J.-F. Hennequin

Auger electron emission by ion bombardment of light metals

Abstract The energy distribution of secondary electrons ejected from a metallic target upon ion bombardment (Ar + , 10 keV) is studied with a 180° magnetic analyser, particularly in the vicinity of the Auger peaks that appear in the electron spectra of the light metals (Li, Be; Na, Mg, Al, Si). A qualitative explanation based on the correlation diagrams which described the evolution of the electronic levels during the collision of two atoms inside the target is proposed to interpret the variation of the Auger peak intensity with the atomic number of the target.

Ar+ excited aluminium Auger electron emission from Cu-Al alloys

The aluminium Auger electron emission from Cu-Al alloys in solid solution bombarded with 2–16 keV Ar+ ions is studied as a function of the Al concentration. A linear law is observed for the intensity of the high energy Auger peak at 76 eV which originates only from the primary asymmetric collisions Ar → Al where two vacancies are created in the 2p level of the Al atom. On the contrary, a parabolic law is found for the intensity of the principal Auger peak at 63.5 eV (one Al 2p vacancy) which originates from the asymmetric collisions Ar → Al and from the symmetric collisions Al → Al together. The proportion of asymmetric collisions among collisions effective for the principal Auger emission from pure aluminium can be deduced from these results. It appears as an increasing function of the bombardment energy: its value is nearly equal to 6% at 10 keV and 18% at 15 keV.

On the origin of ion-induced Auger electron emission from metals

Abstract Auger electron emission by ion bombardment of solids originates from two kinds of collision: asymmetric collisions of the incident particles with the target atoms and symmetric collisions of the target atoms between themselves. Their relative contributions for Auger emission are discussed.

Intrinsic emission of secondary ions from silver-magnesium alloys: II. Magnesium emission

Some Ag-Mg alloys, and pure Ag and Mg samples, were sputtered in ultrahigh vacuum with 10 keV Ar+ ions and the emission intensities of monoatomic Ag+, Mg+ and Mg2+ secondary ions were studied at a given initial energy as functions of the Mg concentration. The experimental procedure was detailed in part I of this study, where the measured Ag+ ion intensity ratio, normalized to pure silver, was found to be in good agreement with the value calculated after adjustment of the ionization probability by surface excitation to the experimental Ag+ ion energy spectrum from pure silver, taking into account the variations of the work function, of the sputtering yield and of the surface binding energy. However, secondary ions of light elements can also be produced by the collisional mechanism, i.e. by Auger de-excitation of excited atoms ejected outside the target with an inner electronic vacancy. In part II, the Mg2+ ion emission is shown to originate from the collisional process only, like the multicharged ionic species from other light elements. Both mechanisms contribute to the Mg+ ion emission and their respective sharing for initial energies between 20 and 400 eV can be deduced from the concentration dependence of the Mg+ ion intensity ratio, if the contribution of the ionization by surface excitation is assumed to be calculable by the same method as that used for Ag+ ions.

Intrinsic emission of secondary ions from silver-magnesium alloys: I. Silver emission

Some Ag-Mg alloys, and pure Ag and Mg samples, were sputtered in ultra-high vacuum with 10 keV Ar+ ions and the emission intensities of monoatomic Ag+, Mg+ and Mg2+ secondary ions were studied at a given initial energy as functions of the Mg concentration. In part I of this study, the Ag+ ion intensity ratio, normalized to pure silver, is measured for initial energies between 5 and 400 eV. The ionization law of Ag atoms was adjusted to the experimental energy spectrum of Ag+ ions sputtered from pure silver, assuming the Ag+ ions to be created by surface excitation, i.e. by electron tunneling during the separation of an outgoing Ag atom from the target. The ratio of the ionization probabilities from an alloy and from pure silver can then be evaluated at every initial energy from the variation of the work function, accurately measured by the shift of the narrow energy spectrum of re-sputtered Ar+ ions. Taking into account the variations of the sputtering yield and of the surface binding energy, the Ag+ ion intensity ratio has been calculated and appears to be in good agreement with the measured value.

Multicharged Secondary Ions from Light Metals (Mg, Al, Si)

Only light metals (Mg, Al, Si) bombarded with noble gas ions in the some keV energy range show a non-negligible emission of true multicharged secondary ions [1]. The few multicharged ions observed from heavy metals at very high bombardment density [2] are in fact mostly created by direct ionization of sputtered neutral atoms by primary ions in the vacuum at some distance from the target [3,4].