. The fabricated device exhibits superior piezoelectric energy harvesting performance with 400.4 mV and 40.7 nA.

In this paper, by contacting a monolayer MoSe₂ with a 2D ferromagnetic semiconductor Cr₂Ge₂Te₆, a novel spin-valley functional device that exhibits both electrical and magnetic tunability is demonstrated. This provides a new physical knob that may effectively manipulate the spin-valley polarization in the device context.

Abstract

The emergence of atomically thin valleytronic semiconductors and 2D ferromagnetic materials is opening up new technological avenues for future information storage and processing. A key fundamental challenge is to identify physical knobs that may effectively manipulate the spin-valley polarization, preferably in the device context. Here, a novel spin functional device that exhibits both electrical and magnetic tunability is fabricated, by contacting a monolayer MoSe₂ with a 2D ferromagnetic semiconductor Cr₂Ge₂Te₆. Remarkably, the valley-polarization of MoSe₂ is found to be controlled by a back-gate voltage with an appreciably enlarged valley splitting rate. At fixed gate voltages, the valley-polarization exhibits magnetic-field and temperature dependence that corroborates well with the intrinsic magnetic properties of Cr₂Ge₂Te₆, pointing to the impact of magnetic exchange interactions. Due to the interfacial arrangement, the charge-carrying trion photoemission predominates in the devices, which may be exploited to enable drift-based spin-optoelectronic devices. These results provide new insights into valley-polarization manipulation in transition metal dichalcogenides by means of ferromagnetic semiconductor proximitizing and represent an important step forward in devising field-controlled 2D magneto-optoelectronic devices.

Recent advances and significant developments of chemical vapor deposition (CVD)-grown graphene toward flexible optoelectronics are comprehensively reviewed. The challenges of improvement of optoelectronic properties, work function tuning, as well as interfacial control of CVD-grown graphene for large-area optoelectronic devices are discussed. Various prototype devices are demonstrated, showing great potential for CVD-grown graphene in wearable optoelectronics.

Abstract

Graphene shows great potential for flexible optoelectronic devices owing to its unique 2D structure and excellent electronic, optical, and mechanical properties. Chemical vapor deposition (CVD) is the most promising method for fabricating large-area and high-quality graphene films at an acceptable cost; therefore enormous efforts have been attempted to investigate the flexible optoelectronic devices based on CVD-grown graphene. Here, recent advances and significant development of CVD-grown graphene towards flexible optoelectronics including photodetectors, organic solar cells, and light-emitting diodes are reviewed. Insight into the challenges of improvement of optoelectronic properties, work function tuning, as well as interfacial control of CVD-grown graphene for high-performance devices is provided. In particular, the availability to fabricate large-area devices on the flexible substrates is discussed, which is crucial to drive the practical use of CVD-grown graphene for future wearable optoelectronics.

A new platform of stacked polyethylene single crystal and monolayer MoSe₂ is created to accurately measure the mechanical properties of polymer single crystals where monolayer MoSe₂ provides strong mechanical support to enable a suspended stack over micro-holes. This structure also represents an ultimate polymer-ceramic crystalline laminate that may be modeled as a composite unit for complex composite design.

Abstract

Polymer single crystal (SC) is a key building block of semicrystalline polymers. However, direct experimental measurement of freestanding mono-lamella polymer SC has not been demonstrated. This is, in large part, due to the difficulties associated with manipulating freestanding individual mono-lamella SC because of its extremely low rigidity and low robustness. Here, we demonstrate a new strategy to successfully suspend and test a polymer SC by using a 2D material as backing. In particular, mono-lamella polyethylene (PE) SC is stacked on monolayer MoSe₂, and the hybrid stacks can be suspended over microholes. Nanoindentation is used to probe the suspended PE-SC/MoSe₂ stacks and MoSe₂ monolayers. The results suggest the first experimentally-measured in-plane moduli of PE-SC and 2D MoSe₂ as 32 ± 3 and 237 ± 15 GPa, respectively. Such a stacked unit represents an ultrathin structure of polymer-ceramic laminate and the idea can be applied to other laminated composite systems. Therefore, this research will pave the way to accurately measure the mechanical properties of polymer SCs and their composites, as well as provide a key insight on designing composite structures.

Ultrasensitive solar-blind ultraviolet photodetector based on FePSe₃/MoS₂ heterodiode is demonstrated. The exciting experimental results include a high R of 33 600 A W⁻¹, which is the highest performance compared with the state-of-the-art 2D material SBUV detectors, the noise equivalent power lower than 5.7 × 10^-16 W Hz^−1/2, high D* of 1.51 ×  10¹³ cm Hz^1/2 W⁻¹ in SBUV (230–280 nm) range. This finding promotes the development of SBUV photodetectors.

Abstract

Metal phosphorous tri-chalcogenides are a category of new ternary 2D layered materials with a wide range of tuneable bandgaps (1.2–3.5 eV). These wide-bandgap semiconductors exhibit great potential applications in solar-blind ultraviolet (SBUV) photodetection. However, these 2D solar-blind photodetectors suffer from low photoresponsivity, slow photoresponse speed, and narrow operation spectral region, thereby limiting their practical applications. Here, an ultra-broadband photodetection based on a FePSe₃/MoS₂ heterostructure with coverage ranging from solar-blind ultraviolet 265 nm to longwave infrared (LWIR) 10.6 µm is reported. Notably, the device exhibits excellent weak light detection capability. A high photoresponsivity of 33 600 A W⁻¹ and an external quantum efficiency of 1.57 × 10⁷% are demonstrated. A noise-equivalent power as low as 5.7 ×  10^–16 W Hz^−1/2 and a specific detectivity up to 1.51 × 10¹³ cm Hz^1/2 W⁻¹ are realized in the SBUV region. The room temperature LWIR photoresponsivity of 0.12 A W⁻¹ is realized. This work opens a route to design high-performance SBUV photodetectors and wide spectral photoresponse applications.

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDCs)-based heterostructures open the door to fabricate various promising hybrid photodetectors, while it is still a challenge to achieve excellent and stable near-infrared (NIR) photoresponse. Here, a MoS₂—2DPI (2D-polyimide (2DPI)) heterojunction-based phototransistor (HPT) was fabricated. Near-infrared photodetection with excellent performance has been realized. This HPT exhibited a photoresponsivity of 390.5 A/W, a specific detectivity of 5.10 × 10¹² Jones, a photogain 1.04 × 10⁵, and a photoresponse rise and decay time of 400 and 430 ms (λ = 900 nm, P = 16.2 µW/cm²), respectively. It also shows a broadband wavelength response from 405 to 1,020 nm. This superior performance could be attributed to the strong near-infrared absorption and the type-II (staggered) band alignment which ensures efficient charge transfer from 2DPI to MoS₂. The face-to-face spatial configuration of MoS₂—2DPI heterostructures ensures efficient transfer of photoinduced carriers through the interface, electron and holes can be separated due to the large band offsets. This work presents a significant step for the manipulation of high-performance NIR photodetector of two-dimensional covalent organic polymer-sensitized monolayer TMDCs.

Nature Energy, Published online: 16 June 2022; doi:10.1038/s41560-022-01035-4

Nature Materials, Published online: 16 June 2022; doi:10.1038/s41563-022-01277-3

Nature Materials, Published online: 16 June 2022; doi:10.1038/s41563-022-01275-5

Nature Materials, Published online: 16 June 2022; doi:10.1038/s41563-022-01285-3

Nature, Published online: 16 June 2022; doi:10.1038/d41586-022-01653-8

Nature, Published online: 15 June 2022; doi:10.1038/s41586-022-04715-z

Nature, Published online: 15 June 2022; doi:10.1038/s41586-022-04771-5

Nature, Published online: 15 June 2022; doi:10.1038/d41586-022-01568-4