Investigation of interfaces by high resolution electron energy loss spectroscopy

Recent measurements performed on epitaxial layers clearly demonstrate the capability of HREELS to observe interface optical phonons in dielectric layered materials. Two examples are presented: First, the case of epitaxial CaF on Si(111) where the CaF interface phonon is detected for a whole range of CaF layer thicknesses. Discrepancies with theoretical predictions are interpreted as resulting from the residual strain in the CaF layers. The second example is a III-V semiconductor superlattice GaAs-AlGaAs in which an Al-As type interface mode is clearly identified and quantitatively interpreted by the dielectric theory.