DOMAIN-WALL STRUCTURES IN AN ORDERED SI/FE(110) SURFACE ALLOY

During the annealing process of an Fe96.5Si3.5(100)/(110) bicrystal, silicon and impurity carbon segregate to the surface. The structures formed by the segregands on the (110) surface have been studied by STM (geometry) and AES (chemical information). Silicon substitutes iron surface atoms and forms a two-dimensional alloy, whereas carbon occupies hollow sites in the first monolayer, leading to a distortion of the substrate lattice. The structures are based on a c(1 x 3)Si theta = 1/3 ordered surface alloy. Additional silicon as well as the co-segregating impurity carbon are inserted into this structure by formation of domain walls. If the density of these nearly straight and parallel domain walls becomes high enough, commensurate domain wall structures with c(1 x n) supercells can be observed.