[labnetwork] Carbon contamination from Ar

[Kevin McPeak]

Dear Mike,

That is a good point. We should totally do that and will. What else do you
think this black stuff could be?

Regards,
Kevin

--
Kevin McPeak
Assistant Professor
Department of Chemical Engineering
Louisiana State University
email: kmcpeak at lsu.edu
phone: 225-578-0058

On Oct 28, 2017 09:58, "Mike Young" <myoung6 at nd.edu> wrote:

> Hi Kevin. Have you confirmed the deposits are in fact carbon? Scrape some
> off and perfom EDX in a SEM, for example?
>
> --Mike
>
> On 10/28/2017 12:19 AM, Kevin McPeak wrote:
>
> Dear Colleagues,
>
> In my lab at LSU we are interested in evaporating Au under high Ar
> pressures, 10 - 50 mTorr. We are using Ar 5.0 purity (99.999%), which
> has a THC of 1 ppm.
>
> Our procedure is such:
>
> 1). Pump chamber down to low -7 Torr range
> 2). Inject 30 SCCM Ar and throttle gate valve to the desired pressure
> (say 50 mTorr)
> 3). Increase power to Tungsten boat till Au pellets evaporate
>
> When we vent the chamber *we notice a lot of carbon deposition* near the
> outlet of the Ar line (see attached image). We have a THC of 1 ppm in
> the Ar tank. We also tried hooking up a GP-100 gas purifier from RD
> Mathis. Unfortunately, that didn't solve the problem, still lots of
> carbon deposition in the chamber. The GP-100 is currently connected
> upstream from the MFC. I am using SS tubes with all VCR fittings
> (total length 6 ft). We could move the GP-100 closer to the chamber,
> post-MFC.
>
> Based on the photo I think it is pretty clear that the carbon is
> coming from the Ar. So my current thought is that either I have a leak
> in my tubes post GP-100 or I need to flame bake the lines (I have not
> done this). I am trying to get access to an RGA to investigate this
> more quantitatively. I do have access to a He checker so I could try
> pumping on the Ar lines.
>
> Have any of you seen Carbon contamination like this before when doing
> high-pressure evap (I know that is not a normal thing)? I am curious
> what people think. Thanks!
>
> Regards,
> Kevin
>
>
>
> --
> Michael P. Young                                (574) 631-3268 (office)
> Nanofabrication Specialist                      (574) 631-4393 (fax)
> Department of Electrical Engineering            (765) 637-3784 (cell)
> University of Notre Dame                         mike.young at nd.edu
> B-38 Stinson-Remick Hall
> Notre Dame, IN 46556-5637
>
>
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