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

基于热力学的界面终止控制方法研究了外延氧化铝与金属衬底之间的界面电势和能带排列。从以往的实验中得知，当界面是通过在α-氧化铝上沉积铜(111)和镍(111)形成界面时，界面是由氧(O项)终止的，根据从头计算，当铝与铜或镍混合时，热力学上稳定的界面是铝终止的。据报道，界面原子的种类取决于Al在衬底中的活度。在此基础上，通过在最佳温度下，在氧分压为5×108托的超高真空中将氧化铝置于1024L氧气中，形成了氧化铝与铜铝合金(111)和NiAl(110)之间的界面。在外延氧化铝的生长过程中，原位获得了Al2p的结合能和价带光谱。通过对这些光谱结果的解释，量化了界面电势和能带排列。我们从从头计算中证实，当Al加入到铜或镍中时，界面是Al端接的。在界面电势、界面能带排列、能带偏移、氧化铝的价带最大值与衬底的费米能级之间的能量差方面，我们的实验结果是比较大的。这一结果与第一性原理计算所给出的结果吻合得很好。总之，我们澄清了界面势是由界面原子的种类决定的。在此基础上，我们成功地通过在金属中加入Al来修正能带偏移量，从而将终止原子的界面类型从氧改变为铝。该方法以热力学为基础，不仅适用于金属-氧化铝界面，也适用于许多感兴趣的体系。

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.