THE CHANGE OF ATOMIC STRUCTURES AND COMPOSITIONS OF (PB,SN) SI(111) SURFACES BY THERMAL ANNEALING/

Changes of atomic structures and compositions of (Pb,Sn)/Si(111) surfa ces by isochronal annealing have been studied by means of low energy e lectron diffraction-Rutherford backscattering spectroscopy (LEED-RBS) techniques. It is found that on isochronal annealing the (Pb,Sn)/Si(11 1) surfaces show a new superstructure of root 8 X root 3 at Pb and Sn coverage of around 0.3 and 0.6 ML, respectively. Moreover, the Ph cove rage on the Sn Si(111)root 7 X root 3-(Pb,Sn) surface decays at a temp erature a little bit higher due to coexistence of root 7 X root 3 Pb a toms than that on the Si(111)root 7 X root 3-Pb surface, while the Sn coverage shows a little decrease. These results suggest that the binar y atoms of Pb and Sn form a 2-dimensional (2D) alloy on the Si(111) su rface, in contrast to those of Ag and Cu which have a very similar bul k phase. (C) 1998 Elsevier Science B.V. All rights reserved.