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Séminaire des doctorants de l’INSP

Segregation and reconstruction at the surfaces of Fe0.85Al0.15 single crystal alloy - Zongbei Dai - Jeudi 24 novembre 2016 à 11 h

INSP - UPMC - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Zongbei Dai, doctorante dans l’équipe Oxydes en basses dimensions

Abstract

The orientation effects on the segregation and reconstruction at the surfaces of Fe0.85Al0.15 single crystal alloy in the ferric phase have been studied by combining Scanning Tunnelling Microscopy (STM), Low Energy Electron Diffraction (LEED) and X-ray Photoelectron Spectroscopy (XPS). The behaviours of the (110), (111) and (100) orientations have been compared. For the (110), it was found that carbon impurities segregate on top of a reconstructed bare surface in the form of parallel stripes, spaced by approximately 18 nm. These stripes run along the [001] direction with a temperature dependent coverage ; terraces widen at high temperature while the step edges are denser and parallel to the stripes at lower annealing temperatures. The carbon free areas of the substrate show superstructure LEED satellite diffraction spots which correspond to a local pseudo-hexagonal arrangement as imaged by STM (periodicity is about 2 nm). As a more open surface, FeAl (111) has a much higher roughness and displays triangular features in the form of nano-pyramids. Both (111) and (100) present a (1x1) LEED pattern above 600 K annealing, with more obvious Al surface enrichment as compared to (110).