Jing Zhang

Low-temperature grown gallium arsenide (LT-GaAs) is one of the best photoconductive materials for detecting terahertz radiation. However, the large bandgap of LT-GaAs prevents its use with robust telecom lasers. This work presents a photoconductive LT-GaAs metasurface that uses the concept of perfect absorption to strongly enhance a very weak two-step optical absorption at 1.55 µm via midgap states, enabling sensitive terahertz detection.

Abstract

Superior ultrafast photoconductive properties make low temperature grown (LT) GaAs one of the best materials for photoconductive terahertz (THz) detection. However, the large bandgap of LT-GaAs limits its operation to gating at wavelengths shorter than 870 nm. Here, it is demonstrated for the first time that nanostructuring the LT-GaAs into a highly absorbing metasurface enables THz photoconductive detection with a pulsed laser at λ = 1.55 µm. The very weak sub-bandgap absorption mediated by midgap states in LT-GaAs is strongly enhanced using the concept of perfect absorption via degenerate critical coupling. Integrated with a THz antenna, the LT-GaAs metasurface enables high sensitivity THz detection with a high dynamic range of 60 dB and large bandwidth up to 4.5 THz. The LT-GaAs metasurface has the potential to serve as a universal ultrafast switching element for THz applications, enabling low-cost, turn-key THz systems for a variety of real-world applications.

Multi-configurational 2D heterojunctions constructed from Cr_xTe_y self-intercalated crystals are demonstrated by TEM diffraction and atomic STEM imaging. In a Cr₂Te₃-Cr₅Te₈ lateral heterojunction, two phases share the layered CrTe₂ as the backbone, whereas different arrangements of intercalated Cr in vdW gap form distinct magnetic phases. A novel magneto-optical behavior of a sharply stepped hysteresis loop with twice spin flips is revealed for the first time.

Emerging 2D magnetic heterojunctions attract substantial interest due to their potential applications in spintronics. Achieving magnetic phase engineering with structural integrity in 2D heterojunctions is of paramount importance for their magnetism manipulation. Herein, starting with chromium ditelluride (CrTe₂) as the backbone framework, various lateral and vertical magnetic heterojunctions are obtained via self-intercalated 2D chromium telluride (Cr _x Te _y ). A Cr₂Te₃-Cr₅Te₈ lateral heterojunction prototype is demonstrated for the manipulation of magnetic moments under different magnitudes of magnetic excitation, showing a sharply stepped hysteresis loop with a dual spin-flip transition at high Curie temperatures up to 150 and 210 K by magneto-optical Kerr measurement. High-resolution scanning transmission electron microscopy and first-principles calculations reveal a preferred random location of Cr intercalants at the phase boundary, allowing lowering energy associated with crystal field splitting. The overall structural rigidity of chromium-telluride heterostructure with magnetic phase decoupled behaviors is promising for 2D spintronic devices.

The largest functional crossbars incorporating molecular materials to date are fabricated, in which all the memristors are consistent, robust, and reliable. An 8-bit serial and 4-bit parallel adders are experimentally demonstrated. For performance benchmarking, a 32-bit adder with 268 million inputs is simulated that outperformed a multicore complementary metal–oxide–semiconductor (CMOS) platform.

Abstract

A breakthrough in in-memory computing technologies hinges on the development of appropriate material platforms that can overcome their existing limitations, such as larger than optimal footprint and multiple serial computational steps, with potential accumulation of errors. Using a molecular switching element with multiple non-monotonic and deterministic transitions, the device count and the number of computational steps can be substantially reduced. With molecular materials, however, the realization of a reliable and robust platform is an unattained goal for decades. Here, crossbar arrays with up to 64 molecular memristors are fabricated to experimentally demonstrate 8-bit serial and 4-bit parallel adders that operate for thousands of measurement cycles with an estimated error probability of 10⁻¹⁶. For performance benchmarking, a 32-bit parallel adder is designed and simulated with 268 million inputs including contributions from the peripheral circuitry showing a 47× higher energy efficiency, 93× faster operation, and 9% of the footprint, leading to 4390 times improved energy–delay product compared to a special purpose complementary metal–oxide–semiconductor (CMOS)-based multicore adder.

Leveraging highly oriented thin films, a ferrielectric phase is observed in PbZrO₃ at room temperature and low field. Ferrielectricity is observed in modulations of amplitude and direction of the spontaneous polarization and large anisotropy for critical electric fields, and is qualitatively consistent with theoretical predictions, and correlates with high dielectric tunability and large strains.

Abstract

Antiferroelectric materials, where the transition between antipolar and polar phase is controlled by external electric fields, offer exceptional energy storage capacity with high efficiencies, giant electrocaloric effect, and superb electromechanical response. PbZrO₃ is the first discovered and the archetypal antiferroelectric material. Nonetheless, substantial challenges in processing phase pure PbZrO₃ have limited studies of the undoped composition, hindering understanding of the phase transitions in this material or unraveling the controversial origins of a low-field ferroelectric phase observed in lead zirconate thin films. Leveraging highly oriented PbZrO₃ thin films, a room-temperature ferrielectric phase is observed in the absence of external electric fields, with modulations of amplitude and direction of the spontaneous polarization and large anisotropy for critical electric fields required for phase transition. The ferrielectric state observations are qualitatively consistent with theoretical predictions, and correlate with very high dielectric tunability, and ultrahigh strains (up to 1.1%). This work suggests a need for re-evaluation of the fundamental science of antiferroelectricity in this archetypal material.

Nature Nanotechnology, Published online: 31 October 2022; doi:10.1038/s41565-022-01237-7

The interfacial shear modulus controls the sliding friction of supported two-dimensional materials. Now, experiments demonstrate a reciprocal relationship between friction force per unit contact area and the interfacial shear modulus.

Nature Nanotechnology, Published online: 01 November 2022; doi:10.1038/s41565-022-01231-z

A strong and tough human muscle-like actuator fibre is developed by exploiting 2D graphene fillers within a liquid crystalline elastomer matrix. Reversible percolation of the graphene filler network endows the artificial muscle with a work capacity and power density beyond those of human or mammalian muscles.

Nature Synthesis, Published online: 27 October 2022; doi:10.1038/s44160-022-00185-3

Atomically thin materials have exciting physicochemical properties but multi-element and non-layered 2D materials are difficult to prepare by conventional methods. Now, a flux-assisted method is reported, enabling the synthesis of such 2D materials by confining reaction space.

Nature Photonics, Published online: 27 October 2022; doi:10.1038/s41566-022-01093-w

Computing with silicon photodiodes

Nature Communications, Published online: 27 October 2022; doi:10.1038/s41467-022-33978-3

The ferroelectric material α-GeTe(111) is an excellent playground for spin-to charge conversion due to its strong Rashba coupling. Here, the authors reveal an ultrafast modulation of its Rashba coupling on the femtosecond timescale.

Nature Communications, Published online: 29 October 2022; doi:10.1038/s41467-022-34192-x

Twisted double bilayer graphene (tDBG) comprises two Bernal-stacked bilayer graphene sheets with a twist between them. Here, the authors report a strong anomalous Hall effect in the correlated-metal regime of tDBG, indicating time reversal symmetry breaking from orbital ferromagnetism, likely associated with valley polarization.

Nature Materials, Published online: 27 October 2022; doi:10.1038/s41563-022-01386-z

Using molecular-beam epitaxy, we synthesize heterostructures of topological insulator Bi2Se3 and the Ising superconductor monolayer NbSe2. By changing the Bi2Se3 thickness, they demonstrate a crossover from Ising- to Rashba-type superconducting pairing.

Nature Electronics, Published online: 27 October 2022; doi:10.1038/s41928-022-00849-0

Gate-tunable heterojunction diodes—or triodes—that are based on van der Waals heterostructures formed from two-dimensional indium selenide and three-dimensional silicon can exhibit subthreshold slopes of 6.4 mV decade–1 and on-state current densities of 0.3 µA µm–1 at a drain bias of –1 V.

Immunostimulant In Situ Hydrogels

In article number 2204288, Ye Zhou and co-workers propose a time-saving ultraviolet ozone technique to tune the work function of MXene electrodes. Van der Waals contact between MXene and MoS₂ can alleviate the Fermi level pinning effectively, and the pinning factor can be greatly optimized to 0.87. This study provides a new strategy to eliminate the negative effects of Fermi level pinning.

The synthesis of centimeter scale CsPbCl_{3(1– x )}Br_{3 x} single crystal thin films (SCTFs) with tunable compositions via vapor-phase deposition process is reported. These high-quality CsPbCl_{3(1– x )}Br_{3 x} SCTFs show tunable amplified spontaneous emission from blue region to green region at room temperature. This stu opens up the possibility to further develop wafer-scale CsPbCl_{3(1– x )}Br_{3 x} SCTFs with tunable electronic and optoelectronic properties, in particular, scalable integrated device arrays.

Abstract

Single crystal metal halide perovskites thin films are considered to be a promising optical, optoelectronic materials with extraordinary performance due to their low defect densities. However, it is still difficult to achieve large-scale perovskite single-crystal thin films (SCTFs) with tunable bandgap by vapor-phase deposition method. Herein, the synthesis of CsPbCl_{3(1– x )}Br_{3 x} SCTFs with centimeter size (1 cm × 1 cm) via vapor-phase deposition is reported. The Br composition of CsPbCl_{3(1– x )}Br_{3 x} SCTFs can be gradually tuned from x = 0 to x = 1, leading the corresponding bandgap to change from 2.29 to 2.91 eV. Additionally, an low-threshold (≈23.9 µJ cm⁻²) amplified spontaneous emission is achieved based on CsPbCl_{3(1– x )}Br_{3 x} SCTFs at room temperature, and the wavelength is tuned from 432 to 547 nm by varying the Cl/Br ratio. Importantly, the high-quality CsPbCl_{3(1– x )}Br_{3 x} SCTFs are ideal optical gain medium with high gain up to 1369.8 ± 101.2 cm⁻¹. This study not only provides a versatile method to fabricate high quality CsPbCl_{3(1– x )}Br_{3 x} SCTFs with different Cl/Br ratio, but also paves the way for further research of color-tunable perovskite lasing.

Here, the substrate-orientation independent growth of Hf_0.5Zr_0.5O₂ (HZO) thin films is realized with uniform ferroelectricity by using HfO₂ seed layers. Further device simulation studies suggest that the proposed scheme contributes to realizing uniform memory properties in 3D vertical HZO-based ferroelectric field-effect transistors.

Abstract

The highly scalable ferroelectric hafnia-based thin films can be easily integrated into ferroelectric field-effect transistors (FeFETs) by existing Si technology, which are regarded as one of the promising candidates for fast read/write, energy-efficient, and high-density nonvolatile memories. However, device-to-device variation in threshold voltage (V _TH) caused by non-uniformity of ferroelectric properties is a serious challenge for implementing hafnia-based FeFETs in high-density nonvolatile memories. Here, the substrate-orientation independent growth of Hf_0.5Zr_0.5O₂ (HZO) thin films is realized with uniform ferroelectricity by using HfO₂ seed layers. The HfO₂ seed layers are beneficial to improving the ferroelectric polarization of HZO thin films grown on differently oriented Si substrates and reducing the variation in ferroelectric properties. Moreover, device simulation confirms that the proposed scheme contributes to realizing uniform memory properties in 3D vertical HZO-based FeFETs. This study suggests the possibility to implement hafnia-based FeFETs into 3D vertical high-density memory.

During the potential-driven semiconductor-to-metal phase transition, more electrons are injected into the metallic phase than the semiconducting phase under same electrode potential. MoTe₂ is chosen as a prototypical example to study the phase transition by utilizing the fixed-potential method, which verifies the mechanism and agrees well with the experimental results. The calculations can provide experimental groups with an explicit picture of the potential effects on the phase transition directly.

Abstract

The potential-driven semiconductor-to-metal transition is investigated in monolayer transition metal dichalcogenides by employing a new proposed method, i.e., the fixed-potential method (FPM). Under the same voltage, the semiconducting and metallic phases will be charged differently due to their different electronic properties. The potential-driven phase transition process is simulated by the injection of unequal electrons in the semiconducting and metallic phases. The unequal electron injection is more consistent with the actual experimental process, although equal electron injection also can theoretically induce a phase transition. MoTe₂ is chosen as a prototypical example to examine the physical mechanism. When the fixed electrode potential is above the potential of zero-charge, excess electrons are injected into the metallic 1T’ phase instead of the semiconducting 2H phase, stabilizing the 1T’ phase. In addition, the potential-dependent kinetics, in which the charge transfer is fluctuating, suggests that increasing the electrode potential will decrease the kinetic barrier of the 2H→1T’ transition process. The calculated relative transition voltage of 2.5 V agrees well with the experimental results, demonstrating the validity of the FPM. This study provides new insight into potential-driven semiconductor-to-metal phase transitions and suggests a new theoretical approach for studies under constant voltage conditions.

A carbon dots-intercalated strategy is proposed to fabricate flexible MXene film electrodes through gelation of calcium alginate within the MXene nanosheets followed by carbonization, which achieves both high ion-accessible active surface and density. The resulting carbon dots-intercalated MXene films exhibit dramatically enhanced volumetric performance and rate capability, much superior to the dense pristine MXene film.

Abstract

2D MXenes have emerged as promising supercapacitor electrode materials due to their metallic conductivity, pseudo-capacitive mechanism, and high density. However, layer-restacking is a bottleneck that restrains their ionic kinetics and active site exposure. Herein, a carbon dots-intercalated strategy is proposed to fabricate flexible MXene film electrodes with both large ion-accessible active surfaces and high density through gelation of calcium alginate (CA) within the MXene nanosheets followed by carbonization. The formation of CA hydrogel within the MXene nanosheets accompanied by evaporative drying endow the MXene/CA film with high density. In the carbonization process, the CA-derived carbon dots can intercalate into the MXene nanosheets, increasing the interlayer spacing and promoting the electrolytic diffusion inside the MXene film. Consequently, the carbon dots-intercalated MXene films exhibit high volumetric capacitance (1244.6 F cm⁻³ at 1 A g⁻¹), superior rate capability (662.5 F cm⁻³ at 1000 A g⁻¹), and excellent cycling stability (93.5% capacitance retention after 30 000 cycles) in 3 m H₂SO₄. Additionally, an all-solid-state symmetric supercapacitor based on the carbon dots-intercalated MXene film achieves a high volumetric energy density of 27.2 Wh L⁻¹. This study provides a simple yet efficient strategy to construct high-volumetric performance MXene film electrodes for advanced supercapacitors.

A series of lanthanide(III)-Cu₄I₄ heterometallic organic frameworks (Ln-Cu₄I₄ MOFs)-based X-ray scintillators is developed by rationally assembling X-ray absorption centers ([Cu₄I₄] clusters) and luminescent chromophores (Ln(III) ions) in a specific manner. High-efficient excitation energy transfer from the cluster-based antenna to the Ln(III) ions enables Ln-Cu₄I₄ MOFs and their flexible film with excellent scintillation performance and high spatial resolution of 12.6 lp mm⁻¹.

Abstract

Scintillator-based X-ray imaging has attracted great attention from industrial quality inspection and security to medical diagnostics. Herein, a series of lanthanide(III)-Cu₄I₄ heterometallic organic frameworks (Ln-Cu₄I₄ MOFs)-based X-ray scintillators are developed by rationally assembling X-ray absorption centers ([Cu₄I₄] clusters) and luminescent chromophores (Ln(III) ions) in a specific manner. Under X-ray irradiation, the heavy inorganic units ([Cu₄I₄] clusters) absorb the X-ray energy to populate triplet excitons via halide-to-ligand charge transfer (XLCT) combined with the metal-to-ligand charge-transfer (MLCT) state (defined as the X/MLCT state), and then the ³X/MLCT excited state sensitizes Tb³⁺ for intense X-ray-excited luminescence via excitation energy transfer. The obtained Tb-Cu₄I₄ MOF scintillators exhibit high resistance to humidity and radiation, excellent linear response to X-ray dose rate, and high X-ray relative light yield of 29 379 ± 3000 photons MeV⁻¹. The relative light yield of Tb-Cu₄I₄ MOFs is ≈3 times higher than that of the control Tb(III) complex. X-ray imaging tests show that the Tb-Cu₄I₄ MOFs-based flexible scintillator film exhibits a high spatial resolution of 12.6 lp mm⁻¹. These findings not only provide a promising design strategy to develop lanthanide-MOF-based scintillators with excellent scintillation performance, but also exhibit high-resolution X-ray imaging for biological specimens and electronic chips.

Although research on low-dimensional nanomaterials has been booming for decades, more research is needed on how to utilize them to construct efficient information sensing, processing, and feedback devices. A review of recent representative studies on information sensing, processing, and feedback devices based on low-dimensional nanomaterials to provide a perspective on developing human–machine–thing natural interaction technologies is presented.

Abstract

A wide variety of low-dimensional nanomaterials with excellent properties can meet almost all the requirements of functional materials for information sensing, processing, and feedback devices. Low-dimensional nanomaterials are becoming the star of hope on the road to pursuing human–machine–thing natural interactions, benefiting from the breakthroughs in precise preparation, performance regulation, structural design, and device construction in recent years. This review summarizes several types of low-dimensional nanomaterials commonly used in human–machine–thing natural interactions and outlines the differences in properties and application areas of different materials. According to the sequence of information flow in the human–machine–thing interaction process, the representative research progress of low-dimensional nanomaterials-based information sensing, processing, and feedback devices is reviewed and the key roles played by low-dimensional nanomaterials are discussed. Finally, the development trends and existing challenges of low-dimensional nanomaterials in the field of human–machine–thing natural interaction technology are discussed.

Simple twisted stacking of two layers of nanomaterials can produce ultrathin planarized nanostructures with optical chirality. This review thoroughly examines the recent progress in ultrathin chiroptical metasurfaces prepared through chiral stacking, discussing the monolayer materials, fabrication strategies, and the induced circular dichroism. A special focus is placed on the flexible tunability of the chiroptical responses and relevant optical applications.

Abstract

Artificial chiral nanostructures have been subjected to extensive research for their unique chiroptical activities. Planarized chiral films of ultrathin thicknesses are in particular demand for easy on-chip integration and improved energy efficiency as polarization-sensitive metadevices. Recently, controlled twisted stacking of two or more layers of nanomaterials, such as 2D van der Waals materials, ultrathin films, or traditional metasurfaces, at an angle has emerged as a general strategy to introduce optical chirality into achiral solid-state systems. This method endows new degrees of freedom, e.g., the interlayer twist angle, to flexibly engineer and tune the chiroptical responses without having to change the material or the design, thus greatly facilitating the development of multifunctional metamaterials. In this review, recent exciting progress in planar chiral metasurfaces are summarized and discussed from the viewpoints of building blocks, fabrication methods, as well as circular dichroism and modulation thereof in twisted stacked nanostructures. The review further highlights the ever-growing portfolio of applications of these chiral metasurfaces, including polarization conversion, information encryption, chiral sensing, and as an engineering platform for hybrid metadevices. Finally, forward-looking prospects are provided.

Structured liquids provide a route to self-assemble functional materials at the liquid–liquid interface and to shape liquids into arbitrary geometries. In this work, the high conductivity of MXenes is leveraged to create conductive pathways at the interface. The electrical properties of the assemblies are characterized and initial all-liquid electronic devices are presented.

Abstract

Rigid, solid-state components represent the current paradigm for electronic systems, but they lack post-production reconfigurability and pose ever-increasing challenges to efficient end-of-life recycling. Liquid electronics may overcome these limitations by offering flexible in-the-field redesign and separation at end-of-life via simple liquid phase chemistries. Up to now, preliminary work on liquid electronics has focused on liquid metal components, but these devices still require an encapsulating polymer and typically use alloys of rare elements like indium. Here, using the self-assembly of jammed 2D titanium carbide (Ti₃C₂T _x ) MXene nanoparticles at liquid–liquid interfaces, “all-liquid” electrically conductive sheets, wires, and simple functional devices are described including electromechanical switches and photodetectors. These assemblies combine the high conductivity of MXene nanosheets with the controllable form and reconfigurability of structured liquids. Such configurations can have applications not only in electronics, but also in catalysis and microfluidics, especially in systems where the product and substrate have affinity for solvents of differing polarity.

Huge magneto-transverse and longitudinal power factors are simultaneously detected in the magnetic Weyl semimetal TbPtBi. This can be ascribed to the magnetic field-enhanced transverse and longitudinal thermopower induced by bipolar effect, and large Hall angle related to the large net Berry curvature and high carrier mobility, and the incompletely compensated charge carriers and large transverse magnetoresistance, respectively.

Abstract

Magnetic topological semimetals provide new opportunities for power generation and solid-state cooling based on thermoelectric (TE) effect. The interplay between magnetism and nontrivial band topology prompts the magnetic topological semimetals to yield strong transverse TE effect, while the longitudinal TE performance is usually poor. Herein, it is demonstrated that the magnetic Weyl semimetal TbPtBi has high value for both transverse and longitudinal thermopower with large power factor (PF). At 300 K and 13.5 Tesla, the transverse thermopower and PF reach up to 214 µV K⁻¹ and 35 µW cm⁻¹ K⁻², respectively, which are comparable to those of state-of-the-art TE materials. Combining first-principles calculations, longitudinal magnetoresistance and planar Hall resistance measurements, and two-band model fitting, the large transverse thermopower and PF are attributed to both bipolar effect and large Hall angle. Moreover, the imperfectly compensated charge carriers and large transverse magnetoresistance induce the maximum magneto-longitudinal thermopower of 251 µV K⁻¹ with a PF of 24 µW cm⁻¹ K⁻² at 150 K and 13.5 Tesla, which is two times higher than that at zero magnetic field. This work demonstrates the great potential of topological semimetals for TEs and offers a new excellent candidate for magneto-TEs.

Nature Nanotechnology, Published online: 27 October 2022; doi:10.1038/s41565-022-01230-0

Isothermal dissolution–diffusion–precipitation of carbon drives continuous epitaxial growth of single-crystal multilayer graphene.

High-resolution multicolor patterning is achieved in a hybrid perovskite nanosheet, of which the linewidth can be down to ≈150 nm. A single perovskite nanosheet can not only gradually alter the color of the same pattern in a wide wavelength range, but also display different colors simultaneously. A perovskite photodetector with short channel length exhibits high responsivity.

Abstract

Ultrathin hybrid perovskites, with exotic properties and two-dimensional geometry, exhibit great potential in nanoscale optical and optoelectronic devices. However, it is still challenging for them to be compatible with high-resolution patterning technology toward miniaturization and integration applications, as they can be readily damaged by the organic solvents used in standard lithography processes. Here, a flexible three-step method is developed to make high-resolution multicolor patterning on hybrid perovskite, particularly achieved on a single nanosheet. The process includes first synthesis of precursor PbI₂, then e-beam lithography and final conversion to target perovskite. The patterns with linewidth around 150 nm can be achieved, which can be applied in miniature optoelectronic devices and high-resolution displays. As an example, the channel length of perovskite photodetectors can be down to 126 nm. Through deterministic vapor-phase anion exchange, a perovskite nanosheet can not only gradually alter the color of the same pattern in a wide wavelength range, but also display different colors simultaneously. The authors are optimistic that the method can be applied for unlimited perovskite types and device configurations for their high-integrated miniature applications.