Studies of Mineral compounds
My last XPS experiments coupled with Ar+ sputtering tend to show an increase of the carbon content in the etched surface composition. Does it mean that the adventitious carbon is re-deposited and concentrated onto the surface after the etching session? Could we think the analysis chamber pressure would be a key parameter?
Dear Jean-Charles,
There are following possible mechanisms and reasons.
Straying of the few near-surface layers (due to sputtering) and then backward re-deposition.
Why re-deposition occurs? The sample is charging under XPS(except well conducting samples) due to the loss of photoelectrons. That is the reason.
Charge neutralizer sometimes does not help, especially in the case of wide-gap insulators (like SiO2).
Another possible reason - vaccum hydrocarbons (depends on the quality and type of vacuum system).
Regards
Dmitry
Thank you for these interesting points. I'm going now to check out what's going on in regard of all the given hypothesis.
With my best regards
First of all I would check the Ar purity. If the gas line was pumped by a rotary pump you might have a lot of carbon even if the pumping was weeks ago. Try to degas the ion source very carefully. The next point will be the sample. Has the investigated surface an affinity to react with carbon species from the background pressure from your chamber. If your vacuum in the chamber is 10-8 you have with an reactive surface within 100 sec a carbon surface layer. Check the position of your sputtered spot by using an oxidized Ta sheet. It will show a blue luminescence where it is hit by Ar ions. If your analyzer has a hole in the spheres in the line of the lens and a window on the top you might see the spot and align it with the focus of the lens of your spectrometer.
I think C contamination in your Ar source has to be checked. Is it a filament type Ar ion source, if so a poorly degassed filament will certainly lead to this problem. The other thing is you don't say what material you looking at but are you sure it is C? If you are looking at oxide materials they are often contaminated with K which has a peak about 5 eV above C which at first glance might appear to be C in a wide scan.
Most of the previous answers should be checked, but my large experiencia with Ar-etching/ XPS suggest to me as more likely the contamination of the gun or the presence of carbonates in your sample
Dear Jean Charles:
Perhaps, you may find some information about the significant chemical changes that may occur in the C1s XPS high resolution peak when FeCO3 specimens are etched
with argon ions for even short periods of time (1 minute)
in the following manuscript
An XPS characterization of FeCO3 films from CO2 corrosion
Corrosion Science, Volume 41, Issue 7, 1 July 1999, Pages 1231-1243
J.K. Heuer, J.F. Stubbins
Kind Regards
I would agree with the points already discussed here in. Certainly gas purity has a large effect (and can reduce the lifetime of your argon gun), although carbonates should be investigated - this would easily be seen on the high resolution scan of the C(1s) region as opposed to just a wide scan for example.
As an aside, are you using a standard argon ion gun as opposed to an argon cluster source? The former will be more damaging to the minerals due to preferential sputtering
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