Concentration Of Hot Electrons Research Articles

Effect of κ-deformed Kaniadakis distribution on the modulational instability of electron-acoustic waves in a non-Maxwellian plasma

In this paper, the modulational instability (MI) of the high-frequency electron-acoustic waves (EAWs) is reported in a non-Maxwellian plasma composed of two distinct types of electrons and stationary ions. One type of electrons is treated as a cold inertial fluid, whereas the other type is considered as inertialess species following κ-deformed Kaniadakis distribution. The fluid equations to the current model are reduced via a reductive perturbation technique to a nonlinear Schrödinger equation, which is then used to compute the MI and the growth rate of the EAWs. It is instructive to note that the deformation parameter (which develops the Kaniadakis entropy) and the hot-to-cold electron density ratio (hot electron concentration) significantly affect the conditions for MI. The modulated envelope black (dark and gray) solitons are investigated. The current results are beneficial in analyzing the spectrum of the cosmic rays, which violates manifestly the Boltzmann–Gibbs statistics. Moreover, the obtained results can be used to understand the mystery of many observations in stars where the presence of non-Maxwellian particles dominates.

Parametric excitation of electron acoustic wave by Langmuir wave in the Earth’s inner magnetospheres

A kinetic model for the parametric decay of Langmuir wave (LW) into sideband LW and electron acoustic wave (EAW) in plasmas containing hot and cold electrons is developed. The parametric instability for LW decaying into EAW in the Earth’s inner magnetosphere is numerically analyzed. The maximum growth rate and the range of wavenumber for the existence of parametric instability increase with the increase of pump wave strength and hot electron concentration. The frequency of excited EAW corresponding to the maximum grow rate goes up as the enhancement of pump wave strength, but lowers as the reduction of hot electron concentration. The frequencies of excited EAW are comparable to the observed frequencies of whistler wave in the inner magnetosphere. The growth rate will be about a few tens per second when pump LWs is strong enough. The results obtained may be helpful for the explanation of the observed electrostatic field spectrum in the inner magnetosphere.

Interfacial engineering of Ni-phytate and Ti3C2Tx MXene-sensitized TiO2 toward enhanced sterilization efficacy under 808 nm NIR light irradiation

Constructing a near-infrared (NIR) light-responsive antibacterial material keeps a preferential goal yet a huge challenge. Herein, we controllably manufactured a sandwich architecture comprised of plasmon (Ti3C2Tx MXene) and photosensitizer (PANi (Ni-phytate)) locating on wide-bandgap semiconductor (TiO2), named as PANi/TiO2/Ti3C2Tx (PTM), which can achieve bidirectional transfer of hot-electrons under 808 nm NIR light irradiation, significantly augmenting the carrier concentration of TiO2 surface. The increase of hot-electron concentration not only strengthens the chemical activity through the O2 uptake simulations by the theoretical investigations, but also elevates the photothermal conversion efficiency up to 43.3 %, which is far superior to other reported photocatalytic-photothermal system. The 808 nm NIR-activated germicide can realize 99.9 % sterilization efficacy against the Escherichia coli (E. coli) with the collaboration of photocatalytic and photothermal treatment. This work offered a brand-new idea to construct a NIR-driven antimicrobial material achieving the synergistic interaction of photocatalytic therapy and photothermal therapy.

High fuel production rate and excellent durability for photothermocatalytic CO2 reduction achieved via the surface plasma effect of NiCu alloy nanoparticles

Upon UV-VIS-IR illumination, the strong LSPR effect of NiCu alloy nanoparticles can generate a high concentration of hot electrons, which can not only enhance the fuel yield but also reduce the carbon deposition rate.

Kinetic Alfvénic cnoidal waves in Saturnian magnetospheric plasmas

The characteristics of kinetic Alfvénic cnoidal waves (KACWs) in Saturn's magnetosphere plasma composed of two temperature superthermal electrons and inertial ions are presented. The Korteweg–de Vries (KdV) equation and its cnoidal wave solution are derived by adopting reductive perturbation technique. Only positive potential kinetic Alfvénic cnoidal and solitary waves are evolved in Saturnian magnetospheric plasma. The influence of superthermality of cold electrons, concentration of hot electrons, plasma beta and angle of propagation of the wave with respect to the magnetic field has been analyzed on the characteristics of KACWs. The findings of this investigation may shed the light on the possible existence of KACWs and acceleration as well as energy transportation in space plasmas especially in Saturn's magnetosphere.

Kinetics and Mechanism of Plasmon-Driven Dehalogenation Reaction of Brominated Purine Nucleobases on Ag and Au.

Plasmon-driven photocatalysis is an emerging and promising application of noble metal nanoparticles (NPs). An understanding of the fundamental aspects of plasmon interaction with molecules and factors controlling their reaction rate in a heterogeneous system is of high importance. Therefore, the dehalogenation kinetics of 8-bromoguanine (BrGua) and 8-bromoadenine (BrAde) on aggregated surfaces of silver (Ag) and gold (Au) NPs have been studied to understand the reaction kinetics and the underlying reaction mechanism prevalent in heterogeneous reaction systems induced by plasmons monitored by surface enhanced Raman scattering (SERS). We conclude that the time-average constant concentration of hot electrons and the time scale of dissociation of transient negative ions (TNI) are crucial in defining the reaction rate law based on a proposed kinetic model. An overall higher reaction rate of dehalogenation is observed on Ag compared with Au, which is explained by the favorable hot-hole scavenging by the reaction product and the byproduct. We therefore arrive at the conclusion that insufficient hole deactivation could retard the reaction rate significantly, marking itself as rate-determining step for the overall reaction. The wavelength dependency of the reaction rate normalized to absorbed optical power indicates the nonthermal nature of the plasmon-driven reaction. The study therefore lays a general approach toward understanding the kinetics and reaction mechanism of a plasmon-driven reaction in a heterogeneous system, and furthermore, it leads to a better understanding of the reactivity of brominated purine derivatives on Ag and Au, which could in the future be exploited, for example, in plasmon-assisted cancer therapy.

Theoretical analysis of electron acoustic shock waves in magnetized superthermal plasma with electron beam

AbstractWe have analysed the small‐amplitude non‐linear electron acoustic shock waves by taking into account the effects of electron beam in magnetized plasma. Satellite observations in different regions of the Earth's magnetosphere have shown that the electrostatic solitary waves are generally associated with electron or/and ion beams. The nonlinear Korteweg‐de‐Vries Burgers (KdVB) equation has been derived by considering the basic fluid equations and dissipation effects. The nonlinear coefficient of KdVB equation comes out to be negative. Only dip‐shaped potential structures are reported here. For the parameters discussed in this paper, we did not find positive polarity shocks. This could be due to the restrictions on the plasma parameters since we are using the fixed densities of the cold, hot, and beam electrons as observed by the Viking satellite in the auroral region. In this paper, the importance of the cold electron to hot electron temperature in conjunction with the beam speed is pointed out. Increase in beam density, kinematic viscosity, and magnetic field results in increase in the amplitude while the increase in hot electron concentration and superthermality leads to decrease in potential. The numerical analysis is presented for the parameters corresponding to the observation of burst b event by Viking satellite in the dayside auroral zone of the earth's magnetosphere.

Kinetic-theory-based investigation of electronegative plasma–wall transition with two populations of electrons

Kinetic theory has been employed to investigate the magnetized plasma-sheath structure and its characteristics in the presence of more than one species of negatively charged particles: hot electrons, cold electrons, and negative ions. The cold electrons and negative ions are considered to obey a Maxwellian distribution, whereas the hot electrons follow a truncated Maxwellian distribution. The Bohm sheath condition has been extended for the case of more than one species of negatively charged particles, in which the concentration of hot electrons has a crucial role in achieving the Bohm velocity. The thermal motion of hot electrons is much higher compared to cold electrons and negative ions, such that the variation of hot electron concentrations and the temperature ratio of hot to cold electrons play a key role in the determination of the plasma-sheath parameters: particle densities, electrostatic potential, the flow of positive ions towards the wall, and sheath thickness. We have estimated the deviation of the resultant drift velocity of positive ions on the plane perpendicular to the wall from the parallel component at the presheath–sheath interface. It is found that the deviation between the two velocity components increases with an increase in the obliqueness of the magnetic field. Furthermore, the results obtained from the kinetic trajectory simulation model are compared with the results obtained using a fluid model; the results are qualitatively similar, although the potential varies by less than 4% in terms of the magnitude at the wall.

Plasma-wall transition in two ion species plasma with bi-Maxwellian electrons

Presheath and sheath structures of collisional two ion species (helium and argon) plasma in the presence of bi-Maxwellian electrons have been investigated by using a fluid model. As the thermal energy of hot electrons is higher than cold electrons, the electron impact ionization process is governed by the concentration of hot electrons. The velocity of positive ions at the sheath boundary, i.e., the Bohm criterion, gets modified in the presence of ion–neutral drag force, source term, and bi-Maxwellian electrons. It is found that the ion–neutral drag force, ionization rates, and volumetric composition of electrons affect the characteristics of the presheath and sheath. The scale length of the sheath region widens from about 1.09 mm to 5.80 mm with the increase in the concentration of hot electrons. The acoustic speed of helium ions at the sheath boundary is higher than its common speed, whereas the acoustic speed of argon ions is lower than its common speed. The common speed of positive ions at the sheath boundary is slower by 13% in magnitude than in the collisionless case. Furthermore, the effect of ion–neutral drag force on streaming instability for two ion species plasma has been systematically presented.

Au nanorods decorated TiO2 nanobelts with enhanced full solar spectrum photocatalytic antibacterial activity and the sterilization file cabinet application

TiO2 photocatalysts have been widely studied and applied for removing bacteria, but its antibacterial efficiency is limited to the ultraviolet (UV) range of the solar spectrum. In this work, we use the gold (Au) nanorods to enhance the visible and near-infrared (NIR) light absorption of TiO2 NBs, a typical UV light photocatalyst, thus the enhancement of its full solar spectrum (UV, visible and NIR) photocatalytic antibacterial properties is achieved. Preliminary surface plasmon resonance (SPR) enhancement photocatalytic antibacterial mechanism is suggested. On one hand, transverse and longitudinal SPR of Au NRs is beneficial for visible and NIR light utilization. On the other hand, Au NRs combined with TiO2 NBs to form the heterostructure, which can improve the photogenerated carrier separation and direct electron transfer increases the hot electron concentration while Au NRs as the electron channel can well restrain charge recombination, finally produces the high yield of radical oxygen species and exhibits a superior antibacterial efficiency. Furthermore, we design a sterilization file cabinet with Au NR/TiO2 NB heterostructures as the photocatalytic coating plates. Our study reveals that Au NR/TiO2 NB heterostructure is a potential candidate for sterilization of bacteria and archives protection.

Influence of ionization on sheath structure in electropositive warm plasma carrying two-temperature electrons with non-extensive distribution

A collisional electropositive plasma having two-temperature (hot and cold) electrons with non-extensive distribution and warm ions is investigated for the sheath structure by taking into account the ionization in plasma. A modified Bohm's sheath criterion is realized in such a plasma, which shows considerable dependence on the non-extensive parameter, collisional parameter, ionization, ion temperature, and concentration and temperature of hot electrons. The corrected choice for the initial value of the electric field at the sheath edge is obtained for a given set of plasma parameters. The sheath thickness and the electric potential in the sheath show significant modification under the effect of non-extensive parameters and temperature and concentration of hot electrons. A noticeable change in the sheath characteristics is also recorded for different ionization rates, collisional parameters, and ion temperatures. A comparative study for the two-temperature electrons having non-extensive distribution with the electrons having Boltzmann distribution and single-temperature electrons having non-extensive distribution is also done in order to uncover the role of two-temperature, i.e., hot and cold electrons.

Effect of two temperature electrons in a collisional magnetized plasma sheath

A collisional magnetized plasma consisting of two temperature electrons has been investigated numerically to study the sheath structure and the ion flux to the wall. The low-temperature electrons are described by Maxwellian distribution, and the high-temperature electrons are described by truncated Maxwellian distribution. It has been observed that sheath width and ion flux to the wall are non monotonous functions of collision frequency as well as hot electron concentration. A sheath formation criterion has been analytically derived and is used to find the ion velocity at the sheath edge. The sheath edge velocity is found to decrease with the increase of hot electron concentration and hot electron temperature. The study of such a system can help in understanding of plasma surface interaction.

Localized Surface Plasmon Resonance Enhanced Photocatalytic Hydrogen Evolution via Pt@Au NRs/C3N4 Nanotubes under Visible‐Light Irradiation

AbstractAu nanorods (NRs) decorated carbon nitride nanotubes (Au NRs/CNNTs) photocatalysts have been designed and prepared by impregnation–annealing approach. Localized surface plasmon resonance (LSPR) peaks of Au NRs can be adjusted by changing the aspect ratios, and the light absorption range of Au NRs/CNNTs is extended to longer wavelength even near‐infrared light. Optimal composition of Pt@Au NR769/CNNT650 has been achieved by adjusting the LSPR peaks of Au NRs and further depositing Pt nanoparticles (NPs), and the photocatalytic H2 evolution rate is 207.0 µmol h−1 (20 mg catalyst). Preliminary LSPR enhancement photocatalytic mechanism is suggested. On one hand, LSPR of Au NRs is beneficial for visible‐light utilization. On the other hand, Pt NPs and Au NRs have a synergetic enhancement effect on photocatalytic H2 evolution of CNNTs, in which the local electromagnetic field can improve the photogenerated carrier separation and direct electron transfer increases the hot electron concentration while Au NRs as the electron channel can well restrain charge recombination, finally Pt as co‐catalyst can boost H+ reduction rate. This work provides a new way to develop efficient photocatalysts for splitting water, which can simultaneously extend light absorption range and facilitate carrier generation, transportation and reduce carrier recombination.

Femtosecond laser-induced damage threshold in snow micro-structured targets

Enhanced acceleration of protons to high energy by relatively modest high power ultra-short laser pulses, interacting with snow micro-structured targets was recently proposed. A notably increased proton energy was attributed to a combination of several mechanisms such as localized enhancement of the laser field intensity near the tip of $1~\unicode[STIX]{x03BC}\text{m}$ size whisker and increase in the hot electron concentration near the tip. Moreover, the use of mass-limited target prevents undesirable spread of absorbed laser energy out of the interaction zone. With increasing laser intensity a Coulomb explosion of the positively charged whisker will occur. All these mechanisms are functions of the local density profile and strongly depend on the laser pre-pulse structure. To clarify the effect of the pre-pulse on the state of the snow micro-structured target at the time of interaction with the main pulse, we measured the optical damage threshold (ODT) of the snow targets. ODT of $0.4~\text{J}/\text{cm}^{2}$ was measured by irradiating snow micro-structured targets with 50 fs duration pulses of Ti:Sapphire laser.

Light-Enhanced Carbon Dioxide Activation and Conversion by Effective Plasmonic Coupling Effect of Pt and Au Nanoparticles.

Photocatalytic reduction of carbon dioxide (CO2) is attractive for the production of valuable fuels and mitigating the influence of greenhouse gas emission. However, the extreme inertness of CO2 and the sluggish kinetics of photoexcited charge carrier transfer process greatly limit the conversion efficiency of CO2 photoreduction. Herein, we report that the plasmonic coupling effect of Pt and Au nanoparticles (NPs) profoundly enhances the efficiency of CO2 reduction through dry reforming of methane reaction assisted by light illumination, reducing activation energies for CO2 reduction ∼30% below thermal activation energies and achieving a reaction rate 2.4 times higher than that of the thermocatalytic reaction. UV-visible (vis) absorption spectra and wavelength-dependent performances show that not only UV but also visible light play important roles in promoting CO2 reduction due to effective localized surface plasmon resonance (LSPR) coupling between Pt and Au NPs. Finite-difference time-domain simulations and in situ diffuse reflectance infrared Fourier transform spectroscopy further reveal that effective coupling LSPR effect generates strong local electric fields and excites high concentration of hot electrons to activate the reactants and intermediate species, reduce the activation energies, and increase the reaction rate. This work provides a new pathway toward the efficient plasmon-enhanced chemical reactions via reducing the activation energies by utilizing solar energy.

Hot-Electron Electroluminescence Under RF Operation in GaN-HEMTs: A Comparison Among Operational Classes

Electroluminescence microscopy and spectroscopy are used to compare the average hot-electron concentration and temperature under radio frequency (RF) operation class A, class B, and class F modes. From the results obtained, class A results, on average, in the highest hot-electron concentration, while class F is the mode with the lowest concentration due to its “L”-shaped load line. The electron temperature extracted from the electroluminescence spectra is reduced with increasing RF power, reflecting the dominance of electroluminescence from the portion of the load line in the semi-on region. The electroluminescence method is not able to give substantial information on the portion of the load line with high field and low current density which will be responsible for the potentially damaging hottest electrons present in the channel.

Surface Ligand-Mediated Plasmon-Driven Photochemical Reactions.

Contrary to the general expectation that surface ligands reduce the reactivity of surfaces by blocking the active sites, we present experimental evidence that surface ligands can in fact increase reactivity and induce important reaction pathways in plasmon-driven surface photochemistry. The remarkable effect of surface ligands is demonstrated by comparing the photochemistry of p-aminothiophenol (PATP) on resonant plasmonic gold nanorods (AuNRs) in the presence of citrate, hexadecyltrimethylammonium bromide (CTAB), and no surface ligands under visible light irradiation. The use of AuNRs with citrate and no surface ligand results in the usual azo-coupling reaction. In contrast, CTAB-coated AuNRs oxidize PATP primarily to p-nitrothiophenol (PNTP). Strong correlation has been observed between the N-O and Au-Br vibration band intensities, suggesting that CTAB influences the reaction pathway through the Br- counterions that can minimize the electron-hole recombination rate by reacting with the hole and hence increasing the concentration of hot electrons that drive the oxidation reaction.

Study of hot electrons in AlGaN/GaN HEMTs under RF Class B and Class J operation using electroluminescence

Electroluminescence microscopy and spectroscopy have been used to investigate hot electron concentration and electron temperature during RF operation. Two modes of operation were chosen, Class B and Class J, and compared with DC conditions. Hot electron concentration and temperature were on average lower for both RF modes than under comparative DC conditions. While these average values suggest that degradation due exclusively to hot electrons may be lower for RF than for DC conditions, the peak values in EL intensity and electric field along dynamic load lines have also to be taken into account and these are higher under Class J than Class B.

Degradation of AlGaN/GaN high electron mobility transistors related to hot electrons

This paper reports on an extensive analysis of the degradation of AlGaN/GaN high electron mobility transistors (HEMTs) submitted to on-state and off-state stresses. The results of this study indicate that: (i) the analyzed devices do not show any degradation when submitted to off-state stress tests up to 100 V; (ii) during on-state stress, devices show a significant decrease in drain current and in the electroluminescence (EL) signal; (iii) degradation rate is strongly dependent on the intensity of the EL signal measured during stress on the devices, which is related to the concentration of hot electrons in the channel. Based on the experimental evidence collected within this paper, the on-state degradation of HEMTs is ascribed to the trapping of negative charge in the gate-drain access region, triggered by hot electrons. By considering the intensity of the EL signal as a measure of the stress acceleration factor, we have derived an acceleration law for the hot-electron induced degradation.

Plasmonic Energy Collection through Hot Carrier Extraction

Conversion of light into direct current is important for applications ranging from energy conversion to photodetection, yet often challenging over broad photon frequencies. Here we show a new architecture based on surface plasmon excitation within a metal-insulator-metal device that produces power based on spatial confinement of electron excitation through plasmon absorption. Plasmons excited in the upper metal are absorbed, creating a high concentration of hot electrons which can inject above or tunnel through the thin insulating barrier, producing current. The theoretical power conversion efficiency enhancement achieved can be almost 40 times larger than that of direct illumination while utilizing a broad spectrum of IR to visible wavelengths. Here we present both theoretical estimates of the power conversion efficiency and experimental device measurements, which show clear rectification and power conversion behavior.