[3dem] plasma cleaners

[Zaluzec, Nestor J.]

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.
> 
> --
>      politics is more difficult than physics.
>                                               A. Einstein
> 
>              David Gene Morgan
>          Electron Microscopy Center
>               047D Simon Hall
>               IU Bloomington
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-- 
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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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Past President Microscopy Society of America
Adjunct Professor of Physics - Northern Illinois University &
	the University of Illinois at Chicago
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