Strain accumulation for Fe/Ir(111) and the related strain driven phase transition
Chen-Yuan Hsieh1, Pei-Yuan Tsai1*, Geng-You Lin1, Pei-Cheng Jiang1, Wei-Hsiang Chen1, Jyh-Shen Tsay1
1Department of Physics, National Taiwan Normal University, Taipei, Taiwan
* Presenter:Pei-Yuan Tsai,
In terms of introducing heterogeneous interfaces, the stabilization of crystallographic phases is critical to a viable strategy for the development of new materials with novel characteristics [1,2]. Because of the different lattice structures, body-centered cubic (bcc)/face-centered cubic (fcc) interfaces serve as a platform for controlling pseudomorphic growth, nanostructure evolution and formation of strained clusters. Here we report on the structures and strain accumulation for ultrathin Fe/Ir(111) films. We demonstrate a strain driven phase transition in which fcc-Fe is transformed to a bcc phase. By converting the experimental data for the interlayer distance and in-plane lattice parameters into lattice parameters in cubic geometry, the interfacial strain energy can be calculated for different Fe thicknesses [3]. A limited distortion mechanism is proposed for correlating the increasing interfacial strain energy and the surface energy. The calculation results, which indicate that the strained layers undergo a phase transition to the bulk structure above a critical thickness, are entirely consistent with the experimental measurements. In additional, a smaller critical thickness of 2 ML for Fe/Pt(111) can be explained by a larger lattice misfit for Fe/Pt(111) as compared to a Fe/Ir(111) system. The strain driven phase transition and mechanism presented herein provide a fundamental understanding of strain accumulation at the bcc/fcc interface.

[1] Chang, C.H.T., Jiang, P.C., Chow, Y.T. & Tsay, J.S., Formation of surface alloys and related applications, in Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, Editor-in-Chief: Klaus Wandelt, Vol. 3, pp 119-128, 2018, Elsevier.
[2] Hwang, Y., Choi, S., Choi, J. & Cho, S. Induced high-temperature ferromagnetism by structure phase transitions in strained antiferromagnetic γ-Fe50Mn50 epitaxial films, Sci. Rep. 9, 3669 (2019).
[3] Hsieh, C.Y., Jiang, P.C., Chen, W.H., Tsay, J.S., Strain driven phase transition and mechanism for Fe/Ir(111) films, Scientific Report, under review.

Keywords: iron, iridium, face-centered cubic, body-centered cubic, interfacial strain energy