Chimisorption du monoxyde de carbone sur la face (110) du molybdéne: III. Interprétation des résultats obtenus par spectrométrie Auger

Auger electron spectroscopy reported in part I has shown an Auger yield attenuation for C and O atoms during the adsorption of CO on Mo (110) substrate. In this part III, we give an interpretation of this phenomenon taking in account results obtained in part II on the relative positions of C and O atoms with respect to the Mo atoms. We show that Auger yield attenuation for C and O is due to a screen factor.     

Laser-enabled Auger decay in rare-gas atoms

In rare-gas atoms, Auger decay in which an inner-valence shell ns hole is filled is not energetically allowed. However, in the presence of a strong laser field, a new laser-enabled Auger decay channel can open up to increase the double-ionization yield. This process is efficient at high laser intensities, where an ns hole can be filled within a few femtoseconds of its creation. This novel laser-enabled Auger decay process is of fundamental importance for controlling electron dynamics in atoms, molecules, and materials.     

三元合金Cu76Ni15Sn9的离子溅射研究

在２７ｋｅＶ Ａｒ⁺离子轰击时,用收集膜技术结合俄歇谱仪（ＡＥＳ）,研究了三元合金Cu₇₆Ni₁₅Sn₉系统的择优溅射行为。同时使用扫描电子显微镜（ＳＥＭ）与电子探针微分析（ＥＰＭＡ）．观察了靶点表面形貌变化并测定了形貌特征微区的合金组份原子的相对百分浓度。结果表明,Ｃｕ原子较Ｎｉ原子、Ｎｉ原子较Ｓｎ原子,在所测定范围（０─６０°）内择优发射。最后讨论了靶点表面形貌特征和“元素局域富集”现象对择优溅射过程的影响。 关键词：     

Auger rates of second-row atoms calculated by many-body perturbation theory

Many-body perturbation theory is applied to calculate the KLL Auger rates of all terms of atoms C, N, F and Ne. Theoretical rates are compared with experiment and other theories for Ne and O. A new set of the Auger satellites, corresponding to the main photoelectron line binding energy is proposed. The intensities of these satellites are calculated and some of these satellites are identified in experimental KLL Auger spectra of Ne.     

Specific features of the formation of ytterbium films on the Si(111) surface at room temperature

The processes accompanying the formation of ytterbium films on the Si(111) surface at room temperature are investigated by the contact potential difference method, Auger electron spectroscopy, low-energy electron diffraction, and thermal desorption spectroscopy. It is shown that the grown metal films are uniform in thickness and that Si atoms virtually do not dissolve in the films. The atoms of the silicon substrate can diffuse in limited amounts into the Yb metal film only when the surface is bombarded by high-energy primary electron beams employed in Auger electron spectroscopy. The results obtained permit the conclusion that the previously observed oscillations of the work function in Yb-Si(111) thin-film structures cannot originate from dissolution of silicon atoms in the ytterbium film.     

PCA-Based Analysis of X-Ray-Excited Auger Spectra from Non-ordered Ag(110)

Principal-components analysis (PCA) followed by factor analysis enables one to decompose the structure of Auger lines originating from large effects such as energy shifts induced by chemical effects. The aim of the present contribution is to show that PCA can also be effectively used for detection of composed structure in a set of Auger spectra even if the observed changes in line shape are very subtle. The analysed set of X-ray-excited MNN Auger spectra from Ag(110) shows a clear correlation between peak shifts and peak widths. This correlation can be explained as a result of the composed structure of the recorded Auger lines. It is suggested that the resultant Auger lines may consist of a number of constituents, each referred to Ag atoms differing in the value of their co-ordination number.     

Surface analysis by ion-electron spectroscopy; Silicon target

The energy spectra of secondary elections emitted from a Si(111) surface due to bombardment by 6 keV He⁺ and O⁺₂ ions have been examined. The fine structure in the spectra is explained on the basis of a novel mechanism of creation of Auger electrons at the surface. There are two stages of interaction between incoming ions and the substrate via adsorbed atoms. In the first stage, due to a level promotion mechanism, vacancies in the adsorbed atoms are created. In the second stage, Auger neutralization processes accompanied by the emission of electrons from a solid with characteristic energies take place. These electrons provide a good indication of the degree of coverage of the silicon surface with contaminant atoms. The energy losses of escaping electrons are also discussed.     

Extra-atomic relaxation energies and the Auger parameter

A simple procedure is used to derive several of the models that have been developed to understand relaxation energies, and especially the relationship between the Auger parameter and the extra-atomic relaxation energy. The approach shows clearly the assumptions that are made in these models and the next level of higher-order terms needed in the evaluation of extra-atomic relaxation energies from the Auger parameter. Numerical evaluation of these higher-order terms shows that they are probably small, except when comparison is made between atoms in very dissimilar environments. The problems that arise when the final orbitals of the Auger transition are not entirely in the core are considered.     

A study of Al/Si(111)-cleaved interface by photoemission,Auger electron yield,and Auger electron spectroscopies

Photoemission, Auger electron yield, and Auger electron spectra are observed for Al/Si(111)-cleaved interfaces. The Al 3p derived state which becomes metallic at monolayer coverage is introduced near the top of the valence band. The Fermi level is stabilized in this metallic state. The present result favors the on-top geometry of Al atoms on a Si(111)-cleaved surface.     

Initial stage of Pd adsorption on Si(111)7 × 7 surface studied by AES and EELS

The initial stage of adsorption of Pd on a Si(111)7 × 7 surface has been studied by means of Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and surface work-function change. For Pd deposition at room temperature (RT) the Si(LVV) Auger signal intensity decays in a broken linear line. The structure factor, defined as the intensity ratio of the subpeak to the main one in Si(LVV) Auger spectra, increases up to a maximum around one monolayer coverages. In EELS spectra two peaks, characteristics of Pd, appear at the completion of the first Pd layer. Pd atoms deposited on Si(111) at RT form initially flat layers of a few monolayers height without mixing with substrate Si atoms. For Pd deposition at a moderately high temperature (MT) of about 300°C, however, the structure factor for Si(LVV) Auger spectra does not change. EELS peaks, characteristic of Si substrate, remain clearly even beyond one monolayer coverage. Pd atoms deposited at MT are unstable and easily diffuse into the bulk. We present evidences to support the “screening” model for the bond-breaking mechanism at the Pd/Si interface.     

Angle resolved auger surface spectroscopy

The angular distribution of electrons ejected in core-valence-valence Auger transitions of atoms chemisorbed on metal surfaces is considered theoretically. Since the valence electrons participating in the Auger transition are also involved in chemical bonding to the surface, these initial states contain information pertaining to the chemisorption bonding geometry. The role of the initial state symmetry in determining the angle resolved Auger surface spectrum (ARASS) is investigated through model calculations and is found to be small. Thus the ARASS is expected to be a smoothly varying function of angle with ? ± 15% modulations due to diffraction effects, in agreement with recent experimental results for S adsorbed on Ni(100).     

Magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> surface

The magnetic properties of the magnetite Fe₃O₄(110) surface have been studied by spin resolved Auger electron spectroscopy (SRAES). Experimental spin resolved Auger spectra are presented. The results of calculation of Auger lines polarization carried out on the basis of electronic state density are presented. Problems related to magnetic moments of bivalent (Fe²⁺) and trivalent (Fe³⁺) ions on the Fe₃O₄(110) surface are discussed. It is established that the deposition of a thin bismuth film on the surface results in significant growth of polarization of iron Auger peaks, which is due to additional spin-orbit scattering of electrons by bismuth atoms.     

Quantitative aspects of Auger electron spectroscopy; On the importance of attenuation of the primary electron beam

Measurements of Auger electron currents at different energies of the primary electrons and at different angles of incidence suggest that attenuation of the primary electron beam in the crystal has a significant influence on the measured Auger currents. This makes it possible to distinguish between a monolayer and a multilayer system, i.e. between impurity atoms in the top atomic layer and impurity atoms dispersed through the surface region. Comparison of AES and ellipsometric measurements of monolayer and multilayer systems on silicon and germanium surfaces shows that AES results can be interpreted to give quantitative information about the number of atoms of the type investigated.     

Surface structure from angular dependence of auger electron emission

Auger electrons emitted from atoms in the vicinity of a solid surface can show strong angular dependence in their emission due to elastic scattering from the surrounding ion cores of the solid. Model calculations for the emission of Auger electrons from sulphur adsorbed on a Ni (100) surface show that these angular features are very sensitive to the adsorption site of the emitting atoms, and that a study of these effects should produce a method of surface structure analysis for the location of preferred surface adsorption sites. This approach would appear to be an improvement over LEED because of its high sensitivity to structural changes and because it does not require long range order in the adsorbate layer.     

Excitation and decay dynamics of 1s2s inner-shell double-vacancy states of neon atoms

The photo-excitation and Auger decay processes of inner-shell double vacancy states 1s2s2p^6（1,3^S）3s3p of neutral neon atoms have been studied theoretically. Multi-configuration Dirac-Fock （MCDF） calculations have been carried out, with electron correlation effects taken into consideration. The relaxation of core and excited orbitals and configuration interaction are found to be crucial to creating the double vacancy states by single photo-absorption. The predominant decay paths for the double vacancy states turn out to be of the LLM Auger decay to 1s 2s^22p^53s（3p）, KLL Auger decay to 1s^22s2p^43s3p, and KLM Auger decay to 1s^22p^63s（3p）. They lead to further Auger decay, creating the neon ions of multiple charge states. For both double and single vacancy states the spectator type of Auger process is dominated in all the Auger decay processes. Theoretical Anger electron spectra are presented for further investigations, experimental and theoretical.     

Surface composition of Co79Ru21 alloy contaminated with phosphorus measured by AES

The surface of a polycrystalline Co₇₉Ru₂₁ alloy contaminated with phosphorus displays temperature dependent Auger peak heights of Co, Ru and P. In agreement with theoretical predictions, enrichment of Co atoms in the detected volume is observed. The atoms of phosphorus compete mainly with cobalt atoms in the surface region.     

Polarization and dichroism in atomic Auger spectroscopy following absorption of circularly polarized light

Spin resolved Auger current is shown to be different for the absorption of left and right circularly polarized light. This current is produced in non-radiative spontaneous decay of photoexcited atoms or of excited atomic photoions. Circular dichroism in such polarized Auger electrons exists even in the absence of spin-orbit interaction. Physical and geometrical conditions, necessary for the occurrence of dichroic effects in atomic Auger spectroscopy, have been obtained. Calculations for Ba and Xe show that the effect is substantially large and can be readily observed.     

Electron depletion in mesic atoms

Assuming there is no serious electron depletion in mesic atoms, most previously calculated Auger electron spectra for nuclear emulsion have ignored a large low energy (18–25 keV) contribution. A method for investigating electron depletion in mesic atoms is suggested.     

Survival of He+ ions during grazing scattering from a Ag(111) surface

He+ ions as well as neutral He atoms with keV energies are scattered under a grazing angle of incidence from a clean and atomically flat Ag(111) surface. From a comparison of ion fractions observed after scattering of He+ ions and He atoms we find for energies below some keV small but defined fractions of ions that have survived the complete scattering event with the surface. This feature allows us to clear up the microscopic interaction scenario for Auger neutralization of He+ ions at a Ag(111) surface. The Auger neutralization rates are 2 to 3 orders of magnitude smaller than conventional rates derived from experiments for He+-metal systems and agree with recent calculations.     

Metastable helium atom stimulated desorption of H+ Ion

H+ desorption induced by the impact of metastable helium atoms has been found for H(2)O/Na/Ni(110) coadsorption systems. The measurements were carried out using a time-of-flight technique and a pulsed-discharge type metastable helium atom ( He(*)) source. It is concluded that the H+ desorption by He(*) is induced by a hole created on the valence levels via the Auger deexcitation of He(*). The H+ desorption by He(*) may be understood within the framework of the Menzel-Gomer-Readhead model.