Physical Principles of Electron Microscopy: An Introduction to TEM ...

The Transmission Electron Microscope 77
One disadvantage of the side-entry design is that mechanical vibration,
picked up from the TEM column or from acoustical vibrations in the
external air, is transmitted directly to the specimen. In addition, any thermal
expansion of the specimen holder can cause drift of the specimen and of the
TEM image. These problems have been largely overcome by careful design,
including choice of materials used to construct the specimen holder. As a
result, side-entry holders are widely used, even for high-resolution imaging.
In a top-entry stage, the specimen is clamped to the bottom end of a
cylindrical holder that is equipped with a conical collar; see Fig. 3-11b. The
holder is loaded into position through an airlock by means of a sliding and
tilting arm, which is then detached and retracted. Inside the TEM, the cone
of the specimen holder fits snugly into a conical well of the specimen stage,
which can be translated in the (x and y) horizontal directions by a precision
gear mechanism.
end-stop
specimen
(a) Side-entry stage
specimen
highvacuum
valve
specimen holder
specimen loading rod
movable
stage
top of objective lens
specimen holder
airlock
airlock
(b) Top-entry stage
Figure 3-11. Schematic diagrams of (a) a side-entry and (b) a top-entry specimen holder.