STM and TEM studies of a model catalyst: Pd/MoS2(0001)

Combined in situ scanning tunnelling microscopy (STM) and ex situ transmission electron microscopy (TEM) experiments performed on the same samples have been used to characterize in detail a model catalyst: Pd/MoS2(0001). The Pd clusters were epitaxially grown under ultrahigh vacuum conditions by condensing a calibrated beam of atoms on a natural single crystal of MoS2 kept at high temperature (T=220°C). Atomic-resolution STM images of the clean MoS2(0001) surface were found to vary with the tip to sample distance, in good agreement with the theoretical predictions of Altibelli et al. [Surf. Sci. 367 (1996) 209] for the origin of contrast in such images. TEM and STM investigations of the statistical properties of the Pd clusters (spatial and size distributions, epitaxial orientation) are shown to be coherent and complementary.