Near-surface segregation during ion-beam modification
The thermodynamic basis for equilibrium surface segregation was formulated by Gibbs in the previous century. Several additional, nonequilibrium driving forces for segregation manifest themselves during ion irradiation. Because large numbers of excess point defects are created, one effect of irradiation is simply to enhance the rate at which Gibbsian surface segregation approaches equilibrium. In addition to this radiation-enhanced diffusion (RED), there exist at least four other kinetic effects that can alter the near-surface composition of an alloy during irradiation: implantation, preferential sputtering, displacement mixing, and radiation-induced segregation (RIS). The altered layer produced in the near-surface, ion-implanted region is driven to substantially greater depths at elevated temperatures by RED and RIS. Theoretical modeling of the compositional changes beneath the implanted layer is simplified because only these two processes operate there. Actual RED coefficients have been extracted from measurements in this region. The compositional change due to RIS has also been observed at great depths in the specimen. Radiation-induced segregation is significantly more effective than RED at producing compositional changes very deep in the target. This greater effectiveness may prove beneficial in practical applications of ion-beam surface modification.
- Research Organization:
- Argonne National Lab., IL (USA)
- OSTI ID:
- 6881703
- Report Number(s):
- CONF-8711195-; TRN: 88-028821
- Journal Information:
- Trans. Am. Nucl. Soc.; (United States), Vol. 55; Conference: American Nuclear Society winter meeting, Los Angeles, CA, USA, 15 Nov 1987
- Country of Publication:
- United States
- Language:
- English
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