In film growth on quasicrystalline surfaces, the epitaxy-imposed ordering cannot compete with the stable bulk phases of thick films due to absence of translational order in the structure of the substrate. Energetically, this renders the formation of crystalline domains in the native structure of the film material more favorable, while their global orientation is prescribed by the quasicrystalline order. We present experimental results on the dissociative chemisorption of oxygen at the decagonal surface of Al70Co15Ni15 as well as molecular-dynamics simulations of the diffusion of adatoms on the surface of the partially covered substrate. (C) 2009 Elsevier B. V. All rights reserved.