[3dem] glow discharge question

[Farzad]

Dear David,

Let me share my experience with semiconductor gas systems.

For supplying the gas from a liquid source like amylamine in a vacuum
system like Pelco easiGlow, you need a "precursor gas generator". Despite
its fancy name, it can be a very simple setup. In fact, this setup is very
common in various systems like Chemical Vapor Deposition (CVD) and maybe
you have already seen it in the environmental scanning electron microscopes
(for water vapor supply or some liquid precursors for EBID, etc). In this
set up you keep the liquid in a closed vessel like a glass balloon, and you
keep the temperature around it fixed. The temperature determines the
partial pressure of the gas which is necessary for the repeatability of the
process. Normally, people put the balloon in a laboratory balloon heater or
an ice bath, depending on the boiling point of the precursor and the
desired partial pressure. The selection of the temperature is up to you. If
your lab environment is stable enough and your gas consumption is also low
enough, you can do it at room temperature without any additional device. In
this case, you just need to have a big enough balloon and leave it to
equilibrate.

Also, for more repeatability, you are advised to keep the pressure over the
liquid vessel (the balloon) at a constant level. The reason is that for
non-ideal gasses the partial pressure is slightly dependent on the system's
pressure. For achieving that level of stability, you can set up a carrier
gas inlet to the balloon like a bobbler. The carrier gas can be nitrogen,
argon, or even air (just leave an open inlet to the bobbler. You can also
keep balloons under a vacuum condition which is also another strategy for
keeping the pressure constant! In this case, the setup is similar except
the carrier gas pipe is not submerged in the liquid and it is connected to
a vacuum pump.

*Caution 1: There is a safety consideration for heating the vessel to near
boiling point or working at high carrier gas pressure. If you want to have
high partial pressure and hence you decide to heat the precursor to near
its boiling temperature you need to consider a safety release valve and a
reliable suction hood OR a higher pressure chamber. It is worthy of note
that since evaporation needs time and energy, heating is always
preferred for a more uniform gas composition. Glass balloons are not made
to maintain very high pressures.*

*Caution 2: Should you need to inject multiple gasses you need to install
mass flow controllers at the inlets after the bobblers. This guarantees a
constant gas composition.*

Hope these details help you make your bobbler (precursor gas generator).

Cheers,

Ferrie

Farzad Hamdi, Dr.-Ing
Scientist,
Kastritis Laboratory for Biomolecular Research
Interdisciplinary research center HALOmem,
Institute of Biochemistry and Biotechnology, Biocenter,
Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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On Wed, Jan 11, 2023 at 10:43 PM Morgan, David Gene <dagmorga at indiana.edu>
wrote:

> Hi,
>
> Has anyone modified a Pelco glow discharge device so that one can
> introduce something like amylamine into the chamber during the glow
> discharge?  I can think of several ways that this could be done, but if
> someone already has a working model, I would love to chat with them.
>
> Thanks in advance.
>
> --
>     politics is more difficult than physics.
>                                              A. Einstein
>
>             David Gene Morgan
>         Electron Microscopy Center
>              047E Simon Hall
>              IU Bloomington
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