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 have characterized in detail a model catalyst (Pd/graphite). The Pd clusters were epitaxially grown at high temperature on clean natural graphite substrates under ultra high vacuum (UHV) conditions. For the chosen growth conditions the density of clusters is rather low (10(9) cm(-2)), and their size is typically few tens of nanometers. TEM diffraction studies reveal that most of the clusters (92%) are in a same epitaxial orientation which is defined by: (1 1 1)Pd parallel to (0 0. 1)Gr and [1 1 (2) over bar ]Pd parallel to [1 (1) over bar . 0]Gr. Moreover, both STM imaging and TEM observations show that the clusters have truncated tetrahedron shapes. The combination of TEM and STM characterizations of the same samples appears to be a very efficient way to get a detailed knowledge of the global properties of a collection of supported clusters (spatial and size distributions) as well as of their individual properties (structure, morphology).