The Debye-temperature of the pentagonal surface of the icosahedral AlPdMn quasicrystal (QC) is measured by means of low-energy electron diffraction after the absorption of different amounts of Si. We observe an increase of the surface Debye-temperature from 300 +/- 7 K for the freshly prepared surface to 330 +/- 7 K after the absorption of 60-angstrom Si. Because the quasicrystalline order persists at the surface in spite of the diffusion of Si into the substrate, we suggest that the diffusion is dominated by a vacancy-mediated process. (c) 2007 Elsevier B.V. All rights reserved.