Electronic structure and surface-mediated metastability of Bi films on Si(111)-7x7 studied by angle-resolved photoemission spectroscopy

We have observed using angle-resolved photoemission a structural phase transformation of Bi films deposited on Si(111)-7x7. Films with thicknesses 20 to similar to 100 A degrees, 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 Gamma, whereas the RH phase shows a Dirac-like subband around M along K-M-K. The formation of the metastable phase over a wide thickness range can be attributed to a surface nucleation mechanism.