Extra-atomic Relaxation Energy Research Articles

Direct measurement of the kinetic energy shift between the molecular and atomic M4.5N4.5N4.5 Auger spectra of iodine

The M4.5N4.5N4.5 Auger electron spectrum of iodine has been measured from molecular and atomic iodine vapours. The energy shift of 3.25 = 0.10 eV between molecular and atomic Auger spectra has been determined using a least-squares fitting procedure to spectra containing both molecular and atomic contributions. Different initial and final state splittings for atomic and molecular spectra, as well as the extra-atomic relaxation energy, are discussed.

X-ray photoelectron spectroscopy of quick-frozen aqueous solutions of sodium salts

X-ray photoelectron spectra were observed on the quick-frozen aqueous solutions of sodium halides. The separation between Na KLL Auger peak and Na 1s peak was found to be different between the quick-frozen aqueous solution and the crystal of the salt, while the separation of Na 1 s peak and a core-electron peak of anion little differs between the two states. Discussion is given on the extra-atomic relaxation energy and other energy terms which are affecting the shifts of KLL Auger and core-electron peaks.

Chemical Shifts of Sulfur KLL Auger Electron Energies in Its Compounds

Abstract The sulfur 1s and 2p photoelectron spectra and KL23L23 Auger electron spectra in various sulfur compounds involving solid sulfur were measured by means of irradiation by Al Kα and Cr Kα X-rays. The chemical shifts of the S1s and S2p photoelectron spectra for compounds referred to the data for solid sulfur differ from each other in magnitude, but all are larger than that for the Auger electron spectra in the corresponding compound. The shift of the Auger electron spectra is different in fashion from those of the photoelectron spectra; the difference is largely attributable to the differences in relaxation energies. The extra-atomic relaxation energies due to core-electron emission were estimated by combining the atomic spectral data and the XPS and AES data of compounds; they were found not necessarily to depend upon the atomic charges. From the calculated sulfur Kα X-ray spectra corresponding to the difference in the binding energy between 1s and 2p, the number of electrons on each sulfur atom was obtained by using the method derived from Coulson et al., while the isolation was attempted on the basis of the contribution of polarization energies due to surrounding atoms to the extra-atomic relaxation energies.

Free-atom core binding energies from x-ray photoelectron spectroscopy I. Zinc and cadmium

Gas phase photoelectron spectra of zinc and cadmium have been obtained with AlKα radiation. The binding energies measured are: Zn2p1/2 (1052.3 eV), Zn2p3/2 (1029.1 eV), Cd3d3/2 (418.8 eV), and Cd3d5/2 (412.0 eV). Combining x-ray emission data on the solid with free atom optical energy results gives binding energies in close agreement with our values. A decrease of 2.8 eV for Zn2p and 3.3 eV for Cd3d was found in going from the free atom to the metal. This difference is discussed in relation to the various calculations of extra atomic relaxation energies in solids.

Studies on the Chemical Shifts of Auger Electron Energies for Magnesium and Zinc in Their Compounds

Abstract The energy shifts of X-ray excited Auger electrons and photoelectrons for zinc and magnesium in their metals, oxides, halides, and chelate compounds are analyzed in terms of the relaxation effect. Zn 2p3⁄2, 3d photoelectron, Zn L3M45M451G Auger electron, Mg 1s, 2p photoelectron and Mg KL23L231D Auger electron peaks were provided for the investigation. The quantitative estimation of the extra-atomic relaxation energies for core electron emission was performed by combining atomic spectral data, XPS and AES data of the compounds. For zinc compounds, extra-atomic relaxation energies increase in the order of ZnF2<ZnCl2<ZnBr2≈ZnO<ZnI2≈ZnS<Zn(acac)2, whilst the values are not fairly systematic for magnesium compounds. The nearest neighbored atom is found to be the important function for the extra-atomic relaxation energies.

Initial and final state effects in the ESCA spectra of cadmium and silver oxides

The factors which influence chemical shifts are examined in order to elucidate the cause of the anomalous chemical shifts for Cd and Ag oxides. The effects of extra-atomic relaxation are accounted for using a procedure employing experimental Auger and binding energies. Atomic partial ionic charges for some simple Cd, Ag, and Zn compounds are calculated from experimental binding energies using a model which includes the effects of lattice potentials and extra-atomic relaxation. Inclusion of extra-atomic relaxation effects did not have a drastic effect on the relative ionicities computed for these selected compounds. However, for CdO, a large extra-atomic relaxation energy contribution reduces the binding energy by 0.5 eV more than is predicted from nearest neighbor electronegativity arguments.

Surface relaxation energies in core level spectroscopies of adsorbed atoms and molecules

Core level holes which are created in electron emission spectroscopies of atoms and molecules adsorbed or condensed onto metal surfaces induce a screening charge at the surface. The Coulomb interaction between the induced and the hole charge, called the extra-atomic relaxation energy, shifts the apparent binding energy of the ejected electron from the value inferred from an orbital energy. In this paper, linear response screening shifts are calculated for a number of different response functions which also allow for the polarizability of the adsorbed layers. The relation between classical image potential shifts and those obtained here is quantitatively compared. As an example, the X-ray photoelectron spectrum of SF 6 physisorbed on Ru surfaces is interpreted in terms of the present theory.

Line shape analysis and relaxation energies in the MVV Auger spectra of zinc and zinc oxide

The oxidation of polycrystalline zinc has been studied by recording the evolution of the line shape of the corresponding Auger spectra. The fine structure of the surface-sensitive low energy M 1 VV and M 23VV ( V = 4 s − 3 d valence band) lines in pure zinc has been analyzed and a new feature involving the 4s band tentatively identified. In the course of oxidation the main peaks broaden and shift to lower energies. This behaviour is explained in terms of increase of the 3d band width and decrease in the extraatomic relaxation energies. The extraatomic relaxation is found to decrease in the oxide by ~3.8 eV. A derivation of Auger intra and Extraatomic energies involving basically experimental data is presented. These values are compared to theoretical evaluations and their connection with photoemission dynamical relaxation data is discussed.

Calculation of adsorbate relaxation energies in X-ray photoelectron spectroscopy

The ΔSCF method has been employed to estimate extra atomic relaxation energies of ionised adatoms. Unrestricted Hartree–Fock calculations were carried out for Be adsorbed on different sites of large cubium clusters. Extra atomic relaxation energies for different sites were found to be similar and of the order of 4 eV.

Electronic relaxation processes in the KLL′ auger spectra of the free magnesium atom, solid magnesium and MgO

The K-Auger spectrum of the free magnesium atom and the magnesium metal is calculated. The Friedel model is used to account for extra-atomic relaxation effects. Theoretical Auger electron energies are compared with the corresponding experimental values. In general the agreement between theory and experiment is good. The evolution of the extra-atomic relaxation energy in going from the metal to the oxide is presented.

X-ray photoemission from mercury in vapor and condensed phases

The $4f$ ionization potentials for mercury in the vapor phase have been measured relative to the vacuum level; those for mercury condensed on gold, silver, and copper have been measured relative to the Fermi level. Correction for the work function of the solids, determined in a separate experiment, gives the ionization potentials of the condensed mercury relative to the vacuum. The vapor-phase ionization potentials are greater than those for condensed phases by 3.3 eV for ${f}_{\frac{7}{2}}$ electrons and 3.0 eV for ${f}_{\frac{5}{2}}$ electrons; these differences are nearly independent of the substrate. This shift is attributed to extra-atomic relaxation energies. Two models, a localized electron (exciton) model and an equivalent-cores thermochemical model, predict relaxation energies for these and other systems with reasonable accuracy. The splitting between the ${f}_{\frac{7}{2}}$ and ${f}_{\frac{5}{2}}$ levels is 4.01 eV in the gas phase and 3.7 eV in the solid phase. The change in splitting on condensation may be due to energy-loss phenomena peculiar to the surface.

Interatomic transitions and relaxation effects in Auger spectra of several gas adsorbates on transition metals

A systematic investigation of the fine structure of adsorbate peaks in Auger spectra is presented. Spectra of a wide range of systems involving carbon, sulphur, oxygen, chlorine, and nitrogen adsorbates on copper, nickel, iron, and zinc substrates are reported with a resolution $\frac{\ensuremath{\Delta}E}{E}\ensuremath{\sim}0.006$. According to a previous suggestion two types of transitions are identified and separated in such spectra. Interatomic transitions involve deexcitation of the initial adsorbate core hole from electrons in the substrate valence band. These transitions are rather similar to the ones involved in ion neutralization spectroscopy and are relatively unperturbed by final-state effects. Intra-atomic transitions show the same type of perturbation already observed in other investigations of Auger spectra involving rather localized valence bands, like $d$ bands in transition metals. We identify peaks associated to spectral terms corresponding to final-state configuration interaction. Measurements of the energy of these peaks are used, in connection with photoemission binding energies of other authors, for calculating energy shifts. These shifts are then tentatively analyzed in terms of relaxation energies and, particular, extra-atomic relaxation energies are estimated. A discussion of the general conditions for correlating Auger-electron data and valence-band density of states is offered.

Extra-atomic relaxation energies for the 3d-transition metal series obtained with SCF hole-state calculations

A method to calculate extra-atomic relaxation energies is presented. It is based on the use of SCF hole-state calculations. The E R ea (2s) and E R ea (2p) values obtained for the 3d-transition metal series are in fair agreement with experimental values.

X-ray photoelectron spectroscopy of thermally grown silicon dioxide films on silicon

At various stages of in situ thermal oxidation of Si(111) monocrystals, X-ray photoelectron spectroscopy (XPS or ESCA) reveals a shift in the silicon core-level binding energies which varies continuously from 2.4 to 4.2 eV. From the oxygen and silicon ESCA peak intensities, these films can be said to have the silicon dioxide composition with an excess in oxygen concentration. By correlating the silicon 2p or 2s binding-energy shifts with oxygen KLL Auger energy and oxygen 1s binding-energy shifts, it is shown that a Fermi level shift and differential extra-atomic relaxation energy in the interfacial region must be invoked, in addition to chemical structure considerations, to interpret these data.

Relative effect of extra-atomic relaxation on Auger and binding-energy shifts in transition metals and salts

The relation between shifts in Auger energies and shifts in electron binding energies is explored. The prediction of Auger energies in metals from one-hole and two-hole optical energies as well as from electron binding energies in metals is described, with proper accounting for final-state coupling, relaxation, and reference energies. A decrease in values of extra-atomic relaxation energies for $3d$ metals between Ni and Cu, arising from the loss of $d$-wave screening at the $3d$-shell closure, was derived for the ${L}_{3}{M}_{23}{M}_{23}$ Auger transition in which the final state is localized. A similar decrease can be derived from the data on the ${L}_{3}{M}_{45}{M}_{45}$ transition, suggesting that the $3d$ hole state may be localized. Shifts in either Auger or electron binding energies between solids have no direct significance when taken alone, but the difference between the two is shown to be equal to the difference in the corresponding extra-atomic relaxation energies. Differential shifts are reported for sodium and its salts and for zinc and its salts. The differential shift between sodium metal and NaF is 8.7 eV, while the Zn-to-Zn${\mathrm{F}}_{2}$ shift is 5.2 eV, in good agreement with expectations. The $\mathrm{Zn}(3d)\ensuremath{-}\mathrm{F}(2p)$ peak in the Zn${\mathrm{F}}_{2}$ spectrum gives clear evidence for crystal-field splitting in the final state.

X-Ray Photoemission from Zinc: Evidence for Extra-Atomic Relaxation via Semilocalized Excitons

X-ray-photoelectron-spectroscopy studies on clean metallic zinc are reported. A well-defined Fermi edge was observed, and the $3d$ band peak was located at ${E}_{F}\ensuremath{-}10.2$ eV. The data analysis raised the question of the extent to which valence-band photoemission spectra of metals are distorted, relative to one-electron frozen-orbital band-structure calculations, by differential relaxation. Atomic hole-state calculations by Lindgren and by Gelius and Siegbahn indicate that (intra-) atomic relaxation can vary by up to 5 eV between $3d$ and $4s$ shells. Thus valence-band spectra in $3d$ transition metals can be seriously distorted by atomic relaxation alone. It is argued that the $3d$ bands probably lie below the $4s$, $4p$ valence bands in zinc in the initial state, but not in the photoemission spectrum. The nickel photoemission spectrum may well be distorted by relaxation. The magnitude of the extra-atomic relaxation energy $\ensuremath{\Delta}{E}_{B}$ was estimated in several ways. Empirical estimates were based on comparisons among photoemission and optical data on several elements. Semiempirical estimates were based on theoretical atomic binding energies and experimental binding energies in metals. All estimates were in rather good agreement, showing extra-atomic relaxation energies of up to \ensuremath{\sim} 15 eV. A theoretical model was derived, based on the assumption that extra-atomic relaxation occurs through screening of the hole state by formation of a semilocalized exction. This process was described by Friedel as positive phase shifts in the conduction bands. The model predicts a slow rise in $\ensuremath{\Delta}{E}_{B}$ in the $3d$ series and a sudden drop between Ni and Cu, in excellent agreement with experiment.

L2,3M45M45Auger Spectra of Metallic Copper and Zinc: Theory and Experiment

The ${L}_{2}{M}_{45}{M}_{45}$ and ${L}_{3}{M}_{45}{M}_{45}$ Auger spectra of clean metallic copper and zinc were measured. A theory was developed to predict the Auger energies. The theory employs experimental electron binding energies, which were also measured, two-electron integrals, and Hartree-Fock energies. It accounts for multiplet splitting in the ${d}^{8}$ final state, predicting structure in excellent agreement with experiment in zinc and in very good agreement in copper. It also accounts for atomic relaxation and for static extra-atomic relaxation (screening), which is related to the Friedel theory of alloys. The theory developed here predicts the Auger energies to within 1 eV in zinc and 2-3 eV in copper. Since atomic integrals were used, the success of the theory implies that an atomistic approach to Auger energies is valid for these metals. The magnitude of the extra-atomic relaxation energy (\ensuremath{\sim} 10 eV) suggests that it may be a crucial factor in Auger energy shifts arising from chemical environment or surface condition.