Jiuxiang Dai

A Cl vacancy strategy results in a lower Fe oxidation state with sharp d-states characteristics to enhance the adsorption and activation of NO, which overcomes the sluggish kinetics of NORR and competitive HER over FeOCl-V_Cl, especially at low concentrations of NO, and improves the catalytic activity and selectivity towards NORR.

Abstract

Electroreduction of nitric oxide (NO) to NH₃ (NORR) has gained extensive attention for the sake of low carbon emission and air pollutant treatment. Unfortunately, NORR is greatly hindered by its sluggish kinetics, especially under low concentrations of NO. Herein, we developed a chlorine (Cl) vacancy strategy to overcome this limitation over FeOCl nanosheets (FeOCl-V_Cl). Density functional theory (DFT) calculations revealed that the Cl vacancy resulted in defective Fe with sharp d-states characteristics in FeOCl-V_Cl to enhance the absorption and activation of NO. In situ X-ray absorption near-edge structure (XANES) and attenuated total reflection-infrared spectroscopy (ATR-IR) verified the lower average oxidation state of defective Fe to enhance the electron transfer for NO adsorption/activation and facilitate the generation of key NHO and NH_x intermediates. As a result, the FeOCl-V_Cl exhibited superior NORR activities with the NH₃ Faradaic efficiency up to 91.1 % while maintaining a high NH₃ yield rate of 455.4 μg cm⁻² h⁻¹ under 1.0 vol % NO concentration, competitive with those of previously reported literatures under higher NO concentration. Further, the assembled Zn-NO battery utilizing FeOCl-V_Cl as cathode delivered a record peak power density of 6.2 mW cm⁻², offering a new route for simultaneous NO removal, NH₃ production, and energy supply.

Nature, Published online: 20 December 2023; doi:10.1038/s41586-023-06791-1

Nature, Published online: 20 December 2023; doi:10.1038/d41586-023-03791-z

Author(s): Liyang Ma, Jing Wu, Tianyuan Zhu, Yiwei Huang, Qiyang Lu, and Shi Liu

Ferroelectrics and ionic conductors are important functional materials, each supporting a plethora of applications in information and energy technology. The underlying physics governing their functional properties is ionic motion, and yet studies of ferroelectrics and ionic conductors are often cons…

[Phys. Rev. Lett. 131, 256801] Published Wed Dec 20, 2023

Nature Materials, Published online: 20 December 2023; doi:10.1038/s41563-023-01762-3

A novel method is presented, based on the proximity effect in combination with scanning tunnelling microscopy manipulation, which enables to introduce superconductivity at will in any graphene region. This represents a crucial breakthrough, both to shed light in the fundamental understanding of superconductivity in graphene-based systems, and also to build functional superconducting-graphene hybrid structures.

Abstract

Graphene holds great potential for superconductivity due to its pure 2D nature, the ability to tune its carrier density through electrostatic gating, and its unique, relativistic-like electronic properties. At present, still far from controlling and understanding graphene superconductivity, mainly because the selective introduction of superconducting properties to graphene is experimentally very challenging. Here, a method is developed that enables shaping at will graphene superconductivity through a precise control of graphene-superconductor junctions. The method combines the proximity effect with scanning tunnelling microscope (STM) manipulation capabilities. Pb nano-islands are first grown that locally induce superconductivity in graphene. Using a STM, Pb nano-islands can be selectively displaced, over different types of graphene surfaces, with nanometre scale precision, in any direction, over distances of hundreds of nanometres. This opens an exciting playground where a large number of predefined graphene-superconductor hybrid structures can be investigated with atomic scale precision. To illustrate the potential, a series of experiments are performed, rationalized by the quasi-classical theory of superconductivity, going from the fundamental understanding of superconductor-graphene-superconductor heterostructures to the construction of superconductor nanocorrals, further used as “portable” experimental probes of local magnetic moments in graphene.

The unique microstructure of the ferrocene-derived multilayer graphene film is responsible for its physicochemical properties, allowing for the transformation of graphene from a non-magnetic to a magnetic metal at room temperature. The synthesized material exhibits defect-induced Fermi level pinning at the Dirac point, resulting in the suppression of ambipolar behavior in graphene.

Abstract

Spin polarization is a very important condition for spintronics applications which can easily be achieved by using ferromagnetic materials. Graphene-based magnetic materials, which have long spin lifetime and diffusion length, are very promising as spin channel materials. In this work, Ferrocene molecules are chosen as the precursor carbon source using the chemical vapor deposition method, facilitating the synthesis of multilayer graphene films decorated with magnetic nanoclusters. This resultant material manifested planar ferromagnetism with a Curie temperature exceeding room temperature (≥300 K) and a saturation magnetization as high as 4.1 × 10⁻⁷ emu mm⁻². The robust ferromagnetic coupling can plausibly be attributed to the presence of magnetic nanoclusters interspersed within the synthesized graphene, enhancing the localized magnetic moment and promoting ferromagnetic long-range ordering. Furthermore, the Fermi level pinning at the Dirac point is observed and predominantly ascribed to the pervasive defects in the graphene derived from ferrocene. The oxygen functional groups within these defects act as charge traps, effectively anchoring the Fermi level to the Dirac point, intrinsically suppressing the ambipolar behavior of graphene. This work sheds light on potential avenues for the exploration of novel, high-performance carbonaceous spintronics materials with economic feasibility.

This study introduces a method for creating titanium dioxide (TiO₂) films with varied structures using continuous-wave laser-processing. Controlling the laser-processing conditions transforms an a-TiS₂ thin-film precursor into different TiO₂ phases, identified using optical spectroscopy techniques. The synthesized films' photocatalytic activities, influenced by phase combinations and ambient humidity, are evaluated, demonstrating the potential of the technique for studying structure-property relationships.

Abstract

Local laser-induced oxidation is an extremely valuable technique to perform high-throughput optimization across multidimensional parameter sets. In this work, a versatile method is presented for the synthesis of titanium dioxide (TiO₂) thin-films with varying crystalline structures through the use of localized, visible, continuous-wave laser-processing. By controlling the laser intensity and the exposure time, the conversion of amorphous titanium disulfide (a-TiS₂) precursor films into distinct phases of TiO₂ is achieved and a laser-induced oxidation phase diagram is constructed with the resulting material phases, including anatase, rutile, and black TiO₂. By utilizing the dependence of phase formation on the rate and duration of laser energy input, mixtures of anatase and rutile phases are fabricated with controlled spatial arrangements. Photocatalytic properties of the synthesized films are evaluated using the degradation of nitrogen oxide (NO_x) gas under UV illumination and an organic dye under white-light illumination, revealing that mixtures of anatase and rutile phases demonstrate superior photocatalytic activity. The laser-induced oxidation method highlighted showcases a strategy for precisely tailored phase composition for directly tunable properties, paving the way for in-depth studies into structure-property relationships in photocatalysis and other applications of metal oxide films.

The electrochemistry is performed at the 1D edge of graphene in hBN/graphene/hBN van der Waals heterostructures. The edge forms an electrochemical nanoelectrode, enabling the investigation of electron transfer using redox probes, e.g., ferrocene(di)methanol, hexaammineruthenium, methylene blue, dopamine and ferrocyanide, down to micromolar concentrations. The edge nanoelectrode facilitates cyclic voltammetry at scan rates ≤ 1000 V s⁻¹ and in water without added electrolyte.

Abstract

Artificial van der Waals heterostructures, obtained by stacking two-dimensional (2D) materials, represent a novel platform for investigating physicochemical phenomena and applications. Here, the electrochemistry at the one-dimensional (1D) edge of a graphene sheet, sandwiched between two hexagonal boron nitride (hBN) flakes, is reported. When such an hBN/graphene/hBN heterostructure is immersed in a solution, the basal plane of graphene is encapsulated by hBN, and the graphene edge is exclusively available in the solution. This forms an electrochemical nanoelectrode, enabling the investigation of electron transfer using several redox probes, e.g., ferrocene(di)methanol, hexaammineruthenium, methylene blue, dopamine and ferrocyanide. The low capacitance of the van der Waals edge electrode facilitates cyclic voltammetry at very high scan rates (up to 1000 V s⁻¹), allowing voltammetric detection of redox species down to micromolar concentrations with sub-second time resolution. The nanoband nature of the edge electrode allows operation in water without added electrolyte. Finally, two adjacent edge electrodes are realized in a redox-cycling format. All the above-mentioned phenomena can be investigated at the edge, demonstrating that nanoscale electrochemistry is a new application avenue for van der Waals heterostructures. Such an edge electrode will be useful for studying electron transfer mechanisms and the detection of analyte species in ultralow sample volumes.

Highlights

• Presenting the first investigation into the structurally bubbling-failure mechanism of graphitic film during cyclic liquid nitrogen shocks.

• Proposing an innovative design about seamless heterointerface constructing a Cu-modified structure.

• Inventing a new ultra-stable species of highly thermally conductive films to inspire new techniques for efficient and extreme thermal management.

Nature Electronics, Published online: 19 December 2023; doi:10.1038/s41928-023-01095-8

A ferroelectric Rashba semiconductor owns a definite Rashba spin-texture that can be manipulated and reversed by an applied electric field. Such a material is highly sought-after for spintronic transistors and/or memories. This work presents an original demonstration of a new ferroelectric Rashba semiconductor, by confronting its measured structural ferroelectric distortion to its observed Rashba electronic properties.

Abstract

Fast, reversible, and low-power manipulation of the spin texture is crucial for next generation spintronic devices like non-volatile bipolar memories, switchable spin current injectors or spin field effect transistors. Ferroelectric Rashba semiconductors (FERSC) are the ideal class of materials for the realization of such devices. Their ferroelectric character enables an electronic control of the Rashba-type spin texture by means of the reversible and switchable polarization. Yet, only very few materials are established to belong to this class of multifunctional materials. Here, Pb_{1− x} Ge _x Te is unraveled as a novel FERSC system down to nanoscale. The ferroelectric phase transition and concomitant lattice distortion are demonstrated by temperature dependent X-ray diffraction, and their effect on electronic properties are measured by angle-resolved photoemission spectroscopy. In few nanometer-thick epitaxial heterostructures, a large Rashba spin-splitting is exhibiting a wide tuning range as a function of temperature and Ge content. This work defines Pb_{1− x} Ge _x Te as a high-potential FERSC system for spintronic applications.

Uniform, metal-catalyst-free graphene grown directly on dielectric substrate enables the creation of biosensor chips with high yields and cutting-edge performances (328 of 384 devices on a 4-inch wafer).

Abstract

To fabricate label-free and rapid-resulting semiconducting biosensor devices incorporating graphene, it is pertinent to directly grow uniform graphene films on technologically important dielectric and semiconducting substrates. However, it has long been intuitively believed that the nonideal disordered structures formed during direct growth, and the resulted inferior electrical properties will inevitably lead to deteriorated sensing performance. Here, graphene biosensor chips are constructed based on direct plasma-enhanced chemical vapor deposition (PECVD) grown graphene on a 4-inch silicon wafer with excellent film uniformity and high yield. To surprise, optimal operations of graphene biosensors permit ultrasensitive detection of SARS-CoV-2 virus nucleocapsid protein with dilutions down to sub-femtomolar concentrations. Such impressive limit of detection (LOD) is comparable to or even outperforms that of the state-of-the-art biosensor devices based on high-quality graphene. Further noise spectral characterizations and analysis confirms that the LOD is limited by molecular diffusion and/or known interference signals such as drift and instability of the sensors, rather than the electrical merits of the graphene devices along. Hence, result sheds light on processing directly grown PECVD graphene into high-performance sensor devices with important economic benefits and social significance.

This study presents a rational approach for synthesizing MoS₂-derived 2D quaternary semiconductors using structurally unstable (NH₄)₂MoS₄ host films. By co-doping oxygen with rhenium, structural instability, compensating for MoS₂ lattice inconsistencies, and enabling rhenium substitution despite lattice mismatch are enhanced. This approach enables the large-scale synthesis of a 2D quaternary semiconductor with broad optical adsorption, suitable for nanophotonic devices.

Abstract

Although the structural and electrical engineering of transition metal dichalcogenides using atomic doping or doping-induced phase modulation can be used to attain high-performance and wavelength-tunable optoelectronic devices, accessible substitutional doping to overcome the large lattice mismatch between the host and guest atom-related bonding states remains elusive. This study corroborates an innovative synthetic route for molybdenum disulfide (MoS₂)-derived two-dimensional (2D) quaternary semiconductors substitutionally doped with Re and O using a solution-based large-area compatible approach combined with the thermal evaporation of dopants. The substitutional doping of Re into MoS₂ crystals with a large lattice mismatch is effectively accomplished by adopting structurally unstable host films, resulting in the large-scale synthesis of 2D quaternary multi-layers with a Re doping concentration >10%. Comprehensive spectroscopic and microscopic evaluations are performed to determine the efficacy of the host films with structural instability for the synthesis of 2D Re_xMo_(1-x)O_2yS_2(1-y) quaternary multi-layers. The capability of the quaternary semiconductor for versatile nanophotonic devices is validated by ascertaining the simultaneous enhancement of the photoelectrical properties with wide-range optical absorption and photoelectrochemical properties, as compared with those of their binary counterparts.

A chemical-scissor intercalation protocol medicated by molten salt is proposed for functional intercalation of layered NbS₂. The intercalated superlattice exhibits improved dielectric properties due to the heteroatoms and the reduced Brillouin zone size. This work sheds light on the editing of van der Waals materials, whilst intercalation via the molten salt strategy is considered a feasible intercalation strategy to further enrich their applications.

Abstract

Intercalation of layered materials offers an effective approach for tunning their structures and generating unprecedented properties. The multiple van der Waals (vdW) gap combined with long-range ordering guests can change the interaction of layered host materials and electromagnetic field. Herein, a chemical-scissor intercalation protocol medicated by molten salt is proposed for tailing the electromagnetic properties of transitional metal dichalcogenides (TMDCs). NbS₂ is functional intercalated by heteroatoms (Fe, Co, Ni). The intercalated NbS₂ with superlattice exhibit improved dielectric properties due to the reduced Brillouin zone size and the local electron distribution. Both the computational and experimental investigations indicate enhanced electron transport and additional polarized centers caused by intercalation. Overall, this work shows the great potential of structure editing of vdW materials, whilst intercalation via the chemical scissor in molten salts is considered a feasible intercalation strategy to further enrich their applications.

Nature Nanotechnology, Published online: 18 December 2023; doi:10.1038/s41565-023-01559-0