In Situ Focused Ion Beam Redeposition Surface Coatings for Site-Specific, Near-Surface Characterization by Atom Probe Tomography.

Abstract

Atom probe tomography (APT) enables three-dimensional chemical mapping with near-atomic scale resolution. However, this method requires precise sample preparation, which is typically achieved using a focused ion beam (FIB) microscope. As the ion beam induces some degree of damage to the sample, it is necessary to apply a protective layer over the region of interest (ROI). Herein, the use of redeposition, a (frequently considered negative) side effect of FIB sputtering, is explored as a technique for targeted surface coatings in site-specific, near-surface APT investigations. In addition, the concept of "self-coating" is presented, which is the application of a capping layer using material from the same, or a similar, sample. It is shown to provide a pathway for high-quality coatings, as well as a method of minimizing the field evaporation threshold difference at the cap-sample interface, thus greatly reducing the likelihood of premature fractures. In situ redeposition surface coatings are shown to be versatile, with four materials used in the coating and analysis of two Si-based semiconductors and a Fe-Mn alloy. Several factors are discussed, such as the specimen yield, the capping layer quality, and the ease of ROI identification, all of which demonstrate its effectiveness in routine sample preparation workflows.