An ordered surface ternary alloy of a c(6 × 4) structure formed on Cu(0 0 1) by substitutional coadsorption of Mg and Bi

A c(6 × 4) structure formed on Cu(0 0 1) by the coadsorption of Mg and Bi atoms at room temperature has been determined by a tensor low energy electron diffraction analysis. It is an ordered surface ternary alloy with a thickness of single layer, in which Mg, Bi and Cu atoms are mixed in the top layer. In the primitive unit cell, there are one Mg, four Bi, six Cu atoms and one vacancy in the top layer, and substituted Mg and Bi atoms form MgBi₄ plane clusters being arranged in the c(6 × 4) order. Structural parameters show that Mg-Bi bond distances in the MgBi₄ cluster are 3.01 and 3.07 Å, which are shorter than the summation of metallic radii of Mg and Bi. It is concluded that a direct, attractive interaction between Mg and Bi atoms plays critical role in the formation of the c(6 × 4) structure.