In-situ atom probe specimen preparation with a planar region of interest

Abstract

Techniques for rapid preparation of atom probe specimens extracted from the surface of a bulk crystal sample are further developed with regards to samples having a planar region of interest. An atom probe specimen is a needle-shaped structure several microns long and approximately 100 nm in diameter. The conventional method for preparing these specimens maintains the sample orientation throughout the process of extracting sample segments from the bulk crystal, mounting them onto microtips, and shaping them into specimens. For samples having a planar region of interest parallel to the surface, that method produces a small disc-shaped region of interest oriented perpendicular to the specimen axis (horizontally). If the planar region of interest of the sample is composed of atoms susceptible to migrating along the curved surface of the specimen tip during atom probe tomography, this horizontal orientation makes it difficult to quantify and account for any such surface migration. By reorienting the sample with a 90 degree rotation, specimens were produced with the planar region of interest oriented parallel to the specimen axis. This vertically oriented plane is up to 5 times larger than the horizontally oriented planes produced with previous specimen preparation methods. According to the model of field driven surface migration proposed herein, this orientation also makes it possible to quantify and account for surface migration leading to more accurate atom probe data.