Interference-enhanced Raman scattering of F16CuPc thin films

Interference-enhanced Raman scattering (IERS) was observed for thin films of copper(II) hexadecafluorophthalocyanine (F16CuPc) deposited on SiO2 layers on a Si substrate. The enhancement of the Raman scattering originates from the interference of the light in the transparent SiO2 layer. Stripes of SiO2/Si with gradually varying oxide layer thickness were used as IERS substrates for a systematic study of the enhancement parameters. Raman measurements were carried out using three laser lines (325, 514.7, and 632.8 nm) in order to probe the F16CuPc thin films at non-resonant and resonant Raman conditions. Spectroscopic ellipsometry was used to determine both the SiO2 layer and thin film thicknesses. The intensity enhancement of the F16CuPc Raman peaks occurs periodically, corresponding to the alternating interference conditions for the Raman scattered light with increasing SiO2 layer thickness. The enhancement factors were calculated using the optical constants of the layers involved and the geometric parameters. This allows a straightforward application of IERS for optical studies of thin films and interfaces by calculating the dielectric thickness where maximum Raman enhancement is expected.