Small Science最新文献

Vanadium oxides and their polymorphs are transforming electromagnetic radiation security in communications and infrastructure. This arises from their broadband response and potential for wavelength attenuation across the ultraviolet, optical, infrared, and radio regions of the electromagnetic spectrum. More specifically, monoclinic vanadium dioxide's sharp, reversible insulator-to-metal transition near room temperature enables ultrafast, tuneable switching of conductivity and optical properties, triggered by thermal, optical, or electrical controls. Chalcogenide phase-change materials require high crystallisation temperatures and nanosecond switching times, whereas VO₂'s volatile Mott transition operates near ambient conditions with femtosecond response and cycling stability exceeding 100 million cycles. This dynamic modulation supports real-time absorption, shielding, and beam steering across terahertz, infrared, and radiofrequency domains, with demonstrated absorption rates tuneable from 2% to 100% and bandwidths up to 6.35 THz. VO₂ metasurfaces offer polarisation insensitivity and multifunctionality, protecting against jamming, interception, and signal leakage. Advances in large-area synthesis, nanostructuring, and durability have enabled both highly sensitive sensors and long-lived smart coatings. These findings position vanadium oxides as transformative materials for physical-layer electromagnetic security in wireless communications, infrastructure protection, and smart sensing systems.

The sluggish hydrogen evolution reaction (HER) kinetics in alkaline media, primarily attributed to the additional water dissociation step, has led to a significant activity gap between acidic and alkaline conditions. Metal-supported electrocatalysts leveraging hydrogen spillover have garnered significant attention due to sufficiently utilized reaction sites; however, designing active catalysts remains a formidable challenge, primarily due to the limited understanding of the specific regulatory mechanisms governing proton spillover. Herein, a facile strategy is reported for the fabrication of Pt nanoclusters (Pt_NC) on oxygen-defect-rich NiO nanowires (Pt_NC-D-NiO). The electrocatalyst demonstrates excellent intrinsic and mass-normalized HER activity and remarkable long-term stability, outperforming Pt_NC on pristine NiO nanowires and commercial Pt/C. Notably, its alkaline HER activity is fairly close to its acidic counterpart, significantly narrowing the activity gap compared to commercial Pt/C. Advanced ex situ/operando physicochemical characterizations, including in situ electrochemical impedance spectroscopy, reveal that oxygen defects substantially lower the water dissociation energy barrier. This facilitates rapid H* spillover and enhances local H* coverage on Pt_NC, thus accelerating subsequent H* recombination to boost alkaline HER. This work not only offers a cost-effective catalyst design strategy but also provides fundamental insights into the role of hydrogen spillover in optimizing electrocatalytic performance.

Organic memristors with tunable resistive switching (RS) are promising candidates for brain-inspired neuromorphic computing. This study reports a self-assembled organic nanowire network memristor based on copper (II) hexadecafluoro-phthalocyanine (F₁₆CuPc), exhibiting digital, multilevel, and analog switching through compliance current (I _CC) modulation. Current-voltage and impedance analyses reveal that the transition in RS behavior is primarily driven by a shift from trap-limited to trap-free space charge-limited conduction as I _CC increases. In low I _CC, Ag⁺-cation migration plays a central role in conduction through redox-assisted Ag-F/ Ag-π interwire interactions, causing abrupt switching. In contrast, higher allowed injection at high I _CC enables predominant intrawire current conduction via π-π intermolecular interactions, resulting in a gradual RS transition. The novelty of this work lies in the controlled growth of nanowire structures via self-assembled 2D molecular stacking, which is key to enabling multifunctionality within a pristine, nanowire network-based molecular memristive system designed for hybrid digital-neuromorphic applications. These findings significantly broaden the functional scope of metal phthalocyanine-based nanowire network architecture, advancing their application toward flexible, energy-efficient, multifunctional, and wearable smart electronics.

Layered perovskites form a versatile class of ferroelectrics in which structural anisotropy gives rise to periodic electrostatics and, consequently, unconventional ferroelectric properties. These materials fall into four main families: Aurivillius, Carpy-Galy, Ruddlesden-Popper, and Dion-Jacobson phases, each forming natural superlattices by interleaving perovskite slabs with spacer layers. For a long time, these materials were considered too structurally complex to prepare as high-quality thin films. However, recent breakthroughs in deposition and advanced characterization have made it possible to stabilize epitaxial films with atomic-scale control, uncovering novel ferroelectric functionalities. These include robust in-plane polarization without a critical thickness, the emergence of charged domain walls and non-trivial polar textures, resilience to doping with magnetic ions and charge carriers, and the possibility to epitaxially integrate them into standard perovskite heterostructures. This review aims to unify current knowledge on the fabrication and characterization of layered ferroelectric thin films, and to present research findings across all four structural families, with the goal of highlighting their common features despite differences in crystal structure and polarization mechanisms. We also discuss promising research directions, including polar metallicity, (alter-)magnetoelectricity, exfoliation, and soft-chemistry-driven phase transformations, hoping to encourage exploration of these materials for both fundamental studies and applications.

Bacterial infections often involve small, local populations of bacteria, yet antibiotic treatment decisions are generally based on bulk population susceptibility assays. Stochastic variability among local small populations can influence susceptibility, limiting the predictive capability of bulk assays. Therefore there is a need to better understand antibiotic response in small populations. Droplet-based microfluidics enables the high-throughput production of tens of thousands of picolitre droplets, in which small populations of bacteria (e.g., 8 cells) can be encapsulated and their responses to different environmental conditions tracked. Here, we use a combinatorial droplet-generation platform, combined with microscopy and image analysis, to interrogate the responses of small populations of Escherichia coli to different bulk-determined sub-inhibitory concentrations of the antibiotics tetracycline, streptomycin, and ampicillin within a single experiment. We observe qualitatively distinct small-population responses for these antibiotics. For the bacteriostatic ribosome-targeting antibiotic tetracycline, growth varies nonmonotonically at low antibiotic concentrations. For the bactericidal ribosome-targeting antibiotic streptomycin, we observe apparent bistability, some replicate populations growing while others die. For the bactericidal cell-wall targeting antibiotic ampicillin, we observe stochastic bacterial filamentation. Our study shows how distinct phenomena impacting antibiotic susceptibility may emerge in small bacterial populations, laying a foundation for deeper studies into potential treatment implications.

Electrochemical CO₂ reduction (eCO₂R) in acidic electrolytes is appealing due to its high CO₂ utilization efficiency. For this reaction, bismuth (Bi)-based catalysts have drawn considerable attention for their potential in producing formate/formic acid. However, the presynthesized materials for Bi-based catalysts often undergo restructuring during electrocatalysis, resulting in altered electrochemical performance. Furthermore, the mechanisms underlying the restructuring of Bi-based catalysts in acidic environments have not yet been clearly elucidated. Herein, distinct restructuring mechanisms are revealed in structurally different Bi-based compounds, such as Bi₉O_7.5S₆ and Bi₂O₂S. Among them, the Bi₉O_7.5S₆ precatalyst exhibits high selectivity and activity for formic acid production, attributed to its unique structure, featuring stacking of [Bi₂O₂]²⁺ and [BiS₂]^- layers. In contrast, the conventional Bi₂O₂S catalyst, characterized by alternating [Bi₂O₂]²⁺ layers with S^2- ions, delivers inferior eCO₂R performances. Quasi-in situ X-ray diffraction and in situ Raman spectra results reveal that metal elements situated between two [Bi₂O₂]²⁺ layers can resist decomposition and prevent the over-reduction of catalysts, leading to the restructuring in Bi/Bi₂O₂CO₃ composite material with active Bi-Bi₂O₂CO₃ interface for formic acid production. As a result, the Bi₉O_7.5S₆ precatalyst achieves a high Faraday efficiency above 95% at 100 mA cm^-2 and remarkable stability of 117 h in a flow cell.

Perovskite solar cells (PSCs) are emerging as a promising technology for indoor photovoltaics due to their high efficiency and cost-effective manufacturing. In this article, three strategies are explored to reduce costs and enable perovskite materials (PSK) as power sources for indoor internet of things (IoTs): 1) using dual perovskite absorber layer (PSK1/polyethylene glycol (PEG)/PSK2) to replace both the absorber and hole transport layers, 2) utilizing spray-coating for perovskite deposition under ambient conditions with 45%-65% relative humidity (RH), and 3) replacing metal electrodes with carbon electrodes. The dual absorber layer improves charge transport, while the spray-coating process minimizes solution waste, making large-scale production more feasible. Additionally, the use of PEG as an interlayer effectively enhances defect passivation, improving charge transport and stability. The proposed carbon-based device architecture offers the lowest material cost ($11.98 m^-2) and the modified levelized cost of electricity for indoor light (m-LCOE-i) of 1.54 ¢ Wh^-1, outperforming traditional Spiro-OMeTAD/Au or carbon designs along with enhancing the commercial viability of PSCs. To demonstrate its practicality, connected PSCs are utilized to power IoT devices for over a month under typical laboratory lighting conditions (300-400 lux) at 40%-65% RH.

Spirometry is influenced by the patient's subjective condition, which limits the reproducibility of diagnostic results despite being a key diagnostic tool for respiratory diseases. To overcome this, an extended-gate field-effect transistor-type aptasensor for detecting granzyme B (GzmB) and perforin (PRF) is introduced as a proof-of-concept for diagnosing localized immune responses in respiratory diseases. The novel GzmB and PRF aptamers are synthesized using systematic evolution of ligands by exponential enrichment and are subsequently truncated to enhance the target-binding affinity. Au-ReS₂ and the alternating current electrothermal flow technique are applied to amplify the biosensing signal and accelerate detection within 10 min, respectively. Under the 10% human serum, a linear response is observed depending on the target concentration, with the detection limits of 330 fM for GzmB and 440 fM for PRF. The targeted dual-biomarker indicates a strong clinical correlation with bronchial conditions in chronic obstructive pulmonary disease patients. The proposed device demonstrates clear advantages in rapid, selective, and sensitive detection, suggesting its use as a preemptive diagnostic tool for respiratory diseases. This approach is expected to establish promising diagnostic strategies for early detection and therapeutic monitoring of various respiratory diseases, potentially replacing conventional spirometry.

The COVID-19 pandemic has underscored the urgent need for broad-spectrum antivirals (BSAs) capable of countering diverse and rapidly emerging viral threats. Unlike virus-specific drugs, BSAs offer cross-family protection and can serve as adaptable therapeutic platforms for pandemic preparedness. Advances in nanotechnology have further strengthened this approach by improving the solubility, stability, and targeted delivery of antiviral agents. Several repurposed drugs, such as niclosamide, favipiravir, remdesivir, nitazoxanide, and zinc-ionophores, have demonstrated potential broad-spectrum activity when formulated at the nanoscale. These nanoengineered platforms enhance pharmacokinetic performance, tissue penetration, and bioavailability, thereby enabling lower effective doses and reduced systemic toxicity. Such nanotechnological strategies not only improve antiviral efficacy across multiple viral families, including Coronaviridae, Flaviviridae, Orthomyxoviridae, and Poxviridae, but also support scalable, cost-effective production suitable for global deployment. By integrating drug repurposing with nanoengineering, BSAs can form the cornerstone of future pandemic preparedness, bridging the gap between laboratory innovation and rapid clinical response to emerging infectious diseases.

The phenomenon of surface facet formation during ion implantation has captured considerable scientific and technological interest. Surface facets-including wavy, pyramidal, and terraced morphologies-are typically formed during off-normal keV and MeV ion beam implantation, and due to injected gas effects. In certain circumstances, these features may also emerge during irradiation at normal incidence: when differential sputtering occurs in biphasic regions, when contaminants are inadvertently added as dopants, or when the experimental arrangement permits the coimplantation of metals. The formation of surface nanopatterns in nanocrystalline nickel under high-temperature ion irradiation at normal incidence has been observed-a phenomenon that conventional mechanisms fail to explain. A novel mechanism driving nanopattern formation under these conditions is presented. These findings offer compelling evidence that facets result from voids forming on the surface and in its vicinity. A strong correlation between the crystallographic orientation and the facet type has also been identified. Specifically, grains oriented in the <100> and <111> directions display smooth and wavy morphologies, while grains with orientations in between exhibit more complex shapes. The research indicates that grains with low stress and surface energies tend to exhibit wavy facets, while higher values lead to the formation of more complex shapes.