Reflection high energy electron diffraction (RHEED) and synchrotron radiation photoemission spectroscopy (SRPES) have been used to investigate the evolution of the crystallinity and interface reaction of Co thin films deposited on Sb/GaAs(1 1 0). The RHEED images have allowed us to qualitative observe an improvement of the Co bee crystal structure compared to the deposition on the bare substrate. Additionally, the use of high energy resolution synchrotron radiation photoemission spectroscopy has shown that the interdiffusion process behaves differently from that observed for the non-passivated surface. (C) 2004 Published by Elsevier B.V.