Elastic properties of silicene: Spinodal instabilities

TL;DR

This study explores the elastic behavior and mechanical stability of silicene under various stresses and temperatures, revealing temperature-dependent softening and identifying instability points indicating limits of structural stability.

Contribution

It provides detailed molecular dynamics analysis of silicene's elastic properties and stability limits, highlighting temperature effects and spinodal instabilities not previously characterized.

Findings

Elastic constants decrease with temperature.

Mechanical instabilities occur at specific biaxial stresses.

Elastic anomalies appear at spinodal points.

Abstract

Silicene, a two-dimensional (2D) allotrope of silicon, has attracted significant interest for its electronic and mechanical properties, alongside its compatibility with various substrates. In this study, we investigate the structural and elastic characteristics of silicene using molecular dynamics simulations based on a tight-binding Hamiltonian, calibrated to align with density-functional theory calculations. We focus particularly on the material's elastic properties and mechanical stability, analyzing its behavior under extensive compressive and tensile in-plane stresses and across temperatures up to 1000 K. Key properties examined include in-plane area, Si--Si bond length, atomic mean-square displacements, elastic constants, and 2D compression modulus. Our findings reveal a notable reduction in stiffness elastic constants, Poisson's ratio, and compression modulus with increasing temperature. Additionally, we identify mechanical instabilities in the silicene structure at specific compressive and tensile biaxial stresses, signaling the material's stability limits or spinodal points. At the corresponding spinodal pressures, structural and elastic properties exhibit anomalies or divergences.