Growth of Ag on Cu(100) studied by STM: From surface alloying to Ag superstructures

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The nucleation and growth of Ag on Cu(100) and the resulting surface structures have been studied with variable temperature (150-330 K) scanning tunneling microscopy (STM). At temperatures below 250 K, islands of Ag, having a pseudohexagonal, c(10×2) overlayer structure, nucleate and grow on Cu terraces and at step edges at Ag subsaturation coverages. However, at temperatures at or above 300 K, a substitutional Ag-Cu surface alloy forms, showing that the formation of the surface alloy phase is an activated process. It is found that only a limited amount of Ag (∼0.13 ML) can be accommodated within the Cu(100) surface layer. At higher coverages (0.13 ML⩽(Formula presented)<0.9 ML), the strain energy induced by the alloyed Ag becomes so high that the Ag atoms segregate into small patches of c(10×2) superstructure located within the Cu surface layer. Upon Ag deposition at or above the first monolayer at 425 K, a simple pseudohexagonal overlayer structure is observed, indicating that the Ag-Ag interaction dictates the overall structure. Based on atomically resolved STM images of the c(10×2) superstructure, a structural model is presented, and a mechanism is suggested which explains how the surface alloy phase is converted into the overlayer structure. © 1996 The American Physical Society.

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Physical Review B - Condensed Matter and Materials Physics

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