The mechanism of nitrogen transport has been investigated in an austenitic
stainless steel (AISI 304) under high flux and low energy nitrogen ion beam
irradiation at moderate temperatures in the range 270-550 degreesC, The pr
ofiles of the distribution of nitrogen have been analyzed with nuclear reac
tion analysis (NRA) and glow discharge optical spectroscopy (GDOS), and the
surface roughness with scanning AFM. The modeling is based on the study of
the stochastic mixing of atoms 'ballistically' displaced by incident ions.
The development of surface roughness and the formation of an altered layer
highly enriched by nitrogen are analyzed, and it is concluded that the tra
nsport of nitrogen into the bulk results from a flux of matrix atoms driven
by mobile vacancies at temperatures above 350 degreesC. This behavior is c
onsistent with an altered layer 'growth' that is controlled by the ion-beam
-induced displacements of surface atoms. (C) 2001 Elsevier Science B.V. All
rights reserved.