3.4.2 Equipment
Troubleshooting
Poor Chamber Vacuum
The system should reach better than 2 Â 10
À6 mbar at room
temperature and better than 7 Â 10
À7 mbar at cryogenic temperatures. If these are not satisfied, the chamber seals especially those on
the front door and the quickloader should be inspected and
cleaned. Poor vacuum may lead to an increased rate of water
vapor accumulation on the sample resulting in an increase in the
lamella thickness that reduces imaging quality.
Frost on Heat Exchanger
Tubing
Frost buildup on the heat exchanger tubing is due to loss of
vacuum insulation. The typical causes are pump failure, a leak in
the outer tubing, or a leak in the internal nitrogen lines. Continued
use of the system with frost buildup may lead to poor stage cooling.
Amorphous Ice
Contamination
From our experience, poor stage cooling will lead to accumulation
of amorphous ice or even “leopard skin” ice when observed at the
TEM. The temperature of the top of the stage (where the shuttle is
inserted) should be measured using a thermocouple. Starting from
room temperature, the stage top should be able to reach below
À170
C within 30 min. If this is not the case, the stage should be
disassembled and thoroughly cleaned. We have found that buildup
from the sputter coater and GIS can be responsible for stage temperature issues.
Crystalline/Atmospheric Ice
Contamination
Check that the o-rings on the transfer arm and transfer lid are clean
and in good condition. Ensure that all tools and loading equipment
are dry before handling samples. Ensure that the venting line on the
transfer lid has been purged for at least 10 min, and keep purging
continuously for the duration of the session. Ensure that any liquid
nitrogen having direct contact with samples is free of frost.
Inaccurate Ion Beam
Currents
When the beam is blanked, the FIB is deflected into a faraday cup to
measure the beam current. If the reported value is much higher
(10–15%) than the nominal value, the ion beam aperture strip is
likely worn out (Fig. 8). Typical FIB milling may use one particular
aperture (e.g., 10 or 30 pA) much more than the others, which may
cause them to wear out earlier and become much larger than the
initial size. This leads to drastically increased ion beam currents and
poor control over milling. On certain microscopes, it may be
necessary to switch to an unused “parking position” FIB aperture
when the microscope is idle but the ion source is left on, due to the
continual exposure of the aperture strip to the ion beam.
74
Vinson Lam and Elizabeth Villa
Troubleshooting
Poor Chamber Vacuum
The system should reach better than 2 Â 10
À6 mbar at room
temperature and better than 7 Â 10
À7 mbar at cryogenic temperatures. If these are not satisfied, the chamber seals especially those on
the front door and the quickloader should be inspected and
cleaned. Poor vacuum may lead to an increased rate of water
vapor accumulation on the sample resulting in an increase in the
lamella thickness that reduces imaging quality.
Frost on Heat Exchanger
Tubing
Frost buildup on the heat exchanger tubing is due to loss of
vacuum insulation. The typical causes are pump failure, a leak in
the outer tubing, or a leak in the internal nitrogen lines. Continued
use of the system with frost buildup may lead to poor stage cooling.
Amorphous Ice
Contamination
From our experience, poor stage cooling will lead to accumulation
of amorphous ice or even “leopard skin” ice when observed at the
TEM. The temperature of the top of the stage (where the shuttle is
inserted) should be measured using a thermocouple. Starting from
room temperature, the stage top should be able to reach below
À170
C within 30 min. If this is not the case, the stage should be
disassembled and thoroughly cleaned. We have found that buildup
from the sputter coater and GIS can be responsible for stage temperature issues.
Crystalline/Atmospheric Ice
Contamination
Check that the o-rings on the transfer arm and transfer lid are clean
and in good condition. Ensure that all tools and loading equipment
are dry before handling samples. Ensure that the venting line on the
transfer lid has been purged for at least 10 min, and keep purging
continuously for the duration of the session. Ensure that any liquid
nitrogen having direct contact with samples is free of frost.
Inaccurate Ion Beam
Currents
When the beam is blanked, the FIB is deflected into a faraday cup to
measure the beam current. If the reported value is much higher
(10–15%) than the nominal value, the ion beam aperture strip is
likely worn out (Fig. 8). Typical FIB milling may use one particular
aperture (e.g., 10 or 30 pA) much more than the others, which may
cause them to wear out earlier and become much larger than the
initial size. This leads to drastically increased ion beam currents and
poor control over milling. On certain microscopes, it may be
necessary to switch to an unused “parking position” FIB aperture
when the microscope is idle but the ion source is left on, due to the
continual exposure of the aperture strip to the ion beam.
74
Vinson Lam and Elizabeth Villa