It was recalled that the use of the square-root-of-time solution to the diffusion equation that was associated with a linear temperature ramp had recently been proposed as a convenient means for determining bulk diffusion parameters by surface segregation. An exact solution was given here for diffusion problems involving a time-dependent diffusion coefficient, together with some simple approximations for the case of a linear temperature ramp. The time-constant for the establishment of equilibrium between the first and second atomic layers was given, as well as an estimate of the temperature at which this equilibrium would be established during temperature ramping. The condition for a vanishing concentration in the second layer was considered, and its range of validity was estimated.

I.Jager: Surface Science, 1996, 366[1], 166-76