Temperature-dependent EXAFS analysis of embedded Pt nanocrystals

The vibrational and thermal properties of embedded Pt nanocrystals (NCs) have been investigated with temperature-dependent extended x-ray absorption fine structure (EXAFS) spectroscopy. NCs of diameter 1.8-7.4nm produced by ion implantation in amorphous SiO₂ were analysed over the temperature range 20-295K. An increase in Einstein temperature (∼194K) relative to that of a Pt standard (∼179K) was evident for the smallest NCs while those larger than ∼2.0nm exhibited values comparable to bulk material. Similarly, the thermal expansion of interatomic distances was lowest for small NCs. While the amorphous SiO₂ matrix restricted the thermal expansion of interatomic distances, it did not have a significant influence on the mean vibrational frequency of embedded Pt NCs. Instead, the latter was governed by finite-size effects or, specifically, capillary pressure.