HELIUM DIFFRACTION STUDY OF THE NUCLEATION AND GROWTH OF SUPPORTED METAL-CLUSTERS

A new method for the in situ study of the nucleation and growth of met al clusters on an ionic substrate from vapor beam deposition is presen ted. It is based on the diffraction of helium atoms from the ionic sub strate. From the attenuation of the first order diffraction peak durin g the growth of metal clusters the nucleation and growth kinetics are obtained. The only additional information needed is the final size dis tribution of the clusters which can be obtained from transmission elec tron microscopy. This method has been applied to the nucleation and gr owth of Pd clusters on MgO (100). With the same method but using the d iffraction (specular peak) from the metal clusters it is possible to f ollow the evolution of the cluster shape during an annealing experimen t.