Disclaimer: I'm
an experimentalist and not a theorist.
I'm not sure that
Zhao and Montano's calculations are correct. I think their calculation for
the transition probability assumes that the electron density is constant when,
in actuality, there is a spatial dependence resulting from quantum confinement
effects. As a result, the energy of the surface plasmon peak as calculated
by Zhao and Montano is constant for all cluster sizes at approximately the
classical value of omega(bulk plasmon)/3^0.5 and shows an increase with
decreasing particle size. Including quantum confinement results in a blue
shift of the surface plasmon resonance with decreasing particle size and a
decrease in transition probability for decreasing particle sizes (as suggested
by Anatoly). This change in the calculation will also impact the bulk
plasmon and I don't know what that trend will be.
As far as their
experimental demonstration with Fe nanoparticles is concerned, I really can't
make an assessment about the experiment since they don't indicate how the
nanoparticle size was determined and I'm not familiar with their preparation of
the nanoparticles.
I'm not sure from
this paper what the impact on the MFP will be although there very well could be
some effect on the EXAFS. Personally, when I began working on EXAFS of
nanoparticles and small clusters (Au13), I was leery of using the bulk phase and
amplitudes to fit the data. My experience to this point has been that
there have not been observable deviations of coordination numbers for
nanoparticle systems using these FEFF inputs. That being said, I tend to
agree with Matt that this is something that people working in this area need to
think about a bit more than it seems they have judging by the literature.
I would like to see some (correct) theoretical assessments that support the
assertion that bulk phases and amplitudes are ok for nanoparticles that I think
has been demonstrated by validating EXAFS results with other techniques (mostly
electron microscopy).
-Laurent