Atomic-scale studies of silver segregation at MgO/Cu heterophase interfaces

Atom-probe field-ion microscopy (APFIM) is used to measure quantitatively the absolute values of the Gibbsian interfacial excess of Ag, Gamma(Ag), at semi-coherent {222} MgO/Cu(AE) heterophase interfaces. Atomically clean metal oxide/metal heterophase interfaces were obtained by internal oxidation of a pure ternary Cu(Mg,Ag) single-phase alloy to produce octahedral-shaped MgO precipitates, 10 to 30 nm in diameter, in a single-phase Cu(Ag) matrix. Precipitates are faceted on {222} planes. Random-area APIM analysis was performed in the [111] direction of the Cu(Ag) matrix, perpendicular to one pair of {222} facets of every MgO precipitate. For a single precipitate dissected on an atomic scale, segregation levels at both ''front'' and ''rear'' interfaces are determined. The average measured value of Gamma(Ag), at 500 degrees C, is (2 +/- 0.6) X 10(15) atoms cm(-2). This corresponds to about one monolayer coverage.