Auger Energies Research Articles

Physical genetics: Cross-breeding density functional theory and X-ray photoelectron spectroscopy to rationalize chemical shifts of binding energies in solid compounds

Like other spectroscopic methods XPS and AES show characteristic chemical shifts depending on the elemental matrix of a compound, however, a satisfactory rationalization of the variance of such values is often difficult. By an extension of a previous approach we present a theory in a unifying equation which combines several parameters - some of them resulting from DFT calculations - which influence the energy of the outgoing electrons and thereby seemingly the binding energy. By calculating Bader charges, atomic volumes and site potentials we have produced a data basis for a set of chalcogenides and halides of Ba, Zn, Pb and Cu to rationalize the spread of measured binding energies and Auger energies. It has thereby become possible to quantify different factors separately which bias the measurement of the kinetic energies of the outgoing core electrons, both the photo-emitted and the Auger electrons. Such an analysis can also trace special features of an open-shell configuration and even show up effects of a semiconductor-type.

Channel-resolved molecular Auger spectroscopy

SynopsisMolecular Auger spectra typically consist of many overlapping lines that are hard or impossible to resolve experimentally even with highest-resolution electron spectroscopy techniques. Since molecular Auger energies depend on non-adibatatic dynamics, they can also be difficult to calculate precisely, such that the assignment of molecular Auger transitions is often ambiguous. Here we show that by measuring Auger-electron multi-ion coincidences, we can disentangle the spectra into the contributions from specific ionic final states, which helps significantly with their interpretation and assignment.

Multireference quantum chemistry protocol for simulating autoionization spectra: Test of ionization continuum models for the neon atom

In this contribution we present a protocol to evaluate partial and total Auger decay rates combining the restricted active space self-consistent field electronic structure method for the bound part of the spectrum and numerically obtained continuum orbitals in the single-channel scattering theory framework. On top of that, the two-step picture is employed to evaluate the partial rates. The performance of the method is exemplified for the prototypical Auger decay of the neon $1s^{-1}3p$ resonance. Different approximations to obtain the continuum orbitals, the partial rate matrix elements, and the electronic structure of the bound part are tested against theoretical and experimental reference data. It is demonstrated that the partial and total rates are most sensitive to the accuracy of the continuum orbitals. For instance, it is necessary to account for the direct Coulomb potential of the ion for the determination of the continuum wave functions. The Auger energies can be reproduced quite well already with a rather small active space. Finally, perspectives of the application of the proposed protocol to molecular systems are discussed.

Fock-space multireference coupled cluster calculations of Auger energies of noble gas elements using relativistic spinors.

We report the Auger and Coster-Kronig transition energies (related to double ionization potentials) of noble gas elements obtained using the Fock-space multireference coupled cluster (FSMRCC) method with relativistic spinors. The resulting Auger and Coster-Kronig lines are found to be in agreement with the experimental data and with other reference theoretical estimates. To the best of our knowledge, no prior report of relativistic calculations is available for Auger transition energies at the FSMRCC level of theory. The ionization potentials resulted from this method with no extra cost are also found to be in agreement with experiment, particularly the outer-valence ones. Interestingly, the FSMRCC and the multiconfiguration Dirac-Fock calculations exhibit an inversion in the 3P energy levels of the xenon atom for N4,5-O23O23 Auger transitions, where the 3Pj state energies appear in the order J = 1, 0, 2, a feature which can be verified experimentally.

X- ray wavelengths and Auger transition energies of 1s2p4 (2S, 2,4P, 2D) resonances in B-like (Z = 6-18) ions

SynopsisPlease Auger energies and X-ray wavelengths of the 1s 2p4 (2S, 2,4P, 2D) resonances in B-like ions (Z = 6-18) are reported. New Auger energies and wavelengths for B-like N2+, F4+, Na6+, Al8+, P10+, S11+, Cl12+, and Ar13+ ions are tabulated as benchmarked values for future experimental and theoretical studies.

X-ray wavelengths and Auger transition energies of 1s 2p4 (2S, 2,4P, 2D) resonances in B-like (Z = 6–18) ions

We report Auger energies of the 1s 2p4 (2S, 2,4P, 2D) resonances belonging to the 1s 2p4 (2S, 2,4P, 2D) → 1s2 2p2 (1S, 1P, 1D) and to the 1s 2p4 (2S, 2,4P, 2D) → 1s2 2s2p 1,3P transitions in B-like ions (Z = 6–18). X-ray wavelengths of the 1s2p4 (2S, 2P, 2D) resonances are also reported. The calculations are carried out in the framework of the screening constant by unit nuclear charge (SCUNC) formalism. The present results for the core-excited 1s 2p4 (2S, 2,4P, 2D) resonances in B-like C+, O3+, Ne5+, Mg7+ and Si9+ ions agree well with recent saddle-point variation and saddle-point complex-rotation (SPCR) results (Sun et al 2013 Phys. Rev A 87 032509). The new Auger energies and wavelengths for the 1s 2p4 (2S, 2,4P, 2D) resonances in B-like N2+, F4+, Na6+, Al8+, P10+, S11+, Cl12+ and Ar13+ ions provide benchmarked values for future experimental and theoretical studies on these B-like ions in connection with the diagnostic of astrophysical and laboratory plasma.

Auger energies, branching ratios, widths and x-ray rates of double K-vacancy states of Ne2 +: a close-coupling calculation

A close-coupling calculation is performed for the photoionization cross section of the high-lying core-excited state 1s2s22p5 1Po of Ne2 + in the energy region of the double K-vacancy resonance 1s02s22p6 1S. The calculation is carried out by using the R-matrix method in the LS-coupling scheme, which includes 27 target states and extensive configuration interaction. The KK-KL x-ray energy, rate and autoionization width of the double K-vacancy state, together with KK-KLL Auger energies and branching ratios of the main channels, are obtained from the cross sections and the contributions of these channels. The calculated resonance energy and x-ray rate are in good agreement with the existing experimental and theoretical results. For the Auger width, our result agrees well with the available experimental result and it is very close to the average of other theoretical data, which shows considerable differences with each other. The Auger energy of the predominate channel KK-KL23L23 2D is in rather good agreement with recent experiments on the Auger spectra. Our branching ratios for the channels KK-KL23L23 2D and KK-KL23L23 2S are larger than the results obtained by the multi-configuration Dirac–Fock method by ∼20% on average, which may be due to the coupling of the continuum channels.

Accurate atom–solid kinetic energy shifts from the simultaneous measurement of the KLL Auger spectra for Na, Mg, Al and Si

KLL Auger-energy shifts between free atoms and their solid surfaces were determined from spectra measured simultaneously in identical experimental conditions. Essentially, the shift values obtained for Na, Mg, Al and Si were more accurate than those achieved by combining the results from separate vapour and solid measurements. Using atomic Auger energies and determined shifts, reliable absolute solid state Auger energies with respect to the vacuum level were also obtained. Experimental shift values were also compared with calculations obtained with the excited atom model. 2s and 2p binding energy shifts were estimated from recent high resolution and due to open shell strongly split vapour phase spectra and corresponding published solid state results. Also, the question of the extent to which the 2s and 2p shifts deviate has been discussed here.

Formation of GaAs 1− xN x nanofilm on GaAs by low energy N 2+ implantation

Nitridation of GaAs (1 0 0) by N 2 + ions with energy E i = 2500 eV has been studied by Auger- and Electron Energy Loss Spectroscopy under experimental conditions, when electrons ejected only by nitrated layer, without contribution of GaAs substrate, were collected. Diagnostics for quantitative chemical analysis of the nitrated layers has been developed using the values of NKVV Auger energies in GaN and GaAsN chemical phases measured in one experiment, with the accuracy being sufficient for separating their contributions into the experimental spectrum. The conducted analysis has shown that nanofilm with the thickness of about 4 nm was fabricated, consisting mainly of dilute alloy GaAs 1− x N x with high concentration of nitrogen x ∼ 0.09, although the major part of the implanted nitrogen atoms are contained in GaN inclusions. It was assumed that secondary ion cascades generated by implanted ions play an important role in forming nitrogen-rich alloy.

Mapping the most energetic cosmic rays

The Pierre Auger Collaboration has shown that the cosmic rays detected to August 2007, with estimated energies above 57 EeV, were mostly very close to the direction of a catalogued AGN within ∼ 75 Mpc . The closeness of the sources to us, and their association with the locality of moderate Seyfert galaxies rather than the most striking radio galaxies, were surprising, leading some authors to question the reality of the apparent associations. Here, three further techniques for examining the correlation of cosmic ray arrival directions with directions of AGNs are introduced to confirm and extend this correlation. These include the uniform-exposure polar plot to examine large-scale associations, and a sensitive “right-ascension resonance” test to show the rapidity of the decoherence when the two patterns are displaced. The latter test avoids the choice of a correlation window radius, which makes it possible to see an AGN correlation in other data at a lower energy, and to seek it in HiRes data. On the basis of the closeness of correspondence of the cosmic ray and AGN maps, and the equally significant correspondence with directions of extended radio galaxies listed by Nagar and Matulich but not used in the Auger group’s investigation, it is argued that the association with these two sets of objects is by no means accidental, although the efficacy of the 57 EeV “cut” in selecting this revelatory sample may have been accidental. The arrival directions of these cosmic rays (average energy 75 EeV) can be well described if most of the sources are in or around rather typical Seyfert galaxies, in clusters typically at ∼ 50 Mpc , with the cosmic rays being scattered by 3–4° on their way to us. Because of close clustering of AGNs, it cannot usually be ascertained which object within 2–3 Mpc is the actual source, but more than a third of the cosmic rays appear to come from FRI or similar radio galaxies in the clusters. It thus seems likely that these and also weaker jet-forming Seyfert galaxies are indeed causing acceleration to 10 20 eV . Neither the brightest (nearby) radio galaxies nor the Virgo cluster dominate the cosmic ray sky as had been expected, and Cen A is probably one of the currently inactive 10 20 eV accelerators, as much more distant FRI galaxies play such a large role. The deflections cannot be much more than 3–4° without destroying the coherence. Intergalactic magnetic fields ∼ 1 nG could be responsible, but in one part of the sky a displaced “resonance” suggests a possible 4° deflection by the B z component of our local Galactic magnetic field. A source region limited to <120 Mpc for the Auger cosmic rays is supported. This is compatible with a GZK survival horizon but only if (a) the sudden fall in the energy spectrum is not simply a GZK effect but essentially reflects the energy cut-off in the accelerators, and (b) the Auger energies are underestimated by ∼ 25 % .

One-electron binding and auger energies of sulfur in atomic and molecular states

We present reasonably accurate one-electron binding and Auger energies in S (most accurate), H2S, H2SO, H2SO2, H4SO2, and SO2. These are computed at the ΔSCF level or ΔSCF plus relativistic, correlation, and radiative effects. For the S atom, only those correlation effects which contribute the most to the difference of total energies are considered. These are computed by CI using variationally optimized virtual orbitals. The relativistic corrections for S are included at the Fock-Dirac level. The radiative corrections for the K shell are computed by our previously simple but seemingly accurate approach.

Metallization of the Ge(111) surface at high-temperature probed by energy-loss and Auger spectroscopies

We present new electron energy-loss spectroscopy (EELS) and Auger (AES) experiments aimed to study the structural transition of the Ge(111) surface taking place at high temperatures. Our advanced high-temperature set-up allowed us to collect accurate EELS spectra near the M 2,3 excitation edges and AES MMV and MVV spectra, corresponding to different probing depths ranging from 4 to 10 Å. The metallization of the surface has been clearly detected by the shift of the M 2,3 edge and of the MMV, MVV Auger energies. A detailed study of the transition has been performed using a fine temperature step under thermal equilibrium conditions. The AES and EELS experiments show that a sudden semiconductor-metal transition takes place at about 1000 K involving mainly the topmost layers. Deeper layers within 10 Å are also involved in the metallization process (in a range of 10 above 1010 K) and a smooth change in the topmost layers is also observed at higher temperatures up to 1070 K. These transitions are not fully reversible upon cooling (down to 870 K). Structural and electronic characteristics of the surface transition are discussed in light of available models.

Auger parameters of ternary Pd–Ni–P amorphous alloys

A series of bulk ternary amorphous alloys of Pd100−3 x Ni2 x P x were prepared and their amorphicity checked by X-ray diffraction (XRD) and neutron scattering. Auger parameters of these alloys have been derived from X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectra (AES). Experiments of XPS and AES on each elemental metal and Ni2P were also performed for comparison. The results show a clear compositional dependence for the 3d binding energies and the MNN Auger energies of Pd on alloying, while Ni 2p core levels and the Ni LMM Auger lines show a weaker variation. Analysis of the data using “excited atom” models indicates electron transfer from Pd, with P carrying negative charge, but the differences in behaviour of the two metallic species suggests that covalent bonding changes may be significant.

Model dependence of lateral distribution functions of high energy cosmic ray air showers

The influence of high and low energy hadronic models on lateral distribution functions of cosmic ray air showers for Auger energies is explored. A large variety of presently used high and low energy hadron interaction models are analysed and the resulting lateral distribution functions are compared. We show that the slope depends on both the high and low energy hadronic model used. The models are confronted with available hadron–nucleus data from accelerator experiments.

Comparison of hadronic interaction models at Auger energies

The three hadronic interaction models DPMJET 2.55, QGSJET 01, and SIBYLL 2.1, implemented in the air shower simulation program CORSIKA, are compared in the energy range of interest for the Pierre Auger experiment. The model dependence of relevant quantities in individual hadronic interactions and air showers is investigated.

Theoretical molecular Auger spectra with electron population analysis

An approximation method is proposed to simulate the molecular Auger spectra. Auger transition rates are estimated with atomic populations of valence orbitals on an excited atom by Mulliken and Löwdin population analyses. Normal Auger energies and relative rates for H 2O and NH 3 molecules are evaluated using a full CI wave functions among the valence orbitals constructed from SCF orbitals for the neutral ground state and for the core-hole excited state. Theoretical spectra show fairly good correspondence with the experimental spectra. It is demonstrated that the present approach is applicable for qualitative assignment and analysis of Auger spectra for larger molecules.

Formation of the hollow1so1Sstate ofNe2+by electron impact: Observation by means of an Auger hypersatellite

A weak Auger transition at $870.5\ifmmode\pm\else\textpm\fi{}0.3 \mathrm{eV}$ has been observed in neon for electron impact energies above the double K-shell ionization threshold (1863 eV). The Auger energies and transition rates identify the transition as the strongest Auger hypersatellite decay channel, $\mathrm{KK}\ensuremath{-}{\mathrm{KL}}_{23}{L}_{23}^{2}D,$ of the hollow ${1s}^{o}{}^{1}S$ state of ${\mathrm{Ne}}^{2+}.$ The production cross section of the ${1s}^{o}{}^{1}S$ state by electron impact was determined for energies up to three times the threshold ionization energy and found to agree reasonably with the binary encounter calculations.

The angle-resolved Kr L2,3M4,5M4,5 Auger multiplet following proton impact ionization

The angle-resolved Kr L2,3M4,5M4,5 Auger spectra induced by proton impact ionization were measured at 1, 2.6 and 3.6 MeV proton energies where high-resolution spectroscopy techniques have been applied. The Auger energies and relative line intensities are compared with different earlier experimental data as well as our numerical results which have been obtained within a multiconfigurational Dirac-Fock approach. The alignment parameter 20 of the singly ionized krypton atoms has been extracted from the experimentally accessible anisotropy parameter A2 applying a special method, using the theoretical values of the angular distribution parameter 2 .

Observation of angular correlation between subsequently emitted Auger electrons

In an exploratory feasibility study we have measured the angular correlation between Auger electrons that were emitted in a cascadelike decay process after resonant photoexcitation, using synchrotron radiation from the Brookhaven National Synchrotron Light Source. While the monochromator was tuned to the argon $1\stackrel{\ensuremath{\rightarrow}}{s}4p$ resonance (3203.5 eV) we recorded Ar $\mathrm{LMM}$ Auger electrons in coincidence with ${\mathrm{KL}}_{2,3}{L}_{2,3}{,KL}_{1}{L}_{2,3},$ and ${\mathrm{KL}}_{2,3}{M}_{1,2,3}$ Auger electrons. We found different nonisotropic angular correlations between distinct energy regions of the $\mathrm{LMM}$ group of Auger lines and the ${\mathrm{KL}}_{2,3}{L}_{2,3}$ Auger electrons, while for other kinetic energies the $\mathrm{LMM}$ Auger electrons exhibit isotropy. Because the $\mathrm{KLL}$ and $\mathrm{LMM}$ Auger energies are so different, we believe that the nonisotropic angular correlation observed is due to an alignment effect rather than a dynamical postcollision interaction effect.

Calculation of Al and Si KLV Auger energies and intensities

Abstract KLV Auger spectra of Al and Si were measured with the electron-beam excitation method. A new semi-empirical method for calculating the kinetic energies of these spectra originated from inner and valence shells is proposed. In this method, the measured energy of a Kβ X-ray satellite emitted from a K 1 L 1 doubly ionized state and a calculated Hartree-Fock-Slater type potential acting between inner shells, i.e. K and L shells, for an isolated atom were used. The absolute kinetic energies of the Al and Si KLV Auger spectra were simply but accurately estimated without any complicated multiplet calculations involving the interaction potential between the L and V shells.