SAXS and EXAFS studies of ion beam synthesized Au nanocrystals

We have used small-angle X-ray scattering (SAXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy to investigate Au nanocrystals (NCs) fabricated by high dose ion implantation into thin SiO₂ and subsequent annealing at different temperatures. Size distributions were determined from SAXS and structural parameters were extracted from EXAFS measurements, the latter analyzed as a function of NC size. Increasing implantation dose leads to an increasing average NC size and broadening of the size distribution. A significant size-dependent bond length contraction with respect to bulk material was observed. For samples annealed at 1100 °C our analysis suggests that an increased structural disorder is predominantly located at the NC surface. Post-implantation annealing at temperatures of 500 °C and 800 °C for 1 h in forming gas had no detectable influence on the NC size distribution, however, a significant influence on the structural parameters, in particular increased disorder was observed. This is potentially the result of stress induced disorder due to the different thermal expansion of the NC and matrix materials.