Auger Transitions Research Articles

Ab Initio Manganese Kα and Kβ Energy Eigenvalues, Shake-Off Probabilities, Auger Rates, with Convergence Tests.

This work presents ab initio calculations for the Kα spectrum of manganese (Z = 25, [Ar]3d54s2), a highly complex system due to the five open orbitals in the 3d shell. The spectrum is composed of the canonical diagram line [1s]→[2p] and shake-off satellite lines [1snl]→[2pnl] (nl∈{2s,2p,3s,3p,3d,4s}), where square brackets denote a hole state. The multiconfiguration Dirac-Hartree-Fock method with the active set approach provides the initial and final atomic wavefunctions. Results are presented as energy eigenvalue spectra for the diagram and satellite transitions. The calculated wavefunctions include over one hundred million configuration state functions and over 280,000 independent transition energies for the seven sets of spectra considered. Shake-off probabilities and Auger transition rates determine satellite intensities. The number of configuration state functions ensures highly-converged wavefunctions. Several measures of convergence demonstrate convergence in the calculated parameters. We obtain convergence of the transition energies in all eight transitions to within 0.06 eV and shake-off probabilities to within 4.5%.

Energy-Conserving Surface Hopping for Auger Processes.

Auger-type processes are ubiquitous in nanoscale materials because quantum confinement enhances Coulomb interactions, and there exist large densities of states. Modeling Auger processes requires the modification of nonadiabatic (NA) molecular dynamics algorithms to include transitions caused by both NA and Coulomb couplings. The system is split into quantum and classical subsystems, e.g., electrons and vibrations, and as a result, energy conservation becomes nontrivial. In surface hopping, an electronic transition induced by NA coupling is accompanied by a classical velocity readjustment to ensure conservation of the total quantum-classical energy. A different treatment is needed for Auger transitions driven by Coulomb interactions. We develop a nonadiabatic molecular dynamics methodology that meticulously differentiates the energy redistribution accompanying hops induced by the NA coupling and the Coulomb interaction and correctly conserves the total energy at each transition. If the transition is driven by a Coulomb interaction, the hop energy is redistributed within the quantum electronic subsystem only. If the transition is NA, the energy is redistributed between the quantum and classical subsystems. Properly maintaining energy conservation for both types of transitions is crucial to generate a correct order of events, obtain accurate transition times, maintain a proper statistical distribution of state populations, and reach thermodynamic equilibrium. We test the method with biexciton annihilation and Auger-assisted hot electron relaxation in a CdSe quantum dot. The sequence of Auger and phonon-driven processes and the calculated time scales are in excellent agreement with the experimental results. The developed approach can be coupled with any surface-hopping method and provides a crucial practical advance to study charge-carrier dynamics in the nanoscale and condensed matter systems.

Plasmon Excitation in the Interaction of Slow Singly Charged Argon Ions with Magnesium

We report angle-resolved energy spectra of electron emitted in the interaction of slow singly charged heavy ions with Mg surface. The work is focused mainly on the excitation of plasmons of Mg under Argon impact. Potential excitation of plasmons occurs when incoming ions are neutralized at the expense of the potential energy carried by incoming ions. The process competes with the known mechanisms of neutralization via Auger transitions. Differently from Al samples, our results show that the neutralization of Ar+ ions at Mg is dominated by the excitation of surface plasmons by the potential energy released in the electron capture process that neutralizes incoming ions. Bulk plasmon excitation is observed at higher impact energy and is ascribed to fast electrons excited by the transfer of the kinetic energy of incoming particles. The data show that bulk plasmon excitation occur inside the bulk, while the theoretically predicted excitation by potential energy transfer of incoming projectiles is not observed.

Resonant photoemission studies on Fe-Ni alloys

This paper investigates the electronic structure of Fe1−xNix (x = 0.32, 0.36, 0.4, 0.5) alloys employing high resolution photoelectron spectroscopy using synchrotron radiation. The valence bands and the core levels have been recorded at various on-resonance and off-resonance photon energies of Fe and Ni. An anti-resonance dip observed in the valence bands taken at Fe 3p → 3d resonance lies closer to the Fermi level compared to that observed at Ni 3p → 3d resonance, indicating larger density of itinerant Fe 3d electrons. Whereas, Ni 3d states are comparatively less itinerant in these alloys. The hybridization effects increase with increase of Fe content in the alloy system. The intensity of Ni L3M4,5M4,5 Coster-Cronig Auger transition observed with 853 eV (Ni 2p → 3d resonance) photon energy, drops down drastically for the Invar alloy (Fe0.64Ni0.36) as compared to other Fe-Ni alloys due to the existence of Ni in more than one local chemical surroundings as expected for Invar alloy. The electron-electron interaction energy (Udd) of Ni 3d shell is found to decrease with the decrease of Ni concentration. The 3p and 3s core levels of Fe and Ni recorded at 707 eV (Fe 2p → 3d resonance) are overwhelmed by various intense resonant Auger features such as Fe L3M2,3M2,3, Fe L3M2,3M4,5 and Fe L3M1M4,5. The 1S state of Fe L3M2,3M2,3 is greatly enhanced in the Invar alloy as compared to other alloys. The microscopic compositional in-homogeneity present in Invar alloy plays a crucial role in the screening of holes in Ni sites but does not contribute in screening the holes in Fe sites.

The development of laboratory‐based high energy sources for XPS

Over the last fifty years, a number of higher energy X‐ray sources have been suggested as alternatives for the usual AlKα source found in the first commercial XPS systems and still the standard anode material for XPS today. This paper reviews the development of a number of such sources, predominantly in the authors' laboratory, and the rationale behind the desire to extend the binding energy range of the technique. The achromatic sources SiKα, ZrLα and TiKα are described along with monochromatic sources AgLα and CrKβ, both based on the standard quartz monochromator geometry but taking higher orders of diffraction. The driving force for much of this development was the desire to probe deeper core levels and CCC Auger transitions. These could be combined into initial or final state Auger parameters as described in much of the work cited in this review. The highest energy source considered is the CuKα source based around an external X‐ray tube, which provides much insight into the electronic structure of steels by measurement of the Fe1s and FeKLL peaks. The last decade or so has seen a significant increase of interest in HAXPES, and all manufacturers of turn‐key XPS instruments offer HAXPES options of one form or another, there are three dedicated HAXPES systems commercially available, which are very briefly described.

HAXPES reference spectra of UO2 generated with Ga Kα x-ray source

HAXPES measurements were carried out using a Scienta Omicron HAXPES instrument to provide reference spectra for depleted uranium dioxide. High purity uranium dioxide, as confirmed by trace elemental analysis and x-ray diffraction, was synthesized via the integrated dry route from uranium hexafluoride. The material was fixed on double sided carbon tape for the analysis with charge control measures in place. The expanded energy range, using a Ga Kα x-ray source, presents core level photoelectrons not observed in traditional XPS. In addition, a region associated with the x-ray induced Auger transitions MNN is evident at binding energies only achievable with HAXPES. The reference spectra presented here act as the first in a line of proposed investigations into the comparison of XPS and HAXPES from surface to bulk as well as a fundamental understanding of the electronic structure of uranium materials.

Symmetry breaking via alloy disorder to explain radiative Auger transitions in self-assembled quantum dots

Symmetry breaking via alloy disorder to explain radiative Auger transitions in self-assembled quantum dots

Auger Transition Probabilities and Electron Emission Cross Sections for Vacancy Decay into the 2pπ-Orbital in the Ne+–Ne Quasimolecule

Auger Transition Probabilities and Electron Emission Cross Sections for Vacancy Decay into the 2pπ-Orbital in the Ne+–Ne Quasimolecule

Deep core level hard X‐ray photoelectron spectroscopy for catalyst characterization

AbstractHeterogeneous catalysts are the crucial element for many catalytic processes. In most of the cases, the pivotal structure consists of catalytic metals/alloy particles supported by oxides. Knowledge of the interaction between metal and oxide is central to understand the structure–performance relationship of such systems. X‐ray photoelectron spectroscopy provides access to the chemical–physical properties of metal and oxide interface as well as polarization effects. The results are usually derived from changes of the measured binding energies based on initial state analysis. We propose to extend the analysis using photoelectron as well as Auger transition to include final state effects (Wagner/Hohlneichner plots). This gives additional information on the specific chemical neighborhood of the excited atom. Three archetypal systems are investigated by hard X‐ray photoelectron spectroscopy (HAXPES) to introduce two approaches to this analysis for the most common support elements Al and Si.

Resonant Auger spectromicroscopy in ultrathin Fe films on W(110)

L3MM Auger transition is measured near the L3 resonance of ferromagnetic Fe films on W(110). The kinetic energies of the Auger peaks display the typical Raman behaviour for photon energies well below the absorption threshold, where the Auger energy follows the changes in the photon energy. Classical Auger behaviour with constant kinetic energy sets in at about 1.5 eV below the L3 resonance independently from the number of Fe layers down to the monolayer thickness. Strong x-ray circular magnetic dichroism is observed at the L3 edge in the entire L3MM Auger spectrum. Different Auger features originating from the final state with two 3p core holes show slight variations in the dichroic signal, which is attributed to the exchange interaction between the core holes and the valence band. Finally, XMCD-PEEM magnetic domain imaging using Auger electrons is demonstrated with a high level of contrast and lateral resolution approaching that of imaging with secondary photoelectrons.

Experimental investigations of two‐electron relaxation processes in Rydberg hollow atoms

AbstractThe two‐electron relaxation processes in Rydberg hollow atoms (RHA), formed in collisions of slow highly charged ions (HCI) of Xe (q = 23–36) with metallic Be surface, were studied experimentally by means of X‐ray spectroscopy. The pulsed beams of HCI were delivered by the electron beam ion source while the emitted X‐rays were observed by a silicon drift detector. From the measured spectra of M‐X‐rays, dominated by the Paschen series of nf3d one‐electron‐one photon radiative (R) transitions, the relaxation processes involving two electrons, namely, the internal dielectronic excitation, interatomic Coulombic decay, two‐electron‐one photon transitions and the Auger transition (A), were extracted. The dead‐time effect in X‐ray detector for a pulsed ion beam of HCI was considered in order to estimate the Auger decay rates. Finally, we demonstrate that the present results give access to estimate a time‐scale of relaxation of RHA in solids.

Obrazovanie i raspad avtoionizatsionnykh sostoyaniy - osnovnoy mekhanizm neuprugikh poter' pri stolknoveniyakh atomov keV-energiy

It has been shown that the formation of autoionization states makes the dominant contribution to inelastic energy loss and to ionization in keV atomic collisions, i.e., at velocities lower than the velocities of atomic electrons. Scaling laws have been proposed to calculate the cross sections for the formation of vacancies in inner K and L electron shells of colliding atoms. A model has been proposed to relate ionization processes and the observed inelastic energy losses. Auger transitions in a short-lived quasimolecule formed by two atoms approaching each other have been studied. The nature of the continuous component in electron spectra emitted in collisions has been determined. It has been shown that the excitation of autoionization states determines the stopping cross sections for keV atoms in matter.

Calculations of term energies, radiative transition wavelengths and Auger electron energies for resonances of F4+

In this work, the saddle-point variation combined with complex-rotation methods are used to calculate term energies, radiative transition wavelengths and Auger transition energies of the 1s2s22p2 (2S, 2P, 2D, 4P), 1s2s22p3p (2S, 2P, 2D), 1s2s2p3 (2,4S°, 2,4P°, 2,4D°), and 1s2p4 (2S, 2P, 2D, 4P) resonances for F4+. The present term energies, radiative rates, radiative transition wavelengths, Auger rates and corresponding transition energies agree well with the multiconfiguration Dirac-Fock calculation results listed in the literature. Other transition data in this work are expected to offer reference values for future studies.

Search for the interatomic Auger effect in Nitrous Oxide

The interatomic Auger effect following O 1s ionization in N2O has been experimentally investigated using multi-electron coincidence spectroscopy. The expected transition energies have been established by comparison to the measured N 1s−1v−1 core-valence double ionization energies. We describe a procedure to eliminate the background of two competing processes contributing spectroscopic signatures to the same energy range, namely double Auger decay of the O 1s vacancy and direct single-photon double ionization into the N 1s−1v−1 states. While the interatomic Auger transitions could not be successfully isolated, we provide an upper boundary of the transition probability of 0.07% with respect to the dominant single Auger decay after O 1s ionization.

Energy variation of double K -shell photoionization of Ne

We report on an experimental and theoretical study of double $K$-shell photoionization of Ne over the 2.3--8.5 keV x-ray energy range. The ratio of double-to-single $K$-shell photoionization cross sections was determined experimentally by measuring the relative rates of the $KK\ensuremath{-}K{L}_{2,3}{L}_{2,3}$ ($^{2}D$) Auger hypersatellite and the $K\ensuremath{-}{L}_{2,3}{L}_{2,3}$ ($^{1}D$) diagram Auger transitions. By scaling the hypersatellite-diagram Auger-electron ratios to $KK/K$ cross-section ratios, comparison was made with theoretical cross-section ratios of He-like ${\mathrm{Ne}}^{8+}$ determined by the $R$ matrix with pseudostates method. The experimental Ne and theoretical ${\mathrm{Ne}}^{8+}$ cross-section ratios show similar variations with energy, but the experimental ratios systematically exceed the calculated ratios and also show a lower threshold energy for double $K$-shell photoionization onset compared to the computed ${\mathrm{Ne}}^{8+}$ threshold. The discrepancy is attributed to effects of $L$-shell electrons not included in the He-like ${\mathrm{Ne}}^{8+}$ calculations. Quantified scaling with nuclear charge $Z$ along the He-like isoelectronic sequence indicates that the measured 10-electron $Z=10$ double $K$-shell photoionization cross section behaves like the computed He-like $Z=8.9$ cross section, suggesting an effective nuclear screening parameter of ${s}_{L}=1.1$ by the additional eight outer $L$-shell electrons. Experimental results for the energy variations of Auger electron transitions from other multielectron hole states are also discussed.

Cu Kα3,4 satellite spectrum with ab initio Auger-rate calculations

This work investigates the capability of the multiconfiguration Dirac-Hartree-Fock (MCDHF) method in predicting the Cu $K{\ensuremath{\alpha}}_{3,4}$ spectrum. Ab initio energy eigenvalues, relative intensities, and radiative widths are calculated for the Cu $2p$ and $2s$ satellite transitions. By fitting to the most accurate experimental Cu $K{\ensuremath{\alpha}}_{3,4}$ spectra available, we show that our $2p$ satellite energy eigenvalues agree with experiment to within 0.35 eV and that our $2p$ shake probability agrees with the $2p$ fitted intensity to within 0.05%. Our fits suggest a $I(2s)$:$I(2p)$ satellite intensity ratio (as a percentage of the total $K\ensuremath{\alpha}$ spectrum) of 0.03(1):0.76(1) Theoretical predictions of this ratio can be examined using shake probabilities. We calculate the probability of shake-off due to the sudden creation of a $1s$ hole in Cu, yielding an ab initio $I(2s)$:$I(2p)$ shake probability ratio of 0.194:0.742. Using MCDHF, the rates at which hole states, created through the shake processes, depopulate via Auger transitions are determined. These results explain the apparent discrepancy between experimental satellite intensities and shake probabilities, and characterize the Cu $K{\ensuremath{\alpha}}_{3,4}$ spectrum with a satellite intensity ratio of 0.04(1):0.76, consistent with the experiment.

Coherent treatment of transfer-excitation processes in swift ion-atom collisions

For more than 40 years since the first ion-atom collision investigations of the two-electron process of electron transfer with excitation and its resonant and nonresonant features, a satisfactory quantum mechanical treatment has been lacking. We present now such a comprehensive transfer excitation treatment using a three-electron atomic orbital close-coupling approach within a full configuration interaction formalism, exemplified by ${\mathrm{C}}^{4+}(1{s}^{2})+\mathrm{He}$ collisions at 0.5--18 MeV impact energies. The calculated cross sections for the production of ${\mathrm{C}}^{3+}(1s2{p}^{2}\phantom{\rule{0.16em}{0ex}}^{2}D)$, which shows the strongest resonance signature among the KLL Auger transitions, are found to be in excellent agreement with zero-degree Auger projectile spectroscopy measurements covering the maximum of the resonance peak and its high energy wing. At the lower energies, the theoretical results show a second maximum which is interpreted through a nonresonant one-step transfer excitation mechanism, never considered to date. The present, fully coherent, many-body treatment provides an important advance in the modeling and understanding of multielectronic processes in quantum systems under strong and ultrafast perturbations.

Manifestation of postcollision interaction in Krypton LMN Auger spectra following K -shell photoionization

We report on an experimental and theoretical study of postcollision interaction (PCI) effects on ${L}_{2}\ensuremath{-}{M}_{4,5}{N}_{2,3}$ Auger electrons measured above the Kr $K$-edge in which ${L}_{2}$ vacancies are primarily generated by $K{L}_{2}$ x-ray emission. Such cascade processes, in which a deep inner-shell vacancy decays first by x-ray emission followed by Auger electron emission, is a strong decay mode in heavy atoms. The ${L}_{2}\ensuremath{-}{M}_{4,5}{N}_{2,3}$ Auger electron peak is observed to become increasingly asymmetric with a shifting peak maximum as the absorbed x-ray energy approaches the $K$-shell ionization threshold. This is attributed to PCI energy exchanges of the Auger electron with the $1s$ photoelectron. To model the PCI effects, we have applied a semiclassical approach modified to account for the combined lifetimes of the $K$ and ${L}_{2}$ hole states. In addition, our analysis treats several closely spaced Auger transitions with final ionic states having different terms and angular momenta.

The N4,5 - OO Auger and “N3” N4,5O2,3 Coster-Kronig spectra of xenon induced by electron impact

The N4,5OO Auger electron spectrum in the kinetic energy region (14–37) eV has been measured with high resolution at electron incident energies between 71 eV and 2019 eV. The Auger and satellite lines are assigned by comparison with previous literature data. Several states which correspond to the resonant Auger transitions from the 4d3/2, 5/2 6p states are observed. The PCI effects on the N5-O2,3O2,3(1S0) Auger peak when the incident electron energy approaches to the N5 edge (67.55 eV) is investigated and it is found that the dependence of the energy shift on the excess energy, Eexc, is well represented by the function Eexcβ with β = (-1.40 ± 0.05). The “N3” N4,5O2,3 Coster-Kronig spectrum is measured at various electron incident energies. The assignments of the features are made in comparison with a similar spectrum from synchrotron radiation measured by Kivimäki et al. [J. Electron Spectrosc. Relat. Phenom. 1999, 101–103, 43–47]. The Auger spectrum in the kinetic energy regions (68–78) eV and (90–138) eV is observed for the first time in an electron impact experiment and a comparison is made with the photoionization experiment by Hikosaka et al. [Phys. Rev. A 2007, 76, 032708].

Мезоатомын гадаад Оже эффектийг бодох нэгэн арга

A method for calculating mesic-atom external Auger transition is proposed. The transition proceed in two stages. In the first stage, the quasi-molecular complex, consisting of the mesic atom and the atom is formed in their collisions and on the second stage, the decay of this complex leads to external Auger effects. At given distance between two atoms of the quasi-molecular system, the partial and total width of external Auger transition are calculated. The average Auger transition rates of pionic helium (Helium gass pressure 59.44 atm, velocity of the pionic atom is v=105 cm/s) are calculated and compared the rates of other competitive processes (Internal Auger and Radiation transitions).