Structure and morphology of nanometer-sized Pd clusters grown at high temperature on natural graphite single crystals

Performing both ex situ transmission electron microscopy (TEM) and in situ scanning tunnelling microscopy (STM) experiments on the same samples, we ha ve characterized in detail a model catalyst (Pd/graphite). The Pd clusters were epitaxially grown at high temperature on clean natural graphite substr ates under ultra high vacuum (UHV) conditions. For the chosen growth condit ions the density of clusters is rather low (10(9) cm(-2)), and their size i s typically few tens of nanometers. TEM diffraction studies reveal that mos t of the clusters (92%) are in a same epitaxial orientation which is define d by: (1 1 1)Pd parallel to (0 0. 1)Gr and [1 1 (2) over bar ]Pd parallel t o [1 (1) over bar . 0]Gr. Moreover, both STM imaging and TEM observations s how that the clusters have truncated tetrahedron shapes. The combination of TEM and STM characterizations of the same samples appears to be a very eff icient way to get a detailed knowledge of the global properties of a collec tion of supported clusters (spatial and size distributions) as well as of t heir individual properties (structure, morphology).