Influence of Pb on an In/Si(111) surface on the phase transition and the surface structure

The influence of Pb atoms adsorbed on an In/Si(111) surface on the phase transition was investigated by using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). LEED data showed that the transition temperature for the 4×1 → 8×2 structural phase transition decreased in proportion to the amount of Pb deposition. The Pb adatoms appeared as bright protrusions in an STM image taken at 90 K, suggesting that they were located high above the In atomic wires. The regions surrounding the Pb adatoms remained in the 4×1 phase while the other areas turned into the 8×2 or 4×2 phase at this temperature below the transition temperature. Near each Pb adatom, a Friedel-oscillation-like modulation with a double (×2) periodicity in the wire direction was developed. This ×2 modulation was found to be different in nature from the low-temperature 8×2 (or 4×2) phase. We suggest that a Pb-adatom-induced deep potential well is responsible for the Tc lowering and the ×2 modulation.