[Ifeffit] EXAFS mean free path in small particles

Anatoly Frenkel frenkel at bnl.gov
Tue Jun 14 10:39:08 CDT 2005

[Ifeffit] EXAFS mean free path in small particlesMatthew,

This is one of the references stating that surface plazmon intensity
vanishes as the particle size gets smaller than 2nm: C.N.R.Rao et al,
Size-Dependent Chemistry: Properties of Nanocrystals, Chem. Eur. J. 2002, 8,
No. 1, p. 29. Here is the quote: "Gold nanocrystals of varying diameters
between 2 and 4nm exhibit distinct bands around ~ 525 nm, the intensity of
which increases with size (ref, ref). The intensity of this feature becomes
rather small in the case of 1 nm diameter particles basically due to a
reduced number of "itinerant" electrons in the electron cloud." There are
other evidences that small particles have DOS similar to molecules, not
typical metals. Most notable is the evidence that HOMO-LUMO band grows to
more than 1 eV at sizes of 1 nm range.

The point is, to my opinion, that since In the most interesting range, below
2nm, the plasmon activity decreases, therefore its effect on EXAFS
interpretation, if any, should be negligible.



  -----Original Message-----
  From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov]On Behalf Of matthew
  Sent: Tuesday, June 14, 2005 11:09 AM
  To: ifeffit at millenia.cars.aps.anl.gov
  Subject: [Ifeffit] EXAFS mean free path in small particles

  I'm working on a couple of projects involving nanoparticles, and a
collaborator pointed out an old paper
  by Zhao and Montano (PRB 40,3401(1989)) which claimed theoretical reasons
why the electron mean free
  path in nanos should be smaller than in bulk.  This would cause
coordination numbers to be underestimated.
  The effect is supposedly due to a surface plasmon which grows in
importance as particle size shrinks.

  I have reasons why I think this paper exaggerates the possible effects,
but I'm posting this to see what
  other people think about this effect.  The paper seems to have gone down
into obscurity, but that doesn't
  mean it isn't right.  Thanks.
          Matthew Marcus
  Ifeffit mailing list
  Ifeffit at millenia.cars.aps.anl.gov
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