Why are the band-like states suppressed in the M3–M4,5M4,5 super Coster–Kronig electron spectrum of Cu metal compared to those in the L3–M4,5M4,5 Auger electron spectrum?

The relative spectral intensity of the band-like two M_4,5-hole state to the atomic-like localized one is much suppressed in the coincidence M₃–M_4,5M_4,5 super Coster–Kronig (sCK) electron spectrum of Cu metal compared to the one in the coincidence L₃–M_4,5M_4,5 Auger electron spectroscopy (AES) spectrum. The M₃-hole lifetime width of Cu metal is calculated by an ab initio atomic many-body theory (the extended relaxed core random phase approximation with exchange). The calculated M₃-hole lifetime width of Cu metal agrees well with the experimental one. The M₃–M_4,5M_4,5 sCK decay width of Cu metal decreases much with delocalization of the two M_4,5 holes in the sCK final state, whereas the Auger decay width is fairly independent of localization and delocalization of the two M_4,5 holes in the Auger final state. Thus, the relative spectral intensity of the band-like state is much suppressed in the coincidence M₃–M_4,5M_4,5 sCK-electron spectrum of Cu metal compared to the one in the coincidence L₃–M_4,5M_4,5 AES spectrum.     

Effect of relaxation and decay of a charge transfer shakeup satellite on Auger-electron spectroscopy spectra and Auger-photoelectron coincidence spectroscopy spectra of adsorbates

An electron excited to an unoccupied part of adsorbate–substrate hybrid states in a chemisorbed molecule by a resonant core electron excitation or charge transfer (CT) shakeup may delocalize on time scale of core-hole decay so that the excited core-hole state relaxes partly or completely to a fully relaxed one. The Auger decay of the fully relaxed core-hole state via the relaxation of the excited one introduces an additional feature in the resonant Auger-electron spectroscopy (RAES) spectrum and the AES spectrum. However, the additional feature in the RAES spectrum is a normal AES spectrum by decay of the fully relaxed core-hole state, whereas the one in the AES spectrum is the AES spectrum by decay of the fully relaxed core-hole state broadened by the photoelectron spectroscopy (PES) CT shakeup satellite weighted by the branching ratio of the relaxation width. The discrepancies between the AES spectrum measured at high above the ionization threshold and the additional feature in the RAES spectrum consist of the symmetric-like part by the decay of the fully relaxed core-hole state via the relaxation of the CT shakeup state and the asymmetric part by the direct decay of the shakeup states. The asymmetric part increases with a decrease in the hybridization strength. This explains the variation with the hybridization strength in the discrepancies between the RAES spectra and the AES spectra of chemisorbed molecules such as CO/Ni, CO/Cu and CO/Ag. A comparison of the singles PES spectrum with the one measured in coincidence with the AES main line of a selected kinetic energy (KE) provides the delocalization rate of the excited electron in the CT shakeup state as a function of photoelectron KE. The coincidence measurement to obtain the partial singles PES spectrum is discussed.     

Many-body effect in the M45–N23N45–N45N45N45 coincidence spectroscopy spectra of metallic elements around Cd

The quasi-particle approximation for the 4p4d state of the metallic elements around Cd breaks down because of very rapid 4p4d–4d³ super Coster–Kroning (sCK) decay of the 4p hole in the presence of the spectator 4d hole. Here the underbar is a hole. As a result, the 4p4d multiplet coupling breaks down. We can examine the presence or absence of the 4p4d multiplet by Auger-electron sCK-electron coincidence spectroscopy measurement of the 3d–4p4d–4d³ Auger-preceded sCK transitions. We collect the sCK-electrons in coincidence with the Auger-electrons of a selected kinetic energy (KE) and vice versa. If the multiplet coupling breaks down and does not exist, the coincidence sCK-electron (or Auger-electron) lines shift as much as the Auger-electron (or sCK-electron) analyzer's selected KE is varied. We can determine not only the three 4d-hole sCK final-state energy but also the presence or absence of the 4p4d multiplet by Auger-electron sCK-electron coincidence spectroscopy. The unique capability of the coincidence measurement by which one can determine the correlation between an Auger-electron and a sCK electron generated, respectively, by creation and annihilation of the same Auger two-hole final state is very useful, even when the quasi-particle approximation of the two-hole state breaks down.     

Effect of the competition between relaxation and core hole decay on the Auger-photoelectron coincidence spectroscopy (APECS) spectrum of Ni metal

The valence hole created in Ni metal either by the L2-L3V Coster–Kronig (CK) transition or by the L3V shakeup/off becomes screened out prior to the L3-hole decay. We denote the atomic shell Lx (x = 2, 3) by LX. The metastable two-hole L3V state relaxes to the fully relaxed single L3-hole state before the L3-hole decays. Thus, the coincidence L2-L3(V)-VV(V) Auger-electron spectrum resembles closely the coincidence L3-VV Auger-electron spectrum. The final state of the CK transition preceded Auger transition is a two-hole state rather than a three-hole state. The four-hole satellite about 8 eV below the L3-VV main line in the singles (non-coincidence) Auger-electron spectrum is partly due to the L3VV-VVVV transition and the L2-L3VV-VVVV transition. The valence holes created either by the L2-L3VV transition or by the L3VV double shakeup/off remain localized during the L3-hole decay. The L3-hole lifetime widths of Fe, Co and Ni metals are determined from the APECS spectra. The agreement between experiment and theory (the independent-particle approximation) is poor.     

Many-body effect in the coincidence L3 and M3 photoelectron spectroscopy spectra of Cu metal

The coincidence L₃ and M₃ photoelectron spectroscopy (PES) main lines of Cu metal are calculated by a many-body theory. There is no peak-energy shift between the singles PES main line and the coincidence one. The asymmetric narrowing of the coincidence PES main line on the low kinetic energy (KE) side is very small. This is in accord with recent experimental findings. In Cu metal, the shakeup satellite intensity is small and the main-line satellite separation energy is much larger than the core–hole lifetime width. The interference via the final-state interaction is negligible. In the PES main line, the imaginary part of the self-energy by shakeup excitations, which is very small compared to the core–hole lifetime width, decreases very slowly in linear with photoelectron KE. The branching ratio of Auger decay of a single hole state then increases very slowly in linear with photoelectron KE so that the deviation of the coincidence PES main line from the singles one is very small. The 939 eV structure seen only in the coincidence L₃ PES spectrum of Cu metal is attributed to the enhancement of the inelastic peak of a smaller energy loss due to electrons of a smaller average emission depth measured in coincidence with the elastic Auger peak. The structure will not be enhanced in the singles PES spectrum. The background subtraction in the coincidence spectrum cannot be the same as that in the singles one. Such consideration is necessary before we can conclude about the asymmetric narrowing on the low KE side. A unique capability of APECS by which one can determine the photoelectron KE dependent part of the imaginary part of the self-energy is pointed out.     

Many-electron effect in the angle resolved L3-M23M23 Auger-photoelectron coincidence spectroscopy (APECS) spectrum of metallic Zn

The many-body effect in the L₃-M₂₃M₂₃ Auger-electron spectroscopy (AES) spectrum of metallic Zn is discussed. The lifetime width and residual relaxation energy shift of the two M₂₃-hole state are governed by the (super) Coster-Kronig (sCK) transitions of two M₂₃-hole state. The residual relaxation energy shift and decay width of the two M₂₃-hole state are calculated in an average configuration by an ab initio atomic many-body theory. The agreement with experiment is good. To elucidate the many-body effect in the two-hole states, it is necessary to be able to discriminate individual components of the multiplet-split AES spectrum. We discuss how to discriminate individual components of the multiplet-split L₃-M₂₃M₂₃ AES spectrum of metallic Zn by angle-resolved Auger-photoelectron coincidence spectroscopy (AR-APECS) in order to determine accurately their line shapes, multiplet splitting energies, and spin states (singlet etc.).     

The origin of narrowing of the Si 2p coincidence photoelectron spectroscopy main line of Si(1 0 0) surface

The Si 2p photoelectron spectroscopy (PES) main line of Si(1 0 0) surface measured in coincidence with the singles (noncoincidence) Si L_2,3-VV Auger-electron spectroscopy (AES) elastic peak is calculated. The agreement with the experiment is good. The present work is the first many-body calculation of the experimental coincidence PES spectrum of solid surface. The narrowing of the coincidence Si 2p PES main line compared to the singles one is due to the mechanism inherent in the coincidence PES. The inherent mechanism is explained by a many-body theory by which photoemission and Auger-electron emission are treated on the same footing.     

Analysis of the Auger-photoelectron coincidence spectroscopy (APECS) spectra of metallic Pd,Ag, and Sn

The M45-level photoelectron spectrum of Ag metal measured in coincidence with the M45–VV(¹G) Auger-electron line is analyzed by taking into account the possibility of the M4–M5–VV Coster–Kronig (CK)-transition preceded Auger transition. We denote the atomic shells Mx(Mxy) and Nxy (x, y = 4,5) by MX(MXY) and V, respectively. The M4–M5 CK-transition rate is very small. The M45–VV Auger-electron spectra of metallic Pd and Sn measured in coincidence with the M4 (or M5)-level photoelectron line are analyzed. The M4–M5 CK-transition rates are also very small in metallic Pd and Sn. The coincidence Auger-electron line previously interpreted as the M4–M5–VV (or M4–M5V–VVV) Auger-electron line is largely due to the inelastically scattered M5-level photoelectron background beneath the M4-level photoelectron line. The APECS spectrum of Pd metal shows the first evidence of the M5V–VVV transition of the localized M5V shakeup two-hole state. The intensity ratio of the inelastically scattered Auger-electron background to the M5–VV Auger-electron main line of Ag metal measured in coincidence with the inelastically scattered M5-level photoelectron background beneath the M4-level photoemission line increases, as compared to that measured in coincidence with the M5-level photoelectron main line. This is because when the probability of the photoelectron being inelastically scattered increases, that of the Auger electron emitted by the same ionized atom, being inelastically scattered increases. In other words the photoelectrons and the Auger electrons are originated from the deeper atomic sites (longer pathlength).     

Charge-transfer hole-lifetime broadening of the Cu Auger-electron spectra of high Tc superconductors

The satellite intensity in the Cu L₂₃-VV Auger-electron spectrum of the high T_c superconductor (YBa₂Cu₃O_7−x, 123) is much more enhanced as compared to that of CuO. This enhancement was previously interpreted by Ramaker et al. [D.E. Ramaker, N.H., Turner, F.L. Hutson, Phys. Rev. B 38 (1988) 11368] as a result of the mixing between the ddp and dpp states. Here, d is a hole in the Cu 3d band and p is a hole in the O 2p band. However, the dramatic Auger electron spectroscopy (AES) spectral lineshape change from CuO to 123 is not only in the charge-transfer (CT) satellite but also in the main-line width. The change arises from the transit of the “pairing” of two bound d holes in the ddp state to that of two bound p holes in the dpp state. As a result, in CuO there is no CT satellite but the dd state becomes a resonant state broadened by the CT hole-lifetime broadening, whereas in 123 the dd state becomes a mixture of a resonant-like state and nonresonant band states. The present many-body theory can explain the overall AES lineshape change from CuO to 123.     

KLL Auger resonant Raman transition in metallic Cu and Ni

High energy resolution KL₂₃L₂₃ Auger spectra of polycrystalline Cu and Ni were measured using photon energies up to about 50 eV above the K-absorption edge and down to 5 eV (Cu KLL) and 4 eV (Ni KLL) below threshold. The spectra show strong satellite structures varying considerably as a function of the photon energy. In the sub-threshold region the linear dispersion of the diagram line energy positions and a distortion of the line shape as a function of photon energy, attributable to the Auger resonant Raman process, is clearly observed, indicating the one-step nature of the Auger emission. These changes in the resonant spectra are interpreted using a simple model based on resonant scattering theory in combination with partial density of states obtained from cluster molecular orbital (DV-Xα) calculations.     

EELS characterization of TiN grown by the DC sputtering technique

Titanium nitride thin films were deposited on monocrystalline silicon (mc-Si) substrates by direct current reactive magnetron sputtering. Auger electron spectra (AES) of deposited films at different nitrogen partial pressures, show the typical N KL₂₃L₂₃ and Ti L₃M₂₃M₂₃ Auger transition overlapping. Also, changes in the Ti L₃M₂₃M₄₅ Auger transition peak are observed. X-ray diffraction and high resolution electron microscopy (HRTEM) of a golden color TiN/mc-Si sample, reveal a preferential polycrystalline columnar growth in the 〈111〉 orientation. This sample was also analyzed by electron energy-loss spectroscopy (EELS). The N/Ti elemental ratio is slightly different to the value determined by AES. Atomic distribution around the N atoms is in agreement with that expected from the N atom in the fcc unit cell of TiN. This distribution was obtained via an extended energy-loss fine structure (EXELFS) analysis from EELS spectra.     

Comparison of the CKLL first-derivative auger spectra from XPS and AES using diamond,graphite, SiC and diamond-like-carbon films

The carbon KLL first-derivative Auger spectra obtained by numerically differentiating the XPS N(E) line gives a better fine-structure fingerprint of the carbon state than conventional AES. The first-derivative of the X-ray excited (XAES) CKLL spectrum from a diamond-like-carbon (DLC) film exhibited almost the same spectrum as both the XAES and AES spectra from natural diamond. However, the AES spectrum of the DLC film indicated a graphite-like structure due to electron beam damage. Comparison of the XAES and AES spectra suggested that the electron beam used in conventional AES partially changed the plasmon loss structure of carbon in diamond, graphite and β-SiC as well.     

Chemical effects on Al and Cu Auger electron spectra for the intermetallic compound CuAl2

This paper describes an experimental study of the intermetallic compound CuAl₂ using Auger electron spectroscopy (AES). Chemical effects in the CuAl₂ spectrum are observed corresponding to energy shifts of the Cu and Al peaks and the appearance of a new peak for the compound. These results are found to be in good agreement with those obtained using the technique of soft X-ray emission spectroscopy (SXES). The origin of the new peak appears to be a transition from a hybridised s-d band localized at the Cu site in the compound to an Al core state. This gives a band-like contribution to the CuAl₂ AES spectrum.     

Laser spectroscopy of the B[21.68]8-X8, B′[21.65]8-X8 and C[22.3]7-X27 transitions of holmium monofluoride

The spectrum of holmium monofluoride (HoF) in the blue (420-480 nm) region has been studied using laser-induced fluorescence. Previous work [J. Phys. B 7 (1974) L234] had assigned several bands in this region to the B8-X8 transition. By obtaining wavelength selected laser excitation spectra at high resolution and rotationally analyzing seven bands in this region, we have shown that not all the bands previously assigned to the B8-X8 system belong to the same electronic transition and have identified three separate transitions which we have labelled B8-X8, B′8-X8, and C7-X₂7. Preliminary low resolution dispersed fluorescence spectra have shown several excited states at energies greater than 4000 cm⁻¹ above the ground state and, though not all could be assigned, ligand field theory calculations are consistent with assigning them to the first excited spin-orbit component of the Ho⁺(4f¹⁰6s²)F⁻ ground state configuration or to the first excited configuration, Ho⁺(4f¹¹6s)F⁻. The results of the dispersed fluorescence experiments also tentatively place the X₂7 state at ∼70 cm⁻¹ above the ground X7 state.     

Nitrogen implanted in iron: AES and Pes study

AES and PES studies of nitrogen in iron implanted with molecular nitrogen ions having an energy of 120 keV and doses on the order of 10¹⁷ N-atoms/cm² were performed. Measuring nitrogen concentration depth profiles, a remarkable accumulation of nitrogen near surface was found besides the ordinary concentration maximum at the depth of mean projected range R_p of nitrogen ions. In addition to strong nitride bonding state a weakly bonded nitrogen was also observed. It manifested itself by time-dependent changes in spectra and by a distinct value of N 1s binding energy. The reasons for the concept of weakly bonded nitrogen, probably of molecular form, are discussed.     

Development of a miniature double-pass cylindrical mirror electron energy analyzer (DPCMA), and its application to Auger photoelectron coincidence spectroscopy (APECS)

We have developed a miniature double-pass cylindrical mirror electron energy analyzer (DPCMA) with an outer diameter of 26 mm. The DPCMA consists of a shield for the electric field, inner and outer cylinders, two pinholes with a diameter of 2.0 mm, and an electron multiplier. By assembling the DPCMA in a coaxially symmetric mirror electron energy analyzer (ASMA) coaxially and confocally we developed an analyzer for Auger photoelectron coincidence spectroscopy (APECS). The performance was estimated by measuring the Si-LVV-Auger Si-1s-photoelectron coincidence spectra of clean Si(1 1 1). The electron-energy resolution of the DPCMA was estimated to be E/ΔE = 20. This value is better than that of the miniature single-pass CMA (E/ΔE = 12) that was used in the previous APECS analyzer.     

Cs adsorption on a polar NbC(111) surface: photoemission and auger electron spectroscopy studies

The Cs adsorption process on a NbC(111) surface has been studied with core-level photoemission spectroscopy (PES) and Auger electron spectroscopy (AES). Coverage-dependent Cs 4d core-level PES shows that the polarization-depolarization transition of the Cs overlayer occurs in the coverage region of 0.5 ≤ θ ≤ 0.8 ML where the work function shows a minimum value. The charge transfer in the initial stage of adsorption is investigated using valence-related AES, and it is found that the transfer of the Cs 6s charge to the substrate occurs in the polarized phase.     

Some anomalies in the Ne(I)(744/736 Å) photoelectron spectra of N2O

The Ne(I) 774/736 Å photoelectron spectra of N₂O are reported for the X?²Π state of N₂O⁺. The spectra in general do not show any autoionization behavior to the extent reported for CO₂ and CS₂. There is an apparent “enhancement” of the 101 level by the 744 Å line. In contrast to the He(I) 584 Å PES, the intensity ratio for the 100 and 001 levels are reversed when excited by Ne(I) 736 Å radiation.The spectra also show excitation to higher vibrational levels of N₂O⁺X²Π. This can be explained within the framework of autoionization of a Rydberg state whose core is similar to that of the B? state of N₂O⁺.     

The Ag M5N45N45 Auger photoelectron coincidence spectra of disordered Ag0.5Pd0.5 alloy

An effect of disorder broadening (DB) on the Ag M₅N₄₅N₄₅ Auger spectra in the random substituted Ag_0.5Pd_0.5 has been investigated by Auger photoelectron coincidence spectroscopy (APECS). Data were collected for the Ag M₅N₄₅N₄₅ Auger line coincident with the Ag 3d_5/2 photoelectron line (and its higher and lower binding energy sides). It is shown that the broadening of the Ag M₅N₄₅N₄₅ line is directly associated with the presence of disorder broadening of the Ag 3d_5/2 photoelectron line. The APECS experiment is used to demonstrate the broadening in a novel way.     

Investigating the structure of the Tin M45N45N45 auger spectrum using auger photoelectron coincidence spectroscopy

Auger photoelectron coincidence spectroscopy (APECS) data were collected for the M₄₅N₄₅N₄₅ Auger peak in coincidence with the 3p_3/2, 3d_3/2 and 3d_5/2 photoelectron lines of Tin. Model spectra were created to fit the APECS data from sets of Gaussian curves defined by Parry-Jones et al., J. Phys. C: Solid State Physics, 12 (1979) 1587. These models were then combined using information about the relative intensities of the peaks from the aforementioned paper to produce a model of the Auger peak which proved a good comparison to high resolution AES spectra. The APECS data revealed satelite structure in the M₅N₄₅N₄₅ peak in coincidence with the 3d_5/2 photoelectron line (M₅N₄₅N₄₅:3d_5/2) due to the Mg Kα₃ line of the X-ray source. There was evidence of a small Coster–Kronig component in the M₄N₄₅N₄₅:3d_3/2 data and the M₄₅N₄₅N₄₅:3p_3/2 data showed intensity in the M₄N₄₅N₄₅ and M₅N₄₅N₄₅ regions also arising from Coster–Kronig processes. The contribution of the M₄N₄₅N₄₅ plasmon was included in each of the APECS models and was reflected in the high resolution AES spectra. Slight oxidation of the surface of the sample during each 24-h period produced a 0.7 eV shift of the singles Auger peak to lower kinetic energies. The shift was not reflected in the coincidence peak which produced a spectrum of a clean surface due to the nature of the coincidence experiment.