Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 39: Nanostructures at Surfaces IV (Dots, Particles, Clusters, Arrays)
O 39.2: Vortrag
Mittwoch, 28. März 2007, 16:00–16:15, H36
Collective optical properties of silver nanocrystal arrays — •Herbert Wormeester1, Stefan Kooij1, Anne-Isabelle Henry2, Marie-Paule Pileni2, and Bene Poelsema1 — 1Solid State Physics, MESA+ Institute for Nanotechnology, University of Twente, Netherlands — 2LM2N, Université Pierre et Marie Curie, Paris, France
Silver nanocrystal arrays of 5 nm diameter Ag nanoparticles surrounded by a shell of dodecanethiol are formed by drop-casting. This gives an ordered system of close-packed spherical nanocrystals that enables a thorough analysis of the electromagnetic inter-particle interactions. The position of the two plasmon resonances observed in these nanocrystals is the result of their collective interaction. This collective interaction leads to a low and a high energy plasmon resonance, excited by the electric field components parallel and perpendicular to the interface, respectively. The magnitude of the plasmon resonance splitting previously observed using a variety of different techniques is also found in ellipsometry spectra. We analyzed that the peak separation in the silver nanocrystal arrays is comparable to the optical response of isolated, non-interacting oblate nanocrystals. The optical deformation of the spherical particles as a result of the interaction can be compared with oblate particles that have a depolarization factor of 0.25 parallel to the interface. The ellipsometry measurement shows a better resemblance between calculation and measurement as compared to polarized reflection measurements. Most likely, this is due to the sensitivity for diffuse scattering of the latter technique.