Electron microscopy has played an undeniably important role in the development and understanding of new materials. One particular method, plan-view transmission electron microscopy (TEM), has been used to reveal many aspects of materials and to help answer questions that are not accessible by other methods. In planview TEM, materials are studied either by the image contrast caused by diffraction or by direct diffraction analysis. The studies are often at a somewhat lower resolution than is possible with some other electron-based microscopies or, in the case of diffraction, must be interpreted in terms of an average effect. Nevertheless, plan-view TEM is very useful because properties at these intermediate length scales typically determine important materials characteristics. It is plan-view microscopy that gives us the big picture of what is happening in a material.

Until recently, TEM studies of materials have entailed comparing samples taken at various stages of processing and trying to observe and understand the mechanisms that determine the material behavior. With the advent of controllable specimen environments, materials processing has been taken into the TEM, allowing direct observation of the microstructural development. Here we will focus particularly on surface and near-surface processes, such as oxidation.