Nanofilm allotrope and phase transformation of ultrathin Bi film on Si(111)-7×7

Nanofilm allotrope and phase transformation of ultrathin Bi film on Si(111)-7 × 7 were analyzed using scanning tunneling microscopy and electron diffraction experiments. It was observed that this pseudocubic {012}-oriented allotrope is stable up to four atomic layers at room temperature. The entire volume of the film started to transform into a bulk single-crystal (001) phase, as the bulk contribution in the cohesion became dominant, above the critical thickness. It was proposed that the allotrope consists of black phosphorus-like puckered layers stabilized by saturating all the p_z dangling bonds in the film, based on ab initio calculations.