Radiative Auger Effect Research Articles

Ab initio calculations of Auger electron kinetic energies: Breadth and depth

Ab initio theoretical calculations for Auger electron kinetic energies are presented for twenty prominent Auger peaks for the 3d transition metals (21≤Z≤30). These are the twenty Auger peaks listed for these elemental solids in the National Institute of Standards and Technology (NIST) X-ray photoelectron spectroscopy database. Adding to these values, over one hundred Auger electron kinetic eigenenergies are calculated for titanium. Many of these transition lines are not established in current literature due to their relatively small yields and overlapping widths. These data can be of importance for determination of previously unaccounted Auger electron peaks with titanium and will be useful for X-ray fluorescence studies into the radiative Auger effect. The consistency between our values and the empirical data is an improvement compared with previous binding energy approaches and the methodology is convergent. The methods presented can be extended to other elements for future investigations of Auger electron kinetic energies which is particularly useful where current experimental values do not exist. Furthermore, these calculations provide evidence in the success of multiconfigurational Dirac–Hartree–Fock approaches in complex quantum mechanics.

L-shell ionization of Cd: Structure of the x-ray emission spectrum

The cadmium L x-ray spectrum induced by electron impact was analyzed in detail. The measurements were performed on a bulk pure sample using a commercial wavelength dispersive spectrometer, and the spectrum was processed with a parameter optimization method previously developed. This procedure permitted the determination of characteristic energies, relative transition probabilities and natural linewidths for this element. The results obtained here were compared to the data found in the literature, when available. Spectral structures related to satellite and radiative Auger Effect emissions were also analyzed, assessing energy shifts and relative intensities. Some of these parameters were determined for the first time, even in overlapping peaks and weak transitions, which was possible due to the robustness of the spectral processing method used.

Radiative Auger process in the single-photon limit.

In a multi-electron atom, an excited electron can decay by emitting a photon. Typically, the leftover electrons are in their ground state. In a radiative Auger process, the leftover electrons are in an excited state and a redshifted photon is created1-4. In a semiconductor quantum dot, radiative Auger is predicted for charged excitons5. Here we report the observation of radiative Auger on trions in single quantum dots. For a trion, a photon is created on electron-hole recombination, leaving behind a single electron. The radiative Auger process promotes this additional (Auger) electron to a higher shell of the quantum dot. We show that the radiative Auger effect is a powerful probe of this single electron: the energy separations between the resonance fluorescence and the radiative Auger emission directly measure the single-particle splittings of the electronic states in the quantum dot with high precision. In semiconductors, these single-particle splittings are otherwise hard to access by optical means as particles are excited typically in pairs, as excitons. After the radiative Auger emission, the Auger carrier relaxes back to the lowest shell. Going beyond the original theoretical proposals, we show how applying quantum optics techniques to the radiative Auger photons gives access to the single-electron dynamics, notably relaxation and tunnelling. This is also hard to access by optical means: even for quasi-resonant p-shell excitation, electron relaxation takes place in the presence of a hole, complicating the relaxation dynamics. The radiative Auger effect can be exploited in other semiconductor nanostructures and quantum emitters in the solid state to determine the energy levels and the dynamics of a single carrier.

Study of Kβ X-ray emission spectroscopy applied to Mn(2−x)V(1+x)O4 (x=0 and 1/3) oxyspinel and comparison with XANES

Oxidation state and coordination of transition metal cations seems to be hard to assess when considering multiple cations, each one with different possible oxidation states. In fact, this is the case of the spinel-type double oxides family. High resolution Kβ X-ray fluorescence spectra were measured in Mn(2−x)V(1+x)O4 (x=0 and 13) spinels-type double oxides in order to determine the oxidation state and coordination of V and Mn cations. The relative intensity of radiative Auger effect KM2,3M4,5 to the total intensity and the integral absolute difference value were used as reference parameters for the characterization of Mn oxidation states. The coordination of Mn ions was inferred by the intensity of the Kβ5 line. In the case of V compounds, it was used as the intensity of the line Kβ′ relative to the total area of Kβ region. The obtained results were further compared with X-ray absorption spectra analysis, showing good agreements regarding the oxidation state characterization. However, there were found some discrepancies in coordination, due to customary oversimplifications in the Kβ5 line origin. The obtained results might represent valuable and useful data for chemical scopes of characterizing spinel-type oxides family.

Two-electron-satellite transition of donor bound exciton in ZnO: Radiative Auger effect

Two-electron-satellite (TES) transition of donor bound exciton (D0X) is an interesting many-body quantum process. In this letter, precise luminescence spectra and temperature behaviors of the TES transition of aluminum bound exciton in two kinds of zinc oxide single crystals were investigated in detail. It is found that the TES transition can be treated as a radiative Auger process in which the temperature dependence of the emission intensity of the transition can be fitted very well with a model taking into account the temperature dependent Auger term and thermal dissociation of the D0X excitons.

X-ray emission–photoion coincidence spectroscopy of the CO2 molecule at the O 1s edge

Molecular dissociation following radiative decay of O 1s hole states in CO2 has been studied by detecting photoions in coincidence with undispersed soft X-ray emission. The production of ions after radiative decay is observed to increase from practically nothing at the O 1s→π∗ excitation to the appearance of CO2+, CO+, C+ and O+ ions when core-valence double excitations and O 1s shake-up transitions are induced. De-excitation pathways involving radiative decay from different core–hole states are discussed in order to interpret the results. A weak CO22+ signal is attributed to the radiative Auger effect.

Satellites, hypersatellites and RAE from Ti, V, Cr, Mn and Fe in photoionisation

AbstractK x‐ray satellites, hypersatellites and lines due to radiative Auger effect (RAE) of Ti, V, Cr, Mn and Fe were measured after exciting the samples with Ag bremsstrahlung at 35 kV. All the lines were measured with the ‘Spectroscan VY’ spectrometer of Spectron—OPTEL, Russia, in which a curved LiF(200) crystal was used. The spectra were deconvoluted using Voigt functions, and the peak positions of the satellites and hypersatellites were determined with errors of ± (1–5) eV. The energy shifts of the satellite lines with respect to their parent lines were also obtained. Multi‐configuration Dirac–Fock (MCDF) calculations with the inclusion of higher‐order corrections were carried out to predict the peak positions of the satellite and hypersatellite lines. Our data were then compared with our own calculated values and also with the data of others. Our measured energy shifts for KαL1, KαL2, Kαh and KβL1, when compared with our MCDF calculations, show a maximum deviation of 8, 12, 2 and 20% respectively. Copyright © 2008 John Wiley & Sons, Ltd.

A study of K x‐ray hyper‐satellites and KMM radiative Auger effect (RAE) of the elements 19 ≤ Z ≤ 25 by photon excitation

AbstractK x‐ray emission spectra were generated by photon excitation to study the Kα hyper‐satellites, KβL1, Kβ5 satellites and KMM RAE structures of the elements 19⩽Z⩽25 using a wavelength dispersive spectrometer with LiF 200 and LiF 220 crystals. The Z‐dependence of the energy shift and relative intensity of these lines with respect to the diagram lines were studied except in the case of KMM RAE constituent peaks, for which only energy shifts were examined. The measured energy shifts and relative intensities are compared with the available theoretical predictions. Three of the constituent peaks in the KMM RAE structure are assigned K‐M1M2 (3P), K‐M1M2 (1P) and K‐M1M1 (1S) transitions. Copyright © 2006 John Wiley & Sons, Ltd.

Radiative Auger Effect and Extended X-Ray Emission Fine Structure (EXEFS)

Radiative Auger spectra are weak X-ray emission spectra near the characteristic X-ray lines. Radiative Auger process is an intrinsic energy-loss process in an atom when a characteristic X-ray photon is emitted, due to an atomic many-body effect. The energy loss spectra correspond to the unoccupied conduction band structure of materials. Therefore the radiative Auger effect is an alternative tool to the X-ray absorption spectroscopy such as EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure), and thus it is named EXEFS (Extended X-ray Emission Fine Structure). By the use of a commercially available X-ray fluorescence spectrometer or an electron probe microanalyzer (EPMA), which are frequently used in materials industries, we can obtain an EXEFS spectrum within 20 min. The radiative Auger effect, as an example, demonstrates that the study on atomic many-body effects has become a powerful tool for crystal and electronic structure characterizations. The EXEFS method has already been used in many industries in Japan. Reviews about the applications and basic study results on the radiative Auger effect are reported in this paper.

Radiative Auger study of transition-metal/silicon contacts

Silicon K-LL radiative Auger effect (RAE) spectra of annealed nickel/silicon and iron/silicon contacts together with that of a crystalline silicon were measured nondestructively using soft X-ray emission spectroscopy (SXES) apparatus. The K-LL RAE spectra give us similar information to K-edge X-ray absorption spectra, i.e. unoccupied p-electron density of states (DOS), while the SXES give us the information on occupied valence band DOS. We demonstrate that the single apparatus without synchrotron radiation facility can give the information on both occupied and unoccupied electron states. Also we carried out the similar analysis of the oscillation in the RAE spectra to that of the extended X-ray absorption fine structure (EXAFS) to obtain inter-atomic lengths around a central atom. The result for annealed nickel/silicon was in good agreement with the crystal data of NiSi 2. The RAE and SXES complement each other in the investigation of buried interface.

Extended x‐ray emission fine structure and high‐energy satellite lines state measured by electron probe microanalysis

AbstractThe Kα satellite or shake‐off lines can be observed by wavelength‐dispersive spectrometry on the high‐energy side of the main Kα peak. Occasionally, chemical state analysis of an emitting atom has been attempted using the shape and position of these lines. Recent extensive theory and experiment have shown that it is fruitful to take a similar approach using extended x‐ray emission fine structure (EXEFS) arising from the radiative Auger effect (RAE). This fine structure is found in a low‐intensity spectrum on the low‐energy side of the Kα peak.We have studied the RAE spectra of the Kα lines of the elements F through to Ca by EPMA. The RAE peaks have energies close to the KLL energies of Auger transitions. In the lighter elements in this series, it was found that the difference between Kα and the RAE peak energies becomes quite small. For elements lighter than fluorine, it is difficult to observe the RAE peaks because they are overlapped by the main Kα line. At the higher energy end of the series, the intensity of the RAE lines becomes very small. The utility of the RAE lines for state analysis is limited, in practice, to the elements F through to Ca. The extended x‐ray emission fine structure (EXEFS) of the RAE spectra has been used to calculate local bonding parameters.Both shake‐off and RAE spectra associated with the F Kα line have been studied experimentally in the rare earth fluorides. The KLL RAE moves to lower energy as the atomic number of the rare earth cation increases. This has been confirmed theoretically by calculating electron energies using discrete variational Xα molecular orbital theory. The shake‐off peaks increase in intensity relative to the main Kα peak because atomic number increases, contrary to expectation. It is considered that this could be due to temporary covalency. The EXEFS of the RAE spectra has been used to calculate local bonding parameters. Copyright © 2001 John Wiley & Sons, Ltd.

蛍光Ｘ線スペクトルの微細構造について

X-ray fluorescence spectra have a tail in their low-energy side of characteristic discrete lines. Though the origin of the tailing was believed to be a response of electron gas in the conduction band to the creation of a core hole, the author proposes a new interpretation; the radiative Auger effect is an additional origin of the tailing. Information contained in the shape of tailing is discussed.

Theory of radiative Auger effect – an alternative to X-ray absorption spectroscopy

Abstract The present author and his coworkers discovered a similarity between the K–LL radiative Auger X-ray emission spectra and the K-edge X-ray absorption spectra for Na, Mg, Al and Si. The XANES-like and EXAFS-like spectra were observed in the X-ray fluorescence spectra as well as X-ray emission spectra excited by electron beam. A representative example of the similarity is presented and the reason for this similarity is rationalized using molecular orbitals expressed by the linear combination of atomic orbitals within the two-step model (photoionization and X-ray emission are independent).

K-LM radiative Auger effect in argon

The K–LM radiative Auger (RA) x-ray spectrum of argon was observed. The transitions were photoinduced by means of an x-ray tube and measured with two different high-resolution curved crystal spectrometers of reflection-type geometry. From the first measurements performed at the Paul Scherrer Institute (PSI), only an upper limit of 0.25% relatively to the intensity of the Kα1,2 diagram line could be obtained for the total K—LM RA yield. From a second experiment carried out at the University of Fribourg, a I(K–LM RA)/I(Kα1,2) ratio of 0.18±0.05% was obtained. This value is consistent with the PSI result but in strong disagreement with theoretical predictions based on the shake model, which are about four times larger. © 1998 John Wiley & Sons, Ltd.

Measurement of relative X-ray intensity ratios for elements in the 22≤ Z≤29 Region

X-ray spectra obtained by pure element targets photoionization using an X-ray tube were recorded with the Si(Li) detector calibrated for efficiency and peak shape. The spectra were analyzed taking into account the radiative Auger effect and satellite lines. K β/K α X-ray intensity ratios for Ti, V, Cr, Mn, Fe, Co, Ni and Cu were compared with those obtained from radionuclides decaying by electron capture. The K-shell fluorescence yields were reviewed for the same Z range, pointing out the lack of experimental data.

Experimental evidence for theK-LMradiative Auger effect in medium-mass atoms

High-resolution measurements of the $K{\ensuremath{\alpha}}_{1,2}$ low-energy satellites were performed for the elements ${}_{42}$Mo, ${}_{44}$Ru, ${}_{46}$Pd, ${}_{48}$Cd, and ${}_{50}$Sn. The photoinduced x-ray spectra were measured using a high-resolution transmission-type bent-crystal spectrometer in modified DuMond slit geometry. Experimental evidence for the $K$-$\mathrm{LM}$ radiative Auger effect (RAE) in solid medium-mass atoms was found and particular groups of the $K$-$\mathrm{LM}$ RAE transitions were identified. The experimental intensity ratios $I(K$-$\mathrm{LM}$ RAE$)$ / $I(K{\ensuremath{\alpha}}_{1,2})$ as well as the relative intensity of the $K$-${L}_{3}{M}_{4,5}$ transition group were extracted from the measured spectra. A comparison of the experimental results with relativistic Hartree-Fock theoretical predictions from Scofield shows a good agreement. The experimental energies of the $K$-$\mathrm{LM}$ RAE edges are compared with calculated Auger transition energies.

Si(Li) detector response and PIXE spectrum fitting

Departures from Gaussian lineshape in Si(Li) spectra arise from the radiative Auger effect, the intrinsic Lorentzian shape of X-ray emission lines, double ionization and spectator vacancy satellites, electron escape from the detector and carrier diffusion within it, and from imperfections in the charge collection process. Rather than describe empirically the tailing function that arises collectively from these effects, we prefer to incorporate those that are fundamental in nature into the lineshape model, and to reserve empirical description for the minority component that is truly an artefact reflecting imperfections in the device. A useful alternative to such a lineshape description is a weighting scheme that de-emphasises the tails of intense peaks in a least-squares fitting process.

High-resolution measurements of the K-MM radiative Auger effect in medium-mass atoms.

High-resolution measurements of the K-MM radiative Auger effect in medium-mass atoms.

Radiative dielectronic recombination and correlated processes

A new quasi-resonant radiative dielectronic recombination (RDR) process is formulated as an off-shell extension of the dielectronic recombination. It is an electron-ion recombination process in which dielectronic-excitation capture is accompanied by simultaneous radiation emission, and can occur at all continuum energies of the electron being captured. The RDR can be the dominant mode of recombination at off-resonance energy regions, and may provide an important distortion correction to the direct recombination. The distinct signature of the RDR is the quasi-discrete low energy x-rays emitted during the capture, shifted down in energy by the excitation energies of the core electrons. The analog of the RDR must also take place in the ion-atom collisions, as radiative transfer excitation (XTE). Evaluation of the RDR cross section is difficult because of the correlated nature of the transition operator, but detailed qualitative discussions of the RDR are presented. A crude estimate of the cross section is obtained and compared with the other recombination modes. The radiative Auger effect is roughly an inverse of RDR, and the charge dependence of its cross section is improved, using a correlated vertex.

Radiative Auger effect: an explanation for discrepancies between theoretical and experimental K β/K α X-ray emission probability ratios?

New effects have appeared in the field of low-energy X-ray spectrometry as a consequence of the simultaneous improvement of detector characteristics and mathematical codes for spectra processing. In the present study, X-ray spectra in the low-energy range are obtained with a Si(Li) spectrometer with a FWHM of 153 eV. The mathematical fitting code (CALGARY) includes a complex function with background, peak and tailing, which takes into account the Lorentzian shape corresponding to the X-ray natural width. The fitting residuals exhibit a systematic hump in the low-energy tail of the K β peak: this can be attributed to the KMM radiative Auger effect. This phenomenon could explain some of the discrepancies observed between the theoretical and experimental K β/K α X-ray emission probability ratios.