Competitive surface segregation of C, Al and S impurities in Fe(100)

Abstract

The stoichiometries and geometric structures formed by the segregation of C, Al and S on a Fe(100) surface have been investigated by Auger electron spectroscopy and quantitative low-energy electron diffraction (LEED). Stepwise annealing of a sputtered surface with increasing annealing temperature reveals the successive segregation of C, Al and S. According to quantitative LEED analyses, each segregand forms a distinct c(2 × 2) long-range ordered structure. Also, each segregand removes the preceding one from the surface entirely, i.e. segregation in the Fe(100)-(C, Al, S) system is purely competitive with no ordered co-segregation regimes involving two or even three elements. The c(2 × 2) phases of segregated carbon and sulfur consist of elemental surface adlayers with the adatoms residing in four-fold symmetric hollow sites of the iron substrate. This is in contrast to segregated Al which, according to an earlier analysis, forms a c(2 × 2)-symmetric surface alloy layer with iron. In all cases there is some chemical disorder within subsurface layers with Fe atoms substituted by Al. The bond lengths between the segregated adatoms and iron neighbours are close to the sum of the covalent radii of the elements involved whereby carbon appears to be five-fold coordinated, in contrast to four-fold coordinated sulfur.

One‐dimensional surface states induced by segregated impurities at transition‐metal surfaces

“…Å higher than those located just below the C atoms. We note that relatively similar trends, but involving relaxations smaller in magnitude, were observed experimentally, and also obtained in firstprinciples calculations, for the 1/2-ML covered C/Fe(001) (2 2) c ¥ surface [10,13].…”

Spin filtering effects in monocristalline Fe/MgO/Fe magnetic tunnel junctions

“…A complete RHEED analysis concludes that in samples type A, the Fe surface postannealing presents a c(2 × 2) super-structure. In agreement with results of previous Auger electron spectroscopy and quantitative low-energy electron diffraction (LEED) studies [12], we associate this reconstruction to the segregation of C at the Fe(0 0 1) surface. Using Auger analysis we checked the chemical nature the surface and we confirmed that for sample type A, a carbon monolayer was segregated during the Fe annealing.…”

Submonolayers of carbon onα-Fefacets: Anab initiostudy

“…A minimum of energy E c as function of carbon concentration occurs at the coverage of 6/9 = 0.667 ML at an adsorption configuration "3 (2)× (2)" that has been reported earlier in an experimental 19 and theoretical 20 study; in this adsorption configuration, carbon atoms form an infinite, two atom wide ribbon on the C-1 sublattice. There exists even more favorable coadsorption configuration "c(2×2)" which takes place at the coverage of 0.50 ML 17,18,20 . Both of these stable structures have been analyzed using STM and/or LEED 18,19 For the 6/9 ML coadsorption structure presented in Fig.6 we observe same phenomena as reported in an earlier study 20 , most notably the displacements of iron atoms in the topmost layer as illustrated schematically in Fig.6.…”

“…There exists even more favorable coadsorption configuration "c(2×2)" which takes place at the coverage of 0.50 ML 17,18,20 . Both of these stable structures have been analyzed using STM and/or LEED 18,19 For the 6/9 ML coadsorption structure presented in Fig.6 we observe same phenomena as reported in an earlier study 20 , most notably the displacements of iron atoms in the topmost layer as illustrated schematically in Fig.6.…”

“…The (100) facet has drawn some attention very recently, as segregated carbon atoms form stable, periodic structures on this facet [18][19][20] . Some carbide surfaces have been studied with ab initio methods by Chiou and Carter 21 .…”