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

Abstract

Surface-enhanced Raman spectroscopic (SERS) experiments on thin films of free base phthalocyanine (H 2 Pc)with embedded silver clusters are reported. The thin films were produced by thermal evaporation of H 2 Pc together with different amounts of silver (8, 15 and 26 vol.%). From transmission electron microscopy it turned out that the average silver cluster diameter changes from approximately 4 to 7 nm with increasing silver concentration. The plasmon wavenumber of the silver clusters was obtained from spectrophotometric measurements and was close to 22 000 cm −1 (approximately 450 nm), nearly independent of the silver filling factor. Raman spectra of H 2 Pc were recorded at two different exciting laser wavelengths (441.6 and 568.2 nm), being either close to or well separated from the plasmon resonance. The intensity of the Raman scattering increased with increasing silver filling factor in the films, while the lineshape of the Raman spectra was not seriously influenced by the cluster incorporation. A systematic correlation between the intensity of the plasmon absorption line and the Raman enhancement could be established and is discussed in terms of an electromagnetic enhancement mechanism.

Controlling the Optical Properties of Plasmonic Disordered Nanohole Silver Films

“…Surface plasmons (SP), collective electron oscillations at the surface of noble metals, have demonstrated tremendous potential as a route to tailor and selectively amplify myriad optical phenomena in molecular thin films. − A simple method for the integration of plasmon active materials into opto-electronic devices is the addition of metal nanoparticles. ,− An alternate route to introduce plasmon effects is the addition of subwavelength scale holes in a metal surface. − We have recently used this approach in an organic photovoltaic device . Here we present a thorough characterization of the electrical and optical properties of random nanohole arrays as a function of hole density.…”