TABLE OF CONTENTS To allow observation in different brands or models of microscope, TEM specimens are always made circular with a diameter of 3 mm. Perpendicular to this disk, the specimen must be thin enough (at least in some regions) to allow electrons to be transmitted to form the magnified image. The specimen stage is designed to hold the specimen as stationary as possible, as any drift or vibration would be magnified in the final image, impairing its spatial resolution (especially if the image is recorded by a camera over a period of several seconds). But in order to view all possible regions of the specimen, it is also necessary to move the specimen horizontally over a distance of up to 3 mm if necessary.
The design of the stage must also allow the specimen to be inserted into the vacuum of the TEM column without introducing air. This is achieved by inserting the specimen through an airlock, a small chamber into which the specimen is placed initially and which can be evacuated before the specimen enters the TEM column. Not surprisingly, the specimen stage and airlock are the most mechanically complex and precision-machined parts of the TEM. There are two basic designs of the specimen stage: side-entry and top-entry.
In a side-entry stage, the specimen is clamped (for example, by a threaded ring) close to the end of a rod-shaped specimen holder and is inserted horizontally through the airlock. The airlock-evacuation valve and a high-vacuum valve...
