Hi Michael,

On Mon, Jul 7, 2014 at 10:49 AM, Michael Weir <mgweir@udel.edu> wrote:

Hi Matt and Zhan,
I think this is the point where adding another approach would be very useful. In my limited experience, XAFS was much more powerful when combined with other techniques to eliminate potential models. We also needed to use our "chemical sense".

Oh, yeah, that's absolutely correct. The example was definitely "what Z sensitivity does XAFS alone have?". Zn-Rb and Zn-Ga make absolutely no sense (part of the fun, really!). Zn-Br would be at a very different distance (again, the bond-valence idea).

Is there a reason you would suspect Se, Ge, Ga, or any of the other elements in your material? Could you use your beamline to look for these elements by a quick scan of one of their stronger transitions? If there is a full coordination shell, detecting the other element this way is feasible. However, as someone else mentioned recently, dopants would be much more difficult to detect.

Is there another analytical technique you could use to narrow down the possible elements in your system?

Yes, just having an XRF spectrum for the sample can probably tell you that many atomic species are not present, which might be obvious but is highly useful. For ZnSe, I think we could confidently conclude that the Ge and As concentrations were something below 10 ppm.

Anyway, yes, definitely use "chemical sense", either qualitative (Zn-Rb makes no sense) or quantitative (the As concentration is at least 2 orders of magnitude lower than Se concerntration).

--Matt