High-Density Cascade Effects in Ion-Implanted Ag-Au Alloy
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HIGH-DENSITY CASCADE EFFECTS IN ION-IMPLANTED AG-AU ALLOY
F.
R.
VOZZO*
Physics Department, State University of New York at Albany, Albany, *present address: Naval Research Lab, Washington, DC 20375
NY 12222
ABS TRACT
High-purity, polycrystalline foils of 12 atomic percent gold Ag-Au alloy were implanted with polyatomic ions of arsenic and antimony at energies of 45 keV per atom. During fluence intervals before and after the steady state, sputtered material was collected on high-purity strips of aluminum foil. Subsequent backscattering analysis of the targets and collectors showed that significant redistribution and segregation occurred in the implanted layer, with relative depletion of silver consistently observed. The results suggested that preferentiality in sputtering is dependent on composition of an alloy and the ion beam used (even at low fluence), but there appears to be no major difference between the redistribution behavior of targets sputtered with atomic ions and equal-velocity molecular ions. A model is presented which predicts the sputtering behavior and surface configuration of a binary alloy implanted to steady state with a third species. INTRODUCTION Certain conditions are known to promote preferential loss from the surface of one or more of the original species in an alloy subjected to sputtering. Sputtering and redistribution ultimately determine the final surface composition and the surface properties of implanted alloys. Among the parameters on which redistribution effects depend are the amount of energy available for atomic displacements and the rate of production of mobile defects. High-density collision cascades, readily produced by molecular-ion bombardment [f1 , could be expected to produce changes in preferential sputtering and redistribution behavior accordingly. This paper presents the observed and modelled surface changes in targets of Ag-Au alloy, implanted by a third species to the steady state under conditions of both low and high density of energy in the atomic collision cascades. EXPERIMENT High-purity, (111>-textured polycrystalline foils of silver, gold and 12 atomic percent gold Ag-Au alloy were implanted at normal incidence and at room temperature with monomer, dimer and trimer ions of arsenic and antimony at energies of 45 keV per atom. During fluence intervals before and after the steady state of implantation, sputtered material was collected on high-purity strips of aluminum foil mounted on a cylinder centered about the beam spot. Steady state was determined by monitoring the changes in intensity of light emitted by sputtered neutral atoms [21 . All implants were done in ultra-high vacuum (3 x 10-9 torr). The collection and analysis apparatus is shown schematically in figure 1.
Mat. Res. Soc. SYmP.Proc. Vol.
27 (1984) GElsevier Science Publishing Co., Inc.
182
FOIL HOLDER
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FOIL MASK
BEAM
FIG. 1. Geometry of implantation and sputtered product collection. Sputtering yields and the relative angular distributions of sputtered atoms were determined from
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