Table of contents

Characterisation plays a vital role in both the academic and industrial worlds, providing a feedback loop between the design and optimisation of device performance. The rapid development of hardware and software has pushed characterisation techniques to new extremes, while their combination has provided new insight in cross-disciplinary fields, where multi-physics and multi-scale measurements are needed. In the Special Issue of the Journal of Physics D: Applied Physics, entitled 'Advanced Characterisations of Materials, Devices and Applications', we have compiled a comprehensive collection of 29 articles, showcasing the latest advancements in various fields, such as semiconductor materials and devices, plasmonics and nanophotonics, and two-dimensional materials and devices, among others. In this editorial, we concisely summarise the key research highlights of these studies.

Carbon fiber reinforced polymer composites (CFRPs) are widely used in aerospace, transportation, and defense industries due to their excellent properties such as lightweight, high specific strength and stiffness, superior thermal stability, and corrosion resistance. However, the smooth and chemically inert surface of carbon fiber (CF) results in poor interfacial adhesion between the fiber and matrix, thereby impacting the mechanical performance of CFRPs. To address this issue, nanomaterials have been introduced to the fiber surface, leveraging their exceptional mechanical properties and large specific surface area to enhance the interfacial properties of CFRPs. Compared to conventional modification methods like sizing, plasma treatment, and oxidation treatment, nanomaterials provide a superior approach by creating a robust transition layer at the interface. This layer can enhance mechanical interlocking, balance the modulus of the CF with that of the matrix, and effectively disperse interfacial stress, thus improving load transfer from the matrix to the fiber. This review examines recent advances in CF surface modification using nanomaterials and discusses the mechanisms behind interfacial enhancement. It also explores the potential future directions for research in this field, aiming to promote nanomaterial applications for advancing the use of higher-performance CFRPs from lab to industry.

In the early stages of introducing the term superatom to describe atomic clusters exhibiting chemical properties similar to periodic table elements, the electronic structures of these clusters were understood through simplified calculations based on the jellium model with spherical potential. Against this backdrop, a superatomic physical image based on the sequence of electronic energy levels predicted by the model was formed. In this work, the analysis of the development of superatoms first indicates that, due to their non-ideal spherical structures, density functional theory calculations that take into account realistic atomic potential without relying on the simplified jellium sphere model can yield more reliable results. Although the electronic structure of some single-element atomic clusters under this calculation may agree with the results of jellium model, their orbitals with the same angular momentum actually split. Moreover, in more complex multi-element systems, the sequence may change further. Nevertheless, these systems still maintain well-defined electronic shell structures, allowing them to be classified as superatoms. This work also verifies these findings through calculations of specific stereoscopic, planar and compressed superatoms. Thus, superatoms intrinsically surpass the results from the jellium model approximation, the realistic atomic potential provides more detailed insights into their electronic structures. This finding will contribute to both fundamental and applied research of superatoms.

Whether in the form of zinc blende, wurtzite, or a composite structure of the two, silicon carbide (SiC) crystals possess a pair of polar crystal faces along the stacking direction of Si–C bilayers, namely the Si-face and the C-face. These two faces have different atomic structures and surface properties, resulting in anisotropic and surface polarity (SP)-dependent effects on growth and mechanical processing of SiC materials and electrical performance of SiC-based devices. Although much effort has been spent on the studies of the SiC polarity and SP-dependent effects, no systematic review of these studies has been reported. Herein, we aim to comprehensively outline the main aspects of the polarity-dependent effects of SiC, starting from the origin of polarity and culminating in a discussion on how SP affects device performance. Along the way, we will cover several methods for identifying SP and SP-dependent effects on crystal growth, mechanical processing and heteroepitaxy. The particular significance of this study lies in providing a clear research framework and overview that serves as a reference for future research and applications.

Experimental evidence indicates that significant exchange coupling may exist between magnetic nanoparticles (MNPs) in dense MNP aggregates such as nanoflower clusters. Here, we examine the role of inter-particle exchange interactions in determining the magnetic properties of MNP clusters, in particular their athermal hysteresis in a low-frequency alternating field. We consider mechanically fixed close-packed clusters where each particle is modeled as a single macrospin coupled to the others by both dipolar interactions and nearest-neighbor exchange. Upon simulating the quasi-static hysteresis curves, we compute the loop area, remanent moment and coercive field, and we classify each curve by its shape. Computing curve types across parameter space reveals how their shape is determined by the interplay between exchange coupling, dipolar interactions, and uniaxial anisotropy. Strong exchange coupling produces fully saturated loops with coherent moment rotation. Moderate exchange and anisotropy result in magnetically soft clusters with high susceptibility. Finally, for complex clusters, weak to moderate exchange and strong anisotropy may produce highly irregular curves with several abrupt changes in magnetization. Our analysis demonstrates that exchange coupling between MNPs significantly increases the cluster energy product, thereby contributing to explain the exceptional heating power of nanoflowers.

Working reliably at elevated operating temperatures is a key requirement for semiconductor lasers used in optical communication. InAs/GaAs quantum-dot (QD) lasers have been considered a promising solution due to the discrete energy states of QDs. This work demonstrates temperature-insensitive and low threshold InAs/GaAs QD lasers incorporating co-doping technique, compared with p-type modulation doping. 2 mm long co-doped QD lasers exhibit a low threshold current density of 154 A cm⁻² (210 A cm⁻²) and operate at a high heatsink temperature of 205 °C (160 °C) under the pulsed (continuous-wave) mode, outperforming the p-type doped QD lasers. The results reveal that co-doping effectively enhances both high-temperature stability and threshold reduction in InAs/GaAs QD lasers, surpassing the performance of conventional p-type modulation doping. This approach offers a pathway toward cooling-free operation, making co-doped QD lasers suitable for data and telecommunication applications.

The capability of characterizing low-bandgap two-dimensional (2D) materials is crucial for a wide range of applications from fundamental science to commercial implementation. Current techniques rely heavily on expensive characterization equipment and thus hinder focused research on low-bandgap materials, compared to their counterparts in the visible range of the electromagnetic spectrum. This work demonstrates a cost-efficient and easily rebuildable optical setup to probe low-bandgap 2D materials using photocurrent spectroscopy. The heart of the setup consists of a supercontinuum laser in combination with a diffraction grating to create a tunable light source working from 500 to 2000 nm, allowing to access bandgaps in the short-wave infrared (IR), far from what is possible using standard silicon detector technology. Apart from a complete technical guide to facilitate reproduction of the system, two popular narrow-gap materials (MoTe₂ and black phosphorus) have been studied to extract bandgaps and excitonic features of these materials. The results highlight the simple, yet powerful approach of utilizing photocurrent spectroscopy in the IR and thus expanding the analysis toolbox for narrow-gap 2D semiconductor research.

We report on the key design factors for the development of Type-II 'W'-lasers for O-band (1260–1360 nm) applications. We investigate the effects of InGaAs and GaAsSb quantum well composition and thicknesses on the emission wavelength and recombination efficiency as well as of (Al, Ga) As barriers on optimum electrical and optical confinement. Photoluminescence (PL) tests structures and full device structures were fabricated and characterised. 1.25 µm emitting lasers were demonstrated with a threshold current density and J_th values of 480 ± 10 A cm⁻² at 290 K, whereas 1.3 µm lasers showed an increased J_th value of 5.5–7 kA cm⁻² at 290 K. The PL test structures exhibited a similar trend with decreasing intensity with increasing wavelength. Gain measurements of the 1.3 µm device demonstrate reasonably low optical losses of 10–15 ${\text{c}}{{\text{m}}^{ - 1}}$ and a threshold modal gain of ≈25 ${\text{c}}{{\text{m}}^{ - 1}}$.

This paper proposes an actively tunable reflective metasurface containing solely addressable meta-atoms capable of continuous phase adjustment within the microwave frequency range. Each meta-atom's response can be quickly and accurately adjusted by adjusting the external voltage applied to each meta-atom, thereby regulating the phase distribution of the unit structures on the metasurface. Successful generation with three modes of vortex beams (VBs). Additionally, focusing and non-diffracting VBs with limited beam radii are achieved by superposing the vortex phase profile with a focusing phase profile and a non-diffracting zeroth-order Bessel beam phase profile, respectively, by combining laboratory simulations and sample testing, demonstrating the metasurface's high-precision phase control capability in the reflective state. The presented scheme facilitates the development of metasurface devices with more functionalities. It exhibits significant potential for microwave fields, like intelligent wireless communication, antennas, and radars.

As silicon-based field-effect transistors (FETs) are scaled down to the nanometer regime, short-channel effects and doping challenges become increasingly pronounced, hindering their ability to meet the performance standards set by the International Roadmap for Devices and Systems (IRDS). Two-dimensional (2D) semiconductors are of interest for the development of higher performance FET due to their useful properties and all-in-one potentials and 2D materials-based FETs have attracted a large amount of attention. In this work, we propose a new Schottky Barrier FET (SBFET) with a 7.5 nm channel length based on the recently synthetized 2D materials γ-GeSe and studied the electronic properties and device performance by the first-principles quantum transport simulations. It is found that this FET demonstrates a subthreshold swing (SS) of 79 mV dec⁻¹, an on/off current ratio of 3.13 × 10⁴, and an on-current of 1878 μA μm⁻¹ . These metrics not only align with but also surpass IRDS standards, highlighting the γ-GeSe SBFET's ability to mitigate short-channel effects while providing energy-efficient, high-current-drive performance. Its high on-state current, low SS, and substantial on/off ratio establish it as a promising candidate for nanoelectronics, particularly in applications requiring power-sensitive, high-performance 2D transistors.

This paper presents a design strategy for highly compact filters based on ${\lambda _g}/4$ effective localized surface plasmons (ELSPs). Leveraging the robustness of ELSPs to their cross-sectional shapes, the proposed design facilitates easier integration into printed circuit boards (PCBs). However, challenges such as dielectric material stacking and excessive lateral dimensions remain. By employing ${\text{ }}{\lambda _g}/4$ ELSPs, the longitudinal size of the ELSPs-based filters is significantly reduced. Furthermore, embedding the ELSPs directly into the PCB effectively solves the stability problems associated with dielectric material and PCB stacking in conventional dielectric resonator filters, while minimizing the overall filter size. To demonstrate this approach, third-order, fourth-order, and fifth-order ELSPs-based filters were fabricated on a single-layer PCB, achieving center frequencies of 3.6 GHz with fractional bandwidths of 9.3%, 5.1%, and 7.7%, respectively. Experimental results show excellent agreement with simulations. This work provides an ultra-compact filtering solution for next-generation microwave and radio-frequency devices, particularly for applications in 5G and satellite communications.

The organic-inorganic hybrid MAPbI₃ perovskite material has remarkable optoelectronic properties for excellent device performance. However, the poor long-term stability of MAPbI₃ perovskite in light, heat, and humid environments is a major obstacle to commercialization. Degradation of MAPbI₃ and an impairment in non-radiative charge recombination, a major impediment to increasing the stability and efficiency of photovoltaic devices, are made possible by the trap state and surface imperfections between the perovskite and electron transport layer interfaces. Here, the surface defect was healed by 2-amino benzothiazole (2-ABT) (Lewis's base) by activating the heteroatoms of S and N and the amine functional group for defect passivation. In the context of defect passivation, a systematic investigation is conducted on the formation of hydrogen bonds between N–H–I or the coordination between uncoordinated Pb²⁺ and heteroatoms of S and N. The investigations have been done into the optoelectronic properties, chemical interaction, structure, crystal orientation, morphology, and photovoltaic performance characteristics of MAPbI₃ in association with 2-amino benzothiazole surface integration. A high photovoltaic efficiency of 21.5% with improved open circuit voltage (V_oc) and fill factor was demonstrated with the optimum concentration of passivating material (2 mg ml⁻¹ IPA) than the pristine MAPbI₃ PCE of 19.4%. As demonstrated by stability studies, the 2-ABT integrated device outscored the pristine MAPbI₃ device, retaining 87% of its PCE after 500 h.

This paper computationally investigates partial discharges (PDs) in the form of self-sustained gas discharges. It presents two methods for predictive modeling: (1) a new low-fidelity algorithm for the PD inception voltage is introduced. The method is volume-resolved and describes both the strength of the self-sustained Townsend mechanism as well as the conventional streamer (or bulk) mechanism. It also intrinsically computes the inception region, i.e. the region where a first electron also leads to a discharge. (2) We apply a high-fidelity plasma model based on kinetic Monte Carlo, which self-consistently resolves the plasma dynamics during the PD process. The two models are complementary in the sense that the low-fidelity model provides the when and where the PD occurs, while the high-fidelity model resolves the PD process itself, starting from the first electron. Prediction and quantification of the PD processes is provided for four application cases: (1) protrusion-plane gaps, (2) spherical voids, (3) twisted wire pairs, and (4) triple junctions. Validation of the low-fidelity method is done through comparison with published experiments (where available), as well as virtual verification through comparison with the high-fidelity plasma model.

Hollow electrode discharge is commonly utilized across various fields, but the research on hollow electrode discharge plasma jet array and its corresponding anticancer effect remains limited, especially their induced liquid chemistry and biological effects. This study describes the generation of plasma multi-jet through a novel-designed hollow electrode array generator and the anticancer effect of plasma-activated water (PAW) through multi-jet treatment. The rise of O₂ concentration has affected the discharge morphology, electrical characteristics, and gaseous reactive species generation, resulting in differences in the liquid-phase chemical properties of PAW. Among these, the N₂-related gaseous emissive species decrease with the rise of the O₂ ratio, while the O-related species show a first increasing and then decreasing trend. Furthermore, the PAW produced under 0% of O₂ contains more ONOO⁻ and O₂⁻ species, while the PAW generated under 0.3% O₂ contains more H₂O₂ and NO₂⁻ species. On this basis, the PAW generated at a relatively low O₂ percentage (0% and 0.3%) results in a higher inactivation efficiency against cancer cells due to the high concentrated H₂O₂, NO₂⁻, and ONOO⁻/O₂⁻. This study offers insights into the design of plasma generation devices and the preparation of PAW for practical tumor therapy.

This study investigates the horizontal asymmetry of plasma plumes in a pulsed plasma thruster (PPT), focusing on the distribution of electron density and magnetic field strength. Using a triple Langmuir probe, the electron density was measured, revealing a peak density on the right side that was up to 87$\%$ higher than the left side at representative points. Concurrently, magnetic field measurements using a magnetic probe revealed a non-uniform distribution, with the strongest disparities localized near the electrodes during current reversal, exhibiting a 59.11$\%$ higher magnetic field strength in these areas. These magnetic asymmetries were identified as the primary driver of the observed plume canting, influencing the Larmor radius of charged particles and inducing trajectory differences. The experiments demonstrated repeatability errors of 7.43$\%$ for Langmuir probe data and 34.79$\%$ for magnetic probe measurements, confirming the reliability of the results. The findings highlight that plume canting originates from non-uniform Lorentz forces caused by asymmetric magnetic fields near the electrodes. This phenomenon results in a preferential plasma flow direction, leading to risks of component contamination and reduced thruster efficiency. Additionally, plasma backflow was observed traveling at approximately 5 km s⁻¹, occurring approximately 10 µs after the discharge and lasting for 4µs  on both sides of the thruster, further contributing to potential contamination risks. These results underscore the importance of accounting for horizontal asymmetry in PPT designs and suggest that optimizing the magnetic field distribution could improve thruster performance.

A comprehensive solution of the electron kinetics in gas discharges, accounting for dependencies in space, velocity and time, is often unfeasible. Therefore, the electron behavior is frequently coupled to fluid models under one of two assumptions: the local-field approximation (LFA), which equates the electron kinetics to the steady-state calculation with the local and instantaneous value of the reduced electric field; or the local-energy approximation (LEA), in which the rate coefficients and the electron power distribution among different collisional channels depend on the local value of the mean electron energy. In this work, we focus on time-locality to assess the impact of the LFA and LEA assumptions on the calculation of the temporal evolution of the electron kinetics in nanosecond discharges. To do so, we consider an accurate Monte Carlo time-dependent formulation as golden standard. We study electron relaxation in different background gases (air, argon, and mixtures of both) at two pressures (10 and 100 Torr). The LEA generally provides more accurate results than the LFA, with increasing differences at lower pressures, where energy relaxation is slower. The greater accuracy of the LEA comes from the temporal effects introduced by the equation for the mean electron energy, which is absent in the LFA. Opting by the LFA in conditions of slow relaxation can lead to serious degradation of the model results, with errors on the production of excited species up to several tens of percent. Hence, in those scenarios, and when a kinetic approach is not possible, the LEA should be adopted instead of the LFA. The comparison is extended to a two-term time-dependent solver based on a quasi-stationary assumption for the first anisotropy. This method provides a good description of the electron kinetics, except at early times ($\lesssim0.2$ ns) at 10 Torr, where the quasi-stationary assumption becomes inaccurate.

The influence of sputtering parameters on the size distribution of silver (Ag) nanoparticles (NP) synthesized by sputtering onto castor oil and polyethylene glycol (PEG600) was investigated. The sputtered species arriving at the substrate were described in terms of flux and kinetic energy. In both liquids, about 99% of the NPs measured were ⩽5 nm in diameter, with most NPs in the range 1–2 nm and 1–2.5 nm in PEG600 and castor oil, respectively. Overall, larger NPs were obtained in castor oil than in PEG600 (40%–55% and 8%–35% of NPs >2 nm in castor oil and PEG600, respectively). In PEG600, the grey color of the solutions indicated aggregation, already after deposition. The flux variation, ranging from ∼120 to 300 µg·cm⁻²·min⁻¹, did not appear to strongly influence the NP size. Larger proportions of NPs >2 nm seemed primarily triggered by higher kinetic energies, as almost 30% more NPs >2 nm were counted for kinetic energies of 12–18 eV compared to 3–6 eV. The castor oil solutions exhibited an orange color, suggesting no notable aggregation of the NPs. The size distributions were not significantly dependent on flux and kinetic energy, as the proportion of NPs <2 nm varied from 45%–59% for all conditions studied here. This difference in behavior between liquids was attributed to their chemical structures, governing the NP coordination. Hence, limiting the species mobility, the higher coordinating castor oil restricted NP aggregation. While the sputtering parameters influenced the NP size differently depending on the liquid chemistry, their impact on the NP size was overall limited in the deposition parameter range investigated herein.

In this study, plasma activated water (PAW) was prepared by a pin-hole discharge, generating plasma directly in liquids with air flowing into the discharge. Radish (Raphanus sativus) plants were grown in pots filled with soil for 30 d. Pots were divided to 4 variants based on the PAW application: PAW prepared from distilled water (PAW DW), PAW prepared from tap water (PAW TW), foliar application of PAW on leaves and irrigated by TW (TW/PAW DW) and control group irrigated by TW. Results have indicated enhancement of the growth of the plant fresh matter in all variants treated by PAW. Vitality of the plants was determined by chlorophyll fluorescence. Fluorescence measurement results have shown inhibition of photosynthesis activity in case of plants treated with PAW compared to control group (TW), which means the treatment of plants with PAW lowers the overall vitality. Elemental analysis results showed that the PAW treatment of plants increased the content of nitrogen in the root part of the radish plants. The sensory evaluation showed that the PAW treatment influenced a certain taste and aesthetic characteristics of R. sativus. Overall, the foliar application of PAW seems to be more convenient option as a plant fertilizer compared to the soil irrigation.

In response to the increasing demand for environmentally sustainable alternatives to SF₆ gas in arc-quenching applications, comparative studies are performed in the present work to explore the arc-quenching performance of a novel eco-friendly gas mixture composed of C₄F₇N, CO₂ and O₂. Through a combination of experimental studies and numerical modelling, the arc dynamic characteristics are firstly evaluated for ternary C₄F₇N/CO₂/O₂ gas mixtures with different mixing ratios. The results demonstrate that the variations in the volume concentrations of C₄F₇N and O₂ only have an insignificant influence on the arc performance, which is attributed to their similar thermophysical properties. Under the same operation conditions, the flow field distributions of the C₄F₇N/CO₂/O₂ gas mixture differ from those of SF₆ and lead to a noticeable gap in its arc-quenching performance in comparison with SF₆. Further analysis is performed on the effects of gas-filling pressure to assess whether the performance of C₄F₇N/CO₂/O₂ gas mixture can be improved or not. Our findings suggest that a 6% C₄F₇N/84% CO₂/10% O₂ gas mixture, when used at a higher filling pressure, is a more optimal choice. Finally, the decomposition characteristics of the C₄F₇N/CO₂/O₂ gas mixture are compared to support the evaluation of its arc-quenching performance.

Negative ion production is of significant interest for materials processing and neutral beam injection systems for magnetic confinement fusion reactors. The surface production mechanism can be required for high current applications. Dielectric materials, including doped diamond, are of interest for increasing surface production as a potential alternative to low-work function metals and further understanding of the underpinning mechanisms is needed. In this study we use photoemission yield spectroscopy, in conjunction with the Fowler model and mass spectrometry, to measure the negative ion yield and ionization threshold of micro-crystalline diamond (µc-D), micro-crystalline boron doped diamond (µc-BDD) and single crystal phosphorus doped diamond (PDD) under deuterium plasma exposure at sample temperatures between 30 ^∘C and 700 ^∘C. We observe that deuterium plasma exposure of PDD at 400 ^∘C reduces its ionization threshold from approximately 4.0 eV to 2.1 eV, which is similar to the work function of cesium. While the ionization threshold of diamond is observed to be sensitive to sample temperature and the dopant used, this appears to have negligible effect on negative ion production. Developing a better understanding of which material properties are most significant for negative ion production will assist the development of improved negative ion sources.

The insulating polymer with high electrical properties is demanded for the high voltage direct current (HVDC) transmission. Regulating the aggregation structure of the insulating polymer is an effective strategy to improve its electrical properties. In this paper, the effects of the DC assisted electric field on the aggregation structure and electrical properties of low-density polyethylene (LDPE), a typical insulating polymer, were investigated. The LDPE treated with the assisted electric field of 0, 0.1, 0.3, 0.5, 1.0 and 2.0 kV mm⁻¹ were prepared, respectively. Aggregation structure, conductivity, breakdown strength and surface potential decay were characterized. The experimental results show that the assisted electric field is helpful for the increase in spherulite amount and for the reduction in spherulite size, which leads to more deep traps to improve the electrical properties. With the increase in the assisted electric field, the conductivity decreases at first and then increases, whereas the breakdown strength is just the opposite. It is worth noting that the LDPE treated with the assisted electric field of 0.5 kV mm⁻¹ has the lowest conductivity and the highest breakdown strength. This work provides a guideline for the design of electrical insulating polymers.

Two-dimensional (2D) van der Waals heterostructures (vdWHs) incorporating ferroelectric properties and Rashba effects hold attractive applications in spintronics. In this work, the 2D α-tellurene and typical piezoelectric α-In₂Se₃ are selected to form the bilayer α-tellurene/α-In₂Se₃ (Te/In₂Se₃) vdWHs and the novel electronic, optical and spin characteristics are explored utilizing the first-principles calculations. We show that, firstly, the Te/In₂Se₃ vdWH exhibits semiconductor nature as well as the super strong optical absorption characteristics in the visible region. Then, the pronounced spin–orbit coupling effect is revealed, which results from the heterostructure disrupting the symmetries of the individual monolayers. Furthermore, reversing the direction of ferroelectric polarization for the In₂Se₃ monolayer can transform the Te/In₂Se₃ vdWH between type-I and type-II heterostructures, also tuning the Rashba effect. And such electronic properties and Rashba effect can be tailored by strain and electric field. Our proposed Te/In₂Se₃ vdWH will be potential candidate for applications in nanodevices, especially spin-field effect transistors.

Developing dielectric capacitors with high power-density, fast charge-discharge rates and excellent temperature stability has become a key component of advanced pulsed power electronic systems. Here, lead-free (1−x)(Sr_0.7Ba_0.255Ca_0.045Ti_0.9Zr_0.1O₃)-xBi_0.5Na_0.5TiO₃ ceramics were designed and prepared to improve the energy storage performance via multiple synergistic strategy. On the one hand, the disordered distribution of multiple ions at perovskite A and B sites increases the molar configurational entropy and thus enhances the degree of phase transition relaxation and the breakdown electric field. On the other hand, the coexistence of rhombohedral (R), tetragonal (T) and cubic (C) phases can not only provide more polarization rotation pathways but also hinder the grain and domain growth. In addition, the introduction of Bi³⁺ ions with 6 s lone-pair electrons can increase the polarization. As a result, high recoverable energy storage (W_rec) of 4.29 J cm⁻³ and efficiency (η) of 90.1% were realized in the ceramic with x = 0.4 at a moderate electric field of 404 kV cm⁻¹. Moreover, the ceramic exhibited superior temperature stability across a broad temperature range up to 140 °C and outstanding fatigue resistance up to 10⁶ cycles.

The adhesion/friction interplay continues to be an enigma when soft matter is involved. By utilizing a simple two-stage (loading and then unloading) mixed-type (normal and tangential) indentation testing of a transparent layer of adhesive rubber-like gel material, the normal and tangential contact forces acting on a rigid spherical probe are monitored along with the in situ variation of the apparent contact area between the probe and the layer surface. Whereas the force/area relations for the oblique loading and normal unloading do almost coincide, as seen with the naked eye, the postpredictive analysis reveals a drastic difference in variation of the apparent work of adhesion in the concord to fluctuations of the friction force. Each of the interface slips such exposed starts with simultaneous minimum and maximum values of the normal and tangential force sensors, respectively, and proceeds with a non-monotonic variation of the contact area, indicating adhesive reattachment. The occurrence of sliding instabilities upon unloading is supported by the on-the-spot observations of the contact area.

This article introduces a new type of graphene-based perfect absorber that features tunability across four wave peaks and high sensitivity, consisting of Ag–SiO₂–graphene. By controlling the Fermi level and relaxation time of graphene, the tunability of the absorber is achieved, and by changing the refractive index of SiO₂, the selectivity of the resonant wavelength is realized. The results show that the absorber has an average absorption rate of 98.54% at four wavelengths: 2092.24 nm, 2180.67 nm, 2230.08 nm, and 2336.17 nm. The electric field distribution intensity is simulated to verify whether it meets the impedance matching theory, exploring the physical mechanism behind the high absorption rates at these four peaks. Different polarizations and inclined incidence angles are investigated to explore the absorber's insensitivity to polarization, demonstrating excellent insensitivity within an inclination angle range from 0° to 65°. The sensitivities of the four peaks are 501.54 nm RIU⁻¹, 565.76 nm RIU⁻¹, 605.47 nm RIU⁻¹, and 582.70 nm RIU⁻¹, respectively. Finally, the practical application of the absorber in detecting aqueous solutions of 10%, 20%, 25% glucose solutions, and 30%, 50% sugar solutions is simulated, and the results show that the absorber has good sensing performance. This paper's absorber features four-peak perfect absorption and excellent tilt insensitivity, good refractive index sensitivity, and holds great potential applications in detectors and optical communication systems.

Metal-oxide interactions are pivotal for the functionality of supported-metal catalysts. In this work, x-ray photoelectron spectroscopy and scanning tunneling microscopy (STM) are employed to study the interface reaction between Ti metal and crystalline Cu₂O/Pt(111) films. Already at room-temperature, deposited Ti spontaneously oxidizes to predominately +4 and +2 charge states at low and high coverage, respectively. The electron transfer is accompanied by oxygen migration towards the Ti ad-layer, whereby Cu₂O gradually reduces to Cu and Ti converts to TiO₂. The process gets reinforced by heating the system to 450 K. The local nature of the interface reaction is derived from STM conductance spectroscopy. At low Ti load, electron transfer out of the ad-layer leads to a downward bending of the Cu₂O electronic bands. With increasing coverage, the band bending ceases and formation of a Cu_xO/TiO_x hetero-junction is revealed in the spectra. The signature of metallic ad-particles is only detected at high Ti load, when electron tunneling into Ti deposits bound to the oxide spacer leads to Coulomb-charging effects. The observed strength of the redox reaction at the Ti/Cu₂O interface impressively demonstrates the high reductive power of titanium.

This study evaluates the erosion resistance and thermal stability of Cu/W–La₂O₃ composite electrodes exposed to plasma arc conditions in ambient air. Through comparative analysis with pure copper and W–La₂O₃ electrodes, it was found that the Cu/W–La₂O₃ composites exhibit superior erosion resistance, with a notably advantageous negative erosion rate due to a self-formed oxide layer that mitigates surface degradation. Detailed microstructural characterization revealed that this oxide layer, primarily consisting of copper tungstates and lanthanum tungstates, enhances electrode durability by reducing oxidation rates and improving heat dissipation. This adaptive surface layer also contributes to a more stable arc, effectively minimizing material loss, particularly at higher current intensities where pure copper electrodes experience rapid thermal and oxidative degradation. The findings suggest that Cu/W–La₂O₃ composites, with their negative erosion rates, offer significant benefits for air plasma torches, making them promising candidates for applications demanding high-performance and long-lasting electrodes in oxidizing environments.

Amorphous oxide thin films are crucial materials for micro- and nanoelectronics device fabrication and have frequently been employed as a component of device stacks (e.g. gate dielectrics), as well as hard masks for lithography and protective layers for ion etching. In this work, we report thin films of $a$-SiO_x deposited on Si substrates using reactive magnetron sputtering techniques. By adjusting the oxygen content and silicon magnetron power during the deposition process we found that it is possible to obtain films with a density up to 7% lower and up to 25% higher compared to the bulk counterpart (ρ = 2.20 g cm⁻³). Through first-principles density functional theory simulations, we investigated the formation of native point defects in amorphous silicon dioxide ($a$-SiO₂). Radial distribution function analysis of defective $a$-SiO₂ revealed substantial changes in the structural properties due to defect formation. We thus provide an atomistic explanation and understanding for the significant variation in mass density and correlate it with the different point defect formations that occur under varying deposition conditions.

Separation is a crucial step in the analysis of living microparticles. In particular, the selective microseparation of phytoplankton by size and shape remains an open problem, even though these criteria are essential for their gender and/or species identification. However, microseparation devices necessitate physical membranes which complicate their fabrication, reduce the sample flow rate and can cause unwanted particle clogging. Recent advances in microfabrication such as High Precision Capillary Printing allow to rapidly build electrode patterns over wide areas. In this study, we introduce a new concept of membrane-less dielectrophoretic (DEP) microseparation suitable for large scale microfabrication processes. The proposed design involves two pairs of interdigitated electrodes at the top and the bottom of a microfluidic channel. We use finite-element calculations to analyse how the DEP force field throughout the channel, as well as the resulting trajectories of particles depend on the geometry of the system, on the physical properties of the particles and suspending medium and on the imposed voltage and flow rates. We numerically show that in the negative DEP regime, particles are focused in the channel mid-planes and that virtual pillars array leads either to their trapping at specific stagnation points, or to their focusing along specific lines, depending on their DEP mobility. Simulations allow to understand how particles can be captured and to quantify the particle separation conditions by introducing a critical DEP mobility. We further illustrate the principle of membrane-less DEP microseparation using the proposed setup, by considering the separation of a binary mixture of polystyrene particles with different diameters, and validate it experimentally.

This study provides an in-depth analysis on the electronic properties of CuInP₂S₆/MoSSe (CIPS/MoSSe) heterojunctions under the conditions of spontaneous polarization reversal and mechanical strain based on first-principles calculations. The results indicated that the polarization of the heterojunctions range from 45.82 μC cm⁻² for CIPS↑/MoSSe↑ to 46.53 μc cm⁻² for CIPS↓/MoSSe↓, with the bandgap varying from 1.23 eV to 0.19 eV. Furthermore, the CIPS↑/MoSSe↓ heterojunctions maintain a type II band alignment in the range of −6% to 6% in plane strain and ±0.3 Å layer spacing variations. In addition, Moreover, the power conversion efficiency of heterojunctions increased from 4.5% to 19.3% under external strain. The polarity configurations, mechanical strain and layer spacing affect the cation displacement and charge redistribution, providing building blocks for the design of novel heterojunctions with tailored polarization and electronic properties.

Under DC voltage, space charge inevitably accumulates within the spacer, thereby influencing the dissipation of surface charges. In this study, a charge measurement platform for epoxy resin spacers is constructed. The temporal variation of the surface charge distribution under space charges is compared. The results indicate that homopolar space charges enhance the surface charge dissipation. This is because about 95% of the total dissipation charge depends on the recombination of surface charges with heteropolar charged particles in the air. The homopolar space charge inside the spacer augments the normal electric field intensity in the gas side, facilitating the surface charge dissipation. It is inferred that the effect of the space charge inside the spacer should be considered when measuring the surface charge after disconnecting the operation voltage. This study provides important theoretical support for revealing the decay characteristic of surface charge on the spacer.