Interfaces, Confinement, Matériaux et Nanostructures - ICMN

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Jeudi 13 Juillet 2017

10h - bibliothèque de l’ICMN

Growth and solid-liquid transition of bismuth on an insulating substrate by Surface x-ray diffraction SXRD


The European Synchrotron- ESRF, Grenoble

Nanostructured ultrathin bismuth films have recently attracted a lot of interest as they reveal exotic functional properties that do not exist in bulk [1-5]. In this contribution, we report on the controlled growth of bismuth on the α-Al2O3(0001) surface investigated by surface x-ray diffraction and x-ray reflectivity using synchrotron radiation.
We also found a route towards the creation of Bi(110) nanodots, very promising for their electronic properties. The deposition of bismuth just below the transition temperature leads to the formation of well-defined nanodots which growth, thanks to the high-brilliance and the spatial coherence of the synchrotron x-ray beam, was followed in–situ and real- time as a function of temperature. Similar to the (111) films, the nanodots go through the solid-liquid-solid phase transition during slow annealing and subsequent cooling, which finally leads to their unexpected recrystallization on the surface.
The presented results show a variety of bismuth nucleation scenarios on an insulating substrate which is also very beneficial for practical applications, as the interface between film and insulating substrate, expected to reveal topological states, will also be protected from influencing oxidation effects arising from ambient exposure in technological applications.
In details, at temperatures as low as 40 K, unanticipated pseudo cubic Bi(110) films are grown with the thickness between few up to few tens of nanometre [6]. The roughness at the film-vacuum and film-substrate interfaces can be decreased by mild heating, followed by a phase transition of Bi(110) towards Bi(111) at 400 K. From 450 K onwards the high quality and ultrasmooth Bi(111) films are formed. Growth at temperatures around the transition temperature results in competing growth of Bi(110) and Bi(111) thin-film domains. The solid- liquid transition of (111) films is observed at 548 K and the liquid recrystallizes to (110) crystallographic phase at 440 K, one hundred degrees bellow Bi melting point (supercooling). Ex-situ AFM investigations revealed the formation of large sub-microcrystals.
The last part of this talk will be dedicated to the ID03 surface x-ray diffraction beamline at ESRF, its experimental opportunities, recently developed software for the fast data analysis, and some experimental examples focused on the structural determination of single crystal (bi)metallic surfaces under oxidizing catalytic conditions.

[1] M.-Y. Yao, et al, Sci. Rep. 6 (2016) 21326. [2] H. Du, et al, Nat. Commun. 7 (2016) 10814. [3] F. Song, J.W. Wells, Z. Jiang, M. Saxegaard, E. Wahlström, ACS Appl. Mater. Interfaces. 7 (2015) 8525–8532. [4] Y. Lu, et al , Nano Lett. 15 (2015) 80–87. [5] I.K. Drozdov, et al , Nat. Phys. 10 (2014) 664–669. [6] M. Jankowski, D. Kamiński, K. Vergeer, M. Mirolo, F. Carla, G. Rijnders, T.R.J. Bollmann, Nanotechnology 28 (2017) 155602.