NUCLEATION AND GROWTH OF METALLIC CLUSTERS ON MGO(100) BY HELIUM DIFFRACTION

Nucleation and growth of palladium clusters on MgO(100) have been stud ied, in situ, under UHV by using the diffraction of thermal energy hel ium atoms from the MgO surface. The width of the diffuse scattering ba nd around the growing clusters has been precisely determined. It is eq ual to 1.1 +/- 0.15 nm and does not depend either on the temperature o r on the size of the clusters (in the range 2.5-7.5 nm). From the atte nuation curves of the diffraction peaks, the variations of the number density and of the mean size of the clusters are obtained in a single experiment that is a great improvement regarding the classical ex situ TEM studies. Results are compared with the nucleation and growth theo ries.