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.     

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).     

The participant Coster–Kronig preceded Auger transition in the resonant L2,3-M2,3V Auger electron spectrum of Ti metal

The L_2,3-M_2,3V resonant Auger electron spectroscopy (RAES) spectrum of Ti metal measured by Le Fêvre et al. [P. Le Fêvre, J. Danger, H. Magnan, D. Chandesris, J. Jupille, S. Bourgeois, M.-A. Arrio, R. Gotter, A. Verdini, A. Morgante, Phys. Rev. B69 (2004) 155421] is analyzed in the light of relaxation and decay of the resonantly excited L_2,3-hole states. The relaxation time of the resonantly excited L_2,3-hole state to the fully relaxed (screened) one is much shorter than the L_2,3-hole Auger decay time, whereas the participant Coster–Kronig (CK) decay time of the resonantly excited L₂-hole state to the fully relaxed L₃-hole state at the L₂ resonance is as short as the relaxation time of the resonantly excited L₂-hole state to the fully relaxed one. The excited electron is predominantly either rapidly decoupled from the L_2,3-hole decay or annihilated by the participant CK decay. Thus, near the L_2,3 edges the L_2,3-M_2,3V RAES spectral peak appears at constant kinetic energy. The L_2,3-M_2,3V RAES spectrum shows a normal L_2,3-M_2,3V Auger decay profile not modulated by the density of empty d states probed by the resonant excitation. Not only the relaxation time but also the participant CK decay time depends on photon energy because they depend on the density of empty d states probed by the resonant excitation. As a result, the L_2,3 X-ray absorption spectroscopy spectral line broadening depends on photon energy.     

Energy and angular distributions of electrons emitted by direct double auger decay

We have observed the direct L(2,3)MMM double Auger transition after photoionization of the 2p shell of argon by angle-resolved electron-electron coincidence spectroscopy. The process is responsible for about 20% of the observed Auger electron intensity. In contrast to the normal Auger lines, the spectra in double Auger decay show a continuous intensity distribution. The energy and angular distributions of the emitted electrons allow one to obtain information on the electron correlations giving rise to the double Auger process as well as the symmetry of the associated two-electron continuum state.     

On the Auger-photoelectron coincidence spectroscopy spectra of Cu(100), Cu metal and CuOx/Cu surface

The M₃–VV Auger-photoelectron coincidence spectroscopy (APECS) spectrum of Cu(100) and the L₃–VV APECS spectra of Cu metal and CuOx/Cu surface are analyzed in detail. The narrowing and energy shift of the photoelectron line in the M₃–VV APECS spectrum is well predicted by the present theory. The spectrum shows the presence of the M₂–M₃(V)–VV(V) decay in which a hole in the 4s band hops away prior to the decay of M₃ hole. The analysis of the L₃ photoelectron spectra of Cu metal measured in coincidence with the ³F or ¹G Auger line raises a question concerning the presence of two different core–hole states upon the L₃ level ionization recently proposed by Thurgate and Jiang [Surf. Sci. 466 (2000) L807]. The analysis of the L₃–VV APECS spectrum of CuOx/Cu shows that the final-state charge–transfer interaction plays an important role in CuO.     

Nuclear dissociation after the O 1s $\rightarrow (^4\Sigma_\text{u}^-)$3sσ excitation in O$_2$ molecules

We investigate the dissociation dynamics of core-excited $\mathrm{O}_2$ molecules using a high-resolution energy-resolved electron-ion coincidence experimental setup. The excited cationic states with two valence holes and one Rydberg electron are created after spectator Auger decay induced by $\mathrm{O}$ 1s $\rightarrow (^4\Sigma_{\rm u}^-)3{\rm s}\sigma$ core excitation in $\mathrm{O}_2$. From the energy correlation between the kinetic energy of the Auger electron and the ion kinetic energy release, we distinguish several dissociation channels. Rather complex dissociation channels of the spectator Auger final states are disclosed, which can be explained by the increased number of the crossing point due to the existence of Rydberg electron. The quantum system will evolve into different dissociation limits at each crossing point between the potential energy curves.     

Desorption of H ions from water chemisorbed on Si(100) by O 1s excitation - an Auger electron-photoion coincidence spectroscopy study

Auger electron-photoion coincidence (AEPICO) spectroscopy, which has been recently developed and proved to be a very powerful technique for investigating the dynamics of desorption induced by the core-level excitation, is applied to the investigation of Auger-stimulated ion desorption from the chemisorbed-water-Si(100) surface induced by O 1s excitation. It is shown that the fast relaxation of the excited state with a core hole and an excited electron takes place before the core hole decay, and that the desorption yield is enhanced by the shake-up (and/or shake-off) excitation. The relative cross-section for Auger-stimulated ion desorption is estimated, and is shown to increase as holes are created at deeper levels of the valence bands as the final state of the Auger decay. A comparison is also made with condensed H₂O.     

On the satellite in the Auger electron spectrum

The satellite line profile in the C–VV Auger electron spectroscopy spectrum depends upon how the initial core hole state and the final multiple hole state are created. Even if the numbers of the holes in the satellite states are the same, the Auger electron spectroscopy spectral profiles of the final multiple hole states are different. The localization of the three hole satellite state is discussed.     

Experimental evidence of interatomic coulombic decay from the auger final states in argon dimers

Interatomic Coulombic decay (ICD) from an Auger-final dicationic state is observed in the Ar dimer. A 2p inner-shell vacancy created by photoionization is replaced with 3s and 3p vacancies via intra-atomic Auger decay. The Auger-final dicationic state is subject to ICD in which one of the 3p electrons in the same Ar atom fills the 3s vacancy while one of the 3p electrons from the neighboring Ar atom is emitted as an ICD electron. This ICD process is unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ICD electron and the kinetic energy release between Ar+ and Ar2+ are measured in coincidence.     

Direct evidence for dynamic broadening of the energy spectra associated with the later steps of an Auger cascade

Auger cascade decay processes are of critical importance in x-ray-induced biological damage, chemical reactions, and desorption. Here, we report the first measurements of the isolated energy spectra of electrons emitted during the later steps of an Auger cascade process in a solid (MnO). The large widths and energy gains observed in cascade-induced Mn MVV Auger spectra (as compared to the spectra resulting from direct photoexcitation of the M core hole) provide strong evidence that valence holes created in previous cascade steps participate dynamically in later cascade steps.     

Many-electron effect in the Fe L3-M4,5M4,5 Auger electron spectrum of ultrathin Fe films grown on Cu(1 0 0)

D’Addato et al. [S. D’Addato, P. Luches, R. Gotter, L. Floreano, D. Cvetko, A. Morgante, A. Newton, D. Martin, P. Unsworth, P. Weightman, Surf. Rev. Lett. 9 (2002) 709] studied the variation with Fe coverages in the relative Fe L₃-M_4,5M_4,5 Auger electron spectroscopy (AES) spectral satellite intensity of ultrathin Fe films grown on Cu(1 0 0) by sweeping photon excitation energy through the Fe L₂-level ionization threshold. They interpreted that the M_4,5 hole in the L₃M_4,5 double-hole state created by the L₂-L₃M_4,5 Coster–Kronig (CK) decay remains localized for longer than the L₃-hole lifetime for the 0.3 and 10 ML coverages but has a lifetime comparable to the L₃-hole lifetime for the 1 ML coverages. The present many-body theory shows that when the M_4,5 hole created either by the CK decay or by the L₃M_4,5 shakeoff hops away from the ionized atomic site and becomes completely screened out prior to the L₃-hole decay, the Fe L₂-L₃M_4,5-L₃-M_4,5M_4,5 AES main line as well as the Fe L₃ M_4,5 (satellite)-L₃-M_4,5M_4,5 one, both of which are identical in line shape to the Fe L₃-M_4,5M_4,5 one, dominate in the Fe CK preceded AES spectrum. The present analysis shows that the delocalization time of the M_4,5 hole created in the 1 ML Fe/Cu(1 0 0) system by the L₂-L₃M_4,5 CK decay is much shorter than the L₃-hole lifetime so that the Fe L₃-M_4,5M_4,5 AES spectral line shape hardly changes, except for the presence of a very weak spectator L₂-L₃M_4,5-M_4,5M_4,5M_4,5 AES satellite, when the photon excitation energy is swept through the Fe L₂-level ionization threshold. For the 0.3 ML coverages the M_4,5-hole delocalization time is still shorter than the L₃-hole lifetime.     

Cs Ⅳ离子4d内壳层激发态衰变过程的相对论理论研究

在相对论多组态Dirac-Fock理论方法基础上,通过系统考 虑电子关联效应和由于内壳层电子激发而导致的电子自旋-轨道波函数的弛豫效应,详细研究了Cs Ⅳ离子的4d内壳层电子激发组态4d95s25p5、辐射末态4d105s25p4及Auger末态4d105s25p3和4d105s15p4的能级结构及各种可能的辐射和Auger衰变过程.获得了与已有的实验结果和相关的半经 验准相对论组态相互作用计算结果相符的辐射跃迁能、振子强度以及线宽,预言了4d95s25p5态的以Auger衰变为主的 Auger电子谱的特 关键词： 内壳层激发态 辐射衰变 Auger衰变     

Intramolecular electron scattering and electron transfer following autoionization in dissociating molecules

Resonant Auger decay of core-excited molecules during ultrafast dissociation leads to a Doppler shift of the emitted electrons depending on the direction of the electron emission relative to the dissociation axis. We have investigated this process by angle-resolved electron-fragment ion coincidence spectroscopy. Electron energy spectra for selected emission angles for the electron relative to the molecular axis reveal the occurrence of intermolecular electron scattering and electron transfer following the primary emission. These processes amount to approximately 25% of the resonant atomic Auger intensity emitted in the studied transition.     

Dynamics and post-collision interaction effects in two electron decay from the Xenon 4d hole

Two Auger electrons, one very slow, one fast, have been detected in coincidence following near threshold 4d photoionization of the Xe atom. The distribution in the energy the two electrons share has been measured for the first time revealing the presence of post-collision interaction effects that provide unique information on the decay dynamics of the 4d hole. Analysis of the distorted line shapes indicates that the dominant process is decay of Xe+(4d(-1)) to Xe3+ through cascade emission of a zero kinetic energy Auger electron followed by a fast Auger electron. The widths of the intermediate Xe2+* states are estimated to be about 60 meV.     

Observation of selection rules and restricted valence band self convolution for the KVV Auger transition of alkali graphite intercalation compounds

The Auger spectrum of the KVV transition in alkali graphite intercalation compounds (AGIC's) gives unambiguous evidence that the electron states from the alkali metals in the valence band of the compound form a narrow structure in the KVV Auger spectrum which corresponds to the self convolution of these states and that they are not convoluted with the whole valence band. This observation shows that strong matrix element effects or selection rules for KVV Auger transitions have to be taken into account.     

Double core hole creation and subsequent Auger decay in NH3 and CH4 molecules

Energies of the hollow molecules CH(4)(2+) and NH(3)(2+) with double vacancies in the 1s shells have been measured using an efficient coincidence technique combined with synchrotron radiation. The energies of these states have been determined accurately by high level electronic structure calculations and can be well understood on the basis of a simple theoretical model. Their major decay pathway, successive Auger emissions, leads first to a new form of triply charged ion with a core hole and two valence vacancies; experimental evidence for such a state is presented with its theoretical interpretation. Preedge 2-hole-1-particle (2h-1p) states at energies below the double core-hole states are located in the same experiments and their decay pathways are also identified.     

Direct emission and Auger decay from multiplet final states in Zr observed by ultraviolet photoemission CFS techniques

Photoemission techniques have been used to investigate the structures accompanying excitation of shallow p-core states in crystalline Zr. The continuum nature of synchrotron radiation has been exploited between hv = 20 and 45 eV to determine the Constant Final-state-energy Spectra (CFS) over a range of kinetic energies of the emitted electrons. The results reveal strong direct emission from the multiplet final states and indicate that the final states are broadened by configuration interaction. Auger processes appear to be a probable mode of decay of the p-hole. Secondaries resulting from the Auger processes give rise to structures in the CFS's which compare well to structures in the optical absorption coefficient.     

N23-core losses and autoionization emissions of clean and oxygen exposed zirconium

The electron energy loss spectra associated with N₂₃-excitation and the low energy N₂₃VV Auger emission have been studied for both the clean and oxygen exposed zirconium. In the high energy side of the N₂₃VV Auger spectrum, autoionization emission of electrons of the valence band due to the decay of 4p electrons excited to states ≈9eV above the Fermi level has been identified. The excitation process can be also observed in the electron energy loss spectra. This is the first time that an autoionization feature is observed in a electron excited Auger spectrum of a 4d transition metal.     

Tracking the excitation dynamics in the Mn:Ge(111) metallic interface by resonant electron spectroscopy

Resonant photoemission from the valence band of a (√3 × √3)R30° reconstructed Mn:Ge(111) metallic interface has been carefully analyzed with the aim to track the transition from resonant Raman to normal Auger emission. The transition energy has been compared with the Mn 2p binding energy, as well as with the Mn L(3) absorption edge energy. Close similarities emerge with respect to the case of elemental Mn thin films, suggesting that the excitation dynamics is dominated by the electronic properties of Mn 3d states, in spite of the bonding with Ge atoms. The switching from the resonant Raman Auger (RRAS) to the normal Auger regime is found about 2 eV below the Mn L(3) absorption edge. A change of the lineshape due to the transition from an overall N - 1 electron final state (RRAS channel) to an N - 2 electron final state (normal Auger channel) is evidenced by the analysis of the experimental data, which also allowed the ratio to be tracked between charge delocalization and core-hole time scales as the photon energy is tuned across the Mn L(3) edge.     

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.