5 OPERATION
EM210F-1
5-25
5.3 METHOD
B
5.3.1 Conditions for High Resolution Microscopy
■
The electron bean divergence angle must be small
High resolution micrographs will be difficult to obtain due to low coherence when the
electron beam divergence angle is large. Therefore, use a small condenser aperture (100
or 40 micron meters in diameter), manipulate the BRIGHTNESS knob to obtain 2 to 4
seconds of exposure time and set the beam divergent angle as follows using the
The
a
-SELECTOR No. is displayed on the left main screen (
F
Sect. 4.4.4a). The No.
can be varied using the
a
-SELECTOR knob (L1-
③
). No. 3 covers all the range of
magnification except when very high resolution photographs are required. No.2 and 1 are
recommended for microscopy at very high magnifications required small divergence
angle. The smaller the divergence angle (i, e, the smaller the
a
-SELECTOR No.), the
higher the image quality with smaller field of view. Refer to the following when
selecting the
a
-SELECTOR No.
a
-SELECTOR No. 3: For any magnification
a
-SELECTOR No. 2: For 100,000 times or higher
a
-SELECTOR No. 1: For 500,000 times or higher
■
The voltage center must be properly aligned.
Fig. a shown below shows a hole image when the voltage center is properly aligned. In
this figure, the background structure (phase contrast) is readily discernible, and the edge
of the hole can be clearly observed all the way round. On the other hand, Fig. b shows a
hole image when the voltage center is misaligned. In this figure, the image is indistinct,
the background structure appears unidirectional, and the edge of the hole is blurred as if
astigmatism exists.
a: Hole image when voltage center
is aligned
b: Hole image when voltage center is
misaligned
Fig. 5.25 Effect of voltage center alignment
For high magnification photography, realign the voltage center at the photographing
magnification by using the HT-WOBBLER switch (R1-
①
).
