Jing Zhang

Nature, Published online: 18 May 2023; doi:10.1038/d41586-023-01684-9

A flexible, conductive membrane that can pass sensory information to the brain and muscles is a step towards artificial skin.

Second harmonic generation (SHG) in few-layer ReS₂ can be controlled by stacking order and layer number. In the SHG-active AB_y-stacked even-layers, the SHG intensities can be greatly enhanced when the photon energy matches with the exciton level, and bulk SHG susceptibility χ(2)${\chi}^{(2)}$ always shows the largest value for the bilayer.

Abstract

The second harmonic generation (SHG) is systematically investigated in mechanically exfoliated, few-layer ReS₂ samples. The stacking orders are identified as (AA)_nA and (AB_y)_nA for (2n+1)-layer samples and (AA)_n and (AB_y)_n for 2n-layer samples. The layer structure A stands for that of a monolayer, and the layer structure B_y is mirror to A followed by a one-tenth unit cell translation along the mirror axis, that is, the b -axis of the crystal. Only the even-layer samples with (AB_y)_n stacking order are SHG active. After carefully extracting the effective bulk susceptibility for SHG, it is found that the spectra are greatly enhanced as the fundamental photon energy matches exciton levels. The polarization dependence is strongly anisotropic, and each susceptibility component shows very different wavelength dependence. The results demonstrate that few-layer ReS₂, with its unique SHG, can be considered as an ideal platform for fundamental research in anisotropic nonlinear optics.

The synthesis of InP nanocrystals with different phosphorus sources is briefly summarized. The research progress in the optical properties of InP/ZnE and InP/ZnE/ZnE nanocrystals, including absorption, fluorescence, carrier dynamics, and nonlinear optics, are summarized. In addition, the relevant applications based on InP/ZnE and InP/ZnE/ZnE nanocrystals are also presented, ranging from light emitting diodes, bioimaging, and solar cells to photocatalytic hydrogen production.

Abstract

As the most promising candidate for luminescent semiconductor materials in the future environmentally friendly society, InP nanocrystals (NCs) have attracted strong attention in the past decade. Tremendous efforts have been devoted to address the unstable and poor optical properties of InP NCs for practical applications. An extensive and in-depth summary of existing literatures can not only provide an important reference for further optimizing of the optical properties of InP NCs, but also lay a foundation for subsequent related applications. In this review, the methods for the synthesis with different P sources and different ZnE (E = Se, S) shells are briefly summarized. The research progress in the optical properties investigation of InP/ZnE and InP/ZnE/ZnE NCs, including absorption, fluorescence, carrier dynamics, and nonlinear optics, are summarized. The relevant applications based on InP/ZnE and InP/ZnE/ZnE NCs are also presented, ranging from light emitting diodes, bioimaging, and solar cells to photocatalytic hydrogen production.

Ferrocene crystals are grown using a bottom-up method and self-assembled at liquid–liquid capillary interfaces. Their unique molecular arrangement results in high birefringence, low dichroism, and low loss over a broad range (≈550 nm – 20 µm). Facet orientations along the b-axis are synthesized at the acetone–water interface, and the naturally grown a–c planes, exhibiting the highest birefringence and suit for on-chip applications.

Abstract

As basic optical elements, waveplates with anisotropic electromagnetic responses are imperative for manipulating light polarization. Conventional waveplates are manufactured from bulk crystals (e.g., quartz and calcite) through a series of precision cutting and grinding steps, which typically result in large size, low yield, and high cost. In this study, a bottom-up method is used to grow ferrocene crystals with large anisotropy to demonstrate self-assembled ultrathin true zero-order waveplates without additional machining processing, which is particularly suited for nanophotonic integration. The van der Waals ferrocene crystals exhibit high birefringence (Δn (experiment) = 0.149  ±  0.002 at 636 nm), low dichroism Δκ (experiment) = −0.0007 at 636 nm), and a potentially broad operating range (550 nm to 20 µm) as suggested by Density Functional Theory (DFT) calculations. In addition, the grown waveplate's highest and the lowest principal axes (n₁ and n₃, respectively) are in the a–c plane, where the fast axis is along one natural edge of the ferrocene crystal, rendering them readily usable. The as-grown, wavelength-scale-thick waveplate allows the development of further miniaturized systems via tandem integration.

Semi-floating-gate-controlled 2D lateral homojunctions based on InSe (MoS₂)/hBN/graphite van der Waals heterostructures with an atomically sharp interface on a Si substrate, can be ultrafast-programmed in ≈20 ns. The high rectification ratio of ≈10⁵ and four dynamically switchable non-volatile memory states make them work as rectifiers, non-volatile memories, and reconfigurable multi-valued logic inverters.

Abstract

The development of electrically ultrafast-programmable semiconductor homojunctions can lead to transformative multifunctional electronic devices. However, silicon-based homojunctions are not programmable so that alternative materials need to be explored. Here 2D, multi-functional, lateral homojunctions made of van der Waals heterostructures with a semi-floating-gate configuration on a p⁺⁺ Si substrate feature atomically sharp interfaces and can be electrostatically programmed in nanoseconds, more than seven orders of magnitude faster than other 2D-based homojunctions. By applying voltage pulses with different polarities, lateral p−n, n⁺−n and other types of homojunctions can be formed, varied, and reversed. The p−n homojunctions possess a high rectification ratio of up to ≈10⁵ and can be dynamically switched between four distinct conduction states with the current spanning over nine orders of magnitude, enabling them to function as logic rectifiers, memories, and multi-valued logic inverters. Built on a p⁺⁺ Si substrate, which acts as the control gate, the devices are compatible with Si technology.

Surface chemistry and interlayer engineering determines the electrical properties of 2D MXene. The electrical and electromagnetic properties of Ti₃C₂T_x are investigated in detail with respect to KOH and ammonia concentrations, and the electrical properties of Ti₃C₂T_x are optimized using surface and interfacial chemistry to provide a framework for enhancing the electromagnetic wave loss of intrinsic MXene.

Abstract

Surface chemistry and interlayer engineering determines the electrical properties of 2D MXene. However, it remains challenging to regulate the surface and interfacial chemistry of MXene simultaneously. Herein, simultaneous modulation of Ti₃C₂T_x MXene surface termination and layer spacing by alkali treatment are achieved. The electrical and electromagnetic properties of Ti₃C₂T_x are investigated in detail with respect to KOH and ammonia concentration dependence. A high concentration of KOH caused the Ti₃C₂T_x layer spacing to expand to 13.7 Å and the surface O/F ratio to increase to 33.84. Because of its weaker ionization effect, ammonia provides finer tuning compared to the drastic intercalation of KOH with a thorough sweeping of the F-containing groups. Ti₃C₂T_x is enriched with conductive -OH termination after ammonia treatment, which achieves an effective balance with the increased interlayer resistance. Therefore, NH₃H₂O-Ti₃C₂T_x achieves broad-band impedance matching and exhibits an efficient microwave loss of −49.1 dB at a low thickness of 1.7 mm, with an effective frequency bandwidth of 3.9 GHz. The results herein optimize the electrical properties of Ti₃C₂T_x using surface and interfacial chemistry to achieve broad microwave absorption, providing a framework for enhancing the electromagnetic wave loss of intrinsic MXene.

Nature Nanotechnology, Published online: 22 May 2023; doi:10.1038/s41565-023-01399-y

A large array of ferroelectric field-effect transistors with record memory windows, ON/OFF ratios and ON-current density is presented at ~80 nm channel length.

Nature Synthesis, Published online: 18 May 2023; doi:10.1038/s44160-023-00305-7

Polyoxoniobate (PONb) clusters are ideal candidates for synthesizing 2D clusterphenes but niobate reactivity is low. Now, 2D hexagonal PONb-clusterphenes have been prepared through a wet-chemical synthesis at ambient conditions, providing atomically precise models for examination of cluster electronic structures.

A series of Sb³⁺and lanthanide (Ln³⁺) co-doped Cs₃InCl₆ nanocrystals (NCs) with dual-emission from self-trapped excitons (STEs) and Ln³⁺ ions have been fabricated. Excited by 340 nm, the Ln³⁺ emissions are sensitized mainly by energy transfer from the STEs to Ln³⁺ ions for most of Cs₃InCl₆:1%Sb,40%Ln¹ (Ln¹ = Nd/Sm/Tb/Dy/Ho/Er/Tm/Yb) NCs. For Cs₃InCl₆:1%Sb,40%Ce/Eu NCs, this energy transfer process does not exist.

Abstract

Doping impurity ions, such as lanthanide (Ln³⁺) ions, can introduce unique emissions over the visible and near infrared (NIR) region and enrich the optoelectronic properties for lead-free perovskites. Here, tetragonal Cs₃InCl₆:Sb nanocrystals (NCs) with bright self-trapped excitons (STEs) emission have been synthesized. Interestingly, tetragonal Cs₃InCl₆:1%Sb can transform into monoclinic Cs₃InCl₆:1%Sb and orthorhombic Cs₂InCl₅·H₂O:1%Sb under different solvent triggers. Further, a series of Ln³⁺ ions are doped into Cs₃InCl₆:Sb NCs, along with the appearance of Ln³⁺ ions emissions over the visible and NIR region. Benefiting from the different photoluminescence (PL) origins of the STEs and Eu³⁺ emissions, Cs₃InCl₆:Sb,Eu NCs enable varied color delivery and exhibit great potential as anti-counterfeiting materials. Meantime, Cs₃InCl₆:Sb,Nd NCs with strong NIR emissions demonstrate great potential for NIR light-emitting diode (LED) applications. This work not only presents an effective strategy to tune the optoelectronic properties of lead-free perovskites, but also provides insight into applications in the anticounterfeiting and LED fields.

A series of molybdenum ditelluride (MoTe₂) homobilayers with precisely controlled twist-angles from 0° to 60° exhibit varying exciton-emission behaviors at low temperatures, as the twist-angle increases resulting in changes in interlayer interactions and different moiré superlattices. In a dual-gated 1.4° twisted bilayer MoTe₂, the intralayer neutral and charged excitons from the K-K valleys are identified through gate-dependent and field-dependent photoluminescence measurements.

Abstract

Layered 2H-molybdenum ditelluride (MoTe₂) is a promising near-infrared material with optical activity, which enables hybrid-integrated with silicon photonics for communication purposes. The use of various artificial hetero-stacking or twist-stacking techniques can further expand the emission bandwidth and offer more choices of optical-active materials used as building blocks in on-chip optoelectronic devices. However, while the twisting technique is an effective tool for adjusting interlayer interaction in van der Waals materials, a systematic experimental study of twisted MoTe₂ homobilayers is currently lacking. Here, a series of MoTe₂ homobilayers were prepared with precisely controlled twist-angles from 0° to 60°, with a particular focus on the small-twist region. Conducting photoluminescence measurements at low temperatures enabled observation of the evolution of exciton emission as the twist angle increases. Neutral and charged excitons were also identified in a dual-gated 1.4° twisted MoTe₂ through gate-dependent and field-dependent photoluminescence measurements. Furthermore, spatially-resolved photoluminescence measurements revealed the critical role of the interface conditions, including interlayer spacing and strain, in addition to the twist-angle, in determining the excitonic behavior of the material. This study provides compelling experimental evidence for understanding the twist-angle-dependent excitonic behaviors in atomically thin semiconductors.

An optical encoder is fabricated utilizing an individual sub-micrometer sphere of CsPbBr₃, possessing an encoding frequency of 200 GHz. Through the implementation of an upstream encoding method to regulate the radiation state, combined with the carrier's radiation process, a noteworthy energy-saving efficiency of 84% is achieved.

Abstract

Optical coding is widely applied in communication and data processing fields due to its practical and powerful characteristics, such as high transmission rate and operational convenience. However, improvements in the loading information capacity of optical encoders always result in increased energy consumption. It is a challenge to realize an optical encoder that combines energy savings, high bandwidth, and miniaturization. Here, both the concept and the demonstration of a perovskite sub-micro-encoder with an 84% energy-saving efficiency and a tunable bandwidth of up to 200 GHz are reported. The way to code the radiative dynamics of the light source allows for the reduction of unnecessary energy consumption from the initial stage through the control of the radiation core. Moreover, the miniature encoder generates code sequences of good coherence, stimulating the development of perovskite-based optical microchips for ultrafast information processing.

A dynamically responsive hydrogel medium composed of two self-assembling materials, chitosan, and SDS, can be reversibly patterned using electronic inputs that switch chitosan between crystalline and electrostatically crosslinked supramolecular states. In addition, salt and water treatments can induce transitions in SDS's supramolecular structure that can reversibly conceal the electronically written patterns by either obscuring the pattern or making it invisible (evanescent).

Abstract

A dynamically responsive hydrogel medium is prepared from two self-assembling components, a polysaccharide (chitosan) and a surfactant (sodium dodecyl sulfate; SDS). It is shown that this medium can be patterned using an electrode “pen” to reconfigure supramolecular structure: cathodic writing induces neutral chitosan chains to form a crystalline network, while anodic writing generates cationic chitosan chains that electrostatically crosslink with anionic SDS micelles. Both supramolecular structures are re-configurable and each is stabilized by structure-induced shifts in chitosan's pKa, thus electronically written patterns can be erased, new patterns can be written, and patterns can be written in three dimensions. Further, it is shown that NaCl-induced morphological transitions of the SDS micelles allow patterns to be reversibly concealed or revealed. To demonstrate the versatility of this medium for information storage, a quick response (QR) code is electronically written and it is shown that this code can be recognized by a standard cellphone app. This QR code can be concealed by making the medium opaque (i.e., by obscuring the pattern) or by making the pattern evanescent (i.e., by making pattern invisible). Overall, this work demonstrates that a dynamically responsive medium composed of simple, safe and sustainable components can be reversibly patterned with spatial and quantitative control using top-down electronic inputs.

The demand for augmented reality (AR), virtual reality (VR), wearables, and head-up display (HUD) technology has fueled the rapid growth of next-generation microdisplays. Despite their promise, challenges remain. This review analyzes performance metrics across various scenarios and provides valuable materials and technology perspectives for ongoing display technology. Our guidance for advanced microdisplay design aims to overcome obstacles and improve the field.

Abstract

The field of next-generation microdisplays is flourishing. Relevant display technologies, such as mini-light emission diodes (mini-LEDs), micro-organic light emission diodes (micro-OLEDs), and micro-light emission diodes (micro-LEDs) are thus in the urgent stage of development. From this perspective, comprehensive and systematical analyzes are conducted for the aforesaid microdisplay configurations. A holistic view of microdisplay technologies is developed with the corresponding performance metrics, providing a path for miscellaneous scenarios. Among these scenarios, the applications in augmented reality (AR), virtual reality (VR), wearable devices, and head-up displays (HUD) are currently attracting considerable attention for deeper human-digital interactions. However, there is a multiplicity of obstacles and challenges hindering such development. Nevertheless, recent advances in microdisplay technologies hold tremendous promise for the paradigms of these applications, taking a leap forward for next-generation microdisplays. This review presents perspectives, relevant materials, and the technology landscape for such ongoing display technologies, offering guidance on the design of advanced microdisplays.

This study presents a solution method derived dual-band photodetector based on silicon nanowires/PbS nanocrystalline film n–n heterojunction, exhibiting an enhanced photoresponse in both near-infrared and short-wave infrared bands. The fabricated heterojunction device with a huge difference between energy barriers of conduction and valence bands are characterized by a bias-selectable spectral response, showing three operation modes in distinct IR regions.

Abstract

In this study, a solution method derived dual-band photodetector (PD) based on silicon nanowires /PbS nanocrystalline film n–n heterojunction, which exhibits typical bias-selectable spectral response in both near-infrared (NIR) and short-wave infrared (SWIR) bands, is presented. It is found that by adjusting the polarity of the bias voltage, the photoresponse of the device can be switched between three operation modes. The device exhibits high responsivities of 2100 mA W⁻¹ at −0.15 V and 31 mA W⁻¹ at 0 V, respectively, in the NIR region. Remarkably, the maximum responsivity and detectivity under 2000 nm illumination are determined as 290 mA W⁻¹ and 2.4 × 10¹⁰ Jones, comparable to or even better than some PbS commercial PDs. The enhanced performance comes from the improved optical absorption and higher efficiency of charge separation and collection owing to the heterojunction geometry. It's also revealed that the bias-controllable spectral response is attributed to the selectively transportation of photocarriers across the junction barrier. The study demonstrates the capability of detecting two distinct IR regions with the same pixel, which has great potential in future optoelectronic systems for IR imaging applications.

A multilayer heterojunctions interface passivation strategy is developed to simultaneously reduce the ionic and electronic conductivity of organic–inorganic hybrid perovskite single crystals. The MAPbBr₃ perovskite X-ray detectors achieve high sensitivity of 19 370 µC Gy_air ⁻¹ cm⁻², low detection limit, negligible baseline drift after 210 days and outstanding irradiation stability with an accumulated dose equaling 9720 times posteroanterior chest examinations.

Abstract

Organic-inorganic hybrid perovskites are promising candidates for direct X-ray detection and imaging. The relatively high dark current in perovskite single crystals (SCs) is a major limiting factor hindering the pursuit of performance and stability enhancement. In this study, the contribution of dark current is disentangled from electronic (σ_e ) and ionic conductivity (σ_i ) and shows that the high σ_i dominates the dark current of MAPbBr₃ SCs. A multilayer heterojunctions passivation strategy is developed that suppresses not only the σ_i by two orders of magnitude but also σ_e by a factor of 1.6. The multilayer heterojunctions passivate the halide vacancy defects and increase the electron and hole injection barrier by inducing surface p-type doping of MAPbBr₃. This enables the MAPbBr₃ SC X-ray detectors to obtain a high sensitivity of 19 370 µC Gy_air ⁻¹ cm⁻² under a high electric field of 100 V cm⁻¹, a record high sensitivity for bromine self-powered devices, and a low detection limit of 42.3 nGy_air s⁻¹. The unencapsulated detectors demonstrate a stable baseline after storage for 210 days and outstanding operational stability upon irradiation with an accumulated dose of up to 1944 mGy_air.

Major challenges in stretchable electronics occur when connecting rigid chips and soft parts. Thus, a reliable solder and soldering process are necessary. To solve the issue, this study presents a room-temperature universal stretchable sticker-like soldering process that solders multiple spots at once and directly fabricates a stretchable device while a target conductor is installed on one's body.

Abstract

Researchers are eagerly developing various stretchable conductors to fabricate devices for next-generation electronics. Most of the major problems in stretchable electronics happen at the connection between rigid and soft parts and the development of reliable soldering material is a major hurdle in stretchable electronics. Though there are attempts to devise new soldering processes for integrating chips and stretchable conductors, they still possess limitations such as mechanical stability, mass production, sophisticated processes, and restricted candidates for conductors and substrates. Here, this study presents a room-temperature universal stretchable sticker-like soldering process that can stretchably solder multiple spots at once and directly fabricates a stretchable device in an in situ manner while a target conductor is installed on one's body. The solder developed in this research possesses high conductivity with a unique freestanding feature enabling the process. It can be elongated when directly positioned between a rigid chip and a rigid conductor, demonstrating its extraordinary stretchability. It is expected that this simple but unique stretchable soldering technique utilizing the invented solder will allow the integration of functional stretchable conductors with highly advanced rigid chips for next-generation stretchable electronics.

Nature Materials, Published online: 11 May 2023; doi:10.1038/s41563-023-01553-w

An ultra-microporous metal–organic framework glass foam shows outstanding gas sieving properties for challenging gas mixtures.

Nature Physics, Published online: 11 May 2023; doi:10.1038/s41567-023-02060-0

Phase transitions during which electrons recover their Dirac nature are shown to produce a spin resonance response that allows the characterization of spin and valley couplings in twisted bilayer graphene.

Nature, Published online: 11 May 2023; doi:10.1038/s41586-023-06162-w

Absence of near-ambient superconductivity in LuH_2±xN_y

Ultrafine ZnS nanodots grown on 2D MXene nanosheets by a low-temperature hydrothermal method with abundant active site can not only act as a redox accelerator to promote the bidirectional conversion of lithium polysulfides and mitigate the shutting effect, but also as a regulator for enabling uniform Li plating/stripping to inhibit the growth of Li dendrite.

Abstract

Lithium−sulfur (Li−S) battery is a promising energy storage system due to its cost effectiveness and high energy density. However, formation of Li dendrites from Li metal anode and shuttle effect of lithium polysulfides (LiPSs) from S cathode impede its practical application. Herein, ultrafine ZnS nanodots are uniformly grown on 2D MXene nanosheets by a low-temperature (60 °C) hydrothermal method for the first time. Distinctively, the ZnS nanodot-decorated MXene nanosheets (ZnS/MXene) can be easily filtered to be a flexible and freestanding film in several minutes. The ZnS/MXene film can be used as a current collector for Li-metal anode to promote uniform Li deposition due to the superior lithiophilicity of ZnS nanodots. ZnS/MXene powders obtained by freeze drying can be used as separator decorator to address the shuttle effect of LiPSs due to their excellent adsorbability. Theoretical calculation proves that the existence of ZnS nanodots on MXene can obviously improve the adsorption ability of ZnS/MXene with Li⁺ and LiPSs. Li−S full cells with composite Li-metal anode and modified separator exhibit remarkable rate and cycling performance. Other transition metal sulfides (CdS, CuS, etc.) can be also grown on 2D MXene nanosheets by the low-temperature hydrothermal strategy.

Exotic Superconductivity

In article number 2207841, Fucong Fei, Zhicheng Zhong, Fengqi Song, Xuefeng Wang, and co-workers report boosted superconductivity with a transition temperature of about 7.5 K in Ta-doped MoTe₂ single crystals under ambient pressure. An enhanced upper critical field beyond the Pauli limit is also observed in Ta-doped Weyl semimetal T _d-MoTe₂, which is likely due to the mixed singlet–triplet superconductivity.

Nature Nanotechnology, Published online: 11 May 2023; doi:10.1038/s41565-023-01403-5

Domain wall formation and propagation using a small electric voltage are demonstrated in ferro-rotational 1T-TaS2, although the ferroic order does not couple with electromagnetic fields, providing an opportunity for the manipulation and application of ferro-rotational order.