[3dem] [External] Re: glow discharge "fireball"

[Naylor, Claire E.]

Hi,
  Previously, I have observed that this can often be resolved by wiping the aluminium block and the inside of the chamber with IPA – as described here:
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Under Technical Queries – Why do lots of my grids have broken windows after glow discharge.

Hopefully this might help you as well,
Claire

From: 3dem <3dem-bounces at ncmir.ucsd.edu> On Behalf Of Mathew Peet via 3dem
Sent: 05 February 2026 22:08
To: Morgan, David Gene <dagmorga at iu.edu>
Cc: 3dem at ncmir.ucsd.edu; Jason Kaelber <jason.kaelber at rutgers.edu>
Subject: Re: [3dem] [External] Re: glow discharge "fireball"

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Dear David,

I had two different explanations.

1) Anything which changes the chemical environment locally, like contamination / hydrocarbon / water which outgasses during the plasma. The most unfortunate I can think of is steel from the tweezers reacting with the aluminium. Different contaminants should have different colour flame. Change in aluminium surface properties, e.g. oxide film thickness / chemical modification from previous plasma treatments. Contamination of glow discharge chamber / vacuum system.

2) Increased field strength at the surface due to height and surface profile. Flatter Aluminium block should be less likely to have this, or aluminium block with more shallow holes to locate grids. Is this always random? Or does it happen more at edge of block? Block shown isn’t centered or flat, the glowing hole is slightly higher than others. You could make it to fit in the location for the glass slide.

Possibly thin metal slide would be better. Im not sure about advantages of insulator vs conducting plate here. You might be able to see if there is any difference in dark zone above the surface.

Best wishes,

Mathew




On 5 Feb 2026, at 17:37, Morgan, David Gene via 3dem <3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>> wrote:

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To everyone who is putting parafilm into a glow discharge device:

I have always been told that the inclusion of something like parafilm in a glow discharge device changes the properties of the "glow" by including some unknown amount of hydrocarbon ripped from the parafilm.  This may or may not be true, and the overall effect may be minimal.  However, it is something I have always worried about and avoided except in devices that were dedicated to making carbon films hydrophobic.

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From: 3dem <3dem-bounces at ncmir.ucsd.edu<mailto:3dem-bounces at ncmir.ucsd.edu>> on behalf of Debakshi Mullick via 3dem <3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>>
Sent: Thursday, February 5, 2026 12:08 PM
To: Jason Kaelber <jason.kaelber at rutgers.edu<mailto:jason.kaelber at rutgers.edu>>
Cc: 3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu> <3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>>
Subject: [External] Re: [3dem] glow discharge "fireball"


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Hello Jason,

We have seen this on our Emitech glow-discharge and were baffled. Also, our grids looked kind of 'fried'. I say 'kind of' because we could not see the carbon support film being obliterated every time, but, only on a few occasions. In order to avoid it, we placed an insulator below this grid-holder (either a silicone pad or a glass slide covered with Parafilm. That took care of the pretty-pink fireball and all grids survived!

I hope that helps.

Cheers,
Debakshi

-Dr. Debakshi Mullick
Senior Cryo-EM Support Scientist
464 Bearsden Rd,
Glasgow G61 1QH



On Wed, 4 Feb 2026, 21:20 Jason Kaelber via 3dem, <3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>> wrote:
Dear 3DEM,
When glow discharging with our Pelco easiGlow (e.g. at 15 mA, 0.39 mBar room air for 25 seconds) on the aircraft aluminum grid blocks, sometimes a ball of plasma will be observed above one grid, or one ball each among several randomly-placed grids in the block. The ball is light pink and may manifest at any time during the discharge, typically enduring until the end of the cycle but perhaps flickering in and out of existence. Below I enclose a photograph of the phenomenon:
<Outlook-editibs0.jpg>
Have any of you observed this? Do you know the cause or solution? It doesn't happen when we glow discharge on glass slides—but on the other hand, we we using the aluminum blocks for a couple years without issue before ever seeing this, and ordering a brand-new block doesn't help.

Thank you in advance for your helpful replies,
Jason Kaelber

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