Jing Zhang

This study introduces a novel Optical Tracking-based Magnetic Sensor (OTMS) for precisely measuring the magnetic moment of individual cells. By applying the OTMS, a distinct population of magnetic monocytes in humans is identified, whose percentage significantly differs between systemic lupus erythematosus (SLE) patients and healthy individuals. These findings suggest a potential correlation between magnetic monocytes with autoimmune diseases.

Abstract

Intrinsically magnetic cells naturally occur within organisms and are believed to be linked to iron metabolism and certain cellular functions while the functional significance of this magnetism is largely unexplored. To better understand this property, an approach named Optical Tracking-based Magnetic Sensor (OTMS) has been developed. This multi-target tracking system is designed to measure the magnetic moment of individual cells. The OTMS generates a tunable magnetic field and induces movement in magnetic cells that are subsequently analyzed through a learning-based tracking-by-detection system. The magnetic moment of numerous cells can be calculated simultaneously, thereby providing a quantitative tool to assess cellular magnetic properties within populations. Upon deploying the OTMS, a stable population of magnetic cells in human peripheral monocytes is discovered. Further application in the analysis of clinical blood samples reveals an intriguing pattern: the proportion of magnetic monocytes differs significantly between systemic lupus erythematosus (SLE) patients and healthy volunteers. This variation is positively correlated with disease activity, a trend not observed in patients with rheumatoid arthritis (RA). The study, therefore, presents a new frontier in the investigation of the magnetic characteristics of naturally occurring magnetic cells, opening the door to potential diagnostic and therapeutic applications that leverage cellular magnetism.

Photothermal Therapy

With wide spectral absorption and high photothermal conversion efficiency, the photothermal treatment based on 2D MXenes at NIR-II has significant advantages in biological tissue penetration depth and biocompatibility, which is a promising biomedical treatment. In article number 2305645, Yisen Wang and co-workers introduced the photothermal properties, conversion mechanism and influencing factors of 2D MXenes, and summarized the application status of photothermal treatment of 2D MXenes in NIR-II region.

The in-plane phonon thermal transport in PdSe₂ flakes with different thicknesses ranging from few nanometers to several tens of nanometers is characterized by the thermal bridge method, where the thermal conductivity increases from 5.04 W mk⁻¹ for 60 nm PdSe₂ to 34.51 W mk⁻¹ for the few-layer one. This work promotes the potential thermal management at nanoscale.

Abstract

Research on 2D materials originally focused on the highly symmetrical materials like graphene, h-BN. Recently, 2D materials with low-symmetry lattice such as PdSe₂ have drawn extensive attention, due to the interesting layer-dependent bandgap, promising mechanical properties and excellent thermoelectric performance, etc. In this work, the phonon thermal transport is studied in PdSe₂ with a pentagonal fold structure. The thermal conductivity of PdSe₂ flakes with different thicknesses ranging from few nanometers to several tens of nanometers is measured through the thermal bridge method, where the thermal conductivity increases from 5.04 W mk⁻¹ for 60 nm PdSe₂ to 34.51 W mk⁻¹ for the few-layer one. The atomistic modelings uncover that with the thickness thinning down, the lattice of PdSe₂ becomes contracted and the phonon group velocity is enhanced, leading to the abnormal increase in the thermal conductivity. And the upshift of the optical phonon modes contributes to the increase of the thermal conductivity as well by creating less acoustic phonon scattering as the thickness reduces. This study probes the interesting abnormal thickness-dependent thermal transport in 2D materials, which promotes the potential thermal management at nanoscale.

Light is a potential power source for small-scale robotic systems. This work presents a graphene-mica-based photo-thermal actuator for small-scale soft robots, allowing actuation at high speeds with large curvature changes. A comprehensive model for the design is presented and the fundamental properties of the actuator are described and compared to the state-of-the-art. Further, integration of the actuator into various applications is demonstrated.

Abstract

Small-scale soft robots demonstrate intricate life-like behavior and allow navigation through arduous terrains and confined spaces. However, the primary challenges in soft robotics are 1) creating actuators capable of quick, reversible 22D-to-3D shape morphing with adjustable stiffness, 2) improving actuation force and robustness for wider applications, and 3) designing holistic systems for untethered manipulation and flexible multimodality in practical scenarios. Here, mechanically compliant paper-like robots are presented with multiple functionalities. The robots are based on photothermally activated polymer bimorph actuators that incorporate graphene for the photo-thermal conversion of energy and muscovite mica, with its high Young's modulus, providing the required stiffness. Conversion of light into heat leads to thermal expansion and bending of the stress-mismatched structures. The actuators are designed on the basis of a modified Timoshenko model, and numerical simulations are employed to evaluate their actuation performance. The membranes can be utilized for light-driven programmable shape-morphing. Localized control allows the implementation of active hinges at arbitrary positions within the membrane. Integrated into small-scale soft robots in mass production, the membrane facilitates locomotion, rolling, and flipping of the robots. Further, grasping and kicking mechanisms are demonstrated, highlighting the potential of such actuators for future applications.

A smartphone-based detection system using a colorimetric reaction integrated with proximity-induced bio-barcode and the CRISPR/Cas12a assay is first developed for on-site, rapid, and accurate detection of f/t-PSA ratio. In tests with clinical samples, the method successfully diagnosed prostate cancer patients from benign prostatic hyperplasia patients and healthy cases with high sensitivity and specificity.

Abstract

The free-to-total prostate-specific antigen (f/t-PSA) ratio is of great significance in the accurate diagnosis of prostate cancer. Herein, a smartphone-based detection system is reported using a colorimetric reaction integrated with proximity-induced bio-barcode and the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a assay for f/t-PSA ratio detection. DNA/antibody recognition probes are designed to bind f-PSA or t-PSA and induce the release of the DNA bio-barcode. The CRISPR/Cas12a system is activated by the DNA bio-barcode to release Ag+ from the C-Ag+-C structure of the hairpin DNA. The released Ag+ is used to affect the tetramethylbenzidine (TMB)-H2O2-based colorimetric reaction catalyzed by Pt nanoparticles (NPs), as the peroxidase-like activity of the Pt NPs can be efficiently inhibited by Ag+. A smartphone with a self-developed app is used as an image reader and analyzer to analyze the colorimetric reaction and provide the results. A limit of detection of 0.06 and 0.04 ng mL⁻¹ is achieved for t-PSA and f-PSA, respectively. The smartphone-based method showed a linear response between 0.1 and 100 ng mL⁻¹ of t-PSA or f-PSA. In tests with clinical samples, the smartphone-based method successfully diagnosed prostate cancer patients from benign prostatic hyperplasia patients and healthy cases with high sensitivity and specificity.

Nature Photonics, Published online: 14 February 2024; doi:10.1038/s41566-024-01393-3

Researchers demonstrate a size-dependent lanthanide energy transfer effect in upconversion nanoparticles with depleted surface quenching, resulting in upconversion quantum yields of 13.0 ± 1.3%.

Nature Communications, Published online: 07 February 2024; doi:10.1038/s41467-024-45482-x

2D vertical transport transistors (VTFETs) may promote the downscaling of electronic devices, but their performance is usually restricted by the thermionic limit. Here, the authors report the realization of short-channel steep-slope VTFETs based on MoS2/MoTe2 heterojunctions integrated with resistance threshold switching cells.

Nature Communications, Published online: 12 February 2024; doi:10.1038/s41467-024-45623-2

The combination of strong light-matter interactions and controllable magnetic properties make magnetic semiconductors attractive for both fundamental physics and the development of devices. Here, Hendriks et al show how the optically driven magnetization dynamics in Cr2Ge2Te6 can be controlled via electrostatic gating.

Nature, Published online: 14 February 2024; doi:10.1038/d41586-024-00231-4

By combining materials-synthesis techniques, researchers have come up with a way of building layered structures that display intriguing wave-like patterns of electric polarization, and could be useful for next-generation electronics.

Nature, Published online: 14 February 2024; doi:10.1038/d41586-024-00190-w

Magnetic materials with zero net magnetization fall into two classes: conventional antiferromagnets and altermagnets. Physicists have identified a property in altermagnets that widens the divide between the two groups.

Nature, Published online: 14 February 2024; doi:10.1038/s41586-023-06978-6

The stacking of freestanding ferroelectric perovskite layers with controlled twist angles results in a peculiar pattern of polarization vortices and antivortices that emerges from the flexoelectric coupling of polarization to strain gradients.

Nature Electronics, Published online: 09 February 2024; doi:10.1038/s41928-024-01121-3

Large-area two-dimensional materials can be transferred at low temperatures and without solvents using conformable tapes whose adhesive force varies with ultraviolet illumination, allowing transfer to various planar and non-planar substrates.

Nature Electronics, Published online: 09 February 2024; doi:10.1038/s41928-024-01117-z

Tapes whose adhesive force is controlled by ultraviolet illumination can be used to cleanly transfer large-area graphene, molybdenum disulfide and other two-dimensional materials with a low thermal budget and using no organic solvents.

Analysis and summarization of energy migration, cross relaxation, and energy cycling processes are facilitated by modulating the concentration of energy transfer ions (Yb³⁺) in lanthanide nanoparticles. By exploiting thermal quenching and the enhancement of visible and near-infrared emissions under different excitations, fluorescence temperature sensing is achieved with deep penetration and high sensitivity within the biological temperature range.

Abstract

Fluorescent temperature sensing is considered as a research hotspot in the fields of life sciences and medicine. Despite the existence of numerous materials, the low sensitivity still limits their broader application. Herein, a core-shell-shell structure of lanthanide-doped nanoparticles is designed, which can adjust the energy transfer process by controlling the Yb³⁺ concentration in the energy migration layer, so as to generate different but regular visible upconversion and near-infrared downshifting emission modes depending on 808 or 980 nm excitation wavelengths. And the energy migration, cross relaxation, and energy cycling processes involved in energy migration ions are analyzed and summarized. Subsequently, unlike traditional thermal coupled fluorescence thermometers, the visible and near-infrared emission under different excitations is selected as the fluorescence intensity ratio by combining both thermal quenching and enhancement. Thus, a new type of fluorescence thermometer with deep penetration capability and high sensitivity within the biological temperature range is obtained, which can inspire a new design strategy for the future biosensing field.

Monolayerα-Tellurene

Monolayer α-tellurene, which has a 1T-MoS₂-like lattice structure, has been predicted to be a novel two-dimensional semiconductor. The article number 2309023 by Xiaochun Huang, Baisheng Sa, Roland Wiesendanger, and co-workers reports on a novel bottom-up approach, using three atom-long Te chains, derived from the dynamic non-equilibrium growth of an α -Si:Te alloy, as building blocks for the self-assembly of monolayer α-tellurene on a Sb₂Te₃ substrate.

2D materials hold great promise in strain engineering. By introducing out-of-plane deformations, localized and non-uniform strain can be induced, leading to novel phenomena and unique properties. This review systematically outlines the recent progress in the preparation, properties, and applications of locally strained 2D materials, aiming to broaden the scope of the 2D family for diverse applications.

Abstract

2D materials are promising for strain engineering due to their atomic thickness and exceptional mechanical properties. In particular, non-uniform and localized strain can be induced in 2D materials by generating out-of-plane deformations, resulting in novel phenomena and properties, as witnessed in recent years. Therefore, the locally strained 2D materials are of great value for both fundamental studies and practical applications. This review discusses techniques for introducing local strains to 2D materials, and their feasibility, advantages, and challenges. Then, the unique effects and properties that arise from local strain are explored. The representative applications based on locally strained 2D materials are illustrated, including memristor, single photon emitter, and photodetector. Finally, concluding remarks on the challenges and opportunities in the emerging field of locally strained 2D materials are provided.

Thermochromism, a solid's temperature-dependent change in color, is the fundamental basis of optical thermometry. Herein, it is demonstrated that InSeI, a 1D van der Waals solid, shows strong thermochromism and a pronounced temperature-dependent optical band edge absorption shift from 450 to 530 nm over a 380 K temperature range with an experimental (dE _g/dT)_max value of 1.26 × 10⁻³ eV K⁻¹.

Abstract

Thermochromism, the change in color of a material with temperature, is the fundamental basis of optical thermometry. A longstanding challenge in realizing sensitive optical thermometers for widespread use is identifying materials with pronounced thermometric optical performance in the visible range. Herein, it is demonstrated that single crystals of indium selenium iodide (InSeI), a 1D van der Waals (vdW) solid consisting of weakly bound helical chains, exhibit considerable visible range thermochromism. A strong temperature-dependent optical band edge absorption shift ranging from 450 to 530 nm (2.8 to 2.3 eV) over a 380 K temperature range with an experimental (dE _g/dT)_max value extracted to be 1.26 × 10⁻³ eV K⁻¹ is shown. This value lies appreciably above most dense conventional semiconductors in the visible range and is comparable to soft lattice solids. The authors further seek to understand the origin of this unusually sensitive thermochromic behavior and find that it arises from strong electron–phonon interactions and anharmonic phonons that significantly broaden band edges and lower the E _g with increasing temperature. The identification of structural signatures resulting in sensitive thermochromism in 1D vdW crystals opens avenues in discovering low-dimensional solids with strong temperature-dependent optical responses across broad spectral windows, dimensionalities, and size regimes.

Field-free topological (anti)meron chains with a topological charge of ±1/2 due to the noncollinear magnetic structure of Tb atoms are observed in centrosymmetric rare-earth magnet Tb₆Co_2.17Si_2.5. The topological magnetic texture is strongly correlated with the 4f electrons of rare-earth atoms, enriching and stimulating alternative generation mechanisms of topological spin textures from emerging rare-earth magnets, and further applications in spintronics.

Abstract

Exploration and manipulation of topological protected magnetic swirls, such as skyrmion, antiskyrmion, meron, and vortex, holds significance for fundamental research and practical applications in high-density magnetic information storage and spintronics because of their high storage density and low driven current. This study unveils the existence of field-free spontaneous (anti)meron chains with a topological charge of ±1/2 in the centrosymmetric rare-earth magnet Tb₆Co_2.17Si_2.5 via in situ real-space observation. The spin reorientation transition from in-plane to uniaxial anisotropy contributes to the spontaneous transformation from straight domain walls to topological (anti)meron chains and to stripe domains along the [110] zone axis during in situ cooling. The study further confirms the critical role of the noncollinear magnetic structure of Tb atoms in the formation of topological (anti)meron chains via real-space observations, first-principles calculations, and micromagnetic simulations. The spontaneous topological magnetic texture is strongly correlated with the 4f electrons of rare-earth atoms, enriching and stimulating alternative generation mechanisms of topological spin textures from emerging rare-earth magnets, and further applications in spintronics.

This article presents the design and characterization of a new 2D organic–inorganic hybrid perovskite ferroelectric, (6-BHA)₂CdBr₄ (6-BHA = 6-bromohexylamine), which crystallizes in point group C_c , possesses multiaxial ferroelectric properties, and exhibits a large spontaneous polarization of 3.26 µC cm⁻² in the thin film. A proof-of-concept device based on this material shows potential for next-generation in-memory computing, nanoelectronics, and ultra-high-density memories.

Abstract

2D ferroelectric materials with out-of-plane polarization are crucial for future nanoscale logic devices due to the increasing demand for energy-efficient architectures in artificial intelligence. However, only a few 2D out-of-plane ferroelectrics are confirmed experimentally. As an important branch of ferroelectrics, organic–inorganic hybrid perovskite ferroelectrics show flexible structures, making them eligible for constructing multifunctional materials. Here, a 2D organic–inorganic hybrid perovskite ferroelectric (6-BHA)₂CdBr₄ (6-BHA is 6-bromohexylamine) is designed, which crystallizes in polar point group C_c . It experiences the reversal phase transition at 317.8 K and possesses multiaxial ferroelectric properties. More interestingly, it exhibits a large spontaneous polarization value of 3.26 µC cm⁻² in out-of-plane direction of the film compared with typical 2D ferroelectrics. Moreover, an inverter based on (6-BHA)₂CdBr₄ is fabricated, which serves as a proof of concept for the feasibility for logic-in-memory devices. This work not only enriches the family of molecular ferroelectrics but also shows the potential to create the next generation of in-memory computing devices, nanoelectronics devices, and ultra-high-density memories.

A universal, energy efficient, environmental friendly, and ultrafast targeted thermal shock strategy is developed to realize the heteroatom doping of MXene within seconds. The MXene film can be selectively heated to a high-temperature followed with generating dazzling plasma. The high-temperature combined with plasma irradiation enables the rapid lattice/surface functional group substitutions between dopant atoms and MXene.

Abstract

Heteroatom doping can efficiently tailor the physicochemical properties of 2D MXene materials for enhancing the energy storage performance. However, in mostly applied doping strategies, the wet chemistry method typically suffers tedious separation and abstersion process while the solid-phase thermal strategy (traditional furnace heating) employed long-time （several hours） high-temperature treatment may cause degradation of MXene. In this work, a universal, energy efficient and environmental-friendly strategy is reported to realize the heteroatom doping of MXene within seconds by microwave-induced targeted thermal shock. The MXene film can self-heat to >800 °C within seconds followed by generating dazzling plasma under microwave field. The high temperature combined with plasma create a localized ultrahigh-energy environment in MXenes, which promotes the rapid decomposition of preloaded dopant precursors and lattice/surface functional group substitutions between dopant atoms and MXene. The resulted nitrogen (N) and sulfur (S) co-doped MXene showed significantly improved capacity and performance stability under deformations. Compared with the traditional furnace heating, the targeted heating strategy have significantly higher energy and time efficiencies and reduced carbon footprint. In addition, this method can be readily extended to various element doping of MXene. The microwave-induced targeted thermal-shock represents a general and efficient strategy for the fast heteroatom doping of MXene.

The bi-directional growth enables the simultaneous control of in-plane and out-of-plane orbital occupation. This paves the way for unprecedented thin films with an additional degree of freedom compared to thin films grown on conventional substrates, thereby enabling anisotropic transport properties such as ferromagnetism and superconductivity.

Abstract

The pursuit of breakthroughs in thin film technology drives the exploration of novel growth strategies for quantum materials that surpass conventional limitations. Departing from the prevailing unidirectional growth approach, the methodology allows for atomic precision in both the in-plane and out-of-plane directions. To demonstrate the capabilities of this transformative technique, a bi-directionally grown superlattice comprised of alternating LaMnO₃ and SrMnO₃ layers is engineered, enabling the emergence of interfacial ferromagnetism. By adopting this superlattice as a model system, the vast potential of the approach is highlighted through comprehensive analysis and characterization. Furthermore, the application of the method is extended to the growth of superconducting La_1.84Sr_0.16CuO₄ thin films on various offcut substrates. Remarkably, these substrates induce an anisotropic critical current originating from two distinct mechanisms.

Topotactic phase transitions can have strong impact on the magnetic and electronic properties of oxide thin films. Here, polarized neutron reflectivity is utilized to quantitatively extract oxygen content of La_0.6Sr_0.4CoO_3−δ perovskite thin films upon step-wise reduction into the brownmillerite phase. These findings reveal that electronic and magnetic transitions occur apart from the structural phase transition.

Abstract

Topotactic phase transitions induced by changes in the oxygen vacancy concentration can largely alter the physical properties of complex oxides, including electronic and magnetic phases, while maintaining the structural integrity of the crystal lattice. An oxygen-vacancy-induced topotactic phase transition from perovskite (PV) to brownmillerite (BM) is achieved in epitaxial La_0.6Sr_0.4CoO_3−δ (LSCO) thin films. Two novel intermediate states with different oxygen content are identified by X-ray diffraction, which involves a single-phase reduced PV state and a mixed state of co-existing PV and BM. The combination of depth-sensitive polarized neutron reflectometry (PNR) and Rutherford backscattering (RBS) allows a quantitative determination of magnetization and the mean oxygen content in all states, revealing a continuous transition from La_0.6Sr_0.4CoO_2.97 to La_0.6Sr_0.4CoO_2.5. BM formation is observed for an LSCO layer with an oxygen content of 2.67, while the magnetic and electronic transition already occurs for a layer with a higher oxygen content of 2.77 (and above) and in the absence of a BM signature. These results demonstrate that the physics of electronic metal-to-insulator transition (MIT), magnetic ferromagnet-to-non-ferromagnet transition (FM-to-non-FM), and structural PV-to-BM phase transition should be considered within the framework of separate but interrelated processes.

Epitaxial ferroelectric Hf_0.5Zr_0.5O₂ (HZO) film has been deposited using Atomic Layer Deposition onto single crystalline YSZ in low temperature (280 °C). Optical and structural characteristics of epitaxial HZO film has been performed by Second Harmonic Generation and Scanning Transmission Microscope. Additionally, epitaxial HZO film has been obtained on CMOS compatible YSZ buffered Si substrate, with distinct ferroelectric switching currents.

Abstract

The groundbreaking discovery of unconventional ferroelectricity in HfO₂ opens exciting prospects for next-generation memory devices. However, the practical implementation, particularly its epitaxial stabilization and a clearer understanding of its intrinsic ferroelectricity has been a significant challenge. The study arouses the potential importance of atomic layer deposition (ALD) for mass production in modern industries, demonstrating its proficiency in achieving epitaxial growth of ferroelectric Hf_0.5Zr_0.5O₂ (HZO) thin films on Yttria-stabilized zirconia (YSZ) substrates. Moreover, with distinct ferroelectric switching currents, the work reveals the ferroelectric characteristics of epitaxial HZO thin films deposited through ALD on YSZ-buffered Si substrates, which aligns well with CMOS technology. Overall, the results pave the way for a scalable synthesis system for ferroelectric HfO₂-based materials, hinting at a bright future for low-temperature epitaxial nanoelectronics.

Traditional ZnS: Mn²⁺ mechanoluminescent materials have been developed for realizing performance improvement and wavelength tunability. ZnS: Mn²⁺ sintered under a thermal carbon-reducing atmosphere exhibits tunable blue-to-red, cyan-to-red, and yellow-to-red emissions under photo-, thermal-, and mechano-stimulation, respectively, and has great potential for anti-counterfeiting and security applications. This study provides opportunities to discover the multiband emission of Mn²⁺ ion in other compounds.

Abstract

Self-recoverable mechanoluminescence (ML) is becoming a novel technology widely used in the fields of sensing, display, and artificial intelligence. The dominant ML material, ZnS: Mn²⁺, is reported to solely present a yellow emission color, which limits the applications of self-recoverable ML materials to a large extent. Herein, an effective strategy to extend the ML emission range of ZnS: Mn²⁺ by the ferromagnetic coupling of Mn²⁺ ions are reported. Under the thermal carbon-reduction atmosphere (TCRA), the emission ranges of ML, photoluminescence (PL), and persistent luminescence spectra of ZnS: Mn²⁺ phosphors are all successfully broadened from yellow to red. Furthermore, as for the PL and ML intensities of ZnS: Mn²⁺, they are intensified to 1.76 and 3.23 folds larger under the TCRA treatment than those in pure nitrogen, respectively. Various spectra and magnetic test results reveal that the red emission bands of ZnS: Mn²⁺ @TCRA phosphors originate from the ferromagnetic coupling of Mn²⁺ ions. This study is the first to realize strong red emission and tunable multicolor luminescence in the conventional ZnS-based phosphors, which introduces opportunities for discovering the multiband emissions of Mn²⁺ ion in other compounds. Brightly multicolored ZnS: xMn²⁺ @TCRA elastic films have been fabricated to demonstrate their anti-counterfeiting and security applications.

Ti₂AlN MAX phase thin-film in HfO₂ memristors enables ultra-low reset current-density, high on-off ratio, multi-level functionality, and strong endurance. The unique properties of Ti₂AlN MAX phase, such as low thermal, high electrical conductivity, and ultra-thin layered structure, contribute to these advancements, demonstrating its potential for energy-efficient devices for sustainable AI.

Abstract

A Ti₂AlN MAX phase layered thin film electrode and oxygen getter layer for HfO₂-based two-terminal memristors is presented. The Ti₂AlN/HfO_x/Ti memristor devices exhibit enhanced resistive switching performance, including an ultra-low reset current density (< 10⁻⁸ MΩ cm²), substantial on-off ratio (≈ 6000), excellent multi-level functionality (≈ 9 distinct states), impressive retention (up to 300 °C), and robust endurance (>200 million) as compared to conventional TiN and other alternative materials based memristors. Experimental measurements and modeling suggest that the distinctive combination of low thermal conductivity, high electrical conductivity, and unique ultra-thin layer-by-layer structure of the Ti₂AlN MAX phase thin film contribute to this exceptional performance with good reproducibility and stability. The results demonstrate for the first-time the potential of this innovative sputtered MAX phase material for engineering energy-efficient, high-density non-volatile digital, and analog memory devices aimed toward next-generation sustainable artificial intelligence.

This study reports a novel approach to eliminate the magnetic dead layer in atomically thin oxides, by using the epitaxial interface that reconciles both strong exchange interaction and large uniaxial magnetic anisotropy. A largely enhanced saturation magnetization (2 μ_B Mn⁻¹) and Curie temperature (80 K) are observed for the single manganite monolayer when interfacing with 5d oxides.

Abstract

Discoveries of ferromagnetic materials with ultrathin thickness are of great importance for both fundamental science and technological applications. Transition metal oxides (TMOs) provide promising candidates in the context of next-generation spintronics, despite the severe decay of ferromagnetism as the thickness reduces to the nanometer regime. Here, an efficient strategy to eliminate the magnetic dead layer in atomically thin oxides is presented, by using the epitaxial interface of 3d and 5d oxide monolayers that reconciles both strong exchange interaction and large uniaxial magnetic anisotropy. Combining multiple experimental methods, a ferromagnetic transition in an ultrathin oxide heterostructure comprised of only one La_0.2Sr_0.8MnO₃ monolayer sandwiched by SrIrO₃ monolayer (total thickness of three unit-cells) is unambiguously demonstrated. Remarkably, a largely enhanced saturation magnetization (2 µ_B Mn⁻¹) and Curie temperature (80 K) are observed for the single manganite monolayer, as compared to previously reported ferromagnetic monolayer oxides. The results demonstrate a general strategy for creating robust ferromagnetism in ultrathin TMOs, potentially enabling novel oxide spin-orbitronic devices.

Ferroic properties are predicted in vdW transition metal dioxydihalides, which lacks experimental validation so far. Here, the authors find that vdW perovskite-like materials WO₂I₂ possess robust ferroelasticity with low switching strain. The origin of ferroelasticity is the spontaneous shift of W atoms in [WO₄I₂] octahedra. In addition, the significant recombination and hindrance to photogenerated carriers at the domain wall are revealed.

Abstract

As a new group of van der Waals (vdWs) ferroic materials, transition metal dioxydihalides MO₂X₂ (M: Mo, W; X: halogen) with a perovskite-like structure are theoretically predicted to exhibit intriguing physics and versatile ferroic characteristics, which is not achieved experimentally as far as it is known. In this work, the robust ferroelasticity in vdWs WO₂I₂ with the switching strain as low as ≈0.3%, accompanied with the striped optical contrast between adjacent domains, spot splitting of selected area electron diffraction (SAED) patterns at domain wall, and 90° domain wall is demonstrated. With the aid of ab-initio calculations, the origin of ferroelasticity in WO₂I₂ is unveiled, where the imaginary phonon mode in the high-symmetry paraelastic phase leads to the spontaneous displacement of W atom away from the center of the [WO₄I₂] octahedron, resulting in the switchable spontaneous strain under an external strain field. Moreover, transient absorption microscopy (TAM) measurements demonstrate that the diffusion of photogenerated carriers is significantly hindered by the ferroelastic domain walls. This study provides deep insights into the ferroic order and domain wall in perovskite-like vdWs MO₂X₂ for new physics and functionalities.

Biodegradable NIR-II rare-earth nanoprobes enhance neural imaging by providing excellent photostability, high-contrast imaging, and programmable biodegradation time in vivo. These nanoprobes improve imaging depth and resolution in a mouse model of neural activity, aiding in understanding the structure and function of the nervous system. Their biodegradability ensures minimal long-term toxicity and enables repeated monitoring of damaged nerves during recovery or deterioration process.

Abstract

Neural imaging plays a crucial role in understanding the structure and function of the living body. While near-infrared-II (NIR-II) imaging techniques have emerged as potential tools for non-invasive and high-resolution imaging of neural activity, there have been rare relevant reports on in vivo neural imaging. This study presents the development of biodegradable NIR-II rare-earth nanoprobes as a novel contrast agent for enhanced neural imaging. The biodegradable NIR-II rare-earth nanoprobes exhibit excellent long wavelength emission, high quantum yield, and tunable biodegradation time in vivo. This work demonstrates the effectiveness of these nanoprobes in enhancing the imaging depth and resolution in a mouse model of neural activity, thereby facilitating a better understanding of the structure and function of the nervous system. Furthermore, their biodegradability ensures minimal long-term toxicity and allows for repeatedly monitoring of damaged nerves during the recovery or deterioration process. The results highlight the potential of biodegradable NIR-II rare-earth nanoprobes for advancing neural imaging techniques and facilitating deeper insights into neuroscience research and clinical diagnostics.

Nature Nanotechnology, Published online: 07 February 2024; doi:10.1038/s41565-024-01610-8

Challenges remain for 2D semiconductor growth