Transmission Kikuchi diffraction mapping induces structural damage in atom probe specimens

TL;DR

This study demonstrates that transmission Kikuchi diffraction (TKD) mapping can induce structural damage in atom probe tomography specimens, leading to artefacts in compositional analysis, especially due to energetic electron recoil effects.

Contribution

It provides the first evidence of TKD-induced damage in atom probe specimens and elucidates the damage mechanism involving surface species and electron recoil effects.

Findings

TKD mapping causes detectable damage in APT specimens.

Damage results in artefacts like solute segregation and void formation.

Recoil from energetic electrons implants surface species, damaging the structure.

Abstract

Measuring local chemistry of specific crystallographic features by atom probe tomography (APT) is facilitated by using transmission Kikuchi diffraction (TKD) to help position them sufficiently close to the apex of the needle-shaped specimen. However, possible structural damage associated to the energetic electrons used to perform TKD is rarely considered and is hence not well-understood. Here, in two case studies, we evidence damage in APT specimens from TKD mapping. First, we analyze a solid solution, metastable \b{eta}-Ti-12Mo alloy, in which the Mo is expected to be homogenously distributed. Following TKD, APT reveals a planar segregation of Mo amongst other elements. Second, specimens were prepared near {\Sigma}3 twin boundaries in a high manganese twinning-induced plasticity steel, and subsequently charged with deuterium gas. Beyond a similar planar segregation, voids containing a high concentration of deuterium, i.e. bubbles, are detected in the specimen on which TKD was performed. Both examples showcase damage from TKD mapping leading to artefacts in the compositional distribution of solutes. We propose that the structural damage is created by surface species, including H and C, subjected to recoil from incoming energetic electrons during mapping, thereby getting implanted and causing cascades of structural damage in the sample.