Pre-Thinning for FIB TEM Sample Preparation using the Small Angle Cleavage Technique

Abstract

The Small Angle Cleavage Technique (SACT) can produce samples from brittle and cleavable materials very quickly. It is possible for a skilled person to produce about 10 XTEM specimens in an hour. However, there are materials related limitations to the technique. These include 1) the ductile/brittle nature of the substrate, i.e. the fracture mechanics of the materials, 2) the strength of the interfaces between multi-layers, 3) the thickness of any ductile layers, and 4) the strength of the layer materials. in most of the cases where SACT fails, the sample is near electron transparency at the apex of the sample. Where there is a weak interface as in some multi-layer systems, or where the material itself is weak such as when an evaporated Ge layer is used, some of the film near the substrate is sufficiently thin, but there is a jog in the film stack and further back from the apex it is not transparent. If such a SACT sample is viewed from the surface in an SEM, this apparent delaminating of the top layers is evident and usually within 1 μm of the apex.

The purpose of this paper is to show that the geometry of a SACT-prepared sample is well suited for applying FIB milling for further thinning of the sample to electron transparency. in addition, the FIB can be easily applied to SACT specimens that fail to produce usable samples for the reasons cited above. The SACT method allows two main options for mounting the samples that are illustrated in Fig 1.