- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
In situ laser reflectivity to monitor and control the nucleation and growth of atomically-thin 2D materials
摘要： The growth of atomically-thin two-dimensional (2D) layered and other quantum materials is typically performed without in situ monitoring or control. Here, a simple laser reflectivity approach is demonstrated to provide in situ control over sub-monolayer thickness and growth kinetics during pulsed laser deposition (PLD) of MoSe2 layers. First, the general technique is presented with emphasis on designing the maximum sensitivity of the optical contrast through consideration of Fresnel’s equations with proper choice of layer thickness, substrate, and laser monitoring wavelength, incidence angle, and laser polarization. Then the 633 nm optical reflectivity of MoSe2 layers on SiO2/Si substrates was predicted and compared with in situ monitoring of MoSe2 growth by PLD under actual growth conditions using a probe HeNe laser beam. The measurements showed high sensitivity and excellent agreement with MoSe2 surface coverages calculated from atomic resolution STEM analysis of 2D layers deposited in arrested growth experiments. Growth kinetics revealed by these measurements showed sigmoidal nucleation and growth stages in the formation of the 2D MoSe2 layers that are described by a simple model, indicating the promise of the laser reflectivity technique for in situ monitoring and control of 2D materials deposition.
关键词： pulsed laser deposition (PLD),MoSe2,kinetic modeling,in situ reflectivity,2D materials
更新于2025-09-16 10:30:52
-
Electron-positron pair production in frequency modulated laser fields
摘要： The momentum spectrum and the number density of created electron-positron pairs in a frequency modulated laser field are investigated using the quantum kinetic equation. It is found that the momentum spectrum presents an obvious interference pattern. This is an imprint of the frequency modulated field on the momentum spectrum, because the momentum peaks correspond to the pair production process by absorbing different frequency component photons. Moreover, the interference effect can also be understood qualitatively by analyzing turning-point structures. The study of the pair number density shows that the number density is very sensitive to modulation parameters and can be enhanced by 2 or 3 orders of magnitude for certain modulation parameters, which may provide a new way to increase the number of created electron-positron pairs in future experiments.
关键词： number density,quantum kinetic equation,electron-positron pair production,frequency modulated laser fields,momentum spectrum
更新于2025-09-16 10:30:52
-
Prediction of Carbofuran Degradation Based on the Hydroxyl Radical’s Generation using the FeIII impregnated N doped-TiO2/H2O2/Visible LED Photo-Fenton-like Process
摘要： Hydroxyl radicals (?OH) are the dominant reactive species during most photocatalytic reactions. Therefore, ?OH generation as an index could be beneficial in comparing the obtained results in different experimental setup designs, thereby providing new insights for understanding the photocatalytic mechanism. Heterogeneous Photo-Fenton like processes are one of the most effective technologies for degradation of organic pollutants through ?OH production. Nevertheless, kinetic models that take into account the dependence of the contaminant degradation on ?OH generation under homogeneous oxidant supply, are still limited in such processes. In this paper, a photo-Fenton like reagent (FeIII impregnated N-doped TiO2 (FeNT)/H2O2) involving both heterogeneous and homogeneous phases was employed for carbofuran (CBF) degradation, frequently used pesticide in many developing countries from the carbamate group. In addition, a commercial visible LED lamp (Vis LED) with high power output was utilized as an innovative and efficient visible light source to simulate solar energy. Accordingly, a new kinetic model was proposed to predict CBF degradation in the FeNT/H2O2/Vis LED process under high Vis LED light intensities based on intrinsic reaction parameters, including the Vis LED light intensity, FeNT dosage, initial H2O2 concentration, and ?OH generation. The developed model was verified and validated successfully under various reaction conditions. However, a standard error ranging from 3 % to 15% was observed at extreme cases such as high [FeNT] and I or low [H2O2]0 when comparing model predictions and experimental results. This is due to the use of averaged conditions to forecast the rate constants.
关键词： Fe-N doped TiO2,Hydroxyl radicals,kinetic modeling,Carbofuran,Visible LED,impregnation
更新于2025-09-16 10:30:52
-
A new concept for estimating the influence of vegetation on throughfall kinetic energy using aerial laser scanning
摘要： Soil loss caused by erosion has enormous economic and social impacts. Splash effects of rainfall are an important driver of erosion processes; however, effects of vegetation on splash erosion are still not fully understood. Splash erosion processes under vegetation are investigated by means of throughfall kinetic energy (TKE). Previous studies on TKE utilized a heterogeneous set of plant and canopy parameters to assess vegetation’s influence on erosion by rain splash but remained on individual plant- or plot-levels. In the present study we developed a method for the area-wide estimation of the influence of vegetation on TKE using remote sensing methods. In a literature review we identified key vegetation variables influencing splash erosion and developed a conceptual model to describe the interaction of vegetation and raindrops. Our model considers both amplifying and protecting effect of vegetation layers according to their height above the ground and aggregates them into a new indicator: the Vegetation Splash Factor (VSF). It is based on the proportional contribution of drips per layer, which can be calculated via the vegetation cover profile from airborne lidar datasets. In a case study, we calculated the VSF using a lidar dataset for La Campana National Park in central Chile. The studied catchment comprises a heterogeneous mosaic of vegetation layer combinations and types and is hence well suited to test the approach. We calculated a VSF map showing the relation between vegetation structure and its expected influence on TKE. Mean VSF was 1.42, indicating amplifying overall effect of vegetation on TKE that was present in 81 % of the area. Values below 1 indicating a protective effect were calculated for 19 % of the area. For future work, we recommend refining the weighting factor by calibration to local conditions using field-reference data and comparing the VSF with TKE field measurements.
关键词： Throughfall Kinetic Energy,Remote Sensing,Vegetation Splash Factor,Splash Erosion,LiDAR
更新于2025-09-16 10:30:52
-
UV-LED fluence determination by numerical method for microbial inactivation studies
摘要： The Ultraviolet Light-Emitting Diode (UV-LED) is a new UV source suitable for small to mid-size water disinfection units. The design of a UV-LED reactor entails the integration of hydrodynamics, radiation, and kinetics data. The kinetics of microbial inactivation are necessary for UV-LED reactor design and the determination of kinetic rate constants depends on the accuracy of fluence rate measurement. However, there is not an easy way to measure the fluence rate inside a solution. In this study, a computational method is proposed to calculate irradiance and fluence rate based on the LED’s relative radiation profile and its radiant power, which are two standard pieces of information available in an LED’s datasheet. UV-LED was modeled as a polychromatic point source with a specific radiation profile and the fluence rate was calculated by solving the Radiative Transfer Equation by considering the refraction, reflection, and absorption of the medium. The irradiance and fluence rate predictions on the surface of the water were evaluated successfully by radiometry and actinometry measurements, respectively. The fluence rate imposed by 265-nm UV-LED and 275-nm UV-LED in Petri dishes with internal diameters of 5 cm and 9 cm were measured using biodosimetry with E. coli and MS2, when the UV-LED germicidal factor was obtained by considering the LED emission spectrum and the microorganism action spectra. Biodosimetry experiments using E. coli and MS2 at exposure times over 200 seconds indicated a close agreement between the simulation and experimental data. Such results are indicating the kinetic rate constants of a microorganism can be estimated without performing kinetic study using the action spectrum of microorganisms. Further, the results showed the proposed method can be applied for fluence rate determination for any LED’s radiation profile, LED position, and the experimental apparatus’s regardless of the availability of the action spectrum of microorganisms.
关键词： kinetic rate constant,polychromatic,fluence determination,UV-LED,irradiation model
更新于2025-09-16 10:30:52
-
Atomistic kinetic Monte Carloa??Embedded atom method simulation on growth and morphology of Cua??Zna??Sn precursor of Cu <sub/>2</sub> ZnSnS <sub/>4</sub> solar cells
摘要： An atomistic kinetic Monte Carlo coupled with the embedded-atom method is used to simulate film growth and morphology evolution of a Cu–Zn–Sn precursor of Cu2ZnSnS4 solar cells by single-step electrodeposition. The deposition and diffusion events of three different metallic atoms are described by the simulation. Moreover, the multibody Cu–Zn–Sn potential is used to calculate diffusion barrier energy. The effects of process factors, including temperature and electrode potential, on the cross-section morphology and surface roughness are explored, while keeping the elemental composition ratios constant. The lowest roughness with the smoothest morphology is obtained at the optimal parameters. The distribution and transformation behaviors of cluster sizes are investigated to describe the alloy film growth process. Furthermore, the comparison between deposition events and diffusion events reveals that deposition events depend primarily on individual deposition rates of different metallic atoms, but diffusion events are mainly dependent on the interaction of metallic atoms. The film morphology evolution is visualized by three-dimensional configuration with increasing numbers of atoms, which suggests a competing mechanism between nucleation and growth of the thin film alloy.
关键词： Cu–Zn–Sn precursor,film growth,Cu2ZnSnS4 solar cells,electrodeposition,atomistic kinetic Monte Carlo,morphology evolution,embedded-atom method
更新于2025-09-16 10:30:52
-
On the use of the envelope model for down-ramp injection in laser-plasma accelerators
摘要： The path towards high 6D-brightness electron beams coming from plasma accelerators relies on numerical simulations to investigate and explain novel physics and parameter regimes. Particle-in-cell codes are a reliable tool for this purpose, but full-scale simulations can be computationally challenging, specifically when performing large parameter scans. Approximate models and solvers are an alternative to quickly assess new regimes, but one needs to understand the validity of these models for each specific problem. In this work, we investigate the usefulness of a ponderomotive guiding center solver to model density down-ramp injection in laser wakefield accelerators. We also report results for density down-ramp injection in the context of EuPRAXIA, where we find that this method can produce 250 MeV, 30 pC beams that fulfill all the requirements for the injector stage, with <1 % energy spread and <100 nm emittance.
关键词： particle-in-cell,ponderomotive guiding center,simulations,density down-ramp injection,EuPRAXIA,laser wakefield acceleration,kinetic
更新于2025-09-12 10:27:22
-
Numerical simulations to study turbulent magnetic field amplification by nonlinear interaction of high-power laser and kinetic Alfvén waves in laboratory and astrophysical plasmas
摘要： The model contouring the dynamics of transient nonlinear interaction between the high-frequency extraordinary-elliptically polarized laser (HFXPL) and low-frequency kinetic Alfvén wave (LFKAW) dynamics in the magnetized plasma is the focal point of the present investigation. The quasistatic ponderomotive force driven by the HFXPL pump induces density cavitation and humps in the low-frequency kinetic Alfvén wave. In order to study the intricate localized structures of HFXPL pump waves that evolve with time, the requisite dimensionless equations of the coupled system (HFXPL and LFKAW) are evaluated by using numerical methods in the nonlinear stage. The typical scale sizes of these structures in the early phase are ≈9 μm, and the typical time to grow is ≈10 ps. The ensemble-averaged magnetic power spectra are also presented, indicating energy cascade. The rendered investigations follow direct relevance to the experimental observations and are imperative in understanding turbulence in astrophysical scenarios.
关键词： kinetic Alfvén waves,high-power laser,astrophysical plasmas,laboratory plasmas,nonlinear interaction,turbulent magnetic field amplification
更新于2025-09-12 10:27:22
-
Nonequilibrium site distribution governs charge-transfer electroluminescence at disordered organic heterointerfaces
摘要： The interface between electron-donating (D) and electron-accepting (A) materials in organic photovoltaic (OPV) devices is commonly probed by charge-transfer (CT) electroluminescence (EL) measurements to estimate the CT energy, which critically relates to device open-circuit voltage. It is generally assumed that during CT-EL injected charges recombine at close-to-equilibrium energies in their respective density of states (DOS). Here, we explicitly quantify that CT-EL instead originates from higher-energy DOS site distributions significantly above DOS equilibrium energies. To demonstrate this, we have developed a quantitative and experimentally calibrated model for CT-EL at organic D/A heterointerfaces, which simultaneously accounts for the charge transport physics in an energetically disordered DOS and the Franck–Condon broadening. The 0–0 CT-EL transition lineshape is numerically calculated using measured energetic disorder values as input to 3-dimensional kinetic Monte Carlo simulations. We account for vibrational CT-EL overtones by selectively measuring the dominant vibrational phonon-mode energy governing CT luminescence at the D/A interface using fluorescence line-narrowing spectroscopy. Our model numerically reproduces the measured CT-EL spectra and their bias dependence and reveals the higher-lying manifold of DOS sites responsible for CT-EL. Lowest-energy CT states are situated ～180 to 570 meV below the 0–0 CT-EL transition, enabling photogenerated carrier thermalization to these low-lying DOS sites when the OPV device is operated as a solar cell rather than as a light-emitting diode. Nonequilibrium site distribution rationalizes the experimentally observed weak current-density dependence of CT-EL and poses fundamental questions on reciprocity relations relating light emission to photovoltaic action and regarding minimal attainable photovoltaic energy conversion losses in OPV devices.
关键词： organic electronics,Franck–Condon vibronic progression,energetic disorder,electroluminescence at organic interfaces,3D kinetic Monte Carlo model
更新于2025-09-12 10:27:22
-
Improving impact wear resistance of Ti-6Al-4V alloy treated by laser shock peening
摘要： The effects of laser shock peening (LSP) on the impact wear behavior of Ti?6Al?4V alloys were investigated by a homemade impact wear test rig. The microstructure and mechanical properties of the peened samples were studied. During the impact wear test, the energy absorption, impact force, wear contact time and wear mechanism of all the test samples were investigated in terms of the influence of the impact kinetic energy. The results showed that microhardness, elastic modulus and residual compressive stress of the treated samples were markedly improved. The wear resistances of both treated samples were highly improved after LSP, and a higher pulse energy corresponded to a more obvious effect. Besides, the wear in all test samples involved a combination of abrasive and oxidation wear and fatigue spalling.
关键词： laser shock peening,wear mechanism,impact wear,impact kinetic energy,Ti?6Al?4V alloy
更新于2025-09-12 10:27:22