[labnetwork] liquefaction of O2 on MBE walls cooled with LN2

[Gila,Brent P]

Hello Saba,

I have done a lot of oxide MBE growth using RF O2 plasma (similar flow 
rates and pressures as you have listed) and have never had any issue 
with liquid O2 in the chamber.  We did quick regens of the cryo pumps 
after long runs (warm the pump up to 125K while pumping on it with a 
turbo) then cool it back down.  This removed all the N2 and O2 from the 
pump.  As with any gas based MBE system, you want to have a fail safe 
pressure relief valve somewhere in the vacuum side just in case the 
power fails or the pumps goes out while you are warming up the cryo 
panels.  I have had a lot of gas come off the panels during the warm up 
process, but nothing that created a pressure spike.

If you have a mass spec on the chamber, record the N2 and O2 spectra 
during the warm up cycle and see how much evolves.

Best Regards,
Brent
-- 
Brent P. Gila, PhD.
Director of the Nanoscale Research Facility
University of Florida
1041 Center Drive
Gainesville, Florida 32611
Tel:352-273-2245, Fax:352-846-2877
email: bgila at ufl.edu


On 2/26/2020 1:23 PM, Saba Sadeghi wrote:
> *[External Email]*
>
> Dear all,
>
>
> I have a question about MBE systems that are used for metal-oxide growth.
>
> In our MBE system we use oxygen flow rate of 0.3 - 0.4 sccm, 
> which leaves the chamber pressure at about 1E-5 Torr.
>
> The chamber incorporated LN2 cooling shrouds.  My question is that do 
> you think that there is any concern regrading liquefaction of 
> oxygen on the chamber's wall, that might end up dripping down the 
> walls, evaporating and causing a pressure burst.
>
>
> I have not encountered the problem yet, but I was wondering if over 
> time, and for long growth time this might become an issue. Has anyone 
> encountered this issue before?
>
>
> Any input is much appreciated,
>
>
> Best,
>
> --
>
> /Saba Sadeghi, PhD/
> /Quantum Devices Fabrication Scientist/
> /Institute for Quantum Computing, University of Waterloo/
> /Email: //saba.sadeghi at uwaterloo.ca <mailto:saba.sadeghi at uwaterloo.ca>/
>
>
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