EXAFS-cumulant study of nanoparticles: differentiating real thermodynamics from artifacts

CARUSO, M.; GIOVANETTI, L. J.; JOSE MARTIN RAMALLO LOPEZ; REQUEJO, F.G.; KOEBEL, M. M.; SOMORJAI, G. A.

Campinas, Brasil

Congreso; XVII Reunión Anual de Usuarios, Laboratorio Nacional de Luz Síncrotron; 2007

Laboratorio Nacional de Luz Síncrotron

The standard treatment of the thermal disorder in EXAFS trough the harmonic Debye-Waller factor exp(-2k2S2) has become inadequate with respect to the increasing accuracy of experimental data and analysis techniques. Recent works have shown that enharmonic effect can not be neglected even in the case of bulk material like Ge when trying to obtain structural information as a function of temperature. In the case of nanoparticles, the effects of not including the third order cumulant in the analysis routine, gives a non physical distance contraction in metallic system, when increasing the temperature. In this work Pt nanoparticles (NP) of about 2-3 nm were synthesized by seeded growth and direct ethylene glycol reduction methods and stabilized with poly-(vinylpyrrolidone) (PVP). EXAFS experiments were performed at seven different temperatures to investigate the thermal behavior of these nanoparticles. We shown the different trend observed when the third order cumulants in the interatomic distance is introduced. To correlate the distance distribution moments with temperature we parameterize the near-neighbor interaction in our material as a one-dimensional enharmonic potential in interatomic distances.