Nucleation and growth kinetics of Pd and CuPd particles on NaCl(100)

Pd and CuPd nanometric particles have been grown by UHV condensation of the metal beams on UHV-cleaved NaCl(100) surfaces. The nucleation and growth k inetics have been determined from TEM measurements of the size distribution while the chemical composition has been determined by EDX. From these meas urements the mechanisms of the nucleation and growth have been determined. The nucleation of the bimetallic particles is chiefly controlled by the Pd adatoms. The Pd atoms are essentially incorporated in the bimetallic cluste rs by a diffusion-capture mechanism while Cu atoms are mainly incorporated by direct impingement on the clusters. Thus the composition of the bimetall ic particles changes during the deposition time from pure Pd in the early s tages to a progressive increase of the Cu concentration. The difference bet ween the adsorption and diffusion energies of an adatom on NaCl has been de termined for the two metals.