Co-adsorption of Cu and Pb on the Si(111)-(7x7) surface:: interface formation

The adsorption of Cu and Pb atoms on a Si(I 1 l)-7 x 7 surface was studied by means of scanning tunnelling microscopy (STM). After deposition of less than or equal to, 0.1 monolayer (ML) of copper on the Pb root3 x root3 mosaic phase. and a subsequent annealing up to similar to373 K, new objects of a hexagonal shape appear on a surface. They,are scattered over the surface and localised next to the mosaic phase islands. The difference between atomically resolved images of filled and empty states suggests strong covalent bonding within a hexagon. Increasing the concentration of Cu atoms leads to an in, creasing number of hexagons and their agglomeration. Annealing of this surface, at a higher temperature. (>470 K) leads to the transformation of these hexagonal-like objects and their agglomeration into the pseudo-"5 x 5" structure, commonly observed for the Cu/Si(l 1 I)system. The absence of hexagons at very low Cu concentration demonstrates the presence of a long-range, attractive interaction among Cu atoms and their strong diffusion just above room temperature (RT). (C) 2003 Elsevier Science B.V. All rights reserved.