Correlation between linear optical constants and Raman enhancement in phthalocyanine thin solid films with incorporated silver clusters

Surface-enhanced Raman spectroscopic (SERS) experiments on thin films of fr ee base phthalocyanine (H2Pc) with embedded silver clusters are reported, T he thin films were produced by thermal evaporation of H2Pc together with di fferent amounts of silver (8, 15 and 26 vol.%), From transmission electron microscopy it turned out that the average silver cluster diameter changes f rom approximately 4 to 7 nm with increasing silver concentration The plasmo n wavenumber of the silver clusters was obtained from spectrophotometric me asurements and was close to 22 000 cm(-1) (approximately 450 nm), nearly in dependent of the silver filling factor. Raman spectra of H2Pc were recorded at two different exciting laser wavelengths (441.6 and 568.2 nm), being ei ther close to or well separated from the plasmon resonance, The intensity o f the Raman scattering increased with increasing silver filling factor in t he films, while the lineshape of the Raman spectra was not seriously influe nced by the cluster incorporation. A systematic correlation between the int ensity of the plasmon absorption line and the Raman enhancement could be es tablished and is discussed in terms of an electromagnetic enhancement mecha nism. Copyright (C) 1999 John Wiley & Sons, Ltd.