Jiuxiang Dai

Through a combined experimental and computational study, it is demonstrated that an ultrathin Mg capping layer effectively suppresses the oxidation of tantalum (Ta), a promising material for superconducting qubits. With Mg acting as an oxygen barrier and getter, the superconducting properties of the underlaying Ta thin films are improved, exhibiting sharper transition to the Meissner state at higher critical temperature.

Abstract

Scaling up superconducting quantum circuits based on transmon qubits necessitates substantial enhancements in qubit coherence time. Over recent years, tantalum (Ta) has emerged as a promising candidate for transmon qubits, surpassing conventional counterparts in terms of coherence time. However, amorphous surface Ta oxide layer may introduce dielectric loss, ultimately placing a limit on the coherence time. In this study, a novel approach for suppressing the formation of tantalum oxide using an ultrathin magnesium (Mg) capping layer is presented. Synchrotron-based X-ray photoelectron spectroscopy studies demonstrate that oxide is confined to an extremely thin region directly beneath the Mg/Ta interface. Additionally, it is demonstrated that the superconducting properties of thin Ta films are improved following the Mg capping, exhibiting sharper and higher-temperature transitions to superconductive and magnetically ordered states. Moreover, an atomic-scale mechanistic understanding of the role of the capping layer in protecting Ta from oxidation is established based on computational modeling. This work provides valuable insights into the formation mechanism and functionality of surface tantalum oxide, as well as a new materials design principle with the potential to reduce dielectric loss in superconducting quantum materials. Ultimately, the findings pave the way for the realization of large-scale, high-performance quantum computing systems.

Nearly atom-layered MoS₂ nanosheets (ALMS) is synthesized by a facile and scalable solvent-free mechanochemical approach employing graphene quantum dots as exfoliation agents. ALMS catalyst exhibits excellent electrochemical performance in the hydrogen evolution reaction and exceptional long-term durability. The impressive yield of ALMS reached 63%, indicating its potential for scalable production of stable nanosheets.

Abstract

The development of advanced and efficient synthetic methods is pivotal for the widespread application of 2D materials. In this study, a facile and scalable solvent-free mechanochemical approach is approached, employing graphene quantum dots (GQDs) as exfoliation agents, for the synthesis and functionalization of nearly atom-layered MoS₂ nanosheets (ALMS). The resulting ALMS exhibits an ultrathin average thickness of 4 nm and demonstrates high solvent stability. The impressive yield of ALMS reached 63%, indicating its potential for scalable production of stable nanosheets. Remarkably, the ALMS catalyst exhibits excellent HER performance. Moreover, the ALMS catalyst showcases exceptional long-term durability, maintaining stable performance for nearly 200 h, underscoring its potential as a highly efficient and durable electrocatalyst. Significantly, the catalytic properties of ALMS are significantly influenced by ball milling production conditions. The GQD-assisted large-scale machinery synthesis pathway provides a promising avenue for the development of efficient and high-performance ultrathin 2D materials.

Nature Reviews Methods Primers, Published online: 11 January 2024; doi:10.1038/s43586-023-00281-4

Nature Physics, Published online: 11 January 2024; doi:10.1038/s41567-023-02317-8

Nature Materials, Published online: 11 January 2024; doi:10.1038/s41563-023-01780-1

Nature Nanotechnology, Published online: 10 January 2024; doi:10.1038/s41565-023-01582-1

White-light illumination into α-In₂Se₃-based ferroelectric memories generates the enhanced downward built-in electric field (F_bi) within the α-In₂Se₃ channel due to the upward shift of α-In₂Se₃ Fermi level. This intensification of downward F_bi, causing preferential downward reorientation of α-In₂Se₃ ferroelectric domains, improved the linearity of long-term-depression characteristics. White-light-assisted artificial neural networks have significantly improved the recognition accuracy for hand-written digit numbers.

Abstract

α-In₂Se₃ semiconductor crystals realize artificial synapses by tuning in-plane and out-of-plane ferroelectricity with diverse avenues of electrical and optical pulses. While the electrically induced ferroelectricity of α-In₂Se₃ shows synaptic memory operation, the optically assisted synaptic plasticity in α-In₂Se₃ has also been preferred for polarization flipping enhancement. Here, the synaptic memory behavior of α-In₂Se₃ is demonstrated by applying electrical gate voltages under white light. As a result, the induced internal electric field is identified at a polarization flipped conductance channel in α-In₂Se₃/hexagonal boron nitride (hBN) heterostructure ferroelectric field effect transistors (FeFETs) under white light and discuss the contribution of this built-in electric field on synapse characterization. The biased dipoles in α-In₂Se₃ toward potentiation polarization direction by an enhanced internal built-in electric field under illumination of white light lead to improvement of linearity for long-term depression curves with proper electric spikes. Consequently, upon applying appropriate electric spikes to α-In₂Se₃/hBN FeFETs with illuminating white light, the recognition accuracy values significantly through the artificial learning simulation is elevated for discriminating hand-written digit number images.

A highly stretchable (534.5%), conductive (4.54 S m⁻¹), thermogalvanic (1.82 mV K⁻¹) hydrogel is fabricated, which remains conductive (3.86 S m⁻¹) at −20 °C and hardly shows degradation in thermoelectrical performance over 10 days. Besides, acting as a self-powered e-skin, the hydrogel is combined with deep learning technology for signature recognition and biometric authentication, achieving an accuracy of 92.97%.

Abstract

Self-powered electronic skins (e-skins), as on-skin human-machine interfaces, play a significant role in cyber security and personal electronics. However, current self-powered e-skins are primarily constrained by complex fabricating process, intrinsic stiffness, signal distortion under deformation, and inadequate comprehensive performance, thereby hindering their practical applications. Herein, a novel highly stretchable (534.5%), ionic conductive (4.54 S m⁻¹), thermogalvanic (1.82 mV K⁻¹) hydrogel (TGH) is facilely fabricated by a one-pot method. Owing to the formation of Li⁺(H₂O)_n hydration structure, the TGH presents excellent anti-freezing and non-drying performance. It remains flexible and conductive (3.86 S m⁻¹) at −20 °C and shows no obvious degradation in the thermoelectrical performance over 10 days. Besides, acting as a self-powered e-skin, the TGH combined with deep learning technology for signature recognition and biometric authentication is successfully demonstrated, achieving an accuracy of 92.97%. This work exhibits the TGH-based e-skin's tremendous potential in the new generation of human-computer interaction and information security.

Nature Communications, Published online: 13 January 2024; doi:10.1038/s41467-024-44792-4

The optoelectronic synapse based on a stoichiometry-controlled LaAlO₃/SrTiO₃ heterostructure is developed. By increasing La/Al ratio, the UV-light-induced persistent photoconductivity is enhanced, and the background conductivity is suppressed effectively. The spectral noise analyses reveal that the improvement is mainly attributed to charged point defects. The optoelectronic plasticity, paired-pulse facilitation, and the self-noise cancellation of La-rich LAO/STO heterostructures are successfully demonstrated.

Abstract

Emulating synaptic functionalities in optoelectronic devices is significant in developing artificial visual-perception systems and neuromorphic photonic computing. Persistent photoconductivity (PPC) in metal oxides provides a facile way to realize the optoelectronic synaptic devices, but the PPC performance is often limited due to the oxygen vacancy defects that release excess conduction electrons without external stimuli. Herein, a high-performance optoelectronic synapse based on the stoichiometry-controlled LaAlO₃/SrTiO₃ (LAO/STO) heterostructure is developed. By increasing La/Al ratio up to 1.057:1, the PPC is effectively enhanced but suppressed the background conductivity at the LAO/STO interface, achieving strong synaptic behaviors. The spectral noise analyses reveal that the synaptic behaviors are attributed to the cation-related point defects and their charge compensation mechanism near the LAO/STO interface. The short-term and long-term plasticity is demonstrated, including the paired-pulse facilitation, in the La-rich LAO/STO device upon exposure to UV light pulses. As proof of concepts, two essential synaptic functionalities, the pulse-number-dependent plasticity and the self-noise cancellation, are emulated using the 5 × 5 array of La-rich LAO/STO synapses. Beyond the typical oxygen deficiency control, the results show how harnessing the cation stoichiometry can be used to design oxide heterostructures for advanced optoelectronic synapses and neuromorphic applications.

This study rigorously examines the air-induced self-assembled native oxide skin on topological semimetal NbAs₂. Utilizing DFT and experimental analyses, the facile oxidation process and the consequent alterations in electronic properties, pivotal for NbAs2application in technologically relevant devices are revealed. Insights into the formation of protective oxide heterostructures provide a pathway for enhanced performance of quantum materials.

Abstract

NbAs₂, a topological semimetal, has stirred considerable interest for its potential usage in magnetic and fault-tolerant quantum computation superconductor devices, owing to its superconductivity, enormous magnetoresistance, and anisotropic magneto-transport attributes. Yet, its environmental stability, a crucial factor for practical applications, remains largely unexplored. Herein, a comprehensive examination of the stability and electronic properties of the (001) surface of NbAs₂ utilizing density functional theory (DFT) and surface science experiments is conducted. The theoretical deductions reveal that As atoms, organized in a buckled honeycomb configuration, terminate the bare (001) surface, akin to the tensile blue arsenene monolayer along the armchair direction. This study further demonstrates that the oxidation barrier is particularly low (only 0.2 eV), highlighting that the (001) surface is highly prone to oxidation under standard conditions, forming a As₂O₅+Nb₂O₅/NbAs₂ heterostructure. Additionally, it observes that oxidation adversely affects the electronic characteristics of the topological semimetal NbAs₂. The conclusions underscore the need for NbAs₂ to be managed under high vacuum conditions or to be encapsulated for any usage in the ambient atmosphere in order to retain its electronic properties for practical purposes.

Sodium alginate/carbon nanotubes/magnesium complexes (SA/CNTs/MC) composite aerogel is developed with high water uptake and rapid water vapor absorption/desorption kinetics. A fully solar-driven autonomous atmospheric water generator is designed and constructed with two SA/CNTs/MC-based absorption layers, which can alternately conduct the water absorption/desorption process without any other energy consumption.

Abstract

Sorption-based atmospheric water harvesting (SAWH) offers a sustainable strategy to address the global freshwater shortage. However, obtaining sorbents with excellent performance over a wide relative humidity (RH) range and devices with fully autonomous water production remains challenging. Herein, magnesium chloride (MgCl₂) is innovatively converted into super hygroscopic magnesium complexes(MC), which can effectively solve the problems of salt deliquescence and agglomeration. The MC are then integrated with photothermal aerogels composed of sodium alginate and carbon nanotubes (SA/CNTs) to form composite aerogels, which showed high water uptake over a wide RH range, reaching 5.43 and 0.27 kg kg⁻¹ at 95% and 20% RH, respectively. The hierarchical porous structure enables the as-prepared SA/CNTs/MC to exhibit rapid absorption/desorption kinetics with 12 cycles per day at 70% RH, equivalent to a water yield of 10.0 L kg⁻¹ day⁻¹. To further realize continuous and practical freshwater production, a fully solar-driven autonomous atmospheric water generator is designed and constructed with two SA/CNTs/MC-based absorption layers, which can alternately conduct the water absorption/desorption process without any other energy consumption. The design provides a promising approach to achieving autonomous, high-performance, and scalable SAWH.

Nature Photonics, Published online: 15 January 2024; doi:10.1038/s41566-023-01364-0

Nature Nanotechnology, Published online: 15 January 2024; doi:10.1038/s41565-023-01593-y

Light: Science & Applications, Published online: 16 January 2024; doi:10.1038/s41377-023-01365-2

A Tb³⁺ ion doped glass-ceramic (GC) obtained by the traditional melt-quenching method, is employed as the converter to combine with a silicon photo-resistor for the development of a solar-blind UV detector. Due to the efficient conversion of broadband solar-blind UV light (188–400 nm) into visible light by the GC, the device exhibits meaningful photovoltage response at a low bias voltage. The research results of this work are of great significance for the development of efficient broadband solar-blind UV detectors at a low cost.

Abstract

Oxyfluoride transparent glass-ceramics (GC) are widely used as the matrix for rare-earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb³⁺ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb³⁺ doped oxyfluoride GC is developed by using the melt-quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si-based photo-resistor,a solar-blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar-blind UV detectors.

Nature Physics, Published online: 16 January 2024; doi:10.1038/s41567-023-02381-0

Nature Physics, Published online: 16 January 2024; doi:10.1038/s41567-023-02327-6