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

During the annealing process of an Fe96.5Si3.5(100)/(110) bicrystal, s ilicon and impurity carbon segregate to the surface. The structures fo rmed by the segregands on the (110) surface have been studied by STM ( geometry) and AES (chemical information). Silicon substitutes iron sur face atoms and forms a two-dimensional alloy, whereas carbon occupies hollow sites in the first monolayer, leading to a distortion of the su bstrate 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-segregatin g impurity carbon are inserted into this structure by formation of dom ain 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.