Research Article|
November 10 2003
Electron Gun Using a Field Emission Source
Rev Sci Instrum 39, 576–583 (1968)
Article history
Rev Sci Instrum 39, 576–583 (1968)
A new electron gun has
been built which features mechanical and optical simplicity.
Theoretically, it can produce a focused spot having a radius smaller
than 50 Å and provide 1000 times more intensity than a hot filament
system having a similar final spot size. The increase in intensity is
made possible by using a field emission electron source operating at a
pressure of 10−9 Torr, which is provided (without baking)
using commercially available pumps. The small spot is produced by using
two properly shaped electrodes which accelerate and focus the electrons
from the tip. It would take a hot filament gun and at least two
additional lenses to replace this field emission gun when a spot radius
less than 100 Å is required. Even then the brightness of the
conventional source would be too low to make use of the small spot size
obtained. The optical properties for the new gun were predicted on a
computer and experimentally confirmed in a new scanning electron
microscope. The aperture aberration coefficient was measured to be no
more than a factor of two greater than the theoretical value of 1.5 cm. A
spot radius of 250 Å has been measured, and this value is to be
compared with the theoretical value of 150 Å. Although it was convenient
to measure the spot directly only at a relatively large image distance
(11.3 cm), calculations imply that the gun can provide a spot radius
less than 25 Å when very small image distances are used. The gun can be
used in pulsed operation because all optical properties are constant for
a given voltage ratio so that application of the electrode voltages by
means of a voltage divider provides automatic focusing for arbitrary
changes in the applied voltage. The methods used to make and operate
reliable high field emission tips are reviewed, and a technique is
described for changing the required tip voltage to obtain a given
emission current.
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© 1968 The American Institute of Physics.
https://pubs.aip.org/aip/rsi/article/39/4/576/304088/Electron-Gun-Using-a-Field-Emission-Source
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