A comparative study of single crystal magnesium oxide and oxidised magnesium by auger electron spectroscopy

In a study by AES of the surfaces of single crystal magnesium oxide and magnesium after various stages of oxidation, it has been shown that Auger energy shifts are produced by surface charging. Recognition of the charging effects has enabled the peak in the low energy spectrum of magnesium oxide crystal to be assigned. The low energy secondary electron spectra of both MgO crystal and oxidised magnesium are complicated by the presence of extra features which arise from diffraction of true secondary electrons, and in particular for oxidised magnesium a cross-transition occurring at the metal-oxide interface. Oxidation studies of sodium also reveal transitions arising from a similar process.     

Quadrupolar transitions evidenced by resonant auger spectroscopy

From absorption spectra, the only way to bring to the fore the occurrence of quadrupolar transitions is to study their angular dependence. Resonant spectroscopies offer a new opportunity to obtain more insight into excited electronic states by studying lineshape and intensity of decay processes. We show here that resonantly excited Ti KL(2,3)L(2,3) Auger spectra of TiO2(110) carry a clear signature of quadrupolar transitions to localized e(g) and t(2g) d-like states, giving access to a direct measurement of crystal field splitting.     

Relaxation energies of oxygen auger transitions in some oxides

Relaxation effects are of major importance in the so-called chemical shifts observed in XPS and AES. These chemical shifts mainly arise from changes in the electrostatic environment due to the field of the neighbouring atoms in the initial neutral state and from electron redistribution in the surrounding electron cloud in order to screen the final state holes of the excited atom. Using a three-step model for the Auger process, we succeeded in deriving cross-relaxation energies from the KLL spectrum of oxygen in oxides, provided a careful calibration of experimental binding and Auger kinetic energies is achieved. It has been shown that the extra-atomic relaxation energy increases with ionicity for oxides of non-transition metals. In the case of transition metal oxides, it has been found that the cross-relaxation energies are larger than for the other oxides; it is believed that this is due to a more efficient screening effect of the d-electrons of the neighbouring metal atoms.     

The forbidden transitions for magnesium isoelectronic sequences

Using the full relativistic quantum mechanics(GRASP2),we have calculated systematically the 3p2-3p1 and 3p1 -3p0 magnetic dipold m1 energy level scparations,transition probabilities and cscillator strengths in the 3s3p configuration of the magnesium seque     

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.     

Raman active soft modes and phase transitions in sodium tungsten bronzes

The temperature dependence of the Raman spectra of Na_xWO₃ for x > 0.5 is reported. A group theoretical analysis of the data confirms the space group assignments of Clarke⁸ and supports the existence of several phases derived from rigid tilts of the WO₆ octahedra. The phase diagram for high concentration Na_xWO₃ deduced from Raman measurements is in excellent agreement with that obtained from x-ray results particularly with regard to the previously undetected tetragonal to tetragonal transition.     

K Auger transitions of the free sodium atom

TheK Auger spectrum of the free sodium atom, following electron impact ionization, was measured with 0.16% resolution using a sodium atomic beam as target. The absolute energies and relative intensities ofKLL, KLM and numerous satellite transitions have been determined. The absolute energies of theKLL transitions of the free sodium atom were found to be smaller by 13.1 eV than the corresponding energies found for sodium in Na₂O (relative to the Fermi level) by Fahlmanet al. Also the relativeKLL intensities differed in two cases indicating solid state and/or chemical effects. The present relative intensities agree better with theoretical values calculated by McGuire, Walters and Bhalla, and Chen and Crasemann than those of Na₂O. In an Appendix the natural line widths of theKLL andKM-LLM transitions of sodium have been calculated.     

Matrix effects in auger analysis

The Pamler model of matrix effects for Auger analysis becomes ineffective for the Ag-Pd data reported by Sekine et al. An attempt is made herein to solve this problem by modifying Pander's formalism. This modification takes into account the difference in escape depth of the Auger electrons associated with the different elements in a binary alloy. The results are then applied to the Ag-Pd, Al-Cu and Ni-Pd systems.     

Indirect electronic transitions in alkali halate crystals-II (sodium bromate and iodate) crystals

In the case of NaClO₃ and KClO₃ crystals, analysis of the long wavelength tail of their fundamental absorption revealed the active participation of the internal vibrations of the chlorate ion (Part I). In order to test the validity of the above interpretation the absorption spectra of two more halates with different anions namely sodium bromate and sodium iodate are analysed in a manner similar to that given in Part I. It is found that the principle internal vibrations of bromate and iodate ions are involved in the indirect transitions. The variation of indirect band gap with temperature is found to be ?2·5 × 10^?4 eV/K and ?2·9 × 10^?4 eV/K for sodium bromate and sodium iodate respectively.     

Nuclear auger effect in muonic atoms

In a muonic atom electromagnetic transitions proceed via emission of X-rays, electrons from the atomic cloud (Auger electrons), or neutrons from the nucleus (nuclear Auger effect). We calculate the neutron spectrum for muonic ²⁰⁷Pb and ²⁰⁹Bi within a microscopic theory of nuclear reactions. The compound nucleus mechanism is dominant. Most of the neutrons arise from the E2 transition 3d → 1s. Agreement between experiment and calculation is achieved to within a factor of 2.     

Indirect electronic transitions in alkali halate crystals-I (sodium and potassium chlorate crystals)

The long wavelength tail of the fundamental absorption in NaClO₃ and KClO₃ crystals has been analysed based on the theory of band to band transitions of Bardeen et al.[8] developed in the case of semi-conducting crystals. Evidence of phonon involvement in the transitions giving an indirect band gap is observed. The energies of the phonons involved in the process are the same for both the crystals, and agree well with combinations of prinicple frequencies of ClO₃^? ion, their overtones and also lattice phonons. The indirect band gap in these crystals varies with temperature more or less linearly and the rate of variation is ?3·8 × 10^?4 eV/K and ?5·0 × 10^?4 eV/K for sodium chlorate and potassium chlorate respectively.     

Phonon-assisted auger recombination in degenerate semiconductors

Phonon-assisted Auger recombination is studied in strongly degenerate semiconductors since normal Auger recombination is negligible in this case. The results are discussed in connection with an electron-hole-plasma. There are some indications that phonon-assisted Auger recombination is an important process in this case.     

XVV auger spectra in substitutional alloys

Summary Theoretical computations on the shape of the Auger spectra for a substitutional Cu−Ni alloy are reported. Cini's theory and a cluster theory for the hole density of states have been used. The results are compared with available experimental data and the effect of the configurational averages, as compared with single-configuration results, is discussed.

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Riassunto Si sono presentati i risultati di un calcolo teorico della forma degli spettri Auger di una lega sostituzionale Cu−Ni. Si fa uso della teoria di Cini e di una teoria a cluster per la densità degli stati per le buche. Si confrontano i risultati con i dati sperimentali disponibili e si discute l'effetto delle medie configurazionali.

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Резюме Приводятся результаты теоретических вычислений Оже-спектров для сплавов замещения Cu−Ni. Используются теория Чини и кластерная теория для плотности состояний дырок. Полученные результаты сравниваются с имеющимися экспериментальными данными. Обсуждается эффект конфигурационных средних.

     

Phonon-assisted auger recombination in quantum well semiconductors

Phonon-assisted Auger recombination (AR) is shown to be an important loss mechanism in a quantum well semiconductor in addition to the direct AR. Theoretical investigations demonstrate that it is of the same order of magnitude and has the same temperature dependence as in bulk material, just as direct AR, provided that the material parameters and the carrier concentrations are the same as in the bulk.     

Electron and ion beam effects in auger electron spectrometry

In Auger Electron Spectrometry relatively high primary electron current density is usually used in order to obtain a good signal-to-noise ratio. As a consequence, a number of phenomena occurs, which can substantially modify—or even destroy—the sample, and impair the results of the analysis.

In this communication we report some observations on the electron and ion beam interaction on some of the insulating and conducting films used in the silicon device technology. Among the materials considered, silicon nitride and P-doped silicon dioxide are of primary interest, and will be treated in some detail; results on other films, both insulating (Al₂O₃, B-doped SiO₂, etc.) and conducting (Al-Si alloys) will also be reported.

The electron beam causes the oxides (B, Al, Si, P) to be reduced, as shown by the decrease of the height of the low energy, chemically shifted peaks (B_KVV, Al_LVV, Si_Lvv, P_Lvv) and by the contemporary increase of the height of the elemental peaks. In phosphorus doped glasses the electron beam also induces a strong surface P enrichment, followed by a P desorption. Silicon nitride was found to be quite stable against the e-b irradiation in “good” vacuum, but very sensitive to the e-b induced oxidation even at (total) pressure as low as 5 × 10¹⁰ torr. This is a very important fact to be taken into account when evaluating thin Si₃N₄ films, because it can change the apparent film stoichiometry.

Some metallic films are also preferentially oxidized by the electron beam; in Al/Si diluted alloy (0.1÷2% silicon) a strong surface silicon enrichment was found to take phase on small-grained thin films, but not on bulk material.

Our results show that much care has to be taken when performing or interpreting the AES data, and how to use, in some cases, the e-b irradiation effects to increase the sensitivity of the method.     

Anisotropy of auger processes in monocrystalline graphite

The angular dependence of the KVV Auger spectrum fine structure in the graphite monocrystal has been found. It cannot be explained by the influence of surface defects and roughness; therefore it has been determined in terms of the local electron density anisotropy in graphite.     

Theoretical calculation for the equations of state and phase transitions of sodium and potassium hydrides

Abstract

The ionic overlap-compression model is used to calculate the equations of state, as well as the equilibrium properties, of sodium and potassium hydrides (NaH and KH). The present results agree with the experimental ones well. The NaC1-to-CsC1 phase transition pressures for both crystals are also determined. The agreement of the theoretical pressures (23.0 GPa for NaH and 4.9 GPa for KH) with the experimental measurements (29.3 GPa and 4 GPa) is rather good. The calculation shows that the effect of the zero-point vibration to the equilibrium properties and the transition pressures should not be ignored.     

Effect of structural phase transitions on the magnetic properties of sodium superoxide

The dramatic temperature dependence of the magnetic susceptibility and Electron Spin Resonance in sodium superoxides between 77 and 300 K is attributed to various structural phase transitions. One of our important observations is a switchover from a weak ferromagnetically coupled 3-dimensional system to a strong antiferromagnetically coupled 1-dimensional system with decreasing temperature. There is no magnetic ordering.