Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Nanoscale. 2013 Oct 21;5(20):9659-65. doi: 10.1039/c3nr02343e.
The oxygen stoichiometry has a large influence on the physical and chemical properties of complex oxides. Most of the functionality in e.g. catalysis and electrochemistry depends in particular on control of the oxygen stoichiometry. In order to understand the fundamental properties of intrinsic surfaces of oxygen-deficient complex oxides, we report on in situ temperature dependent scanning tunnelling spectroscopy experiments on pristine oxygen deficient, epitaxial manganite films. Although these films are insulating in subsequent ex situ in-plane electronic transport experiments at all temperatures, in situ scanning tunnelling spectroscopic data reveal that the surface of these films exhibits a metal-insulator transition (MIT) at 120 K, coincident with the onset of ferromagnetic ordering of small clusters in the bulk of the oxygen-deficient film. The surprising proximity of the surface MIT transition temperature of nonstoichiometric films with that of the fully oxygenated bulk suggests that the electronic properties in the surface region are not significantly affected by oxygen deficiency in the bulk. This carries important implications for the understanding and functional design of complex oxides and their interfaces with specific electronic properties in catalysis, oxide electronics and electrochemistry.
氧化学计量对复杂氧化物的物理和化学性质有很大影响。例如，催化和电化学等功能大多特别依赖于氧化学计量的控制。为了了解氧空位复杂氧化物本征表面的基本特性，我们报告了在原始氧空位、外延锰酸盐薄膜上进行的原位温度依赖扫描隧道谱实验。尽管这些薄膜在后续所有温度下的非原位面内电子输运实验中都是绝缘的，但原位扫描隧道谱数据显示，这些薄膜的表面在 120 K 处表现出金属-绝缘体转变（MIT），与氧空位薄膜体相中小团簇的铁磁有序的开始相一致。非化学计量薄膜的表面 MIT 转变温度与完全氧化体的温度如此接近，这表明表面区域的电子性质不受体相氧空位的显著影响。这对理解和功能设计具有重要意义复杂氧化物及其与催化、氧化物电子学和电化学中具有特定电子性质的界面。
