Aspects of SIMS Evaluation of Tracer Diffusion and Its Isotope Effect

Tracer techniques are still the dominant experimental approach to the microscopic mechanisms of atomic transport /1/. In today’s “state of the art”, however, in order to extract reliable new information from diffusion measurements one requires a precision considerably above that furnished by conventional instrumentation a decade ago. During recent years, the technique of SIMS has proven its particular usefulness in this freld /2,3/. The tasks include the delineation of very slight curvatures in the Arrhenius plot of diffusion /4,5/. Even higher requirements apply in measurements of the isotope effect of diffusion /1,3/, potentially a very powerful technique for pinpointing atomic mechanisms of diffusion /6,7/. With increasing sophistication of such applications, however, several particular artifacts of SIMS have emerged as non-negligible obstacles. The present paper attempts to discuss the following factors in the evaluation, from in-depth profiles, of diffusion coefficients and particularly of their isotope mass dependence: a)Counting dead-timeb)Assignment of correct time coordinate at each peak countc)Geometry of diffusion profiled)Determination of effective position of specimen surface, x=0 in the profile.