The geometrical structure of a Pd cluster (diameter of approximate to3.1 nm) protected by n-octadecanethiolate monolayer has been investigated by high-resolution TEM (HRTEM), XRD, and EXAFS spectroscopy. The HRTEM and XRD measurements have revealed that the cluster core is comprised of an fcc single crystal of Pd. The mean coordination numbers of the Pd-Pd and Pd-S shells determined by the Pd K-edge EXAFS analysis suggest that the surface of the Pd core is sulfurized to form a mixed Pd-S layer underneath the thiolate monolayer. (C) 2003 Elsevier Science B.V. All rights reserved.