Hot Electron Density Research Articles

Synthesis of nano-silver decorated β-Bi2O3/Bi2O2CO3 heterojunction using Bi-MOF precursor: Precisely controllable structure and enhanced photocatalytic activity for sulfadiazine degradation

In this study, a novel Ag/β-Bi2O3/Bi2O2CO3 nanocomposite was prepared by in-situ decomposition of a three-dimensional bismuth-trimesic acid complex (Bi–BTC) precursor at 300 ℃. The multilayered morphology and heterojunction structure of the prepared Ag/β-Bi2O3/Bi2O2CO3 nanocomposite were characterized by a series of technologies. The photocatalytic performance of Ag/β-Bi2O3/Bi2O2CO3 was evaluated by removal of sulfadiazine (SD) antibiotic from water under visible-light irradiation, and the degradation efficiency of SD was up to 96.8 % within 160 min. The superior catalytic activity of Ag/β-Bi2O3/Bi2O2CO3 is attributed to the p-n heterojunction structure constructed by β-Bi2O3 and Bi2O2CO3, as well as the surface plasmon resonance effect of nano-silver, which not only promoting the charge separation and transfer, but also increasing the hot electron density. Electron paramagnetic resonance (EPR) and active species trapping experiments indicated that ∙O2 and h+ play a major role in the oxidative degradation of sulfadiazine. The possible degradation pathway of sulfadiazine was identified, and the ecological toxicity of SD and its degradation intermediates was estimated using T.E.S.T. software. In addition, the as-prepared Ag/β-Bi2O3/Bi2O2CO3 showed excellent photo-corrosion resistance capacity and good reusability in photocatalytic degradation of SD.

Bifurcation analysis of electron-acoustic waves in electron beam-plasma with suprathermal electrons

It has investigated the properties of nonlinear electron-acoustic waves propagating in a four-component collisionless, unmagnetized plasma. The system consists of cool inertial background electrons of temperature T c , the cool inertial electron beam of temperature T b , hot inertialess suprathermal electrons modeled by a κ-distribution of temperature T h , and ions. The nonlinear modified Korteweg-de Vries-Burgers (mKdV-Burgers) equation that characterizes the electron acoustic waves in such a plasma model is derived. The wave solutions of the resultant mKdV-Burgers equation are investigated using planar dynamical system bifurcation theory. The unperturbed hot, cool, and beam electron densities and the superthermal electron parameter are revealed to have a considerable influence on the nonlinear electron-acoustic traveling waves and the associated electric fields. The system evolves also monotonic shock waves when the dissipation term dominates over the dispersion term. The current model might be useful for understanding the generation of nonlinear electron-acoustic waves in a variety of astrophysical plasma settings, including the Earth's magnetosphere.

Properties of the ionization region in a magnetron plasma at gas-aggregation-source-relevant pressure regime explored using a global model

A global (volume averaged) model is developed for the ionization region (IR) of a gas aggregation source (GAS) plasma. The case of using argon gas and a copper target is considered. The model describes the densities of thermal and hot electrons, argon and copper ions, copper atoms and argon atoms in different excited states, the temperature of thermal electrons, the kinetic energies of the ions with which they bombard the target, the sheath width near the target cathode and the energy fluxes by different plasma species to a planar probe in the IR. Also, the fraction of input power is estimated which is dissipated to energize the thermal electrons in the IR. The gas discharge properties are analyzed for different pressures and discharge currents under conditions corresponding to the experimental conditions (Gauter et al 2018 J. Appl. Phys. 124 073301). The calculated pressure- and current-dependences for the GAS properties are used to explain the measured dependences for the deposition rate and the energy flux. It is found that the deposition rate increases with increasing discharge current because of the growth of currents of copper atoms and ions. With increasing pressure, the rate decreases due to drop of the densities of copper atoms and ions because of decreasing the kinetic energies of the ions with which they bombard the target. The model indicates that in the gas-aggregation-source relevant pressure regime, the energy flux by ions dominates over the energy fluxes of other plasma species.

Charge fluctuations on the dust grains in the presence of energetic electrons

Abstract Dust charging is an arbitrary process occurring at random times which results in fluctuations of dust charge around its equilibrium value. To have a better insight into the mechanism of charge fluctuations, a numerical simulation of the statistical nature of the dust charging process is investigated. Here, a multicomponent non-Maxwellian hydrogen plasma comprising two electron groups, positive ions, and dust grains is modelled. An increase in the overall negative dust charge number is reported in the presence of non-Maxwellian electrons. Additionally, the study emphasizes the role of electron distribution and hot electron temperature and density on the charge fluctuations of the dust grains.

Electron beam driven ion-acoustic solitary waves in plasmas with two kappa-distributed electrons

Formation and the basic features of arbitrary amplitude ion-acoustic solitary waves (IASWs) in a plasma consisting of warm positive ions, two kappa-distributed electrons and an electron beam are investigated by using the Sagdeev pseudopotential approach. It is shown that the soliton existence domain (Mach number limits) sensitively depends on temperature of ions, spectral index of cool electrons and concentration of hot electron species while spectral index of hot electrons, hot-to-cool electron temperature ratio and also concentration of electron beam do not considerably affect this domain. It is also found that temperature of electron beam only affect the existence domain of rarefactive solitons. Furthermore, it is shown that considered plasma medium supports the coexistence of positive and negative IASWs. Moreover, effect of different plasma parameters such as hot-to-cool electron density ratio, ion-to-cool electron temperature ratio, beam-to-ion density ratio, hot-to-cool electron temperature ratio and superthermality index of electron species on the basic features of positive and negative IASWs is investigated numerically. Finally, the effect of plasma parameters on the parametric regime of coexistence of compressive and rarefactive IASWs is studied and, for example, effect of temperature of positive ions and number density of hot electrons on polarity of IASWs is numerically investigated.

Hot-Electron Dynamics Mediated Medical Diagnosis and Therapy.

Surface plasmon resonance excitation significantly enhances the absorption of light and increases the generation of "hot" electrons, i.e., conducting electrons that are raised from their steady states to excited states. These excited electrons rapidly decay and equilibrate via radiative and nonradiative damping over several hundred femtoseconds. During the hot-electron dynamics, from their generation to the ultimate nonradiative decay, the electromagnetic field enhancement, hot electron density increase, and local heating effect are sequentially induced. Over the past decade, these physical phenomena have attracted considerable attention in the biomedical field, e.g., the rapid and accurate identification of biomolecules, precise synthesis and release of drugs, and elimination of tumors. This review highlights the recent developments in the application of hot-electron dynamics in medical diagnosis and therapy, particularly fully integrated device techniques with good application prospects. In addition, we discuss the latest experimental and theoretical studies of underlying mechanisms. From a practical standpoint, the pioneering modeling analyses and quantitative measurements in the extreme near field are summarized to illustrate the quantification of hot-electron dynamics. Finally, the prospects and remaining challenges associated with biomedical engineering based on hot-electron dynamics are presented.

An Implication of Detecting the Internal Modulation in a Pulsating Aurora: A Conjugate Observation by the Arase Satellite and All‐Sky Imagers

AbstractA physical mechanism to produce pulsating aurora (PsA) has been considered to be the interaction of the electron and the chorus wave generated near the equatorial plane of the magnetosphere. A recent observation of high temporal resolution of chorus waves by the Arase satellite revealed that the presence or absence of the internal modulation of PsA, which is a characteristic sub‐second scintillation at 3 ± 1 Hz within each optical pulsation, is closely related to the discreteness of the element structure of the chorus wave. However, it is still unclear what parameters (or conditions) control the discreteness of the element and the existence of the internal modulation of PsA. In this study, we discuss parameters that determine the presence or absence of the internal modulation of PsA and element structure of chorus by showing a conjugate observation of PsA/chorus by ground‐based cameras and the Arase satellite. During the event, the occurrence of internal modulation increased temporally. The wave data from the satellite show that the repetitive frequency of elements was ∼6 Hz when the internal modulation was indistinct, while the repetitive frequency was ∼3 Hz when the internal modulation was distinct. The particle measurements suggest that this difference was caused by changes in the density and the temperature anisotropy of the hot electron. The internal modulation was clearly observed when the density of hot electrons decreased and the temperature anisotropy relaxed after the injection. Observations of internal modulations from the ground might allow us to estimate the parameters such as energetic electron density and temperature anisotropy in the magnetosphere.

Angle-resolved and time-resolved spectroscopic study on large-area silver gratings fabricated via optical interference lithography

Plasmonic resonators, which can enhance the near-field due to plasmon excitation, have attracted extensive research interest due to their significant potential in photodetection, photocatalysis, photovoltaics, and other applications. Here, we experimentally present spectroscopic results of plasmonic resonances on large-area nanoscale silver (Ag) gratings, fabricated by optical interference lithography based on angle-resolved optical absorption spectroscopy and femtosecond transient absorption spectroscopy (TAS). Specifically, we have measured plasmon resonances as a function of azimuthal angles and detection angles under p- and s-polarization. TAS reveals the non-radiative decay of plasmon resonances by transferring energy to nearby species, including exciting plasmonic hot electrons, which can be harvested by coupled semiconductors through a metal-semiconductor Schottky barrier. Our numerical simulation provides insight into the near-field analysis and quantifies the density of plasmonic hot electrons excited in our Ag-gratings.

Study of two-electron temperature plasma sheath using non-extensive electron distribution in presence of an external magnetic field

In this study, the physics of sheath formation in a collisional two-electron temperature plasma in the presence of an oblique external magnetic field has been investigated. At first, a comparative study among the fluid electron model, Boltzmann electron model, and the non-extensive electron model has been carried out and a suitable range of non-extensive parameter q has been predicted. In the latter part, a collisional two-electron temperature plasma is considered. Both the hot and cold electron densities are described using the non-extensive distribution, whereas cold ions are described by the fluid equations. The properties of the sheath are investigated in different collisional regimes by varying the non-extensive parameter (q) and the hot to cold electron densities and temperatures. The magnetic field inclination angle is varied in the limit 1° ≤ α ≤ 5°. It is observed that electron distribution significantly deviates from Boltzmann distribution for nearly parallel magnetic field. Moreover, collision enhanced flux deposition for highly magnetized case is a significant finding of the study. The results obtained in this study can enhance the understanding of plasma–matter interaction processes where multiple electron groups with near parallel magnetic field are found.

Giant hot electron thermalization via stacking of graphene layers

The capability of graphene to generate hot electrons is predicted to be effective in converting low energy photons into electrical currents for the mid-infrared photodetection [1,2]. However, the quantum yield of such hot electrons is not sufficient due to the limited thickness of two-dimensional graphene [3-5]. Therefore, it raises the question whether the electron thermalization is efficient enough to generate a large number of hot electrons in graphitic materials as a detectable photocurrent. Here, an experimental demonstration of the sufficient hot electron generation in Bernal stacking sequence nano-graphite films is presented. A comprehensive layer number dependence (1–120-layers graphene) study verifies the strong hot electron scattering correlations, exhibiting intriguing two-dimensional properties into their bulk counterparts. Consequently, the spectral coverage of hot electrons promoted from mid-infrared (4 μm) to near-infrared (1.2–1.6 μm) energy level is achieved, leading to a 109 eV−1 cm−2 populated hot electron density for the mid-infrared photodetection. In addition, the consistently increased number of photo-excited electrons via stacking of graphene layers, results in a gradual evolution of subsequent electron thermalization. The proposed scheme for exploring the thickness dependence electron thermalization property of the graphitic material paves the way to design ultrafast and sensitive mid-infrared photodetecters.

Dust charge fluctuation and ion acoustic wave propagation in dusty plasma with q-nonextensive hot and Maxwellian cold electrons

We have employed the self-consistent kinetic theory to study the linear dispersion relation of ion acoustic waves in a four-component plasma consisting of nonextensive hot electrons, Maxwellian cold electrons, positive ions, and dust particles. The dust charging process with the modified ion acoustic wave damping, as well as its unstable mode, has been graphically illustrated. It is found that the dust charging mechanism depends on the density of hot electrons, the degree of nonextensive electron distribution, and the temperature ratio of hot to cold electrons. It is shown that the damping and instability rates of ion acoustic waves due to dust charge fluctuations explicitly depend on the choice of electron distribution and the magnitude of dusty plasma parameters. In addition, we have studied the ion acoustic Landau damping in the absence of dust particles. It is found that the weak damping region broadens, while the strong damping region shrinks and is shifted toward the short wavelength region for the increase in the temperature ratio of hot to cold electrons.

H- and D- production efficiency in a multi-dipole ECR-plasma source as a function of gas pressure

The electron cyclotron resonance (ECR) negative ion source “Prometheus I” is operated either with high purity H2 (> 99.999%) or D2 (> 99.8%) to probe H- and D- ions, respectively, and examine the isotope effect within a wide range of gas pressure. These ions are predominantly formed in the bulk plasma by dissociative attachment (DA) of low-energy (cold) electrons to highly ro-vibrationally excited molecules. The latter result mainly from the radiative decay and excitation (EV) process sustained by high-energy (hot) electrons heated in the ECR zones. Langmuir probe and laser photo-detachment measurements are realized within the pressure range 0.27 to 2.67 Pa under constant microwave power (0.9 kW). It is revealed that: (i) the plasma potential, cold electron temperature, and cold electron density tend to be higher in deuterium; (ii) no pronounced difference in the hot electron density and temperature is found between the two plasmas; and (iii) overall a similar H- and D- negative ion yield (up to 6×109 cm-3; under the present conditions) is achieved. However, for equal plasma densities an isotope effect is exhibited showing higher H- density over the entire pressure range. Finally, the nH- / n ratio is constantly higher than the nD- / ne one and they both peak around 1.33 Pa.

Experimental study on controlled production of two-electron temperature plasma

A two-electron temperature plasma is produced by the method of diffusion of two different plasmas with distinct temperatures and densities. The method is simple and provides an adequate control over the plasma parameters. The study reveals that the temperature and density of both the electron groups can be effectively controlled by just changing the discharge currents of both the plasmas. An ion-acoustic wave is excited in the plasma and is detected using a planar Langmuir probe. The damped amplitude of the wave is measured and is used as a diagnostic tool for establishing the presence of two-electron components. This production method can be helpful in controlling the hot electron density and temperature in plasma processing industries.

Propagation of Chorus Waves Generated in Minimum‐B Pockets

AbstractWe present the first ray tracing results of chorus waves generated in minimum‐B pockets. A new ray tracer is developed to accommodate an arbitrary magnetic field model, which enables us to construct minimum‐B pocket geometries using the Tsyganenko (1989) model. Rays with different frequencies and initial wave normal angles are launched from minimum‐B pockets and traced under different geomagnetic activity and hot electron density conditions. Our results indicate that chorus waves generated from minimum‐B pockets are usually highly localized and thus are unlikely to be detected unless the spacecraft is very close to the source region. These waves are also very unlikely to propagate into the plasmasphere. The propagation distances generally decrease with increasing geomagnetic activity.

Simulation study on parametric dependence of whistler-mode hiss generation in the plasmasphere

We conduct electromagnetic particle simulations to examine the applicability of nonlinear wave growth theory to the generation process of plasmaspheric hiss. We firstly vary the gradient of the background magnetic field from a realistic model to a rather steep gradient model. Under such variation, the threshold amplitude in the nonlinear theory increases quickly and the overlap between threshold and optimum amplitude disappears correspondingly, the nonlinear process is suppressed. In the simulations, as we enlarge the gradient coefficient of the background magnetic field, waves generated near the equator do not grow through propagation. By examining the range of suitable values of inhomogeneity factor S (i.e., |S|<2), we find the generation of wave packets is limited to the equatorial region when the background field is steep, showing a good agreement with what is indicated by critical distance in the theory. We then check the dependence of generation of hiss emissions on different hot electron densities. Since the overlap between threshold and optimum amplitude vanishes, the nonlinear process is weakened when hot electron density becomes smaller. In the simulation results, we find similar wave structures in all density cases, yet with different magnitudes. The existence of suitable S values implies that the nonlinear process occurs even at a low level of hot electron density. However, by examining J_E that closely relates to the wave growth, we find energy conveyed from particles to waves is much limited in small density cases. Therefore, the nonlinear process is suppressed when hot electron density is small, which agrees with the theoretical analysis.Graphical

Multivariate scaling of maximum proton energy in intense laser driven ion acceleration

The production of high-energy ions is a momentous goal of ultraintense laser lights. So far a number of experiments and numerical simulations have been conducted to obtain the scaling of the ion energy to find the optimal experimental condition. Due to the complexity of the relativistic laser-plasma interactions, it is not easy to evaluate the ion energy for different experimental configurations. We propose a statistical approach using the Bayesian inference to obtain a multivariate scaling to predict the maximum proton energy via the target normal sheath acceleration. We derive the scaling for the experimental parameters and also for the hot electron temperature and density observed in the corresponding particle-in-cell simulations. We demonstrate the effectiveness of our approach in the prediction of the maximum proton energy and provide the experimental condition to achieve a proton energy over 100 MeV.

Simulations of laser plasma instabilities using a particle-mesh method

A physical model is presented for the study of parametric instabilities in inertial confinement fusion (ICF), which considers the coupling of the incident and scattered electromagnetic waves with plasma electrons and ions. Specially, this model is solved numerically with the particle-mesh method, where the plasma is represented by macro-particles both for electrons and ions, and the velocity and position of each macro-particle are numerically updated by using the particle-mesh method. The developed particle-mesh code in one-dimensional geometry (PM1D) is utilized to study the development of parametric instabilities at the nonlinear stages, where electron plasma wave breaking, particle trapping, hot electron generation and density cavity formation can occur. Particle-in-cell (PIC) simulations are carried out to verify this PM1D code. By comparison, it is found that this PM1D code is able to capture the kinetic effects and precisely describe the developments of parametric instabilities at nonlinear stages as the PIC simulations while saving the computation time obviously. Furthermore, a test simulation of the stimulated Raman scattering evolution up to 200 ps verifies the robustness of this PM1D code.

Beam-driven ECH waves: A parametric study

Electron cyclotron harmonic (ECH) waves play a significant role in driving the diffuse aurora, which constitutes more than 75% of the particle energy input into the ionosphere. ECH waves in magnetospheric plasmas have long been thought to be excited predominantly by the loss cone anisotropy (velocity–space gradients) that arises naturally in a planetary dipole field. Recent THEMIS observations, however, indicate that an electron beam can also excite such waves in Earth's magnetotail. The ambient and beam plasma conditions under which electron beam excitation can take place are unknown. Knowledge of such conditions would allow us to further explore the relative contribution of this excitation mechanism to ECH wave scattering of magnetospheric electrons at Earth and the outer planets. Using the hot plasma dispersion relation, we address the nature of beam-driven ECH waves and conduct a comprehensive parametric survey of this instability. We find that growth is provided by beam electron cyclotron resonances of both first and higher orders. We also find that these waves are unstable under a wide range of plasma conditions. The growth rate increases with beam density, beam velocity, and hot electron temperature; it decreases with increasing beam temperature and beam temperature anisotropy (T⊥/T∥), hot electron density, and cold electron density and temperature. Such conditions abound in Earth's magnetotail, where magnetospheric electrons heated by earthward convection and magnetic reconnection coexist with colder ionospheric electrons.

Non‐linear coherent structures in multi‐species dusty plasma

AbstractIn a fluid description, theoretical investigation has been carried out to explore how the presence of two‐temperature electron fluids (hot and cold) influences the characters of dust acoustic solitary waves, double layers, bipolar structures, etc. in a multi‐component dusty plasma, composed of isothermal electrons and ions, along with the negatively charged, cold dusts. A reductive perturbation method is used to derive the well‐known Korteweg‐de Vries (KdV) equation, which describes the basic nature of the dust acoustic solitary waves. Two values of critical ion density exist, which distinguish the regions of compressive and rarefactive solitary waves in parametric space. The critical points directly depend on the densities and temperatures of the electron fluids. With increasing temperature of hot electron fluid, one of the two critical ion densities decreases, and the other one increases. Ultimately, they merge with each other when the temperature of hot electrons reaches a particular value. The amplitude of the dust acoustic soliton gets modified due to the presence of two‐temperature electron fluids. The study is extended further by deriving modified KdV and Gardner equations at the vicinity of critical points. The Gardner equation reveals the existence of double layer and bipolar structures. In these processes, the effects higher‐order nonlinearities are incorporated methodically, by implementing appropriate stretching of the coordinates. Sagdeev's pseudopotential analysis shows that large amplitude rarefactive solitary waves only exist when the corresponding Mach number (M) lies within 1 &lt; M &lt; Mc. The upper bound, Mc increases with the hot electron temperature and cold electron density. The results presented in this investigation are believed to be applicable in the laboratory and astrophysical plasmas.

Control of Plasma Parameters by Hot Ionizing Electrons Using a Mesh Grid

In this article, we are reporting about the effect of energy and number density of hot primary electrons on plasma parameters in a new experimental configuration of a double plasma device. Here, we have controlled the plasma parameters in two plasma regions by a single discharge circuit. The discharge voltage is applied between hot filaments and a mesh grid. The energy of the hot primary electrons is increased by increasing the discharge voltage, and their number density is increased by increasing the filament heating voltage. It has been observed that the variations in plasma parameters are significant when the number density of primary electrons is increased.