Abstract
We address the role of “surfactant” adsorbates in determining changes in the homoepitaxial growth mode of metals, discussing the case of Sb on Ag (111). From ab initio calculations, we extract evidence that the mechanism operative in this system is that Sb induces an irregular shape and an increase in density of the growing Ag islands, and an ensuing increase of the number of attempts for an adatom to descend to a lower terrace. This results from a combination of peculiar properties of this system: Sb is adsorbed insubstitutional surface sites, leading to the formation of a Sb−Ag surface alloy; deposited Ag has reduced mobility on Sb-covered Ag (111), from which follows a higher nucleation probability. The island shape is irregular since the surface alloy is disordered. Surface seggregation of Sb once the growing layer is completed furthers the phenomenon for many deposited Ag layers. Our explanation of the surfactant action of Sb on Ag (111) does not require a reduction of the downstep diffusion barrier, which may, however, be a concurrent factor helpful to interlayer mass transport and layerby-layer growth.
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Sb gains only about 0.2 eV by being lifted to the upper layer by exchange with asingle Ag from the upper layer. One thus expects that to create on-surface Sb at an appreciable rate from substitutional Sb, more upper-layer Ag neighbors are needed to provide sufficient coordination to the Sb atom being lifted
Indeed, recent STM results indicate the presence of Sb not only on the substrate, but also on the growing islands ([10], and private communication by J. Meyer)
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Fiorentini, V., Oppo, S. & Scheffler, M. Towards an understanding of surfactant action in the epitaxial growth of metals: The case of Sb on Ag (111). Appl. Phys. A 60, 399–402 (1995). https://doi.org/10.1007/BF01538341
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DOI: https://doi.org/10.1007/BF01538341