Electron Loss Processes Research Articles

Observations of the impenetrable barrier, the plasmapause, and the VLF bubble during the 17 March 2015 storm

AbstractVan Allen Probes observations during the 17 March 2015 major geomagnetic storm strongly suggest that VLF transmitter‐induced waves play an important role in sculpting the earthward extent of outer zone MeV electrons. A magnetically confined bubble of very low frequency (VLF) wave emissions of terrestrial, human‐produced origin surrounds the Earth. The outer limit of the VLF bubble closely matches the position of an apparent barrier to the inward extent of multi‐MeV radiation belt electrons near 2.8 Earth radii. When the VLF transmitter signals extend beyond the eroded plasmapause, electron loss processes set up near the outer extent of the VLF bubble create an earthward limit to the region of local acceleration near L = 2.8 as MeV electrons are scattered into the atmospheric loss cone.

Strong asymmetry of the electron-loss-to-continuum cusp of multielectronU28+projectiles in near-relativistic collisions with gaseous targets

The process of electron-loss to the continuum (ELC) has been studied for the collision systems ${\mathrm{U}}^{28+}+{\mathrm{H}}_{2}$ at a collision energy of 50 MeV/u, ${\mathrm{U}}^{28+}+{\mathrm{N}}_{2}$ at 30 MeV/u, and ${\mathrm{U}}^{28+}+\mathrm{Xe}$ at 50 MeV/u. The energy distributions of cusp electrons emitted at an angle of ${0}^{\ensuremath{\circ}}$ with respect to the projectile beam were measured using a magnetic forward-angle electron spectrometer. For these collision systems far from equilibrium charge state, a significantly asymmetric cusp shape is observed. The experimental results are compared to calculations based on first-order perturbation theory, which predict an almost symmetric cusp shape. Some possible reasons for this discrepancy are discussed.

Plasmon Response and Electron Dynamics in Charged Metallic Nanoparticles.

Using the time-dependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spill-out from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment.

Multiple loss processes of relativistic electrons outside the heart of outer radiation belt during a storm sudden commencement

AbstractBy examining the compression‐induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP‐A/B), we find that the relativistic electrons (>2 MeV) outside the heart of outer radiation belt (L* ≥ 5) undergo multiple losses during a storm sudden commencement. The relativistic electron loss mainly occurs in the field‐aligned direction (pitch angle α < 30° or >150°), and the flux decay of the field‐aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30°–150° increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL| < 0.25) of the RBSP‐B (RBSP‐A) location, and the electron fluxes in the quasi‐perpendicular direction display energy‐dispersive oscillations in the Pc5 period range (2–10 min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high‐L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850 km), and magnetic field fluctuations in the Pc5 band. The intense EMIC waves and whistler mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 h. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high‐L region with a negative electron phase space density gradient.

Study of Transient Spark Discharge Properties Using Kinetic Modeling

The kinetic model simulating plasma chemistry induced by Transient Spark (TS) discharge in air is presented in this paper. TS is a dc-driven self-pulsing discharge of streamer-to-spark transition type. The presented kinetic model defines the temporal evolution of reduced electric field strength $E/N$ , gas temperature, and density of neutrals $N$ during the evolution of TS discharge, so that calculated electron density is in agreement with experimental results. We studied the mechanism of the streamer-to-spark transition and breakdown in TS using this model. We assume that the breakdown mechanism in TS is based on the gas density decrease and can be summarized as follows: heating of the channel $\rightarrow $ increase in the pressure $\rightarrow $ hydrodynamic expansion $\rightarrow $ decrease in $N$ in the core of the channel $\rightarrow $ increase in $E/N~\rightarrow $ acceleration of ionization processes. However, this mechanism is influenced by species accumulated due to previous TS pulses at higher TS repetition frequencies. Sensitivity analysis focused on major electron loss and production processes indicates an important role of the amount of O2 dissociated by the previous pulses. A lower density of O2 means a lower rate of electron attachment, while accumulated atomic oxygen atoms lead to acceleration of electron detachment processes.

Classical treatment of Li2++Ar and He2++Ar collisions

SynopsisClassical Trajectory Monte Carlo calculations are carried out for Li2++Ar and He2++Ar collisions, motivated by recent experiments on these systems. Cross sections for electron capture, projectile electron loss and target multiple ionization processes are evaluated and compared to the experimental values in the 75-500 keV/amy impact energy range.

A numerical lattice approach for ionization and capture processes in ion-H2O collisions

SynopsisWe present a semi-classical numerical integration method for studying electron loss processes in ion collisions with water molecules. Capture and ionization cross section are calculated in the intermediate-high energy range, and the kinetic energy distribution of the ejected electrons is analyzed. The results are compared with those obtained with a classical Monte Carlo method.

Rapid MeV electron precipitation as observed by SAMPEX/HILT during high‐speed stream‐driven storms

AbstractA number of relativistic electron loss processes exist in the inner magnetosphere, and the extent to which MeV electron precipitation into Earth's atmosphere plays a role in radiation belt dynamics is a topic of much debate. In this work, we investigate the contribution of electron precipitation to radiation belt losses, looking at what times and locations precipitation is important. Through high‐cadence low‐altitude measurements from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite, we examine the distributions of millisecond (microburst) as well as longer‐duration (band‐type) precipitation and the relative contributions of these two precipitation types to radiation belt dynamics during high‐speed stream (HSS)‐driven storms. Different local time and radial distributions between microbursts and precipitation bands suggest different scattering mechanisms as the causes of the two precipitation types. In a superposed epoch study of 42 HSS‐driven storms, enhanced main and recovery phase losses to the atmosphere are observed. Microburst occurrence rates peak in the recovery phase of the storms, while their magnitudes remain fairly constant over storm phase. Precipitation bands show an increase in both occurrence and magnitude at storm onset, particularly at the inner edge of the outer radiation belt. The observations, enabled by the high time resolution and large geometric factor and field of view of the SAMPEX/Heavy Ion Large Telescope (HILT) instrument, reveal when and where microburst and band‐type precipitation are contributing to radiation belt dynamics during HSS‐driven storms.

The cause for the low efficiency of dye sensitized solar cells with a combination of ruthenium dyes and cobalt redox.

It has been a concern that the cobalt redox cannot give a good performance for the dye-sensitized solar cells when it is used with ruthenium dyes. The electron dynamics measurements clarified the electron loss processes, and clarified the cause. The result indicated the direct interaction between the ruthenium dyes with the cobalt redox, and it reduced the charge injection from the triplet state of the dyes to the titanium oxide, and also it increased the electron recombination process with the cobalt redox species. Both the problems of injection and recombination were solved by using the ruthenium dye with alkyl chains keeping a distance between the dye and the cobalt redox.

Crystal orientation dependence of charge distributions of He ions scattered from rutile TiO2(1 1 0) surfaces

It is well known that the charge distributions of medium energy He ions scattered from solid surfaces depend on emerging energy and angle as well as surface materials. We analyzed emerging energy and angle dependence of He+ fractions for medium energy He ions scattered from top-layer Ti atoms at the [11¯0]- and [001]-azimuth of rutile TiO2(110). He+ fractions for the [001]- and [11¯0]-azimuth were equilibrated at emerging angles (scaled from surface normal) above ∼75° and ∼85°, respectively. It was also found that non-equilibrated He+ fractions observed at smaller emerging angles for the [11¯0]-azimuth were larger more than 20% than those for the [001]-azimuth and the difference between the He+ fractions for the [11¯0]- and [001]-azimuth increased with increasing emerging energy. The Ti–Ti bond length along the [11¯0]-axis is more than twice that along the [001]-axis. Thus the He ions scattered from top-layer Ti atoms at the [001]-azimuth interact with many outer electrons of the aligned top-layer Ti atoms until leaving from surfaces. A He ion immediately after a large-angle collision has no bound electron because of time–energy uncertainty. The He2+ ion then undergoes electron capture and loss processes during passing through the surface. In this regard, the non-equilibrated He+ fractions for the [001]-azimuth are smaller than those for the [11¯0]-azimuth.

ChemInform Abstract: Energy Loss Structures in HAXPES Spectra of Solids

AbstractReview: 49 refs.

Absolute cross sections for electron loss, electron capture, and multiple ionization in collisions of Li2+ with argon

Exclusive absolute cross sections for the electron loss and capture processes, accompanied by target multiple ionization and pure target multiple ionization, as well as total electron loss and capture cross sections, in collisions of Li2+ with Ar have been measured in the 0.5–3.5 MeV energy range. The experimental data of the total electron loss cross section are compared with theoretical results based on the plane-wave Born approximation and the free-collision model, and with the available experimental data. Some discrepancies are observed when comparing the experimental data with the theoretical models, which can be attributed to the competitive mechanisms that lead to electron loss. The dependences of the single-capture and transfer-ionization processes on the projectile charge state are similar to those observed for collisions between other low-charged light ions and noble-gas targets. The same behaviour is observed when one compares the present data for the single- and double-ionization cross sections with those for He2+ projectiles on Ar. These facts indicate that the dynamics of the collision does not seem to depend on the projectile species, so that few-electron projectiles may act as structureless point charges in the intermediate- to high-velocity regime.

Structural and optical characterization of SiO2 under irradiation with swift heavy ions

SiO2 single crystals irradiated with 600keV, 4 and 5MeV Kr ions using the 320kV High Voltage Experimental Platform (IMP, Lanzhou) were investigated with infrared, fluorescence spectroscopes and TEM. In the low-energy regime, single ion tracks are well separated and the damage process is dominated by the formation of simple color centers such as F+ and F2 centers. For the high energy ions, the energy density in ion tracks produced at a high stopping power is larger, and consequently the defect concentration increases significantly. At higher defect densities, the distance between single defects is smaller facilitating the aggregation of individual electron center to defect cluster and defect annihilation by recombination of hole and electron centers. The latter process determines the limited efficiency of color-center creation under heavy-ion irradiation. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes.

Ion-impact-induced interatomic Coulombic decay in neon and argon dimers

We investigate the contribution of interatomic Coulombic decay induced by ion impact in neon and argon dimers (Ne${}_{2}$ and Ar${}_{2}$) to the production of low-energy electrons. Our experiments cover a broad range of perturbation strengths and reaction channels. We use 11.37 MeV/u S${}^{14+}$, 0.125 MeV/u He${}^{1+}$, 0.1625 MeV/u He${}^{1+}$, and 0.150 MeV/u He${}^{2+}$ as projectiles and study ionization, single and double electron transfer to the projectile, as well as projectile electron loss processes. The application of a COLTRIMS reaction microscope enables us to retrieve the three-dimensional momentum vectors of the ion pairs of the fragmenting dimer into Ne${}^{q+}$-Ne${}^{1+}$ and Ar${}^{q+}$-Ar${}^{1+}$ ($q=$ 1, 2, 3) in coincidence with at least one emitted electron.

Theoretical investigation of the electron capture and loss processes in the collisions of He2+ + Ne

Based on the time-dependent density functional theory, a method is developed to study ion-atom collision dynamics, which self-consistently couples the quantum mechanical description of electron dynamics with the classical treatment of the ion motion. Employing real-time and real-space method, the coordinate space translation technique is introduced to allow one to focus on the region of target or projectile depending on the actual concerned process. The benchmark calculations are performed for the collisions of He(2+) + Ne, and the time evolution of electron density distribution is monitored, which provides interesting details of the interaction dynamics between the electrons and ion cores. The cross sections of single and many electron capture and loss have been calculated in the energy range of 1-1000 keV/amu, and the results show a good agreement with the available experiments over a wide range of impact energies.

Energy loss structures in HAXPES spectra of solids

Energy loss processes of high energy electrons induced by hard X-rays are significantly influencing the shape of the measured electron spectra, therefore the consideration and deeper understanding of these processes is important for extracting information on electronic structure or chemical composition of bulk or near surface region of solids using Hard X-ray Photoelectron Spectroscopy (HAXPES). Beginning with fundamental concepts and definitions, through discussion of models describing energy loss processes of energetic electrons in the near surface regions of solids and finally discussing methods of corrections for these processes turned to be useful when evaluating hard X-ray induced electron spectra, this review intends to provide a brief summary on this field for users of the HAXPES method.

Color center creation in SiO2 under irradiation with swift heavy ions: Dependence on energy loss and fluence

SiO2 single crystals irradiated with 600keV, 2MeV, 4MeV and 95MeV Ar ions using 320kV high voltage Experimental platform (IMP, Lanzhou) and the HIRFL-SFC (Heavy Ion Research Facility in Lanzhou) facility in Lanzhou were investigated by Infrared spectra and fluorescence spectroscopes. PL spectra peaks of silicon dioxide irradiated with 600keV, 2MeV, 4MeV and 95MeV Ar ions were located at 445nm (F2 color center), 570nm (F4 color center) and 650nm (F2+ and F3+ color centers) emission band etc. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses derived from the reciprocity approach, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes.

Distorted wave calculations for electron loss process induced by bare ion impact on biological targets

Distorted wave models are employed to investigate the electron loss process induced by bare ions on biological targets. The two main reactions which contribute to this process, namely, the single electron ionization as well as the single electron capture are here studied. In order to further assess the validity of the theoretical descriptions used, the influence of particular mechanisms are studied, like dynamic screening for the case of electron ionization and energy deposition on the target by the impacting projectile for the electron capture one. Results are compared with existing experimental data.

The study of influence of doping by iodine or gallium on the lifetime of photogenerated current carriers in CdTe

This study investigated how doping by iodine or gallium affects processes associated with current carriers by undertaking a kinetics investigation of electron loss processes in the CdTe samples prepared by direct ampoule method. Owing to these processes, the current carriers generated by light can be trapped or recombined after a thermalization process and fail to reach electrodes during their lifetime and adversely impact the photovoltaic performance of solar cells. The microwave photoconductivity method provides an effective means of obtaining direct data on the lifetime and energy distribution of traps for current carriers. The obtained lifetimes in doped materials were compared to those in initial polycrystalline CdTe and monocrystalline CdTe. The experimental results indicate that the free electron lifetimes become higher after the doping. We found that the lifetime in the doped polycrystalline samples was equal (for I-doped samples) or even higher (for Ga-doped samples) than in CdTe monocrystals. The model based on the self compensation effect was suggested for the explanation of the experimental results.

High Photoconductive Response of Gas-Sensitized Porous Nanocrystalline TiO2 Film in Formaldehyde Ambience and Carrier Transport Kinetics

We propose a gas-sensitized porous nanocrystalline TiO2 film with a potential application in photovoltaic devices and report about the systematic photoconductivity study of it. The quantitative results show that the gas-sensitized TiO2 film in formaldehyde atmosphere exhibits much higher photoconductivity (3–4 orders of magnitude) and longer carrier lifetime than usual. The intriguing performance of the gas-sensitized TiO2 film indicates the distinct charge carrier transport kinetic courses, whose contributions to the photoconductivity are shown in a designed flowchart. From the flowchart, it is clearly found that two electron loss processes, recombination and electron scavenging, are suppressed for the gas-sensitized TiO2 film in formaldehyde gas, leading to large improvements of photoconductivity and carrier lifetime. The results provide the potential of improving efficiency of photovoltaic devices, and measuring photoconductivity under target gas appears to be a useful tool for research on photocatalytic and photoelectrical processes.