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
>>
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