Jiuxiang Dai

Abstract

Broadband photodetectors with polarization-sensitive ability have received extraordinary attention for modern optoelectronic devices. Ideal photodetectors should possess high responsivity, fast response, and good stability, which are rare to meet at the same time in one low-symmetric two-dimentional (2D) material. In this work, neodymium diantimonides (NdSb₂), a member of light rare-earth diantimonides RSb₂ (R = La−Nd, Sm) with low-symmetry structure, is introduced as a fascinating highly anisotropic 2D material for broadband detection (532 nm to 4 µm). The photodetector exhibits a responsivity of 0.49 mA·W⁻¹ with 15 µs response time at 532 nm and highly stable performance under ambient conditions over 8 months. Furthermore, we identify the polarization-sensitive photoresponse of the detector and demonstrate a high anisotropic factor ∼ 1.6. In addition, strong in-plane anisotropy is revealed by anisotropic phonon response and the photodetection mechanism is investigated by scanning photocurrent microscopy measurements. This pioneer work on NdSb₂ paves the way for further exploration of 2D RSb₂ for high performance polarized photodetectors with fast photothermoelectric response.

The synthesis of the 2D SnP nanosheets on liquid tin (Sn) substrate via the atmospheric pressure chemical vapor deposition (APCVD) method is demonstrated here. HRTEM and SAED reveal high-quality and single crystalline structure of the SnP nanosheet. The temperature-dependent and angle-resolved polarization Raman spectra from an experimental perspective are performed. Furthermore, the 2D SnP FET devices show a typical n-type semiconductor characteristic.

Abstract

As an important metal phosphides material, 2D tin phosphides (SnP_x 0 <  x ≤ 3) have been theoretically predicted to have intriguing physicochemical properties and potential applications in electronics, optoelectronics, and energy fields. However, the synthesis of high-quality 2D SnP single crystal has not been reported due to the lack of efficiency and reliable growth method. Here, a facile atmospheric pressure chemical vapor deposition (APCVD) method is developed to realize the growth of high-quality 2D SnP nanosheets, by employing tin (Sn) foil as both liquid metal substrates and reaction precursor. Temperature-dependent and angle-resolved polarization Raman spectra observed Raman peaks located at 142.6, 303.3, and 444.2 cm^-1 are concluded to belong to A_1g mode, which are consistent with the theoretical calculation results. Moreover, the field-effect transistor (FET) devices based on SnP nanosheets show a typical n-type characteristic with an on/off ratio of 10³ at 200 K. SnP nanosheets also demonstrate excellent photoresponse performance under the illumination of 473, 532, and 639 nm lasers, which can be tuned by V _gs, V _ds, and light power density. It is believed that these findings can provide the first-hand experimental information for the future study of 2D SnP nanosheets.

The increasing interest in 2D ultrawide bandgap materials requires in-depth research on their crystal structures, physical properties, preparation, and potential applications. In this review, comprehensive progress of 2D ultrawide bandgap semiconductor materials is discussed. Proposed challenges need to be addressed in the future to unveil their potential applications.

Abstract

2D ultrawide bandgap (UWBG) semiconductors have aroused increasing interest in the field of high-power transparent electronic devices, deep-ultraviolet photodetectors, flexible electronic skins, and energy-efficient displays, owing to their intriguing physical properties. Compared with dominant narrow bandgap semiconductor material families, 2D UWBG semiconductors are less investigated but stand out because of their propensity for high optical transparency, tunable electrical conductivity, high mobility, and ultrahigh gate dielectrics. At the current stage of research, the most intensively investigated 2D UWBG semiconductors are metal oxides, metal chalcogenides, metal halides, and metal nitrides. This paper provides an up-to-date review of recent research progress on new 2D UWBG semiconductor materials and novel physical properties. The widespread applications, i.e., transistors, photodetector, touch screen, and inverter are summarized, which employ 2D UWBG semiconductors as either a passive or active layer. Finally, the existing challenges and opportunities of the enticing class of 2D UWBG semiconductors are highlighted.

Nature Communications, Published online: 11 March 2022; doi:10.1038/s41467-022-29127-5

Author Correction: Observation of Weyl fermions in a magnetic non-centrosymmetric crystal

The two-dimensional (2D) metal nitrides (MNs), including group IIA nitrides, group IIIA nitrides, nitride MXene and other transition metal nitrides (TMNs), exhibit unique electronic and magnetic characteristics. The 2D MNs have been widely studied by experimental and computational approaches and some of them have been synthesized. Herein we systematically reviewed the structural, electronic, thermal, mechanical, magnetic and optical properties of the 2D MNs that have been reported in recent years. Based on their unique properties, the related applications of 2D MNs on fields like electronics, spintronics, sensing, catalysis, and energy storage were discussed. Additionally, the lattice structures and synthetic routes were also summarized as supplements of the research progress of 2D MNs family. Furthermore, we provided insights into the research prospects and future efforts that need to be made on 2D MNs.

Nature Communications, Published online: 14 March 2022; doi:10.1038/s41467-022-29042-9

Excitons in 2D semiconductors suffer from a weak response to in-plane electric fields, inhibiting their transport beyond the diffusion length. Here, the authors demonstrate the directional, long-range transport of interlayer excitons in bilayer WSe2 driven by the propagating potential traps induced by surface acoustic waves.

npj 2D Materials and Applications, Published online: 14 March 2022; doi:10.1038/s41699-022-00294-9

2D transistors rapidly printed from the crystalline oxide skin of molten indium

npj 2D Materials and Applications, Published online: 14 March 2022; doi:10.1038/s41699-022-00293-w

The resurrection of tellurium as an elemental two-dimensional semiconductor

Nature Nanotechnology, Published online: 14 March 2022; doi:10.1038/s41565-021-01068-y

This Review discusses the recent progress in the emerging field of exciton phenomena in semiconductor moiré superlattices.

Nature Nanotechnology, Published online: 14 March 2022; doi:10.1038/s41565-022-01073-9

Nonlinear optical parametric polaritons are observed in a WS2 monolayer microcavity, opening the way for all-optical valley polariton nonlinear devices.

On epitaxial substrates with moderate surface interactions, density functional theory calculations show that a step with appropriate height can not only promote simultaneous nucleation of thickness-matched MoS₂ domains with aligned edges but also suppresses the nucleation of thinner MoS₂ domains, by which uniform multilayer MoS₂ with targeted thickness can be grown.

Abstract

Multilayer MoS₂ shows superior performance over the monolayer MoS₂ for electronic devices while the growth of multilayer MoS₂ with controllable and uniform thickness is still very challenging. It is revealed by calculations that monolayer MoS₂ domains are thermodynamically much more favorable than multilayer ones on epitaxial substrates due to the competition between surface interactions and edge formation, leading accordingly to a layer-by-layer growth pattern and non-continuously distributed multilayer domains with uncontrollable thickness uniformity. The thermodynamics model also suggests that multilayer MoS₂ domains with aligned edges can significantly reduce their free energy and represent a local minimum with very prominent energy advantage on a potential energy surface. However, the nucleation probability of multilayer MoS₂ domains with aligned edges is, if not impossible, extremely rare on flat substrates. Herein, a step-guided mechanism for the growth of uniform multilayer MoS₂ on an epitaxial substrate is theoretically proposed. The steps with proper height on sapphire surface are able to guide the simultaneous nucleation of multilayer MoS₂ with aligned edges and uniform thickness, and promote the continuous growth of multilayer MoS₂ films. The proposed mechanism can be reasonably extended to grow multilayer 2D materials with uniform thickness on epitaxial substrates.

npj 2D Materials and Applications, Published online: 15 March 2022; doi:10.1038/s41699-022-00298-5

Direct observation of ferroelectricity in two-dimensional MoS₂

Moiré lattice in artificially stacked monolayers of two-dimensional (2D) materials effectively modulates the electronic structures of materials, which is widely highlighted. Formation of the electronic Moiré s...

Light: Science & Applications, Published online: 16 March 2022; doi:10.1038/s41377-022-00747-2

Artist’s impression (not to scale) showing a fanciful concept of how a glass microsphere produces a photonic nanojet that significantly improves resolution when examining microchip wafers with a microscope.

In this article, the wide variety of electromechanical responses of liquid metal stretchable electronics reported in the literature are reviewed. Complementing this review with our own measurements, the relative change in resistance of EGaIn is found to be lower than that of a bulk conductor. Then, possible explanations for the discrepancies are dicussed and suggestions are provided on experimental design for future research.

Abstract

Stretchable electronics have potential in wide-reaching applications including wearables, personal health monitoring, and soft robotics. Many recent advances in stretchable electronics leverage liquid metals, particularly eutectic gallium-indium (EGaIn). A variety of EGaIn electromechanical behaviors have been reported, ranging from bulk conductor responses to effectively strain-insensitive responses. However, numerous measurement techniques have been used throughout the literature, making it difficult to directly compare the various proposed formulations. Here, the electromechanical responses of EGaIn found in the literature is reviewed and pure EGaIn is investigated using three electrical resistance measurement techniques: four point probe, two point probe, and Wheatstone bridge. The results indicate substantial differences in measured electromechanical behavior between the three methods, which can largely be accounted for by correcting for a fixed offset corresponding to the resistances of various parts of the measurement circuits. Yet, even accounting for several of these sources of experimental error, the average relative change in resistance of EGaIn is found to be lower than that predicted by the commonly used bulk conductor assumption, referred to as Pouillet's law. Building upon recent theories proposed in the literature, possible explanations for the discrepancies are discussed. Finally, suggestions are provided on experimental design to enable reproducible and interpretable research.

Ferroelastic–ferroelectric multiferroic materials can switch orientations of crystal structure and polarization with external strain. 2D ferroelastic–ferroelectric multiferroicity in single-crystalline rhenium dichalcogenides is discovered. Reorientation of the physical properties based on reversible bond switching between the rhenium atoms provides insights for 2D multiferroic phase transitions and opens up new opportunities for applications such as multilevel memory.

Abstract

2D multiferroics with combined ferroic orders have gained attention owing to their novel functionality and underlying science. Intrinsic ferroelastic–ferroelectric multiferroicity in single-crystalline van der Waals rhenium dichalcogenides, whose symmetries are broken by the Peierls distortion and layer-stacking order, is demonstrated. Ferroelastic switching of the domain orientation and accompanying anisotropic properties is achieved with 1% uniaxial strain using the polymer encapsulation method. Based on the electron localization function and bond dissociation energy of the Re–Re bonds, the change in bond configuration during the evolution of the domain wall and the preferred switching between the two specific orientation states are explained. Furthermore, the ferroelastic switching of ferroelectric polarization is confirmed using the photovoltaic effect. The study provides insights into the reversible bond-switching process and potential applications based on 2D multiferroicity.

Nature Communications, Published online: 16 March 2022; doi:10.1038/s41467-022-29001-4

Graphene and related two-dimensional (2D) materials have remained an active field of research in science and engineering for over fifteen years. Here, the authors investigate why the transition from laboratories to fabrication plants appears to lag behind expectations, and summarize the main challenges and opportunities that have thus far prevented the commercialisation of these materials.

npj 2D Materials and Applications, Published online: 17 March 2022; doi:10.1038/s41699-022-00291-y

Robust all-electrical topological valley filtering using monolayer 2D-Xenes