The fabrication of small-scale electronics usually involves the integration of different functional materials. The electronic states at the nanoscale interface plays an important role in the device performance and the exotic interface physics. Photoemission spectroscopy is a powerful technique to probe electronic structures of valence band. However, this is a surface-sensitive technique that is usually considered not suitable for the probing of buried interface states, due to the limitation of electron-mean-free path. This article reviews several approaches that have been used to extend the surface-sensitive techniques to investigate the buried interface states, which include hard X-ray photoemission spectroscopy, resonant soft X-ray angle-resolved photoemission spectroscopy and thickness-dependent photoemission spectroscopy. Especially, a quantitative modeling method is introduced to extract the buried interface states based on the film thickness-dependent photoemission spectra obtained from an integrated experimental system equipped with in-situ growth and photoemission techniques. This quantitative modeling method shall be helpful to further understand the interfacial electronic states between functional materials and determine the interface layers.

小型电子产品的制造通常涉及不同功能材料的集成。纳米级界面的电子态在器件性能和奇异的界面物理中起着重要作用。光电发射光谱是探测价带电子结构的强大技术。然而，这是一种表面敏感技术，由于电子平均自由路径的限制，通常被认为不适合探测埋入界面态。本文回顾了用于扩展表面敏感技术以研究埋入界面态的几种方法，其中包括硬 X 射线光电子能谱、共振软 X 射线角分辨光电子能谱和厚度相关光电子能谱。特别是，引入了一种定量建模方法，根据从配备原位生长和光电发射技术的集成实验系统获得的薄膜厚度相关光电发射光谱来提取掩埋界面态。这种定量建模方法将有助于进一步了解功能材料之间的界面电子态并确定界面层。