It seems like one of the problems we have been solving, the analysis of thiol-stabilized Pd nanoparticles where the nanoparticles coexist with low molecular weight Pd-thiol complexes, or polymers. It is another example of a heterogenous mixture you described. We found that it to be very speculative to attempt to determine the nanoparticle size by the method you described, since the Pd-S bonds in our cases were present in the surface of the nanoparticles, and in the polymers, both types contributing the same peak in r-space of EXAFS. In your case, I assume, the problem is how to discriminate the contribution of Co-O to the low r-peak: what portion of it is due to the nanoparticles, and what - due to the Co oxide. It is, perhaps, possible to construct a model that will account for the: 1) mixing fraction of the two phases, 2) size of the particles, and 3) the surface coverage of the oxides. However, there are many options in the S binding on the Pd particle, or O binding on Co particle, and I find this procedure a sort of circular reasoning. What we did with Pd particles: we obtained their size by TEM and used that information to calculate the average coordination number of Pd-Pd first nearest neighbors. After that, we obtained the relative mixture of nanopartlces and polymers, so it is sort of a backward approach, may be conservative but not too ambiguous.

******************
Anatoly Frenkel, Ph.D.
Associate Professor
Physics Department
Yeshiva University
245 Lexington Avenue
New York, NY 10016

(YU) 212-340-7827
(BNL) 631-344-3013
(Fax) 212-340-7788

anatoly.frenkel@yu.edu
http://www.yu.edu/faculty/afrenkel

Dear all,

I have a question to ask all of you as follows.

We have been investigating the EXAFS of some partially reduced Co materials (by Co EXFAS) and would wish to obtain some qualitative information on the Co metal particles. If, in fact, the Co had some average coordination environment because we have a distribution of Co particle sizes with oxygen adsorption, analyzing the windowed Co-O and Co-Co peaks together as a linear combination and assessing the average oxygen and Co coordination from the Co edge absorption (what we do with Athena) would appear to give a useful answer. However, if what we have is closer to a physical mixture of small Co metal particles and Co oxide particles, it would seem that it would be more appropriate to analyze separately the windowed Co-O and Co-Co peaks in R-space, to somehow normalize the Co-Co to the fraction of metal in the sample and use this as a qualitative measure of metal particle size. Is there a way to do this with Athena or other method? Or do you know of a reference where this has been discussed? Of course, we can (and will) make experimental mixtures as references but wonder if there is a different way of doing the analysis or if there is some literature on this problem (which we have not been able to locate).

Thank you.

Steven