A Investigation of Sputtering and Secondary Ion Emission from Polycrystalline Metal Foils Under Mev Heavy Ion Bombardment.

In these experiments, sputtering and secondary ion emission from metals have been studied during MeV heavy ion bombardment. One purpose of the measurements was to determine if the ejection of the sputtered particles was consistent with a collisional description of the sputtering process. Another purpose was to determine if the large electronic excitation of the sample during the high energy irradiations would result in patterns of secondary ion emission that were significantly different from those observed during keV ion bombardments. During the investigation, three analytical techniques were used: secondary ion mass spectrometry, secondary ion energy spectrometry, and total sputtering yield measurements. The mass spectrometric measurements consisted, in part, of a comparison of positive secondary ion emission during 100 keV ('40)Ar('+) and 70 MeV ('79)Br('7+) ion bombardment of several targets. The results of these measurements demonstrated that the MeV projectiles were substantially more efficient in producing positive secondary ions of electronegative surface constituents. To supplement these observations, the variation of ion emission from Al, V, and Y surfaces was measured as a function of ('79)Br projectile energy. In these measurements, it was observed that the emission of Al('+) and V('+) secondary ions was roughly proportional to the nuclear stopping cross section for Br in the targets. Measurements of integrated secondary ion energy spectra were obtained from Cu, Nb, and Ta foils during 75 MeV ('79)Br('8+) ion bombardment. The energy distributions were observed to peak at about 2 eV. This result is consistent with the conclusion that the energy spectra are dominated by non-metallic secondary ions. Total sputtering yields were obtained from Nb and Y targets during 70 MeV ('79)Br('7+), 100 keV ('40)Ar('+), and 100 keV ('79)Br('+) bombardment. The yields for the 70 MeV projectiles were 0.14 (+OR-) 0.03 and 0.14 (+OR -) 0.04 for Nb and Y, respectively. In both cases, the measured yields are consistent with the predictions of collision cascade theory. This consistency indicates that collisional sputtering is the dominant mechanism for the sputtering of metals during high energy projectile bombardments. The observations that the yields of Al('+) and V('+) are proportional to the nuclear stopping cross sections indicate that these ions were also produced as a result of a collision cascade. (Abstract shortened with permission of author.).