J. Phys. Colloques
Volume 38, Numéro C2, Juillet 1977Conférence Internationale sur les Petites Particules et Amas Inorganiques / International Meeting on the Small Particles and Inorganic Clusters
|Page(s)||C2-161 - C2-161|
J. Phys. Colloques 38 (1977) C2-161-C2-161
MÖSSBAUER SPECTROSCOPY OF SMALL GOLD PARTICLESM.P.A. VIEGERS and J. M. TROOSTER
Department of Physical Chemistry, University of Nijmegen, Toernooiveld, Nijmegen, The Netherlands
The intensity of Mössbauer absorption lines is proportional to fa = exp(- <x2>/λ 2), where <x2> is the mean squared vibrational amplitude of the absorbing atoms and 2 πλ = λ is the wavelength of the absorbed radiation. Intensity measurements of the Mossbauer effect in small particles can thus give information on changes in the phonon spectrum. A short review will be given of earlier work, which shows conflicting results. In this report results will be given of measurements on nine samples of small gold particles suspended in frozen gelatin. Average sample diameters range from 30 Å to 170 Å. The intensity of the Mossbauer absorption of the 77 keV transition of 197Au as measured as function of temperature between 4.2 K and 60 K. It is found that the Mössbauer fraction fa (and therefore <x2>) at the lowest temperature does not deviate considerably from the value of bulk gold. However, with increasing temperature fa decreases more rapidly than in bulk, with strongest decrease for the smallest particle size. The various models for the phonon spectrum which were used to calculate the temperature dependence of fa will be discussed, but it appears that to explain the observed fa(T) it is necessary to take account of the vibrational amplitude of the particle as a whole. The implications for the study of small particles by means of the Mössbauer effect will be discussed.