The Auger electron spectrum of water vapour

The Auger electron spectrum of water vapour has been recorded and analyzed. For the analysis, an approximate formula for calculating the intensities of the Auger electron lines is derived. It is shown, that the calculated intensities along with theoretical energies of the Auger transitions account well for the observed spectrum. In particular, new assignments in terms of transitions to triplet final states are suggested.     

Study of electron states of solids by techniques of electron spectroscopy

Studies of valence bands and core levels of solids by photoelectron spectroscopy are described at length. Satellite phenomena in the core level spectra have been discussed in some detail and it has been pointed out that the intensity of satellites appearing next to metal and ligand core levels critically depends on the metal-ligand overlap. Use of photoelectron spectroscopy in investigating metal-insulator transitions and spin-state transitions in solids is examined. It is shown that relative intensities of metal Auger lines in transition metal oxides and other systems provide valuable information on the valence bands. Occurrence of interatomic Auger transitions in competition with intraatomic transitions is discussed. Applications of electron energy loss spectroscopy and other techniques of electron spectroscopy in the study of gas-solid interactions are briefly presented.     

Determination of low atomic number elements by X-ray fluorescence fundamental parameter method

Two versions of the X-ray fluorescence fundamental parameter method are compared in the analysis of the materials that contain low atomic number elements (fluorine, oxygen, nitrogen, carbon, and boron). It is shown by the examples of carbon and oxygen that, in using the classical version, the account of C and O atom ionization by photo and Auger electrons of the irradiated sample is obligatory. A change to absolute intensities in combination with the regression approach makes the method more flexible. In particular, the computational modeling of analytical signals for elements with Z < 10 becomes possible without taking into account the ionizing effect of photo and Auger electrons when the contribution of these electrons to the fluorescence intensity changes insignificantly. The error of the analysis grows with an increase in the variation of this contribution. If the contributions for the test samples differ significantly, the computational modeling of the effect of photo and Auger electrons in the iterative process becomes necessary.     

Auger photoelectron coincidence spectroscopy using synchrontron radiation

The technique of Auger-photoelectron coincidence spectroscopy (APECS) is described and illustrated with a case study of the Cu(100) 3p and M₂₃VV spectra. APECS offers many advantages over the conventional singles spectroscopy such as isolating overlapping spectral features, reducing secondary electron background, and revealing new decay modes. In the coincidence Cu Auger spectra discussed here, the multiplet structure of the quasi-atomic 3d⁸ Auger final state is clearly observed, as well as different intensities for the multiplet components for the p_1/2 and p_3/2 transitions. Furthermore, the spectra reveal evidence for a Coster-Kronig decay channel for 3p_1/2 core holes, and illustrate that the sum of the Auger electron and photoelectron kinetic energies is conserved. Possible technical improvements that can increase the counting efficiency are also discussed.     

Effect of semi-empirical parameters on the triplet energy levels and triplet–triplet transition in benzene

Triplet energy levels and triplet–triplet transition in benzene have been calculated semi-empirically by considering CI up to and including doubly excited configurations and using various values of the core resonance and electron repulsion integrals. The usual method of calibrating β (core resonance integral) from one of the observed transitions in the semi-empirical methods is critically examined with respect to the triplet levels of this molecule. Semi-empirical parameters are found to have a pronounced effect on the energy of the triplets and the triplet–triplet transitions; but the intensities of such transitions are quite insensitive to the choice of such parameters. Numerical results show several ³B_1u → ³E_2g transitions of various intensities. Out of these, the transitions which correspond energetically to the observed triplet–triplet bands are found to have low intensity. Some strong triplet–triplet bands are predicted in the far ultra violet region.     

Prediction of iron K-edge absorption spectra using time-dependent density functional theory

Iron K-edge X-ray absorption pre-edge features have been calculated using a time-dependent density functional approach. The influence of functional, solvation, and relativistic effects on the calculated energies and intensities has been examined by correlation of the calculated parameters to experimental data on a series of 10 iron model complexes, which span a range of high-spin and low-spin ferrous and ferric complexes in O(h) to T(d) geometries. Both quadrupole and dipole contributions to the spectra have been calculated. We find that good agreement between theory and experiment is obtained by using the BP86 functional with the CP(PPP) basis set on the Fe and TZVP one of the remaining atoms. Inclusion of solvation yields a small improvement in the calculated energies. However, the inclusion of scalar relativistic effects did not yield any improved correlation with experiment. The use of these methods to uniquely assign individual spectral transitions and to examine experimental contributions to backbonding is discussed.     

Resonance hyper-Raman excitation profiles and two-photon states of a donor-acceptor substituted polyene

Resonance Raman and resonance hyper-Raman spectra and excitation profiles have been measured for a "push-pull" donor-acceptor substituted conjugated polyene bearing a julolidine donor group and a nitrophenyl acceptor group, in acetone at excitation wavelengths from 485 to 356 nm (two-photon wavelengths for the nonlinear spectra). These wavelengths span the strong visible to near-UV linear absorption spectrum, which appears to involve at least three different electronic transitions. The relative intensities of different vibrational bands vary considerably across the excitation spectrum, with the hyper-Raman spectra showing greater variation than the linear Raman. A previously derived theory of resonance hyper-Raman intensities is modified to include contributions from purely vibrational levels of the ground electronic state as intermediate states in the two-photon absorption process. These contributions are found to have only a slight effect on the hyper-Rayleigh intensities and profiles, but they significantly influence some of the hyper-Raman profiles. The absorption spectrum and the Raman, hyper-Rayleigh, and hyper-Raman excitation profiles are quantitatively simulated under the assumption that three excited electronic states contribute to the one- and two-photon absorption in this region. The transition centered near 400 nm is largely localized on the nitrophenyl group, while the transitions near 475 and 355 nm are more delocalized.     

Experimental auger electron spectrum of ammonia

The first electron excited Auger electron spectrum for gas-phase ammonia has been obtained and is compared with an existing theoretical prediction. Decomposition of the spectrum using a gaussian approximation reveals close agreement in both intensity and energy for the higher energy components provided the theoretical data is shifted toward lower energies by ≈ 2.7 eV. As the transitions involve progressively deeper final state levels there is a general trend of increasing widths and increasing discrepancy towards lower energy with respect to their predicted positions. Such behavior has been seen in other experimental—theoretical comparisons of gas-phase Auger results and while the variation in widths is interpreted in terms of transitions to a manifold of final state vibrational levels, the nature of the differential shift in the lower energy components is unclear.     

Quantitative surface analysis by Auger and x-ray photoelectron spectroscopy

Recent developments in quantitative surface analysis by Auger (AES) and x-ray photoelectron (XPS) spectroscopies are reviewed and problems relating to a more accurate quantitative interpretation of AES/XPS experimental data are discussed. Special attention is paid to consideration of elementary physical processes involved and influence of multiple scattering effects on signal line intensities. In particular, the major features of core-shell ionization by electron impact, Auger transitions and photoionization are considered qualitatively and rigorous approaches used to calculate the respective transition probabilities are analysed. It is shown that, in amorphous and polycrystalline targets, incoherent scattering of primary and signal Auger and photoelectrons can be described by solving analytically a kinetic equation with appropriate boundary conditions. The analytical results for the angular and energy distribution, the mean escape depth, and the escape probability as a function of depth of origin of signal electrons as well as that for the backscattering factor in AES are in good agreement with the corresponding Mote Carlo simulation data. Methods for inelastic background subtraction, surface composition determination and depth-profile reconstructions by angle-resolved AES/XPS are discussed. Examples of novel techniques based on x-ray induced photoemission are considered.     

Calculation of sulphur L(S2p)-MM Auger energies of H2S

The Auger energies of the L(S2p)-MM transitions of H₂S have been computed using MC SCF methods. The results are sufficiently accurate to assign the experimental spectrum and indicate large relaxation as well as large single-triplet splitting for low energy transitions.     

A review of auger photoelectron coincidence spectroscopy

The application of coincidence detection techniques produces a dramatic increase in the information obtained from particle and photon scattering studies. A clear illustration of this is given by Auger Photoelectron Coincidence Spectroscopy (APECS). By coincident detection of the ejected photoelectron and the resulting Auger electron during x-ray excited Auger spectroscopy, it is possible to distinguish the true origin of peaks and satellites within the Auger spectra. For example, it becomes possible to separate standard Auger processes from those occurring in conjunction with Coster-Kronig transitions and from those either followed or preceded by shake-off or shake-up transitions. In addition, the technique often allows the separation of overlapping series of Auger peaks, thus permitting the study of individual elements within compounds and alloys. These possibilities will be illustrated primarily by reference to APECS studies of 3d transition metal elements.     

Electronic transitions in 1,4-naphthoquinone derivatives

Single electronic transitions in 1,4-naphthoquinone and seven of its derivatives substituted in the quinoid system have been theoretically studied semi-empirical SCF MO CI calculations, in the frame of π and all valence electron (AVE) approximations. Dipole electrostatic contributions to the shifts originating from the solvent have been calculated and the local nature of the most significant transitions has been analyzed. The results agree satisfactorily with experiment, showing the effects of the substituents, which in some cases are underestimated.     

Binding and L23MM auger energies in atomic and metallic zinc

An analysis of the photoelectron and photon-induced L₂₃MM Auger spectra of Zn metal has been performed. The relaxation processes involved in the Auger transitions have been investigated. They account well for the experimental Auger energies.     

The change of the LMM auger spectra in 3d-metals due to oxidation and its correlation with the change of the atomic magnetic moment.

The surfaces of crystalline samples of 3d-metals (Mn, Fe, Co, Ni, and Cu) and their stoichiometric oxides have been studied by Auger spectroscopy. A correlation between the change in the LVV (L-inner level-valence-valence electron transition) Auger intensities and the change of the squares of the corresponding atomic-magnetic moments has been observed. This is because of the complicated nature of the Auger process. That is, the Auger electron emission is a result of the inner atomic level excitation by electron impact and Auger annihilation of the inner-level hole. Therefore, the Auger process has been considered a second-order process, and spin polarization of the valence states has been taken into account for the LMM (L-inner level-M-inner level-M-inner level electron transition) Auger spectra of 3d-metals.     

Application of positron annihilation induced Auger Electron Spectroscopy to the study of surface chemistry

Positron annihilation induced Auger Electron Spectroscopy (PAES), makes use a beam of low energy positrons to excite Auger transitions by annihilating core electrons. This novel mechanism provides PAES with a number of unique features which distinguishes it from other methods of surface analysis. In PAES the very large collisionally induced secondary electron background which is present under the low energy Auger peaks using conventional tecniques can be eliminated by using a positron beam whose energy is below the range of Auger electron energies. In addition, PAES is more surface selective than conventional Auger Spectroscopy because the PAES signal originates almost exclusively from the topmost atomic layer due to the fact that the positrons annihilating with the core electrons are trapped in an image correlation well just outside the surface. In this paper, recent applications of Positron Annihilation Induced Auger Electron Spectroscopy (PAES) to the study of surface structure and surface chemistry will be discussed including studies of the growth, alloying and inter-diffusion of ultrathin layers of metals, metals on semiconductors, and semiconductors on semiconductors. In addition, the possibilities for future application of PAES to the study of catalysis and surface chemistry will be outlined.     

Directional elastic peak and directional Auger electron spectroscopies — New tools for investigating surface-layer atomic structure

Intensities of elastically scattered electrons and Auger electrons emitted from a crystalline sample depend strongly on the direction of the primary electron beam with respect to the sample. Namely, distinct maxima of those intensities appear when the primary beam is parallel to one of the close-packed rows of atoms in the sample,

In an RFA analyzer, the angular distribution of the elastically scattered electrons or Auger electrons is integrated over a large scattering angle and does not influence the dependence of intensities mentioned above on the primary beam incidence angle (DEPES or DAES polar profiles). Those profiles can be obtained simply by rotation the sample positioned in front of the RFA analyzer around the axis parallel to the sample surface,

Maxima in DEPES and DAES polar profiles connected with the close-packed atom rows can be easily recognized because their position does not depend on the primary electron energy. Those maxima are the evidence for presence of the crystalline structure in the surface layer. They also enable characterization of this structure even for a crystalline layer composed of very small islands or maintained at temperatures too high to observe LEED patterns. This was shown for the Ag/Cu(111), Ag/Cu(011), and Ag/Ni(111) adsorption systems.

DEPES and DAES profiles are sensitive to the disorder in the surface layer. For example, the surface roughening transitions on the Ni(O11) and Cu(O11) faces was clearly demonstrated and the temperatures of these transitions in both cases were determined with the use of those methods.

A background on which maxima of the DAES and DEPES profiles appear is calculated using a simplified model. It is indicated that the shape of this background should contain information about the sample composition profile.     

Metastable states in NO2+ probed with Auger spectroscopy

High-resolution N 1s and O 1s photoelectron spectra (PES) of NO are presented together with spectra of the subsequent Auger decay. The PES are analyzed by taking spin-orbit splitting of the (2)Π ground state into account providing detailed information on equilibrium distances, vibrational energies, and lifetime widths of the core-ionized states. In the Auger electron spectra (AES) transitions to five metastable dicationic final states are observed, with two of them previously unobserved. A Franck-Condon analysis of the vibrational progressions belonging to these transitions provides detailed information on the potential-energy curves of the dicationic final states as well as on the relative Auger rates. The present calculations of the potential-energy curves of NO(2+) agree well with the experimental results and allow an assignment of the two hitherto unresolved Auger transitions to excited states of NO(2+), C(2)Σ(+)and c(4)Π.     

High energy resolution Auger spectroscopy on a CMA instrument

An experimental method that increases the analyzer resolution of cylindrical mirror analyzer CMA‐based Auger spectrometers is described. By means of electrically biasing the sample, the effective energy resolution obtainable from the CMA instrument is improved from the native 0.5 to 0.1% or even better for higher kinetic energy Auger transitions. In addition, the maximum kinetic energy Auger transition observable by the CMA Auger instrument is increased from 3200 to 5700 eV, in the current realization. It is also shown that the sensitivity of the energy scale calibration to sample working distance with respect to the analyzer is simultaneously reduced, making the method suitable for chemical surface analysis. The biasing is accomplished using a special sample holder with electronics and software that can be added to an existing instrument. The overall capability of the Auger instrument for chemical analysis is, therefore, increased, while preserving all the analytical functionality and features of the CMA. Copyright © 2011 John Wiley & Sons, Ltd.     

Simple calculations of Franck-Condon factors for electronic transition bands of polyacenes

Progressional intensities have been calculated for the L_a and L_b transitions of the polyacenes, on the basis of semi-empirical SCF CI calculations of geometry changes upon electronic excitation and from normal analyses. The results give the Franck-Condon intensity distributions over various totally symmetric modes in good agreement with the vibrational structures observed in high resolution spectra.     

Resonant Auger spectroscopy at the carbon and nitrogen K-edges of pyrimidine

The resonant Auger electron spectra obtained after photoexcitation below the C and N 1s ionization thresholds in the pyrimidine molecule have been measured at several photon energies. The results show the relevance of the localization of the inner hole and of the matching between the symmetries of the intermediate and final states in the decay spectra via participator transitions. The comparison with the Auger electron spectra suggests some assignment for the two-hole-one-particle states reached via spectator transitions. The analysis of the participator decay is supported by state-of-the art density functional theory calculations.