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(i) On the lower right-hand side of the page, select CURR (under rot center VOLT CURR) so that it
becomes highlighted. This will cause the objective lens current to modulate (the inner STEP SIZE
knob adjusts the amplitude of modulation). If the chosen feature shifts off center laterally, the
beam is not aligned along the optical axis of the microscope and must be corrected.
(ii) Use the MULTIFUNCTION X/Y knobs to stabilize the feature at the center of the screen,
eliminating all lateral movement. The feature should appear to be pulsating.
(iii) Press the ALGN button to return to the TEM BRIGHTFIELD page.
7. Centering the Objective Lens Aperture
For this procedure a specimen must be in place. Choose an area for which it is acceptable to
sustain beam damage. With the OBJECTIVE APERTURE out, set the magnification to 5800x
and overfocus the beam by turning the INTENSITY knob clockwise from crossover.
7.1 Set the focus step size (inner STEP SIZE knob) to 5 and press the Zoom button to put the 'scope
in diffraction mode.
7.2 If necessary, adjust the CAMERA LENGTH to 620 mm using the MAG knob.
7.3 Center the diffraction spot using the MULTIFUNCTION X/Y knobs.
7.4 Using the focus (outer STEP SIZE) knob, refocus the beam to the smallest, brightest spot. It may
also be necessary to adjust the INTENSITY knob.
7.5 Insert the OBJECTIVE APERTURE by rotating the aperture displacement lever below it to the
left.
7.6 Apertures may be selected by rotating the largest knurled knob on the objective aperture assembly
to any one of four numbered positions. (The APERTURE MEMO lists the diameters and
positions of the apertures currently installed in the 'scope. It may be accessed from the TEM
BRIGHTFIELD page by clicking MODES and then CONFIGURATION.)
7.6.1 Once the aperture has been selected, center it using both the smaller knurled knob in the series on
the aperture assembly and the small knurled knob to the right. Remember not to manipulate the
smallest, innermost knob, which is not knurled and will unscrew the aperture rod.
7.6.2 Press Zoom to exit diffraction mode.
8. Objective Lens Astigmatism Correction
8.1 Select an area that may be imaged at high magnification without harming any desirable portions
of the specimen. Increase the magnification to 175,000x or higher and adjust the illlumination so
that the substructure or background grain of the specimen may be observed easily. The
INTENSITY will have to be modified and the beam will have to be recentered using the SHIFT
X/Y knobs (Deflectors) as the magnification is increased. This latter function may alternatively
be controlled using the RST button, on the panel to the left of the column.
8.2 Set the focus step size to 2 and obtain a slightly underfocused image for maximum contrast.
8.3 Press the STIG button to open the STIGMATOR CONTROL page. If it is not already
highlighted, press the OBJ key on this page.
8.4 Use the MULTIFUNCTION X/Y knobs, one at a time, to obtain the sharpest possible image of
the grain substructure.
8.5 Confirm that any astigmatism has been corrected by varying the focus (back and forth through
focus, from underfocus to overfocus) and watching to see if a "streaking" pattern emerges and
changes direction between under- and overfocus. If the astigmatism has been corrected, the
specimen will vary only in focus, with no pattern evident. Repeat steps 4 and 5 until no pattern is
apparent.
8.6 Press the STIG button again to return to the TEM BRIGHTFIELD page.
9. Condense Lens Astigmatism Correction
This procedure is necessary if the beam spot is not a symmetric circle when the intensity knob is
rotated.
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