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.     

Plasmon energy gain and double ionization satellites in the Be Auger spectrum

Two relatively weak, higher energy satellites are observed at 18 and 38 eV above the Be KVV Auger spectrum. The lower energy satellite is assigned to coupling of energy from bulk plasmon de-excitations $\text{(}\text{h}\text{?}\text{ω ～ 18 eV)}$ with Auger electrons and the higher energy event to Auger electrons ejected from Be atoms with doubly ionized K levels.     

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.     

Auger and other characteristic energies in secondary electron spectra from Al surfaces

The energy spectra of secondary electrons back-scattered from clean, oxygen covered, and Cu covered Al surfaces have been determined. The data support the previous suggestion that Auger electrons can experience both characteristic energy loss and absorption phenomena. From the experimental results it was not possible to determine whether densities of states of electrons in the valence band affected the Al L_2,3 VV Auger spectrum. This portion of the spectrum was greatly changed by oxygen absorption on the Al surface, but little affected by less than a monolayer of Cu. Conversely, characteristic loss spectra were less sensitive to oxygen on the surface, but were highly sensitive to the presence of copper at even less than monolayer coverage. A correlation between characteristic loss and “true” secondary spectra from clean surfaces was established and possible reasons for the correlation are discussed.     

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Low energy Auger and loss electron spectra from magnesium and its oxide

Data have been obtained from Auger and energy loss processes in clean metallic Mg, Mg during stages of oxidation, and UHV cleaved MgO(100) surfaces. Particular attention has been paid to twenty features below 200 eV in the Auger spectra from these surfaces. A comparison of spectra from the metal, oxidised metal surface, and single crystal MgO has enabled estimates to be made of surface charging effects, and the MgO steady state surface potential is found to be near + 10 V above ground. All the Auger features are given assignments, two of which are interfacial processes involving ionic initial states and metallic final states. Several features in the low energy Auger spectrum are attributed to diffraction of true secondary electrons.     

The sub-bandgap energy loss satellites in the RIXS spectra of beryllium compounds

Resonant X-ray inelastic scattering spectra have been measured in BeO, phenakite (Be₂SiO₄) and chrysoberyl (BeAl₂O₄) with the excitation energy near the beryllium K edge.The RIXS spectra excited in the vicinity of the Be 1s core resonance show two principal features: the scattering on a valence excitation (which at higher excitation energies verges into the characteristic K_α emission), and a remarkably strong energy loss sideband to the elastic scattering peak. The energy loss shoulder appears to result from lattice relaxation in the absorption site. The comparison of the RIXS spectra of phenakite, chrysoberyl and BeO shows that the strength of the low energy sideband differs greatly; it is strongest in BeO and weakest in phenakite. The Si 2p RIXS spectra of phenakite also display a similar strong sub-bandgap energy loss tail.To gain further insight to this process, transitions in a system with a single vibrational mode have been modelled. The phonon relaxation has been simulated empirically by “smearing” the photoabsortion-populated vibrational levels with lower levels. This simple model is able to qualitatively explain this wide energy loss shoulder.     

The diamond surface: II. Secondary electron emission

The total secondary electron emission spectrum from diamond has been examined, and details of the Auger spectra, characteristic loss spectra and K-level ionisation loss spectra have been presented. These features from the clean diamond surface were contrasted to those from graphite and amorphous-carbon. The fine structure in the carbon Auger spectra were compared with the line shape calculated using the band structure model, and the chemical sensitivity of the Auger spectra was demonstrated. A high energy Auger satellite peak in the diamond spectrum was ascribed to the Auger transition occurring from a doubly ionised carbon atom. This result was substantiated by the observation of loss peaks associated with the singly ionised level. The characteristic energy losses were assigned to interband transitions and plasma losses, and have been compared to optical data where possible.     

Evidence for an ultrafast breakdown of the BeO band structure due to swift argon and xenon ions

Auger-electron spectra associated with Be atoms in the pure metal lattice and in the stoichiometric oxide have been investigated for different incident charged particles. For fast incident electrons, for Ar7+ and Ar15+ ions as well as Xe15+ and Xe31+ ions at velocities of 6% to 10% the speed of light, there are strong differences in the corresponding spectral distributions of Be-K Auger lines. These differences are related to changes in the local electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions.     

Auger electron and characteristic energy loss spectra of plutonium

The Auger electron and characteristic loss spectra of plutonium have been obtained for the first time using a four grid retarding potential analyzer. The surface of this reactive metal was prepared by scribing in situ in good vacuum with a titanium carbide blade. Oxygen and carbon impurities were still present after scribing. The origin of the Auger electron and loss peaks is suggested, and a correlation is made with the peaks observed for uranium dioxide by Ellis and Campbell.     

Plasmon effects in electron energy loss and gain spectra in aluminium

Oberservations of the low energy secondary and Auger electron spectra and the electron energy loss spectra from a clean aluminium surface have been made and the results are compared with other recent studies including that of Jenkins and Chung (1971). Low energy emissions at 5.7 eV and 10.3 eV are associated with the creation of single electron excitations in the valence band by plasmon decay. An apparent anomaly in the plasmon loss and gain peaks associated with the Auger spectrum is discussed.     

Auger transitions initiated from singly and doubly ionized states in Li metal

Major events in Auger spectra from Li surfaces containing both Na and K have been identified. Li Auger transitions initiated from both singly and doubly ionized K shells of Li have been observed. However, no higher energy satellite corresponding to the coupling of the energy of a plasmon decay with that of the Li K VV Auger electrons was detected.     

Effet de l'oxydation en surface et en volume sur les spectres de pertes caractéristiques d'énergie d'électrons dans les couches minces de titane

Transmission and reflection electron energy loss spectra, together with electronic diffraction patterns and Auger spectra have been registered on evaporated titanium thin films. The optical, crystallographic and chemical properties for the bulk and the surface of the films are compared. The 25 eV energy loss observed in the spectra of the low-energy electrons seems to give evidence for the formation of a superficial oxide layer. This assumption is confirmed by the transmission energy loss spectrum of pure rutile which is also presented.     

Auger and electron energy loss spectra of adsorbed species: α and β states of carbon monoxide and nitrogen on W(100)

Auger and electron energy loss spectra have been recorded for both α and β chemisorbed states of carbon monoxide and nitrogen on W(100). The α state spectra have been analysed with reference to results for the gas phase molecules, those for the β states have been analysed following a quasi-atomic final state model. The results illustrate both the potential and the limitations of AES and ELS in surface chemical analysis.     

Multiquantum scattering processes and transmission electron energy loss spectra

Microscopic many-body theory for electronic properties of solid states is developed with an emphasis on the role of correlation memory effects. Heisenberg equation of motion, fluctuation-dissipation theorem and operators of commutation have been used to calculate multiplasmon transmission electron energy loss spectra. Multiquantum integral kinetic equation for the longitudinal complex dielectric function is derived. Strong interaction between high-energy probe beam electrons penetrating the solid state and plasma of valence electrons is taken into account. It is shown that average number of high-frequency plasmons generated in every collision process is more than one for typical values of metal parameters. It is obtained that excitation of a good few plasmons is simultaneous event. Calculated multiplasmon structure of electron energy loss spectra coincides with experimental.     

ESCA studies of Cu,Cu2O and CuO

Cu 2p, Cu 3d and O 1s electron spectra and Cu L₃M_4,5M_4,5 Auger electron spectra from Cu, Cu₂O and CuO have been studied at 25°C and at 400°C. The height of the Cu 2p satellite peaks from copper oxides was lowered when the temperature was raised. The intensity of the satellites also decreased if the sample stayed in vacuum for prolonged periods.Two commercial cuprous oxides were different with respect to the behaviour of the satellite peaks. One produced very weak satellites, while the other produced strong ones as previously reported in the literature for cuprous oxide. The colour of the oxides was slightly different, indicating that the stoichiometry was not the same.The change in satellite intensity is accompanied by changes in oxygen spectra, Cu L₃M_4,5 M_4,5 Auger spectra and valence band spectra.It is useful to study Auger electrons in addition to the direct electron spectrum, since Auger signals can be more sensitive to surface conditions than direct electron spectra.     

Energy loss spectra,auger spectra and high energy electron diffraction of A-15 superconductors

We have measured the electron energy loss spectra of V₃Si, Nb₃Al, Nb₃Sn, Nb₃Ge (annealed) and Nb₃Ge (sputtered) from 3 to 70 eV. Numerous new structures were discovered in this study which could be related to interband transitions, plasma excitations, and core transitions. We have also measured the high energy electron diffraction patterns and Auger spectra which characterized the lattice structures and compositions of these surfaces.     

Electron energy loss and Auger study of epitaxially grown Cu on Ni(100)

Auger and electron energy loss spectra have been measured on films of Cu epitaxially grown on Ni(100). The films were prepared under UHV conditions using a quartz crystal for monitoring the deposition rate. LEED measurements were taken to determine the orientation of the films. The presence of a monolayer of Cu on Ni(100) is enough to suppress the 3p-3d transition on the surface of the sample. The electron energy loss spectra were studied as a function of the primary electron energy (50 to 300 eV). The experimental results were qualitatively analyzed using recent theoretical calculations of Cooper and co-workers. The effect of a small Cu coverage on Ni(100) on the chemisorption of CO and O₂ was also studied. A strong suppression of CO chemisorption at room temperature was observed. In the case of O₂, large exposures are necessary in order to observe a significant amount of oxygen on the surface. The absence of any appreciable chemisorption on the surface of the metal is attributed to the lack of empty d-surface states.     

Measurement and interpretation of the electron energy loss spectra of iron and its oxides

The characteristic electron energy loss spectra of high purity samples of iron and its oxides were measured using cpmbined electron microscopy and energy analysis. By comparing these with X-ray absorption spectra it was possible to identify the single electron excitation processes and to deduce the plasmon energy of the electrons in iron.