Surface-Enhanced Raman Scattering of Silicon Nanocrystals in a Silica Film

Surface-enhanced Raman scattering (SERS) is an intriguing effect, efficiency of which depends on many factors and whose applicability to a given system is not obvious before the experiment. The motivation of the present work is to demonstrate the SERS effect on silicon nanocrystals (Si-nc) embedded in silica, the material of high technological importance. Using the Ag overlayer method, we have found the SERS effect for this material. The best result is obtained for Ag layers of a weight thickness of 12 nm, whose surface plasmons are in a resonance with the laser wavelength (488 nm). The enhancement obtained for the Raman signal from 3-4-nm Si-nc in a 40-nm SiOx film is above 100. The SERS effect is about twice stronger for ultra-small Si-nc (similar to 1 nm) and/or disordered silicon compared to Si-nc with sizes of 3-4 nm. The SERS measurements with an Ag overlayer allow detecting silicon crystallization for ultrathin SiOx films and/or for very low Si excess and suppress the Raman signal from the substrate and the photoluminescence of the film.