[3dem] glow discharge question

Thu Jan 12 03:11:29 PST 2023

Hi,

maybe a very simple solution: Place a pleated filter paper next to the 
grids, add 50 µl Amylamine and pump and glow-discharge as usual ... you 
should notice a change in the color of the plasma.

Cheers,

Thorsten

On 12.01.2023 12:04, Farzad wrote:
> 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.
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>
>                 David Gene Morgan
>             Electron Microscopy Center
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