Abstract Optically pumped rare gas lasers (OPRGLs) are recognized as a promising candidate for high-energy laser systems, benefiting from excellent beam quality and chemically inert gain media. Power scaling of OPRGLs imposes two simultaneous requirements, namely high number density of metastable rare gas atoms and a large-volume uniform gain medium. However, previous single-mode discharge schemes suffer from an inherent trade-off between these two targets. Nanosecond-pulsed direct current (DC) discharges yield high metastable densities but suffer from filamentation at large electrode areas, while radio-frequency (RF) discharges produce diffuse large-volume plasmas but deliver insufficient metastable densities for efficient lasing. Nanosecond-pulsed DC/RF hybrid discharges provide a potential route to alleviate this trade-off, but no time-dependent kinetic model has yet been developed for OPRGLs in the hybrid discharge to quantify their laser performance. In this work, a time-dependent kinetic model is developed for an optically pumped metastable argon laser in a nanosecond-pulsed DC/RF hybrid discharge. Numerical results indicate that the hybrid discharge scheme reduces the threshold repetition rate for quasi-continuous-wave operation. At a discharge repetition rate of 50 kHz, the hybrid discharge scheme increases the cycle-averaged laser power by 17%–20% at low pump intensity, and achieves an approximately 40% enhancement in average laser intensity at a high pump intensity of 20 kW cm −2 . The sub-breakdown RF field elevates the afterglow electron temperature and enhances collisional energy transfer from Ar(1s 4 ) to Ar(1s 5 ), extending the high-metastable-density time window and optimizing the Ar(1s 5 )/Ar(1s 4 ) population ratio. The effects of RF peak voltage and timing parameters are analyzed, and an optimal timing configuration is determined.
Abstract Models based on plasma physics are becoming increasingly relevant in electrical engineering for the simulation of partial discharges (PDs). This phenomenon is the inception of small-scale electrical discharges that cause ageing and degradation of insulating materials in power networks. In recent years, electrical treeing has also been simulated. Treeing is a complex interplay between PDs and the propagation of internal defects in dielectric materials. These studies highlight the need to evaluate the accuracy of classical continuous low-temperature weakly ionized plasma models at very high electric fields of the order of 100 MV m − 1 or even higher. In this work, we show that continuous plasma models can fail in these conditions, even for relatively simple geometries. The model becomes unstable and predicts unbounded electron and ion concentrations. We analyze the physical mechanism underlying this behavior and introduce a proper electron multi-group approach to address this issue. We show that our approach is capable of producing stable and bounded solutions with an improved accuracy.
Abstract Colloidal semiconductor quantum dots (QDs) enable tuneable emission via the quantum size effect, yet their emission is limited by non-radiative Auger recombination. Although metal nanostructures supporting surface plasmons provide a pathway for emission enhancement, the resulting QD emission typically remains broad. Here, we demonstrate narrow-band tuneable emission of CdSe/ZnS QDs by exploiting high-order resonant cavity modes of plasmonic nanorod arrays. An optimised PMMA spacer between the QDs and the plasmonic nanorod arrays maximises the emission enhancement. By varying the resonant cavity modes of the plasmonic nanorod arrays, discrete narrow-band emission peaks are obtained at 646, 652, 657, 662, and 670 nm, with linewidths narrowed to 5–6 nm. This approach offers a promising route for high-performance, tuneable light-emitting devices.
Abstract We investigate the in-plane magneto-optical conductivity (MOC) of Floquet-driven Weyl semimetal (WSM) slabs in an exponentially decaying nonuniform magnetic field. Circularly polarized light induces helicity-dependent band renormalization and drives transitions between WSM and gapped trivial phases. Using a spinor-resolved projection, we derive a finite set of guiding-center-dependent Landau levels (LLs) that recovers the exact uniform-field spectrum in the corresponding limit. Within the Kubo formalism, we find that adjacent-LL transitions remain dominant, while nonuniform magnetic confinement activates weaker nonadjacent channels. Pauli blocking at zero temperature produces characteristic half-peak features. The penetration length, magnetic field, and Floquet dressing modify the LL spectrum and optical matrix elements, whereas carrier density and temperature primarily control the occupation of optically active states. These results clarify the combined effects of Floquet dressing and nonuniform magnetic confinement on the MOC of WSM slabs.
Abstract Multimode interference (MMI) fiber sensors with singlemode–multimode–singlemode (SMS) structures based on no-core multimode fiber (NC-MMF), have been widely employed for refractive index (RI) sensing of liquid samples due to their simplicity, low cost, and high sensitivity to changes in the immersion medium. In this work, we investigate the temperature-dependent spectral response of an SMS/MMI fiber sensor immersed in aqueous solutions with closely similar RI. Aqueous solutions of tris(hydroxymethyl)aminomethane (Tris), urea, and fructose were selected as model analytes because they exhibit nearly indistinguishable RI properties under conventional room-temperature conditions. The thermo-optic response of the sensor was studied by performing controlled temperature sweeps from 25 °C to 45 °C. Experimental results reveal that, although the three solutions produce comparable concentration-dependent refractometric responses, they exhibit distinct nonlinear temperature-dependent spectral shifts. To explain this behavior, a numerical model based on MMI theory was developed, showing that the observed nonlinearities arise from the intrinsic nonlinear dependence of the MMI peak wavelength on the RI of the immersion medium. Consequently, small thermo-optic variations in the liquid samples are transformed into measurable nonlinear spectral signatures. The results demonstrate that SMS/MMI fiber sensors can provide access to thermo-optic information that is not available through conventional single temperature refractometry. The proposed approach highlights the potential of MMI devices as simple optical platforms for thermo-optic characterization of aqueous media and for the study of temperature-dependent optical properties in liquid samples with closely similar RI.
Abstract Composition engineering modifies local ligand fields, orbital hybridization, and crystal symmetry, providing a route to tailor the band topology of two-dimensional magnetic materials. Here, we apply this approach to the VCl 3 − x Br x monolayer system using first-principles density-functional theory. The pristine end members VCl 3 ( x = 0 ) and VBr 3 ( x = 3 ) preserve lattice inversion symmetry ( D 3 d ) and exhibit no gapless edge states, whereas the Janus VCl 1.5 Br 1.5 structure ( x = 1.5 ) lowers the symmetry to C 3 v , and the asymmetric Cl/Br ligand field drives band inversion which together with ferromagnetic time-reversal symmetry breaking, gives rise to a quantum anomalous Hall (QAH) with Chern number C = 1 and chiral edge states within the valence band. Monte Carlo simulations parameterized by a b i n i t i o exchange couplings predict a Curie temperature T c ≈ 29 K. Crucially, representative hole doping of 0.4 holes per unit cell brings the Fermi level closer to the nontrivial gap. The topological band characteristics remain preserved, suggesting a possible route toward the QAH regime through electrostatic tuning. In contrast, random-like alloy configurations at the same nominal compositions fail to sufficiently break lattice symmetry, yielding only tunable anomalous Hall conductivity without quantization. These results demonstrate an ordering-dependent modulation of band topology in VCl 3 − x Br x monolayers and identify the ordered Janus phase as a metastable theoretical candidate.
Abstract In this work, the effects of He + ion fluence and implantation temperature on strain, damage, and the bandgap energy of LiNbO 3 crystals were studied. High-resolution transmission electron microscopy (HRTEM) was used to observe the defect morphology in the damage layer. Secondary ion mass spectrometry (SIMS) was applied to investigate the He distribution at different implantation temperatures. High-resolution x-ray diffraction (HRXRD) were utilized to analyze the distribution of damage and elastic strain in the implantation damage layers. At an identical ion fluence, the extent of damage and strain within the LN thin-film region decreases with increasing implantation temperature. In stark contrast, the damage and strain in the damage-layer region exhibit an opposite trend, increasing monotonically with rising implantation temperature. The transmission and absorption spectra of the ion-implanted samples were investigated, and bandgap shrinkage was observed with increasing ion fluence and temperature. Systematic exploration of helium-ion implantation into LiNbO 3 provides insights into optimizing implantation conditions for high-quality lithium-niobate-on-insulator (LNOI) fabrication.
Abstract Pulse-controlled atmospheric-pressure streamer discharges generate reactive oxygen and nitrogen species, and for many applications it is the O/N balance, not the amount of a single radical, that governs the outcome. Building on our previous study, which varied the voltage waveform at fixed gas composition, we examine how the N₂:O₂ ratio reshapes prompt O and N radical production. We performed 258 two-dimensional fluid simulations of a needle-to-plane streamer in dry N₂:O₂ = (100 − x):x mixtures (x = 20, 40, 60, 80%), independently varying the peak voltage (15–40 kV), rise time and pulse width with our previous fluid model. As the oxygen fraction rises, the deposited energy falls while the O-production efficiency increases; these partly offset, so at fixed peak voltage the O-atom yield declines only modestly (≈ 1.4-fold) whereas the N-atom yield falls sharply (≈ 3.6-fold) and the O/N selectivity rises roughly two-fold. A two-stage description, in which electron attachment first reduces the deposited energy and the yield is then proportional to that energy with a composition-dependent efficiency, organises these trends through the established oxygen-attachment mechanism, which suppresses the nitrogen channel mainly by N₂ dilution (≈ 90% of the logarithmic N-source decrease) with a smaller reduced-field contribution. A variance decomposition over all 258 cases attributes 96% of the variance in O-atom yield to Vmax and 80% of that in O/N selectivity to composition, so to a useful approximation the peak voltage sets the amount of O production and the composition the O/N selectivity. The two axes are not fully separable: the nitrogen yield is jointly controlled and the O/N ratio keeps a residual voltage dependence, but the simulations still provide a control map linking gas composition and voltage waveform to the radical output for this dry single-filament regime.
Abstract The O3 generation in the atmospheric air or O2 plasmas poses a significant hindrance to the design and development of atmospheric plasma devices for the preparation of plasma activated water (PAW), which are operated not in a sealed chamber. In this study, water is activated by N2-based instead of O2-based spark discharge over water to generate PAW at atmospheric pressure. Our analysis shows that the biological reactivity of N2 non-thermal plasma activated water (N2-PAW) is much higher than the one of O2 non-thermal plasma activated water (O2-PAW). The E. coli with their concentration of 1.8106 CFU/mL are completely inactivated in N2-PAW after the plasma treatment time of ≥40 s. The short-lived species such as OH, N, H, N2+, OH+, H2O+, and H- can be formed due to the collisions of N2 and H2O with electrons in the N2 spark discharge over water, and they are important intermediates for the subsequent gas-phase reactions and the dissolution of reactive nitrogen species. Fourier transform infrared spectrometer (FTIR) analysis shows that no O3 is detectable in the gas-phase N2 spark discharge over water. Our LC-MS measurements show that the functional groups in the side chains of amino acids such as -SS-, -SH, and aromatic rings are either oxidized, hydroxylated or nitrated in N2-PAW, which constitutes permanent chemical modifications of amino acids in proteins. The tertiary and quaternary structures of proteins in E. coli can be seriously destroyed in N2-PAW, where hydrophobic interactions, supplemented by auxiliary forces such as hydrogen bonds, salt bridges (ionic bonds), van der Waals forces, disulfide bonds, and ester bonds get unstable due to their interactions with aqueous RNS under weakly acidic conditions.
Abstract Topological semimetals (TSMs) have attracted significant attention for interconnect applications due to their unusually low electrical resistivity at reduced length scales. Despite this potential, TSM candidates for interconnect applications remain very scarce. Herein, we investigate the electrical resistivity of the TSM family MoP and XMoP (X = Hf, Zr, Ru) using a combination of density functional theory and semiclassical Boltzmann transport theory. At low temperatures, MoP-based TSMs exhibit chemically tunable and extremely low electrical resistivity and yield large residual resistivity ratios that rank among the highest reported for interconnect materials, exceeding those of state-of-the-art copper by more than two orders of magnitude. Being the most promising candidate, we demonstrate that MoP nanowires in the ultrathin regime exhibit a typical resistivity scaling attribute of TSMs. Analysis of scattering mechanisms indicates that acoustic phonons dominate the electron-phonon scattering. Despite higher scattering rates in ultrathin nanowires, bulk MoP exhibits lower resistivity due to its higher electronic group velocities. Our results identify the XMoP family as promising candidates for interconnect applications and clarify the microscopic origin of resistivity scaling in ultrathin TSM nanowires.
Abstract We investigate angular-momentum transfer efficiencies in hybrid Rb-Cs- 129 Xe vapor cells with different alkali compositions. Experiments were performed at a pump power of 40mW and a cell temperature of 110℃, where the Rb-Cs spin-exchange rate is comparable to the alkali electron-spin relaxation rate and complete spin-temperature equilibrium is not established. Using Rb-rich cells under Cs pumping and Cs-rich cells under Rb pumping, we measured the steady-state 129 Xe polarization and build-up time and determined the corresponding spin-exchange and photon efficiencies. Within each cell series, both efficiencies exhibit systematic composition-dependent trends arising from the combined effects of optical pumping, incomplete Rb-Cs polarization transfer, alkali relaxation, and alkali-Xe spin exchange. The Rb-Cs polarization-transfer factor converts the nominal alkali density ratio into an effective polarization-weighted ratio, which governs the relative contributions of the Rb-Xe and Cs-Xe spin-exchange channels. These results clarify angular-momentum transfer in hybrid Rb-Cs- 129 Xe systems and provide guidance for optimizing low-power hybrid spin-exchange optical pumping and alkali--noble-gas sensor platforms.
Abstract Hollow cathodes are indispensable electron sources in electric propulsion systems, and their operational stability and lifetime are strongly influenced by plume discharge instabilities and energetic-ion bombardment. Under ion-acoustic-wave-induced unstable operating conditions, enhanced plasma oscillations can lead to excessive emitter erosion, increased plume noise, distorted ion energy distributions, and severe sputtering of the keeper and orifice, thereby degrading thrust stability and limiting the service life of electric thrusters. Although extensive experimental and numerical studies have been conducted, the physical mechanisms linking ion acoustic turbulence, discharge instability, anomalous electron transport, and energetic-ion generation remain incompletely understood. This review systematically summarizes recent advances in experimental diagnostics and numerical simulations of hollow cathode plume instabilities under ion-acoustic oscillations. Experimental diagnostic techniques, including emissive probes, ion saturation probes, high-speed imaging, Thomson scattering, retarding potential analyzer, electrostatic energy analyzer, and laser-induced fluorescence, are critically reviewed with emphasis on their measurement principles, applicability, advantages, limitations, and complementary capabilities. Furthermore, fluid, particle-in-cell (PIC), hybrid-PIC, and kinetic models are comparatively analyzed in terms of physical assumptions, applicable plasma regimes, predictive accuracy, and agreement with experimental observations. Particular attention is devoted to the treatment of anomalous collisions and wave–particle interactions responsible for energetic-ion acceleration. Beyond summarizing previous studies, this review identifies common bottlenecks in experimental diagnostics and numerical simulations, analyzes the physical origins of discrepancies across numerical approaches, and discusses future research priorities, including synchronized non-invasive diagnostics, multiscale self-consistent simulations, and lifetime-oriented hollow cathode design. A unified framework linking ion acoustic turbulence, discharge instability, energetic-ion generation, and cathode erosion is established, guiding the development of next-generation long-life electric propulsion systems.
Abstract Nanosecond pulsed electric fields (nsPEFs) enable non-thermal and precise ablation, holding promising potential for fertility-sparing treatment of endometrial cancer. While biological impedance can be used as a physical marker to predict nsPEFs efficacy, the reliability of single-impedance monitoring needs improvement because pulse parameters influence the mapping between impedance and ablation effects. In this study, we systematically investigated the effects of key pulse parameters—including amplitude, pulse width (PW), inter- and intra-train pulse numbers (N1=20-120; N2=5-50), and their respective pulse repetition frequencies (f1=1-6 Hz and f2=0.2-1.2 kHz)—on biological impedance and ablation outcomes (ablation area and temperature) in Hec-1B cells. An optimized ablation prediction model integrating pulse parameter influence factors was then developed based on equivalent impedance variation to improve prediction accuracy. Experimental findings demonstrate that, for a given impedance change ratio (η ~8.6%), altering the pulse parameters (pulse width and amplitude) led to a nearly 1.5-fold variation in the ablation area (8.3 vs. 5.94 mm²). Validation in Ishikawa cells, a well-differentiated endometrial cancer cell line, confirmed the robust performance of the proposed model, which reduced the prediction error of ablation effects from 20.36% to 9.5%. Furthermore, validation in potato tissues showed that incorporating pulse parameters decreases the prediction error from 22.4% to 10.1%. This work offers theoretical and experimental support for the adaptive regulation of pulse parameters.
Abstract Polycrystalline vanadium nitride (VN) thin films with competitive superconducting transition temperature were achieved by a chemical solution deposition route. The VN thin films annealed at 850 °C, 900 °C and 950 °C show normal-state resistivity that decreases with decreasing measured temperature and undergo a superconducting transition with values between 6.9 and 8.4 K. Among the three VN thin films, the VN thin film annealed at 900 °C shows the highest superconducting transition temperature ( T C ), lowest transition width ( Δ T C ), lowest normal-state resistivity ( ρ n ), and highest residual resistivity ratio. X-ray photoelectron spectroscopy results reveal that the annealing temperature of 900 °C promotes the highest degree of nitridation, which correlates well with the observed improvement in superconductivity. This work demonstrates an easily realized solution-based process route for preparing polycrystalline superconducting VN thin films.
Abstract Hollow cathode discharge features a higher electron energy spectrum with a certain degree of tunability, making it more effective for exciting gas media, thus providing some advantages in producing metastable rare gas atoms. In this study, based on the spectral lines at 823.16 nm (6p[3/2] 2 → 6 s[3/2] 2 ) and 828.01 nm (6p[1/2] 0 → 6 s[3/2] 1 ), we investigate the kinetic processes involved in the generation of metastable Xe atoms in hollow cathode discharge. It has been speculated that the ‘electron-impact excitation + radiation’ process may dominate the production of metastable 6 s[3/2] 2 level Xe atoms, while the impact of the ‘ion-electron recombination’ process is extremely weak. Based on the temporal evolution of the spectral intensity at 823.16 nm, we obtained the total collisional decay rate constant k col for the 6p[3/2] 2 level as (2.10 ± 0.16)× 10 −11 cm 3 s −1 , and the total radiative decay rate k rad as (0.56 ± 0.02) ×10 7 s −1 , speculating that highly excited Xe atoms can replenish the number of particles in the 6p[3/2] 2 level through collision and radiation processes. The total decay rate of the intensity of the 828.01 nm spectral line exhibits an inflection point with increasing pressure, it is speculated that a fast process may be dominated by the near-resonance energy transfer pathway 5d[7/2] 4 → 6p[1/2] 0 → 5d[1/2] 1 , as well as a slow process governed by the collisions of ground state and highly excited Xe atoms, and electrons affecting the 6p[1/2] 0 level. In the pressure range of 100–300 Pa, these two processes exhibit opposing collisional decay dynamic parameters. In the pressure range of 300–700 Pa, the corresponding energy transfer process and collision process probably approach the equilibrium state.
Abstract Flexible electrochromic devices (ECDs) face significant challenges in simultaneously achieving high optoelectronic performance and robust mechanical flexibility. Herein, we propose a strategy employing dual aluminum-containing layers to synergistically enhance both the electrochemical functionality and mechanical durability of nickel oxide (NiO) thin films. First, Al 3+ doping into the NiO lattice (denoted as Al–NiO) substantially improves the electrochromic properties, yielding an optical modulation (Δ T ) of 40.2% at 550 nm. This represents a 44.1% enhancement relative to that of pure NiO (Δ T = 27.9%). The performance improvement is attributed to grain refinement, an increased Ni 3+ /Ni 2+ ratio, and a higher concentration of oxygen vacancies, which collectively promote charge transfer and ion diffusion kinetics. Second, the introduction of a 30 nm thick Al 2 O 3 buffer layer between the PET-ITO substrate and the Al–NiO film dramatically improves mechanical flexibility. The resulting Al 2 O 3 /Al–NiO heterostructure withstands over 2000 bending cycles (with a radius of 4 mm) without performance degradation, whereas the unbuffered film fails after only 200 cycles. The Al 2 O 3 layer serves dual functions: it acts as a chemical passivation barrier to suppress interfacial side reactions and as a physical stress-relief interlayer to effectively dissipate bending-induced strain. Furthermore, a complete flexible ECD fabricated with the Al 2 O 3 /Al–NiO anode and a WO 3 cathode demonstrates a high initial Δ T of 42.4% at 550 nm and exceptional cycling stability, maintaining 41.4% Δ T after 5000 cycles—a degradation of merely 2.3%. This work establishes a generic interface-bulk cooperative design strategy for developing durable, high-performance flexible optoelectronic devices.
Abstract Although sulfur hexafluoride (SF 6 ) is widely used in high-voltage power equipment due to its excellent arc quenching performance, its extremely high global warming potential (GWP) has motivated the search for environmentally friendly alternatives. The design of such alternative gases requires the simultaneous optimization of arc quenching performance, environmental impact, and operational constraints such as liquefaction temperature, leading to a highly coupled and constrained multi-objective optimization problem. To address this challenge, a surrogate-assisted multi-objective optimization framework is proposed by integrating Deep Operator Networks (DeepONet) with decomposition-based, preference-conditioned reinforcement learning. Specifically, an Arc-DeepONet model is developed to efficiently predict arc temperature fields and extract thermal and pre-dielectric recovery characteristics, while a dielectric recovery DeepONet is constructed to evaluate post-arc dielectric recovery performance. Based on these surrogate models, a three-objective constrained optimization problem is formulated in the gas composition-pressure space under GWP and liquefaction temperature constraints. To enable flexible decision-making under different engineering requirements, preference vectors are introduced to encode trade-offs among objectives, and a shared scoring network is trained to directly recommend feasible solutions conditioned on given preferences. Taking the C 4 F 7 N–CO 2 mixture as a representative case, the proposed framework achieves an exact hit rate of 0.965 with a mean regret of 1.738 × 10 −4 over 200 unseen preference vectors under the GWP constraint. When both GWP and liquefaction temperature constraints are imposed, the exact hit rate further improves to 0.986, while the mean regret remains on the order of 10 −4 . In both cases, the Pareto precision remains 1.0. Furthermore, a balanced operating region is identified under dual constraints, corresponding to a C 4 F 7 N fraction of 10.5%–11.5% and an operating pressure of 0.65 MPa-0.71 MPa. Once trained, the proposed framework enables rapid generation of high-quality solutions for arbitrary preferences with significantly reduced computational cost. These results demonstrate that the method provides an efficient, reliable, and physically consistent approach for the design and screening of environmentally friendly SF 6 alternative gases.
Abstract Intravascular lithotripsy (IVL) has significantly improved stent delivery success rates and clinical outcomes in patients with severely calcified coronary artery disease. However, existing experimental methods cannot directly characterize the microsecond-scale stress evolution induced by shock wave propagation in multi-layered calcified coronary arteries. To address this, we developed a two-dimensional axisymmetric finite element model for multi-medium shock wave propagation, comprising the fluid domain, the three-layer anisotropic hyperelastic arterial wall, the linear elastic calcified plaque, and the hyperelastic semi-compliant balloon. Using this framework, shock waveforms with varying amplitudes and pulse profiles were applied to evaluate the effects of shock wave parameters on mechanical responses within the calcified plaque and vessel wall. Results reveal that shock wave propagation generates complex mechanical responses within calcified plaques, including compressive stress concentration, shear stress localization, tensile stress concentration, and wave-induced dynamic squeezing effects. The tensile stress response was influenced by the temporal characteristics of the shock waveform and transient stress wave propagation within the calcification. Parametric analysis indicates that a more rapidly varying compressive phase profile is associated with earlier and more localized stress concentration within calcification but may also increase mechanical loading on surrounding vascular tissues. The present model adopts an idealized axisymmetric geometry and a linear acoustic–structure interaction framework based on the small-perturbation assumption. Therefore, the results primarily provide mechanistic insights into transient stress evolution during IVL rather than quantitative prediction of plaque fracture. These findings provide mechanistic insights into IVL induced transient stress evolution and highlight the importance of shock waveform characteristics in regulating stress distributions within calcified plaques and surrounding vascular tissues.
Abstract This study employs a λ /4 coaxial resonant cavity to generate a pulsed-modulated microwave plasma jet and compares discharge behaviors in N 2 , N 2 H 2 and Ar systems. Time-resolved optical emission spectroscopy is combined with incident and reflected microwave power measurements and phase diagrams to diagnose the ignition and decay processes. The results show that a stable localized enhanced electric field forms at the needle tip, enabling reliable discharge. Power signals and phase diagrams indicate stable microwave-plasma coupling, while the power-balance analysis at 60% duty cycle shows only minor differences in absorbed power and coupling efficiency among the three gas systems. Time-resolved spectroscopy reveals distinct temporal evolution among the three gases. At 25 kHz and 80% duty cycle, the N 2 and N 2 /H 2 emissions reach their observed maxima within the first 0.2 μ s acquisition interval and relax toward quasi-steady levels within 2.6 and 2.2 μ s, respectively. Their detectable afterglow durations are both 0.4 μ s. The Ar emission reaches its first transient maximum after 1.2 μ s and remains detectable for 3.2 μ s after microwave termination. A simplified CR framework relates these characteristic intervals to the competition between effective excitation and loss processes. The slightly shorter N 2 /H 2 relaxation is consistent with an additional H 2 -induced collisional-loss contribution, whereas the prolonged Ar afterglow supports the involvement of long-lived metastable species and residual stepwise excitation. The results indicate that gas-dependent kinetic processes contribute substantially to the observed emission dynamics under matched pulse-modulation and incident-power settings.
Abstract Protein-based molecular devices are gaining prominence for their potential to integrate biomimetic functionality into conventional electronic architectures. However, realizing these technologies requires a quantitative understanding of charge transport across biomolecule-modified electrode junctions. In this study, we investigate bias-driven electron tunneling and barrier modulation in amyloid beta-42 (A β -42) modified highly oriented pyrolytic graphite junctions using scanning tunneling microscopy-based spectroscopy. Comparative current–voltage ( I − V ) and differential conductance (d I /d V ) measurements reveal a pronounced modification of the tunneling barrier upon molecular adsorption, giving rise to distinct molecular conductance onsets. Temperature-dependent transport analysis within a double-barrier tunnel junction framework rules out thermally activated conduction and demonstrates electric-field-assisted tunneling, yielding an effective zero-field barrier of approximately 88 meV. Fowler–Nordheim analysis confirms a field-induced transition from direct to field-assisted tunneling across the composite junction. Furthermore, low-temperature inelastic electron tunneling spectroscopy identifies specific inelastic channels associated with the molecular vibrational modes of A β -42, confirming direct electronic coupling to the peptide backbone and aromatic residues. These results demonstrate that physisorbed A β -42 on graphite surface introduces dipole-mediated, field-dependent modulation of the effective tunneling barrier. This study establishes tunneling spectroscopy as an effective approach for probing localized barrier modifications in peptide-modified graphite junctions, providing insights relevant to protein-based bioelectronics.
