Structural stability and energy-gap modulation through atomic protrusion in freestanding bilayer silicene

TL;DR

This study uses first-principles calculations to identify stable bilayer silicene structures, revealing atomic protrusions as key to stability and showing the material as a semiconductor with a 1.3 eV energy gap.

Contribution

It uncovers four new stable bilayer silicene structures and highlights atomic protrusion as the main relaxation pattern influencing stability and electronic properties.

Findings

Identified four new dynamically stable bilayer silicene structures.

Atomic protrusion stabilizes bilayer silicene and affects its periodicity.

Most stable bilayer silicene is a semiconductor with a 1.3 eV gap.

Abstract

We report on first-principles total-energy and phonon calculations that clarify structural stability and electronic properties of freestanding bilayer silicene. By extensive structural exploration, we reach all the stable structures reported before and find four new dynamically stable structures, including the structure with the largest cohesive energy. We find that atomic protrusion from the layer is the principal relaxation pattern which stabilizes bilayer silicene and determines the lateral periodicity. The hybrid-functional calculation shows that the most stable bilayer silicene is a semiconductor with the energy gap of 1.3 eV.