Jiuxiang Dai

In conventional switching heterostructures based on spin-orbit torque (SOT), a spin source material with strong spin-orbit coupling or broken inversion symmetry is typically required to generate SOT when a charge current is applied. In this study, we achieved current-induced self-switching of magnetization at room temperature using a layered polar magnetic metal, Fe_2.5Co_2.5GeTe₂, thereby greatly simplifying the structure for magnetization switching.

Abstract

2D layered materials with broken inversion symmetry are being extensively pursued as  spin source layers to realize high-efficiency magnetic switching. Such low-symmetry layered systems are, however, scarce. In addition, most layered magnets with perpendicular magnetic anisotropy show a low Curie temperature. Here, the experimental observation of spin–orbit torque magnetization self-switching at room temperature in a layered polar ferromagnetic metal, Fe_2.5Co_2.5GeTe₂ is reported. The spin–orbit torque is generated from the broken inversion symmetry along the c-axis of the crystal. These results provide a direct pathway toward applicable 2D spintronic devices.

Nature Materials, Published online: 28 November 2023; doi:10.1038/s41563-023-01692-0

Nature Materials, Published online: 28 November 2023; doi:10.1038/s41563-023-01730-x

Submicron-thick (≈0.4 µm) zincophilic CrN coatings on Zn substrate are fabricated by a facile and industry-compatible magnetron sputtering approach. The prepared Zn@CrN anode exhibits high performance and prolonged lifespan due to CrN coatings can effectively suppress the formation of Zn dendrites and the occurrence of side reactions.

Abstract

For exploring advanced Zn-ion batteries (ZIBs) with long lifespan and high Coulombic efficiency (CE), the critically important point is to limit the undesired Zn dendrite and parasitic reactions. Among the coating for electrode is a promising strategy, relying on the trade-off between its thickness and stability to achieve the ultra-stable Zn anodes in ZIBs. Herein, a submicron-thick (≈0.4 µm) zincophilic CrN coatings are fabricated by a facile and industry-compatible magnetron sputtering approach. It is exhilarating that the ultrathin and dense CrN coatings with strong adsorption ability for Zn²⁺ exhibit an impressive lifespan up to 3700 h with ≈100% CE at 1 mA cm⁻². Along with the experiments and theoretical calculations, it is verified that the introduced CrN coatings cannot only effectively suppress the dendrite growth and notorious parasitic reactions, but also allow the uniform Zn deposition due to the reduced nucleation energy. Moreover, the as-assembled Zn@CrN‖MnO₂ full cell delivers a high specific capacity of 171.1 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹, much better than that of Zn‖MnO₂ analog (97.8 mAh g⁻¹). This work provides a facile strategy for scalable fabrication of ultrathin zincophilic coating to push forward the practical applications of ZIBs.

Ultrathin 2D non-van der Waals γ-Ga₂O₃ with room temperature ferromagnetism is successfully obtained by using supercritical CO₂ (SC CO₂), which selectively modulates the orientation and strength of covalent bonds in γ-Ga₂O₃, leading to the change of atomic structure and magnetic property.

Abstract

Spintronic devices work by manipulating the spin of electrons other than charge transfer, which is of revolutionary significance and can largely reduce energy consumption in the future. Herein, ultrathin two-dimensional (2D) non-van der Waals (non-vdW) γ-Ga₂O₃ with room temperature ferromagnetism is successfully obtained by using supercritical CO₂ (SC CO₂). The stress effect of SC CO₂ under different pressures selectively modulates the orientation and strength of covalent bonds, leading to the change of atomic structure including lattice expansion, introduction of O vacancy, and transition of Ga-O coordination (GaO₄ and GaO₆). Magnetic measurements show that pristine γ-Ga₂O₃ is nonferromagnetic, whereas the SC CO₂ treated γ-Ga₂O₃ exhibits obvious ferromagnetic behavior with an optimal magnetization of 0.025 emu g⁻¹ and a Curie temperature of 300 K.

Publication date: January–February 2024

Source: Materials Today, Volume 72

Author(s): Ehsan Elahi, Muhammad Asghar Khan, Muhammad Suleman, A. Dahshan, Shania Rehman, H.M. Waseem Khalil, Malik Abdul Rehman, Ahmed M Hassan, Ganesh Koyyada, Jae Hong Kim, Muhammad Farooq Khan

Nature, Published online: 29 November 2023; doi:10.1038/s41586-023-06734-w

A novel multi-functional neuromorphic visual system with optoelectronic synergy based on SnS₂/BN/CuInP₂S₆ full van der Waals ferroelectric field-effect transistor is reported. The device demonstrates a high switching ratio of 10⁵, multilevel storage states of 128 (7 bits), excellent synaptic plasticity, and an image recognition accuracy of 93.62% based on reservoir computing.

Abstract

The development and application of artificial intelligence have led to the exploitation of low-power and compact intelligent information-processing systems integrated with sensing, memory, and neuromorphic computing functions. The 2D van der Waals (vdW) materials with abundant reservoirs for arbitrary stacking based on functions and enabling continued device downscaling offer an attractive alternative for continuously promoting artificial intelligence. In this study, full 2D SnS₂/h-BN/CuInP₂S₆ (CIPS)-based ferroelectric field-effect transistors (Fe-FETs) and utilized light-induced ferroelectric polarization reversal to achieve excellent memory properties and multi-functional sensing-memory-computing vision simulations are designed. The device exhibits a high on/off current ratio of over 10⁵, long retention time (>10⁴ s), stable cyclic endurance (>350 cycles), and 128 multilevel current states (7-bit). In addition, fundamental synaptic plasticity characteristics are emulated including paired-pulse facilitation (PPF), short-term plasticity (STP), long-term plasticity (LTP), long-term potentiation, and long-term depression. A ferroelectric optoelectronic reservoir computing system for the Modified National Institute of Standards and Technology (MNIST) handwritten digital recognition achieved a high accuracy of 93.62%. Furthermore, retina-like light adaptation and Pavlovian conditioning are successfully mimicked. These results provide a strategy for developing a multilevel memory and novel neuromorphic vision systems with integrated sensing-memory-processing.

The contributions of tailoring structure-dominated SPPs to SERS effects can be maximized by achieving highly efficient generation, lossless propagation, highly effective focusing, and perfectly coherent interferences of SPPs through careful quantitative design by combining 0D, 1D, 2D, and 3D plasmonic/dielectric nanostructures to enable stronger coupling with LSPR at the hot spots for remarkable SERS performance improvement.

Abstract

Localized surface plasmon resonance (LSPR) excited by an incident light can normally produce strong surface-enhanced Raman scattering (SERS) at the nanogaps among plasmonic nano-objects (so-called hot spots), which is extensively explored. In contrast, surface plasmon polaritons (SPPs) that can be generated by an incident beam via particular structures with a conservation of wave vectors can excite SERS effects as well. SPPs actually play an indispensable role in high-performance SERS devices but receive much less attention. In this perspective, SPPs and their couplings with LSPR for SERS excitations with differing effectiveness through particular plasmonic/dielectric structures/configurations, along with relevant fabrication approaches, are profoundly reviewed and commented on from a unique perspective from in situ to ex situ excitations of SERS enabled by spatiotemporally separated multiple processes of SPPs. Quantitative design of particular configurations/architectures enabling highly efficient and effective multiple processes of SPPs is particularly emphasized as one giant leap toward ultimate full quantitative design of intrinsically high-performance SERS chips and very critical for their batch manufacturability and applications as well. The viewpoints and prospects about innovative SERS devices based on tailored structure-dominated SPPs effects and their coupling with LSPR are presented and discussed.

Nature Electronics, Published online: 30 November 2023; doi:10.1038/s41928-023-01073-0

Nature Chemistry, Published online: 30 November 2023; doi:10.1038/s41557-023-01364-1

Nature Nanotechnology, Published online: 30 November 2023; doi:10.1038/s41565-023-01539-4

Nature Photonics, Published online: 30 November 2023; doi:10.1038/s41566-023-01342-6

Nature Photonics, Published online: 30 November 2023; doi:10.1038/s41566-023-01336-4

Modulated nanoindentation, or MoNI, is an atomic-force-microscopy-based nano-indentation technique for measuring the mechanical properties of 2D materials with angstrom and nN resolution. This technique is demonstrated on the measurement of the transverse Young's modulus and mechanical response of 2D graphene thin films with varying number of atomic layers.

Abstract

As the field of low-dimensional materials (1D or 2D) grows and more complex and intriguing structures are continuing to be found, there is an emerging need for techniques to characterize the nanoscale mechanical properties of all kinds of 1D/2D materials, in particular in their most practical state: sitting on an underlying substrate. While traditional nanoindentation techniques cannot accurately determine the transverse Young's modulus at the necessary scale without large indentations depths and effects to and from the substrate, herein an atomic-force-microscopy-based modulated nanomechanical measurement technique with Angstrom-level resolution (MoNI/ÅI) is presented. This technique enables non-destructive measurements of the out-of-plane elasticity of ultra-thin materials with resolution sufficient to eliminate any contributions from the substrate. This method is used to elucidate the multi-layer stiffness dependence of graphene deposited via chemical vapor deposition and discover a peak transverse modulus in two-layer graphene. While MoNI/ÅI has been used toward great findings in the recent past, here all aspects of the implementation of the technique as well as the unique challenges in performing measurements at such small resolutions are encompassed.

A new approach is developed to extract depth-resolved concentration profiles from single fixed-angle X-ray photoelectron spectra. By analyzing multiple core-level peaks in the spectrum, an energy-resolved measurement can be emulated without the need for a synchrotron. The method is demonstrated using native oxide layers on Ta, Pd, and Ti thin film samples.

Abstract

Many metals form nanometer-thin self-passivating oxide layers upon exposure to the atmosphere, which affects a wide range of interfacial properties and shapes the way how metals interact with their environment. Such native oxide layers are commonly analyzed by X-ray photoelectron spectroscopy (XPS), which provides a depth-resolved chemical state and compositional analysis either by ion etching or modeling of the electron escape depths. The latter is commonly used to calculate the average thickness of a native oxide layer. However, the measurement of concentration profiles at the oxide-metal interface remains challenging. Here, a simple and accessible approach for the depth profiling of ultrathin oxide layers within single fixed-angle XPS spectra is proposed. Instead of using only one peak in the spectrum, as is usually the case, all peaks within the energy range of a standard lab device are utilized, thus resembling energy-resolved XPS without the need for a synchrotron. New models that allow the calculation of depth-resolved concentration profiles at the oxide-metal interface are derived and tested, which are also valid for angular- and energy-resolved XPS. The proposed method not only improves the accuracy of earlier approaches but also paves the way for a more holistic understanding of the XPS spectrum.

Nature Materials, Published online: 27 November 2023; doi:10.1038/s41563-023-01704-z