Surface-enhanced Raman scattering and SERRS imaging of phthalocyanine mixed films

Abstract

The objective of the present work is the study of the surface-enhanced spectroscopy of mixed thin solid films of metallophthalocyanine ( MPc ; M ≡ Cu , Co ) and bis(n-propylimido)perylene ( Bis - PTCDPr ) materials fabricated by vacuum co-evaporation onto silver island films. The surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) of neat Bis - PTCDPr , CuPc and CoPc were also recorded using visible 514.5 and 633 nm laser lines and near-infrared excitation at 780 nm. During the investigation it was found that the Raman scattering (RS) and resonance Raman scattering (RRS) spectra of CuPc and CoPc films were sensitive to the irradiance at the sample. To further explore the effect of local heating on the vibrational spectrum, a temperature dependence (between −180 and 200 °C) study was carried out using the 514.5 nm laser line with constant laser power. The overtones and combinations of the CuPc and CoPc molecules were also clearly observed in the RRS and SERRS spectra. The study of the SER(R)S spectra allowed us to conclude that the dyes of the mixed films were physically adsorbed onto the silver islands. It is also shown that, in mixed films, differences in the absorption properties can be used to tune into the spectrum of any one of the components of the mixture with the appropriate laser line. For the first time, SERRS mapping and global imaging of mixed films obtained with the 514.5 nm laser line are reported. Complementary information about the quality of the films, homogeneity and phase separation may be obtained using SERRS imaging.