Initial stages of Bi/Ge(111) interface formation: A detailed STM study

We present a detailed scanning tunneling microscopy investigation of ultra-thin Bi films on Ge(111)-c(2 × 8) in the range up to 1.5 ML. During growth at 300 K, the second/third atomic layer of Bi already starts to nucleate before the completion of the first/second layer correspondingly. Laterally isolated first layer Bi atoms, clusters and islands posses no electronic states in the range ~ 0.5 eV above the Fermi level of the substrate. In contrast, metallic electronic properties are found for continuous films when Bi coverage nears 1 ML. Annealing the as-deposited Bi films at 450 K causes lateral redistribution of Bi due to surface diffusion: coarsening of two-dimensional Bi islands with no long range order in the adsorbate layer is observed up to 1 ML; long range ordered (√3 × √3)-Bi/Ge(111) interface plus three-dimensional Bi clusters are obtained for coverages in excess of 1 ML.