N. Benazeth

Spectres auger et sections efficaces d'ionisation de la couche L23 du magnésium et de l'aluminium sous impact de protons et d'ions lourds (10–100 keV)

Abstract A comparison of Auger structures observed on the energy distributions of secondary electrons emitted from Mg and A1 solid targets bombarded by either light particles (H + and He + ) or heavy ions (Ne + , Ar + , …) is presented. With incident protons, it essentially appears a broad peak corresponding to a L 23 VV transition and a weak shoulder due to the surface and bulk plasmon excitation. The Auger structures obtained with heavy ions are richer and the peaks which compose it are sharper. Such atomic-like structures correspond to Auger transitions from excited (with one or two L 23 holes) moving recoiling atoms. The experimental L 23 Mg and A1 ionization cross sections were determined from Auger spectra. In H + −Mg (or A1) collisions our results are in good agreement with the theoretical values calculated in a PWBA model. In the case of heavy ion-target interactions, we compared the experimental measurements with ionization cross section calculations obtained in a Landau-Zener model.

Spectres Auger sous bombardement d'ions Ar+ de 60 keV de quelques éléments purs et de composés binaires

Abstract Auger spectra of different elements, alloys and compounds excited by 60 keV argon ions have been obtained. These spectra show a detailed structure with, in particular, a sharp Auger peak. This peak is interpreted as a superposition of two kinds of Auger transitions: the first one occurs with two electrons of the electronic band, the second, takes place from electrons situated on “quasi-atomic” outer shells. On the low energy side of Auger line, two equidistant peaks attributed to Auger electrons having suffered energy losses by ionization of electronic outer shell of target-atoms were observed. From Mg, Al, Si, P and S Auger transitions due to initial double L ii,iii level ionization were detected. The interpretation of the creation of a vacancy in electronic inner shell at the origin of Auger effect by ionic bombardment is given from the electronic promotion model of Fano and Lichten.

Incidence angle and ion energy dependences of absolute Al L23 Auger yields in Ar+-Al collisions: Experiments and computer simulations

Abstract Experiments and computer simulation of Al L 23 absolute Auger yields from single-crystal and polycrystal aluminium targets bombarded by Ar + ions were peformed. From experimental Al Auger Spectra, band-like and atomic-like structures labelled L 23 VV and L 23 MM respectively can be distinguished. The dependences of these experimental Auger yields on the incidence angle and ionic energy were studied. Comparison with calculated variation laws of Auger yields from 2p excited Al atoms decaying inside the crystal (bulk emission) and from excited sputtered atoms was carried out. The model was set up on the basis of the atomic collision cascade as generated by the MARLOWE code. Reasonable agreement between experimental and calculated results was obtained in taking into account the Auger neutralization process involving electron exchange between metal and sputtered atoms.

Electronic emission from solid targets bombarded by noble gas ions (10–100 keV): Energetic and spatial distributions

Abstract The variation of the Be K ionization cross sections as a function of the ionic incident energy was determined by Auger emission from solid targets. The results obtained with Xe + and Ar + ions show a low energy threshold and a break formation situated at about 50 keV for Ar + ions and 80 keV for Xe + ions. The angular distributions of the secondary electrons emitted from single crystals were studied. They show two kinds of anisotropy. The first one is interpreted in terms of electron diffraction. This angular dependence is observed all over the ionic energy range explored in our measurements. In our geometrical conditions, the second kind of anisotropy only rises from an ionic velocity of about 5×10 5 m/s. It may be due to an electron axial channeling along the close packed directions of the direct lattice.

An apparatus for ion-surface collisional process studies and surface analysis

Abstract An experimental setup allowing both surface and interface analysis and ion-surface collisional process studies is described. It consists of an ion beam line which provides 1–80 keV mass analysed rare gas and alkali-metal ions, and an UHV chamber. This one is equipped with two time of flight systems which allow energy and mass analysis of scattered and recoiled particles at scattering angles 180° and in the range 0–165°. In addition a fixed electrostatic hemispherical analyser can record either the positive ions or the emitted electrons, at an angle of 90° from the ion beam. The versatility of the apparatus is illustrated with data on clean Si (111) surface and on impurity- or Cs-covered Si surface: chemical and crystallographic structure analysis, depth profile, ion fractions and ion-induced electron spectroscopy.

Émission d'électrons auger caractéristiques du néon et du sodium, observée lors de collisions de ces ions avec différentes cibles solides

Abstract The Ne and Na Auger emission observed from collisions of these ionized gases with different solid targets, in an energy range from 5 to 50 keV, has been investigated. The Auger electron distributions were analyzed. Moreover, for the Ne + -Mg and Na + -Mg collisions, the Auger yield variation as a function of various parameters which influence the implantation, was studied. The experimental Auger yields ρ A were compared to the calculated ones in a model which takes into account the stationnary concentration profiles of implanted atoms inside the target. For the Ne, the experimental results are in good agreement with the proposed model but this model is inadequate to explain the Na ρ A variations as a function of ionic energy and incidence angle, at the room temperature.

Experimental and theoretical study of the angular resolved auger emission L23 of a single crystal target of aluminium excited by ion impact

Abstract The measured angular distribution N (ϑ) of the L 23 Auger electrons of aluminium excited by Ar + ion impact on (110) and (111) single crystals have been obtained for several polar angles. Two theoretical models based on a LEED formalism which can be used to calculate these angular distributions were briefly described and compared. There is a fair agreement between the line shape of the experimental and calculated curves. However, the calculated angular distributions have more structures and the calculated anisotropy rates are much larger than the measured ones.

Diffraction effects in the angular distribution of secondary electrons emitted under ionic bombardment of a (111) surface of silver: Experimental results and theoretical model

Abstract The angular distributions of secondary electrons emitted from a (111)Ag target, when bombarded by rare gas ions, are presented. A theoretical model based upon multiple scattering effects using the Low Energy Electron Diffraction (LEED) formalism is proposed. The calculated curves are in good agreement with experimental results within the electron energy range we have investigated (10 E

Détermination par spectroscopie auger, des sections efficaces d'ionisation de la couche L23 du magnésium et de l'aluminium sous impact d'ions He+

Abstract The L 23 Mg and L 23 Al Auger spectra excited by helium-ion bombardment have been studied. These spectra essentially show an intensive peak interpreted in terms of L 23 MM atomic-like and L 23 VV transitions. By integration of this peak, the Auger emission cross sections were determined and their variations as a function of the incident particle energy were studied from a few keV up to 100 keV. These results have been compared to the values of the ionization cross sections calculated in a classical binary encounter approximation (BEA). One observed a good agreement for the aluminium target. For the magnesium, the discrepancy in the low energy range shows that, in those case, the electronic promotion in a molecular orbital model added at the electronic excitation due to the direct Coulomb interaction.

Electron emission in multiply charged noble gas ion-gold solid target collisions: Total and Auger yields

Abstract Total secondary electron emission coefficients, γ, and absolute values of ArL 23 Auger yields, ϱ A , were determined for collisions between highly charged noble gas ions and polycrystalline gold targets. Results concerning the electron emission coefficient show that, in the explored ion velocity range, γ is due to both potential and kinetic process contributions. From Ar 9+ the Auger yield decreases from 4.6 to 2% for incident kinetic energy from 16 keV to 70 keV respectively. The position of the ArL 23 Auger structure indicates that the decay takes place from an Ar ion with an L 23 vacancy and electronic outer shells already filled. With Ar 8+ ions, the Auger yield remains negligible showing that the major part of the emission observed with higher charge states is due to the initial L 23 vacancy in the incoming projectile. From Ar 11+ , the shift of the Auger structure towards higher energies indicates that it is essentially the 2p 3 initial configurations which are efficient.