Molecular ejection from low temperature sulfur by keV ions

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Experimental results on the molecular species ejected from condensed S 8 at low temperatures by 10–60 keV H +, He +, N +, Ne +, Ar +, Kr +, and Xe + are presented. Net erosion rates and mass and energy spectra of the ejected species were measured. The net surface erosion rate measured at 15 K was found to exhibit two distinct regimes. For the heavier ions starting with N + the sputtering yield increased linearly with the collisional energy deposited at the surface. For incident keV H + the sputtering yield was determined by electronic excitations and when combined with MeV He + data exhibited a roughly quadratic dependence on the electronic stopping power. For keV He + the expected contributions to the yield from electronic and collisional energy deposition were comparable. The mass spectra for the ejected sulfur species S i , i = 1–8, by incident 34 keV Ne +, Ar +, Kr + and Xe + showed that, whereas the overall yield was nearly linear in the energy deposited at the surface, the relative yields of each molecular species varied from linear for the smallest, S 1 and S 2, to nearly quadratic for S 8, S 4 was the only exception to this trend. Its dependence on the surface deposited energy was also nearly quadratic indicating that it came predominantly from vibrationally dissociated S 8. Correcting the mass spectrometer signal to account for various instrumental sensitivities, we found that ∼ 66% of the total yield corresponded to S 2 ejection. The ejected molecule energy spectrum for S 1 had the usual 1/ E 2 dependence at higher energies (∼ 1 eV) associated with the linear cascade model but S 2, S 3, and S 5 fell off more rapidly with increasing energy. These results are compared to previous measurements of sulfur sputtering and discussed in terms of current ideas concerning the sputtering of monatomic and multicomponent targets.