[Ifeffit] Need an advice

[Anatoly Frenkel]

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

******************
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 at yu.edu
http://www.yu.edu/faculty/afrenkel

  -----Original Message-----
  From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov]On Behalf Of Steven S. Lim
  Sent: Thursday, May 05, 2005 3:13 PM
  To: ifeffit at millenia.cars.aps.anl.gov
  Cc: Gary L. Haller; Yanhui Yang; Yuan Chen; Lisa D. Pfefferle; Dragos
Ciuparu
  Subject: [Ifeffit] Need an advice


  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
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