Abstract: In an electron microscope it is sometimes important that specimens can be studied at a very low temperature (for example, that of liquid helium). In the case of known specimen holders the specimen is cooled by supplying the cooling medium via a bore in the specimen holder; this causes thermal drift of the removed specimen holder each time when a specimen is exchanged, and also an acoustic coupling (i.e. transfer of vibrations) exists with the dewar vessel connected to the specimen holder. In accordance with the invention, the specimen is arranged on the end 20 of the specimen holder 7 by means of a separate transport unit 13, 36 so that it is not necessary to remove the specimen holder 7 in order to exchange a specimen, with the result that the specimen holder is not heated. Moreover, the coupling to the cold source 22, 28 can take place via a flexible cooling conduit 30 which extends directly to the end 20 to be cooled and may be permanently connected thereto, thus avoiding the transfer of vibrations.

Abstract: For the selection of a pure electron beam or ion beam from a mixed beam, use is made of a combined electrostatic/magnetic deflection system, the electrostatic deflection system being formed, for example, by a tilted electrode system of a cascade system of electrodes present in the apparatus. The pure beam is directed onto an object to be irradiated as near to the object as possible in order to prevent renewed mixing.