Advertisement
b. Use the Multifunction X/Y knobs to stabilize the feature at the centre of the
screen, eliminating all lateral movement. The feature should appear to be
pulsating.
c. PRESS the ALGN button to return to the TEM Brightfield page.
11. Centering the Objective Lens Aperture
Note: A specimen must be in place to perform this procedure. Choose an area that is
acceptable to sustain beam damage.
a. RETRACT the Objective Aperture, SET the magnification to 5,800x and OVERFOCUS the
beam by turning the Intensity knob clockwise from crossover.
b. SET the focus step size (inner Step Size knob) to 5 and PRESS the D button to put the
microscope in diffraction mode.
c. If necessary, ADJUST the Camera Length to 620 mm using the MAG knob. [Note that you
can accidentally choose 6.2 m rather than 620 mm.]
d. CENTRE the diffraction spot using the Multifunction X/Y knobs.
e. 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.
f. INSERT the Objective Aperture by ROTATING the aperture displacement lever below it to
the left. 7. 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 CM200.
It may be accessed from the TEM BRIGHTFIELD page by PRESSING the Modes key and
then Configuration.)
g. Once the aperture has been selected, CENTRE it with both the smaller knurled knob in
the series on the aperture assembly and the small knurled knob to the right. Note: Do
NOT manipulate the small, innermost knob, which is not knurled and will unscrew the
aperture rod.
h. PRESS the D button again to exit Diffraction mode.
12. Correcting Objective Lens Astigmatism
Two methods are possible:
A. Using the CCD Camera Live Fast Fourier Transform (Live FFT)
a. SELECT an area of the carbon film on the TEM grid
b. CHANGE the Magnification to 580,000x
c. PRESS the Lift Screen button
d. ACQUIRE a Live Image with the CCD camera.
e. Under the Camera Control, SELECT FFT
2017.07.07
15
Advertisement
