Theory of spin-polarized Auger electron spectra in ferromagnetic materials with particular attention to L23M23M23 Auger spectrum in Fe83B17

Spin polarization of L₂₃M₂₃M₂₃ Auger electrons from ferromagnetic Fe₈₃B₁₇ is calculated with a simplified model, and compared with recent experiments. The Auger electron spectrum has two peaks, corresponding to the singlet and triplet final states of a 3p hole pair. It is shown that the spin polarizations of the singlet and triplet peaks, respectively, originate from the exchange interaction between 3d and 2p spins and that between 3d and 3p spins. Similar effects are expected to be observed commonly for L₂₃M₂₃M₂₃ Auger electrons from various ferromagnetic materials including transition elements.     

Properties of pp annihilations into strange particles at 702 and 757 MeV/c

$\text{p}\text{p}$ annihilations, leading to the production of at least one neutral K meson in the final state, have been studied in the incident momentum region of 700–760 MeV/c. Topological cross sections and cross sections for the various exclusive final states are presented. Detailed analyses of the different final states have been carried out to study the importance of resonance production and of quasi two-body and quasi three-body processes. A detailed study of the $\text{K}\text{K}\text{π}$ system in the four-body final states shows that the F₁ meson is a spurious effect due to systematic biases. In the momentum range investigated, the C = +1 final states are strongly suppressed.     

Electron-induced KLL Auger electron spectroscopy of Fe,Cu and Ge

KLL Auger spectra excited by electrons with energies in the 30–35 keV range of Fe, Cu and Ge films were measured, using thin free-standing films. It was possible to obtain spectra with an energy resolution of about 1 eV. The observed spectra can not be described satisfactorily by just the multiplet splitting of the final state as calculated for an isolated atom. Additional features, due in part to intrinsic (shake satellites) and in part to extrinsic (energy loss of the escaping electron) processes formed a large fraction on the observed intensities. In particular a number of distinct satellite structures that are not predicted by the atomic Auger process are observed. For Fe and Cu the satellite peaks can be explained in terms of shake-up processes from the 3d_5/2–4d_5/2 states. Similar satellite structures observed in Ge are partly attributed to plasmon creation and partly to shake-up processes. It is demonstrated that both the thickness dependence of the observed intensity distributions and transmission electron energy loss measurements contain invaluable information for the interpretation of these spectra.     

Study of chemical states at intergranular fracture planes of iron-phosphorus alloys by auger and electron energy-loss spectroscopies

Auger and electron energy-loss spectroscopies (ELS) have been used to study chemical states at the fracture surfaces of iron-phosphorus alloys. The transgranular (TG) and intergranular (IG) fracture planes have similar Auger P LVV transition energies and similar Fe 3p loss energies. These indicate that phosphorus and iron atoms are dispersed atomically in layers segregated at IG planes. The energy separations between the inter-and intra-atomic Auger transition peaks in P LVV show that the TG and IG planes and Fe₃P have similar energy separations between the P 3p and Fe 3p levels. The layers segregated at IG planes are estimated to be equivalent to a monolayer, as indicated by the dependence of the loss energy of the valence-conduction-band transition on primary-electron kinetic energy from 200 to 500 eV. The phosphorus concentration in the segregated layers is saturated to ~ 20 at.% above a bulk phosphorus concentration of 2 at.%.     

Details of the extended low energy structure in the oxygen K emission spectrum from MgO and CaO

A complicated low energy structure in the O K X-ray emission of MgO and CaO is reported. The onset of this structure falls at about 15 eV and some structure is discernible still at about 80 eV below the Kα line. The main features of this structure are interpreted as KLL radiative Auger transitions. Transitions from initial MO states, consisting mainly of metal p and ligand s wave functions, to the final O 1s state are proposed in CaO.     

C Ⅱ离子1s内壳层激发态的结构和衰变特性的理论研究

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、弛豫效应以及相对论高阶修正,详细研究了C Ⅱ离子1s-2p光激发形成的内壳层电子激发态（1s2s²2p²和1s2s2p³）、辐射和Auger末态的能级结构以及各种可能的衰变过程.计算了C Ⅱ离子1s内壳层光激发能量、辐射和Auger衰变率及其线宽,进一步由不确定关系推出了这些激发态的能级寿命,并与最新的实验结果和已有的理论结果进行了比较. 关键词： 内壳层激发态 线宽 寿命 多组态Dirac-Fock方法     

Structure electronique des oxydes de cobalt CoO et Co3O4

The total density of occupied states in the valence band of CoO and Co₃O₄ is determined by XPS and UPS. From variations of excitation probability of the bands, the 4 e V wide O2_p band is shown to be located around 5 eV for both oxides, while structures obtained from photoionisation of the localized 3d band spread over 10 eV range below the Fermi level overlapping with O2_p band. The 3d peaks located at binding energy <3 eV correspond to the calculated energy of the d_n ?1 manifold final state in the octahedral and tetrahedral crystal field of CoO and Co₃O₄. The 3d levels at higher binding energy are shown to occur from configuration interaction in both final and initial states. These last peaks are higher in intensity for CoO relative to Co₃O₄. A superior limit for the width of the 3d initial band in a one electron energy diagram is given to be <3 eV. This value associated to the Coulomb correlation energy measured equal to ~3 eV. This value associated to the Coulomb correlation energy measured equal to ~3 eV from shake-up and Auger energy confirms the Mott insulator nature of CoO.     

A resonant photoemission model for nickel metal

We present a model for the resonance near the 3p threshold in the photoemission associated with a static 3d pair-hole bound state in paramagnetic nickel. We show that, following Auger processes, the strong intra-atomic screening of the pair hole by the 4s?4p conduction band electrons is essential to explain experimental photoemission data not only in copper but also in nickel. From the energy relaxation of the conduction band states we estimate the bare Coulomb interaction between two d-holes in nickel.     

Interatomic Auger processes and the density of states

The correlation between the line shape of Auger peaks and the density of states near the surface has been the subject of recent controversy. In certain cases, it has been possible to obtain the density of states by numerical deconvolution of a KVV peak (Amelio, 1970) or directly using a KLV peak (Cardona et al., 1973). However, the extension of this technique to transition metals (Cu, Zn) has encountered serious difficulties, related to the perturbation created by the presence of localized charges either in the initial or in the final state, although it is not yet clear why this perturbation is strong only in certain cases. The purpose of the present communication is to show a series of results that can throw some light on the abovementioned problem. The main point is that Auger processes of interatomic type, as those occurring in the INS technique of Hagstrum, are free of these perturbations. Recently, the authors have studied the line shape of the Auger peaks of O, C, N and S adsorbed on Cu, Ni and Fe. These results show that only that part of the Auger structure originated by interatomic transitions between substrate and adsorbate atoms can be related to the local density of states (LDOS). The rest of the structure, due to normal intraatomic processes, is dominated by the spectral terms in the final configuration of the ion. This new interpretation allows a separation of perturbation effects and clarifies the contribution of the LDOS to the peak line shape. In this communication, we present the line shape analysis of the L_2,3 VV and KVV Auger peaks of Mg and O in MgO. Due to the strong ionic character of this compound, the L_2,3 VV peak of Mg⁺⁺ is mainly due to interatomic processes between Mg⁺⁺ and O⁼ ions, whereas the KVV peak of O is mainly due to interatomic processes. This analysis shows that good agreement exists between the L_2,3VV Mg⁺⁺ Auger peak and the self-convolution of MgO density of states, whereas the KVV Auger peak of O⁼ is dominated by the spectral terms of the final configuration. Only a small peak in the high energy side of the latter peak can be related to the density of states and could be interpreted as an interatomic transition between two neighboring oxygen ions, in agreement with the interpretation given by others.     

Observation of the self-convolved spin-split valence band density of states in MVV Auger decay from Fe(100)

By spin-resolved photoemission with synchrotron radiation we have investigated the Auger electrons from Fe(100) above the 3 p-3d resonance. The observed majority- and minority-spin Auger electrons have the expected kinetic energy independent on photon energy and without noticeable reduction because of correlation effects. The spin-resolved Auger electron energy distributions resemble convolutions of theoretical density of states curves of appropriate spin direction.     

Observation of resonance recombination lines in electron excited auger spectra of Gd

Combined measurements of electron excited N_4,5 Auger spectra and photoelectron emission on clean and oxidized Gd lead to a distinction between Auger lines originating from 4d → continuum and 4d → 4? resonance excitations. Several Auger structures are identified as due to the direct recombination of 4d⁹4?⁸ states with the 4f and valence electrons. The shape of the most prominent Auger line for oxidized Gd agrees perfectly with the Fano profile of the 4? photoemission intensity.     

Complete breakdown of the one-electron picture of auger spectra of solids

The very broad M₄₅?N₂₃N₄₅ (3d^-1 → 4p^-14d^-1) Auger spectra for metals in the range Pd to Te arise from complete breakdown of the one-electron picture of the final state double vacancy due to 4p^-14d^-1 ? 4d^-3?f giant Coster-Kronig fluctuation and decay processes. This is an example of atomic-like effects giving rise to level shifts and broadening which are large in comparison with typical widths of d-bands in solids. The 4p^-14d^-1 two-hole spectral function can be approximated by a 4p^-1 single-hole spectral function perturbed by a static, sharp 4d^-1 hole. The resulting Auger line-shapes are different from single-hole 4p^-1 line-shapes from XPS and XES. Analogous effects also occur for double vacancies involving one or two 4s-holes.     

The role of auto-ionization transitions in the formation of the extended fine structure of high-energy secondary electron spectra

Extended fine structure (EFS) of secondary electron (SE) spectra has been detected beyond the high-energy (∼720 and ∼840 eV) LVV Auger lines in iron and nickel. Two mechanisms of its formation are considered: 1) direct transitions of electrons to the final state p according to Fermi’s “golden rule” and 2) second-order processes of auto-ionization type, passing through excitation of a core electron to an intermediate state q of the continuum with subsequent filling of the hole formed during this process by a valence electron and transition of the electron from the intermediate state q to the final state p. Interference of the direct wave with the wave reflected from neighboring atoms generates the EFS both in the final (p) and in the intermediate (q) state with two different periods determined by the wave numbers p and q. Comparison of calculated extended fine structures with the experimentally observed ones leads to the conclusion that the structure is formed by second-order auto-ionization processes. Fiz. Tverd. Tela (St. Petersburg) 40, 1589–1594 (September 1998)     

KLL auger and core level (1s and 2p) photoelectron shifts in a series of gaseous sulfur compounds

Core (1s and 2p) X-ray photoelectron shifts and KLL (¹D₂) Auger shifts for 22 sulfur compounds have been measured. The values have been correlated by means of atomic charge plus remote potential or central atom potential models. Either approach is equally effective tor binding energy correlations. The relaxation corrected and transition state models are in general superior to ground state models. Auger shift predictions are however poor in all cases. Absolute total static relaxation and extra-atomic relaxation values have been assessed by using the Auger parameter of Lang and Williams and relativistic atomic calculations for the free atom and its ions. These extra-atomic relaxation components are not additive but rather obey an average contribution behavior. The relaxation shift values have been compared with those obtained from the original Auger parameter (α) of Wagner. The correlation of 1s and 2p binding energies suggested a revised relationship for the Wagner Auger parameter and an equivalent simple form of the Lang and Williams parameter which can be used with satisfactory results when only the usual experimental binding energy (2p) is available in conjunction with the Auger shift.     

Thermal and Auger processes in p-n junctions based on GaInAs/InAs and InAsSbP/InAs heterostructures

A study is made of the excess-energy relaxation processes and the mechanisms responsible for overheating of the active zone of infrared emitters made from nonisoperiodic structures with stressed InGaAs layers and from nearly isoperiodic InAsSbP structures and emitting in the wavelength range λ=2.5–5.0 μm are investigated. The relationship between the overheat ΔT of the active zone of the structure and Auger processes is established for In_1−x Ga_xAs infrared emitters. It is shown that the efficiency of Auger recombination decreases as x increases in the interval 0–0.09, promoting a sharp reduction in ΔT. At x>0.09 the efficiency of CHHS Auger processes decreases exponentially, but an increase in the density of dislocations due to the appreciable value (∼6.9%) of the lattice mismatch parameter causes ΔT to increase, but slowly. Zh. Tekh. Fiz. 67, 68–71 (September 1997) Deceased.     

Interference effects in alignment and orientation processes of atoms excited by polarized radiation

The dynamics of the processes of alignment and orientation of atoms subjected to the action of polarized radiation has been studied theoretically in the energy range of excitation of autoionization resonances. The alignment parameters A ₂₀ for the 4p ⁴5p states of Kr II populated through the excitation and autoionization decay of Kr I 3d ⁹ np resonances depend on energy due to the interference between different resonance channels and the channel of direct photoionization. It is predicted that the orientation parameter O ₁₀ of some Kr II 4p ⁴5p states and the parameter of the angular distribution of photoelectrons β_e1 strongly depend on energy. The absolute photoionization cross sections are calculated for the population of the Kr II 4p ⁴5p states in the case where the energy of excitation photons corresponds to the first four 3d ⁹ np resonances. A good agreement between the calculated and measured photoionization cross sections proves that it is important to take into account the interference between different resonance channels in order to appreciate the dynamics of the Auger decay of Kr I 3d ⁹ np resonances.     

X-ray photoelectron and auger spectroscopy analysis of Ge:Mn-based magnetic semiconductor layers

Thin (～60 nm) germanium layers supersaturated with a manganese impurity of 10–16 at % have been studied by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The layers have been fabricated by pulsed laser deposition onto a semi-insulating single-crystal GaAs substrate. The results of XPS analysis of the Ge:Mn layers reveal a change in the line shape of germanium and manganese (2p) in the surface region compared to deeper layers, which indicates a transition from the oxidized form of the base material (Ge²⁺ and Ge¹⁺) and impurity (Mn²⁺) near the surface to the unoxidized state of germanium (Ge ⁰) and manganese (Mn⁰) in the interior of the layer. The XPS spectra of the valence electrons of the Ge:Mn structure indicate that the density of states in the valence band of the ferromagnetic Ge:Mn structures is caused not only by mechanical mixing of germanium and manganese. The composition of heterogeneous inclusions in Ge:Mn films has been studied using scanning Auger microscopy.     

Photoemission studies of core exciton decay in KI

The decay of K⁺ 3p-core excitons in KI was studied by using new methods for obtaining photoemission spectroscopy data with synchrotron radiation. The Auger and non-radiative direct-recombination decay processes are separately identified in the data and a measure for the Auger energy distribution is obtained.     

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.     

Two hole spectra and valence states in chromium and chromium silicides

Auger spectra for L₃M₂₃V and L₃V V transitions involving, respectively, one and two valence holes in the final state, have been measured for Cr and CrSi₂ using both X-ray photons and electrons as ionization source. Careful subtraction of the energy losses from the raw data permits determination of the lineshape of the Auger spectra. The valence hole spectral functions derived from the L₃M₂₃V transitions are compared with valence band spectra obtained by X-ray photoemission. The comparison provides direct evidence of the importance of multiplet coupling between the 3p and 3d holes in the final state. Results for the spectral function of two valence holes are consistent with the outcome of band structure calculations, although some correlation effects seem to be present.