Auger Transition Probabilities Research Articles

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

Auger transition probabilities and electron emission cross sections for vacancy decay into the 2pπ-orbital in the Ne-=SUP=-+-=/SUP=--Ne quasimolecule

The paper reports the calculation of the probabilities of Auger transitions taking place in the process of filling a vacancy on the 2pπ-orbital in an Ne+-Ne quasimolecule, a short-lived system which arises when the ion and atom approach each other and decays when they fly apart. Calculations for various ionization degrees of the quasimolecule particles were performed for the first time. It was found out that the system ionization degree increases very significantly (from 2 to 6) with increasing collision energy and decreasing distance of the particles closest approach. Using of the quantum mechanical approach and taking into account the collision dynamics made it possible to quantitatively describe for the first time the experimental Auger electron spectra of a complex many-electron quasimolecule. The contribution of the transition from the initial 3dπ-3dπ state to the 2pπ orbital was shown to be predominant among the whole variety of possible Auger decay channels. Keywords: atomic collisions, quasimolecule, Auger transitions, electron emission cross sections, vacancy decay

Вероятности оже-переходов и сечения эмиссии электронов при распаде вакансии на 2pπ-орбитали в квазимолекуле Ne-=SUP=-+-=/SUP=--Ne

The Auger transition probabilities are calculated while filling a vacancy on 2pπ orbital in a Ne+-Ne quasimolecule, a short-lived system which is formed when ion and atom approach each other and decays when they scatter. For the first time calculations were performed for various degrees of particles ionization in quasimolecule. It was found that with increase of collision energy and decrease of distance of the closest approach of particles the system ionization degree increases very significantly (from 2 to 6). Using of the quantum mechanical approach and taking into account the dynamics of collisions made it possible for the first time to describe quantitatively the experimental spectra of Auge electrons for a complex many-electron quasimolecule. From the whole variety of possible Auger decay channels the dominant contribution of the transition was established, from the initial 3dπ-3dπ state to the 2pπ orbital.

Dynamic Ionization and Auger Transitions in the Quasi-Molecule during Ne+–Ne Collisions

The exponential component of the electron spectrum during Ne–Ne collisions is shown to be associated with the electron transitions from the autoionization term to the continuum. The characteristics of this term have been determined. The exponential shape of the spectrum is explained by the absence of interference between the transition amplitudes as the particles come close together and fly apart due to a high transition probability. For Auger transitions in the quasi-molecule we have determined the dependence of the mean Auger transition energy on the reached internuclear distance, which agrees well with the results of energy level calculations for the Ne–Ne system, and the dependence of the weighted mean Auger transition probability on the observed electron energy Ee. We show that the transition probability decreases significantly with increasing Ee as the internuclear distance decreases, apparently, due to a decrease in the overlap integrals of the wave functions for the interacting electrons. Our analysis allows a coherent picture of ionization in collisions of intermediate-mass ions with keV energies to be formed.

Cascade of elementary processes in Se1+

SynopsisAnalysis of radiative and Auger cascade following creation of the K shell vacancy in the Se atom is presented. Calculations of radiative and Auger transition probabilities are performed by using Dirac-Fock-Slater approximation. Radiative and Auger spectra as well as ion yield produced by cascade are studied.

Enhancement of Double Auger Decay Probability in Xenon Clusters Irradiated with a Soft-X-Ray Laser Pulse

The interaction of large Xe clusters with a soft x-ray laser pulse having a wavelength of 13.9 nm and an intensity of up to 2x10(10) W/cm2 was investigated using a time-of-flight ion mass spectrometer. The corresponding laser photon energy was sufficiently high to photoionize Xe 4d innershell electrons. It was found that Xe3+ ions (which result from double Auger decay of 4d vacancies) became the dominant final ionic product with increasing cluster size and x-ray intensity. This is in contrast to the results of synchrotron radiation experiments involving free Xe atoms, in which Xe2+ is the dominant resultant ion species. Possible mechanisms responsible for the enhancement of the double Auger transition probability in x-ray laser and cluster interaction are discussed.

Vacancy Cascades Following Inner-shell Ionization in Ar And Kr Determined Using Different Atomic Data

The charge state distribution of ions following K-shell ionization in Ar and Kr atoms is calculated using a Monte Carlo simulation technique. A computer program is written to trace successive X-ray and Auger transition probabilities, which fill vacancies in atomic configurations. The radiative and nonradiative branching ratios are evaluated. Electron shake-off probabilities due to atomic rearrangement after inner-shell ionization are considered in the calculation. The obtained results are compared with those determined experimentally and those calculated from the atomic data collected from different literature sources. It is found that using accurate atomic data leads to results that agree well with experimental values.

Multiple-ionization satellites in the L 2, 3 Auger spectra of argon-like molecules

L2, 3 Auger spectra of all argon-like molecules (HCl, H2S, PH3, SiH4) have been calculated with inclusion of the multiple ionization satellites. The Auger transition probabilities were calculated with inclusion of the ligand electron density, multiplet splitting, final-state configuration interaction, and spin-orbit splitting of the initial 2p level. The theoretical integrated intensities of the shake-off and shake-up satellites (“with a spectator”) in the L2, 3 Auger spectra of argon-like molecules make up 8.2–10.4% of the total Auger spectrum intensity.

Mechanism of ion desorption reaction of PMMA thin film induced by core excitation

Abstract Auger electron spectra of PMMA (poly-methylmethacrylate) which show remarkable site-specific ion desorption are calculated using ab initio molecular orbital (MO) calculation and compared with the results of Auger electron-photoion coincidence experiments. Methyl isobutyrate and its trimer are used as model molecules of PMMA. The calculation is based on the single configuration state function and limited configuration interaction methods, and Auger transition probabilities are estimated by overlap between core and valence MOs. The calculated normal Auger spectra obtained on specific atoms reproduce well the experimental resonant Auger spectra for both the carbon and oxygen sites. The careful analysis of the calculated Auger spectra indicates that the desorption of CHn+ ions is strongly concerned with the Auger final states which have holes in the O–CH3 bonding orbitals.

Experimentally derived Auger transition probabilities in X-ray excited Auger electron spectroscopy (XAES)

The capability of Auger transition probabilities experimentally derived from X-ray excited Auger electron spectra in XPS were tested. The relative sensitivity factor (RSF) method has been employed in the quantification by AES (Electron excited Auger electron spectroscopy). However, the difference between experimentally derived RSF and theoretically calculated ones has been found in some reports. One of the great reason of the difference may be caused by the calculated values of the Auger transition yield which has been commonly employed without the consideration of the allotment of coupling scheme in the transition selected in the quantification, for instance, the allotment of each six coupling KL 1L 1, KL 1L 2, KL 1L 3, KL 2L 2, KL 2L 3, and KL 3L 3 in KLL transition. The employment of derived Auger transition probabilities reduce the difference between theoretically calculated RSF and experimentally derived one.

Electron scattering correction of x-ray-excited Ni and Cu KLL Auger spectra emitted from thin and thick metallic samples

High-energy Cu and Ni KLL Auger lines, excited by Mo and Cu bremsstrahlung, were measured for polycrystalline metallic samples as well as for thin (10 nm) films deposited onto Si substrates, to determine the respective Auger transition energies and probabilities. 1 The spectra of homogeneous samples show a broad tail of inelastically scattered electrons. This tail is strongly suppressed in the thin-film spectra. These spectra have been subjected to a recently proposed background subtraction procedure, 2 accurately accounting for the details of the signal electron emission process (depth distribution of the emitting species, elastic scattering, experimental geometry, etc.). As a result, the inelastic tail is removed in the background-corrected spectra. Comparison of the spectra from the thin films and the homogeneous samples after background correction provides an experimental test of the background subtraction procedure. In our case these corrected spectra are essentially identical, proving the consistency of the method applied.

Experimental derivation of Auger transition probabilities from X-ray excited Auger electron spectra in XPS

Auger transition probabilities were experimentally derived from dominant XAES and related XPS peaks observed in XPS spectra. Some values of derived probabilities were higher than 1, because of addition or subtraction of background signal from the XAES or/and XPS peak intensity. However, the probabilities obtained are recognized to be useful for practical quantification by XAES and AES.

Nonradiative electronic deexcitation time scales in metal clusters

The lifetimes due to Auger-electron emission for a hole on a deep electronic shell of neutral and charged sodium clusters are studied for different sizes. We consider spherical clusters and calculate the Auger-transition probabilities using the energy levels and wave functions calculated in the local-density approximation. We obtain that Auger emission processes are energetically not allowed for neutral and positively charged sodium clusters. In general, the Auger probabilities in small ${\mathrm{Na}}_{N}^{\ensuremath{-}}$ clusters are remarkably different from the atomic ones and exhibit a rich size dependence. The Auger decay times of most of the cluster sizes studied are orders of magnitude larger than in atoms and might be comparable with typical fragmentation times.

Charge transfer from Cu in YBa2Cu3O7−δ and Ba2Cu3O4Cl2 crystals determined by Auger electron spectroscopy

A formulation is proposed to estimate the charge transfer ΔqCu from Cu to some anions in metal-oxide crystals, using Auger electron spectroscopy. In the formulation, a parameter, the Auger transition probability ω, is introduced, which is defined as the ratio of Auger intensity due to a certain transition to the total Auger intensity due to other transitions when the same core electrons are primarily excited. By applying the formulation to vacuum-cleaved surfaces of YBa2Cu3O7−δ (YBCO) and Ba2Cu3O4Cl2 (BCOC) crystals, we obtained the following results: (1) YBCO cleaves between CuO2 and BaO layers, and the amount of ΔqCu is 2.3 in units of elementary electric charge. The deviation of ΔqCu from 2.0 suggests the existence of Cu3+-like atoms; (2) for BCOC, ΔqCu varies from 3.3 to 1.7 depending on the Ar ion beam sputtering time.

Electronic structure of Al3Ni and AlNi3 alloys.

Experimental Al KL(23)V and Ni LMM Auger and high-resolution valence band XPS spectra of Al3Ni and AlNi3 alloys are presented and compared to the corresponding spectra of pure metals. The spectra are interpreted in terms of the results of the discrete-variational (DV)-X alpha cluster MO model using atomic Auger transition probabilities. Good agreement has been obtained between the theory and experiment concerning the energy widths of the spectra. For Al3Ni the total number of electrons at the Fermi level obtained from the calculations agrees better with the experimental value than those from previous calculations. In the case of the alloys, the calculated charge transfer is small (<0.4 electrons), playing only a minor role in the filling of the Ni d band. The hybridization between the Ni d and Al s and p bands can be deduced from the reduction of the Al s and p DOS at the Ni d resonance energy. Our results suggest that for these alloys the corresponding Auger matrix elements do not depend on the Auger transition energy. The Ni LMM spectra of the alloys demonstrate the localization of the Ni d band.

Auger electron peaks of Cu in XPS

Intensities of photoelectron and photo-excited Auger electron peaks observed in X-ray photoelectron spectroscopy of copper have been analyzed using a background optimization formalism. The relative intensities of L 2, 3MM peaks are proportional to those predicted by Auger transition probabilities. However, their absolute intensities are stronger than those of holes created by 2p photoemission. Measurement by monochromatic X-ray photoelectron spectroscopy indicates that there is a contribution from a 2s hole by Coster-Kronig transition. Moreover, a spectrum of a conventional (non-monochromatic) source suggests additional 2s and 2p holes by the accompanying Bremsstrahlung.

Spin-resolved Fe L3M45M45 Auger transition on and off resonance: The effect of exchange correlation.

Spin-resolved Fe ${L}_{3}{M}_{45}{M}_{45}$ Auger-electron spectra were recorded with on- and off-resonant ($2{p}_{\frac{3}{2}}\ensuremath{\rightarrow}3{d}^{*}$) photons. The spectra agree with convolution of spin-resolved Fe density of states, except in the degree of spin polarization which was found to be higher (lower) than the spin polarization of Fe valence electrons when using on- (off-) resonant photon excitation. This is consistent with a reduction of the Auger transition probability of the spin-parallel two-hole final state as compared to spin-antiparallel state, which indicates the importance of exchange correlation in $3d$ itinerant ferromagnets such as Fe.

Calculated Auger transition probabilities — from free atom to solids

The behaviour of the calculated Auger transition probabilities σ L has been studied in going from a free atom to an atom in solid. The Mg KLV transition matrix elements have been calculated using the wave functions of the core-ionized impurity embedded into the crystal. It has been shown that the energy dependence of the valence wave functions causes Auger transition probabilities increasing from the bottom of the valence band to the Fermi level. The dependence of the σ L values on the energy of the valence electron state is very close to linear one.

Selective deexcitation of the 4d94fn+1 excited states studied by resonant photoemission in LaCl3 and CeCl3.

Resonant photoemission in the rare-earth 4d\ensuremath{\rightarrow}4f prethreshold absorption region has been investigated in ${\mathrm{LaCl}}_{3}$ and ${\mathrm{CeCl}}_{3}$. It is found that the intensity ratio of the rare-earth 5${\mathit{p}}_{1/2}$ photoemission to the total 5p emission deviates from the statistically expected value in the prethreshold absorption region and depends on the final multiplet states of the 4d\ensuremath{\rightarrow}4f photoexcitation. The ratio reaches 0.7 at the 4${\mathit{d}}^{9}$4${\mathit{f}}^{1}$ ${(}^{3}$${\mathit{D}}_{1}$) photoexcitation in ${\mathrm{LaCl}}_{3}$ and nearly 0.5 at the 106-eV photoexcitation in ${\mathrm{CeCl}}_{3}$. In ${\mathrm{CeCl}}_{3}$, it is also found that the magnitudes of the resonant enhancements of the Ce 4f emission are not proportional to the strengths of the 4d\ensuremath{\rightarrow}4f photoabsorption lines. These resonant aspects are explained by the multiplet dependence of the Auger transition probability involved in the resonant photoemission.

Physical foundation of quantitative Auger analysis

The possibility of using an Auger peak height in the dN (E) /dE spectrum and an integrated N (E) spectrum as a measure of the Auger current is discussed and necessary relations are presented. The methods of the background determination are reviewed and discussed. The relation between the Auger current and the atomic cancentration of a corresponding sample component is derived and the state of art in the field of theoretical and experimental determination of factors appearing in this relation (ionization cross-section, Auger transition probability. backscattering factor, and inelastic mean free path of Auger electrons) is presented. Approaches to the quantitative Auger analysis (QAA) of homogeneous, isotropic samples, including corrections for matrix factors, are presented and discussed. Problems arising when heterogeneous samples are analyzed are discussed and practical approaches to such an analysis are presented. The role of crystalline effects (the dependence of the Auger signal from crystalline samples on the direction of the primary electron beam and angular distribution of Auger electron emission from such samples) in QAA is discussed and examples of such crystalline effects are presented together with their physical foundation. Some rules are suggested allowing the quantitative Auger analysis to be performed with the smallest possible error.