Auger Electron Emission Spectra Research Articles

Ion neutralization and high-energy electron emission in He+scattering by a highly oriented pyrolitic graphite surface

Fil: Iglesias Garcia, Adalberto de Jesus. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Santa Fe. Instituto de Fisica del Litoral; Argentina

Combined electron emission effects on the biologically damaging efficiency of 125I

Purpose: One important obstacle in modeling the biological damage of 125I lies in the collective effects of the emitted electrons. The huge number of possible different ways of atomic rearrangement causes a strong variability in the number and energies of the emitted electrons. The aim of this work is to tabulate, separately for each atomic rearrangement pathway, the absorbed doses and the single-strand breaks (SSB) probabilities for different size nanospheres of liquid water.Methods: A simple deterministic (non-stochastic) atomic rearrangement model of only 265 pathways is appropriate for modeling the electron-capture and internal conversion processes in 125I. The feasibility of the atomic rearrangement model is verified by comparing the SSB yield for ultrasoft X-ray sources with Lobachevsky's experimental data.Results: A linear equation is sufficient for describing the SSB probability as a function of the dose absorbed in a small volume surrounding the labelled nucleotide 125I-dC.Conclusions: The application of a deterministic atomic rearrangement model to Auger electron emission spectra gives a new perspective to the study of low linear energy transfer (LET) radiation effects on DNA. The damages induced by point electron-capture (EC) sources and by macroscopic X-ray sources are compared.

Evidence for Pauli exchange leading to excited-state enhancement in electron transfer.

Single- and double-electron transfer to autoionizing 1s2l2l(') configurations in fluorine ions have been investigated for 1.1 MeV/u collisions of F7+ and F8+ with He and Ne. The resulting Auger electron emission spectra show anomolously large intensities for the formation of the metastable 1s(2s2p 3P) 4P state compared to the similarly configured 1s(2s2p 3P) 2P- and 1s(2s2p 1P) 2P+ states. The large 4P intensity, which cannot be explained on the basis of spin statistics, is attributed instead to the Pauli exchange of similarly aligned electrons.

Magnetic circular dichroism inL3M2,3M2,3Auger emission from Fe and Co metals due to symmetry-breaking interactions

A strong magnetic circular dichroism (MCD) in the ${L}_{3}{M}_{2,3}{M}_{2,3}$ Auger-electron emission spectra was measured on Fe and Co metal in the off-resonance energy region with the light helicity vector perpendicular to the magnetization direction, despite the fact that this emission is expected to be symmetry forbidden in this geometry. The experimental results are explained quantitatively by taking into account the exchange interaction of the spin-orbit split core states with the spin-polarized valence band. It is shown that the local valence-band magnetic moment is strongly suppressed in the presence of a $2p$ hole in the intermediate state. As a result the MCD signal decreases going from Fe to Co metal, while for Ni the MCD is no longer observable. This behavior is completely different for the measurements at resonance---i.e., at the ${L}_{3}$ absorption edge, where the MCD signal is strong $(\ensuremath{\sim}9%)$ for Fe, Co, and Ni due to the large spin polarization of the $2p$ core hole which is caused by unoccupied $3d$ states with predominantly minority spin in the vicinity of the Fermi level.

Doppler interference in dissociative resonant photoemission

Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.

3d-Resonant photo- and auger emission of Ce in CeO 2

The Ce 3d-edge resonant photoelectron and Auger electron emission spectra in CeO 2 have been measured. The 4s-, 4p- and 4d-emission at off-resonance excitations consists of two parts separated by about 13 eV, which correspond to different final-state configurations. The resonantly excited spectra show the different nature of the M 45-main and satellite photoexcitations. The satellites seem to correspond to intermediate states of a more extended character. For M 45N 45N 45 on-resonance decay the most interesting finding (obtained by comparison with the relevant spectra of Ce in CeCl 3 and La in LaF 3) is the considerable suppression of the high energy band related to the upper levels of the 4d 84f n final state configurations. The M 45N 45N 45 decay in CeO 2 appears to be more similar to the situation in metallic cerium than in the insulating CeCl 3.

Effect of edge anomaly on the valence-band Auger spectra of metals

The processes responsible for the anomalous edge behavior in the x-ray band spectra of metals are found to play important roles in modifying the intensity of $\mathrm{CVV}$ Auger-electron emission spectra. The dynamical effects related to the sudden switching of the core-hole potential are known to produce a power-law behavior in the neighborhood of the upper emission edge. Using simplified diagrams and a realistic pseudopotential for the core-hole interaction, we have extended the edge theory to energies well below the Auger emission edge. A significant shift in the position of the maximum of the ${L}_{23}\mathrm{VV}$ Auger emission intensity of Al is calculated.

Auger electron emission spectra from foil and gas excited carbon beams

Auger electron emission spectra from 2 MeV C + ion excited by collisions with thin carbon foils and Ne gas are presented. The similarity of qualitative features for the C + → C (foil) and C + → Ne spectra indicates the similarity of ionization mechanisms for beam foil and beam gas excitation. The spectra were normalized to the lowest lying Li-like quartet state (1s 2s 2p) 4P 0 in carbon by comparison with time delayed foil excited electron decay-in-flight spectra. Comparison to Hartree-Fock calculated transition energies indicates that transitions in three and four electron carbon ions dominate the prompt spectra.

Auger spectra of lithium hydride

Auger electron emission spectra have been observed for lithium hydride in three conditions : (1) cleaved in vacuum, (2) prepared by the reaction of hydrogen gas with clean lithium metal, and (3) by annealing slightly oxidized lithium hydride single crystals in vacuum. The dominant Auger line (40 ± 1 eV) was found to be a KVV transition involving valence electrons from the anion and was indistinguishable from a similar transition for lithium oxide at room temperature. Lithium hydride surfaces lose hydrogen in vacuum causing the formation of a lithium metal phase at room temperature and a significant reduction in surface hydride stoichiometry at 600°C.

Charge state dependence of X ray and Auger-electron emission spectra for rare-gas atoms. III. Krypton atom M-shell

For pt.II, see abstr. A23320 of 1971. A non-relativistic Hartree-Fock self-consistent-field procedure with spin-orbit interaction corrections has been used to investigate the effect of multiple ionization in the valence shell of the krypton atom on M and N shell binding energies and on the transition energies of M shell de-excitation processes. The study of the non-radiative relaxation mechanisms includes intra-shell Coster-Kronig and super-Coster-Kronig transitions as well as normal inter-shell Auger transitions. The predicted energies for Auger transitions have been compared with the experimental spectra available from electron impact studies. In general, with the exception of M-N1N1 discrepancies are discussed.

Inelastic effects and structure in the auger electron emission spectra of V2O5(010) and V(100) surfaces: Study of chemical shifts

Characteristic ionization losses and plasma losses occurring in the AES spectra of V 2 O 5 (010) and V(100) surfaces are discussed. The former are used to evaluate chemical shifts of the VL 2 and VL 3 levels in V 2 O 5 . Values of approximateley 2.5 eV are found. These are smaller than the values obtained with ESCA (± 5 eV). It is described how the electron beam used in AES is thought to be responsible for this effect. ESCA data from partly reduced V 2 O 5 samples tend to confirm the proposed model, based on oxygen loss and decomposition of V 2 O 5 single crystals under the influence of the electron beam. The plasma losses of the larger Auger peaks are discussed. It is shown how some fine structure in the spectra can be partly explained by their presence. The plasma losses were simulated with numerical techniques based on the use of a signal averager. Signal averaging, curve fitting and related numerical techniques improve the resolution of AES spectra. Spectra of V 2 O 5 (010) and V(100) obtained in this manner are discussed. With respect to the transitions involving the valence band it is shown that the complex valence band structure is one of the causes of the observed discrepancies between theoretical and experimental AES data. Furthermore there is an uncertainty concerning the way in which ionization correction should be applied in this case. This correction is thought to increase with the degree of localization of the valence electrons. Auger peak intensities in function of the primary energy were found to show a maximum at about 3.5 times the critical potential, as was expected from theory if a moderate amount of backscattering is taken into account. Finally the intensity variations of the Auger peaks under continuous electron bombardment show the rate of oxygen loss at a V 2 O 5 surface due to the primary beam.

Charge state dependence of X-ray and Auger electron emission spectra for rare-gas atoms. I. The argon atom

A non-relativistic Hartree-Fock self-consistent procedure has been used to investigate some properties of the argon atom and its ions. The electronic binding energies of the various sub-shells have been calculated for both single and double hole states. The energy of the X-ray photon and Auger electron associated with the filling of a vacancy in the L shell has been calculated. The incident- ion energy-dependent line shifts observed in the X-ray and Auger- electron emission spectra obtained from Ar+-Ar collision studies are explained in terms of the filling of the L23 single vacancy in argon ions with different numbers of valence electrons.

Charge state dependence of X-ray and Auger electron emission spectra for rare-gas atoms. II. The neon atom

Charge state dependence of X-ray and Auger electron emission spectra for rare-gas atoms. II. The neon atom