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The response of the point defect and antistructure systems to ion beam irradiation is investigated using methods of linear response on thin single crystals of ordered Cu3Au grown by molecular beam epitaxy. We demonstrate that antisite evolution, as measured by electrical resistance, quantitatively determines both the defect populations and diffusion in the irradiation field, and we explore new linear and nonlinear response processes as the antistructure system is driven from equilibrium.

Thermal and radiation-enhanced diffusion in thin films of the order-disorder alloy Cu{sub 3}Au have been analyzed above and below the transition temperature. It is demonstrated that thin films grown by molecular beam epitaxy are uniquely suited for such experiments as the surface provides a dominant and well-characterized sink for migrating defects. The analysis is applied to recent experiments. Quantitative predictions of radiation-enhanced diffusion agree closely with experimental values. Analysis of the tracer-impurity thermal diffusion experiments provide host diffusion coefficients in a temperature regime through the transition temperature which were heretofore unavailable. {copyright} {ital 1999} {ital The American Physical Society}