(185n) A Monte Carlo Simulation Study of Strain-Relief Patterns In Ag / Pt(111) Heteroepitaxy

Experimental studies of Ag/Pt(111) heteroepitaxy show rich structures that arise due to strain at the Ag/Pt interfaces [1]. Strain-relief structures, such as stripes and patterns consisting of hexagons and triangles, occur in the 2nd monolayer of Ag on Pt(111). In our work, we investigate the origins of these patterns. The Ag(111) surface has a Shockley-type surface state that is sensitive to strain [2]. In first-principles studies with density functional theory (DFT) the pair interactions between Ag atoms have been characterized up to the 53rd neighbor and are shown to correlate with a one-dimensional theoretical expression for the interaction as a function of separation [2]. However, the DFT result exhibits angular variation in the interaction and takes on a two-dimensional character that is not captured by the theory. Here, we show that this angular variation is significant. We use Monte Carlo (MC) simulations to study the structure of Ag layers in which the atoms have pair interactions described by both DFT and theory. We show that, with the DFT interactions, we can reproduce all the key aspects of the striped patterns seen experimentally, including the crystallographic orientation of the stripes and the alternation of the stripes between fcc and hcp registry. These results suggest that electronic surface states play a significant role in determining surface structures and that the angular variations in surface-state-mediated interactions are significant in determining system behavior.

[1] H. Brune, H. Röder, C. Boragno, K. Kern, Phys. Rev. B, 49 2997 (1994).

[2] W. Luo, K. Fichthorn, Phys. Rev. B, 72 115433 (2005).