  Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker
of two structures formed in CaCuO2 at the interface with SrTiO3. For
non-superconducting superlattices, grown in low oxidizing atmosphere, the 425
cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films
with infinite layer structure (planar Cu-O coordination). For superconducting
superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift
to lower energy occurs. This is ascribed to a change from planar to pyramidal
Cu-O coordination because of oxygen incorporation at the interface. Raman
spectroscopy proves to be a powerful tool for interface structure
investigation.
