[3dem] glow discharge vs plasma cleaning

Tue Sep 20 23:29:09 PDT 2016

Dear colleagues,

Many thanks for all your answers. I start to get a better picture of the situation. Sounds like antiques are called glow discharge, and new shiny machines with touchscreen and gimmicks are called plasma cleaners but fundamentally they are not different, provided one can inject a gas of choice. Possibly, necessary glowing times in antique machines are longer than in modern machines that generate plasma with microwaves.

Sergey, have you measured or estimated the resistivity of your home made carbon ? And is it hydrophilic ? If not, do you make it hydrophilic by another mean than plasma treatment before applying a sample ?

Ben

De : 3dem <3dem-bounces at ncmir.ucsd.edu> au nom de Sergey Ryazantsev <sryazant at ucla.edu>
Date : mardi, 20 septembre 2016 22:26
À : "3dem at ncmir.ucsd.edu" <3dem at ncmir.ucsd.edu>
Objet : Re: [3dem] glow discharge vs plasma cleaning

Dear Colleagues
Plasma cleaning is self-explanatory - well, it is cleaning by plasma, sometime using a dedicated device. Plasma cleaning requires normally high energy plasma, which produced using high-frequency generator (microwave?). Most modern "plasma cleaners" do not use high-voltage to generate plasma.

"Glow discharge" is more tricky. Historically, glow discharge was performed to mitigate hydrophobic properties of carbon.Often, home-made "glow-discharge" units were used. Such unit usually constructed using mechanical pump, some sort of "bell-jar," high-voltage power supply and discharge electrodes.  Residual air was used to generate a plasma. Such units are simple, but results sometime inconsistent. "Plasma cleaning" units at low power settings can be used for more reproducible "glow-discharge."

On philosophical note, speaking about "glow-discharge" ... I never was able to understand how electro-conductive carbon can hold a "charge"? My personal theory is that common "carbon" is contaminated by oil from dirty oil-based vacuum-evaporators. "Glow discharge" essentially ionizes residual oil. Oil within the carbon produces many bad effects on carbon: oil can oxidize (carbon aging); oil can decompose for different reasons; oil destabilizes carbon under e-beam etc. From this (my personal) prospective, "glow discharge" has limited beneficial effect on pure, clean carbon. In fact, I am using pure, clean (oil-free) ultrathin carbon for EM for decades. This carbon is remarkable stable under the beam and survived freezing etc. It also has very low background noise because it is not "etched" by "glow discharge."

Sergey
On 9/20/2016 11:46 AM, Mike Strauss wrote:
Hi Sergej,

Just a reminder, because I'm sure you are aware, but there are other factors besides the vacuum that affect the results of the glow discharger (or plasma cleaner in your case).  These include: distance between electrodes, voltage applied across electrodes,  shape of electrodes, nature of carrier (the thing your grids are on), type of residual gas in chamber.

I have always assumed that the name of the instrument depends on its intended use.  So a glow discharger becomes a plasma cleaner when you leave it on too long and burn off all the carbon.

mike

On Tue, Sep 20, 2016 at 7:03 PM, Sergej Masich <Sergej.Masich at ki.se<mailto:Sergej.Masich at ki.se>> wrote:
Dear List, dear Benoît,
I have some different experience that can be wrong though. A colleague and a good friend of mine from Albuquerque successfully used his plasma cleaner to glow-discharge carbon films. I decided to copy his settings in our Lab and ordered the same model. However, that model could not be sold to European customers due to some regulations. I purchased more expensive model from the same supplier. It did not work! As the result of “glow discharge”, I got empty grids, no traces of carbon. To make a long story short, we installed a needle valve and a gauge to control the vacuum degree. We got hydrophilic carbon at poorer vacuum and no carbon at better vacuum. Since then, I used the plasma cleaner for many years to prepare hydrophilic carbon surface.
In my opinion, this also makes sense. The ions in plasma have longer free path at higher vacuum. As the result, they have higher energy that can result in more efficient removal of the “dirt” from the surface.
I never read any confirmation of my “theory” that can be completely wrong but I hope it will contribute to the discussion.
Sincerely,
Sergej Masich
=============================
Dr. Sergej Masich
Dept. of Cell and Molecular Biology
Karolinska Institutet
Box 285
171 77 Stockholm, Sweden
tel: (+)46 - 8 - 524 873 61<tel:%28%2B%2946%20-%208%20-%20524%20873%2061>
mobile: (+)46 - 736 - 833 693
e-mail: Sergej.Masich at ki.se<mailto:Sergej.Masich at ki.se>

On 20 Sep 2016, at 18:33, <benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch>> <benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch>> wrote:

Hi David,

This could be right. However I doubt it. Within 20 to 30 minutes we can completely disintegrate the carbon of quantifoil grids with the glow discharge machine set so that it glows strongly without sparkling.

Cheers
Ben

________________________________________
Von: Morgan, David Gene [dagmorga at indiana.edu<mailto:dagmorga at indiana.edu>]
Gesendet: Dienstag, 20. September 2016 18:12
An: Zuber, Benoît (ANA); 3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>
Betreff: Re: glow discharge vs plasma cleaning

Ben,

   Maybe someone else on the list can shed some light on this, but I don't know whether the strength of the plasma created in an EM "glow discharge device" is comparable to that of what is called a "plasma cleaner."  I suspect not, but could be wrong.

   That said, over zealous use of a plasma cleaner can remove _all_ the carbon from an EM grid (I have done this with a lacy carbon grid), so having too much power can be a bad thing...

--
           David Gene Morgan
       Electron Microscopy Center
            047D Simon Hall
            IU Bloomington
         812 856 1457<tel:812%20856%201457> (office)
         812 856 3221<tel:812%20856%203221> (3200)
     http://iubemcenter.indiana.edu
________________________________
From: benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch> <benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch>>
Sent: Tuesday, September 20, 2016 12:06 PM
To: Morgan, David Gene; 3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>
Subject: Re: glow discharge vs plasma cleaning

Hi David and Luiza,

Many thanks for the explanations. OK this « makes sense ». But it is a shame that people use two different words for the same thing (good job from the marketing team though ! ). It would be much better to use only one term and then give specific gaz conditions. So many people are convinced that glow discharge and plasma cleaning are two different things and that you need two different machines.
We have a so-called glow discharge machine from defunct Balzers. It still functions perfectly well, it looks like what people describe as a glow discharge machine : a glass cylinder with two metal plates below and on top, and it has an needle-valve inlet. We typically let the inlet in contact with the air and let a tiny bit of air flow in to get a constant pressure in the chamber and thereby have a reproducible procedure. We can quite precisely control the pressure that we want inside. However if we want to use whatever gas mixture instead of good old nitrogen and oxygen, we can just buy and connect the relevant gas bottle(s). No need to purchase a new machine.
If I listened to what so many people told me, I would have long bought another machine, which would probably have been a waste of money and lab space. I think people should be more aware of this before spending their (tax payer ?) money.

Cheers
Benoît

De : "Morgan, David Gene" <dagmorga at indiana.edu<mailto:dagmorga at indiana.edu>>
Date : mardi, 20 septembre 2016 17:51
À : Benoit Zuber <benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch>>
Objet : Re: glow discharge vs plasma cleaning

Ben,

   They are technically the same thing _except_ that in common EM usage, "glow discharge" is done using ambient gases (i.e., you just pull a modest vacuum and create a plasma) while "plasma cleaning" is done using a specific mix of gases (Ar, O and with the Gatan device H) instead of ambient gases (i.e., you flush the chamber with specific gases, then pull the vacuum and create the plasma).

   With more O in the plasma, the cleaning tends to be stronger (burns more material in the sample) and the Ar/O mix prevents side reactions that can be caused by the abundant N in the atmosphere.

--
           David Gene Morgan
       Electron Microscopy Center
            047D Simon Hall
            IU Bloomington
         812 856 1457<tel:812%20856%201457> (office)
         812 856 3221<tel:812%20856%203221> (3200)
     http://iubemcenter.indiana.edu
________________________________
From: 3dem <3dem-bounces at ncmir.ucsd.edu<mailto:3dem-bounces at ncmir.ucsd.edu>> on behalf of benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch> <benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch>>
Sent: Tuesday, September 20, 2016 11:28 AM
To: 3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>
Subject: [3dem] glow discharge vs plasma cleaning

Dear colleagues,

I often hear people saying: „Did you treat your grid with glow discharge or with plasma cleaner?” Or : ”It is absolutely essential for application XY to pretreat the grid with a plasma cleaner and not by glow discharge!”.

Can anyone explain what the difference between glow discharge and a plasma cleaning is?

According to Wikipedia, this is the same thing (https://en.wikipedia.org/wiki/Glow_discharge). The page starts with this sentence:
“A glow discharge is a plasma<https://en.wikipedia.org/wiki/Plasma_(physics)<https://en.wikipedia.org/wiki/Plasma_%28physics%29>> formed by the passage of electric current<https://en.wikipedia.org/wiki/Electric_current> through a low-pressure gas”

I look forward to an interesting debate.
Ben

Prof. Benoît Zuber
Institute of Anatomy
University of Bern
Baltzerstrasse 2
Postfach 922
3000 Bern 9
Switzerland
Tel. +41 31 631 84 40<tel:%2B41%2031%20631%2084%2040>
benoit.zuber at ana.unibe.ch<mailto:benoit.zuber at ana.unibe.ch>
http://www.ana.unibe.ch/~exmo/<http://www.ana.unibe.ch/%7Eexmo/>

_______________________________________________
3dem mailing list
3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>
https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem

_______________________________________________
3dem mailing list
3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>
https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem

_______________________________________________

3dem mailing list

3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>

https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem

--

--------------------------------------------

Sergey Ryazantsev Ph.D.

Phone: 310-453-0748

E-mail: sryazant at ucla.edu<mailto:sryazant at ucla.edu>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20160921/4e90b5af/attachment-0001.html>