[3dem] Ambient humidity and glow discharger efficiency?

[Talya Levitz]

Thank you to everyone for your replies on and off the list! Because
multiple others let me know that they are having similar issues, here is a
summary of all the replies I received from the EM hive mind; hopefully it
can help us and others in the future. The biggest take-aways for me were
that grid batch can be a big concern, to pay attention to sample-to-sample
differences, humidity probably helps glow discharge of grids at least to a
point, and that cleaning the discharger is important for ablating foil but
probably less important for hydrophilicity.

Len -- this year we implemented a dehumidifier in our room (~ $200, 30 pt
capacity). It can lower the humidity in the pretty small room (fits glow
discharger, plunger, and clipping station but not too much else) by 10-20%.
We see the biggest improvement in how quickly the clipping station frosts
up in the summer, but we still bring the clipping station into our Tundra
room (humidity controlled to 10-15%) on really humid days or for really
important samples. The biggest challenge we have experienced with the
dehumidifier is that the air turnover is pretty high in the building and so
it can't dehumidify past lowering by 10-20%, but it helps a surprising
amount. There are ones with pumps that can run continuously, but because of
our fire codes we can't use that kind, so we just have one that turns off
when it is full. It does fill up incredibly quickly, in a few hours, and we
usually run it for about an hour or two before starting because we have
some cardboard boxes stored in the room that we were told act as sponges
and store some water.

Summary of the responses I got (also here
<https://urldefense.com/v3/__https://docs.google.com/document/d/1z8XAp-OVXtGGDvCtleajkAHEye9jrlmlbY68qcWLnlM/edit?usp=sharing__;!!Mih3wA!HPoKkOEfkaVASg6qoKwlwAUhaRqw110EMZK6pdgSzFVC2ENtEuFGM8X-SJ66tg7VNNlMT36VPlDTIEZ__LpXqksIxNl3$ >
if the mailing list mangles the formatting):

Overall Issue

   -

   This is an issue seen by multiple facilities and we are not the only
   ones encountering this issue


Sample Variability

   -

   There are considerable differences in how well different samples wet the
   grid. Ensure that any differences seen are for equivalent samples.


Grid Variability

   -

   Grid batch makes a difference; some grid batches are much more difficult
   to glow discharge than others
   -

      Easy thing to try is another box of grids and see if the issue
      persists (grid batch does not correspond directly with grid box, but
      usually using another box will also get you another batch)
      -

      Some batches especially need chloroform washing
      -

   Storage of grids with desiccants can potentially help keep them less
   contaminated


Ambient Air Variability

   -

   Humidity
   -

      Air that is too dry will cause grids to catch on fire (!)
      -

      This website from Tergeo Pro
      https://urldefense.com/v3/__https://piescientific.com/plasma-surface-treatment-process-and-mechanism/__;!!Mih3wA!HPoKkOEfkaVASg6qoKwlwAUhaRqw110EMZK6pdgSzFVC2ENtEuFGM8X-SJ66tg7VNNlMT36VPlDTIEZ__LpXqm7ymNaO$ 
      indicates that water vapour helps with hydrophilicity
      -

         You can try wiping the glass of your chamber with a slightly damp
         wipe to increase the water vapor contents of your chamber
before running
         your glow discharge cycle, this has helped some in the past.
It is easy to
         revert by cleaning the glass with ethanol and wipes and air drying or
         pumping down.
         -

      Easiglo manual (
      https://urldefense.com/v3/__https://docs.research.missouri.edu/emc/Pelco-Easiglow-user-manual.pdf__;!!Mih3wA!HPoKkOEfkaVASg6qoKwlwAUhaRqw110EMZK6pdgSzFVC2ENtEuFGM8X-SJ66tg7VNNlMT36VPlDTIEZ__LpXqvcaEnDn$ )
      states you can use it with maximum relative humidity 80% for temperatures
      up to 31°C decreasing linearly to 50% relative humidity at 40°C
      -

      To glow discharge in a dessicated air environment: order a cylinder
      of compressed air, put a regulator on it down to a hair above atmospheric
      pressure, and hook it to the barbed gas inlet on the back of
your easiGlow.
      Just make sure you have the right inlet selected in your
protocol: you want
      the cylinder for process and the open one for vent.
      -

   Other variables
   -

      Contamination in air after glow discharge could be due to exposure to
      polymers or oils in the lab, for example if you have an oil sealed vacuum
      system that could introduce oil back to the glow discharge machine.
      -

      If you are using oil sealed pump on the glow discharge it could be
      sometimes leaking back into the chamber. It could do this when
vacuum seal
      isn't as good for example, or even when oil is old, or level is low. You
      can look at quality of oil to see if there is a problem with it. (or I
      guess it could be a bit random). You could try to add an oil trap on the
      vacuum line. We use dry scroll pump for these applications, or
try to shift
      EM facility to use dry pumps when we can.


Cleaning Glow Discharger / Blocks

   -

   Quantifoil recommends IPA to clean glow dischargers / blocks
   -

      Others use ethanol / kimwipes
      -

      Ethanol, isopropanol, acetone, or chloroform all seem like reasonable
      solvents to me, depending what might be on the block.
      -

      Ted Pella also makes a Jar Kleen for the glass of the easiglo
      -

   Dirty glow dischargers generally cause plasma concentrations that
   destroy grids, not under-discharge
   -

      If the current fluctuates widely, it indicates that large
      contamination particles are dislodged and accelerated between the
      electrodes and that is likely what ablates the carbon foil.
      -

      In a dirty chamber, the plasma glow tends to flicker, the current
      fluctuates and there are a lot of sparks. I have mainly used isopropanol
      for cleaning the chamber.


Carbon Removal on Grids

   -

   Carbon removal rate is probably of order 1 A/s and might be slightly
   higher due to some water -> if C film is 10-12 nm thick, then it should be
   all removed at ~120 s (2 min glow discharge ish) [this person did not
   specify current]
   -

   I doubt if a long 20 mA glow is expected to destroy a quantifoil film. I
   usually do 15 mA for 45 seconds and observe no significant damage even if
   the grids are processed multiple times.
   -

   For regular QF grids (nominally 20-40 nm), I run for 60-120 seconds with
   20 mA at 0.4 mbar on an EasiGlow and I have never seen any sign of damage
   to the foil. But ultrathin carbon (2-3 nm) is very batch dependent and can
   sometimes break or get too fragile with just 10% of that time (normally, I
   use time as the main variable to fine-tune hydrophobicity).



On Tue, Oct 7, 2025 at 11:37 AM Talya Levitz <tlevitz at crystal.harvard.edu>
wrote:

> Hi all,
>
> We are troubleshooting an issue where our glow discharger(s) seem to be of
> variable efficiency (sometimes making carbon grids appropriately
> hydrophilic, sometimes less so, occasionally not at all). My current theory
> is that the ambient humidity of the room is affecting the efficiency of the
> glow discharge. Has anyone encountered this or looked into it more
> thoroughly, and if so, what was your fix (account for humidity in timing /
> current? move the glow discharger into a more humidity-controlled room?
> desiccate the air going back into the chamber... somehow?). Other variables
> that have been ruled out are a faulty glow discharger, location of grid in
> the metal block, and whether it is the first glow of the day / session.
>
> We regularly have >50% humidity in the room during the summer, even with
> the dehumidifier running at full speed, because of air flow etc. variables
> in the room that we cannot change. We have two glow dischargers, a Pelco
> Easiglo and a Quorum/EMS GloQube, and have seen this with both dischargers,
> although we use the GloQube more so we have seen it more with that. At one
> point I tried to blow all the carbon off a grid with a very prolonged (5
> min @ 20 mA) glow discharge on the GloQube, and all the carbon was still
> entirely intact, which made me a bit nervous.
>
> Relatedly, how often and how do you all clean your metal blocks that grids
> glow discharge on? We were thinking of using acetone and/or alcohol, but
> would appreciate recommendations!
>
> Talya Levitz, PhD
> Scientist I
> talya_levitz at dfci.harvard.edu
> Pronouns: they/she
>
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