Jiuxiang Dai

This study presents the epitaxial growth and stacking sequences of InTe, an intriguing material within III–VI metal chalcogenides. Utilizing aberration-corrected STEM, the interlayer stacking modes are directly revealed, leading to the identification of a new polytype. STEM analysis provided evidence for strong interlayer coupling in the new polytype, with layer-by-layer deposition identified as the mechanism behind the unconventional stacking order.

Abstract

III–VI metal chalcogenides have garnered considerable research attention as a novel group of layered van der Waals materials because of their exceptional physical properties and potential technological applications. Here, the epitaxial growth and stacking sequences of InTe is reported, an essential and intriguing material from III–VI metal chalcogenides. Aberration-corrected scanning transmission electron microscopy (STEM) is utilized to directly reveal the interlayer stacking modes and atomic structure, leading to a discussion of a new polytype. Furthermore, correlations between the stacking sequences and interlayer distances are substantiated by atomic-resolution STEM analysis, which offers evidence for strong interlayer coupling of the new polytype. It is proposed that layer-by-layer deposition is responsible for the formation of the unconventional stacking order, which is supported by ab initio density functional theory calculations. The results thus establish molecular beam epitaxy as a viable approach for synthesizing novel polytypes. The experimental validation of the InTe polytype here expands the family of materials in the III–VI metal chalcogenides while suggesting the possibility of new stacking sequences for known materials in this system.

Abstract

The exfoliation of bulk 2H-molybdenum disulfide (2H-MoS₂) into few-layer nanosheets with 1T-phase and controlled layers represents a daunting challenge towards the device applications of MoS₂. Conventional ion intercalation assisted exfoliation needs the use of hazardous n-butyllithium and/or elaborate control of the intercalation potential to avoid the decomposition of the MoS₂. This work reports a facile strategy by intercalating Li ions electrochemically with ether-based electrolyte into the van der Waals (vdW) channels of MoS₂, which successfully avoids the decomposition of MoS₂ at low potentials. The co-intercalation of Li⁺ and the ether solvent into MoS₂ makes a first-order phase transformation, forming a superlattice phase, which preserves the layered structure and hence enables the exfoliation of bulk 2H-MoS₂ into bilayer nanosheets with 1T-phase. Compared with the pristine 2H-MoS₂, the bilayer 1T-MoS₂ nanosheets exhibit better electrocatalytic performance for the hydrogen evolution reaction (HER). This facile method should be easily extended to the exfoliation of various transition metal dichalcogenides (TMDs).

A water-soluble substrate templates high-quality, free-standing oxide membranes.

Nature Communications, Published online: 26 January 2024; doi:10.1038/s41467-024-44972-2

Here, the authors report the characterization of stable few-layer PdSe2 transistors encapsulated in hexagonal boron nitride, showing field effect mobilities up to 700 cm2/Vs at room temperature and signatures of an 8-fold spin-valley degeneracy of the magnetotransport quantum oscillations at cryogenic temperatures.

Nature Photonics, Published online: 26 January 2024; doi:10.1038/s41566-024-01377-3

An optical readout technique for the chemical potential of an arbitrary two-dimensional material is realized using a monolayer transition metal dichalcogenide semiconductor sensor whose optical response sharply depends on the chemical potential.

2D materials are emerging as promising candidates for fabricating high-performance photodetectors. In this review, recent progress on 2D materials-based photothermoelectric detectors is reviewed. The physical detection mechanism and the photothermoelectric properties of 2D materials are summarized. Strategies to improve the photodetection performance of PTE detectors are reviewed. Finally, the challenges and prospects for future research are also provided.

Abstract

2D materials, with outstanding optical, thermal, and electric properties, are emerging as promising candidates for fabricating high-performance photodetectors. Recently, impressive progresses have been made in this area and some challenges are remaining to improve the properties of photodetectors. As one important part in the mainstream photodetection mechanisms, photothermoelectric (PTE) effect is showing unique priorities in fabricating advanced photodetectors, especially broadband detection operating in the mid-infrared and terahertz spectral regime. Here, recent progress on PTE photodetectors based on layered 2D materials is reviewed. The physical mechanism of PTE effect is first discussed and then the optical and thermoelectric properties of various 2D materials are analyzed. Furthermore, strategies to improve the photodetection performance of PTE detectors are summarized in two major categories including enhanced photothermal conversion and thermoelectric conversion processes. Finally, the challenges and prospects for future research in 2D thermoelectric materials and PTE detectors are also provided.

The family of 2D materials is an unprecedented platform for materials by design, thanks to their ever-expanding material portfolio with rich internal degrees of freedom. The study provides a comprehensive overview of the recent progress, challenges and emerging opportunities in a frontier research area that exploits machine learning—a very powerful data-driven approach and subset of artificial intelligence—for 2D materials.

Abstract

The availability of an ever-expanding portfolio of 2D materials with rich internal degrees of freedom (spin, excitonic, valley, sublattice, and layer pseudospin) together with the unique ability to tailor heterostructures made layer by layer in a precisely chosen stacking sequence and relative crystallographic alignments, offers an unprecedented platform for realizing materials by design. However, the breadth of multi-dimensional parameter space and massive data sets involved is emblematic of complex, resource-intensive experimentation, which not only challenges the current state of the art but also renders exhaustive sampling untenable. To this end, machine learning, a very powerful data-driven approach and subset of artificial intelligence, is a potential game-changer, enabling a cheaper – yet more efficient – alternative to traditional computational strategies. It is also a new paradigm for autonomous experimentation for accelerated discovery and machine-assisted design of functional 2D materials and heterostructures. Here, the study reviews the recent progress and challenges of such endeavors, and highlight various emerging opportunities in this frontier research area.

Adding 16.8 at% of indium to gallium leads to a significant indium enrichment of >83 at% on the topmost layer of the liquid alloy catalyst. Surface enrichment provides suitable catalytic interfaces for a highly efficient carbon dioxide reduction reaction (CO₂RR). The enrichment of indium alters the CO₂RRpathway, from carbon monoxide (CO)-dominated production by gallium to formate-dominated production by indium.

Abstract

Liquid metal alloys can accumulate specific solute metal atoms on their surface, creating distinct quasi-ordered atomic layers. Such atomic layers can be tuned by varying the alloy composition to form catalytic interfaces suited for multi-step reactions. Here, the surface enrichment in gallium-indium alloys is studied and utilized for carbon dioxide (CO₂) electrochemical reduction. The results show that adding a small amount of indium (16.8 at%) to gallium leads to a significant indium enrichment of >83 at% on the topmost layer of the alloy. This enrichment dictates the CO₂ conversion pathway, leading to 98% faradaic efficiency toward formate at −1.90 V vs reversible hydrogen electrode (RHE). This study produces unprecedented insights into key interfacial processes and lays the foundation for significant further work within the areas of catalysis and liquid metals.

A general, supramolecular self-assembly strategy is developed to intercalate unitary cation including NH₄ ⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺ and multiple cations (NH₄ ⁺ + Na⁺, NH₄ ⁺ + Na⁺ + Ca²⁺, NH₄ ⁺ + Na⁺ + Ca²⁺ + Mg²⁺) in ultrathin V₂O₅ nanosheets. The success on multiple cations nanoconfinement enables very fast zinc ion diffusion kinetics and excellent long-term cycling stability. The optimized diffusion coefficient of zinc ion (7.5 × 10⁻⁸ cm² s⁻¹) in this assembly series surpasses most of the V-based cathodes reported up to date.

Abstract

Nanoconfinement of cations in layered oxide cathode is an important approach to realize advanced zinc ion storage performance. However, thus far, the conventional hydrothermal/solvothermal route for this nanoconfinement has been restricted to its uncontrollable phase structure and the difficulty on the multiple cation co-confinement simultaneously. Herein, this work reports a general, supramolecular self-assembly of ultrathin V₂O₅ nanosheets using various unitary cations including Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺, NH₄ ⁺, and multiple cations (NH₄ ⁺ + Na⁺, NH₄ ⁺ + Na⁺ + Ca²⁺, NH₄ ⁺ + Na⁺ + Ca²⁺ +Mg²⁺). The unitary cation confinement results in a remarkable increase in the specific capacity and Zn-ion diffusion kinetics, and the multiple cation confinement gives rise to superior structural and cycling stability by multiple cation synergetic pillaring effect. The optimized diffusion coefficient of Zn-ion (7.5 × 10⁻⁸ cm² s⁻¹) in this assembly series surpasses most of the V-based cathodes reported up to date. The work develops a novel multiple-cations nanoconfinement strategy toward high-performance cathode for aqueous battery. It also provides new insights into the guest cation regulation of zinc-ion diffusion kinetics through a general, supramolecular assembly pathway.

Abstract

Strain engineering, as a powerful strategy to tune the optical and electrical properties of two-dimensional (2D) materials by deforming their crystal lattice, has attracted significant interest in recent years. 2D materials can sustain ultra-high strains, even up to 10%, due to the lack of dangling bonds on their surface, making them ideal brittle solids. This remarkable mechanical resilience, together with a strong strain-tunable band structure, endows 2D materials with a broad optical and electrical response upon strain. However, strain engineering based on 2D materials is restricted by their nanoscale and strain quantification troubles. In this study, we have modified a homebuilt three-points bending apparatus to transform it into a four-points bending apparatus that allows for the application of both compressive and tensile strains on 2D materials. This approach allows for the efficient and reproducible construction of a strain system and minimizes the buckling effect caused by the van der Waals interaction by adamantane encapsulation strategy. Our results demonstrate the feasibility of introducing compressive strain on 2D materials and the potential for tuning their optical and physical properties through this approach.

Nature, Published online: 30 January 2024; doi:10.1038/d41586-024-00261-y

Many explanations have been put forward for insects’ attraction to light, but high tech cameras now suggest a different answer.

npj 2D Materials and Applications, Published online: 30 January 2024; doi:10.1038/s41699-024-00444-1

Stochastic resonance in 2D materials based memristors

Colloidal transition metal dichalcogenide waveguides with tailorable dimensions are prepared by a scalable synthetic approach. Near-field nanoimaging is exploited to study their optical waveguiding properties, which are tunable by incident wavelength, nanowire thickness, and environmental temperature, highlighting the potential for active optical components and integrated photonic devices.

Abstract

Bulk transition metal dichalcogenide (TMDC) nanostructures are regarded as promising material candidates for integrated photonics due to their high refractive index at the near-infrared wavelengths. In this work, colloidal TMDC waveguides with tailorable dimensions are prepared by a scalable synthetic approach. The optical waveguiding properties of colloidal nanowires are studied by the near-field nanoimaging technique. In addition to dependence on thickness and wavelength, the excitonic responses and resultant waveguide modes in TMDC nanowires can be modulated by the environmental temperature. With the high-throughput production and tunable optical properties, colloidal TMDC nanowires highlight the potential for active optical components and integrated photonic devices.

Room-temperature Néel skyrmions in Fe₃GaTe₂ are observed through Lorentz transmission electron microscopy . Upon an optimized field cooling procedure, zero-field skyrmion lattices are successfully generated in nanoflakes with an extended thickness range. Significantly, these skyrmion lattices remain stable up to 355 K, setting a new record for the highest temperature at which skyrmions can be hosted.

Abstract

2D van der Waals (vdW) ferromagnetic crystals are a promising platform for innovative spintronic devices based on magnetic skyrmions, thanks to their high flexibility and atomic thickness stability. However, room-temperature skyrmion-hosting vdW materials are scarce, which poses a challenge for practical applications. In this study, a chemical vapor transport (CVT) approach is employed to synthesize Fe₃GaTe₂ crystals and room-temperature Néel skyrmions are observed in Fe₃GaTe₂ nanoflakes above 58 nm in thickness through in situ Lorentz transmission electron microscopy (L-TEM). Upon an optimized field cooling procedure, zero-field hexagonal skyrmion lattices are successfully generated in nanoflakes with an extended thickness range (30–180 nm). Significantly, these skyrmion lattices remain stable up to 355 K, setting a new record for the highest temperature at which skyrmions can be hosted. The research establishes Fe₃GaTe₂ as an emerging above-room-temperature skyrmion-hosting vdW material, holding great promise for future spintronics.

Herein, by freezing the transfer medium to induce the crosslinking of polymer chains, the adhesion is successfully tuned between graphene and polymer for wafer-scale all-dry of graphene and MoS₂ onto various substrates, compatible with industrial production for future applications.

Abstract

The real applications of chemical vapor deposition (CVD)-grown graphene films require the reliable techniques for transferring graphene from growth substrates onto application-specific substrates. The transfer approaches that avoid the use of organic solvents, etchants, and strong bases are compatible with industrial batch processing, in which graphene transfer should be conducted by dry exfoliation and lamination. However, all-dry transfer of graphene remains unachievable owing to the difficulty in precisely controlling interfacial adhesion to enable the crack- and contamination-free transfer. Herein, through controllable crosslinking of transfer medium polymer, the adhesion is successfully tuned between the polymer and graphene for all-dry transfer of graphene wafers. Stronger adhesion enables crack-free peeling of the graphene from growth substrates, while reduced adhesion facilitates the exfoliation of polymer from graphene surface leaving an ultraclean surface. This work provides an industrially compatible approach for transferring 2D materials, key for their future applications, and offers a route for tuning the interfacial adhesion that would allow for the transfer-enabled fabrication of van der Waals heterostructures.

A BiOCl-assisted chemical vapor deposition method is established to synthesize ultrathin p-type semiconductor α-In₂Te₃ nanoflakes at low temperature. With strong second harmonic generation and a narrow bandgap, it displays a high mobility of 18 cm² V⁻¹s⁻¹ and a broadband photoresponse ranging from 405 nm to 1064 nm, with response time of τ _rise = 1 ms.

Abstract

2D A2IIIB3VI${\mathrm{A}}_2^{{\mathrm{III}}}{\mathrm{B}}_3^{{\mathrm{VI}}}$ compounds (A = Al, Ga, In, and B = S, Se, and Te) with intrinsic structural defects offer significant opportunities for high-performance and functional devices. However, obtaining 2D atomic-thin nanoplates with non-layered structure on SiO₂/Si substrate at low temperatures is rare, which hinders the study of their properties and applications at atomic-thin thickness limits. In this study, the synthesis of ultrathin, non-layered α-In₂Te₃ nanoplates is demonstrated using a BiOCl-assisted chemical vapor deposition method at a temperature below 350 °C on SiO₂/Si substrate. Comprehensive characterization results confirm the high-quality single crystal is the low-temperature cubic phase α-In₂Te₃ , possessing a noncentrosymmetric defected ZnS structure with good second harmonic generation. Moreover, α-In₂Te₃ is revealed to be a p-type semiconductor with a direct and narrow bandgap value of 0.76 eV. The field effect transistor exhibits a high mobility of 18 cm² V⁻¹ s⁻¹, and the photodetector demonstrates stable photoswitching behavior within a broadband photoresponse from 405 to 1064 nm, with a satisfactory response time of τ_rise = 1 ms. Notably, the α-In₂Te₃ nanoplates exhibit good stability against ambient environments. Together, these findings establish α-In₂Te₃ nanoplates as promising candidates for next-generation high-performance photonics and electronics.

An in-depth examination of 2D FeFET advancements over recent years is provided in this review, including the working mechanism, structural evolution, as well as the diverse applications. Moreover, a summary of ongoing research efforts and offers further perspectives on the emerging opportunities for 2D FeFET is concluded.

Abstract

The rapid development in information technologies necessitates rapid advancements of their supporting hardware. In particular, new computing paradigms are needed to overcome the bottleneck of traditional von Neumann architecture. Bottom-up innovation, especially at the materials and devices level, has the potential to disrupt existing technologies through their emergent phenomena. As a new type of conceptual device, 2D ferroelectric field-effect transistor (FeFET) is highly sought after due to its potential integration with modern semiconductor processes. Its low power consumption, area efficiency, and ultra-fast operation provide an extra edge over traditional technologies. This review highlights recent developments in 2D FeFET, covering their device construction, working mechanisms, 2D ferroelectric polarization mechanism, multi-functional applications and prospects. In particular, the combination of 2D semiconductor and ferroelectric dielectric materials for multi-functionality applications is discussed. This includes non-volatile memories (NVM), neural network computing, non-volatile logic operation, and photodetectors. As a novel device platform, 2D semiconductor and ferroelectric interfaces are bestowed with a plethora of emergent physical mechanisms and applications.

This review provides a comprehensive and systematic overview of advancements in 2D transition metal dichalcogenides (2D TMDs) surface-enhanced Raman scattering (SERS) substrates, detailing the enhancement mechanisms, material exploration, material engineering techniques, and practical applications. It also discusses the challenges and future prospects of creating high-performance 2D TMDs SERS substrates and outlines potential directions for achieving significant breakthroughs in practical applications.

Abstract

Surface-enhanced Raman spectroscopy (SERS) is an ultrasensitive surface analysis technique that is widely used in chemical sensing, bioanalysis, and environmental monitoring. The design of the SERS substrates is crucial for obtaining high-quality SERS signals. Recently, 2D transition metal dichalcogenides (2D TMDs) have emerged as high-performance SERS substrates due to their superior stability, ease of fabrication, biocompatibility, controllable doping, and tunable bandgaps and excitons. In this review, a systematic overview of the latest advancements in 2D TMDs SERS substrates is provided. This review comprehensively summarizes the candidate 2D TMDs SERS materials, elucidates their working principles for SERS, explores the strategies to optimize their SERS performance, and highlights their practical applications. Particularly delved into are the material engineering strategies, including defect engineering, alloy engineering, thickness engineering, and heterojunction engineering. Additionally, the challenges and future prospects associated with the development of 2D TMDs SERS substrates are discussed, outlining potential directions that may lead to significant breakthroughs in practical applications.

The morphology of ZnSe epilayers on InP NCs is controlled, ranging from tetrapod to spherical InP/ZnSe heterostructured NCs, under the guidance of DFT calculations. The expanded morphology envelope permits InP/ZnSe heterostructured NCs to customize their photophysical characteristics from stable and pure emission to environment-sensitive ones, which will prompt their practical use in a range of photonic applications.

Abstract

The morphology of heterostructured semiconductor nanocrystals (h-NCs) dictates the spatial distribution of charge carriers and their recombination dynamics and/or transport, which are the main performance indicators of photonic applications utilizing h-NCs. The inability to control the morphology of heterovalent III-V/II-VI h-NCs composed of heavy-metal-free elements hinders their practical use. As a case study of III-V/II-VI h-NCs, the growth control of ZnSe epilayers on InP NCs is demonstrated here. The anisotropic morphology in InP/ZnSe h-NCs is attributed to the facet-dependent energy costs for the growth of ZnSe epilayers on different facets of InP NCs, and effective chemical means for controlling the growth rates of ZnSe on different surface planes are demonstrated. Ultimately, this article capitalizes on the controlled morphology of InP/ZnSe h-NCs to expand their photophysical characteristics from stable and pure emission to environment-sensitive one, which will facilitate their use in a variety of photonic applications.

Nature Electronics, Published online: 02 February 2024; doi:10.1038/s41928-024-01118-y

Polycrystalline thin films of elemental bismuth exhibit a room-temperature nonlinear transverse voltage due to geometric effects of surface electrons that is tunable and can be extended to efficient high-harmonic generation at terahertz frequencies.

Nature Materials, Published online: 02 February 2024; doi:10.1038/s41563-023-01781-0

Electronic moiré patterns can be imprinted remotely onto a target quantum material, inducing exotic interacting behaviour.