SURFACE SUPERSTRUCTURES OF THE PB/SI(001) SYSTEM

In the present work the Pb/Si(001) system has been studied with LEED (low-energy electron diffraction), AES (Auger electron spectroscopy), and EELS (electron energy loss spectroscopy). Five different surface superstructures, i.e., the 2 x 2, c(4 x 8), 4 x 1, 2 x 1 and c(4 x 4) were observed. Four of them are found for the first time, except for the 2 x 1. Their relationship has been investigated as a function of Pb coverage and annealing temperature. As a result, a complete phase diagram of the system has been determined. Upon annealing at 450-degrees-C the 2 x 2 superstructure undergoes an irreversible phase transformation to the c(4 x 8), while the c(4 x 4) reversibly transforms to 2 x 1 at 300-degrees-C. Strong influence of oxygen contamination on the surface superstructures has been observed.