I am trying to evaporate NaBr onto Ta and py-C substrates using a metal buffer layer. I thought Au would work, but the topography of the resulting films is markedly different for the two substrates. Would Cr be better?
It is very difficult to make a closed layer on HOPG and the like. The reason is that the adatom mobility is very high and the bonding not utterly strong. As a result, it is very easy to produce adatom clusters at defects of the substrate surface. There are ample of papers in the literature, where this has therefore been used as a means to fabricate particles.
I recall some work on Ni on graphite, though, where layer formation was seen. I'd have to search it. It could be that H.-J. Freund is among the authors, but I don't recall the first author right now.
If you are electroplating on the c-axis of the PG, Cu electroplating works well. It is easier to plate on the a-b axes....... having urea in the plating bath helps. Different Cu sources work including CuSO4 and Cu(NO3)2. The deposition of
Cu from a CuSO4 aqueous solution shows a bit of sulfate on the surface. In
contrast, the use of Cu(NO3)2 does not. Roux and Belanger in Canada did some theoretical work on this as well.
1) a previous preparation of the graphite surface, e. g. using a strong acid treatment, improves the adhesion of subsequently deposited layers
2) I would go for Ti or Ni evaporated layers; they have a strong affinity for carbon
Thanks James but I need evaporation, not electroplating. Thanks Christian: I was planning Ni but we'll treat the surface first as you suggest.
Actually Cr would work as well, but in my experience (which is actually mostly on diamond substrates), it is a bit less reliable than Ni or Ti.
Well, a treatment with acid (or even better, an Ar:O plasma) leads to an oxygen-rich, contaminant free surface which seems to promote bonding with metals. For Ni, Ti and Cr, it's just that they have a high affinity for carbon.
Christian, a carbon surface which is both, oxigen rich and free of contaminants - that sounds quite like an oxymoron to me. What is known about the fate of the oxygen upon metal adsorption and what is the (oxidation) state of the metal right at the interface? (any good references?)
True, sorry, I was talking about organic contaminants. As for the metal oxidation state, I don't have any reference to provide as 1) the procedure to get a good adhesion on carbon comes from my own experience (there is some literature on similar experiments that I can provide if you are interested) and 2) I am not aware of any good method to get that type of information, except maybe a vary careful experiment using in situ XPS on ultrathin films, which I can't do
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