Self-organized carbon-rich stripe formation from competitive carbon and aluminium segregation at Fe0.85Al0.15(1 1 0) surfaces

Abstract

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A 2 random alloy Fe 0.85 Al 0.15 (110) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900 K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5 nm that run along the [001] B bulk direction and cover up to 34 % of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements.

Aluminium segregation profiles in the (110), (100) and (111) surface regions of the Fe0.85Al0.15 random body-centered cubic alloy

“…The annealing temperature was kept below 1300 K to avoid Al evaporation [35,36]. Bulk contaminants were below the detection level, except on the (110) surface for which a temporary carbon segregation in the form self-organized stripes was observed [53,54]. Fortunately, after several cycles of preparation, a carbon free surface could be obtained.…”

Al-rich Fe0.85Al0.15(1 0 0), (1 1 0) and (1 1 1) surface structures

“…More has been learned on the superstructure by STM experiments. Besides the already reported transient initial segregation of carbon in the form of self-organized stripes [18,28], annealing the (110) surface after sputtering induces a sizable smoothing, a straightening of the step edges and an increase of the average size of terraces which become mostly separated mostly by monoatomic height (2Å) steps, suggesting that defective areas coalesce in some exent [28] (Fig. 4-a).…”

“…Experiments were performed in an ultra-high vacuum (UHV) set-up previously described [28,17], that involves two connected vessels equipped with LEED (ErLEED, SPECS), STM (RT-Omicron) and XPS (Omicron EA125 under non-monochromatic excitation). STM images were acquired in constant current mode with chemically etched W tips and processed with the WsXM and Gwyddion software [29,30,31].…”

“…Bulk contaminants were below the detection level of XPS on all surfaces. Only a transient segregation of carbon in the form of stripes was oberved on the (110) orientation [28]. Due to the high reactivity of aluminum, special care was taken to minimize contamination due to residual background, the Al 2p core level being a good indicator of the associated oxidation phenomenon [18].…”

“…4-a). Magnification at higher resolution clearly reveals a long-range ordered hexagonal-like superstructure [28] at 2.5 V with atomic corrugation (Fig. 4-b).…”