Metal matrix composite (MMC) materials are promising materials because of their higher specific mechanical properties (e.g. strength-to-weight ratio) relative to conventional metallic alloys. However, during the processing of these materials, the development of an interfacial reaction zone between the reinforcing material (generally a ceramic) and the metallic matrix may occur, which typically degrades the mechanical properties of these materials if not controlled. Since these interfaces are generally quite small (from 5 to 500 nm), Transmission Electron Microscopy (TEM) is the technique of choice for characterization because of its outstanding spatial resolution. However, specimen preparation for TEM (e.g. ion milling) is quite difficult for MMC materials, due to the combination of two completely different material types, specifically a hard and brittle reinforcement phase incorporated in a relatively soft metallic matrix. Also, since there is only a small amount of the material which is transparent to electrons after specimen preparation, TEM as a materials characterization technique suffers from a lack of statistical robustness, which is a serious drawback.
To characterize materials with a spatial resolution close to that of TEM, low voltage field emission scanning electron microscopy is an option because of the small interaction volume of low energy electrons, as well as the small probe size of these microscopes (typically < 5 nm).