Thickness-Dependent Raman Scattering from Thin-Film Systems

The intensity of the Raman signal from a thin-film multilayer varies nonmonotonically with the thickness of the thin-film layers due to interference of the excitation and Raman scattered light within the films. This phenomenon can be used to not only enhance the Raman signal but also investigate thin-film thickness and optical properties. Here, we perform an experimental study of the thickness dependence of the Raman signal from several thin-film material systems, including silicon-on-sapphire (SOS) and silicon nitride on SOS thin films, and multilayer MoS2 prepared on silicon substrates. The measured intensities appropriately scaled are compared to an analytical model developed from the transfer matrix method. A good fit is found for the SOS thin films when the laser spot size is sufficiently larger than the film thickness. For the multilayer MoS2, an excellent fit is found for the intensity of the Raman signal from the underlying Si substrate, while the intensity of the MoS2 characteristic Raman shifts is impacted by laser parameters and sample orientation. These results have implications for thin-film metrology and optical properties characterization.