Silicon nanocrystals embedded in a dielectric matrix are of considerable interest for Si-based optoelectronics and the third generation photovoltaics. This work discusses Si nanocrystals embedded in silicon-carbon, Si(1-x)C(x), thin films prepared by plasma-enhanced chemical vapor deposition (PECVD) using a non-conventional fluoride-based precursor mixture, i.e., SiF(4)-CH(4)-H(2)-He plasmas. It is shown that the SiF(4)/H(2) ratio and the He dilution are important parameters to control the volume fraction and the size of nc-Si, and the carbon content of the a-Si(1-x)C(x) matrix. Films nanostructure and optical properties are studied by spectroscopic ellipsometry and Raman spectroscopy. The correlation existing between plasma processes and the film nanostructure and resulting optical properties is discussed. (C) 2010 Elsevier B.V. All rights reserved.