Crystallinity Dependence of the Plasmon Resonant Raman Scattering by Anisotropic Gold Nanocrystals

Au nanocrystals (NCs) with different crystalline structures and related morphologies are unselectively synthesized using an organometallic route. The acoustic vibrations of these NCs are studied by plasmon mediated low-frequency Raman scattering (LFRS). A splitting of the quadrupolar vibration mode is pointed out in the LFRS spectrum. Comparison of the measured frequencies with calculations and careful examination of the NCs morphologies by transmission electron microscopy ascertain this splitting as being an effect of crystallinity. The excitation dependence of the LFRS spectra is interpreted by the shape-selection of the NCs via plasmon−vibration coupling. These results give new insights into the crystallinity influence on both the vibrations of the NCs and their coupling with plasmons and demonstrate the relevance of elastic anisotropy in monodomain NCs.