Trace Oxygen in Carbon Coat

[Probeman]

I have a question: if one wanted to attempt to measure the concentration of oxygen in a typical amorphous 20 nm carbon coat, what substrate should one utilize for this purpose?

Gold comes to mind, but it is a high Z (high background) and difficult to polish...

Any ideas, anyone?
john

[jon_wade]

its going to be pretty blinkin' low if its a carbon evaporation coat, almost by definition.  it can only be there as a consequence of oil contamination, no? 

[Probeman]

its going to be pretty blinkin' low if its a carbon evaporation coat, almost by definition.  it can only be there as a consequence of oil contamination, no?

Well, yes on being "pretty blinkin' low", but no on just from oil contamination...

I figure any trace oxygen in the vacuum (mainly water vapor?) will get converted to CO or CO2 by the hot carbon vapor. But then my question is: can the CO or CO2 get "buried" by carbon vapor as in an ion pump effect such as how noble gases can get "pumped" by sputter "burial"?

And as you say, any contamination from pump oil might have some oxygen depending on the oil variety. Hydrocarbon oil is probably fairly low in oxygen, but silicone pump oil will definitely have some.

[Les Moore]

Trace light element work hmmmm.
Could you attempt anything harder?

How about BN as a substrate? 
True, the B & N will absorb the C but only those X-Rays heading "south".
You will need low kV to get a decent yield from the film.