Successful application of spatial difference technique to electron energy-loss spectroscopy studies of Mo/SrTiO3 interfaces

The electron energy-loss near-edge structure (ELNES) of Mo/SrTiO3 interfaces has been studied using high spatial resolution electron energy-loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)-orientated SrTiO3 surfaces by molecular beam epitaxy at 600 degreesC. High-resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)(Mo) plane parallel to the substrate surface. Ti-L-2,L-3 (similar to460 eV), O-K (similar to530 eV), Sr-L-2,L-3 (similar to1950 eV) and Mo-L-2,L-3 (similar to2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface-specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti-L-2,L-3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO3 , which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO6 octahedra was disturbed. No interfacial Sr-L-2,L-3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface-specific O-K edge was found, which differs from that of the bulk in both position (0.8+/-0.2 eV positive shift) and shape. In addition, a positive shift (0.9+/-0.3 eV) occurred for the interfacial Mo-L-2,L-3 , revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO3 was terminated with TiO2 . The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.