Meyerheim, Holger L.; Zajonz, H.; Moritz, Wolfgang; Robinson, Ian K.
Surface alloying and dealloying in Bi/Cu(001) at low coverage.
In: Surface Science, Vol. 381, Nr. 1:
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Using surface X-ray diffraction we have investigated the structure of the Bi/Cu surface alloy formed after Bi deposition on Cu(001) at room temperature. At low Bi coverage below about 0.35 ML (1 ML = 1.53 × 1015 atoms cm-2), the intensity distribution along the integer order crystal truncation rods indicates surface alloying where Bi atoms substitute Cu surface atoms. The Bi atoms adsorb 0.61 (10) Å above the surface Cu layer. At a coverage above about 0.35 ML where the formation of a well-ordered c(2 × 2) superstructure starts to set in, we observe surface dealloying indicated by a rapid decrease of the fractional Cu occupancy of the surface layer with increasing Bi coverage. The Bi atoms are located in hollow sites at an adsorption height of 2.27 (10) Å corresponding to a hard sphere radius of 1.63 (8) Å, somewhat below the metallic radius of 1.82 Å.