SCATTERING OF LARGE ARGON CLUSTERS FROM A PT(111) SURFACE WITH LOW COLLISION VELOCITIES

We report on classical trajectory calculations for Ar-n (n = 100-4400) scattering from a Pt(lll) surface with low collision velocities. We i nvestigate the effects of surface temperature, cluster size, and incid ent angle on energy transfer and fragmentation behavior. A cluster is first heated at surface impact and then by continuous heating by the s urface while moving laterally tens of nanometers on the surface. When the cluster temperature reaches 130-180 K, extensive fragmentation tak es place and the thermal excitation of the cluster forces it to leave the surface, which inhibits further temperature increase. A large numb er of small particles are ejected during this process, and large fragm ents may survive the surface interaction. The conditions favoring high cluster survival probability are: large cluster size, low incident ve locity normal to the surface and high surface temperature. Final angul ar distributions for monomers are considerably broader than for large fragments. Monomers also have higher final velocities than large fragm ents, and the final distributions depend on the degree of surface corr ugation. The results are concluded to qualitatively reproduce the gene ral trends for angular and velocity distributions found in experimenta l data for similar scattering systems. (C) 1997 Elsevier Science B.V.