Hi everyone,
We are involved in characterisation of DLC and a-C:H thin films for which we determine the sp²/sp³ ratio by XPS.
In order to evaluate the uncertainty applying to the sp²/sp³ measured ratio, we would like to perform an analysis of variance (ANOVA) of our results but for doing that, we need to find a good reference material. The best would be a CRM for which the sp²/sp³ ratio is certified, but as a minimum we need a sample for which this sp²/sp³ ratio is uniform over the all surface so that we can be sure to measure the same thing at different occasions.
Any recommendation for identifying the best candidate will be very welcome.
Many thanks beforehand.
Best regards,
Julien
HOPG would be the idea sample for sp2 sample, maybe a samples of polyethylene and polypropylene would work for the sp3 sample.
Then to make the calibration set you could artificially mix the two samples by summing the spectra with different weights. The hard part would be making sure you have calibrated the binding energy appropriately.
Why not take some organic compounds? E.g. naphtalene as sp2, paraffine as sp3 as well as some "intermediates", e.g. polystyrene as 25% sp3, polybutadiene as 50% sp3, polyisoprene as 60% sp3, ...
I would suggest graphene on a Cu Substrate for sp2 and diamond for sp3. Be aware that a semiconductor may have a surface band bending which might give a different position of the valence band edge to Ef in depth, so a sufficient doping might be de necessary for diamond. Usually even natural samples are sufficiently N-doped.
@Julien: I would suggest HOPG for sp2, a high purity HOPG will work perfectly well for this. And, Diamond will work perfectly well for sp3.
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