Electron mirror microscopy 



In electron mirror microscopy the elec- 

 trons do not penetrate the specimen as they 

 do in conventional electron transmission 

 microscopy nor do they originate from the 

 specimen as they do in the different cate- 

 gories of electron emission microscopy. In 

 electron mirror microscopy the electrons are 

 not reflected by the material of the speci- 

 men, as in conventional electron reflection 

 microscopy, but are reflected without any 

 scattering at the equipotentials in front of 

 the specimen. 



The characteristic feature of an electron 

 mirror microscope is an electron optical mir- 

 ror playing a dual role. The mirror serves as 

 an electron optical element and simultane- 

 ously constitutes the specimen. In general, 

 the mirror-specimen remains untouched by 

 the image-forming electrons because the 

 specimen, being an electron optical mirror, is 



C G L N S B, B 



EO M 



H B, B2 EO M 



Fig. 1. Schematics of two design versions of 

 electron mirror microscopes. 



biased slightly negative with respect to the 

 source of the electrons, that is with respect 

 to the cathode. The electrons approaching 

 the mirror-specimen are slowed down to 

 zero axial velocity shortly before reaching it 

 and then reverse their direction of motion. 

 Any irregularity on the mirror-specimen 

 capable of deflecting the approaching and 

 receding electrons will modify the spatial 

 density distribution of the returning electron 

 beam. This returning electron beam, there- 

 fore, carries back information about the dis- 

 tribution of the irregularities it encountered 

 during the time it was close to the mirror- 

 specimen. Electron mirror microscopy uti- 

 lizes the fact that such information can be 

 presented on a phosphorescent screen as a 

 magnified, visually observable image of the 

 distribution of the electron-deflecting irregu- 

 larities on the mirror-specimen. 



The specific design characteristics dis- 

 tinguishing an electron mirror microscope 

 from other types of electron microscopes 

 stem from the introduction of an electron 

 optical mirror and its dual function. The 

 reversal of the electron beam on the equi- 

 potentials in front of the mirror specimen 

 poses the problem of either magnetically 

 separating the incoming, illuminating elec- 

 tron beam from the outgoing image-carry- 

 ing beam or tolerating the inconveniences of 

 a simpler straight design in which the axes 

 of both beams remain identical. 



Figure 1 shows simplified schematics of 

 these two possible design versions of elec- 

 tron mirror microscopes. The one version 

 (la) uses the straight design (1) in which the 

 two beams are not separated. The incoming 

 illuminating electron beam Bi originating 

 from a cathode C in an electron gun G and 

 coUimated by an electron lens L is shot 

 through a small neck N located in a hole in 

 the center of the viewing screen S. After 

 traversing the electron optical system EO 



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