ELECTRON MIKHOK >IICROSCOPY 



Lorcntz force, which stems from the radial in the center, while patterns of other origin 

 component of the electron's velocity, has the will remain the same or may in many cases 

 same direction at a given object area for ap- become even more contrasty and detailed, 

 proaching as well as receding electrons. This A second criterion for distinguishing mag- 

 radial component will be very small most of netic patterns from those of electrical or re- 

 the time, but immediately in front of the lief origin is most convenient experimentally, 

 mirror-specimen it will generally })ecome It requires the shifting of the pattern in 

 predomhiant, making possible its utilization question through the electrical center to the 

 for image and contrast forming in the mag- opposite side of the viewing screen, an opera- 

 netic case. tion which must result, if the pattern is mag- 

 Image contrast formation in the magnetic netic, in a reversal of the brightness of the 

 case is therefore more complex than in the border lines, i.e., dark border lines must be- 

 other cases; yet this difference provides the come bright and the bright must become 

 criteria which permit the discrimination of dark. 



magnetic patterns from those of other origin, Radial extensions of magnetic pattern ele- 

 a possibility which is of great value for the ments are depicted as more contrasty than 

 practical applications of this novel research those which extend azimuthally. This is in 

 tool. In the magnetic case of electron mirror itself a third criterion if the pattern contains 

 microscopy image contrast-forming deflec- preferred directions azimuthally as w-ell as 

 tion is caused by that component of the radially. If this is not the case, it can still be 

 Lorentz force which stems from the radial used as a third criterion by rotating a pat- 

 component of electron velocity and that tern in such a way as to let the pattern con- 

 component of the magnetic field which is figuration extend preferentially in the radial 

 normal to the plane of the mirror-specimen, direction first and then in the azimuthal di- 

 The sensitivity of electron mirror micros- rection. In the first position the pattern, if 

 copy for magnetic fields is zero at the electri- it is magnetic, will be much more contrasty 

 cal center of the mirror-specimen. (The elec- than in the second position. If one lets elec- 

 trical center is defined as the location on the trons impinge on the electrical center of the 

 specimen plane where the radial velocity of specimen, the image content is lost within 

 the electrons becomes zero or, in practical the area of impinging electrons. The electrons 

 terms, where the electrons first impinge if reflected there, either elastically or as see- 

 the negative bias of the specimen is de- ondary emission, are scattered, thus having 

 creased.) With increasing distance from this lost their predetermined definite direction, 

 electrical center, the magnetic sensitivity This fact then makes the proper kind of 

 increases. image formation of electron mirror micros- 

 To obtain high magnetic sensitivity, a copy impossible, as it is based on a point-to- 

 shift of the electrical center to the border of direction correlation rather than a point-to- 

 the viewing area or even outside is therefore point correlation. 



advantageous. To utilize this advantage one The shape of the spot representing the 

 must, of course, decrease the negative bias of area w^here the electrons impinge will gener- 

 the specimen to permit sufficiently deep elec- ally be circular in the nonmagnetic cases of 

 tron penetration into the magnetic fields electron mirror microscopy. If in the mag- 

 under observation. Shifting of a pattern into netic case, however, magnetic field compo- 

 the electrical center, therefore, is one possible nents are present which are parallel to the 

 criterionfor distinguishing magnetic patterns plane of the mirror-specimen, the shape will 

 from others. If the pattern under considera- be deformed and the spot representing the 

 tion is magnetic in origin, it must disappear impinging electrons will become displaced. 



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