Experimental evidence for slight mass dependence of the final damage state due to energetic ions

Abstract

Single crystals of Mo were bombarded with ⁸⁶Kr, ^2ONe, ¹¹B, ⁴He, and ¹H in such a manner that the energy deposited into elastic collisions (displacement events) in the near surface region was approximately equal for each implant. The ion fluences spanned more than two orders of magnitude, and the resulting damage level at each fluence was monitored by obtaining aligned backscattered (channeling) spectra in a <111> axial direction. As an additional check on the channeling results selected implants were also examined with TEM. The channeling experiments clearly show that the final damage state, at all fluences, for ⁸⁶Kr and ^2ONe is the same. At low fluences, the final damage state for ^8RKr, ^2oNe, ¹¹B, and ⁴He appears to be the same, but for high fluences there are unresolved difficulties with the ¹¹B and ⁴He channeling results.

TEM examinations indicate that there are no gross microstructural differences for ⁸⁶Kr, ^2ONe, and ¹¹B and only moderate differences for ⁴He. Both channeling and TEM indicate a qualitative difference in the final damage state for 0.2 MeV ¹H bombardments as might be expected from the fact that the 0.2 MeV ¹H PKA spectrum is too soft to generate many cascades. However, for 2 MeV ^lH more energetic knock-on-atoms are created in the near surface region leading to a microstructure which begins to resemble that of the heavier ions.