A long time ago when carbon fiber for sputtering was first introduced I ran
an Auger spectrum (surface analysis of the first couple of atomic layers) on
the "coating". It turned out to be a thin layer of partially oxidized
aluminum.

The carbon fiber was held by aluminum clamps.

 

-Joe

Joe Geller

Geller MicroAnalytical Laboratory, Inc.

426e Boston St.

Topsfield, Ma 01983 (USA)

978 887-7000, fax 978 887-6671

www.GellerMicro.com

 

 

 

From: JEOL-Focused Probe Users List <[log in to unmask]> On Behalf Of
Straszheim, Warren E [BIOTC]
Sent: Tuesday, December 17, 2019 4:07 PM
To: [log in to unmask]
Subject: Re: [PROBEUSERS] Sputter coated carbon vs evaporated carbon for
epma

 

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]
<mailto:[log in to unmask]> > On Behalf Of Michael Jercinovic
Sent: Tuesday, December 17, 2019 1:16 PM
To: [log in to unmask] <mailto:[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

1215 West Dayton Street, Madison, WI 53706

mobile 608-438-7480

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