EELS analysis of internal metal-oxide interfaces

The heterophase boundaries between precipitates such as spherical amorphous SiO(2) particles inside a copper matrix as well as crystalline CuO precipitates inside a silver matrix and the surrounding metal matrix are examined with high spatial resolution using a scanning transmission electron microscope equipped with an electron energy loss spectrometer. Typical features of the electron energy loss near-edge fine structure of the oxygen O-K and of characteristic metal ionization edges allow determination of the bonding state of oxygen and thus detection of fine interlayers at the phase boundary. The results obtained are interpreted in a tentative way, supporting basic ideas of Kirchheim's structural vacancy model of oxygen segregation to metal-oxide interfaces. The model predicts that no interfacial accumulation of excess oxygen should occur to the phase boundary of amorphous precipitates. In Ag-Cu alloys there is the additional degree of freedom for the oxidation value of copper and we present indications that structural vacancies change the oxidation value at the phase boundary.