Thickness dependent phase transition of Bi films quench condensed on semiconducting surfaces

Using electron diffraction methods, we have studied the amorphous to crystalline phase transition of quench condensed bismuth films on three semiconducting surfaces: Si(111)-β--Bi, Si(111)-7 × 7, and Si(111)--In. Using reflection high energy electron diffraction (RHEED), we monitored the film growth in real-time, and observed a thickness dependent amorphous to crystalline phase transition. For the same growth conditions, we found a substrate dependent crystallisation thickness: 4 ML on Si(111)-β--Bi, and 8 ML on both the Si(111)-7 × 7 and the Si(111)--In surfaces. We interpret these results in terms of the free energies of crystalline Bi thin films, and hypothesise that the differing thickness results from a lowering of the free energy of crystalline Bi films on the Si(111)–β--Bi surface, with respect to the Si(111)-7 × 7 and the Si(111)–-In surfaces.