Airlocks have many applications in EM systems due to different reasons, for instance, as listed below:
i) Specimen airlock in EM systems is normally evacuated by a separate line from a mechanical pump (called pre-pumping). The operator changes specimens, and accesses electron sources and photographic plates through airlock systems. For instance, the specimens are always inserted through an air lock to prevent loss of vacuum in the TEM column or SEM chamber. In this case, the airlock avoids the need to ventilate the entire column in order to insert a specimen. In most systems, the specimen holder is inserted into the airlock entry and is slid in until stop. At this stop, pre-pumping of the airlock commences, for instance, once the PUMP/AIR shown by the airlock indicator in Figure 2699 is switched to pump. When the pre-pumping is done, the green light will be turned on automatically, and then the holder can slide into the groove in the airlock by vacuum if it is slightly turned.
Figure 2699. PUMP/AIR switch on JEOL 2100 TEMs.
ii) The steady emission current of the electron gun may change to a different steady current if the filament is switched off and on. Therefore, the filament should always be left on even when the TEM specimens or recording film is changed. This requirement needs pre-pumped airlocks between the electron gun and EM column and between the TEM column and film chamber which are common in modern electron beam equipments.