Electron microscope (comprising an auxiliary lens)

#The invention relates to an electron microscope, comprising an electron source, a condenser lens, an objective lens, and a switching device for selection of TEM or STEM operation.

#Contemporary electron microscopes are usually constructed so that operation in the transmission mode (TEM) as well as in the scanning transmission mode (STEM) is possible. Known electron microscopes of this type have the drawback that either the switching between the two modes as such is complex and time-consuming (for example, the excitation of the condensor lens must also be changed) or that the operation in one of the two modes is subject to restrictions (for example, because an excessive part of the imaging electrons is intercepted by the lens system, so that optimum magnification cannot be utilized or in that too little free space is available) so that full detection of the information produced cannot be achieved.

#The invention has for its object to eliminate these drawbacks; to this end, an electron microscope in accordance with the invention is characterized in that an auxiliary lens which is arranged between the condensor lens and the objective lens forms part of the switching device.

#Preferred embodiments in accordance with the invention will be described in detail hereinafter with reference to the accompanying drawings in which:

#FIG. 1 is a diagrammatic sectional view of an electron microscope;

#FIG. 2 is a diagrammatic sectional view of an objective lens, including an auxiliary lens, for the electron microscope of FIG. 1.

#An electron microscope as shown in FIG. 1 comprises an electron source 1 with an anode 2, a beam alignment system 3 and an aperture 4, a condensor system comprising a first condensor lens 5, a second condensor lens 6, and a condensor aperture 7, an objective comprising a first objective pole 8 and a second objective pole 9, a beam scanning system 10, an object space 11, a diffraction lens 12 with a diffraction aperture 13, an intermediate lens 14, a projection system with a first projection lens 15 and a second projection lens 16, a film camera 17 and a viewing screen 18. All these parts are accommodated in a housing 20, comprising an electrical input lead 21 for the electron source and a window 22. An optical viewer 23, a vacuum pumping device 24, and a plate camera 25 are connected to the housing.

#In the described electron microscope, an auxiliary lens 30 is included in the objective lens in accordance with the invention together with an associated power supply 39a and reversing switch 39b. Switch 30b functions to reverse the polarity of current flow in the auxiliary lens 30. The objective lens with auxiliary lens will be described in detail hereinafter with reference to FIG. 2.

#FIG. 2 is a sectional view of an objective lens, comprising two poles 8 and 9 as shown in FIG. 1. The part 8, being the pole of the objective lens which is situated nearest to the condensor, comprises beam deflection coils 31 and 32 whereby an axial electron beam can be deflected in two mutually perpendicular directions, so that a specimen 34 can be scanned, for example, in a raster-like manner.