Chapter Four - Atom Probe Sample Preparation

Abstract

The drastic improvement of micromanipulation, microwelding, and ion beam milling in scanning electron microscopy (SEM) has accompanied the development of atom probe tomography (APT) since 2000. The use of subpicosecond laser, the large field of views, and the rapid acquisition rates of APT have since opened new fields of application of this technique. Looking for a needle in a haystack has now become a routine experiment for APT users thanks to the combination of SEM imaging techniques (eg, transmission Kikuchi diffraction, electron backscattered diffraction, and secondary electron and backscattered electron imaging), focused ion beam–induced deposition, micromanipulation, and focused ion beam (FIB) milling. The aim of this chapter is to describe the standard methods of specimen preparation for APT. The first part briefly introduces the principles of sample preparation by electrochemical polishing and its limitations. The second and main part of this chapter introduces applications of FIB milling to APT sample preparation. Fundamentals of FIB technology and principles of SEM imaging are briefly introduced. The effect of FIB milling on the specimen structure is discussed based on simulations. Ways to preserve the specimen structure (by means of capping layer, annular milling, and low beam energy) are described. The most widely used procedures for sample preparation by FIB are then introduced (ie, the lift-out method, cross-section, and backside preparation) and attention is paid to site-specific analysis, which is enabled by the use of SEM-FIB.