FEI Quanta FEG 250, User'S Operation Manual

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System Options: Cooling Stage / Waterless Cooling Stage
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to this occurs when imaging an oil / water emulsion, in which case the
oil always appears darker than water.
CAUTION!
When using shorter working distances, water from the sample can
splash onto the GSED. To avoid this, start with a longer working
distance until the sample has equilibrated, then move to a shorter
working distance to optimize the image.
With the waterless CS the tilt angle is restricted to +20° when using
BSED or GAD detectors, due to the cooling braids.
Using bulk samples
For more accurate temperature readings, bulk samples should be
placed as flat as possible on the holder. The further away from the
holder surface the sample is, the less accurate the temperature
reading is. Another way to ensure accuracy with bulk samples is to
maintain the temperature of the sample for about 5 minutes before
condensing. This equilibrates the sample so that the temperature is
the same throughout.
High magnification imaging
At magnifications above 20 000×, water moving through the CS
causes small vibrations. To prevent this, shut the water off temporarily
using the valve on the water hose line attached to the chiller. The
Stage continues to cool the sample for about 15 minutes without water
cooling. After this time the sample temperature rises.
CAUTION!
If the cooling stage is used without a heat sink connection, severe
damage may result to the thermoelectric module. Do not operate the
CS for longer than 15 minutes without cooling water, else damage
occurs to the device.
Cooling below Ice Point
In most cases, the power of the thermoelectric module is not sufficient
to freeze large quantities of bulk water. Small water drops can be
frozen on the stage using the following procedure:
1. One can set the external water chiller to 5 °C. Allow the chiller time
to cool the water. Keep the pressure in the chamber below 800 Pa
(6 Torr) to keep water from condensing on the cooling lines.
2. Set the temperature of the cooling stage to -5 °C. As the
temperature drops, decrease the pressure gradually to 400 Pa
(3 Torr) at the same time as the temperature reaches -5°C. If the
pressure is dropped too quickly, the bulk water in the sample
evaporates; conversely, if the pressure is reduced too slowly, water
condenses onto the sample and raise the temperature.