CaF2/Si(111): Thin-film characterization by high-resolution electron-energy-loss spectroscopy

High-resolution electron-energy-loss spectroscopy is used to investigate surface and interface phonons for thin epitaxial CaF2 layers on Si(111). The dielectric approach used to describe the spectra is found to fail for ultrathin films. The spectra seem to show influences of strain in the film and of the crystalline quality at the interface. © 1986 The American Physical Society.