Sputtering from energetic self-ion cascades

Abstract

The rather high primary recoil energies that occur under 14 MeV neutron irradiation can be simulated by self-ion bombardment. However, the primary ion always starts at theentrance surface when self-ion bombardment is used. To examine the effects of cascades in which the momentum of the primary atom is directed towards an exit surface, one has to introduce a second surface that will intersect the cascade in the forward direction. Self-ion transmission sputtering on very thin films has been used for this purpose. The analysis was done in situ by He + backscattering. A backsputtering yield of 120 atoms/ion was observed at 540 keV. At the same energy a forward sputtering yield of 70 atoms/ion is obtained for a film of 660 Å in thickness. These yields are in order of magnitude agreement with theoretical estimates, however, the results seem to indicate that collective and lattice effects play a significant role. It was observed that a tensile stress is built up in the films during irradiation, leading to flattening and rupturing of the film along preexisting faults.