For the last thirty years, ion milling has been an indispensable part of preparing TEM specimens in the physical sciences. While great improvements have been made in our ability to thin most materials to the point where ion milling may not be a requirement, there will still be a need to utilize ion milling to clean and polish specimens and to provide small amounts of incremental thinning as needed. Thanks mainly to the work of Bama we now understand a great deal about the physics of ion milling. We also benefit from the works of a number of investigators who have studied the artifacts produced by ion milling (see Barber for a review).Ion milling is a subset of the topic “dry etching,” which consists of two major categories: glow discharge methods and ion beam methods. Glow discharge methods include plasma etching, reactive ion etching, and glow discharge sputter etching. These techniques have little application in TEM specimen preparation aside from surface cleaning. The reactive ion etching literature is a source for suggesting gas/specimen combinations to perform chemically-assisted ion beam etching (CAIBE), to be discussed below. The other major dry etching category, ion beam methods, includes ion milling, reactive ion beam etching, and CAIBE.
