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Qiu W, Ma Z, Patel D, Sang L, Cai C, Shahriar Al Hossain M, Cheng Z, Wang X, Dou SX. The Interface Structure of FeSe Thin Film on CaF 2 Substrate and its Influence on the Superconducting Performance. ACS Appl Mater Interfaces 2017; 9:37446-37453. [PMID: 29019397 DOI: 10.1021/acsami.7b11853] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The investigations into the interfaces in iron selenide (FeSe) thin films on various substrates have manifested the great potential of showing high-temperature-superconductivity in this unique system. In present work, we obtain FeSe thin films with a series of thicknesses on calcium fluoride (CaF2) (100) substrates and glean the detailed information from the FeSe/CaF2 interface by using scanning transmission electron microscopy (STEM). Intriguingly, we have found the universal existence of a calcium selenide (CaSe) interlayer with a thickness of approximate 3 nm between FeSe and CaF2 in all the samples, which is irrelevant to the thickness of FeSe layers. A slight Se deficiency occurs in the FeSe layer due to the formation of CaSe interlayer. This Se deficiency is generally negligible except for the case of the ultrathin FeSe film (8 nm in thickness), in which the stoichiometric deviation from FeSe is big enough to suppress the superconductivity. Meanwhile, in the overly thick FeSe layer (160 nm in thickness), vast precipitates are found and recognized as Fe-rich phases, which brings about degradation in superconductivity. Consequently, the thickness dependence of superconducting transition temperature (Tc) of FeSe thin films is investigated and one of our atmosphere-stable FeSe thin film (127 nm) possesses the highest Tconset/Tczero as 15.1 K/13.4 K on record to date in the class of FeSe thin film with practical thickness. Our results provide a new perspective for exploring the mechanism of superconductivity in FeSe thin film via high-resolution STEM. Moreover, approaches that might improve the quality of FeSe/CaF2 interfaces are also proposed for further enhancing the superconducting performance in this system.
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Affiliation(s)
- Wenbin Qiu
- Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia
- Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University , Shanghai 200444, People's Republic of China
| | - Zongqing Ma
- Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science & Engineering, Tianjin University , Tianjin 300072, People's Republic of China
| | - Dipak Patel
- Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia
| | - Lina Sang
- Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University , Shanghai 200444, People's Republic of China
| | - Chuanbing Cai
- Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University , Shanghai 200444, People's Republic of China
| | - Mohammed Shahriar Al Hossain
- Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia
| | - Zhenxiang Cheng
- Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia
| | - Xiaolin Wang
- Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia
| | - Shi Xue Dou
- Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia
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