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

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.