Comparative study of phonon spectrum and thermal expansion of graphene, silicene, germanene and blue phosphorene

TL;DR

This study uses first-principles calculations to compare vibrational and thermal properties of four 2D honeycomb materials, revealing how lattice structure influences phonon behavior and thermal expansion.

Contribution

It provides a comparative analysis of phonon spectra and thermal expansion in graphene, silicene, germanene, and blue phosphorene based on first-principles calculations.

Findings

Phonon bandgap develops from graphene to blue phosphorene due to buckling.

Buckling causes mixing of in-plane and out-of-plane phonon modes.

All four materials exhibit negative thermal expansion at room temperature.

Abstract

Based on first-principles calculation using density functional theory, we study the vibrational properties and thermal expansion of mono-atomic two-dimensional honeycomb lattices: graphene, silicene, germanene and blue phosphorene. We focus on the similarities and differences of their properties, and try to understand them from their lattice structures. We illustrate that, from graphene to blue phosphorene, phonon bandgap develops due to large buckling-induced mixing of the in-plane and out-of-plane phonon modes. This mixing also influences their thermal properties. Using quasi-harmonic approximation, we find that all of them show negative thermal expansion at room temperature.