Ion-bombardment-induced selective grain growth is a process that allows for full control of the orientation of vapor-deposited thin films, which can be converted from fiber-textured polycrystalline to single-crystal films. The main mechanisms behind this phenomenon are explained by a new thermal spike model, which takes into account and compares the different driving forces governing the film microstructure evolution upon irradiation and emphasizes the importance of the thermal spike shape and volume. The strong agreement between model and experimental data confirms that selective grain growth is driven by the minimization of the volume free energy. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.