[labnetwork] Johnson Matthey H2 Purifier

[Brian Little]

Hi Rachel,
Palladium cell purifiers work great but are prone to failure due to the
brittle nature of the Pd membrane.
If they are not properly purged before the cell cools down, such as in a
loss of power, the membrane will crack due to Hydrogen getting trapped
inside.
A quick function test can be done by switching the upstream H2 supply over
to full Nitrogen (or other inert gas) while hot. The purified H2 existing
in the pressurized line will eventually back-diffuse through the hot cell
and get carried away by the purge bleed flow. Eventually, it will pull a
vacuum on the H2 downstream line (assuming it is leak right and there are
no downstream valves open.
If it doesn’t pull a vacuum, the membrane is dead.
Hope this helps!
Brian


On Wed, Oct 20, 2021 at 12:09 PM Rachel Schoeppner <rlschoeppner at ucsb.edu>
wrote:

> Good Morning,
>
>
> We have a Johnson Matthey HP-25 hydrogen purifier that we suspect is not
> functioning properly. In its idle state it is kept under low UHP N2 flow,
> and we think that some of this is getting through the purifier into the
> lines of our CVD. At the start of deposition when we start H2 flow and
> ignite the initial plasma we see an unexpected peak in nitrogen (verified
> both in the emission spectrum of the plasma as well as nitrogen that is
> incorporated in the epitaxial film as measured with SIMS). When we flow the
> hydrogen gas through the growth chamber for ~20 min before deposition, no
> nitrogen peak is observed, suggesting that it is coming in as an initial
> “plug” through the purifier at the very beginning that can be flushed
> through. There is also a low amount of background nitrogen throughout the
> deposition (this could be an impurity in the methane, but I am not sure how
> likely that is).
>
> We have leak checked the line running from the purifier to the CVD chamber
> and cannot detect any leaks that might be causing the initial nitrogen
> spike.
>
> We are wondering if anyone has experience with these purifiers or ideas on
> how to diagnose their proper functionality. If it is letting unwanted
> species through, then what would be our options for fixing or replacing it?
>
>
> Thank you!
>
>
> Rachel
>
> —
>
> *Rachel Schoeppner, Ph.D*
>
> Nanostructure Cleanroom Facility Manager
> California NanoSystems Institute (CNSI)
> University of California, Santa Barbara
> rlschoeppner at ucsb.edu
> rachel at cnsi.ucsb.edu
> (805)893-2296
>
>
>
>
>
>
>
>
>
>
>
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-- 

______________
Brian Little, Ph.D.
Senior Research Scholar
Electrical and Computer Engineering Department
Campus Box 7911
2410 Campus Shore Drive, Room 322F
Monteith Engineering Research Center (MRC)
Raleigh, NC 27606
Email: bdlittl2 at ncsu.edu
Mobile: 919-272-4984
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