Subject Number : S-17-JI-0049
Support Type : Technical surrogate
Proposal Title (English) : Atomic Resolution Image Observation and EELS Spectra Analysis of the Interface structures of High-Temperature Superconducting Films and its Multilayer Heteroepitaxial films
Username (English) : L. Lei1) . G. Y. Zhao1), Y. Oshima2)
Affiliation (English) : 1) Xi’an University of Technology (XUT), 2) Japan Advanced Institute of Science and Technology (JAIST)

1. Summary
In this work, Zr-doped CeO2 (Ce1-xZrxO2, CZO) films with (001) preferential orientation were fabricated on biaxially textured Ni5W alloy substrates using a novel sol-gel method. It is found that the inside of CZO thin film exhibits quite dense and uniform without cracks and porosity with the aid of the scanning transmission electron microscopy analysis by which the epitaxial growth relationship of (220)CZO//(200)NiW between CZO and NiW is simultaneously confirmed. The above results indicate that the CZO film is a very promising candidate for single buffer layer architecture of YBCO coated conductor.

2. Experimental
The precursor solutions for fabrication of the Ce1-xZrxO2 (CZO) (where x varies from 0.1 to 0.5) films were synthesized by dissolving zirconium oxychloride (ZrOCl2•8H2O) and cerium nitrate (Ce(NO3)3•6H2O) into methanol under ambient conditions. These solutions were coated on the textured NiW alloy substrates (10mm×10mm×0.1mm) using a dip-coating method. The as-deposited buffer layers were dried at 80℃ for 20 min and pyrolyzed at 230℃ for 30 min in atmosphere and further heated up to 1000℃-1100℃ for 60 min in the reducing atmosphere. The dip-coating process and the heat treatment were repeated for several times to obtain the desired thickness of CZO film. The microstructure of the interface of CZO/NiW was analyzed by a spherical aberration corrected transmission electron microscope (TEM, JEOL JEM-ARM200F).

3. Results and Discussion

The epitaxial growth relationship between CZO films and NiW substrates is analyzed by a Scanning Transmission Electron Microscope (STEM) and the results are presented in Fig. 1. The cross-section HAADF image with low magnification of Ce0.9Zr0.1O2 film on NiW substrate is shown in Fig. 1(a). It can be learned from Fig. 1(a) that the CZO film is quite dense and the thickness of the film is approximately 109 nm. In order to understand the atomic arrangement of the interface between CZO film and NiW substrate, a close-up, HAADF image with atomic resolution, from the green square region in Fig. 1(a) is shown in Fig. 1(b). It can be clearly seen that the atomic arrangement of the CZO/NiW interface is quite neat and a slight dark contrast appears in the interface since there is propably a step caused during focused ion beam etching process between CZO film and NiW substrate. The interplanar spacings of CZO-(220) and Ni-(200) are measured and the corresponding values are 0.190 nm and 0.176 nm, respectively. The epitaxial relationship with (220)CZO// (200)NiW between CZO films and NiW substrate is confirmed by indexing the Fast Fourie Transform (FFT) pattern as shown in Fig. 1(c). It is quite easy to elucidate the atomic arrangement of the CZO/NiW interface through a schematic atomic structure model presented in Fig. 1(d) and the inset of Fig. 1(b).

4. Others
Acknowledgements
This investigation is supported by the National Natural Science Foundation of China (No. 51202190 and 51672212) and also supported by the Project of Science and Technology of Shaanxi Province (No. 2014KJXX-63 and 16JS065). This work was partly supported by Nanotechnology Platform Program (Molecule and Material Synthesis) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. The author would like to acknowledge China Scholarship Council (CSC) for sponsoring my study abroad.

5. Publication/Presentation
N/A.

6. Patent
N/A.

Fig. 1 STEM analysis for the evaluation of epitaxial relationship between CZO film and NiW substrate. (a) Low magnification HAADF image of the interface of CZO/NiW. (b) High resolution HAADF image of the green square region in (a) (Inset: Schematic diagram of atomic arrangement corresponding to atomic position in the high resolution HAADF image). (c) Fast Fourie Transform pattern of (b). (d) Atomic structure model of the interface of CZO/NiW.