Substrate Dependence on the Allotropic Transformation and the Morphology of Ultrathin Bi Films on Si(111)

Bismuth film grows via an intriguing thickness-driven allotropic transformation from a {\{}012{\}}-oriented phase to a bulk-like (001) phase. We compare the growth of Bi films on the Si(111)-7x7 surface with that on the Si(111)-$\beta -\surd $3x$\surd $3-Bi surface by use of electron diffraction and scanning tunneling microscopy. Small amount of Bi(001) nanocrystals can nucleate on the 7x7 substrate from the very beginning of the growth $\sim $ 1 monolayer (ML). They stabilize with 3 bilayer height in a perfect commensurate manner on the 7x7 substrate because of lattice contraction as predicted from our \textit{ab initio} calculations, and thus lead to the growth of the highly-crystalline (001) films. On the $\beta -\surd $3x$\surd $3-Bi surface, on the contrary, the (001) nuclei is not observed in the initial stage of the growth and the Bi{\{}012{\}} films survive, and thus the nucleation of the (001) phase is inhibited up to $\sim $ 15 ML.