A sample preparation technique for cross-sectional AEM of thin films on hard materials

Abstract

Hard materials such as tungsten carbides which contain ceramic protective coatings (from 30 nm to several microns in thickness) present unique electron-transparent sample preparation challenges for TEM observations. A cross-sectional sample would allow one to observe the coating, matrix and related interface between the two. Variations in the hardness as well as differences in the compositions of the coating and substrate make this preparation more difficult. Discs of the material cannot simply be core drilled out and mechanically or ion beam prepared since it is the surface or edge of the material containing the coating which must be retained. Ion milling also causes preferential removal of one phase in relation to others leaving a sample which is not uniformly thin or truly representative of the microstructure. A preparation technique used for many semiconductor materials involves gluing together pieces with surface layers or coatings thus forming a stack which can be further processed to yield thin, electron transparent specimens.