School of Materials Science and Engineering, Shanghai Jiao Tong University
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DOI:
10.7502/j.issn.1674-3962.2016.05.04
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Abstract:
With the technical breakthroughs of creating oxides by novel thin film deposition techniques with well-defined interfaces, oxides have received increasing attention in the electronic and optoelectronic industry due to their unique combination of novel physical properties and the fact that oxides can form “heterostructures” for multiple devices. In order to understand the atomic/electronic structure in oxides, various characterization techniques have been involved. In the past, the characterization has been limited to broad beam techniques though X-ray absorption spectroscopy (XAS), nuclear magnetic resonance (NMR) to achieve the average physical and chemical information. With techniques such as scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS), high-resolution TEM opens the path to the study of chemical composition and bonding information coupled with the atomic level images, and thus provides an ideal tool to investigate individual interfaces. Interface cannot be physically isolated from the bulk, it is difficult to correctly and effectively extract the weak signal from these interfaces presented in a solid bulk. Such extraction remains a very challenging issue even in TEM when thin foils, with thickness is less than 100 nm, area used. The visibility of these interface can be enhanced by picking up corresponding signals since the elastically scattered electrons contributing to signals from these interfaces are distributed unevenly in space and differently compared to the ones contributed by the bulk. Studying cross-sectional samples provides two-dimensional projected information of the three-dimensional interfacial structures. Accordingly, the atomic structure can be constructed though combining information from different projections. Regarding the fact that EELS signals from the defects and the bulk are distributed similarly in space, a new experimental approach, based on a “thickness” series of EEL spectra containing different bulk contributions, was proposed to effectively extract weak EELS signals from these interfaces. The development of characterization techniques such as TEM has lead to improved understanding of oxide interfaces and thus provides great opportunity to create artificial structure for their novel physical properties.