Phase transition in ultrathin Bi films

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Abstract
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 Å 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.