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BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with ω rocking curve full width at half maximum values as narrow as 29 arc sec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films. [ABSTRACT FROM AUTHOR]

In situ ellipsometry experiments have been used to probe the structural changes that occur in the initial stages of the growth of microcrystalline silicon ( μc-Si) on single-crystal Si substrates. The initial nucleation of μc-Si appears to occur at well-dispersed sites and ∼100 Å of material with significantly different optical properties than the bulk is buried at the film/substrate interface. The different optical structure of this interface layer is attributed to voids which are trapped when crystalline nuclei merge. These results are contrasted with recent data for hydrogenated amorphous silicon which show that nuclei converge after about 50 Å, leaving material with bulklike optical properties at the substrate interface. [ABSTRACT FROM AUTHOR]