Segregated Si on Fe96.5Si3.5(110): Domain-wall structures in a two-dimensional alloy

A. Biedermann, M. Schmid, and P. Varga

Institut für Allgemeine Physik, Technische Universität Wien, A-1040 Wien, Austria

Phys. Rev. B 50 (1994) 17518-17524

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 (AES) 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 3rd nearest neighbours and repulsion of nearest neighbours.

Corresponding author: M. Schmid (schmid< encoded email address >).

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Part of this work is on display in the IAP/TU Wien STM Gallery (see the segregation page).