Structure and energetics of Si(111)-(5x2)-Au

TL;DR

This paper introduces a new structural model for the Si(111)-(5x2)-Au surface reconstruction, supported by first-principles calculations that explain experimental observations including periodicity doubling, phase separation, STM images, band structure, and adatom diffusion barriers.

Contribution

The study presents a novel structural model incorporating a specific gold coverage and validates it through comprehensive first-principles calculations, aligning with multiple experimental results.

Findings

Periodic doubling of gold rows with silicon adatoms.

Surface phase separation into empty and covered regions.

Excellent agreement between calculated and experimental STM images, band structure, and diffusion barriers.

Abstract

We propose a new structural model for the Si(111)-(5x2)-Au reconstruction. The model incorporates a new experimental value of 0.6 monolayer for the coverage of gold atoms, equivalent to six gold atoms per 5x2 cell. Five main theoretical results, obtained from first-principles total-energy calculations, support the model. (1) In the presence of silicon adatoms the periodicity of the gold rows spontaneously doubles, in agreement with experiment. (2) The dependence of the surface energy on the adatom coverage indicates that a uniformly covered phase is unstable and will phase-separate into empty and covered regions, as observed experimentally. (3) Theoretical scanning tunneling microscopy images are in excellent agreement with experiment. (4) The calculated band structure is consistent with angle-resolved photoemission spectra; analysis of their correspondence allows the straightforward assignment of observed surface states to specific atoms. (5) The calculated activation barrier for diffusion of silicon adatoms along the row direction is in excellent agreement with the experimentally measured barrier.