Contribution of singly and doubly ionized argon to the autoionization (Auger) spectrum of argon excited by bombardment of magnesium and scandium surfaces

Electron spectra produced by bombarding targets of Mg and Sc using argon ions accelerated through potentials between 300 V and 5 kV are reported for different electron energies in the ionizer box of a hot filament type ion gun. By suitable choice of ionizer energy, beams of Ar+ and beams of mixed Ar+ and Ar2+ ions could be produced. It is shown that Ar+ and Ar2+ ions can both give rise to similar argon Auger spectra but the behaviour of the intensities of the Auger peaks differs with the ionic species. In the case of excitation by Ar+ ions no spectrum is visible below a threshold energy (280 eV for Sc, 2.8 keV for Mg) but beyond threshold the size of the Auger peak increases with ion energy. With Ar2+ excitation no threshold was observed down to the lowest accelerating potential used and the Auger signal was found to decrease with increase in ion energy. This behaviour is consistent with two different mechanisms being responsible for the Ar** state which initiates the autoionization process.

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