Measurements of the velocity spectrum of sputtered Na from a NaI target by a Doppler-shift laser spectrometer

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Abstract
By means of a Doppler‐shift laser spectrometer (DSLS) we have measured the energy spectrum of Na emerging from a NaI surface bombarded with He+, Ne+, Ar+, Kr+, and Xe+ ion beams of about 30 μA/cm2 and within an energy range 10–30 keV. The measured spectra consist of a thermal and a high‐energy contribution, the relative intensities of which strongly depend on the mass of the bombarding ions. The sputter mechanism can be explained by formation of so‐called excitons in the bulk and by the random collision cascade theory. Furthermore, selective sputtering of I in the case of Kr+ and Xe+ bombardment must be taken into account. The use of the DSLS yields a good signal‐to‐noise ratio even for particle densities less than 100 particles/cm3 within a velocity interval Δv=50 m/sec. The velocity resolution achieved was 50 m/sec in the energy region up to 1 eV and 1% in the high‐energy region.