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Non-conductive samples may charge with these settings.
specimens that have been coated usually can be viewed with a lower
accelerating voltage, usually 10 – 15 kV.
to "2" so as to keep the emissions current in a safe range of 30 – 40
lower kV setting usually improves the surface image but also adds "noise" to
the detector signal.
With the Wehnelt gun cap fitted with a 200
Wehnelt distance adjusted 6 small divisions, the following should be
expected at filament saturation:
Bias 1, 25 kv, saturated filament current = 40
Bias 2, 10 kv, saturated filament current = 35
To lower the saturated filament current, increase
the filament to Wehnelt distance.
Select spot size:
Generally speaking, use a large spot size (200 or
500) for low magnification work under 1000 x
magnification.
Smaller spot size is used for higher
magnifications.
detector gain must be increased (and visa versa)
because fewer secondary electrons are generated.
Black level is not affected as much.
µ
10 - 20
spot size.
Stage controls:
Do not adjust the "Z" control. This is set to provide an optimal
(10 – 12 mm for secondary electron detector and 20 mm for the EDAX
detector).
Do not force any stage control knob.
As spot size is reduced, the
With this setting, set the gun bias
µ
aperture, and the filament to
µ
A.
µ
A.
For 5K to 20K magnification work, use a
Biological
µ
Use gun bias 1 for
20 and greater kv
and bias 2 for 10 –
20 kv.
Use a spot size of 500
and the lowest
magnification to align
the electron gun.
distance
A. A
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