Structural correlations with shifts in the extended plasma resonance of gold nanoparticle aggregates

The correlation between the structure and shift of the extended surface plasma band in gold nanoparticle aggregates has been studied using small angle X-ray scattering (SAXS) and ultrasmall angle X-ray scattering (USAXS) techniques. The reduction of HAuCl4 by Na2S produces gold nanoparticle aggregates with an extended surface plasma absorption band in the near infrared region. This absorption blue shifts during the course of the reaction. SAXS and USAXS experiments were used to monitor the structure of the aggregates at different points in the reaction while the corresponding UV-VIS spectra were measured. Based on the data obtained, it is proposed that as the reaction progresses the aggregate structure changes, and this changes is the causes of the blue-shift in the near infrared absorption band during reaction.