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Emission distribution, brightness, and mechanical stability of the LaB6 triode electron gun

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2 Author(s)
Gesley, Mark ; IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 ; Hohn, Fritz

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Experiments have characterized the operation of a LaB6 triode gun in a standard three‐lens column of the type used for Gaussian electron‐beam lithography and scanning electron microscopy. A series of images representing cross sections of the three‐dimensional spatial distribution of current emitted from the gun is obtained by configuring the electron optics as a scanning confocal microscope. The gun acts as an immersion objective whose image is scanned by deflection coils and focused by the condenser lenses onto a pinhole transmission detector. Characteristics of the emission distribution include an emission image of the cathode surface situated between two distinct beam crossovers whose origin is either the apex (001) and {310} planes or the large {110} planes on the machined 90° cone angle of the cathode surface. Virtual objects are imaged when the back focal plane of the condensers falls inside the high‐field region of the gun. The target axial brightness is dependent on gun excitation and angular acceptance angle. The temperature‐dependent brightness of the cathode is used to determine its effective emission area, work function, and surface electric field. Beam positional stability of three‐carbon‐mounted LaB6 directly heated cathodes is measured. However, for measurement times ≤100 h the drift rate is found to be limited by thermal expansion of the movable anode assembly and not the particular cathode mounting technique.

Published in:

Journal of Applied Physics  (Volume:64 ,  Issue: 7 )

Date of Publication:

Oct 1988

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