Interface bonding and manipulation of Ag and Cu nanocrystals on Si(111)-(7x7)-based surfaces

Clusters of pure Ag, pure Cu, and mixed Ag-Cu were grown on solid Xe at 50 K. Subsequent desorption of the Xe buffer layers delivered the nanocrystals to pristine Si(111)-(7 x 7). Imaging with scanning tunneling microscopy showed that these structures ranged in size from 100 to 40000 atoms. We investigated their interactions and bonding with the surface, and attempted to manipulate them on the surface using the tip of the scanning tunneling microscope. Silver nanocrystals could be pushed by mechanical contact, and they left behind a Ag track due to site-selective Ag-atom transfer to the surface. Copper nanocrystals could not be moved but they could be sheared by tip contact. Composite Ag-Cu nanocrystals could be pushed on Si(lll) for low Cu contents, though adhesive interactions with the surface tended to separate the constituents. These results are discussed in terms of the bonding with the surface, the tendency to form necks with the tip, and the dynamics of particle movement. For Ag nanostructures, we also examined interface formation and manipulation on Ag(111), on Si(111)-(root 3 x root 3) Ag, and on Br-exposed and adsorbate-decorated Si(111)-(7 x 7). [S0163-1829(99)06224-4].