Electron Energy-Loss Near-Edge Structure of Metal-Alumina Interfaces

The physical properties of metal-ceramic composites are strongly affected by the local chemistry and atomic bonding across the interface. Information on both are contained in the energy-loss near-edge structure. The spectral component specific for the interface can be obtained by the spatial- difference technique. This method was applied for the investigation of two different interfaces, namely Al/Al$_2$O$_3$ and Cu/Al$_2$O$_3$. The Al-$L_{2,3}$ edge at the Al/Al$_2$O$_3$ interface shows a characteristic energy-loss near-edge structure which was compared to multiple scattering calculations for Al(O$_3$Al) tetrahedra with various Al-Al bond lengths. Good agreement with the experimental data was found for a cluster with an Al-Al bond length larger than the Al-O distance which is nearly that of amorphous Al$_2$O$_3$. No interface-specific component could be detected at the Al-$L_{2,3}$ edge of the Cu/Al$_2$O$_3$ interface. However, the energy-loss near-edge structure of the Cu-$L_{2,3}$ edge indicates that Cu exists at the interface in a Cu$^{1+}$ state and that the chemical bond is established at the interface between Cu and O atoms