Solarus 950 Owner’s Manual and User’s Guide
25
Operating the Gatan Advanced Plasma System
Theory of Operation
The actual Sample cleaning times depend on the amount and type of contamina-
tion as well as the sample material. It is generally recommended to start with short
cleaning times (15-30 seconds) and increase only if necessary.
The primary difference between recipes for different gas mixtures is the time of
plasma ignition (i.e., TEM and SEM H
2
/O
2
recipe is for 1 minute at 50 watts
while the TEM and SEM Ar/O
2
recipe is for 2 minutes at 50 watts). Current
recipes are based on results obtained at Gatan.
A plasma cleaner is more effective in cleaning samples before they are exposed to
an electron beam. Hydrocarbons are much easier to remove before they are
cracked or carbonized.
Most fresh or new EM samples can be cleaned in less than 1 minute. Samples pre-
viously imaged and having carbonized contamination will require additional
cleaning time. Two minute cleaning intervals are recommended to determine the
correct length of time for removing carbonized contamination.
Experience with STEM samples has shown that the current 2-minute preset for
STEM H
2
/O
2
is generally enough time to clean silicon samples for LAB
6
STEM.
For FEG STEM, more time may be recommended.
Carbon films can be cleaned in the Gatan Advanced Plasma Cleaner. Please note
that not all carbon films are equivalent. Carbon films are volatilized and removed
during plasma cleaning, however, pure carbon films will be removed at a slower
and consistent rate. In such cases, the films will decrease in thickness evenly
across the film and EM imaging will not be adversely affected. If carbon films
have high levels of contaminants such as O and H, those areas will be preferen-
tially removed, resulting in uneven C film thickness which may be observed in
EM imaging. Hydrocarbon contamination will be removed much faster than C
films, especially pure C films. Gatan recommends testing of C film plasma clean-
ing prior to cleaning important samples. Once a particular C film type has been
qualified for a given cleaning recipe and time, it should be safe to use with sam-
ples.
Support structures such as Formvar are polymers and thus are removed quite
effectively by the plasma cleaner. Short cleaning times of Formvar films will cre-
ate a roughness of the Formvar that may interfere with imaging small particles.
Carbon films with Formvar or similar support films should be tested in the plasma
cleaner in order to determine if plasma cleaning is appropriate. If possible, remove
the Formvar films prior to depositing your sample on the C film.
Internal Mass Flow Controllers (MFC) accurately control flow rates for the gas
mix chosen. H
2
/O
2
is the preferred gas recipe, offering improved cleaning perfor-
mance, lower sample temperature, less sample damage, and faster cleaning times.
