Phase transition in ultrathin Bi films

Dynamical studies of Bi ultrathin films prepared on carbon at 100 K exhibit a phase transition from nanocrystalline to amorphouslike clusters. Evidence for the transition at a thickness of 8 is provided by the form, intensity, and polarization dependence of in situ Raman-scattering measurements in ultrahigh vacuum. A substantial increase in frequency of the opticlike band with decreasing thickness indicates increased covalent interactions. This contrasts with superconducting Bi films, suggesting a semiconducting amorphous state in clusters.