We have used medium-energy ion scattering to investigate segregation of Cr and impurity (20 ppm) C atoms to the surface of Fe–15 % Cr(100). Nonequilibrium cosegregation (surface nucleated precipitation) of Cr and C leads to formation of a CrC surface compound with a structure related to cubic rocksalt. Such a phase does not exist in the bulk, but is stabilized by epitaxy to the bcc(100) surface. The formation of this surface compound (with C content between 1.6 and 2.4 ML) can be viewed as a structural transformation comparable to a giant expansion (formula presented) between the first two metal layers of the alloy surface. Details of the surface composition and structure have been obtained on a layer-by-layer basis. C atoms in the first two layers are found to be buckled towards the vacuum by (formula presented) characteristic of ionic bonding in which the anion has the higher polarizability. It is suggested that changes in the subsurface carbon concentration could allow for the controlled engineering of thin-film characteristics, such as magnetic properties, by modification of near-surface interlayer spacings.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Jan 1 2001|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics