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的能带对准利用添加Al的Cu和Ni单晶研究了外延氧化铝与金属衬底之间的界面电位和能带对准。从之前的实验可知，在α -氧化铝上沉积Cu（111）和Ni（111）形成界面时，界面是由氧（o项）终止的。根据ab-initio计算，当Al与Cu或Ni混合时，界面应该是由铝终止的热力学稳定界面。据报道，界面上的原子种类取决于衬底中Al的活性。在此基础上，在优化温度下，将衬底仔细暴露于1024L的超高真空中，在5×10^8 Torr的分氧压力下，制备了氧化铝、cu -铝合金（111）和NiAl（110）的界面。在外延氧化铝生长过程中，原位得到了Al 2p的结合能和价带光谱。通过对这些光谱结果的解释，对界面电位和带对准进行了量化。我们证实，当Al加入Cu或Ni时，界面是Al终止的，这是由从头算得出的结论。对于界面电位，我们的实验结果表明，界面处的能带对准、能带偏移、氧化铝价带最大值与底物费米能级之间的能差都比较大。这一结果与第一性原理计算的预测吻合得很好。综上所述，我们澄清了界面势是由界面上原子的种类决定的。在此基础上，通过将界面终止原子的种类由氧改为铝，在金属中加入Al，成功地改变了带偏值。该方法基于热力学，不仅适用于金属-氧化铝界面，而且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.