Interpretation of KL2,3L2,3 radiative auger thresholds in metals and semiconductors

High-resolution measurements of the KL_2,3L_2,3 radiative Auger edge in Mg and Al are reported. The theory of soft X-ray absorption thresholds by Flynn and Lipari is modified to account for the KL_2,3L_2,3 threshold energies. The calculated energies are in excellent agreement with the experimental results including previous measurements on Si.     

On the intensity ratio I(KL2,3L2,3)/I(KL1L1) of the auger carbon lines in series of d-metal carbides

C KVV Auger spectra have been obtained for series of nd-metal carbides (n = 3,4 and 5). The numbers of electrons participating in the C KVV Auger processes for these compounds are estimated by considering the intensity ratio I(KL_2,3L_2,3)/I(KL₁L₁). It is concluded that to explain the high intensities of the KL_2,3L_2,3 Auger lines for the d-metal carbides, it is necessary to consider the participation of conduction-band electrons (and/or interatomic transitions) in the C KVV Auger decay process.     

X-ray photoemission study of MgB<Subscript>2</Subscript> films synthesized from in-situ annealed MgB<Subscript>2</Subscript>/Mg multilayers

Superconducting MgB₂ films were obtained by in-situ annealing of precursor multilayers deposited at low substrate temperature by sputtering from a MgB₂ stoichiometric target and by thermal evaporation of pure Mg. After an in-situ annealing at 500–600 °C, the films showed a zero resistance critical temperature up to 31 K. The as-obtained MgB₂ films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray auger electron spectroscopy (XAES). The electronic structure was studied by monitoring the B 1s, Mg 2p, O 1s core-levels and the Mg KL₂L₃ Auger line. For comparison, the electronic structure of an MgB₂ commercial superconducting sputtering target, of a not-annealed precursor film and of a sample obtained by direct sputtering from the MgB₂ target have also been investigated. Electron spectroscopy showed that in the superconducting systems the Mg KL₂L₃ Auger line kinetic energy position is always higher by about 0.9 eV with respect to the energy position of the same Auger line measured in the non-superconducting samples. PACS 74.25Jb; 74.78.Bz; 74.70.Ad     

DasKLL- Auger-Spektrum von Chlor

TheKLL Auger spectrum of chlorine in CCl₄ has been investigated with an electrostatic energy analyzer. The ionization in theK shell of chlorine was caused by electron impact. Absolute energies and relative intensities of transitionsKL ₁ L ₁(¹ S,KL ₁ L _2,3(¹ P),KL ₁ L _2,3(³ P) andKL _2,3 L _2,3(¹ D) have been determined. Via the width of theK level of chlorine also experimental values of absolute transition probabilities have been calculated. While the relative intensities deviate strongly from theoretical values, the absolute transition probabilities agree better with theoretical values, especially with those calculated byRubenstein. — In an appendix the natural line widths of theKLL components of argon have been calculated theoretically.     

Das K-Auger-Spektrum von Neon

TheKLL-Auger spectrum of neon was investigated with an electrostatic spectrometer with an energy resolution of 0.12%. The ionization in theK-shell was caused by electron impact. The use of a gaseous target made it possible to measure the Auger electrons without any energy loss. The relative intensities of the KLL-lines were determined to be:KL ₁ L ₁(¹ S ₀)=1.0;KL ₁ L _2,3(¹ P ₁)=3.06±0.07;KL ₁ L _2,3(³ P _0,1,2)=0.98±0.05;KL _2,3 L _2,3(¹ S ₀)=1.67±0.08;KL _2,3 L _2,3(¹ D ₂)=13.1±0.6;KL _2,3 L _2,3(² P _0,2)=0. This is in agreement with an earlier measurement byKörber andMehlhorn but disagrees with all theoretical values calculated nonrelativistically for low Z. It is shown that agreement may be achieved by applying quantitatively the configuration interaction, introduced very recently byAsaad, and using improved wave functions for the calculation of the transition amplitudes. As a consequence of the ionization by electron impact also theKL-LLL Auger spectrum was caused. 10 lines of this spectrum were measured and identified. Moreover, from the Auger energies measured, the binding energyE(K) of neon was calculated to be E(K)=(870.0±0.4) eV.     

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 KL₁L₁, KL₁L₂, KL₁L₃, KL₂L₂, KL₂L₃, and KL₃L₃ in KLL transition. The employment of derived Auger transition probabilities reduce the difference between theoretically calculated RSF and experimentally derived one.     

A study of the adsorption of oxygen on Ni(111) using auger electron spectroscopy: Chemical shifts and valence spectra

Auger electron spectra have been recorded when oxygen is adsorbed on a Ni(111) single crystal surface. For the coverage range θ < 1, an analysis of the plot of the peak to peak height (H) of the oxygen KVV (516 eV) transition versus the total number of molecules cm^2? impinging on the surface (molecular beam dosing) shows agreement with the kinetic mechanism proposed by Morgan and King [Surface Sci. 23 (1970) 259] for the adsorption of oxygen on polycrystalline nickel films. In this coverage range, no energy shifts of the nickel or oxygen Auger peaks were recorded.At coverages θ > 1 (standard dosing procedure) shifts in the valence spectra M_{2, 3}VV (61 eV) and L₃M_{2, 3}V (782 eV) of ?2.3 eV and ?1.8eV respectively are recorded at 1.4 × 10^?2 torr-sec. Up to these coverages no shift of the L₃VV transition (849 eV) is observed. A chemical shift of ?2.1 eV is recorded in the L₃M_{2, 3}M_{2, 3} Auger transition (716 eV) at 1.4 × 10^?2 torr-sec.In the coverage range θ > 1, shifts in the energy of the oxygen Auger peaks are observed. At 5.8 × 10^?3 torr-sec. the KVV (516 eV) and KL₁V (495.2 ± 0.3 eV) transitions show shifts of ?1.5 eV and ?(1.0 ±0.3) eV respectively. No shift up to this coverage is recorded in the KL₁L₁ (480.6 ± 0.3 eV) transition.     

The KLL and KLX auger electrons of arsenic from the 75Se decay

The KLL and KLX spectra for Auger electrons of arsenic (Z = 33) emitted during ⁷⁵Se decay were recorded, with an instrumental resolution of 11 eV, using a combined electrostatic spectrometer. The relative energies and intensities of nine KLL and ten KLX transitions were determined by computer analysis of the spectra. The margins of error were estimated to be 1–4 eV for energies and 2–50% for intensities. Except for the KL₁L₂ (¹P₁) transition, the measured relative intensities of the KLL transitions were found to agree, within 3 standard deviations (σ), with those calculated relativistically using the intermediate coupling approximation with configuration interaction. The discrepancy for the KL₁L₂ (¹P₁) transition amounted to 6σ. The KL₃M_2,3/KL₂M_2,3 transition intensity ratio agreed with the prediction based upon the intermediate coupling scheme but deviated by 7 σ from the value predicted by the jj coupling approximation.     

The L1L2,3V Auger transition in Si

The L₁L_2,3V Auger transition in silicon has been analyzed. No substantial differences are observed in the comparison with the deconvolution of the L_2,3VV Auger spectrum. Comparison is also made with other valence band spectroscopies. It is concluded that L₁L_2,3V transition has a band character.     

Effect of surface plasmon oscillations on Auger electron emission

The integrated areas of the Al L₂₃VV and O KL₂₃L₂₃ Auger peaks and the Al surface plasmon energy ?ω_S are reported for the Al(001) surface as a function of exposure to O in the exposure range 0–114 L(1 L=1langmuir=10^?6Torr sec). It is shown that for exposures below a critical value of 15 L, ?ω_S is constant within experimental error while the O Auger peak area increases linearly. For exposures above 15 L, ?ω_S decreases linearly from 10.5 eV to 8.5 eV and the O Auger peak area undergoes relatively slow linear increases correspondingly. The Al Auger peak area decreases by 30% per 1 eV decrease of ?ω_S. The results are discussed with reference to theory relating Auger transition intensities to the spectral density function.     

Aspects of Angular Dependent Auger Spectroscopy (ADAS)

Calculational results are presented which pertain to recent observations that considerable structure exists in the angular distributions of 62 eV M_2,3VV Auger electrons emitted from copper surfaces. A direct interpretation of these results demonstrates that both electron diffraction and anisotropic Auger emission must contribute significantly to the observed angular distributions.     

Das KLL-Auger-Spektrum für 10≦Z≦36

The configuration interaction, applied very recently byAsaad to the calculations ofKLL-Auger spectra, could remove the large discrepancies which existed for lowZ between experimental and theoretical relative group intensities I(KL₁L_2,3)/I(KL₁L₁) and I(KL_2,3L_2,3)/I(KL₁L₁).Asaad's calculations, however, were based on binding energies E(L₁) and energies of the Coulomb and spin-orbit interaction, which were not very accurate. In the present calculations use has been made of more accurate binding energies E(L₁) and Coulomb and spin-orbit interaction energies. It is shown that the absolute error in the results of the new calculations is less than 10%. From this it follows that the remaining discrepancies between theoretical and experimental values of the group intensities for 10≦Z<25 may be solely attributed to the inadequacy of the calculated transition probabilities. This calls for calculations of transition amplitudes of the KLL-process with more accurate wave functions for Z<25, in particular for Z=10.     

Extra-atomic electronic cross-relaxation energies in KL2,3L2,3 Auger transitions in small sodium clusters from SCF-Xα-SW calculations

The self-consistent-field-Xα-scattered-wave method is used to calculate extra-atomic electronic cross-relaxation energies R_C^ea involved in KL_2,3L_2,3 Auger transitions in a series of small sodium clusters. R_C^ea is shown to increase with increasing dimension of the cluster. The R_C^ea value for Na₁₅ already closely approaches the metallic value. It is felt that the present calculational method will also be useful in determining relaxation energies in chemisorption systems.     

KLL Auger and x-ray photoelectron spectra of phosphine,some phosphorus halides and the other hydrides isoelectronic with argon

KL₂L₃(¹D₂) Auger and 1s photoelectron energies have been measured for molecular hydrides isoelectronic with Argon (HCl, H₂S, PH₃ and SiH₄). In addition a detailed comparison of Auger and photoelectron shifts in a series of phosphorus halides (vs phosphine) has been undertaken using additional P_2p binding energies. The potential model is better able to predict 1s binding energy shifts with either ground state or relaxation corrected models than the 2p shifts. These latter values seem also to be reduced by shielding effects. In general, fluorides are better predicted than chlorides. Auger shifts correlate linearly(but not in a 1:1 relationship) with 1s photoelectron shifts throughout the isoelectronic series and also in the case of the phosphorus fluorides and phosphine. The two potential models, however, provide poor prediction of Auger shifts.     

Internal photoemission and plasmon gain in solid and thin films of Al

Weak features in the electron spectrum of Al excited by bremsstrahlung radiation from a Cu anode have been studied using a recently developed multidetector. A feature at ～1410 eV which has been identified as the Al 2p internal photoelectron line was found to have an intensity 4.2 × 10^?3 times that of the Al KL_2,3L_2,3:¹D₂ Auger line, in agreement with a simple theoretical treatment. The identification of this feature is confirmed by the observation of an ～67% decrease in its intensity in spectra obtained from clean Al films in the thickness range 3.1–34.0 nm. The intensity of a plasmon gain peak at ～1404 eV is found to be independent of thickness for films of thickness greater than 7.5 nm.     

Many-body effects in l2mm auger electron spectra of Ge(CH3)4 excited by Mg Kα X-rays

The Ge:L₂MM Auger electron spectra excited by Mg Kα X-rays from Ge(CH₃)₄ free molecules have been compared with the corresponding spectra excited by Al Kα X-rays. The Al Kα excited spectra have characteristic features of the diagram Auger transitions, because the excitation energy is far above the L₂ ionization threshold. The energy of Mg Kα photons is 1.21 eV below the Ge:L₂ ionization threshold and thus the Mg Kα excited L₂MM Auger electron spectra indicate many-body effects, post collision interaction (PCI) effects and spectator Auger satellite structures. The L₂M_4,5M_4,5 type spectrum displays both these features but the L₂M_2,3M_4,5 type spectrum has only a spectator Auger satellite structure, because the (3p⁻¹3d⁻¹nl) final state interferes with the (3s) hole state.     

Energies and chemical shifts of the sulphur 1s level and the KL2L3(1D2) Auger line in H2S,SO2 and SF6

The sulphur 1s binding energies and KL₂L₃(¹D₂) Auger energies have been measured in gaseous H₂S, SO₂ and SF₆. The experimental data, including the chemical shifts, are compared with various theoretical ab initio results. Theoretical and experimental values agree within 1-2 eV for the chemical shift and the binding energy of the 1s level, provided in the latter case relaxation, relativistic and correlation corrections are applied. Likewise, Shirley's method²⁰, which uses empirical energies, predicts the Auger energies satisfactorily. The measured S 1s binding energies are 2478.5(1) eV, 2483.7(1) eV and 2490.1(1) eV, and KL₂L₃(¹D₂) Auger energies are 2098.7(1) eV, 2095.5(2) eV, 2092.6(1) eV for H₂S, SO₂ and SF₆, respectively. The chemical shift for the 1s electron is found to be greater than for the 2s or 2p electron and in better accord with the prediction of the potential model. Data suggest the molecular relaxation energy to be small compared with the atomic relaxation energy.     

The application of tailored modulation techniques to depth profiling with auger electron spectroscopy

Tailored modulation techniques (TMT) are applied to depth profiling to eliminate errors in signal strength measurements caused by Auger line shape changes. The application of TMT is illustrated by profiling through Al₂ O₃Al interfaces. When peak-to-peak heights in first derivative spectra $\text{n}$⁽¹⁾_m (E) are used for profiling, the measured Al KL_2,in3L_2,3 signal strength shows a large decrease near the interface. This artifact is reduced when peak heights in $\text{n}$_m (E) are used but can be eliminated only when Auger area values are used for profiling. The peak heights in $\text{n}$_m (E) and Auger area values can both be obtained in real time with TMT and plotted automatically with conventional multiplexing equipment. Some features of Auger spectra obtained using TMT are illustrated, and a comparison of depth profiles obtained using peak-to-peak heights in $\text{n}$¹_m (E), peak heights in $\text{n}$_m (E) and Auger area values demonstrates the usefulness of TMT in depth profiling.     

Low-field mobilities of rare-earth metals

The KLL Auger spectrum of Ni generated in the electron capture decay of radioactive ⁶⁴Cu in a solid state matrix was measured for the first time using a combined electrostatic electron spectrometer adjusted to a 7 eV instrumental resolution. Energies and relative intensities of the all nine basic spectrum components were determined and compared with data obtained from X-ray induced spectra of metallic Ni and with theoretical results as well. Absolute energy of 6562.5 ± 1.3 eV (related to the Fermi level) measured for the dominant KL₂L₃(¹D₂) than a value obtained from the X-ray induced spectra which is probably caused by the effects of chemical bonding and physico-chemical environment. Moreover, it is higher by 20.4 eV (16??) than a prediction of the semi-empirical calculations by Larkins which indicates an influence of the ??atomic structure effect?? on absolute energies of the Auger transitions following the electron capture decay and, possibly, some imperfections in the calculations. Good agreement of the measured and predicted KL₁L₂(³P₀/¹P₁) transition intensity ratios indicates perceptible influence of the relativistic effects on the KLL Auger spectrum even at Z = 28.