5 OPERATION
5-16
EM210F-1
5.2.5b Objective
aperture
1.
Insert a specimen into the beam path (
F
a specimen holder’s Instruction
manual) and, depress the SA DIFF switch (R1-
②
).
2.
Converge the electron beam with the BRIGHTNESS knob (L1-
⑥
) and keep
the electron beam converged.
3.
Obtain a caustic spot (zero magnification spot) with the DIFF FOCUS knob
(R1-
⑥
) as shown below. If the caustic spot is off the screen center, turn on
the PLA switch (L1-
⑤
) and center the spot with the DEF/STIG knobs (L1-
⑩
,
R1-
④
). Turn off the PLA switch after centering.
Fig. 5.15 Caustic spot
4.
Obtain the smallest illumination spot with the BRIGHTNESS knob (L1-
⑥
)
and make the illumination spot coincide with the screen center by manipulat-
ing the SHIFT-X and -Y knobs (L1-
⑧
, R1-
③
).
5.
Insert the desired objective aperture into the beam path with objective
aperture assembly knob 1.
6.
Focus the aperture image (shadow) with the DIFF FOCUS knob (R1-
⑦
).
7.
Manipulate an aperture assembly knob 2 and3 so that the caustic spot lies in
the center of the aperture hole image.
When the aper ture is not centered
When the aper ture is centered
Fig. 5.16 Objective aperture centering
