Non-linear optically active metal clusters in nanoscaled systems includingself-assembled organic films

Linear and non-linear optical spectroscopies are applied to monitor the for mation of large, several 10-nm-sized alkali clusters near epitaxially grown Au films on mica substrates. The Au films are covered by ultrathin, self-a ssembled alkane thiol films, The growth and morphology of these clusters ar e initially monitored in ultrahigh vacuum by comparison of calculated with measured polarization-dependent extinction spectra. We find that at low sur face temperatures (150 K) the cluster growth is very similar to growth dire ctly on insulating substrates. With increasing surface temperature the size distribution of the clusters changes. A quantitative evaluation of ambient -air measurements with scanning force microscopy (SFM) supports the conclus ions from optical spectroscopy. Field-enhancement effects at the surface of the clusters facilitate the observation of second harmonic (SH) light. Fro m angular- and polarization-dependent SH-measurements we deduce ratios of c hi((2))-tensor components for the cluster-films. (C) 2000 Elsevier Science S.A. All rights reserved.