Jiuxiang Dai

In 2D ferroionic material CuInP₂S₆, the transition and collaboration of ion migration and ferroelectric polarization are engineered to realize function-enriched information devices. Non-volatile digital memory governed by long-range ion migration and fundamental synaptic functions governed by ferroelectric polarization reversal are implemented. The co-modulation of polarization switching and ions migration induced an intriguing transition from potentiation to depression of post-synaptic current.

Abstract

Two-dimensional (2D) ferroionics is appealing in performing complex artificial intelligence tasks due to the interesting property of coexistence of ferroelectricity and ionic activities. CuInP₂S₆ (CIPS), as a typical 2D ferroionic material, is highly conducive to rich functions of information devices due to the displacement of Cu⁺ inducing both ferroelectricity and ionic conductivity. However, the coupling and modulation of polarization and ion migration in CIPS for multifunctional information devices has not been fully explored. Here, this study demonstrates that digital memory and synaptic simulations are realized in Au/CIPS/Au device via engineering ferroelectric polarization reversal and the long-distance migration of the Cu⁺ to change conductive modes. Steep resistive switching behavior based on ion-migration is observed with a high on/off ratio of over 10⁸, long retention time (>2 × 10⁴ s), and current compliance engineered multilevel resistance states, demonstrating reliable nonvolatile high-density memory characteristics. Based on the continuous modulation of polar order, the key synaptic behaviors are successfully simulated. Moreover, by the co-modulation of polarization state and ions migration, the paired-pulse facilitation, paired-pulse depression, and potentiation following depression are achieved. These results suggest that CIPS is a promising candidate for constructing high-performance, function-enriched devices for data storage, information processing, and neuromorphic computing.

The GAA-MOCVD is introduced to realize the epitaxial growth of one additional layer on monolayer MoS₂, resulting in bi-layer MoS₂ film with spatial homogeneity and high-quality, which is challenging to achieve in conventional MOCVD techniques using powder alkali metals. The FETs fabricated by bi-layer MoS₂ films exhibit superior electrical properties including sheet conductance, electron mobility, and on/off ratio.

Abstract

2D MoS₂ has gained attention for the post-silicon material owing to its atomically thin nature and dangling bond-free surface. The bi-layer MoS₂ is considered a promising material for electronic devices due to its better electrical properties than monolayer MoS₂. However, the uniform growth of bi-layer MoS₂ is still challenging. Herein, the uniform growth of bi-layer MoS₂ is demonstrated using gas-phase alkali metal-assisted metal–organic chemical vapor deposition (GAA-MOCVD). Thanks to enhanced metal reactant diffusion length in GAA-MOCVD, the uniform growth of bi-layer MoS₂ film is achieved even at fast nucleation kinetics for a shorter growth time compared to previously reported MOCVD. The bi-layer MoS₂ field-effect transistors (FETs) show superior electrical properties such as sheet conductance and electron mobility than monolayer MoS₂ FETs. The electron mobility of bi-layer MoS₂ FETs with bismuth contacts reaches a maximum of 92.35 cm² V⁻¹ s⁻¹. Using the partially grown epitaxial bi-layer (PGEB) MoS₂, it is demonstrated that a photodetector showed a near-infrared photoresponse with a low dark current that is advantageous for both monolayer and bi-layer applications. The potential expansion of the growth technique to layer-by-layer growth can result in boosted performance across a wide spectrum of electronic and optoelectronic devices employing MoS₂.

Highlights

• This review introduces the potential of 2D electronics for post-Moore era and discusses their current progress in digital circuits, analog circuits, heterogeneous integration, sensing circuits, artificial intelligence chips, and quantum chips in sequence.

• A comprehensive analysis of the current trends and challenges encountered in the development of 2D materials is summarized.

• An in-depth roadmap outlining the future development of 2D electronics is presented, and the most accessible and promising avenues for 2D electronics are suggested.

Nature Communications, Published online: 17 February 2024; doi:10.1038/s41467-024-45986-6

Publication date: March–April 2024

Source: Materials Today, Volume 73

Author(s): Florian M. Arnold, Alireza Ghasemifard, Agnieszka Kuc, Thomas Heine

The positions of spectrally pure quantum emitters in nanoparticle-strained WSe₂ monolayers are mapped to the underlying strain field with a resolution below the diffraction limit (≈30 nm). The quantum emitters are displaced from the local strain maxima by an average distance of 240 nm, which contradicts the assumption that strain-induced quantum emitters are concentrated at the local strain maxima.

Abstract

Strain-engineering in atomically thin metal dichalcogenides is a useful method for realizing single-photon emitters (SPEs) for quantum technologies. Correlating SPE position with local strain topography is challenging due to localization inaccuracies from the diffraction limit. Currently, SPEs are assumed to be positioned at the highest strained location and are typically identified by randomly screening narrow-linewidth emitters, of which only a few are spectrally pure. In this work, hyperspectral quantum emitter localization microscopy is used to locate 33 SPEs in nanoparticle-strained WSe₂ monolayers with sub-diffraction-limit resolution (≈30 nm) and correlate their positions with the underlying strain field via image registration. In this system, spectrally pure emitters are not concentrated at the highest strain location due to spectral contamination; instead, isolable SPEs are distributed away from points of peak strain with an average displacement of 240 nm. These observations point toward a need for a change in the design rules for strain-engineered SPEs and constitute a key step toward realizing next-generation quantum optical architectures.

Nature Reviews Materials, Published online: 13 February 2024; doi:10.1038/s41578-024-00651-8

Thermochromism, a solid's temperature-dependent change in color, is the fundamental basis of optical thermometry. Herein, it is demonstrated that InSeI, a 1D van der Waals solid, shows strong thermochromism and a pronounced temperature-dependent optical band edge absorption shift from 450 to 530 nm over a 380 K temperature range with an experimental (dE _g/dT)_max value of 1.26 × 10⁻³ eV K⁻¹.

Abstract

Thermochromism, the change in color of a material with temperature, is the fundamental basis of optical thermometry. A longstanding challenge in realizing sensitive optical thermometers for widespread use is identifying materials with pronounced thermometric optical performance in the visible range. Herein, it is demonstrated that single crystals of indium selenium iodide (InSeI), a 1D van der Waals (vdW) solid consisting of weakly bound helical chains, exhibit considerable visible range thermochromism. A strong temperature-dependent optical band edge absorption shift ranging from 450 to 530 nm (2.8 to 2.3 eV) over a 380 K temperature range with an experimental (dE _g/dT)_max value extracted to be 1.26 × 10⁻³ eV K⁻¹ is shown. This value lies appreciably above most dense conventional semiconductors in the visible range and is comparable to soft lattice solids. The authors further seek to understand the origin of this unusually sensitive thermochromic behavior and find that it arises from strong electron–phonon interactions and anharmonic phonons that significantly broaden band edges and lower the E _g with increasing temperature. The identification of structural signatures resulting in sensitive thermochromism in 1D vdW crystals opens avenues in discovering low-dimensional solids with strong temperature-dependent optical responses across broad spectral windows, dimensionalities, and size regimes.

In this work, the exfoliated MoS₂ nanosheets (EMoS₂) are used as the artificial solid electrolyte interphase to protect Li anode. The EMoS₂ containing plentiful of 1T phase and sulfur vacancies can greatly affect the lithiophilicity and diffusion behavior of Li⁺. As a result, the EMoS₂@Li pouch battery with LiNi_0.8Co_0.1Mn_0.1O₂ cathode exhibits a high energy density of 403 Wh kg⁻¹ after 100 cycles.

Abstract

Constructing large-area artificial solid electrolyte interphase (SEI) to suppress Li dendrites growth and electrolyte consumption is essential for high-energy-density Li metal batteries (LMBs). Herein, chemically exfoliated ultrathin MoS₂ nanosheets (EMoS₂) as an artificial SEI are scalable transfer-printed on Li-anode (EMoS₂@Li). The EMoS₂ with a large amount of sulfur vacancies and 1T phase-rich acts as a lithiophilic interfacial ion-transport skin to reduce the Li nucleation overpotential and regulate Li⁺ flux. With favorable Young's modulus and homogeneous continuous layered structure, the proposed EMoS₂@Li effectively suppresses the growth of Li dendrites and repeat breaking/reforming of the SEI. As a result, the assembled EMoS₂@Li||LiFePO₄ and EMoS₂@Li||LiNi_0.8Co_0.1Mn_0.1O₂ batteries demonstrate high-capacity retention of 93.5% and 92% after 1000 cycles and 300 cycles, respectively, at ultrahigh cathode loading of 20 mg cm⁻². Ultrasonic transmission technology confirms the admirable ability of EMoS₂@Li to inhibit Li dendrites in practical pouch batteries. Remarkably, the Ah-class EMoS₂@Li||LiNi_0.8Co_0.1Mn_0.1O₂ pouch battery exhibits an energy density of 403 Wh kg⁻¹ over 100 cycles with the low negative/positive capacity ratio of 1.8 and electrolyte/capacity ratio of 2.1 g Ah⁻¹. The strategy of constructing an artificial SEI by sulfur vacancies-rich and 1T phase-rich ultrathin MoS₂ nanosheets provides new guidance to realize high-energy-density LMBs with long cycling stability.

Nature Photonics, Published online: 14 February 2024; doi:10.1038/s41566-024-01393-3

Nature, Published online: 14 February 2024; doi:10.1038/s41586-023-06978-6

Photo-induced surface reconstruction of Co₃Mo₃N forming amorphous Mo-rich@Co-rich bilayer structure leads to a shortened Co−Mo bond length resulting in improved performance for both photocatalytic hydrogen evolution reaction (PHER) and photocatalytic oxygen evolution reaction (POER) compared to pure Co₃Mo₃N.

Abstract

The efficient conversion and storage of solar energy for chemical fuel production presents a challenge in sustainable energy technologies. Metal nitrides (MNs) possess unique structures that make them multi-functional catalysts for water splitting. However, the thermodynamic instability of MNs often results in the formation of surface oxide layers and ambiguous reaction mechanisms. Herein, we present on the photo-induced reconstruction of a Mo-rich@Co-rich bi-layer on ternary cobalt-molybdenum nitride (Co₃Mo₃N) surfaces, resulting in improved effectiveness for solar water splitting. During a photo-oxidation process, the uniform initial surface oxide layer is reconstructed into an amorphous Co-rich oxide surface layer and a subsurface Mo−N layer. The Co-rich outer layer provides active sites for photocatalytic oxygen evolution reaction (POER), while the Mo-rich sublayer promotes charge transfer and enhances the oxidation resistance of Co₃Mo₃N. Additionally, the surface reconstruction yields a shortened Co−Mo bond length, weakening the adsorption of hydrogen and resulting in improved performance for both photocatalytic hydrogen evolution reaction (PHER) and POER. This work provides insight into the surface structure-to-activity relationships of MNs in solar energy conversion, and is expected to have significant implications for the design of metal nitride-based catalysts in sustainable energy technologies.

Nature Communications, Published online: 15 February 2024; doi:10.1038/s41467-024-45709-x

Anomalous and colossal magneto-resistive switching with very high magnetic field dependence is demonstrated in a device composed of a Ge nanochannel with all-epitaxial single-crystalline Fe/MgO electrodes. The new phenomenon is attributed to the formation of d⁰-ferromagnetic filaments by attractive Mg vacancies due to the spin-triplet states with ferromagnetic double exchange interactions and the ferromagnetic proximity effect of Fe on MgO.

Abstract

Exploring potential spintronic functionalities in resistive switching (RS) devices is of great interest for creating new applications, such as multifunctional resistive random-access memory and novel neuromorphic computing devices. In particular, the importance of the spin-triplet state of cation vacancies in oxide materials, which is induced by localized and strong O–2p on-site Coulomb interactions, in RS devices has been overlooked. d⁰ ferromagnetism sometimes appears due to the spin-triplet state and ferromagnetic Zener's double exchange interactions between cation vacancies, which are occasionally strong enough to make nonmagnetic oxides ferromagnetic. Here, for the first time, anomalous and colossal magneto-RS (CMRS) with very high magnetic field dependence is demonstrated by utilizing an unconventional RS device composed of a Ge nanochannel with all-epitaxial single-crystalline Fe/MgO electrodes. The device shows colossal and unusual behavior as the threshold voltage and ON/OFF ratio strongly depend on a magnetic field, which is controllable with an applied voltage. This new phenomenon is attributed to the formation of d⁰-ferromagnetic filaments by attractive Mg vacancies due to the spin-triplet states with ferromagnetic double exchange interactions and the ferromagnetic proximity effect of Fe on MgO. The findings will allow the development of energy-efficient CMRS devices with multifield susceptibility.

Exchange bias in the all-vdW magnetic heterostructure is modulated by the antiferromagnetic spin-flop phase transition of CrPS₄. Via the spin flop, one can select the exchange bias switching among the “ON”, “depressed”, and “OFF” states. This work provides an approach to intrinsically modulate the exchange bias in all-vdW heterostructures and paves avenues to design and manipulate 2D spintronic devices.

Abstract

Exchange bias is extensively studied and widely utilized in spintronic devices, such as spin valves and magnetic tunnel junctions. 2D van der Waals (vdW) magnets, with high-quality interfaces in heterostructures, provide an excellent platform for investigating the exchange bias effect. To date, intrinsic modulation of exchange bias, for instance, via precise manipulation of the magnetic phases of the antiferromagnetic layer, is yet to be fully reached, owing partly to the large exchange fields of traditional bulk antiferromagnets. Herein, motivated by the low-field spin-flop transition of a 2D antiferromagnet, CrPS₄, exchange bias is explored by modulating the antiferromagnetic spin-flop phase transition in all-vdW magnetic heterostructures. The results demonstrate that undergoing the spin-flop transition during the field cooling process, the A-type antiferromagnetic ground state of CrPS₄ turns into a canted antiferromagnetic one, therefore, it reduces the interfacial magnetic coupling and suppresses the exchange bias. Via conducting different cooling fields, one can select the exchange bias effect switching among the “ON”, “depressed”, and “OFF” states determined by the spin flop of CrPS₄. This work provides an approach to intrinsically modulate the exchange bias in all-vdW heterostructures and paves new avenues to design and manipulate 2D spintronic devices.

Author(s): Yubo Yang (杨煜波), Miguel A. Morales, and Shiwei Zhang

Transition metal dichalcogenide superlattices provide an exciting new platform for exploring and understanding a variety of phases of matter. The moiré continuum Hamiltonian, of two-dimensional jellium in a modulating potential, provides a fundamental model for such systems. Accurate computations wi…

[Phys. Rev. Lett. 132, 076503] Published Thu Feb 15, 2024

Nature, Published online: 14 February 2024; doi:10.1038/d41586-024-00231-4