| Abstrakt: |
Using low energy electron microscopy (LEEM), the authors investigated how various phases of the Pb overlayer on Ge(111) grow as the Pb coverage increases in the submonolayer range, for substrate temperatures between 200 and 300 °C during Pb deposition. The authors find that each of the three known Pb phases forms in a distinct manner. The low coverage (√3 × √3)R30°-α phase forms small islands less than 10 nm in size, which then coalesce and saturate the surface at 0.33 ML. During the formation of the α phase, Pb atoms replace Ge adatoms of the c(2 × 8) reconstructed structure of the Ge (111) substrate, and the released Ge atoms diffuse and form islands on terraces or attach to steps. The authors show that the size and density of the Ge islands can be controlled systematically by controlling the film deposition parameters. After the saturation of the α phase, the (1 × 1) phase starts to grow preferentially at the lower side of the step edges. LEEM data provide direct evidence of the (1 × 1) phase being a disordered phase, rather than a Pb-terminated unreconstructed Ge(111) surface, resolving the previous controversy. The (√3 × √3)R30°-β phase forms in a dramatic first-order transition from the (1 × 1) phase, with spontaneous domain switching occurring in the coexistence region of the two phases. [ABSTRACT FROM AUTHOR] |
