We have observed using angle-resolved photoemission a structural phase transformation of Bi films deposited on Si(111)-$7\times 7$. Films with thicknesses 20 to $\sim 100\text{Å}$, upon annealing, first order into a metastable pseudocubic (PC) phase and then transform into a stable rhombohedral (RH) phase with very different topologies for the quantum-well subband structures. The PC phase shows a surface band with a maximum near the Fermi level at $\overline{\Gamma }$, whereas the RH phase shows a Dirac-like subband around $\overline{\text{M}}$ along $\overline{\text{K}}-\overline{\text{M}}-\overline{\text{K}}$. The formation of the metastable phase over a wide thickness range can be attributed to a surface nucleation mechanism.

• Received 24 August 2009

DOI:https://doi.org/10.1103/PhysRevB.80.245407