Structural transformations in Pb/Si(111) phases induced by C60 adsorption

Structural transformations at the Pb/Si(111) surface occurring upon C-60 adsorption onto Pb/Si(111) 1 x 1 phase at room temperature and Pb/Si(111) root 7 x root 3 at low temperatures between 30 and 210 K, have been studied using scanning tunneling microscopy and low-energy electron diffraction observations. Typically, C-60 fullerenes agglomerate into random molecular islands nucleated at the surface defects. C-60 island formation is accompanied by expelling Pb atoms to the surrounding surface area where more dense Pb/Si(111) phases form. Productivity of C-60-induced expelling of Pb atoms is controlled by surface defects and is suppressed dramatically when regular ('crystalline') C-60 islands self-assemble at the defect-free Pb/Si(111) surface. When Pb atoms are ejected by the random C-60 islands, extended structural transformations involving reordering of numerous Pb atoms are fully completed at the surface within the shortest possible time (a few dozen seconds) to reapproach and image the surface after C-60 deposition. Estimations show that the observed transformations cannot be controlled by random walk diffusion of Pb adatoms, which implies a highly correlated motion of the Pb atom displacements within the layer.