Soft landing of metal clusters on graphite: a molecular dynamics study?

Structure and stability of nanometer-sized Ag-887, Au-887 and Ti-787 clusters soft-landed on graphite (at deposition energies E-dep = 0:001 5:0 eV per atom) are studied by means of molecular dynamics simulations. Parameters for the cluster{surface interactions are derived from complementary ab initio calculations. The shape and the contact angle of deposited clusters are systematically analyzed for different deposition energies and temperature regimes. The Ag-887 cluster deposited at E-dep less than or similar to 0:1 eV/atom undergoes collision-induced plastic deformation, thus acquiring an ellipsoidal shape with the contact angle close to 180 degrees. In contrast, Au-887 and Ti-787 clusters undergo a collision-induced melting phase transition followed by their recrystallization; these processes lead to the formation of the droplet-like shapes of the clusters in a form of truncated spheroids. At larger deposition energies all clusters flatten over the surface and eventually disintegrate at E-dep approximate to 0:75 1:0 eV/atom (for Ag-887 and Au-887) and approximate to 3 eV/atom (for Ti-787). It is found also that the shape of deposited clusters is strongly influenced by the strength of cluster-substrate interaction and the corresponding interaction mechanism, namely the weak van der Waals interaction between metal and carbon atoms or the van der Waals interaction with an onset of covalent bonding. Similar phenomena should arise in the deposition of clusters made of other elements, which interact with a substrate by one of the above-described mechanisms.