Browse Articles

Quasi Fe MIL-53 nanozyme inducing ferroptosis and immunogenic cell death for cancer immunotherapy

Composite structure design for broadband metamaterial absorption: Integrated nonlinearity and enhanced performance using lumped resistors

A new ultrathin and broadband metamaterial absorber featuring four integrated lumped resistors is presented and examined. The design incorporates nonlinearity to enhance the absorber's performance. This metamaterial absorber achieves broadband absorption, maintaining absorption levels above 90% across the 1.33–3.57 GHz frequency range. The absorber demonstrates simultaneous negative permittivity and permeability, with bandwidths of approximately 670 MHz in the L-band and around 1.57 GHz in the S-band, resulting in a total bandwidth of 2.24 GHz. The fractional bandwidth is an impressive 91%, exceeding the previously reported absorbers. Furthermore, the design is remarkably thin, at 0.097 λ, at the lowest frequency. The absorber, with its fourfold symmetry, is insensitive to polarization angles up to 180° and maintains stable absorption up to 40° for both TE and TM modes. Validation of the design using advanced design system software shows close agreement with the computer simulation technology simulation results. In summary, the proposed absorber, with a FoM value of 1.68 and an effective medium ratio value of 9.09, is highly desirable, offering significant performance benefits, including high absorption efficiency, broad operational bandwidth, and minimal thickness, making it suitable for advanced applications. Finally, the proposed absorber was manufactured and tested to validate the simulation results. The proposed metamaterial absorber offers a flexible and adaptable solution across various fields. It finds applications in radar systems, satellite and wireless communications, environmental sensing and monitoring, stealth technology, and IoT and smart devices.

Benchmarking third-order cluster perturbation theory for electronically excited states

In this study, we investigate the reliability of cluster perturbation (CP) theory applied to the calculation of electronically excited states through a comprehensive benchmark. In CP theory, perturbative corrections are added to the properties of a parent excitation space, which converge toward the properties of a target excitation space. For the CPS(D-n) model, perturbative corrections through order n are added to the coupled cluster singles (CCS) excitation energies to target the coupled cluster singles and doubles (CCSD) excitation energies. Through a comparative analysis of excitation energy calculations across a diverse set of molecules and wavefunction methods, we present a comprehensive evaluation of the accuracy of the third-order CPS(D) model, CPS(D-3), in calculating excitation energies. Our findings demonstrate that CPS(D-3) is a reliable alternative to established methods, particularly CCSD, while systematically overestimating the excitation energies compared to high-level coupled cluster methods such as CC3. These results highlight the strengths and limitations of CPS(D-3), as well as the promising directions for its future development.

Effects of nitrosyl fluoride based gas treatment on fluorination and redox reaction at GaN surface and Pt/GaN interface

The effects of nitrosyl fluoride (FNO) gas treatment on the surface of GaN(0001) and its interface with sputtered Pt were investigated by hard x-ray photoelectron spectroscopy (HAXPES). Annealing GaN and Pt/GaN samples in an FNO gas atmosphere resulted in the appearance of prominent F 1s peaks in the HAXPES spectra, indicating the efficient formation of Ga–Fx bonding states not only in bare-GaN but also in Pt/GaN, even when the FNO gas treatment was performed after Pt deposition. In addition, the chemical shifts of the Ga 2p3/2 and N 1s peaks corresponded to a Fermi level shift toward the valence band. The FNO gas treatment induced greater oxidation of the GaN surface than the Pt/GaN interface. By contrast, at the Pt/GaN interface, the unintentionally formed oxide GaOx was reduced, resulting in an improvement of the electrical properties. The results of this study suggest that FNO gas treatment is an effective post-processing method for the fluorination of GaN-based systems after metal deposition.

Charge photogeneration dynamics in random terpolymer donor-based non-fullerene polymer solar cells

Random ternary polymerization is a strategy for tuning the energy levels and improving the batch-to-batch reproducibility of polymer semiconductors for the application in polymer solar cells (PSCs). However, the influence of third component incorporation on exciton properties and charge photogeneration processes in terpolymer-based solar cells is still unclear. In this work, time-resolved spectroscopies were employed to study exciton properties and charge photogeneration processes in PSCs based on a series of terpolymers, PM1 and PM2, which have 20% and 50% of thiophene-thiazolothiazole (TTz) building blocks on the PM6 backbone, respectively. For neat terpolymer films, we found that the small amount (20%) of TTz incorporation in PM6 slightly reduces the exciton diffusion coefficient, but the exciton lifetime is significantly increased, resulting in a significant increase in exciton diffusion length. However, further increasing the TTz component (50%) in the PM6 backbone decreases exciton lifetime, the diffusion coefficient, and consequently exciton diffusion length. We found that a small amount of acceptor (Y6) addition can efficiently dissociate terpolymer excitons due to the weak molecular stacking of terpolymers in the blend films. For terpolymer:Y6-based blend films, we find that the small amount of TTz incorporation (PM1) could reduce the phase size of the donor and suppress bimolecular carrier recombination in blend films. Furthermore, we find that the energy level offset plays a critical role in charge photogeneration processes, and a HOMO energy level offset of 0.06 eV can dissociate acceptor excitons in terpolymer-based organic solar cells effectively.

Stability transition conditions of dislocation cores and Peierls stress

At the atomic scale, a dislocation in a crystal possesses two equilibrium cores: One has its symmetric center at the lattice point and is referred to as the O-core; the other has its symmetric center at the middle between two neighboring lattice points and is referred to as the B-core. The possible positions (symmetric centers) of the B-core and the O-core are arrayed alternately, and the dislocation movement undergoes a sequential transformation between the two types of dislocation cores. The core with lower energy is stable, and the energy difference between the O-core and the B-core is the Peierls barrier. It is found that the stability of the core is not fixed. In some materials, the B-one core is stable, and in other materials, the O-core is stable. Furthermore, the core stability can be tuned by exerting pressure or changing the environmental temperature. Because at the stability transition point the energy difference is zero, the Peierls barrier disappears and the dislocation almost moves freely. As a consequence, material plasticity dominated by the dislocation mobility will undergo substantial change in the process of the stability transition. Therefore, it is important to understand under what condition the transition occurs. Using the variational method, the stability phase boundary in the model-parameter space is investigated and the transition condition is approximately described by an analytical equation. Furthermore, it is found that in addition to the disappearance of the Peierls barrier, the B-core and the O-core have the same width at the transition point.

Formation of magnesium clusters in superfluid helium nanodroplets

Magnesium atoms in liquid helium have been hypothesized to form a metastable foam structure, in which a layer of helium atoms surrounds each magnesium atom, inhibiting their coalescence into a compact cluster. This conjecture is based on the weak interaction between the magnesium atoms themselves and with the helium atoms and was used to explain observations in femtosecond two-photon ionization experiments by different groups. However, this theory is incongruent with previous infrared spectroscopic observations, indicating the formation of tightly bound clusters when different atoms and molecules combine inside liquid helium. In this paper, we report the spectra (from 210 to 2210 nm) of magnesium-doped superfluid helium nanodroplets at different averaged droplet sizes and number of dopants. The measured spectra in this study are consistent with the formation of compact magnesium clusters rather than the metastable foam structure.

Bound states in the continuum of three-leg ladder topoelectrical circuits

Bound States in the Continuum (BICs) represent a distinct category of localized states with eigenvalue embeddings within extended states, maintaining strong localization and a high Q factor without hybridization. In this study, we introduce a topological inductor–capacitor circuit constructed using a three-leg ladder lattice model and provide experimental evidence of the existence of the BICs. Furthermore, we confirm that the properties of the system's BICs are derived from the separated subspace Hamiltonian and can be adjusted by manipulating the parameters of the subspace. We investigated the impact of non-Hermitian perturbations on BICs by introducing small resistances, and the results demonstrate that BICs exhibit resistance to non-Hermitian perturbations. Our work validates the potential of topological circuits for realizing BICs, and we anticipate its extension to higher-dimensional and higher-frequency circuits, enabling applications in sensors, filters, and radio frequency devices.

Publisher’s Note: “Work-biased path-sampling calculations of chemical potentials: Principles and applications to uranium oxide” [J. Chem. Phys. 162, 024108 (2025)]

Molecular dynamics simulation of Al (001) surface magnetron sputtering of WS2 thin films

WS2 is a two-dimensional solid lubricant with exceptional thermal stability. The WS2 thin films prepared by the magnetron sputtering method are effective in reducing friction and wear in critical components such as those used in aviation, aerospace, and military applications. The microscopic mechanism of magnetron sputtering significantly influences the properties and quality of these films. Therefore, it is essential to investigate the deposition mechanism of magnetron-sputtered WS2 thin films at the molecular level. In this paper, the effects of incident energy and incident angle on the morphology of Al (001) surface magnetron sputtering WS2 thin films were studied by molecular dynamics simulation, and the growth mode of Al (001) surface magnetron sputtering WS2 thin films was explored. The results reveal that the growth mode of magnetron-sputtered WS2 thin films on the Al (001) surface is a Stranski–Krastanov growth mode. With an increase in the incident energy, the film's surface roughness, thickness, and the atomic ratio of sulfur to tungsten (S/W) are decreasing. Additionally, for low incident energies (0.1–1.0 eV), a decrease in surface roughness without a corresponding decrease in film thickness was observed. Furthermore, with an increase in the incident angle, the surface roughness increases and the thickness of the film decreases, respectively. The study concludes that WS2 thin films at an incident energy of 0.7 eV and an incident angle of 0° exhibit optimal properties, with a surface roughness of 1.453 Å, a film thickness of 7.873 Å, and an S/W of 1.232.

Highly stable inverted perovskite solar cells with all-inorganic selective contact using iron-doped zinc oxide

Perovskite solar cells (PSCs) have achieved remarkable performance advancements over the past decade. In inverted p–i–n PSCs, commonly utilized electron transport layers (ETL), such as C60 and PCBM, are associated with notable stability challenges and high production costs. This study reports on a novel and highly stable perovskite solar cell that employs iron-doped zinc oxide (FZO) nanoparticles as the ETL and nickel oxide (NiOx) as the hole transport layer, demonstrating a power conversion efficiency (PCE) of ∼12%. In comparison with PSCs that utilize zinc oxide (ZnO) as the ETL, those incorporating FZO demonstrated a maximum PCE enhancement of 18.3%. The incorporation of iron doping mitigates the basicity of the ZnO ETL, thereby reducing the deprotonation at the FZO/perovskite interface and enhancing the stability of the PSCs. The unpackaged FZO device maintained an initial PCE of 90% after 400 h at a relative humidity of 45% ± 5%. (2-(9H-carbazol-9-yl)ethyl)phosphonic acid and 2-phenylethylamine hydroiodide were used to passivate the NiOx/perovskite and perovskite/ZnO(FZO) interfaces, respectively, which further improved the PSC performance. Ultimately, FZO-based PSCs with a PCE of 13.65%, an open-circuit voltage (Voc) of 1.04 V, a short-circuit current density (Jsc) of 20.79, and a fill factor (FF) of 63.1% were obtained, and the PCE demonstrated a notable increase of over 35% compared to pristine ZnO-based devices. Results indicate that high device performance, low fabrication costs, and excellent stability can be attained through the use of simple chemically synthesized oxides as inorganic selective charge transport layers in PSCs.

Research on the acoustic performance of MPP and inverse design

Under specifying the noise frequency and sound absorption coefficient in engineering practice, the traditional method cannot quickly get the microperforated panel (MPP) structure size that meets the condition. Therefore, this paper establishes the MPP acoustic impedance model and calculates the sound absorption coefficient of MPP, revealing the change rule of the damping state. Based on the finite element method, the corresponding numerical model is built to explain the MPP sound absorption principle. Experiments were carried out using impedance tubes to verify the accuracy of the acoustic impedance model. It is found that the micropore diameter is directly proportional to the maximum sound absorption frequency, and the plate thickness and acoustic cavity depth are inversely proportional to the maximum sound absorption frequency. Aiming at the low efficiency of MPP inverse design, this paper proposed an inverse design method of MPP based on 1DCNN by constructing a network architecture adapted to the characteristics of MPP data and establishing a mapping model between dimensional parameters and absorption performance. The model training results show that the loss of the test set is as low as 0.703, and the R2 values of the absorption performance indexes are all higher than 0.997. Considering the actual physical constraints and taking the engineering requirements as input, the output designed MPP has an absorption bandwidth of 349 Hz, and the maximal acoustic absorption frequency is α = 0.997; the result meets the engineering demand and provides an essential theoretical basis and engineering application reference for the design of the MPP structure.

Ionic current rectification under concentration gradients and its application in evaluating surface charge properties of micropores

Ionic current rectification (ICR) induced by electroosmotic flow (EOF) under concentration gradients can find many applications in micro/nanofluidic sensing and ionic circuits. Here, we focused on the cases with micropores of moderate length–diameter ratios. Through experimental research and systematic simulations, the EOF-induced ICR was found to exhibit voltage-dependent ratios. In the considered cases with a weak EOF or strong ionic diffusion, a large deviation appears between the ion concentration inside the micropore and the bulk value, which fails the prediction by solution conductivity gradients. Based on our simulation results, effective equations were developed for the theoretical description of ion concentration distributions along the micropore axis under a coupled concentration gradient and electric field. With the predicted ion distributions inside micropores, the ICR ratio can be conveniently calculated using the derived electrical resistance of the microfluidic system, which applies to micropores of 200–1000 nm in diameter. Because the surface charge density is the only unknown input parameter, our developed equations can be used to evaluate the surface charge density of micropores using the measured EOF-induced ICR ratio under concentration gradients.

<i>In-situ</i> reflectance analysis of Si-doped β-Ga2O3 films grown by MOVPE: The influence of doping concentration and substrate conductivity

This study examines the feasibility of using in-situ reflectance measurement for Si-doped β-Ga2O3 films homoepitaxially grown by metalorganic vapor-phase epitaxy on substrates with varying conductivity [semi-insulating (Mg-doped) and conductive (Si-doped)]. Interference oscillation patterns were observed in the wavelength region well below the bandgap absorption, with the oscillation amplitudes showing a significant dependence on the doping concentrations of the grown films. Reflectance spectroscopy enables the estimation of growth rate and doping level based on the period and amplitude of the observed Fabry–Pérot oscillations, respectively. These oscillations occur due to the refractive index difference between the grown film and the substrate, which is influenced by doping in the homoepitaxy process and estimated by the Drude model.

PLUMED Tutorials: A collaborative, community-driven learning ecosystem

In computational physics, chemistry, and biology, the implementation of new techniques in shared and open-source software lowers barriers to entry and promotes rapid scientific progress. However, effectively training new software users presents several challenges. Common methods like direct knowledge transfer and in-person workshops are limited in reach and comprehensiveness. Furthermore, while the COVID-19 pandemic highlighted the benefits of online training, traditional online tutorials can quickly become outdated and may not cover all the software’s functionalities. To address these issues, here we introduce “PLUMED Tutorials,” a collaborative model for developing, sharing, and updating online tutorials. This initiative utilizes repository management and continuous integration to ensure compatibility with software updates. Moreover, the tutorials are interconnected to form a structured learning path and are enriched with automatic annotations to provide broader context. This paper illustrates the development, features, and advantages of PLUMED Tutorials, aiming to foster an open community for creating and sharing educational resources.

A practical theoretical model for Ge-like epitaxial diodes. II. Matching the experimental optical responsivity in <i>pin</i> devices

A theoretical model that can be used to simultaneously fit the I–V characteristics and spectral optical responsivity of Ge-like pin diodes is described in detail and validated experimentally using specially fabricated Ge- and Ge1−ySny devices. The model combines a numerical solution of the basic semiconductor transport equations with a rigorous calculation of the optical generation rate that accounts for multiple reflections in the device structure multilayers. The results can be used to quantify the reduction of photocurrent associated with recombination centers for full optimization of the device structure.

Minimizing interference in low-pressure supersonic beam sources

Free-jet atomic, cluster, and molecular sources are typically used to produce beams of low-energy, neutral particles and find application in a wide array of technologies, from neutral atom microscopes to instruments for surface processing. We present a simple analytical theory that is applicable to many of these sources, when (i) the nozzle-skimmer distance is such that free molecular flow is achieved and (ii) there is negligible interference within the skimmer itself. The utility of the model is demonstrated by comparing experimental data with calculations performed using the theory. In particular, we show that skimmer interference is negligible compared to attenuation by “background” gas for room-temperature beams. Our treatment does not depend on any free parameters and obviates the complexity of previous theories. As a result, we are able to devise a number of design recommendations to minimize interference in sources operating with cryogenic-temperature beams.

The calculation of keyhole depth based on the primary absorption of front keyhole wall in laser deep-penetration welding

The establishment of an accurate prediction model of keyhole depth during laser welding is of great significance for predicting the weld depth or pre-selecting suitable welding process parameters. In this paper, based on the primary absorption of the incident laser by the front keyhole wall, the tilt angle of the keyhole wall was calculated point by point according to the equilibrium relationship between the laser energy absorbed by the material and the energy required for evaporation at any position of the front keyhole wall. A prediction model for the keyhole depth in laser deep penetration welding has been established by taking into account the laser optical parameters, the focusing system parameters, the welding process parameters, and the material properties. The transformation law of the front keyhole wall profile, the Fresnel absorption coefficient, and the keyhole depth with laser power, welding speed, focusing focal length, and other parameters was calculated in the model, which is basically in line with the consensus. At the same time, the keyhole depth results of calculations and measurements under some parameter conditions were compared. It can be found that the prediction model of keyhole depth during laser deep penetration welding can be used to approximate the calculation of weld depth, and the feasibility of the model was preliminarily verified. Moreover, combined with previous experimental results, the conclusion that the primary absorption of front keyhole wall is the key factor determining the keyhole depth can be re-verified by using mathematical calculations. It also shows that the complex energy coupling law in keyhole has a noticeable difference in the influence of different physical phenomena during laser deep penetration welding.

Theoretical methods based on linear response theory to simulate dynamics and absorption spectra of molecular polaritons

In this work, we first derive path integral expressions for the dynamics of molecular polaritons in microcavities. For systems with a large number of molecules in the cavity, i.e., in the thermodynamic limit, it is shown that linear response theory can be employed to describe the molecular response, which can be further modeled by an effective harmonic bath. This leads to analytical path integral expressions for the Dicke model, as well as its extensions that incorporate effects of static disorder and coupling to intramolecular vibrational degrees of freedom. The hierarchical equations of motion are then derived to simulate polariton dynamics and absorption spectra. By further taking advantage of the harmonic nature of both the system and the effective bath, an efficient exact diagonalization method is also obtained. Similar results are also obtained for the Tavis–Cummings model, the rotating-wave approximation of the Dicke model. Utilizing these theoretical findings, we simulate the polariton dynamics and absorption spectra and analyze the critical coupling strength for the superradiant transition in the presence of static disorder and coupling to intramolecular vibrational motion.

Roadblocks to ambient-pressure room-temperature superconductivity in lutetium hydrides

Recently, the reports of room-temperature superconductivity in nitrogen-doped lutetium hydrides at near-ambient pressure (1 GPa) have attracted considerable interest but remain controversial due to the inconsistent experimental reproducibility. Achieving ambient-pressure room-temperature superconductivity remains a challenging goal, and a fundamental understanding is lacking. In this work, we employ first-principles calculations to demonstrate that achieving ambient-pressure room-temperature superconductivity in lutetium hydrides faces two major challenges: (i) At low pressure, the lutetium atoms are poorly squeezed, keeping their inner electrons in core-electron states with limited electron donation. This significantly reduces the chemical pressure, resulting in a low H content and a small H-contributed density of states (DOS) at the Fermi surface, thereby suppressing the superconducting temperature (Tc); and (ii) at low pressure, it is also difficult to increase the DOS at the Fermi surface by chemical tuning to enhance Tc, since this attempt is always impeded by the accompanying structural instability. A fundamental understanding of these two challenges is significant to the future quest of ambient-pressure room-temperature superconductivity in metal hydrides.