Vibrational coherence of self-organized silver nanocrystals in f.c.c. supra-crystals

The coherent vibrations of silver nanocrystals when they are self-organized in face-centered cubic (f.c.c) supra-crystals were analyzed. This vibrational coherence was observed by a substantial change of the quadrupolar low-frequency Raman scattering peak. Silver nanocrystals with 5 nm average diameter and 15% size distribution were deposited either on a highly oriented pyrolitic graphite (HOPG) substrate at 10 °C or 30 °C, or on amorphous carbon (a-C) at 22 °C. It was found that the low-frequency shift of the Raman peaks observed in supra-crystals is likely to be due to the Lorentz electric field created by the excited dipolar plasmons on each nanocrystal.