SEGREGATED SI ON FE96.5SI3.5(110) - DOMAIN-WALL STRUCTURES IN A 2-DIMENSIONAL ALLOY

The surface structures formed by segregated silicon on a bcc Fe96.5Si3.5(110) surface have been studied by scanning tunneling microscopy (STM). Additionally Auger-electron spectroscopy and low-energy ion-scattering spectroscopy have been used to obtain the chemical and structural information necessary to decide between possible configurations suggested by the STM images. Near the expected saturation coverage a substitutional c(1×3)Si superstructure weakly disordered by 110 aligned domain boundaries was observed. Their arrangement is equivalent to the incommensurate domain-wall structures of chemisorption systems like H/Fe(110), which allow a continuous increase of the surface coverage by successive insertion of equidistantly arranged heavy domain walls. Our observations suggest a possible increase of the silicon coverage above the 33.3% of the perfect c(1×3) structure at least up to 40% corresponding to a c(1×5)Si commensurate domain-wall structure. Correlation analysis of the disordered phase at 15% coverage, obtained by short annealing, allows a qualitative determination of the interaction forces among individual silicon atoms on the surface, yielding attraction of third-nearest neighbors and repulsion of nearest neighbors. © 1994 The American Physical Society.