The atomic structure of the $\sqrt{3} \times \sqrt{3}$ phase of silicene on Ag(111)

TL;DR

This study uses first-principles calculations to reveal the atomic structure of the $\,\sqrt{3} imes \sqrt{3}\,$ reconstructed silicene on Ag(111), showing it consists of Si dumbbell units and proposing a new formation mechanism.

Contribution

The paper introduces a detailed atomic model of the $\,\sqrt{3} imes \sqrt{3}\,$ silicene structure and explains its spontaneous formation mechanism from $3 imes 3$ structures.

Findings

Silicene's $\,\sqrt{3} imes \sqrt{3}\,$ phase is made of Si dumbbell units.

The structure's formation is mainly driven by Si atom interactions.

The substrate has a weak influence on the reconstruction.

Abstract

The growth of the $\sqrt{3} \times \sqrt{3}$ reconstructed silicene on Ag substrate has been frequently observed in experiments while its atomic structure and formation mechanism is poorly understood. Here by first-principles calculations we show that $\sqrt{3} \times \sqrt{3}$ reconstructed silicene is constituted by dumbbell units of Si atoms arranged in a honeycomb pattern. Our model shows excellent agreement with the experimentally reported lattice constant and STM image. We propose a new mechanism for explaining the spontaneous and consequential formation of $\sqrt{3} \times \sqrt{3}$ structures from $3 \times 3$ structures on Ag substrate. We show that the $\sqrt{3} \times \sqrt{3}$ reconstruction is mainly determined by the interaction between Si atoms and have weak influence from Ag substrate. The proposed mechanism opens the path to understanding of multilayer silicon.