Competition of arsenic and sulfur segregation on Fe-9%W(100) single crystal surfaces

High-resolution medium-energy ion scattering (MEIS) was used to investigate the segregation of arsenic and sulfur on the (100) oriented surface of a b ody-centered cubic Fe-9 wt%W(100) single crystal containing 53 wt-ppm As an d 10 wt-ppm S. At temperatures ranging from 800 to 1100 degrees C, both seg regants compete for the available surface sites. Arsenic segregation domina tes at temperatures around 800 degrees C where maximum As surface concentra tions of theta(As)(max)=0.40 were found. S segregation is most pronounced a t temperatures around 1000 degrees C with theta(S)(max)=0.43. MEIS shows th e segregated As (S) atoms to be arranged 1.27 Angstrom (1.22 Angstrom) abov e the topmost metal layer. The metal-to-metal layer distances show an oscil latory behavior with an expansion of the first to second metal layer (+0.05 Angstrom). With As and S on the surface, there is a strong W depletion of the topmost three metal layers. (C) 1999 American Institute of Physics. [S0 003-6951(99)01023-2].