Hydrogenated amorphous silicon (a-Si:H) films were deposited by ion-beam-assisted evaporation onto substrates maintained at 200 degreesC. The reactive gas was a 50% argon-50% hydrogen mixture. The energy of the ions was varied by biasing the substrate from 0 to -320 V. By combined infrared spectrometry and thermal desorption spectrometry experiments, it is demonstrated that the ions energy has a great influence on the hydrogen stability and on the structure of the a-SM films. In particular, for bias voltages <20 V, a densification effect is observed and, for bias voltages in the range of 80-320 V, hydrogen and argon present only an intense and narrow effusion peak at very high temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.