In this work, we report on the production of regular (SiGe/SiO 2) 20 multilayer structures by conventional RF-magnetron sputtering, at 350 C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 C leads to the formation of SiGe nanocrystals between SiO 2 thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (t SiGe) from 3.5–2 nm results in a transition from continuous SiGe crystalline layer (t SiGe~ 3.5 nm) to layers consisting of isolated nanocrystals (t SiGe~ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals~ 3–8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe …