From high temperature phase formation to transition metal substitution in the Fe/Al₉Co₂(001) system
Résumé
We report the formation of several complex intermetallics as surface alloys upon the adsorption of Fe on Al 9 Co 2 (001) for different dosing conditions. Up to 4 monolayers equivalent (MLE) of Fe deposited on the substrate held at 593 K, the low energy electron diffraction pattern consists of a (√ 2 × √ 2)R45 • phase with two additional domain types rotated by ±8 • from it. The scanning tunneling microscopy (STM) measurements show that these three types of domains have the same crystallographic structure. The lattice parameters and structural motifs point towards the formation of the high-temperature Al 8 Fe 5 phase (γ-brass of Zn 8 Cu 5-type structure). For Fe deposition between 593 K and 873 K, we have identified the formation of two phases, tentatively assigned to a ternary disordered Al 9 (Co,Fe) 2 overlayer and to the monoclinic Al 13 Fe 4 (100). The stoichiometric evolution of the grown structures have been characterised by angle-resolved x-ray photoelectron spectroscopy measurements. Density functional theory based calculations have been performed to model the Al 8 Fe 5 (100)/Al 9 Co 2 (001) interface, its structural stability and to simulate the corresponding STM images.
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