Hello,
We recently switched from an air plasma (purple/pinkish) to an O2 plasma to do surface activation (mostly to stick PDMS to glass), for more reproducibility.
However, our plasma is now pale purple and not very shiny (and doesn't give a good binding). There is no apparent leak, the chamber has been cleaned, I tried different ranges of pressure and power, but still, no chance.
Some people say it is the normal color of an O2 plasma because it emits in unvisible spectrum, some others claim it should be light blue, some others that it's milky yellow...
I maybe missed it but I could not find any published work quantifying that.
In other words, what is the color of an O2 plasma?
Thank you!
Théo
Hi Théo
,
I also work with a pure O2 plasma, ignited in a DBD reactor. The plasma has a pale purple colour. This should indeed be the normal colour for an oxygen plasma.
Regards,
NielS
O2 plasma in my Harrick Plasma Cleaner is pale purple. Color varies a bit based on humidity and is caused by the inclusion of the hydrogen from water that is desorbing from the chamber interior. Power, pressure, and excitation frequency will also cause color to vary. The color shift to pink in the air plasma is from the inclusion of Nitrogen and more Hydrogen from water.
If you want to make sure that you are getting pure O2 plasma, your will need to bake out your chamber to get rid of the water. When you switch from air to O2, you'll have to reoptimize your process since the surface oxidation rate will change. Over treatment causes surface damage that will prevent bonding. If you have access to an AFM, you can look at the surface morphology vs. treatment time to aid in the optimization.
It is my opinion that air plasma is better than O2 plasma for a number of reasons. First, you don't have to worry about the hazards of pure O2. Second, you need ample OH groups and water is the best place to get them. Otherwise you need to remove hydrogen from the cleaved methyl groups to get the hydrogen required to form the hydroxy groups.
Thank you both Niels Wardenier and Ron Reiserer for your answers.
Indeed, I really have a plasma of oxygen. I was using the parameters of a colleague, which "oxygen" plasma is light blue btw (like what https://en.wikipedia.org/wiki/Plasma_cleaning says)...I guess he has some kind of carbon contaminations?
Since I halved the power of the generator and increased the pressure, it now sticks properly: my plasma was way too strong I guess.
Just to be sure, when we say pale purple, it means purple with low intensity or purple like the last part of this video ? https://www.youtube.com/watch?v=vYnl-wNq0JE
Sources are very misleading...
Best
By "pale" I mean mostly white plasma with a tint of purple. There is considerable variability in plasma color based on power, pressure, excitation method, etc... I think it would be hard specify a truly "correct" color that would apply to all plasma.
It's great that you have it working now.
Depends on oxygen amounts and noble gas.
With He, it's almost completely white. With Ar, you'd expect a light purple to white-ish.
Its a hot discussion going on.
Could anyone share us the photograph of oxygen plasma discharge?
Its a CCP plasma operated with 13.56 MHZ RF power supply. I dont have other details except the photograph.
Our is Harrick. It gives brilliant purple with air (nitrogen), and undetectable white (colourless) with O2.... I am a newbie, and I am figuring out how I may optimise my processes for achieving functionalised surfaces. I have been using 1000 -1300 mTorr over 15mins(!!!) to clean glass slides... Still feeling weird how I may be able to treat the glass slides only for 15s (or 40 - 60s), when the steps/process to stopping the equipment itself takes more than 2 mins.
I think I need all the advice, please.
Thanks ahead.
Hi Ebenezer,
I am using O2 at 0.8 mbar for 20s with a power of 10W. Gives satisfying results.
Best
I haven't worked with O2 in particular, but we witness the same variation in N2. All plasmas (especially diatomic) are sensitive to excitation condition, such as pressure, electron temperature, vibrational temperature, ICP vs CCP, etc. This is important because if you look at the optical emission spectrum for O2, I'm sure you'll see some peaks in the range of
This is what I got at 6.0e-3 mBar pressure with 50 sccm of oxygen
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