Determination of the characteristic interfacial electronic states of {111}Cu-MgO interfaces by ELNES

The chemical bonding of different {111} Cu-MgO interfaces obtained by inter nal oxidation of (Cu, Mg) alloys at T = 900 degrees C and for an high oxyge n activity of a(o2) = 10(-8), is studied by transmission electron energy lo ss spectroscopy (EELS) at high spatial resolution. For polar (111) interfac es (Cu and MgO in topotactical or pseudotwin orientation), it is shown that the terminating lattice plane in magnesia is occupied by oxygen atoms. An important charge transfer is identified at the interface, yielding Cu-L ELN ES features corresponding to those of Cu1+ (Cu(I)) in its oxide. OK edge fi ne structures at the interface are also modified: an edge enlargement and t he presence of a low energy shoulder confirm the bonding of oxygen to Cu1+. Consistent with these results, the Mg-L edge is never modified compared to the MgO bulk phase. Specifically adapted to the heterophase interfaces, a spatial difference method, based on normalised spectra (NSD), is applied to estimate the relative contribution of the ELNES signal in the interface ar ea. In the present case of high oxygen activity, the number of copper atoms in the Cu(I) oxidized state corresponds to a total occupancy of the outerm ost metal plane at the interface.