Sharpening of field-ion specimens and positioning of features of interest by ion-beam milling

Abstract

Atom-probe field-ion microscopy is a powerful technique used to study microstructural features such as precipitates and grain boundaries. However, the amount of material which can be analyzed in a field-ion specimen is usually limited by the blunting effects of field evaporation. This limitation can be overcome by the use of ion-beam milling to resharpen field-ion specimens blunted by evaporation. In addition, ion-beam milling allows the positioning of features of interest in the apex region of electropolished field-ion specimens. Ion milling has been found to proceed in two stages. Stage I is a radius-reduction stage during which there is only limited removal of material directly from the apex region, but the radius of curvature at the apex is reduced. Stage II milling occurs after some sharpening of field-ion specimens has taken place and results in a more rapid translation of the specimen apex position with respect to features in the sample. The rate of material removal along the specimen axis direction depends on the specimen shank angle.