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Short-term forgetting at ultrafast timescales emulated by the depression function of a VCSOA-based photonic synapse
Forgetting, an active optimization mechanism in the human brain, is governed by synaptic plasticity. This insight has motivated the development of artificial synapses for hardware-level emulation of forgetting. Among them, photonic synapses have drawn considerable attention owing to their ultrafast response and low crosstalk. However, short-term forgetting (STF) at ultrafast timescales remains unexplored in photonic synapses. Here, the STF at ultrafast timescales is demonstrated using a photonic synapse based on a vertical-cavity semiconductor optical amplifier (VCSOA). First, STF is realized by replicating bio-realistic paired-spike depression in a VCSOA under a paired optical spike injection, with dynamic control achieved by adjusting injection power and bias current. Subsequently, stimulating the VCSOA with multiple optical spikes produces multiple-spike depression, which can also simulate the STF at ultrafast timescales. To approximate a realistic STF scenario, a letter “T” pattern encoded by different spike numbers and time intervals is injected into the VCSOA-based photonic synapse, and a gradual forgetting trend similar to that of the human brain is clearly observed. Remarkably, all bio-inspired STF occur at nanosecond timescales, providing a tangible artificial synapse for photonic neuromorphic computing at nanosecond timescales.
Polarization-sensitive metasurfaces for tunable structural colors with HSB control
Plasmonic metasurfaces can achieve static structural colors with high resolution, high efficiency, high saturation, and a wide color gamut. Integrating phase change materials and electro-optical components into metasurfaces can further achieve dynamically adjustable structural colors. However, it remains challenging to build a platform with independent control of the basic structural color attributes [HSB (hue, saturation, and brightness)] and dynamic polarization response. Here, we demonstrate a plasmonic metasurface based on an anisotropic Al nanopillar array and achieve independent control over the hue, saturation, and brightness of the structural colors through the geometric parameters of the nanopillar array. It is also shown that dynamic color adjustability can be achieved by adjusting the angles of the polarizer and the analyzer. Our scheme provides a simple method for achieving three-dimensional HSB color control and polarization-driven dynamic response in structural colors. This greatly enhances the information capacity and flexibility of optical metasurfaces in fields such as high-density displays and optical encryption.
Low thermal conductivity and thermal boundary conductance in BiOI crystals and films grown at low temperature
We present measurements of thermal conductivity and thermal boundary conductance (TBC) in the layered crystal BiOI. These measurements are applied to bulk crystals and crystalline films grown at low temperature (623 K) using chemical vapor methods. Such low-temperature growth was enabled by the growth kinetics of halogens in a reduced oxygen environment. The temperature-dependent Raman spectra showed red shifts of −8 × 10−3 and −12 × 10−3 cm−1 K−1for the characteristic A1g peak of the bulk and film samples, respectively. Most peaks also showed broadening with increased temperature, which indicated that phonon lifetimes are limited by anharmonic scattering. Laser heating measurements were combined with thermal models based on the finite-element method to estimate a directionally averaged thermal conductivity of 1.1 W m−1 K−1 in the bulk crystal. This low thermal conductivity was investigated by computing the phonon dispersion from first principles, which revealed extreme hybridization between acoustic and optical modes that is uncommon for layered crystals. The TBC of an exfoliated film and a grown film were measured to be 17 × 106 and 10 × 106 W m−2 K−1, which are at the lower end of solid–solid interfaces at room temperature. These measurements are valuable for applications in thermal isolation and understanding the thermal limits of BiOI electron devices given its semiconducting nature and low-temperature growth that is compatible with three-dimensional integration of electronics.
Toward in-line monitoring of the microstructure of organic semiconductor materials for photovoltaic applications via spectroscopic ellipsometry
High-throughput (HT) and automated fabrication methodologies are transforming the development of thin film organic optoelectronic devices. Organic semiconductor materials typically exhibit morphology-dependent performance, and their integration into lab-scale automated systems and roll-to-roll workflows would benefit from non-destructive, rapid, and reliable characterization tools. Distinguishing vertical segregation and microstructural evolution during processing remains a major challenge for in-line quality control and materials screening. In this work, we evaluate the sensitivity of variable angle spectroscopic ellipsometry (VASE) as a fast and non-invasive technique to monitor vertical microstructure stratification in organic semiconductor thin films based on polymer donor/non-fullerene acceptor bilayers (BLs) using two common materials for photovoltaic applications. We deduce the optical properties of the reference materials using standard critical point and Tauc–Lorentz models and then analyze model BL samples with donor/acceptor interfaces before and after thermal annealing. The ellipsometric response suggests that the technique can distinguish with high accuracy sharp BL interfaces and vertically separated blends. The findings in this work demonstrate that VASE can serve as an effective HT diagnostic tool for tracking layer dynamics in automated fabrication environments, providing a valuable bridge between process control and device optimization.
Substrate-dependent electrical transport in individual single-walled carbon nanotubes grown across SiO2 and hexagonal boron nitride
The electronic transport properties of carbon nanotubes (CNTs) are strongly affected by their surrounding environment, making the underlying substrate a critical factor for device performance. Here, we demonstrate enhanced carrier transport of individual single-walled CNTs on hexagonal boron nitride (hBN) by directly comparing CNT channels on SiO2 and hBN within the same nanotube. This within-tube comparison removes tube-to-tube variability in chirality, diameter, and defect density, allowing the intrinsic substrate effect to be evaluated more reliably. The CNTs were synthesized using gas flow-directed growth, which yields long, well-aligned CNTs without transfer processes, allowing a single nanotube to extend across different substrate regions. Multichannel field-effect transistors fabricated along an individual CNT exhibit clear ambipolar characteristics. CNT channels on hBN consistently exhibit higher field-effect mobility than those on SiO2. In contrast, temperature-dependent transport near the charge neutrality point exhibits thermally activated behavior with similar activation energies (15–20 meV) on both substrates, indicating that the intrinsic small bandgap of CNTs is largely unaffected by the substrate. These results provide direct evidence that hBN enhances low-field carrier transport in CNTs and establish a foundation for the fabrication of high-performance electronics based on hBN-supported CNTs.
Large topological Hall effect in epitaxial NiFeMo/NiFeMoO films with low-temperature exchange bias
We demonstrate exchange bias-driven large topological Hall effect in epitaxial NiFeMo/NiFeMoO heterostructures fabricated on Al2O3 (0001) substrates. Structural analyses confirm high-quality epitaxial growth with distinct strain states in single-layer NiFeMo and bilayer NiFeMo/NiFeMoO thin films. Magnetometry reveals that NiFeMo remains ferromagnetic over the entire temperature range, whereas NiFeMoO undergoes a suggested paramagnetic-to-antiferromagnetic transition near 175 K, inducing robust exchange bias in field cooled NiFeMo/NiFeMoO heterostructures. Magnetic force microscopy, supported by micromagnetic simulations incorporating Dzyaloshinskii–Moriya interactions, uncovers non-coplanar spin textures at room temperature under moderate magnetic fields. Magnetotransport studies identify a pronounced topological Hall-like signal, strongly enhanced by exchange bias at low temperatures. These results establish that epitaxial strain and interfacial exchange coupling act synergistically to stabilize non-coplanar spin textures and tailor the topological Hall response from 10 to 300 K, offering a promising pathway for oxide/metal interface-based topological spintronic applications.
The effect of demagnetization on the susceptibility of single-domain particles and assemblies
According to the classical laws of magnetism, the shape of magnetically soft objects limits the effective susceptibility. For example, spherical soft magnets cannot display an effective susceptibility larger than 3. Although this is true for macroscopic multi-domain magnetic materials, we explain why magnetic nanoparticles in a single-domain state do not suffer from this limitation. For single-domain particles, the differences between demagnetization factors along the principal axes are relevant and can influence susceptibility but do not limit it to an upper value as in the case for multi-domain particles. We experimentally validated this result on spherical nanoparticles with varying diameters (9–150 nm) and varying volume fractions (0.1–47 vol. %). In agreement with our predictions, we measure single-domain particle susceptibilities largely above 3, in fact up to more than 250. Moreover, contrary to an existing model for assemblies of particles, we find that the susceptibility of materials composed of non-interacting single-domain particles in a non-magnetic matrix scales linearly with the volume fraction of particles. This implies that high susceptibilities (>100) are achievable for nanoparticle-based composites and is relevant for the design of magnetically soft materials that are operational at MHz–GHz frequencies with negligible power losses.
Mn-doping with reduced carry-over effect in semi-insulating GaN grown by MOCVD
Semi-insulating GaN layers for high-electron mobility transistors (HEMTs) used in radio frequency applications are typically achieved through Fe-doping, despite its known adverse effects on transport properties. In this paper, we investigate the possibility of using Mn as an alternative dopant to Fe for GaN buffer layers grown by metal-organic chemical vapor deposition and assess its incorporation onto the subsequent non-intentionally doped (nid) layers. For this purpose, two studies were conducted: first, epitaxial heterostructures for HEMTs were grown with varying the thickness of the nid GaN layer, while keeping the total GaN stack thickness and the Mn-doping level, followed by varying the Mn-doping level and keeping the GaN stack thickness. The Mn-doped buffer layers showed a much faster concentration decay into the subsequent nid GaN layers than Fe. The samples maintained good surface morphology and crystalline quality, and their transport properties did not degrade with different GaN stack thicknesses and doping levels, showcasing Mn as a promising dopant for semi-insulating GaN buffer layers.
Spectral-focusing CARS spectroscopy driven by an all-PM-fiber gain-managed nonlinear amplifier
We demonstrate a spectral-focusing coherent anti-Stokes Raman scattering (SF-CARS) spectroscopy system driven by a single all-fiber gain-managed nonlinear amplification laser. By exploiting the synergistic interplay between self-phase modulation and normal group-velocity dispersion in the gain fiber, the source directly delivers spectrally broadened pulses with an intrinsically linear chirp (pulse energy >100 nJ), eliminating external pulse stretchers and chirp-matching optics. Leveraging the intrinsic delay–frequency mapping, we achieve broadband SF-CARS detection covering a significant portion of the fingerprint region (500–1200 cm−1) with a spectral resolution of ∼13 cm−1. The system capability for sensitive and multiplex chemical analysis is validated by measurements of gaseous SF6 and liquid mixtures of benzene and DMSO. These results establish a compact, robust excitation architecture that advances SF-CARS toward turn-key coherent Raman spectroscopy and high-speed multi-component imaging.
Epitaxial layer to boost betavoltaic performance in SiC Schottky diodes
Betavoltaic cells harness the decay of beta-radiation to directly generate electrical power—making them of interest for powering remote or isolated devices. Compound semiconductors are promising materials for use in advanced betavoltaic cells owing to their excellent electronic properties combined with radiation hardness. Modifying the device architecture is one way the electrical power generated from absorbed incoming beta-radiation can be enhanced. In this study, an epitaxial layer is added to a SiC Schottky diode to create a betavoltaic device with greater power output. This output is quantified using simulated beta radiation (electron beam-induced current) and beta radiation from either a 63Ni or a 90Sr/90Y emitter. The epitaxial layer-related enhancement increases as the energy of the incoming simulated radiation increases, which is confirmed in practice for the 90Sr/90Y exposed device having Voc = 0.37 V, Jsc = 0.054 μA/cm2, and Pmax = 0.014 W/cm2.
High-resolution compact computational spectrometer using enhanced mode interference in a chaotic multimode fiber
The development of high-resolution, miniaturized, and cost-effective spectrometers remains a critical technical challenge. In this work, we demonstrate a high-resolution computational spectrometer by exploiting the chaotic effects induced in side-polished multimode fibers (MMFs). The polishing breaks the structural symmetry of the circular fiber, thereby efficiently exciting guided modes and causing chaos. By forming a 5-cm-long polished region, a spectral resolution of ∼0.5 nm is achieved, representing a one-third improvement over an unpolished MMF of the same length. Moreover, we develop a spectral reconstruction algorithm that integrates adaptive regularization and the Savitzky–Golay filter, enabling real-time reconstruction with enhanced accuracy and robustness. Compared to the Tikhonov regularization algorithm alone, the proposed method reduces the reconstruction error by 50%. This scheme, which leverages chaotic effects to enhance spectral resolution, offers an effective design strategy for developing high-resolution spectrometers.
Ultrafast probing of heterostructure dependent coherent acoustic phonon decoherence in AlGaN/GaN HEMT heterostructures
We investigate the influence of heterostructure engineering on the generation, propagation, and decoherence of coherent acoustic phonons (CAPs) in GaN-based materials using ultrafast pump–probe transient differential transmission spectroscopy. Measurements are performed on an AlGaN/AlN/GaN high electron mobility transistor (HEMT) heterostructure, the same structure after selective removal of the AlGaN/AlN layers, and a bare Mg-doped GaN epilayer with embedded InGaN/GaN superlattice layers. Femtosecond excitation launches longitudinal acoustic phonons whose coherent oscillations are tracked in the time and frequency domains using wavelength-resolved probing. The intact AlGaN/AlN/GaN heterostructure exhibits long-lived, narrowband CAP oscillations with a dominant frequency near 40 GHz, whereas etched GaN shows pronounced decoherence, spectral broadening, and mode mixing due to enhanced phonon–phonon and interfacial scattering. The quality factor of the coherent phonons in the heterostructure is approximately three times higher than that of the etched sample, highlighting the role of top layers in preserving phonon coherence and facilitating heat transport. In contrast, Mg-doped GaN epilayer displays strong waveform distortion and rapid dephasing, consistent with phonon scattering from superlattice interfaces. Time–frequency analysis reveals probe wavelength-dependent detection of phonon modes via Brillouin scattering, with shorter probe wavelengths accessing higher-frequency components. These results demonstrate that phonon coherence in GaN can be engineered through heterostructure design and doping control, with direct implications for thermal management and reliability of high-power GaN HEMTs.
Fully automated electrodeposition of perovskite thin films for efficient solar cells
Electrodeposition technology has shown unique application potential in perovskite solar cell fabrication due to its characteristics of requiring only water and alcohol solvents without the need for high-vacuum environments. However, current related research is still in the preliminary exploration stage (fewer than 50 publications), and most are concentrated on manual laboratory preparation, with prominent issues such as rough process control and poor reproducibility, with few systematic studies on automated control of electrodeposition processes and synergistic regulation of additives. Addressing these issues, this work designs and constructs a fully automated electrodeposition preparation system, which achieves high reproducibility in the preparation of MAPbI3 perovskite solar cells. The resulting devices exhibit an efficiency of 7.29%, a 16% improvement over manual preparation, with the efficiency standard deviation reduced from 1.47% to 1.22%. On this basis, by further introducing MACl and FABr additives, the champion efficiency was improved to 15.15%, with the efficiency standard deviation reduced to 0.93%. The automated preparation system and additive regulation strategy proposed in this study provide effective technical support and equipment reference for developing low-cost and environmentally friendly preparation of perovskite solar cells.
Compact, efficient, low-threshold 320 nm continuous-wave ultraviolet laser
This paper reports a compact, efficient, low-threshold continuous-wave 320 nm ultraviolet laser based on a linear cavity with Pr:YLF and LiB3O5 (LBO) crystals. Thermal effects were analyzed via a three-dimensional temperature field model and thermal lens calculations, guiding the selection of crystal parameters that balance pump absorption and heat load. Using a 0.5 at. % doped Pr:YLF crystal of 8 mm length and a 12 mm long LBO crystal, the laser delivers 3.03 W of continuous-wave 320 nm output with a slope efficiency of 35.2% and a threshold power of 60 mW—the highest slope efficiency reported for a CW Pr:YLF laser at this wavelength. The compact linear cavity minimizes length and loss, offering a viable design for future highly integrated ultraviolet lasers using crystal bonding technology.
HYDRA-XAI dual-backbone disaster scene recognition using ResNet50-Swin transformer feature fusion, explainable evidence, and an operational recommender
Assessment of pelvic floor muscle training video information quality and associated factors on Douyin and Bilibili: a cross-sectional study
Maternal Western diet alters milk leptin levels and early postnatal leptin handling in rat offspring
Abstract Lactation is a critical developmental window during which maternal conditions influence breast milk composition, thereby affecting infant growth and long-term health. Leptin, a key bioactive component of breast milk involved in metabolic programming, may have its beneficial effects attenuated under maternal obesogenic diets. This study evaluated whether a maternal Western-style diet (WD) is associated with changes in early postnatal absorption of milk-derived leptin and leptin-related miRNAs, and their relationship with gastric content as an indirect indicator of nutrient intake in the offspring. Female rats were fed a control diet (C-Dams) or a WD (WD-Dams) starting one month before gestation and throughout gestation and lactation. Dams and pups were euthanized at lactation/postnatal day 4 (LD4/PND4). WD-Dams displayed higher leptinemia (3.8 ± 1.5 vs. 2.1 ± 0.67 ng/mL, p = 0.026) and milk leptin levels (1.6 ± 0.46 vs. 1.0 ± 0.33 ng/mL, p = 0.012). Despite increased milk leptin supply and stronger gastric leptin signal detected by immunohistochemistry, WD-pups did not show a quantitative increase in gastric leptin content or circulating leptin levels. Notably, they presented a tendency towards greater gastric content (0.24 ± 0.12 vs. 0.12 ± 0.11 g, p = 0.089). No differences were found in leptin-related miRNAs absorption; however, miR-17 levels were higher in WD-milk (increment of 70.7%) and correlated with duodenal levels only in WD-pups. Maternal WD consumption during the perinatal period alters milk leptin levels and early leptin exposure and is associated with slight differences in gastric content in the offspring, suggesting early alterations in regulatory processes.