Scanning Microscopy


The mass effect of diffusion is of interest in connection with interactions between defects and impurities and with the mechanisms of atomic displacements in the condensed states. The delineation entails the precise measurement of the isotope ratio as function of tracer concentration, varying within several orders of magnitude along the diffusion profile. The measurement by SIMS (secondary ion mass spectrometry), using stable isotopes, has proved to possess advantages compared to familiar techniques with radiotracers. However, the aims require the utmost counting economy and optimal precision available in SIMS, including the control of the mass fractionation and of some features peculiar to cyclic profiling. Very good results have been obtained for the isotope effect at relatively deep profiling, where step scan analysis can be effected. For more shallow profiles, requiring head-on sputtering, more serious artifacts are encountered and the error margins have hitherto been relatively high. The paper discusses salient experimental points of the determination by SIMS of the isotope effect at different diffusion geometry, and briefly reviews the hitherto obtained results.

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