control of nano-insulating film/metal interfaces for investigation of the origin of interface potential

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Band alignment via interface termination control based on thermodynamicsThe interface potential and band alignment between epitaxial alumina and metal substrate were investigated using Cu and Ni single crystals with Al addition.From the previous experiments, it is known that the interface is terminated by, oxygen (O-term) when the interface was made by depositing Cu (111) and Ni (111) on alpha alumina According to the ab-initio calculations, thermodynamically stable interface expected to be aluminum terminated when Al is mixed with Cu or Ni. It reported that the kind of atoms at the interface is dependent on the activity of Al in the substrate. Based on this calculation, the interface between alumina and Cu-Al alloy (111)and NiAl (110) was made by carefully exposing the substrate to 1024L oxygen in ultra high vacuum under the partial oxygen pressure of 5×10^8 Torr at optimized temperature. The binding energy of Al 2p and valence band spectra were obtained in-situ during the growth of epitaxial alumina. The interface potential and band alignment were quantified by interpreting these spectral results.We confirmed that the interface is Al terminated when Al is added to Cu or Ni, as suggested from ab-initio calculations. Regarding the interface potential, band alignment at the interface, the band offset, energy difference between the valence band maximum of alumina and the Fermi level of the substrates were relatively large in our experimental results. This result agreed well with the prediction given by the first-principles calculation.In conclusion, we clarified that the interface potential is governed by the kind of atoms at the interfaces. Based on this, we were successful in modifying the band offset value by adding Al to metals far the changing the kind of interface terminating atoms from oxygen to aluminum. This method is based on thermodynamics and can be applied not only for metal-alumina interfaces but also for many systems of interests.