Specimen Preparation Techniques for Scanning Electron Microscopy

Abstract

It is well known that the Scanning Electron Microscope, hereafter to be known as the SEM, provides an apparent 3-dimensional view of the subject. The contrast, or shading, in the picture is a function of the surface topography, and the apparent overall sharpness of the picture is because of the large depth of focus. The reasons for these are not necessary for this paper, but it is very important to constantly keep in mind that the finished picture is an artifact that either looks like the subject in reality or not, depending upon the viewer’s prior knowledge of the subject. If the viewer has no prior knowledge, he must prepare the specimen in such a manner that he can manipulate it in the SEM so as to be able to build up a mental picture of the subject. It is the very fact that the SEM picture so often looks like something we recognize from the real world that causes us to make some serious misinterpretations about the actual nature of the object in the scanner. For a practical solution to the above problem, it is possible to make stereo pairs in the SEM or, more crudely, to rapidly change the angle of viewing or the rotation and thus come to a mental conclusion about what is under the electron beam.