Ejected Electrons Research Articles

Coulomb focusing in retrapped ionization with near-circularly polarized laser field.

The full three-dimensional photoelectron momentum distributions of argon are measured in intense near-circularly polarized laser fields. We observed that the transverse momentum distribution of ejected electrons by 410-nm near-circularly polarized field is unexpectedly narrowed with increasing laser intensity, which is contrary to the conventional rules predicted by adiabatic theory. By analyzing the momentum-resolved angular momentum distribution measured experimentally and the corresponding trajectories of ejected electrons semiclassically, the narrowing can be attributed to a temporary trapping and thereby focusing of a photoelectron by the atomic potential in a quasibound state. With the near-circularly polarized laser field, the strong Coulomb interaction with the rescattering electrons is avoided, thus the Coulomb focusing in the retrapped process is highlighted. We believe that these findings will facilitate understanding and steering electron dynamics in the Coulomb coupled system.

Strong-field dissociative Rydberg excitation of oxygen molecules: Electron-nuclear correlation

We experimentally investigate strong-field dissociative Rydberg excitation (DRE) of ${\mathrm{O}}_{2}$ molecules by using the photoelectron photoion coincidence spectrum, in which the outgoing neutral Rydberg fragments created by the strong laser fields are postionized by the weak static dc field of the spectrometer and afterwards detected as charged particles. The peak positions of the sum-kinetic energy release (KER) spectrum of the ejected nuclear fragments and electrons of the dissociative single ionization (DSI) channel are measured to be similar to that of the DRE channel, although their nuclear KER spectra are distinct. It indicates that the same number of photons is absorbed by the molecule in accessing the DRE and DSI channels, which are partitioned by the electron and nuclear fragments with various proportions. Different pathways towards the DRE and DSI channels are discussed based on the correlated dynamics of the nuclear fragments and electrons. Our results show that the DRE channel observed here is mostly accessed by the multiphoton resonance excitation process.

Relativistic photoionization cross section calculations and resonance parameters for Mg-like Se XXIII

Photoionization cross sections of the ground state 2p63s2 (1S0) and the first three excited states 2p63s3p (3Po0,1,2) of Mg-like Se XXIII have been reported by employing the fully relativistic Dirac atomic R-matrix code (DARC). For construction of target wavefunctions, multiconfiguration Dirac-Fock calculations are performed for the lowest 21 fine structure energy levels belonging to 2p6nl (3 ≤ n ≤ 5) configurations. Our calculated target state energies of the core ion Se XXIV show close agreement with the energies tabulated in the NIST database. In order to assess the accuracy of our DARC results, photoionization cross section calculations of the ground state configuration have also been performed using the close-coupling Breit-Pauli R-matrix (BPRM) method. Our two independent calculations show a good agreement both in magnitude and resonant photoionization cross sections. The resonance energies (Er) and widths (Γ) of the 3pns (3P1,1P1), 3pnd (3D1, 3P1, 1P1), 3dnp (3D1, 3P1, 1P1) and 3dnf (3D1, 3P1, 1P1) series due to ejection of a 3s electron from the ground state 2p63s2 (1S0) have also been predicted by adopting Quigley and Berrington (QB) method. We believe that our results might be beneficial for the modelling and diagnostics of fusion and laser generated plasmas.

Energy analysis of ejected electrons in the region of the Ar L1-L2,3M Coster-Kronig transitions (25–56 eV) induced by electron impact

The ejected electron spectra between 25 and 56 eV kinetic energy in Ar have been measured at several electron impact energies. When the incident energy is above the Ar 2s ionization potential the peaks due to the L1-L2,3M1 and L1-L2,3M2,3 Coster-Kronig (CK) transitions are expected to occur in this region of kinetic energy, but we observe a series of other narrow structures that overlap and sometime dominate the spectrum due to the CK transitions. These features have been attributed to the autoionizing decay of inner valence doubly excited states to the Ar + ground state.

Ionization and Fragmentation of a Global Warming Gas by EUV and X-Ray Photons

An experimental investigation of the processes leading tothe fragmentation of the singly ionized 1,1,1,2-tetrafluoroethane (HFC-134a, CH2FCF3) by EUV and soft X-rays is presented. HFC-134ais taken into consideration as the most convenient replacement for CFC-12 in refrigeration applications due to the fact that it has null ozone depletion factor. Dissociation of the singly ionized HFC-134amolecule was induced by valence, direct and indirect C 1s core photoionization or photoexcitation and the ionic fragments were detected in coincidence (PEPICO mode) with the ejected electrons without energy analysis. The singly ionized parent ion CF4CH2+can be detected even at photon energies above the C 1s threshold.

Angular Distribution of Ion Products in the Double Photoionization of Propylene Oxide.

A photoelectron-photoion-photoion coincidence technique, using an ion imaging detector and tunable synchrotron radiation in the 18.0–37.0 eV photon energy range, inducing the ejection of molecular valence electrons, has been applied to study the double ionization of the propylene oxide, a simple prototype chiral molecule. The experiment performed at the Elettra Synchrotron Facility (Trieste, Italy) allowed to determine angular distributions for ions produced by the two-body dissociation reactions following the Coulomb explosion of the intermediate (C3H6O)2+ molecular dication. The analysis of the coincidence spectra recorded at different photon energies was done in order to determine the dependence of the β anisotropy parameter on the photon energy for the investigated two-body fragmentation channels. In particular, the reaction leading to + C2H3O+ appears to be characterized by an increase of β, from β ≈ 0.00 up to β = 0.59, as the photon energy increases from 29.7 to 37.0 eV, respectively. This new observation confirms that the dissociation channel producing and C2H3O+ final ions can occur with two different microscopic mechanisms as already indicated by the bimodality obtained in the kinetic energy released (KER) distributions as a function of the photon energy in a recent study. Energetic considerations suggest that experimental data are compatible with the formation of two different stable isomers of C2H3O+: acetyl and oxiranyl cations. These new experimental data are inherently relevant and are mandatory information for further experimental and theoretical investigations involving oriented chiral molecules and linearly or circularly polarized radiation. This work is in progress in our laboratory.

Coulomb exploded directional double ionization of N2O molecules in multicycle femtosecond laser pulses**Project supported by the National Key R&D Program of China (Grant No. 2018YFA0306303), the National Natural Science Fundation of China (Grant Nos. 11425416, 11834004, and 11761141004), and the 111 Project of China (Grant No. B12024).

We experimentally investigate Coulomb exploded directional double ionization of N2O molecules in elliptically polarized femtosecond laser pulses. The denitrogenation and deoxygenation channels are accessed via various pathways. It leads to distinct asymmetries in directional breaking of the doubly ionized N2O molecules versus the instantaneous laser field vector, which is revealed by tracing the sum-momentum spectra of the ionic fragments as a recoil of the ejected electrons. Our results demonstrate that the accessibility of the Coulomb exploded double ionization channels of N2O molecules are ruled by the detailed potential energy curves, and the directional emission of the fragments are governed by the joint effects of the electron localization-assisted enhanced ionization of the stretched molecules and the profiles of the molecular orbitals.

Electronic properties of vacancies in bilayer graphane

We have performed the ab initio hybrid density functional theory (DFT) calculations to investigate the electronic structure of various neutral and charged vacancies (VH, VCH, VC, VC−CH and VC−C) in a diamond-like bilayer graphane. In the neutral state, the identified vacancies create the energetically unfavorable dangling bonds which are significantly stabilize by electron ejection (+1 state) mechanism. The studied vacancies introduce the electronic states within the band gap, which are either metallic or semiconducting in nature. The metallic vacancies posses a magnetic moment of 1.00 μB. The charge states modulation alters the electronic character of the vacancies and suppresses the induced magnetic moment. Our study demonstrates that the vacancies in a diamond-like bilayer graphane structure could have potential applications in nanoelectronics and band gap related energy storage devices.

Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter.

Low-energy electrons (LEEs) are of great relevance for ion-induced radiation damage in cells and genes. We show that charge exchange of ions leads to LEE emission upon impact on condensed matter. By using a graphene monolayer as a simple model system for condensed organic matter and utilizing slow highly charged ions (HCIs) as projectiles, we highlight the importance of charge exchange alone for LEE emission. We find a large number of ejected electrons resulting from individual ion impacts (up to 80 electrons/ion for Xe40+). More than 90% of emitted electrons have energies well below 15 eV. This "splash" of low-energy electrons is interpreted as the consequence of ion deexcitation via an interatomic Coulombic decay (ICD) process.

COMPARISON OF GLOW, ARC, AND MAGNETRON DIRECT CURRENT DISCHARGES

Glow discharge (GD) in a tube, arc discharge (AD) without cathode heating from an external source, and magnetron discharge (MD) in a planar magnetron are compared. In each of the discharges, characteristic areas are distinguished. In MD, electrons trapped in the near-cathode region are not directly involved in ionization processes, but “wake” acceleration of slow ions by electrons that move along Larmor orbits is possible, which gives additional energy to ions moving toward the cathode. In GD in the near-cathode region, the average energy of the ejected electrons is on the order of several electron volts, and the energy of the ions and neutrals is less than 0.1 eV. In MD in the near-cathode region, the average energy of knocked-out electrons, ions, and neutrals is on the order of tens of electron volts. The differential resistance of GD is negative, that of AD is usually negative, and that of MD is positive. The energy of ions in the magnetron plasma can be greater than that of electrons, which gives new possibilities for acoustoplasma control of MD and the creation of appropriate instruments and devices.

COMPARISON OF GLOW, ARC, AND MAGNETRON DIRECT CURRENT DISCHARGES

Glow discharge (GD) in a tube, arc discharge (AD) without cathode heating from an external source, and magnetron discharge (MD) in a planar magnetron are compared. In each of the discharges, characteristic areas are distinguished. In MD, electrons trapped in the near-cathode region are not directly involved in ionization processes, but “wake” acceleration of slow ions by electrons that move along Larmor orbits is possible, which gives additional energy to ions moving toward the cathode. In GD in the near-cathode region, the average energy of the ejected electrons is on the order of several electron volts, and the energy of the ions and neutrals is less than 0.1 eV. In MD in the near-cathode region, the average energy of knocked-out electrons, ions, and neutrals is on the order of tens of electron volts. The differential resistance of GD is negative, that of AD is usually negative, and that of MD is positive. The energy of ions in the magnetron plasma can be greater than that of electrons, which gives new possibilities for acoustoplasma control of MD and the creation of appropriate instruments and devices.

Electron emission cross sections for collisions of heavy ions with atomic targets

A theoretical study of the double-differential cross sections (DDCS) for ejection of electron from hydrogen atom in ground state by the impact of $$\hbox {C}^{6+}$$ ion with energy values 1 and 2.5 MeV/amu is presented. For the final state, we use a continuum distorted wave that contains the product of two Coulomb distortions due to the projectile–electron and target–electron Coulombic interactions for which it is called the two-Coulomb-wave (2CW) model. In this paper, the energy and angular distributions of DDCS for electron emission from atomic hydrogen have been investigated. The ejected electrons are influenced by the combined fields of the target and the projectile ion. Comprehensive comparisons are made between the three-Coulomb-wave model (Jana et al. in Eur Phys J D 66:243, 2012) and the present 2CW model. The emitted electron, the incident projectile ion and the residual ion are considered to be in the same plane. It is found that the two-centre effect has a major influence on the observed forward–backward angular asymmetry in the angular distribution of electron emission spectra. The region of the binary encounter peak is analysed in detail. The present computed results have been compared with the available experimental results as well as other theoretical calculations based on the first Born approximation and the continuum distorted wave eikonal initial state approximation. Moreover, the present computed results are in better agreement with the available experimental data for electron emission cross sections.

Ultrafast structural rearrangement dynamics induced by the photodetachment of phenoxide in aqueous solution

The elementary processes that accompany the interaction of ionizing radiation with biologically relevant molecules are of fundamental importance. However, the ultrafast structural rearrangement dynamics induced by the ionization of biomolecules in aqueous solution remain hitherto unknown. Here, we employ femtosecond optical pump-probe spectroscopy to elucidate the vibrational wave packet dynamics that follow the photodetachment of phenoxide, a structural mimic of tyrosine, in aqueous solution. Photodetachment of phenoxide leads to wave packet dynamics of the phenoxyl radical along 12 different vibrational modes. Eight of the modes are totally symmetric and support structural rearrangement upon electron ejection. Comparison to a previous photodetachment study of phenoxide in the gas phase reveals the important role played by the solvent environment in driving ultrafast structural reorganization induced by ionizing radiation. This work provides insight into the ultrafast molecular dynamics that follow the interaction of ionizing radiation with molecules in aqueous solution.

Spectral line shape and angular momentum

Data have been obtained for ejection of valence shell 4p and 3d electrons in krypton and the 1t2 and 2a1 orbitals in methane. Measurements, with kinematics both on and off the Bethe ridge, examine how the spectral shapes change for fixed energies of 1015 eV for the incident electron, 880 eV for scattered and 120 eV for ejected electron and angular momentum changes. The studied interactions are activated by excitation and ionization of inner shell (-d) electrons and concern complex electron correlations. The triple differential cross sections for the Bethe ridge conditions within the experimental accuracy are similar to the values predicted by the Distorted Wave Impulse Approximation and Born Approximation calculations but need further consideration of electron correlation effects.

Development of Y2O3: Ho3+/Yb3+ Upconverting Nanophosphors for Enhancing Solar Cell Efficiency of Dye-Sensitized Solar Cells

Light scattering behavior of dye-sensitized solar cells (DSSCs) containing Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> : Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> /Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> upconverting (UC) nanophosphor has been studied. To study the influence of UC nanophosphors on photovoltaic performance of DSSCs, UC nanophosphors have been introduced into the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film to form the hybrid film. The electron ejection ability, current density (JSC ), open-circuit voltage (VOC ), and power conversion efficiency (PCE) of DSSCs have been determined. The enhancement of about 31% and 30% for JSC and PCE in DSSCs hybrid film compared with that of DSSCs TiO2 film has been observed due to improved near infrared to visible light harvesting properties of UC nanophosphors.

Populations and Dynamics of Guanine Radicals in DNA strands-Direct versus Indirect Generation.

Guanine radicals, known to be involved in the damage of the genetic code and aging, are studied by nanosecond transient absorption spectroscopy. They are generated in single, double and four-stranded structures (G-quadruplexes) by one and two-photon ionization at 266 nm, corresponding to a photon energy lower than the ionization potential of nucleobases. The quantum yield of the one-photon process determined for telomeric G-quadruplexes (TEL25/Na+) is (5.2 ± 0.3) × 10−3, significantly higher than that found for duplexes containing in their structure GGG and GG sequences, (2.1 ± 0.4) × 10−3. The radical population is quantified in respect of the ejected electrons. Deprotonation of radical cations gives rise to (G-H1)• and (G-H2)• radicals for duplexes and G-quadruplexes, respectively. The lifetimes of deprotonated radicals determined for a given secondary structure strongly depend on the base sequence. The multiscale non-exponential dynamics of these radicals are discussed in terms of inhomogeneity of the reaction space and continuous conformational motions. The deviation from classical kinetic models developed for homogeneous reaction conditions could also be one reason for discrepancies between the results obtained by photoionization and indirect oxidation, involving a bi-molecular reaction between an oxidant and the nucleic acid.

Synthesis of D-A-A and D-A-D Pyrimidine π-Systems Using Triorganoindium Reagents: Optical, Vibrational, and Electrochemical Studies.

A series of donor-acceptor-acceptor (D-A-A) and donor-acceptor-donor (D-A-D) systems based on a pyrimidine π-spacer with various substituents at the C-2 position has been successfully prepared. The synthesis involved site-selective palladium cross-coupling reactions of chloropyrimidines with triorganoindium reagents and proceed in good yields and with atom economy. 4-(N,N-Diphenylamino)phenyl was chosen as the donor group and thien-2-yl dicyanovinylene as the acceptor one. The optical, vibrational, electrochemical, and density functional theory (DFT) calculations of these molecular systems were analyzed, and experimental values show the important role of the substituents at the C-2 position of the pyrimidine with stronger electron accepting ability, absorption in a wide range of UV/vis, acceptable fluorescence lifetime, and effective intramolecular charge transfer (ICT) properties. The ICT was observed in both series by the bathochromic shift on increasing the polarity of the solvent. In addition, DFT calculations found lower lowest unoccupied molecular orbitals of D-A-A molecules that suggest good electron ejection and transportation, being good properties for their application in various organic optoelectronic devices.

Few-body dynamics underlying postcollision effects in the ionization of H2 by 75-keV proton impact

We have measured fully differential cross sections (FDCS) for ionization in $75\text{\ensuremath{-}}\mathrm{keV}p+{\mathrm{H}}_{2}$ collisions for ejected electron speeds close to the projectile speed. The data were analyzed in dependence on both the electron emission angle and the projectile scattering angle. Pronounced postcollisional effects between the projectile and the ejected electrons were observed. Significant differences between experiment and theory and between two conceptually very similar theoretical models were found. This shows that in the region of electron-projectile velocity-matching the FDCS is very sensitive to the details of the underlying few-body dynamics.

Auger Electron Spectroscopy-A Review

Auger electron spectroscopy (AES) is surface sensitive analytical technique mainly,it provides quantitative elemental and chemical state information from surfaces of solid materials.It utilizes a high current, finely focused electron beam as an excitation source.In AES,A sample is probed with electron beam with energy between 3 to 3o Kev which results in ejection of electron in core level, filled by an outer level electron with excess energy being used then, this excess energy used to emit an electron this, emitted electron is said as Auger electron. That result as function of auger electron energy. The resulting spectra is obtained used to determine the composition of samples. The Auger electron kinetic energies are characteristic of emitting atoms and the measurement of their energies is used to identify the elements variation of composition with depth can be determined by ion sputtering technique. Lastly,AES is applicable for detection of thin films, characterization of materials, metallurgy and corrosion science.&#x0D;

Comparative study of electron field emission from randomly-oriented and vertically-aligned carbon nanotubes synthesized on stainless steel substrates

Randomly-oriented carbon nanotubes (CNTs) and vertically-aligned CNTs have been synthesized by a thermal chemical vapor deposition (CVD) process and a plasma enhanced CVD process, respectively, on stainless steel substrates without any external catalyst. Surface topography studies reveal that polishing and chemical etching result in favorable catalytic conditions for nucleation and growth of CNTs. Scanning electron microscopy and transmission electron microscopy observations reveal the growth of CNTs with catalyst particle at the tips. In comparison to randomly-oriented CNTs, vertically-aligned CNTs demonstrate better field emission properties with lower turn-on electric field of ∼2.0 V/μm, lower threshold electric field of ∼3.2 V/μm, and a 2.5-fold increase in the field enhancement factor. The vertical alignment of the emitters benefits the emission process by reducing the screening effect and streamlining the path of ejected electrons directly onto the anode. Vertically-aligned CNTs on conducting substrates are promising emitters in cold cathode vacuum electronics because of their direct contact with the substrate and efficient performance at low operating voltages.