Energy Of Emitted Electrons Research Articles

Secondary electron emission properties of Zn-doped MgO thin films grown via electron-beam evaporation

The secondary electron emission (SEE) properties of Zn-doped MgO thin films (~700 nm thickness) grown via electron-beam evaporation have been studied based on Paschen curve measurements. The Zn-doped (1 at.%) MgO film shows an improved SEE coefficient (γ) compared to that of non-doped MgO from 0.02 to 0.05 in the 100 V Pa−1 m−1 region. The origin of a superior γ is due to the reduction in the band-gap from 6.79 eV to 6.26 eV (the values are measured via ultra-violet photoemission spectroscopy; UPS) because γ is normally determined by the Auger neutralization process, which uses the neutralization energy of ion valence band electron emission. This thin film can be used in new kinds of plasma devices, such as flat-fluorescent lamps, plasma displays, electron emitters, and ionized mass spectrometers.

Nonadiabatic ponderomotive effects in photoemission from nanotips in intense midinfrared laser fields

Transient near fields around metallic nanotips drive many applications, including the generation of ultrafast electron pulses and their use in electron microscopy. We have investigated the electron emission from a gold nanotip driven by midinfrared few-cycle laser pulses. We identify a low-energy peak in the kinetic energy spectrum and study its shift to higher energies with increasing laser intensities from 1.7 to $8.9\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. The experimental observation of the upshift of the low-energy peak is compared to a simple model and numerical simulations, which show that the decay of the near field on a nanometer scale results in nonadiabatic transfer of the ponderomotive potential to the kinetic energy of emitted electrons and in turn to a shift of the peak. We derive an analytic expression for the nonadiabatic ponderomotive shift, which, after the previously found quenching of the quiver motion, completes the understanding of the role of inhomogeneous fields in strong-field photoemission from nanostructures.

Correlation between electron work functions of multiphase Cu-8Mn-8Al and de-alloying corrosion

Low energy electron emission microscopy (LEEM) was used to measure local transition energy that was directly correlated to electron work function (EWF) of multiphase manganese-aluminum bronze alloys. We developed color mapping to distinguish the EWF of multiple phases and clarified that the EWF were in the following order: EWF of α > EWF of β > EWF of κ (EWFα > EWFβ > EWFκ). De-alloying corrosion took place due to the micro-galvanic cell at grain boundaries before it propagated into the β phase that had lower EWF than the α phase. The α phase was a stable phase because it contained high Cu while the β phase contained high Al and Mn. In addition, XRD analysis showed that the texture coefficient of the β phase revealed that almost all of the grains had (2 2 0) orientation, the lowest EWF compared to (1 1 1) and (2 0 0). Furthermore, transmission electron microscopy illustrated that there were fine Cu3Mn2Al precipitates in the Cu2MnAl matrix of the β phase. These precipitates formed micro-galvanic cells which played an important role in accelerating de-alloying corrosion.

Observation of fast and slow interatomic Coulombic decay in argon dimers induced by electron-impact ionization

We investigate the interatomic Coulombic decay (ICD) in argon dimers induced by electron-impact ionization (${E}_{0}=90\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$) using a multiparticle coincidence experiment in which the momentum vectors and, consequently, the kinetic energies for electrons and fragment ions are determined. The signature of the ICD process is obtained from a correlation map between ejected electron energy and kinetic energy release (KER) for ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{+}$ fragment ions where low-energy ICD electrons can be identified. Furthermore, two types of ICD processes, termed fast and slow interatomic decay, are separated by the ICD initial-state energies and projectile energy losses. The dependence of the energies of emitted low-energy ICD electrons on the initial-state energy is studied. ICD electron energy spectra and KER spectra are obtained separately for fast and slow decay processes where the KER spectra for the slow decay channel are strongly influenced by nuclear motion. The KER and ICD electron energy spectra are well reproduced by ab initio calculations.

Double-differential cross sections for single ionization of simple polyatomic molecules by proton impact

A theoretical study of double-differential cross sections (DDCSs) for single ionization of ${\text{CH}}_{{}_{4}}$ and ${\text{NH}}_{{}_{3}}$ molecules by collision with proton is presented at 0.25, 1, and 2 MeV, respectively. For the final state, we use a continuum distorted wave that contains the product of three-Coulomb distortion due to pairwise Coulombic interactions for which it is called the three-Coulomb wave model. In the entrance channel, the Coulomb distortion between the incoming projectile and the target is taken. In this model, the ground state of the polyatomic molecule is described by means of an accurate one-center molecular wave function, which is a linear combination of atomic orbitals. The contributions of DDCSs for different molecular orbitals of the polyatomic molecules to the spectrum of angular distributions at different electron emission energies have also been analyzed. Generally the preference for ionization depends on the binding energy of the active electron in molecular orbital in the ascending order of loosely bound electrons to more tightly bound electrons. At large ejected electron and projectile energy, the lesser bound electrons in the molecules dominate the DDCS at extreme forward emission angles. The present DDCS results are compared with available experimental and the theoretical findings. In case of ammonia molecules, good agreement is observed at all projectile energies, showing that the present model is sufficient to explain all the experimental data for double-differential cross sections. However, some degree of discrepancy is observed at 2 MeV proton impact for small electron emission angles when ${\text{CH}}_{{}_{4}}$ molecular target is considered.

Differential electron emission from polycyclic aromatic hydrocarbon molecules under fast ion impact

Interaction between polycyclic aromatic hydrocarbon (PAH) molecule and energetic ion is a subject of interest in different areas of modern physics. Here, we present measurements of energy and angular distributions of absolute double differential electron emission cross section for coronene (C24H12) and fluorene (C13H10) molecules under fast bare oxygen ion impact. For coronene, the angular distributions of the low energy electrons are quite different from that of simpler targets like Ne or CH4, which is not the case for fluorene. The behaviour of the higher electron energy distributions for both the targets are similar to that for simple targets. In case of coronene, a clear signature of plasmon resonance is observed in the analysis of forward-backward angular asymmetry of low energy electron emission. For fluorene, such signature is not identified probably due to lower oscillator strength of plasmon compared to the coronene. The theoretical calculation based on the first-order Born approximation with correct boundary conditions (CB1), in general, reproduced the experimental observations qualitatively, for both the molecules, except in the low energy region for coronene, which again indicates the role of collective excitation. Single differential and total cross sections are also deduced. An overall comparative study is presented.

Electron emission yield for low energy electrons: Monte Carlo simulation and experimental comparison for Al, Ag, and Si

The electron emission under electron impact between 10 eV and 2 keV is investigated with a Monte Carlo (MC) code in aluminum, silver, and silicon. The code is based on the complex dielectric function theory to describe the inelastic scattering and uses the Mott's model of partial waves to describe the elastic scattering. It takes into account both volume and surface plasmon excitations. The simulation results are compared with the experimental measurements of electron emission yields (EEY) and energy spectra of low energy electrons performed in ultrahigh vacuum on Ar-etched bulk samples. Our MC simulations at low energy are found to be in fairly good agreement with our experimental measurements. The peaks corresponding to the surface plasmon, the volume plasmon and its multiples and to the Auger transitions appear clearly on the energy loss spectra of aluminum, silver, and silicon. The simulated EEY are also in fairly good agreement with our measurements and with data from the literature. The EEY at normal incidence is studied for secondary and backscattered electrons. A focus is made for the EEY below 50 eV where a fairly good agreement is found with Bronstein and Fraiman's measurements on vacuum evaporated samples. Below 2 keV, for silver and aluminum, the total EEY is given for different angles of incidence θ. Some discrepancies are observed between our experimental measurements and our MC simulations for high angles of incidence. These discrepancies can be attributed to the modeling of surface plasmon excitations, surface oxidation, or roughness that occur during the Ar-etching process.

Backscattered electron emission after proton impact on carbon and gold films: Experiments and simulations

This work aims at measuring the proton induced secondary electron energy spectra from nanometer thin films. Backscattered electron energy spectra were measured within an energy range from 0 to 600eV using a Retarding Field Analyser (RFA). This paper presents energy spectra obtained for proton (0.5MeV; 1MeV; 1.5MeV; 2MeV) irradiation of thin carbon films (50 and 100nm thick) and thin gold film (200nm). These experimental spectra were compared with Monte Carlo simulations based on TRAX code and Geant4 simulation toolkit. Good agreement between experimental, TRAX and Geant4 results were observed for the carbon target. For the gold target, we report major differences between both Monte Carlo environments. Limitation of Geant4 models for low energy electron emission was highlighted. On the contrary, TRAX simulations present encouraging results for the modeling of low-energy electron emission from gold target.

Constraints on the Location of the Gamma-ray Emission Region for the Gamma-ray-loud Radio Source GB 1310+487

Abstract We employ a single-zone leptonic jet model, with synchrotron, synchrotron self-Compton, and external Compton (EC) processes, to reproduce the quasi-simultaneous multi-wavelength spectral energy distributions in active and quiescent states of the narrow-line gamma-ray-loud radio source GB 1310+487. In the case of the EC process, the external seed photons from both the broad line region (BLR) and the dust torus are considered by assuming that the gamma-ray emission region is located at the outside boundary of the BLR and inside the dust torus. Comparing the energy density of external photon fields obtained by model fitting with that constrained from the BLR observations. We find that the location of the gamma-ray-emitting region of GB 1310+487 can be tightly constrained at the outer edge of the BLR (the dissipation distance of the γ-ray emission region from central black hole ). The ratio of magnetic energy and emitting-electron energy in the radiation blob ( ) is gradually increased from Flare 1, to Flare 2, to Post-flare, where the magnetic energy increases and the matter energy decreases. These results suggest that the conversion of the magnetic field and the matter (radiation electrons) energy and the location of the γ-ray emission region (or ambient photon field) may play an important role in different radiation states of GB 1310+487.

An experimental setup for studying the core-excited atoms and molecules by electron impact using energy analysed electron–ion coincidence technique

Operation and performance of an apparatus for studying the decay dynamics relevant to core–hole decay processes in atoms and molecules excited by energetic electrons using an energy analysed electron–ion coincidence technique are described in some detail. The setup consists of a time- and position sensitive double-field linear TOF mass spectrometer coupled with a dual MCP detector and a single-pass CMA to select the energy of detected electrons. Details of different components involved in the setup are presented and discussed. To demonstrate the performance and capability of the apparatus, we present some typical results extracted from the TOF argon ion-mass spectra observed in coincidence with 18-energy selected electrons emitted from interaction of a continuous beam of 3.5 keV electrons with a dilute gaseous target of argon atoms. Specifically, the variation of relative correlation probability for the final ion-charge states Ar1+ to Ar4+ produced in the considered collision reactions as a function of energy of emitted electrons is determined and discussed.

Ionizing Doses Calculations for Low Energy Electrons in Silicon and Aluminum

The electron transport at low and very low energy (10 eV–2 keV) is investigated with a Monte Carlo (MC) code in silicon and aluminum. The elastic scattering with nuclei is described by Mott’s model of partial waves, whereas the inelastic collisions with electrons are described by the complex dielectric function theory. Comparisons of MC simulations with electron emission yields (EEY) and energy loss spectra experimentally measured in ultrahigh vacuum on Ar-etched samples are given. The practical ranges and the ionizing dose calculations are presented down to 10 eV for electrons in silicon and aluminum. The simulation results show a correlation between the EEY and the ionizing doses. At low energy, while the electrons stay in the first ~10 nm from the surface due to the elastic scattering, the EEY increases and the ratio of the ionizing dose over the incident energy decreases. Above 200 eV, when the electrons go deeper into the solid due to the inelastic scattering, the EEY decreases and the ionizing dose ratio increases.

Electron emission in collisions between atoms and dressed projectiles

We present theoretical results for electron emission in collisions between helium atoms and dressed projectiles at high energies. Double-differential cross sections (DDCSs) as a function of the emitted electron energies and angles are calculated. In our study we have applied the three-body formalism using the three-Coulomb wave (3CW–3B) model. The interaction between the dressed projectile and the active electron in the target has been approximated by a model potential having both a long-range Coulomb potential part and a short-range part. However, the active electron in the target has been treated as hydrogenic. We have also studied the projectile charge state dependence of the DDCS. Our theoretical results are compared with available experimental data as well as other theoretical calculations. The comparison shows a good agreement between the present calculations and the measurements. The obtained results are also compatible with other theoretical findings.

Ionization of N2 in collisions with fast electrons: Evidence of an interference effect

Absolute double differential cross sections (DDCS) of electron emission were measured for ionization of ${\mathrm{N}}_{2}$ by fast electrons with energy 7 keV. Measurements were performed for different electron emission angles and energies. Evidence of oscillation due to Young-type interference was observed in the DDCS ratios for all angles. The frequency for large backward angle is found to be larger compared to that for small forward angle. Consequently, the forward-backward asymmetry parameter reveals the oscillatory structure even more clearly. The oscillations observed for both experimental-to-theoretical DDCS ratios and forward-backward asymmetry were well explained by the Cohen-Fano model of interference in a molecular double slit. A periodic deviation of the Cohen-Fano model from the asymmetry parameter data reveals the presence of a higher-frequency component. The first Born model was employed to explain the results of molecular nitrogen for which a complete-neglect-of-differential-overlap approximation was used along with an effective atomic number.

Pulse train dependence of electron dynamics during resonant femtosecond laser nonlinear ionization of a Na4 cluster

In this study, a real-time and real-space time-dependent density functional theory (TDDFT) is applied to describe nonlinear electron–photon interactions during a resonant femtosecond laser pulse train photoionization of a Na4 cluster. The effects of key pulse train parameters, such as the spatial/temporal pulse energy distribution, pulse number per train, pulse separation and pulse phase on resonant absorption, are discussed. The calculations show that the resonant effect and the nonlinear electron dynamics, including energy absorption, electron emission, dipole response and ionization probability, can be controlled by shaping the ultrafast laser pulse train.

Evidence for room-temperature in-diffusion of nickel into silicon

Interstitial nickel in crystalline Si is shown to be a fast diffuser at room temperature. In this study, Ni is incorporated in Si by wet chemical etching in nickel-contaminated alkaline solutions. Nickel in-diffusion is observed by means of detecting the electrically active NiVO defect, which is formed due to Ni capture to the vacancy–oxygen complex in electron-irradiated Si. The depth profiles of the NiVO concentration measured by the deep-level transient spectroscopy technique extend to ∼15 μm in the samples doped with Ni at 35 °C for 30 min. This allows us to get a lower estimate for the nickel diffusivity at this temperature as 10−9 cm2/s. The activation energy for electron emission from the NiVO level and the apparent capture cross section are equal to 371 meV and 3 × 10−15 cm2, respectively. The NiVO complex dissociates at 300 °C reestablishing the initial concentration of the VO centers.

Laser-driven micro-Coulomb charge movement and energy conversion to relativistic electrons

Development of robust instrumentation has shown evidence for a multi-μC expulsion of relativistic electrons from a sub-μm-thick foil, laser illuminated with 60–70 J on target at 2 × 1020 W/cm2. From previous work and with electron spectroscopy, it is seen that an exponential electron energy distribution is accurate enough to calculate the emitted electron charge and energy content. The 5–10-μC charge for the >100-TW Trident Laser represents the first active measurement of the >50% laser-light-to-electron conversion efficiency. By shorting out the TV/m electric field usually associated with accelerating multi-MeV ions from such targets, one finds that this charge is representative of a multi-MA current of relativistic electrons for diverse applications from electron fast ignition to advanced radiography concepts. Included with the details of the discoveries of this research, shortcomings of the diagnostics and means of improving their fidelity are discussed.

Ionization of small molecules induced byH+, He+, andN+projectiles: Comparison of experiment with quantum and classical calculations

We report the energy and angular distribution of ejected electrons from $\mathrm{C}{\mathrm{H}}_{4}$ and ${\mathrm{H}}_{2}\mathrm{O}$ molecules impacted by 1 MeV ${\mathrm{H}}^{+}, \mathrm{H}{\mathrm{e}}^{+}$, and 650 keV ${\mathrm{N}}^{+}$ ions. Spectra were measured at different observation angles, from 2 to 2000 eV. The obtained absolute double-differential electron-emission cross sections (DDCSs) were compared with the results of classical trajectory Monte Carlo (CTMC) and continuum distorted wave, eikonal initial state (CDW-EIS) calculations. For the bare ${\mathrm{H}}^{+}$ projectile both theories show remarkable agreement with the experiment at all observed angles and energies. The CTMC results are in similarly good agreement with the DDCS spectra obtained for impact by dressed $\mathrm{H}{\mathrm{e}}^{+}$ and ${\mathrm{N}}^{+}$ ions, where screening effects and electron loss from the projectile gain importance. The CDW-EIS calculations slightly overestimate the electron loss for 1 MeV $\mathrm{H}{\mathrm{e}}^{+}$ impact, and overestimate both the target and projectile ionization at low emitted electron energies for 650 keV ${\mathrm{N}}^{+}$ impact. The contribution of multiple electron scattering by the projectile and target centers (Fermi shuttle) dominates the ${\mathrm{N}}^{+}$-impact spectra at higher electron energies, and it is well reproduced by the nonperturbative CTMC calculations. The contributions of different processes in medium-velocity collisions of dressed ions with molecules are determined.

Modification of internal barrier in hydrogen‐terminated heavily phosphorus‐doped diamond for field emission

In this article, a field‐induced electron emission from hydrogen (H)‐terminated surface of heavily phosphorus (P)‐doped diamond is discussed based on the barrier lowering model. Ultraviolet photoelectron spectroscopy suggested that an upward band bending of 1.45 eV existed at the surface of the diamond. A field emission characteristic as a function of the distance between an anode and diamond was measured to evaluate an average electric field in the vacuum. The barrier lowering model was introduced to estimate the reduction of the internal barrier due to the electric field at the diamond surface. The barrier lowering effect was confirmed from energies of emitted electrons, measured by combined ultraviolet photoelectron spectroscopy/field‐induced electron spectroscopy (UPS/FES). As a result, it was shown that the electron emission from n‐type diamond having NEA surface could be modulated by controlling a local electric field.

Pump laser-induced space-charge effects in HHG-driven time- and angle-resolved photoelectron spectroscopy

With the advent of ultrashort-pulsed extreme ultraviolet sources, such as free-electron lasers or high-harmonic-generation (HHG) sources, a new research field for photoelectron spectroscopy has opened up in terms of femtosecond time-resolved pump-probe experiments. The impact of the high peak brilliance of these novel sources on photoemission spectra, so-called vacuum space-charge effects caused by the Coulomb interaction among the photoemitted probe electrons, has been studied extensively. However, possible distortions of the energy and momentum distributions of the probe photoelectrons caused by the low photon energy pump pulse due to the nonlinear emission of electrons have not been studied in detail yet. Here, we systematically investigate these pump laser-induced space-charge effects in a HHG-based experiment for the test case of highly oriented pyrolytic graphite. Specifically, we determine how the key parameters of the pump pulse—the excitation density, wavelength, spot size, and emitted electron energy distribution—affect the measured time-dependent energy and momentum distributions of the probe photoelectrons. The results are well reproduced by a simple mean-field model, which could open a path for the correction of pump laser-induced space-charge effects and thus toward probing ultrafast electron dynamics in strongly excited materials.

Single ionization of water molecules in collisions with bare ions

We present the double differential cross sections (DDCSs) for the direct ionization of water molecules by impact of fully stripped helium, carbon and oxygen atoms, respectively. In the present formalism, we have represented the wavefunction in the entrance channel as the product of a plane wave for the projectile and an accurate one-center-molecular wavefunction of the water molecule by Moccia (1964 J. Chem. Phys. 40 2186). In the exit channel, we have expressed the total wavefunction as the product of pair-wise Coulomb wavefunctions among the ejected electron, projectile ion and the residual target ion, respectively. The contributions of DDCSs for five different molecular orbitals of water to the spectrum of angular distributions have been analyzed for several electron emission energies. The present results for DDCSs are compared with existing experimental and theoretical findings. We find an overall good agreement between our calculated results and the experimental findings for electron emission cross sections. In addition, DDCS results for ionization from different orbitals at a few electron emission energies are given in tabular form.