Jing Zhang

Nature Communications, Published online: 21 February 2023; doi:10.1038/s41467-023-36619-5

2D nonlayered materials exhibit interesting properties for catalysis, nanoelectronics and spintronics applications, but their growth is still challenging. Here, the authors report a theoretical model and an experimental strategy to synthesize various 2D nonlayered transition metal oxides with room-temperature magnetic properties.

Nature Communications, Published online: 23 February 2023; doi:10.1038/s41467-023-36715-6

Laminated van der Waals (vdW) metallic electrodes can improve the contact of 2D electronic devices, but their scalability is usually limited by the transfer process. Here, the authors report a strategy to deposit vdW contacts onto various 2D and 3D semiconductors at the wafer scale.

Nature Physics, Published online: 23 February 2023; doi:10.1038/s41567-023-01980-1

A new variation on cathodoluminescence provides a view of a sample’s optical response with time resolution shorter than an optical cycle.

Nature, Published online: 22 February 2023; doi:10.1038/d41586-023-00314-8

A system of ultracold rubidium atoms confined by two misaligned laser-beam arrays has been used to simulate remarkable structures called twisted-bilayer materials. The atomic technology exhibits phenomena such as superfluidity — the frictionless flow of atoms — typically observed in these materials.

Nature, Published online: 22 February 2023; doi:10.1038/d41586-023-00537-9

How the Quantum Twisting Microscope could give a better ‘picture’ of atom thin layers, and science in Ukraine a year into Russia’s invasion.

The controllable preparation of ultrathin monoclinic ZrO₂ (m-ZrO₂) single crystals (EOT≈0.29 nm, EOT is equivalent oxide thickness) via thermal oxidation of ZrS₂ is achieved. By using K₃[Fe(CN)₆] as seeding, the large-scale parent ZrS₂ is easily grown. The grown m-ZrO₂ presents a high dielectric constant of ≈19 and a breakdown voltage of ≈7.22 MV cm⁻¹. Using m-ZrO₂ as top gate dielectric, the MoS₂ field effect transistor (FET) shows excellent device performance.

Abstract

High-κ materials that exhibit large permittivity and band gaps are needed as gate dielectrics to enhance capacitance and prevent leakage current in downsized technology nodes. Among these, monoclinic ZrO₂ (m-ZrO₂) shows good potential because of its inertness and high-κ with respect to SiO₂, but a method to produce ultrathin single crystal is lacking. Here, the controllable preparation of ultrathin m-ZrO₂ single crystals via the in situ thermal oxidation of ZrS₂ is achieved. As-grown m-ZrO₂ presents an equivalent oxide thickness of ≈0.29 nm, a high dielectric constant of ≈19, and a breakdown voltage (E _BD) of ≈7.22 MV cm⁻¹. MoS₂ field effect transistor (FET) by using m-ZrO₂ as a dielectric layer shows comparable mobility to that using SiO₂ dielectric. The ultraclean interface of m-ZrO₂/MoS₂ and high crystalline quality of m-ZrO₂ lead to negligible hysteresis in transfer curves. Single crystal m-ZrO₂ dielectric shows potential application in digital complementary metal oxidesemiconductor (CMOS) logic FET.

Blue phosphorene is a new emerging 2D semiconducting material with potential applications. Herein, an evidence of the existence of Dirac fermions in blue phosphorene grown on Cu(111) substrate, similar to graphene, is presented. Therefore, all the expectations held for graphene, such as high-speed electronic devices based on ballistic transport at room temperature, may also be applied to blue phosphorene.

Abstract

2D materials beyond graphene and in particular 2D semiconductors have raised interest due to their unprecedented electronic properties, such as high carrier mobility or tunable bandgap. Blue phosphorene is an allotrope of black phosphorene that resembles graphene as it presents a honeycomb structure. However, it is known to have semiconductor character and the crucial point is to determine whether this hexagonal phase of phosphorene presents Dirac fermions as in graphene. Here, the first compelling experimental evidence of Dirac fermions in blue phosphorene layer grown on Cu(111) surface is presented. The results highlight the formation of a highly ordered blue phosphorene sheet with a clear Dirac cone at the high symmetry points of the Brillouin Zone. The charge carriers behave as massless relativistic particles. Therefore, all the expectations held for graphene, such as high-speed electronic devices based on ballistic transport at room temperature, may also be applied to blue phosphorene.

Layer-controlled growth is difficult due to the higher nucleation potential on the surface of 2D materials. Herein, a seeding solution approach is demonstrated to change the nucleation pattern of seed crystals on the substrate surface by precisely controlling the concentration of metal precursors and grow H-VS₂ nanosheets with tunable layer numbers by temperature-controlled kinetic and thermodynamic synergy.

Abstract

The discovery of layered magnetic semiconductor materials has stimulated a search for the magnetic order of atomically thin-layered materials. However, layer-controlled growth is difficult because of the high nucleation barrier of the material surface during the few-layer formation of 2D materials. Herein, a seeding solution method is demonstrated that changes the nucleation mode of seed crystals on the substrate surface by precisely controlling the concentration of metal precursors and promoting the formation of cluster seed nuclei to ensure a sufficient source of metal for subsequent reactions. It is studied that the kinetic and thermodynamic synergy through temperature control is readily to grow VS₂ with a tunable layer number. Monolayer VS₂ exhibits strong ferromagnetic ordering with a saturation magnetization strength (M_s) of 37 emu per cc and a coercivity (H_c) of 135 Oe at 300 K. Notably, the ferromagnetism of VS₂ has layer-dependent performance of the saturation magnetization and coercivity decreases with increasing number of layers. Monolayer VS₂ exhibits typical semiconductor properties in Hall devices. This study broadens the chemical pathway for the tunable synthesis of 2D layered magnetic materials and provides the possibility for the construction of novel spintronic and magnetoelectronic devices.

A microsphere-cavity-array (MCA) structure is developed to improve the degree of valley polarization (DoP) and PLQY of ML-WSe₂. The MCA demonstrates superior capability to suppress dark exciton formation and intervalley scattering. The boosted localized density of charged excitons by nanofocusing and enhanced population decay by WGM-induced Purcell effect in MCA/ML-WSe₂ achieves the PLQY of 12.4% with DoP > 0.20 near room temperature.

Abstract

Monolayer transition metal dichalcogenides (ML-TMDCs) possess degenerate levels with antiparallel spins in K and K′ valleys, providing the intrinsic valley polarization, which attracts great interest for potential applications on quantum information technology and on-chip nanophotonics. Unfortunately, it is difficult to distinguish the degree of valley polarization (DoP) near room temperature due to the intensive phonon-assisted intervalley scattering and the long-range electron-hole exchange interaction in ML-TMDCs, limiting their practical applications. In this study, a novel design is proposed for great promotion of DoP in ML-WSe₂ with a microsphere cavity array, introducing Purcell effect and nanofocusing effect into the system. The radiative decay rate is dramatically enhanced owing to Purcell effect in microcavity in weak coupling regime, thus locking more polarized excitons in the corresponding valley under certain circularly-polarized pumping. In addition, the nanofocusing effect contributes to increasing the number of charged excitons by suppressing the bright to dark exciton conversion. The present work achieves a great DoP of ML-WSe₂ with a simple configuration and promises broad applications from valleytronic devices to chiral optics in the future.

Two-Photon Lithography is a high-resolution micro and nanofabrication technique. However, it is affected by a low throughput preventing its adoption in industry. In this review, several strategies to increase the throughput and the processing speed are explored. In particular, the principles and advances of the combination of Two-Photon Lithography and Holography are reviewed, toward 3D high-speed processing.

Abstract

Two-Photon Lithography, thanks to its very high sub-diffraction resolution, has become the lithographic technique par excellence in applications requiring small feature sizes and complex 3D pattering. Despite this, the fabrication times required for extended structures remain much longer than those of other competing techniques (UV mask lithography, nanoimprinting, etc.). Its low throughput prevents its wide adoption in industrial applications. To increase it, over the years different solutions have been proposed, although their usage is difficult to generalize and may be limited depending on the specific application. A promising strategy to further increase the throughput of Two-Photon Lithography, opening a concrete window for its adoption in industry, lies in its combination with holography approaches: in this way it is possible to generate dozens of foci from a single laser beam, thus parallelizing the fabrication of periodic structures, or to engineer the intensity distribution on the writing plane in a complex way, obtaining 3D microstructures with a single exposure. Here, the fundamental concepts behind high-speed Two-Photon Lithography and its combination with holography are discussed, and the literary production of recent years that exploits such techniques is reviewed, and contextualized according to the topic covered.

Transition-Metal Phosphorus Trichalcogenide

In article number 2211269, Jiahong Wang, Cong Ye, and co-workers report a flexible memristor fabricated utilizing two-dimensional cadmium phosphorus trichalcogenide nanosheets; the synaptic plasticity, including paired-pulse facilitation and spiking timing-dependent plasticity, are further observed. Owing to the linear conductance modulation capacity, the decimal operation is explored.

The magnetic properties of dysprosium and holmium single atoms adsorbed on barium oxide thin films are investigated and compared with previous results for the same lanthanide elements on magnesium oxide. These results suggest criteria for the choice of the alkaline earth oxide optimizing the magnetic performance of single atom magnets.

Abstract

X-ray magnetic circular dichroism, atomic multiplet simulations, and density functional theory calculations are employed to identify criteria for the optimum combination of supporting alkaline earth oxide and adsorption site maximizing the spin lifetimes of lanthanide single-atom magnets. Dy and Ho atoms adsorbed on BaO(100) thin films on Pt(100) are characterized and compared with previous results for the same two elements on MgO/Ag(100). Dy shows hysteresis in magnetic fields up to ≈3.5 T and long spin lifetime, exceeding 300 s at 2.5 K and 0.5 T. Dy displays superior magnetic stability on the bridge site than on the top-O site. Surprisingly, Ho shows paramagnetism, as opposed to its long spin lifetime on MgO. These differences originate from the local surface distortions induced by the adatoms. On MgO, minimal distortions involve only the closest O atoms, while, on BaO, they affect both the closest anions and cations. This trend reflects the decrease of the lattice energy along the series of the alkaline earth oxides, going from MgO to BaO. This study represents a step ahead in the understanding of the factors determining the spin dynamics of surface-adsorbed single-atom magnets in order to achieve their operation as qubits and memories.

Magnetron sputtering technology and DFT calculations reveal the phase transition mechanism of MoS₂ from semiconductor phase to metallic phase due to the introduction of carbon dopants. The heterogeneous interfaces between 2H and 1T or 1T′ are more conducive to charge transfer and display excellent electrocatalytic activities in both acidic and alkaline electrolytes.

Abstract

Understanding the phase transitions process of 2D transition metal dichalcogenides (2D-TMDs) from semiconducting (2H) to metallic (1T, 1T′) phase provides directionality for the iteration of hydrogen evolution catalysis. So far, the phase engineering methods are intensively explored, serving as practical tools for discovering low-cost novel nanomaterials for electronic and electrode devices in the realm of energy storage and catalysis. However, the heterostructures between 2H/1T, 2H/1T′, or 1T/1T′, functionalizing as critical active sites in the electrocatalytic process, are overlooked. Herein, a facile carbon doping paradigms, enabling augmentation of MoS₂ phase transition, together with density functional theory calculations and rationales to explain the counterintuitive directionality of transitions is reported. The experiment and simulation results indicate that the existence of carbon as interstitial atoms is more favorable to the phase transition than the substitution atoms. The heterogeneous interfaces between 2H and 1T or 1T′ are more conducive to charge transfer. As expected, the trinary-heterostructure nanofilm displays excellent electrocatalytic activities both in micro-electrochemical measurements and conventional electrolytic cells. The results provide a fresh insight into the 2D-TMDs phase transition mechanism and guide for trinary-heterostructure electrocatalysts for scalable production.

In this study, a chelated ion-exchange strategy is proposed to synthesize BiOCl mesoporous single-crystalline nanosheets (BiOCl MSCN) with ultra-thin structure by chelating interaction of Bi³⁺ ions and acetate ions, and ion exchange between Cl⁻ ions and acetate ions. The prepared BiOCl MSCN exhibits excellent photocatalytic activity stability and general adaptability for oxidation of benzyl alcohol to benzaldehyde.

Abstract

The photoresponse and photocatalytic efficiency of bismuth oxychloride (BiOCl) are greatly limited by rapid recombination of photogenerated carriers. The construction of porous single-crystal BiOCl photocatalyst can effectively alleviate this issue and provide accessible active sites. Herein, a facile chelated ion-exchange strategy is developed to synthesize BiOCl mesoporous single-crystalline nanosheets (BiOCl MSCN) using acetic acid and ammonia solution respectively as chelating agent and ionization promoter. The strong chelation between acetate ions and Bi³⁺ ions introduces acetate ions into the precipitated product to exchange with Cl^- ions, resulting in large lattice mismatch, strain release, and formation of void-like mesopores. The prepared BiOCl MSCN photocatalyst exhibits excellent catalytic performance with 99% conversion and 98% selectivity for oxidation of benzyl alcohol to benzaldehyde and superior general adaptability for various aromatic alcohols. The theoretical calculations and characterizations confirm that the superior performance is mainly attributed to the abundant oxygen vacancies, plenty of accessible adsorption/active sites and fast charge transport path without grain boundaries.

2D monolayer transition metal dichalcogenides (TMDCs) are seen as potentially promising candidates for novel light-emission applications, owing to their unique characteristics. This review summarizes the state-of-the-art progress made in the development of 2D TMDC-based light-emitting devices and highlights the remaining challenges.

Abstract

2D monolayer transition metal dichalcogenides (TMDCs) show great promise for the development of next-generation light-emitting devices owing to their unique electronic and optoelectronic properties. The dangling-bond-free surface and direct-bandgap structure of monolayer TMDCs allow for near-unity photoluminescence quantum efficiencies. The excellent mechanical and optical characteristics of 2D TMDCs offer great potential to fabricate TMDC-based light-emitting diodes (LEDs) featuring good flexibility and transparency. Great progress has been made in the fabrication of bright and efficient LEDs with varying device structures. In this review, the aim is to provide a comprehensive summary of the state-of-the-art progress made in the construction of bright and efficient LEDs based on 2D TMDCs. After a brief introduction to the research background, the preparation of 2D TMDCs used for LEDs is briefly discussed. The requirements and the corresponding challenges to achieve bright and efficient LEDs based on 2D TMDCs are introduced. Thereafter, various strategies to enhance the brightness of monolayer 2D TMDCs are described. Following that, the carrier-injection schemes enabling bright and efficient TMDC-based LEDs along with the device performance are summarized. Finally, the challenges and future prospects regarding the accomplishment of TMDC-LEDs with ultimate brightness and efficiency are discussed.

The synthesis of 2D single-element cobalt nanosheets with a sub-millimeter scale via van der Waals epitaxy is demonstrated for the first time, which is guaranteed by the synergistic effect between van der Waals interactions and surface energy minimization. Cobalt nanosheets exhibit significant in-plane magnetic anisotropy and magnetoresistance effects, opening up exciting opportunities for the exploration of 2D single-element magnetism.

Abstract

2D single-element materials, which are pure and intrinsically homogeneous on the nanometer scale, can cut the time-consuming material-optimization process and circumvent the impure phase, bringing about opportunities to explore new physics and applications. Herein, for the first time, the synthesis of ultrathin cobalt single-crystalline nanosheets with a sub-millimeter scale via van der Waals epitaxy is demonstrated. The thickness can be as low as ≈6 nm. Theoretical calculations reveal their intrinsic ferromagnetic nature and epitaxial mechanism: that is, the synergistic effect between van der Waals interactions and surface energy minimization dominates the growth process. Cobalt nanosheets exhibit ultrahigh blocking temperatures above 710 K and in-plane magnetic anisotropy. Electrical transport measurements further reveal that cobalt nanosheets have significant magnetoresistance (MR) effect, and can realize a unique coexistence of positive MR and negative MR under different magnetic field configurations, which can be attributed to the competition and cooperation effect among ferromagnetic interaction, orbital scattering, and electronic correlation. These results provide a valuable case for synthesizing 2D elementary metal crystals with pure phase and room-temperature ferromagnetism and pave the way for investigating new physics and related applications in spintronics.

The underlying mechanism in contact electrification is systematically investigated between 2D MXenes and MoS₂ through density functional theory and triboelectric probes. The work functions dominate the electron transfer direction, while the interfacial potential barrier and the work function difference together modulate the amount of transferred electron. The electron transfer will occur at the attractive force region due to the quantum tunneling.

Abstract

Contact electrification (triboelectrification) (CE) is a universal phenomenon in ambient environment and has been recorded for more than 2600 years. Nonetheless, the intrinsic mechanism of CE still remains controversial. Herein, based on first-principles theory, the underlying mechanism in CE is systematically investigated between metallic MXenes and semiconductive MoS₂. The results show that the work functions of contacting materials dominate the direction of electron transfer during CE process. That is, the electron will be transferred from the material with low work function to the one with high work function. The theoretical prediction is verified experimentally through investigating triboelectric probes based on MXenes and MoS₂ nanomaterials. Additionally, it is noted that the interfacial potential barrier and the work function difference together modulate the amount of transferred electron. Electron transfer mainly occurs in the repulsive forces region where the interaction distance between the two materials is shorter than the normal bonding length. The quantum calculation results agree well with the Wang transition theory. Furthermore, it is also noticed that, due to the wave-particle duality of electron, electron transfer will obviously occur at the attractive force region when the two contacting materials exhibit a larger work function difference.

Nature Communications, Published online: 16 February 2023; doi:10.1038/s41467-023-36531-y

No multi-color RNA fluorescent tags are currently available for use in live cells. Here, the authors show that fluorescence lifetime imaging microscopy is advantageous for multiplexed RNA visualization while achieving robust cellular contrast.

Multiexciton generation (MEG) is found in a 2D organic–inorganic hybrid perovskite, phenylammonium cadmium chloride (PACC). The MEG effect induced by Mn²⁺ doping improves the red phosphorescent quantum yield of PACC from 6% to nearly 200%, thus resulting in a switching from blue to red afterglow.

Abstract

2D organic–inorganic hybrid perovskites (OIHPs) show obvious advantages in the field of optoelectronics due to their high luminescent stability and good solution processability. However, the thermal quenching and self-absorption of excitons caused by the strong interaction between the inorganic metal ions lead to a low luminescence efficiency of 2D perovskites. Herein, a 2D Cd-based OIHP phenylammonium cadmium chloride (PACC) with a weak red phosphorescence (Φ_P < 6%) at 620 nm and a blue afterglow is reported. Interestingly, the Mn-doped PACC exhibits very strong red emission with nearly 200% quantum yield and 15 ms lifetime, thus resulting in a red afterglow. The experimental data prove that the doping of Mn²⁺ not only induces the multiexciton generation (MEG) process of the perovskite, avoiding the energy loss of inorganic excitons, but also promotes the Dexter energy transfer from organic triplet excitons to inorganic excitons, thus realizing the superefficient red-light emission of Cd²⁺. This work suggests that guest metal ions can induce host metal ions to realize MEG in 2D bulk OIHPs, which provides a new idea for the development of optoelectronic materials and devices with ultrahigh energy utilization.

With the NH₄ ⁺ and F⁻ synergy mechanism, the intrinsic growth limit of β-Ni(OH)₂ is broken, realizing record-level thickness (over 700 nm) for the tailored F-substituted β-Ni(OH)₂ (Ni–F–OH) superstructure. The ultrathick plate superstructure is found to have a versatile family, which can open a new era of novel energy-storage materials to meet various future demands.

Abstract

The past decade has witnessed the development of layered-hydroxide-based self-supporting electrodes, but the low active mass ratio impedes its all-around energy-storage applications. Herein, the intrinsic limit of layered hydroxides is broken by engineering F-substituted β-Ni(OH)₂ (Ni–F–OH) plates with a sub-micrometer thickness (over 700 nm), producing a superhigh mass loading of 29.8 mg cm⁻² on the carbon substrate. Theoretical calculation and X-ray absorption spectroscopy analysis demonstrate that Ni–F–OH shares the β-Ni(OH)₂-like structure with slightly tuned lattice parameters. More interestingly, the synergy modulation of NH₄ ⁺ and F⁻ is found to serve as the key enabler to tailor these sub-micrometer-thickness 2D plates thanks to the modification effects on the (001) plane surface energy and local OH⁻ concentration. Guided by this mechanism, the superstructures of bimetallic hydroxides and their derivatives are further developed, revealing they are a versatile family with great promise. The tailored ultrathick phosphide superstructure achieves a superhigh specific capacity of 7144 mC cm⁻² and a superior rate capability (79% at 50 mA cm⁻²). This work highlights a multiscale understanding of how exceptional structure modulation happens in low-dimensional layered materials. The as-built unique methodology and mechanisms will boost the development of advanced materials to better meet future energy demands.

Ultrasensitive and robust active-matrix image sensor circuitry is demonstrated by integrating a wafer-scale nanoporous molybdenum disulfide (MoS₂) phototransistor array with high-performance indium-gallium-zinc oxide (IGZO) switching transistors. A 4-inch wafer-scale 2D)MoS₂ is synthesized and a periodic nanopore array is created on its surface to achieve exceptionally high photoresponsivity of 5.2 × 10⁴ A W⁻¹. The device shows a technically advanced form based on large-area 2D material similar to a commercialized complementary metal–oxide–semiconductor (CMOS) image sensor consisting of a sensor and a driving transistor in the matrix pixel.

Abstract

2D transition-metal dichalcogenides (TMDs) have been successfully developed as novel ubiquitous optoelectronics owing to their excellent electrical and optical characteristics. However, active-matrix image sensors based on TMDs have limitations owing to the difficulty of fabricating large-area integrated circuitry and achieving high optical sensitivity. Herein, a large-area uniform, highly sensitive, and robust image sensor matrix with active pixels consisting of nanoporous molybdenum disulfide (MoS₂) phototransistors and indium–gallium–zinc oxide (IGZO) switching transistors is reported. Large-area uniform 4-inch wafer-scale bilayer MoS₂ films are synthesized by radio-frequency (RF) magnetron sputtering and sulfurization processes and patterned to be a nanoporous structure consisting of an array of periodic nanopores on the MoS₂ surface via block copolymer lithography. Edge exposure on the nanoporous bilayer MoS₂ induces the formation of subgap states, which promotes a photogating effect to obtain an exceptionally high photoresponsivity of 5.2 × 10⁴ A W⁻¹. A 4-inch-wafer-scale image mapping is successively achieved using this active-matrix image sensor by controlling the device sensing and switching states. The high-performance active-matrix image sensor is state-of-the-art in 2D material-based integrated circuitry and pixel image sensor applications.

Ba_0.985Al₄Sb₂O₁₂:0.015Eu²⁺ (BASO:Eu²⁺) features desirable quantum efficiency (IQE, 96.7%) and satisfactory thermal stability (TS, 423 K, 94%) for phosphor-conversion white light-emitting diodes, which is synthesized by the high-temperature solid-state reaction in air. There is sufficient evidence that Eu replaces the lattice of Ba in BASO:Eu²⁺.

Abstract

Despite many Eu²⁺-doped phosphors having been synthesized by different methods, a simple synthetic strategy for Eu²⁺-doped high-performance phosphors remains one of the significant challenges for phosphor-conversion white light-emitting diodes. Herein, a novel broad-band excitation yellow phosphor Ba_0.985Al₄Sb₂O₁₂:0.015Eu²⁺ (BASO:Eu²⁺) with high thermal stability (423 K, 94%) and internal quantum efficiency (96.7%) are reported. More importantly, the novel phosphor is synthesized by solid-state reaction at high temperatures in air. Structural and spectral analyses show that the Eu²⁺ ions in BASO preferably occupy [BaO₈] hexahedra, forming a single luminescence center. This study provides a reliable direction for the facile synthesis of high-performance Eu²⁺-doped phosphors in air.