Nature nanotechnology最新文献

Skyrmions can form regular arrangements, so-called skyrmion crystals (SkXs). A mode with multiple wavevectors q then describes the arrangement. While magnetic SkXs, which can emerge in the presence of Dzyaloshinskii–Moriya interaction, are well established, polar skyrmion lattices are still elusive. Here we report the observation of polar SkXs with a well-defined double-q state in ultrathin BiFeO₃ films on LaAlO₃. The compressive strain induced by the LaAlO₃ substrate yields a dipolar topological texture with a periodic arrangement of skyrmions. The square-like superstructure with a lattice constant of 2.68 nm features a periodic modulation of polarization fields and topological charge density. The film furthermore exhibits an enhanced electromechanical response with an increased converse piezoelectric coefficient (d₃₃) compared with SkX-free films. Transmission electron microscopy experiments in combination with phase-field simulations indicate that the dipole skyrmion texture results from the interference of two orthogonal single-q dipole patterns. We anticipate that the interference of multiple wavevectors may lead to a diversity of topological crystals with a variety of symmetries and lattice constants.

Lipid nanoparticles (LNPs) for nucleic acid delivery often use novel lipids as functional excipients to modulate the biodistribution, pharmacokinetics, pharmacodynamics and efficacy of the nucleic acid. Novel excipients used in pharmaceutical products are subject to heightened regulatory scrutiny and often require data packages comparable to an active pharmaceutical ingredient. Although these regulatory requirements may help to ensure patient safety they also create economic and procedural barriers that can disincentivize innovation and delay clinical investigation. Despite the unique structural and functional role of lipid excipients in LNPs, there is limited specific global regulatory guidance, which adds uncertainty and risk to the development of LNPs. In this Perspective we provide an industry view on the chemistry, manufacturing and controls challenges that pharmaceutical companies face in the use of novel lipid excipients at each stage of development, and propose consensus recommendations on how to streamline and clarify development and regulatory expectations.

Van der Waals (vdW) semiconductors have emerged as promising platforms for efficient nonlinear optical conversion, including harmonic and entangled photon generation. Although major efforts are devoted to integrating vdW materials in nanoscale waveguides for miniaturization, the realization of efficient, phase-matched conversion in these platforms remains challenging. Here, to address this challenge, we report a far-field ultrafast imaging method to track the propagation of both fundamental and harmonic waves within vdW waveguides with femtosecond and sub-50 nanometre spatiotemporal precision. We focus on light propagation in slab waveguides of rhombohedral-stacked MoS₂, a vdW semiconductor with large nonlinear susceptibility. Our method allows systematic optimization of nonlinear conversion by determining the phase-matching angles, mode profiles and losses in waveguides without prior knowledge of material optical constants. Using this approach, we show that both multimode and single-mode rhombohedral-stacked MoS₂ waveguides support birefringent phase matching, demonstrating the material’s potential for efficient on-chip nonlinear optics.

Spin–orbit torques enable energy-efficient manipulation of magnetization by electric current and hold promise for applications ranging from non-volatile memory to neuromorphic computing. Here we report the discovery of a giant spin–orbit torque induced by anomalous Hall current in ferromagnetic conductors. This anomalous Hall torque is self-generated as it acts on the magnetization of the ferromagnet that engenders the torque. The magnitude of the anomalous Hall torque is sufficiently large to fully negate magnetic damping of the ferromagnet, which allows us to implement a microwave spin torque nano-oscillator driven by this torque. The peculiar angular symmetry of the anomalous Hall torque favours its use over the conventional spin Hall torque in coupled nano-oscillator arrays. The universal character of the anomalous Hall torque makes it an integral part of the description of coupled spin transport and magnetization dynamics in magnetic nanostructures.

The miniaturization of light-emitting diodes (LEDs) is pivotal in ultrahigh-resolution displays. Metal-halide perovskites promise efficient light emission, long-range carrier transport and scalable manufacturing for bright microscale LED (micro-LED) displays. However, thin-film perovskites with inhomogeneous spatial distribution of light emission and unstable surface under lithography are incompatible with the micro-LED devices. Continuous single-crystalline perovskite films with eliminated grain boundaries, stable surfaces and optical homogeneity are highly demanded for micro-LEDs, but their growth and device integration remain challenging. Here we realize the remote-epitaxy growth of crystalline perovskite films, enabling their seamless integration into micro-LEDs with a pixel size down to 4 μm. By incorporating a subnanometre graphene interlayer, we enable remote epitaxy and transfer of perovskites with relaxed strain. These micro-LEDs exhibit a high electroluminescence efficiency of 16.7% and a high brightness of 4.0 × 10⁵ cd m⁻². Such high performance stems from suppressed defects and efficient carrier transport in epitaxial perovskites with high crystallinity, relaxed strain and hundreds-of-nanometres thickness. The free-standing perovskites can be integrated with commercial electronic planes for independent and dynamic control of each pixel, thus facilitating both static image and video display. With these findings, we envision on-chip perovskite photonic sources such as ultracompact lasers and ultrafast LEDs.

Interfacial ferroelectricity emerges in non-centrosymmetric heterostructures consisting of non-polar van der Waals (vdW) layers. Ferroelectricity with concomitant Coulomb screening can switch topological currents or superconductivity and simulate synaptic response. So far, it has only been realized in bilayer graphene moiré superlattices, posing stringent requirements to constituent materials and twist angles. Here we report ferroelectricity with concomitant Coulomb screening in different vdW heterostructures free of moiré interfaces containing monolayer graphene, boron nitride (BN) and transition metal chalcogenide layers. We observe a ferroelectric hysteretic response in a BN/monolayer graphene/BN, as well as in BN/WSe₂/monolayer graphene/WSe₂/BN heterostructure, but also when replacing the stacking fault-containing BN with multilayer twisted MoS₂, a prototypical sliding ferroelectric. Our control experiments exclude alternative mechanisms, such that we conclude that ferroelectricity originates from stacking faults in the BN flakes. Hysteretic switching occurs when a conductive ferroelectric screens the gating field electrically and controls the monolayer graphene through its polarization field. Our results relax some of the material and design constraints for device applications based on sliding ferroelectricity and should enable memory device or the combination with diverse vdW materials with superconducting, topological or magnetic properties.

Magnetic random-access memory that uses magnetic tunnel junction memory cells is a high-performance, non-volatile memory technology that goes beyond traditional charge-based memories. Today, its speed is limited by the high magnetization of the memory storage layer. Here we prepare magnetic tunnel junction memory devices with a low magnetization ferrimagnetic Heusler alloy Mn₃Ge as the memory storage layer on technologically relevant amorphous substrates using a combination of a nitride seed layer and a chemical templating layer. We switch the magnetic state of the storage layer with nanosecond long write pulses at a reliable write error rate of 10⁻⁷ and detect a tunnelling magnetoresistance of 87% at ambient temperature. These results provide a strategy towards lower write switching currents using ferrimagnetic Heusler materials and, therefore, to the scaling of high-performance magnetic random-access memories beyond those nodes possible with ferromagnetic memory layers.

The forward design of biosensors that implement Boolean logic to improve detection precision primarily relies on programming genetic components to control transcriptional responses. However, cell- and gene-free nanomaterials programmed with logical functions may present lower barriers for clinical translation. Here we report the design of activity-based nanosensors that implement AND-gate logic without genetic parts via bi-labile cyclic peptides. These actuate by releasing a reporter if and only if cleaved by a specific pair of proteases. AND-gated nanosensors that detect the concomitant activity of the granzyme B protease secreted by CD8 T cells and matrix metalloproteinases overexpressed by cancer cells identify the unique condition of cytotoxic T cell killing of tumour cells. In preclinical mouse models, AND-gated nanosensors discriminate tumours that are responsive to immune checkpoint blockade therapy from B2m^–/– tumours that are resistant to it, minimize signals from tissues without co-localized protease expression including the lungs during acute influenza infection, and release a reporter locally in tissue or distally in the urine for facile detection.

Autophagosome cancer vaccines can promote cross-presentation of multiple tumour antigens and induce cross-reactive T cell responses. However, so far, there is no effective method for obtaining a highly immunogenic autophagosomal cancer vaccine because autophagosomes, once formed, quickly fuse with lysosomes and cannot easily escape from cells. Here we report a functional Ti₂NX nanodot that caps the autophagosome membrane lipid phosphatidylinositol-4-phosphate, blocking the fusion of autophagosomes with lysosomes and producing stable nanodot-coated autophagosomes in tumours. The formed nanodot-coated autophagosomes can escape from cancer cells to lymph nodes, where they activate tumour-specific T cells. We show that our approach reduces tumour burden and provide long-term immune surveillance protection for cured mice. This work provides a method for the direct formation of personalized autophagosome-based cancer vaccines in vivo, offering a promising strategy for tumour treatment.

Quantifying the mechanical response of the biological milieu (such as the cell’s interior) and complex fluids (such as biomolecular condensates) would enable a better understanding of cellular differentiation and aging and accelerate drug discovery. Here we present time-shared optical tweezer microrheology to determine the frequency- and age-dependent viscoelastic properties of biological materials. Our approach involves splitting a single laser beam into two near-instantaneous time-shared optical traps to carry out simultaneous force and displacement measurements and quantify the mechanical properties ranging from millipascals to kilopascals across five decades of frequency. To create a practical and robust nanorheometer, we leverage both numerical and analytical models to analyse typical deviations from the ideal behaviour and offer solutions to account for these discrepancies. We demonstrate the versatility of the technique by measuring the liquid–solid phase transitions of MEC-2 stomatin and CPEB4 biomolecular condensates, and quantify the complex viscoelastic properties of intracellular compartments of zebrafish progenitor cells. In Caenorhabditis elegans, we uncover how mutations in the nuclear envelope proteins LMN-1 lamin A, EMR-1 emerin and LEM-2 LEMD2, which cause premature aging disorders in humans, soften the cytosol of intestinal cells during organismal age. We demonstrate that time-shared optical tweezer microrheology offers the rapid phenotyping of material properties inside cells and protein blends, which can be used for biomedical and drug-screening applications.