The evolution of the structure and of the hydrogen bonding configuration in hydrogenated a-Si/a-Ge multilayers prepared by RF sputtering is analyzed as a function of annealing. Single layers are also investigated to better evaluate the H behavior. IR absorption measurements show that H is released from its bonds to Si and Ge upon annealing. The mono-hydrides already disappear to a large extent for low annealing times (1 and 4 h), being replaced by di-hydrides, especially in the case of Si. For 10 h annealing both mono-and di-hydrides are almost completely destroyed. At the same time surface blisters form which, for the same annealing conditions, increase in size with increasing incorporated H in the as-deposited sample. It is concluded that the blisters in the multilayers are due to the trapping of the released H in cavities that increase in size upon annealing. The enlarged inner surface of the cavities is the candidate site for the formation of the di-hydrides at low annealing times, i.e., when the thermal energy supplied by the annealing is still insufficient to break all of them. (C) 2012 Elsevier B. V. All rights reserved.