[3dem] plasma cleaners
Zaluzec, Nestor J.
zaluzec at anl.gov
Tue Mar 19 13:40:57 PDT 2019
David...
A gentle clean is:
pure Ar, 10 W, 250-300 mtorr, 10-20 sec removes mobile hydrocarbons
This can be used on most holely carbon films used as support
but not graphene, even this is too aggressive for these
monolayers. Also remember Carbon films are never clean nor are
they pure carbon
An slighlty agressive clean:
pure Ar, 20-50 W, 250-300 mtorr, 30sec-10 minutes removes more
serious hydrocarbons, can begin to destroy most holey carbon
films but is good on metals, ceramics, ....
More agressive
Ambient Air (~ 80% N + 20% O) , 250-300 mtorr 10-50W, 30sec-10
minutes will destroy most holey carbon films but is good on
metals, ceramics, ....
More agressive
H + O mixture, 50W, 250-300 mtorr, 1-10 minutes, will destroy most
holey carbon films but is very good on metals, ceramics, ....
This is not convenient as special plumbing is required to
seperate tanks of H & O according to all the good safety
protocols.
Very agressive
Ar + 20% O , 250-300 mtorr 10-50W, 30sec-10 minutes will destroy
most holey carbon films but is good on metals, ceramics, ....
Most agressive
Pure O, 250-300 mtorr, 50W , minutes, death to most carbon
including some tranisition metal carbides
Warning high power levels and pressures can also result in heating
of the specimen and holder.
I always plasma clean my specimens and the holder prior to starting
an experiment and this is at a minimum of "gentle" level, I then
progress upward in power/chemistry if i notice the contamination gets
harder to mitigate.
The above will not be effective, if the contamination is not coming
from your specimen but rather from elsewhere in the column or the
holder. My holders are stored in flowing dry Nitrogen, or in vacuum
when not in use to keep them clean, and of course, wear gloves to
prevent contamination from your hands.
If you are cleaning batches of C films, the optimal setting will vary
with the C batches depending upon what else is incorporated on/on the
film. Also just letting the C films lay around will allow them
to pickup airborne's. Least I forget never, never use gelatin capsules.
I still occassionally see them being used to hold/store specimen.
Gelatin is made to dissolve and humdity in the room is enough to start
the process.
Once the contamination is formed/deposited, the hydrocarbons are
essentially cooked/polymerized onto the specimen by the electron beam.
A very aggressive clean may remove that type contamination (if it is
reactive carbon) but this is also beating heavily on the rest of your
specimen.
Notice, in #1 and #2, I don't use Oxygen, there is enough residual
moisture in most vacuum systems to create an active Oxygen plasma.
I also often use thin amorphous/holey SiNx films for support. They can
be aggressively cleand without problems.
Hope this helps.
Cheers,
Nestor
On 3/19/19 2:50 PM, Morgan, David Gene wrote:
> Hi,
>
> For those of you fortunate enough to have an Ar/O plasma cleaner that can be used to clean TEM holders, what are typical settings (gas mix, flow rate and most importantly, time) for cleaning the holders? Thanks for any advice you can offer.
>
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Dr. Nestor J. Zaluzec
Argonne National Laboratory
Photon Sciences Division
Electron Microscopy
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Senior Scientist - Argonne National Laboratory
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Senior Institute Fellow - NAISE - Northwestern University
Senior Institute Fellow - UChicago CASE
E.P. Wigner Fellow - Oak Ridge National Laboratory
Past President Microscopy Society of America
Adjunct Professor of Physics - Northern Illinois University &
the University of Illinois at Chicago
Visiting Professor of Microscopy - Manchester University
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