STM study of a Pb/Si(111) interface at room and low temperatures

The coexistence of Si~111!-~131!-Pb and Si0.28Pb0.72 /Si(111) phases was investigated using scanning tunneling microscopy. Reversible phase transition Si~111!-~131!-Pb,Si~111!-c(53A3)-Pb at TC’230 °C was observed. Simultaneously, small regions with surface charge ordered states were found on Si0.28Pb0.72 /Si(111) indicating a charge density wave phase transition. Both phases were found to be stable in the temperature interval from T’2240 °C up toTC . @S0163-1829~99!10243-1# Phase transitions and ordering in two dimensions ~2D! represent an important field of surface physics, both from a theoretical and applied point of view. Recently, the understanding of these processes in metal/semiconductor interfaces has improved due to the growing availability of scanning tunnelling microscopy ~STM!. 1‐3 STM has played a decisive role in revealing that in principle there are two kinds of temperature-driven 2D phase transitions possible. The first type involves the rearrangement of adsorbate atoms at a certain transition temperature TC , e.g., the transition of a close packed b-(A33A3)R30°,(131) in Pb/Ge~111! at TC ’180 °C, 2 or similarly incommensurate closed-packed (A3 3A3)R30°,(131) in Pb/Si~111!. 3,4 The second type incor