Fe/Bi Superlattices: Fabrication of Thin Films and Their Characterizations
林廷宇1*, 陳永松1
1物理所, 國立中山大學, 高雄, Taiwan
* Presenter:林廷宇, email:lintingyu15@gmail.com
Iron and bismuth are completely immiscible in condensed state as is seen from their binary T-x phase diagram. Formation into any intermetallic compound has also never been reported until recently when the first compound of FeBi2 was successfully synthesized at about 30 GPa (Walsh, 2016). The physical properties of this material, however, remain elusive due to the formidable technical difficulties in making samples into proper measurable form under this extreme condition. This prompted us to ask if there is any alternative approach toward understanding the novelty, if any, when the two elements are brought together. To answer to this curiosity, we emulated the stoichiometric FeBi2 compound by growing Fe/Bi multilayers in right proportion of relative thickness from which the layer- layer coupling were expected to emerge. We stacked up the Fe-Bi multilayers by using electron-beam evaporation for the deposition of thin films with alternating layers of iron and bismuth on silicon or Al2O3 substrates. Characterizations of the periodic structures were done by measuring X-ray reflectivity, X-ray diffraction (XRD) and cross-sectional transmission electron microscopic (TEM) imaging, while associated electrical measurement was also conducted to obtain temperature-dependent resistance data up to temperatures well above the melting point of bismuth, though magnetization measurement could only be conducted at moderately lower temperatures due to instrumental limitations. Unique magnetic properties are anticipated for the Fe-Bi multilayered samples because pure bismuth is diamagnetic while iron is a ferromagnetic. Also, bismuth exhibits unusually high electron mobility and demonstrates semiconducting behaviors when in form of very-thin films. We conducted first-principles calculations to get a glimpse of the effects of crystallographic orientations as the interfaces form in addition to their electronic structures and crystal structural stabilities. Comparisons with experimental findings will be discussed.

Keywords: superlattice, multilayer, FeBi2, iron-bismuth