Analysis of Gibbsian Segregation at Heterophase Cu-MnO Interfaces

An alternative methodology to analyze Gibbsian segregation at heterophase interfaces with transmission electron microscopy (TEM) is presented and discussed. In this approach the actual concentration of the segregating element in a monolayer at the interface is obtained. This is in contrast to line scans or maps where the concentrations determined are a convolution of the concentration profiles with the electron probe and where for general interfaces the deconvolution problem can not be solved accurately. This is possible because the present approach uses explicitly the information offered by hetero-interfaces. The method is tested on the possible segregation of indium and gallium dissolved in a Cu matrix to interfaces between MnO precipitates and the Cu matrix. The occurrence of indium segregation is clearly demonstrated and the In concentration in the terminating Cu monolayer at the parallel {111} Cu/MnO interface is determined to be 15 ± 3 at.%, whereas the average In concentration in the Cu matrix is 3.8 ± 0.4 at.%. Further it was found that indium effectively blocks gallium segregation towards the oxide side of the interface. On the other hand, the presence of gallium does not influence the segregation of indium. Explanation for the gallium segregation at the oxide side relies on a thin spinel type Ga _x Mn _y O₄, which reduces the misfit at the metal-oxide interface.