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Coplanar nanoscale vacuum electron field emission triode with controllable gate distance

The typical nanoscale vacuum field emission triode with a controllable gate distance, created via focused ion beam etching and photolithography, is presented in this study. The field emission performance under coplanar gate control is distinguished from the gate distance (dg) in a low vacuum environment. It is, therefore, necessary to highlight a vital parameter dg defined by the nanogap between the center of the nanoscale channel and the edge of the coplanar gate, to methodically illustrate the working mechanism. For the case of a device with large dg, the F–N tunneling current was positively increased by up to one order of magnitude when high bias conditions on the anode and coplanar gate were applied. In contrast, the device with short dg displayed a negative drop in F–N tunneling current under the same measurement condition. As the gate bias increased continuously to a critical value, this device became cut off in this situation with an insignificant gate leakage current. This opposite trend of F–N emission current is eventually verified to have a relationship with dg and it is suggested to play a crucial role in the device. This work clarified the role of the coplanar gate when device operated in the F–N tunneling mechanism and conducted a thorough analysis of the charge transport mechanism related to dg. This work will aid coplanar nanoscale vacuum electron field emission device design in the future.

Maternal occupational exposures during early stages of pregnancy and adverse birth outcomes in the NINFEA birth-cohort

Objectives Maternal occupational exposures during early pregnancy can be detrimental to foetus health and have short- and long-term health effects on the child. This study examined their association with adverse birth outcomes. Methods The study included 3938 nulliparous women from the Italian NINFEA mother-child cohort. Their occupational exposures during the first trimester of pregnancy were assessed through prospectively collected questionnaire information and job-exposure matrices. Associations between maternal exposures and birthweight, preterm birth, and delivery by caesarean section were analysed by multivariable linear and logistic regression models. An exploratory factor analysis was carried out to explore co-exposure profiles in association with birth outcomes. Results Women exposed to passive smoking at work and those who reduced their working hours during pregnancy were found to have an increased likelihood of all analysed birth outcomes. Children of mothers performing a demanding work were less likely to be born preterm [OR 0.72 (95% CI 0.54 to 0.95)] and more likely to have a higher birthweight [β = 40.4 g (95% CI 7.5 to 73.4)]. Maternal exposures to heat and dust were associated with a lower birthweight [β = -160.1 g (95% CI -299.6 to -20.7)] and increased odds of caesarean section [OR 6.99 (95% CI 2.36 to 25.47)], respectively. Conclusions This study provides some evidence of the selection of healthy population into the workforce and of association between work-related passive smoking, heat and dust and adverse birth outcomes.

Compositional disordering: Nanoscale engineering of advanced crystalline scintillation materials

This article provides an overview of the latest results in the field of improving the properties of multiatomic inorganic oxide compounds for scintillators. A possibility to control the spatial distribution of nonequilibrium carriers in the ionization track by creating a compositional disorder in the crystalline matrix is in focus. Managing the disorder at the nanoscale level creates an opportunity for the efficient energy loss by carriers during thermalization, smaller spatial dispersion, and, consequently, more efficient binding into excitons and, further, an increase in the scintillation yield. The methods to produce multicationic crystalline scintillation materials have been discussed. The effectiveness of the approach is confirmed for both activated and self-activated scintillation materials.

Acoustic holograms for beam focusing in immersed anisotropic silicon

Ultrasonic inspection of anisotropic materials presents challenges due to directionally dependent wave propagation and beam distortion. Specifically, conventional spherically focused probes, which aim to converge the beam to a small cross section within the solid and increase inspection resolution, can yield spatially and temporally varying focal profiles in anisotropic media. This variability can make interpreting signals from defects within the samples more difficult. To address this challenge, acoustic holograms were designed to enhance ultrasonic beam focusing in silicon wafers. Lens geometries were inversely calculated using ray tracing in pursuit of conical focusing in the solid. Analytical modeling using the angular spectrum approach predicted higher amplitude and more circular focal cross sections for the custom lenses compared to the spherical lenses. The custom lenses, along with conventional spherical lens designs, were fabricated using stereolithographic 3D printing and tested on [3 1 1] and [1 3 5] silicon wafers with etched flat bottom holes. Experimental validation showed the custom lenses produced higher contrast defect signatures with smaller cross-sectional areas from sub-wavelength defects, suggesting improved defect sensitivity and anisotropy-dependent scattering. The results showcase the potential of customized acoustic holograms to enhance ultrasonic inspection of anisotropic materials. The presented design and modeling methods provide the framework for further optimization of acoustic lenses tailored to anisotropic media.

Novel high-<i>T</i>C piezo-/ferroelectric ceramics based on a medium-entropy morphotropic phase boundary design strategy

The medium- or high-entropy strategy has emerged as a new paradigm for designing high-performance piezoelectric ceramics. However, the effectiveness of this approach remains unclear to the development of high Curie temperature (TC) piezo-/ferroelectric materials with outstanding performance. To develop high-performance piezo-/ferroelectric materials suitable for high-temperature environments, in this work, we design a novel ceramic system based on a medium-entropy morphotropic phase boundary (ME-MPB) strategy. Piezo-/ferroelectric ceramics of the formula, Pb(Yb1/2Nb1/2)O3–Pb(In1/2Nb1/2)O3–PbTiO3, meeting the medium entropy criteria, were successfully synthesized using the conventional solid-state reaction method. The crystal structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the ceramics of the ME-MPB compositions were systematically investigated. X-ray diffraction and scanning electron microscopy analyses revealed that these ceramics possess a pure perovskite phase and dense microstructure. Notably, the prepared ceramics exhibited exceptional piezoelectric performance, with a high d33 up to 603 pC/N, a large strain of 0.20%, a high remanent polarization of 44.0 μC/cm2, and a high Curie temperature of 362 °C. This study demonstrates an effective design approach based on the ME-MPB strategy and points out a new pathway for developing high-performance materials for high-temperature applications as sensors, thereby expanding the research perspective on the design of medium-entropy piezo-/ferroelectric ceramics.

CO2 conversion products in α and γ modes of radio frequency capacitively coupled plasma

Radio Frequency Capacitively Coupled Plasma (RF-CCP) exhibits excellent spatial uniformity, high stability, and the capability to generate plasma over large areas, making it highly promising for applications in CO2 resource utilization in space environments. This study investigates the CO2 conversion products under two typical discharge modes (α and γ modes) of RF-CCP and their product selectivity under Martian nominal pressure. The results indicate that the optical emission spectra in both α and γ modes contain CO2+, O, and CO spectral bands/lines. The overall spectral line intensity is enhanced in the γ mode compared to the α mode, indicating a higher electron density and ionization degree in the γ mode. The key product, CO, is primarily generated through electron collisions with CO2, while O2 is produced via the dissociative recombination of electrons with CO2+. After the transition from α to γ mode, the content of CO2 decreases, but the concentrations of electrons and CO2+ increase significantly. This results in CO being the dominant product in the α mode, while in the γ mode, the overall abundance of products is higher and there is a greater selectivity for O2. Therefore, by controlling the discharge mode of RF-CCP, it is possible to achieve targeted regulation of the CO2 conversion products.

Optimizing time-of-flight secondary ion mass spectrometry depth profiles of semiconductor heterostructures

The continuous technological development of electronic devices and the introduction of new materials lead to ever greater demands on the fabrication of semiconductor heterostructures and their characterization. This work focuses on optimizing Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles of semiconductor heterostructures aiming at a minimization of measurement-induced profile broadening. As a model system, a state-of-the-art Molecular Beam Epitaxy (MBE) grown multilayer homostructure consisting of natSi/28Si bilayers with only 2 nm in thickness is investigated while varying the most relevant sputter parameters. Atomic concentration-depth profiles are determined and an error function based description model is used to quantify layer thicknesses as well as profile broadening. The optimization process leads to an excellent resolution of the multilayer homostructure. The results of this optimization guide to a ToF-SIMS analysis of another MBE grown heterostructure consisting of a strained and highly purified 28Si layer sandwiched between two Si0.7Ge0.3 layers. The sandwiched 28Si layer represents a quantum well that has proven to be an excellent host for the implementation of electron-spin qubits.

Accurate machine learning of rate coefficients for state-to-state transitions in molecular collisions

We present an algorithm that combines quantum scattering calculations with probabilistic machine-learning models to predict quantum dynamics rate coefficients for a large number of state-to-state transitions in molecule–molecule collisions much faster than with direct solutions of the Schrödinger equation. By utilizing the predictive power of Gaussian process regression with kernels, optimized to make accurate predictions outside of the input parameter space, the present strategy reduces the computational cost by about 75%, with an accuracy within 5%. Our method uses temperature dependences of rate coefficients for transitions from the isolated states of initial rotational angular momentum j, determined via explicit calculations, to predict the temperature dependences of rate coefficients for other values of j. The approach, demonstrated here for rovibrational transitions of SiO due to thermal collisions with H2, uses different prediction models and is thus adaptive to various time and accuracy requirements. The procedure outlined in this work can be used to extend multiple inelastic molecular collision databases without exponentially large computational resources required for conventional rigorous quantum dynamics calculations.

A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3

This study investigates the impact of structural isomerism on the excited state lifetime and redox energetics of heteroleptic [Ir(ppy)2(bpy)]+ and homoleptic Ir(ppy)3 photoredox catalysts using ground-state and time-dependent density functional theory methods. While the ground- and excited-state reduction potentials differ only slightly among the isomers of these complexes, our findings reveal significant variations in the radiative and non-radiative decay rates of the reactivity-controlling triplet 3MLCT states of these closely related species. The observed differences in radiative decay rates could be traced back to variations in the transition dipole moment, vertical energy gaps, and spin–orbit coupling of the isomers. In [Ir(ppy)2(bpy)]+, transition dipole moment differences play a significant role in controlling the relative lifetime of the triplet states, which we rationalized by a vectorial analysis of permanent dipole moments of the ground and excited states. Regarding the two isomers of Ir(ppy)3, changes in radiative decay rates were primarily attributed to variations in vertical energy gaps and intensity borrowing from other singlet-singlet transitions driven by spin–orbit coupling. Non-radiative decay variations were assessed in terms of differences in reorganization energies, adiabatic energy gap, and spin–orbit coupling. For both complexes, reorganization energies associated with low-energy molecular vibrations and metal–ligand bond length changes following the de-excitation process were major contributors. These insights provide a deeper understanding of how molecular design can be leveraged to optimize the performance of iridium-based photoredox catalysts, potentially guiding the development of more efficient catalytic systems for future applications.

Electronic spectroscopy and excited state mixing of OThF

Electronic spectra for OThF have been recorded using fluorescence excitation and two-photon resonantly enhanced ionization techniques. Multiple vibronic bands were observed in the 340–460 nm range. Dispersed fluorescence spectra provided ground state vibrational constants and evidence of extensive vibronic state mixing at higher excitation energies. Two-photon ionization measurements established the ionization energy for OThF of 6.283(5) eV. To guide the assignment of the OThF spectra, electronic structure calculations were carried out using relativistic equation-of-motion coupled-cluster singles and doubles methods. These calculations indicated that spin–orbit induced mixing of the 32A″ and 42A′ states was mediated by a seam of potential energy surface intersections.

Modeling DNA methyltransferase function to predict epigenetic correlation patterns in healthy and cancer cells

DNA methylation is a crucial epigenetic modification that orchestrates chromatin remodelers that suppress transcription, and aberrations in DNA methylation result in a variety of conditions such as cancers and developmental disorders. While it is understood that methylation occurs at CpG-rich DNA regions, it is less understood how distinct methylation profiles are established within various cell types. In this work, we develop a molecular-transport model that depicts the genomic exploration of DNA methyltransferase within a multiscale DNA environment, incorporating biologically relevant factors like methylation rate and CpG density to predict how patterns are established. Our model predicts DNA methylation-state correlation distributions arising from the transport and kinetic properties that are crucial for the establishment of unique methylation profiles. We model the methylation correlation distributions of nine cancerous human cell types to determine how these properties affect the epigenetic profile. Our theory is capable of recapitulating experimental methylation patterns, suggesting the importance of DNA methyltransferase transport in epigenetic regulation. Through this work, we propose a mechanistic description for the establishment of methylation profiles, capturing the key behavioral characteristics of methyltransferase that lead to aberrant methylation.

Anion photoelectron velocity-map imaging using a tunable laser at a 100 kHz repetition rate

We present velocity-map imaging (VMI) of photoelectrons detached from anions using an optical parametric amplifier operating at a repetition rate as high as 100 kHz. The light source generates femtosecond (fs) laser pulses tunable from near-infrared to ultraviolet (310–2600 nm), which interact synchronously with mass-selected anion bunches. We demonstrate this technique by measuring two-dimensional projections of photoelectrons ejected from silver trimer anions, Ag3−, across a photon energy range from 2.43 to 4.00 eV (509–310 nm), with an average power of 50–300 mW. This high-repetition-rate VMI setup allows rapid data acquisition of photoelectron spectra and laboratory-frame photoelectron angular distributions of anions at various photon energies, facilitating investigation of their electronic and geometric structures. Taking advantage of the fs pulses, this approach will also enable time-resolved photoelectron imaging for tracking electronic and nuclear dynamics of anions with high efficiency.

Slower swimming promotes chemotactic encounters between bacteria and small phytoplankton

Chemotaxis enables marine bacteria to increase encounters with phytoplankton cells by reducing their search times, provided that bacteria detect noisy chemical gradients around phytoplankton. Gradient detection depends on bacterial phenotypes and phytoplankton size: large phytoplankton produce spatially extended but shallow gradients, whereas small phytoplankton produce steeper but spatially more confined gradients. To date, it has remained unclear how phytoplankton size and bacterial swimming speed affect bacteria’s gradient detection ability and search times for phytoplankton. Here, we compute an upper bound on the increase in bacterial encounter rate with phytoplankton due to chemotaxis over random motility alone. We find that chemotaxis can substantially decrease search times for small phytoplankton, but this advantage is highly sensitive to variations in bacterial phenotypes or phytoplankton leakage rates. By contrast, chemotaxis toward large phytoplankton cells reduces the search time more modestly, but this benefit is more robust to variations in search or environmental parameters. Applying our findings to marine phytoplankton communities, we find that, in productive waters, chemotaxis toward phytoplankton smaller than 2 μm provides little to no benefit, but can decrease average search times for large phytoplankton (∼20 μm) from 2 wk to 2 d, an advantage that is robust to variations and favors bacteria with higher swimming speeds. By contrast, in oligotrophic waters, chemotaxis can reduce search times for picophytoplankton (∼1 μm) up to 10-fold, from a week to half a day, but only for bacteria with low swimming speeds and long sensory timescales. This asymmetry may promote the coexistence of diverse search phenotypes in marine bacterial populations.

Pair approximating the action for molecular rotations in path integral Monte Carlo

Typical path integral Monte Carlo approaches use the primitive approximation to compute the probability density for a given path. In this work, we develop the pair discrete variable representation (pair-DVR) approach to study molecular rotations. The pair propagator, which was initially introduced to study superfluidity in condensed helium, is naturally well-suited for systems interacting with a pairwise potential. Consequently, paths sampled using the pair action tend to be closer to the exact paths (compared to primitive Trotter paths) for such systems leading to convergence with less imaginary time steps. Our approach relies on using the pair factorization approach in conjunction with a discretized path integral ground state paradigm to study a chain of planar rotors interacting with a pairwise dipole interaction. We first use the Wigner–Kirkwood density expansion to analyze the asymptotics of the pair propagator in imaginary time. Then, we exhibit the utility of the pair factorization scheme via convergence studies comparing the pair and primitive propagators. Finally, we compute energetic and structural properties of this system including the correlation function and Binder ratio as functions of the coupling strength to examine the behavior of the pair-DVR method near criticality. The density matrix renormalization group results are used for benchmarking throughout.

Strong adsorption of guanidinium cations to the air–water interface

Combining Deep-UV second harmonic generation spectroscopy with molecular simulations, we confirm and quantify the specific adsorption of guanidinium cations to the air–water interface. Using a Langmuir analysis of measurements at multiple concentrations, we extract the Gibbs free energy of adsorption, finding it larger than typical thermal energies. Molecular simulations clarify the role of polarizability in tuning the thermodynamics of adsorption, and establish the preferential parallel alignment of guanidinium at the air–water interface. As a polyatomic cation, guanidinium represents one of the few examples of a positively charged species to exhibit a propensity for the air-water interface. As such, these results expand on the growing body of work on specific ion adsorption.

Modeling ethanol/water adsorption in all-silica zeolites using the real adsorbed solution theory

A comprehensive set of single-component and binary isotherms were collected for ethanol/water adsorption into the siliceous forms of 185 known zeolites using grand-canonical Monte Carlo simulations. Using these data, a systematic analysis of ideal/real adsorbed-solution theory (IAST/RAST) was conducted and activity coefficients were derived for ethanol/water mixtures adsorbed in different zeolites based on RAST. It was found that activity coefficients of ethanol are close to unity while activity coefficients of water are larger in most zeolites, indicating a positive excess free energy of the mixture. This observation can be attributed to water/ethanol interactions being less favorable than water/water interactions in the single-component adsorption of water at comparable loadings. The deviation from ideal behavior can be highly structure-dependent but no clear correlation with pore diameters was identified. Our analysis also demonstrates the following: (1) accurate unary isotherms in the low-loading regime are critical for obtaining physically sensible activity coefficients; (2) the global regression scheme to solve for activity model parameters performs better than fitting activity models to activity coefficients calculated locally at each binary state point; and (3) including the dependence on adsorption potential offers only a minor benefit for describing binary adsorption at the lowest fugacities. Finally, the Margules activity model was found incapable of capturing the non-ideal adsorption behavior over the entire range of fugacities and compositions in all zeolites, but for conditions typical of solution-phase adsorption, RAST predictions using zeolite-specific or even bulk Margules parameters provide an improved description compared to IAST.

The ecdysone-induced bZIP transcription factor MafB establishes a positive feedback loop to enhance vitellogenesis and reproduction in the <i>Aedes aegypti</i> mosquito

Female mosquitoes require a vertebrate blood meal to activate reproduction, transmitting numerous devastating human diseases. Vitellogenesis is a central event of female reproduction that involves the massive production of vitellogenin (Vg) in the fat body and the maturation of ovaries. This process is controlled by the steroid hormone 20-hydroxyecdysone (20E); however, its molecular regulatory basis remains not completely understood. We found that the expression of Aedes aegypti muscle aponeurosis fibromatosis B ( AaMafB ), coding for a basic leucine zipper (bZIP) transcription factor, was significantly up-regulated after a blood meal. The 20E-bound ecdysone receptor–ultraspiracle heterodimer directly targeted the ecdysone response element in the promoter of AaMafB , activating its transcription. Coimmunoprecipitation assays illustrated the interaction between Aa MafB and Cap “n” collar C ( Aa CncC), another bZIP transcription factor. RNA interference–mediated depletion of Aa MafB or Aa CncC led to impaired ovarian growth, decreased expression of AaVg and Halloween genes, and reduced 20E levels. The Aa MafB– Aa CncC heterodimer directly activated the transcription of AaVg and AaShade by targeting the antioxidant response element in their promoters. Together, our results indicate that AaMafB functions as an early 20E response gene, the product of which heterodimerizes with Aa CncC to maintain high 20E levels and facilitates activation of AaVg in mosquitoes after a blood meal.

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Heterogeneous dynamics in aging phosphate-based geopolymer

The time-evolution of dynamics as well as microstructure and mechanical response of phosphate-based geopolymers was probed using x-ray photon correlation spectroscopy and rheological tests. The analyzed relaxation processes in the freshly prepared geopolymer mixes evidenced a q-independent mode of the autocorrelation function, ascribed to density fluctuations of the already established molecular network, undergoing reconfiguration without significant mass transport. Upon curing, the detected motions are localized and depict a system evolving toward structural arrest dominated by slower hyperdiffusive dynamics, characterized by a compressed exponential regime, pointing to a structural relaxation process subjected to internal stresses, in a context of marked dynamical and structural heterogeneity. The system ages through a “densification” process producing declining small angle scattered intensity, as two finely intermixed gel-like reaction products, namely, one hydrated aluminophosphate and one hydrated silica, form a percolated network possessing surface fractal scaling of progressively shorter average correlation length. In this scenario, the nominal Al/P molar ratio of the mix, being an index of network-forming ability, is positively correlated with the dynamic viscosity and the overall kinetics, whereas the contrary occurs for the fraction of water.

An RNase III–processed sRNA coordinates sialic acid metabolism of <i>Salmonella enterica</i> during gut colonization

Sialic acids derived from colonic mucin glycans are crucial nutrients for enteric bacterial pathogens like Salmonella . The uptake and utilization of sialic acid in Salmonella depend on coordinated regulons, each activated by specific metabolites at the transcriptional level. However, the mechanisms enabling crosstalk among these regulatory circuits to synchronize gene expression remain poorly understood. Here, we identify ManS, a small noncoding RNA derived from the 3’ UTR of STM1128 mRNA transcribed from a Salmonella enterica –specific genetic locus, as an important posttranscriptional regulator coordinating sialic acid metabolism regulons. ManS is primarily processed by RNase III and, along with its parental transcripts, is specifically activated by N-acetylmannosamine (ManNAc), the initial degradation product of sialic acid. We found that the imperfect stem-loop structure at the 5’ end of ManS allows RNase III to cleave in a noncanonical manner, generating two functional types of ManS with the assistance of RNase E and other RNases: short isoforms with a single seed region that regulate the uptake of N-acetylglucosamine, an essential intermediate in sialic acid metabolism; and long isoforms with an additional seed region that regulate multiple genes involved in central and secondary metabolism. This sophisticated regulation by ManS significantly impacts ManNAc metabolism and S. enterica ’s competitive behavior during infection. Our findings highlight the role of sRNA in coordinating transcriptional circuits and advance our understanding of RNase III-mediated processing of 3’ UTR-derived sRNAs, underscoring the important role of ManNAc in Salmonella adaptation within host environments.