Atomic Scale Observations of Metal-Induced Gap States at{222}MgO/Cu Interfaces

$\{\}\left(222\right)$ MgO/Cu interfaces produced by internal oxidation are studied by electron energy loss spectroscopy (EELS) using an atomic sized electron beam. We determine interfacial chemistry of this interface with subnanometer spatial resolution and use EELS to measure directly the electronic states pertaining to the buried interface. O, K, and Cu $L_{2,3}$ edges show the formation of metal-induced states within the band gap of MgO, at the interface (which we find to be O terminated). Both experiment and ab initio calculations find the metal-induced gap states to be strongly localized at the interface, resulting in a very small interface core-level shift.