Jiuxiang Dai

Precise and ultrafast ion sieving is highly desirable for versatile applications in environment-, energy-, and resource-related fields. Permselective membranes constructed from parallel stacked 2D nanosheets have recently aroused great research enthusiasm because interior nanochannels with unprecedented diversity could be accurately designed and efficiently modulated.

Abstract

Precise and ultrafast ion sieving is highly desirable for many applications in environment-, energy-, and resource-related fields. The development of a permselective lamellar membrane constructed from parallel stacked two-dimensional (2D) nanosheets opened a new avenue for the development of next-generation separation technology because of the unprecedented diversity of the designable interior nanochannels. In this Review, we first discuss the construction of homo- and heterolaminar nanoarchitectures from the starting materials to the emerging preparation strategies. We then explore the property–performance relationships, with a particular emphasis on the effects of physical structural features, chemical properties, and external environment stimuli on ion transport behavior under nanoconfinement. We also present existing and potential applications of 2D membranes in desalination, ion recovery, and energy conversion. Finally, we discuss the challenges and outline research directions in this promising field.

Nature Physics, Published online: 30 January 2023; doi:10.1038/s41567-022-01889-1

Adatoms on the surface of silicon can create two-dimensional superconductivity, the order parameter symmetry of which is currently not known. Now, evidence suggests it might be a topological chiral d-wave state.

Nature Physics, Published online: 30 January 2023; doi:10.1038/s41567-022-01907-2

Films of the correlated oxide NdNiO3 form a metallic antiferromagnetic phase that can be identified using electrical currents, raising the prospect of applications in spintronics.

Nature Electronics, Published online: 30 January 2023; doi:10.1038/s41928-022-00914-8

Three-dimensional liquid metal structures can be created by manipulating ductile gallium–indium alloy wires that are then encapsulated in an elastomer and heated to recover their fluidity, and can remain in a liquid state for a range of temperatures due to a supercooling effect.

Nature Electronics, Published online: 30 January 2023; doi:10.1038/s41928-022-00912-w

By engineering the upper and lower surfaces of micro-light-emitting-diode chips to have different van der Waals forces, hundreds and thousands of chips can be accurately aligned on substrates and used to create active-matrix displays.

Growth of lateral heterostructures made of graphene and hexagonal boron nitride on Rh(110) is reported. The results shed light on a highly tunable rotational order of these heterostructures. Atomically resolved scanning tunneling microscope images reveal a perfect lattice matching between both 2D materials at the boundary. Additionally, intercalation of oxygen atoms allows to decouple the heterostructures from the metal substrate.

Abstract

In-plane heterostructures of graphene and hexagonal boron nitride (h-BN) exhibit exceptional properties, which are highly sensitive to the structure of the alternating domains. Nevertheless, achieving accurate control over their structural properties, while keeping a high perfection at the graphene-h-BN boundaries, still remains a challenge. Here, the growth of lateral heterostructures of graphene and h-BN on Rh(110) surfaces is reported. The choice of the 2D material, grown firstly, determines the structural properties of the whole heterostructure layer, allowing to have control over the rotational order of the domains. The atomic-scale observation of the boundaries demonstrates a perfect lateral matching. In-plane heterostructures floating over an oxygen layer have been successfully obtained, enabling to observe intervalley scattering processes in graphene regions. The high tuning capabilities of these heterostructures, along with their good structural quality, even around the boundaries, suggest their usage as test beds for fundamental studies aiming at the development of novel nanomaterials with tailored properties.

Liquid metals are a kind of low-melting-point alloys, usually appearing silvery-white. Colorful liquid metals can be prepared by different strategies, including the coating and compounding, physical vapor deposition/chemical vapor deposition, structural color, external stimuli, and fluorescence functionalization. The color and fluorescence functionalization of liquid metals have broken through the limitations of the conventional single-color physical appearance, and opened significant potential for emerging applications in numerous fields owing to their rich colors and unique liquid structure.

Abstract

Liquid metals (LMs) are emerging as new functional materials with rather unique physical or chemical behaviors. They are generally safe and nontoxic, have high boiling points, reflectivities, good thermal and electrical conductivities, flexibility, fluidity, self-healing capability and remain in liquid state at room temperature. However, the further applications of LMs are limited by their single-color physical appearance, such as working in the situations with imposed stringent requirements for color and aesthetics. Recently, the color and fluorescence functionalization of LMs have overcome many conventional technical bottlenecks and opened significant potential for emerging applications in numerous fields owing to their rich colors and unique liquid structure. In this review, the recent developments in the optical properties, color and fluorescence effects of LMs are comprehensively investigated. The synthesis, structures, properties, chromogenic mechanisms, and potential photoelectric applications of colorful LMs are systematically analyzed and compared. The effectiveness and characteristics of colorful LMs induced by coating, mixing, compounding, surface modification, external stimuli are provided, aiming to establish a potential system for the synthesis and practices of colorful LMs. Finally, the challenges and prospects in the field have also been identified and explained to preferably guide further scientific and technical research in the coming time.

A strong interlayer-coupled WSe₂/WSe₂ homostructure is grown by chemical vapor deposition using a heteroatom-assisted approach to overcome the stacking-free energy, showing a uniform moiré superlattice and strong interfacial coupling. The interlayer coupling can be adjusted by altering the twist angle, enabling the investigation of a variety of novel physical phenomena, which is expected to realize single-photon emission and promote the development of coherent quantum light emitters.

Abstract

Moiré superlattices in twisted van der Waals materials offer a powerful platform for exploring light–matter interactions. The periodic moiré potentials in moiré superlattices can induce strongly correlated quantum phenomena that depend on the moiré potential associated with interlayer coupling at the interface. However, moiré superlattices are primarily prepared by mechanical exfoliation and manual stacking, where the transfer methods easily cause interfacial contamination, and the preparation of high-quality bilayer 2D materials with small twist angles by growth methods remains a significant challenge. In this work, WSe₂/WSe₂ homobilayers with different twist angles by chemical vapor deposition (CVD), using a heteroatom-assisted growth technique, are synthesized. Using low-frequency Raman scattering, the uniformity of the moiré superlattices is mapped to demonstrate the strong interfacial coupling of the CVD-fabricated twist-angle homobilayers. The moiré potential depths of the CVD-grown and artificially stacked homostructures with twist angles of 1.5° are 115 and 45 meV (an increase of 155%), indicating that the depth of moiré potential can be modulated by the interfacial coupling. These results open a new avenue to study the modulation of moiré potential by strong interlayer coupling and provide a foundation for the development of twistronics.

npj 2D Materials and Applications, Published online: 27 January 2023; doi:10.1038/s41699-023-00366-4

Atomically-thin single-photon sources for quantum communication

A strategy of using ferroelectric dielectrics in metal halide perovskite (MHP) field effect-transistors (FETs) for effectively addressing the gate-electric-field screening issue is proposed. By using this strategy, FETs based on MAPbCl₃ thin-films are for the first time realized with low-temperature (<150 °C) solution process. The devices function well at room temperature and exhibit high transparency.

Abstract

Transparent field-effect transistors (FETs) are attacking intensive interest for constructing fancy “invisible” electronic products. Presently, the main technology for realizing transparent FETs is based on metal oxide semiconductors, which have wide-bandgap but generally demand sputtering technique or high-temperature (>350 °C) solution process for fabrication. Herein, a general device fabrication strategy for metal halide perovskite (MHP) FETs is shown, by which transparent perovskite FETs are successfully obtained using low-temperature (<150 °C) solution process. This strategy involves the employment of ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as the dielectric, which conquers the challenging issue of gate-electric-field screening effect in MHP FETs. Additionally, an ultra-thin SnO₂ is inserted between the source/drain electrodes and MHPs to facilitate electron injection. Consequently, n-type semi-transparent MAPbBr₃ FETs and fully transparent MAPbCl₃ FETs which can operate well at room temperature with mobility over 10⁻³ cm² V⁻¹ s⁻¹ and on/off ratio >10³ are achieved for the first time. The low-temperature solution processability of these FETs makes them particularly attractive for applications in low-cost, large-area transparent electronics.

Here, the whole assortment of 1D (metal oxide semiconductors, silicon nanowires, carbon nanotubes) and 2D (graphene, transition metal dichalcogenides, phosphorene) materials used in field effect transistor (FET) gas sensors is reviewed, critically dissecting how the material synthesis, surface functionalization, and transistor fabrication impact on electrical versus sensing properties, then pointing out weakness and highlighting future directions.

Abstract

Rapid progress in the synthesis and fundamental understanding of 1D and 2D materials have solicited the incorporation of these nanomaterials into sensor architectures, especially field effect transistors (FETs), for the monitoring of gas and vapor in environmental, food quality, and healthcare applications. Yet, several challenges have remained unaddressed toward the fabrication of 1D and 2D FET gas sensors for real-field applications, which are related to properties, synthesis, and integration of 1D and 2D materials into the transistor architecture. This review paper encompasses the whole assortment of 1D—i.e., metal oxide semiconductors (MOXs), silicon nanowires (SiNWs), carbon nanotubes (CNTs)—and 2D—i.e., graphene, transition metal dichalcogenides (TMD), phosphorene—materials used in FET gas sensors, critically dissecting how the material synthesis, surface functionalization, and transistor fabrication impact on electrical versus sensing properties of these devices. Eventually, pros and cons of 1D and 2D FETs for gas and vapor sensing applications are discussed, pointing out weakness and highlighting future directions.

The interaction between 2D materials and circularly polarized light (CPL) provides an attractive control knob for investigating emergent exotic phenomena, especially for chiral-electronics, photonics, and optoelectronics effects. This review summarizes exciting chiral light-induced phenomena in representative 2DMs, covering from distinct interaction mechanisms, advances, faced challenges and perspectives, attempting to boost tremendous applications in future optoelectronics, spintronics, and valleytronics.

Abstract

2D materials (2DMs), due to spin-valley locking degree of freedom, exhibit strongly bound exciton and chiral optical selection rules and become promising material candidates for optoelectronic and spin/valleytronic devices. Over the last decade, the manifesting of 2D materials by circularly polarized lights expedites tremendous fascinating phenomena, such as valley/exciton Hall effect, Moiré exciton, optical Stark effect, circular dichroism, circularly polarized photoluminescence, and spintronic property. In this review, recent advance in the interaction of circularly polarized light with 2D materials covering from graphene, black phosphorous, transition metal dichalcogenides, van der Waals heterostructures as well as small proportion of quasi-2D perovskites and topological materials, is overviewed. The confronted challenges and theoretical and experimental opportunities are also discussed, attempting to accelerate the prosperity of chiral light-2DMs interactions.

A novel class of thermally-driven, hybrid nanotransistors based on InAs nanowires is developed. Semiconductor nanostructure devices are embedded in Na⁺-functionalized (poly)ethyleneoxide and allow for extracting the parameters featuring ionic thermodiffusion. Reported results open new perspectives for heat-driven nanoelectronic applications and boost the rational design of next-generation polymer-based thermoelectric materials.

Abstract

Thermoelectric polyelectrolytes are emerging as ideal material platform for self-powered bio-compatible electronic devices and sensors. However, despite the nanoscale nature of the ionic thermodiffusion processes underlying thermoelectric efficiency boost in polyelectrolytes, to date no evidence for direct probing of ionic diffusion on its relevant length and time scale has been reported. This gap is bridged by developing heat-driven hybrid nanotransistors based on InAs nanowires embedded in thermally biased Na⁺-functionalized (poly)ethyleneoxide, where the semiconducting nanostructure acts as a nanoscale probe sensitive to the local arrangement of the ionic species. The impact of ionic thermoelectric gating on the nanodevice electrical response is addressed, investigating the effect of device architecture, bias configuration and frequency of the heat stimulus, and inferring optimal conditions for the heat-driven nanotransistor operation. Microscopic quantities of the polyelectrolyte such as the ionic diffusion coefficient are extracted from the analysis of hysteretic behaviors rising in the nanodevices. The reported experimental platform enables simultaneously the ionic thermodiffusion and nanoscale resolution, providing a framework for direct estimation of polyelectrolytes microscopic parameters. This may open new routes for heat-driven nanoelectronic applications and boost the rational design of next-generation polymer-based thermoelectric materials.

npj 2D Materials and Applications, Published online: 25 January 2023; doi:10.1038/s41699-023-00364-6

Linear indium atom chains at graphene edges

By hBN-encapsulation, the focused laser induces highly stable and reliable phase transition and patterning of thin MoTe₂. Various phases of 1T′, Mo₃Te₄, and Te can be produced by laser irradiation, depending on the evaporation and temperature of the MoTe₂. The phase patterned 2H-1T′ heterophase junction shows low contact resistivity of 1.13 kΩ µm.

Abstract

Transition metal dichalcogenides exhibit phase transitions through atomic migration when triggered by various stimuli, such as strain, doping, and annealing. However, since atomically thin 2D materials are easily damaged and evaporated from these strategies, studies on the crystal structure and composition of transformed 2D phases are limited. Here, the phase and composition change behavior of laser-irradiated molybdenum ditelluride (MoTe₂) in various stacked geometry are investigated, and the stable laser-induced phase patterning in hexagonal boron nitride (hBN)-encapsulated MoTe₂ is demonstrated. When air-exposed or single-side passivated 2H-MoTe₂ are irradiated by a laser, MoTe₂ is transformed into Te or Mo₃Te₄ due to the highly accumulated heat and atomic evaporation. Conversely, hBN-encapsulated 2H-MoTe₂ transformed into a 1T′ phase without evaporation or structural degradation, enabling stable phase transitions in desired regions. The laser-induced phase transition shows layer number dependence; thinner MoTe₂ has a higher phase transition temperature. From the stable phase patterning method, the low contact resistivity of 1.13 kΩ µm in 2H-MoTe₂ field-effect transistors with 1T′ contacts from the seamless heterophase junction geometry is achieved. This study paves an effective way to fabricate monolithic 2D electronic devices with laterally stitched phases and provides insights into phase and compositional changes in 2D materials.

By means of universal subsurface oxygen vacancy strategy, the surface Fermi level de-pinning in a series of metal oxide semiconductor are achieved while retaining the active defective structure. The completely splitted quasi Fermi level of holes and electrons induces enhanced open-circuit photovoltage, providing sufficient driving force for charge transfer, to achieve robust photoelectrochemical water splitting.

Abstract

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-O_v) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-O_v were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated O_v located at sub ∼2–5 nm region. Mott–Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm⁻² at 1.23 V vs. RHE were achieved on BiVO₄, Bi₂O₃, TiO₂ with outstanding stability for 72 h, outperforming most reported works under the identical conditions.

Applied Physics Letters, Volume 122, Issue 4, January 2023.
Direct growth of gallium nitride (GaN) thin films is performed using plasma-enhanced atomic layer deposition (PEALD) at 300 °C on a sapphire with a graphene interlayer. The x-ray diffraction and spherical aberration corrected transmission microscope results confirm that the GaN thin films are nearly single-crystalline. Additionally, the interfacial properties and nucleation behaviors of the GaN thin films deposited on graphene are investigated in detail. Therefore, this study offers a perspective on PEALD growth of high-quality nanoscale GaN epilayers and broadens the choice for low-temperature fabrication of GaN based-devices.

Light: Science & Applications, Published online: 24 January 2023; doi:10.1038/s41377-022-01037-7

The crystal growth, defects control, electrical property and corresponding device authentication of N-type, P-type and semi-insulating silicon carbide crystals in Shandong University are introduced.

Flexible Electronics

In article number 2201458, Jordan Bouaziz, Fabio La Mattina, and colleagues describe the use of water-soluble Sr₃Al₂O₆ oxide to enable the fabrication of complex oxide membranes of a few tens of nanometers in size. The transfer of these membranes to other substrates opens the possibility of exploiting the countless oxide properties for the realization of new electronic devices.

Applied Physics Letters, Volume 122, Issue 4, January 2023.
Atomically thin MoSe2 is of interest from the perspective of estimating the layer-dependent material properties necessary for the translation of two-dimensional materials into devices. This work presents Raman spectroscopic protocols to determine a multitude of material parameters of two-dimensional MoSe2 films, including the layer thickness as well as the layer-dependent thermal conductivity, interlayer interactions, and anharmonicity. The Davydov splitting (factor-group splitting) observed in an out-of-plane A1g Raman mode, being layer-dependent in both the number and the peak positions, provides a method for estimating the number of layers. Furthermore, this work demonstrates the determination of the thermal conductivity (K) from the temperature-dependent Davydov split Raman modes of the multi-layers. The measurement of K by conventional methods is otherwise challenging for the micrometer sizes of the two-dimensional materials. The value of K thus determined increases significantly from 9 W m−1 K−1 for a four-layer thick MoSe2 film to 52 W m−1 K−1 for a monolayer. The diminishing effect of anharmonicity observed in the monolayer as compared to multi-layer MoSe2 supports the layer-dependent trend in the thermal conductivity. Overall, the findings are relevant for the applications of 2D MoSe2 in low power electronic, optoelectronic, and thermoelectric devices.