We present an investigation on the transition from amorphous to nanocrystalline silicon and associated hydrogen changes during the first steps of hydrogenated nanocrystalline silicon growth for films elaborated by reactive radiofrequency magnetron sputtering at a substrate temperature as low as room temperature and for deposition times varying from 3 to 60 min. Complementary experimental techniques have been used to characterize the films in their as-deposited state. They are completed by thermal hydrogen effusion experiments conducted in the temperature range, from room temperature to 800 degrees C. The results show that, during the initial stages of growth, the presence of a hydrogen-rich layer is necessary to initiate the crystallization process. (C) 2012 Elsevier B. V. All rights reserved.