Impact of directional walk on atom probe microanalysis

In the atom probe microanalysis of steels, inconsistencies in the measured compositions of solutes (C, N) have often been reported, as well as their appearance as molecular ions. Here we propose that these issues might arise from surface migration of solute atoms over the specimen surface. Surface migration of solutes is evidenced by field-ion microscopy observations, and its consequences on atom probe microanalysis are detailed for a wide range of solute (P, Si, Mn, B, C and N). It is proposed that directional walk driven by field gradients over the specimen surface and thermally activated is the prominent effect.

► Directional walk affects a wide range of solute species in the atom probe microanalysis of steel.
► It primarily affects interstitial elements, but has also been observed for substitutional (Si).
► The influence of experimental parameters such as base temperature and pulsing mode are discussed.