ATOMIC STRUCTURES AT THE BURIED PB SI(111) INTERFACE/

Using surface X-ray scattering and crystal truncation rod (CTR) analys is we have studied the buried atomic structure at the Pb/Si(111) inter face. In agreement with previous studies, we observe that the (7 X 7) reconstruction is preserved at the interface, containing many features of the Si surface reconstruction and decorated with Pb atoms adsorbed at on-top sites. The (7 X 7) reconstruction undergoes an irreversible transition to a (1 X 1) structure between 150 degrees C and 300 degre es C. Changes in the first-order CTR indicate that the transition from the bulk Si lattice to the ''bulk-like'' Pb lattice occurs over a sin gle Pb monolayer at the interface.