Formation of an intermediate 3 x 3 phase from Pb on Si(111) at high temperature

Using high-resolution spot-profile-analysis low-energy electron diffraction (SPA-LEED) we have investigated low-coverage phases of Pb on Si(111) in th e temperature range between 25 degrees C and 600 degrees C. After the annea ling of 1/3 of a monolayer (ML) of Ph on Si(111) at 500 degrees C and cooli ng the sample down to room temperature, we observe a 3 x 3 phase beside the well known Pb/Si(111)root 3 x root 3R30 degrees structure. The 3 x 3 phase is poorly ordered (domain size 20 Angstrom-40 Angstrom) compared to the ro ot 3 x root 3 phase (domain size greater than or equal to 1000 Angstrom) as we conclude from profile analysis of the diffraction spots. The developmen t of the 3 x 3 superstructure with increase of the annealing temperature wa s monitored and we observe a change of the domain size from 20 Angstrom up to 40 Angstrom upon annealing at 500 degrees C and 540 degrees C, respectiv ely. After annealing at 580 degrees C the 3 x 3 phase has vanished and we d etect only the root 3 x root 3 mosaic phase.