I strongly agree with Mike. These carbon layers are not sputtered. They are deposited within a "sputter " coater, but it is not working as a sputtering device. The power is not spent sputtering but in heating a carbon yarn or fiber. It tends to be a much shorter process than high vacuum evaporation. I recall that it is sometimes referred to as flash evaporation.
I have done both, but I prefer the quality and uniformity of the coatings from regular, high-vacuum evaporation. I am concerned that the flash carbon oxidizes in the process if there is any oxygen present. I also suspect bigger clusters of carbon and a less continuous coating.
Warren Straszheim,
Materials Analysis and Research Lab
Iowa State University
From: JEOL-Focused Probe Users List <[log in to unmask]> On Behalf Of Michael Jercinovic
Sent: Tuesday, December 17, 2019 1:16 PM
To: [log in to unmask]
Subject: Re: [PROBEUSERS] Sputter coated carbon vs evaporated carbon for epma
Hi John and John,
Probably not really sputter coated, but more likely vacuum evaporated at low vacuum. Goldstein et al states that "For a variety of reasons (Echlin et al., 1985), it is not possible to sputter carbon by either diode or plasma-magnetron laboratory coaters." These coaters basically generate a plasma from the gas in the chamber using high DC voltage. Ion-beam sputtering could work with a carbon target but that seems less likely as that sort of apparatus is not so common, and low vacuum evaporation would basically do the same thing where there is enough gas in the chamber to scatter carbon to coat reasonably in three dimensions. For flat/polished specimens, I can't imagine why you would use any sort of sputtering technique which has all kinds of contamination and thickness variation problems. We have a (now obsolete) xenon magnetron coater that attempts to deal with this for metal coating by sputtering Ti using Xe as a sputtering gas behind a shield first to get rid of most of the free remaining oxygen, etc. at low vacuum, then introduces more Xe gas so the procedure is very clean when you get to sputtering the second coating target (Pt in our case for SEM) after removing the shield. Yes, Xe and Pt, now those are some cheap consumables there for sure...
Mike J.
On 12/17/2019 1:41 PM, John Donovan wrote:
Hi John,
I've seen significant variation in thickness using sputter coaters, though using metal targets. Here is what Ben Buse showed for Ag on a thin section:
https://probesoftware.com/smf/index.php?topic=1232.0
I would assume it's also a problem for carbon sputter coating, though I have not tested a modern carbon sputter coater.
john
On 12/17/2019 10:33 AM, John H Fournelle wrote:
Does anyone have any comments (direct or indirect evidence) or know of any references, to something I've wondered about for a long time.
Decades ago, someone brought me some samples from materials science here, where I was told that the carbon coating was deposited by sputtering. I had difficulty acquiring good epma results, so I removed the carbon coat, coated in my evaporator, and had good results. From then on, I assumed that
"sputtering of carbon" might not be as "good" as evaporated carbon, though I never did any true test (yes, the coating thickness might have been greatly different from my standards, I know now).
Was I wrong to cast a negative light upon sputtered carbon coating for epma? Any thoughts?
John Fournelle Ph.D.
Senior Scientist
Department of Geoscience, University of Wisconsin
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Michael J. Jercinovic
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