Effects of static charging and exfoliation of layered crystals

TL;DR

This study uses first-principle calculations to explore how static charging affects the structural, electronic, and magnetic properties of various 2D layered materials, revealing charging-induced metallization and exfoliation phenomena.

Contribution

It provides a detailed analysis of charging effects on 2D materials, highlighting the limitations of periodic boundary conditions and identifying thresholds for exfoliation and metallization.

Findings

Positive charging increases band gaps but induces metallicity.

High charging causes bond length expansion and decreased stiffness.

Excessive charging leads to exfoliation of BN and MoS2 layers.

Abstract

Using first-principle plane wave method we investigate the effects of static charging on structural, elastic, electronic and magnetic properties of suspended, single layer graphene, graphane, fluorographene, BN and MoS2 in honeycomb structures. The limitations of periodic boundary conditions in the treatment of charged layers are clarified. Upon positive charging the band gaps between the conduction and valence bands increase, but the single layer materials become metallic owing to the Fermi level dipping below the maximum of valence band. Moreover, their bond lengths increase and their in-plane stiffness decreases. As a result, phonons are softened and frequencies of Raman active modes are lowered. High level of charging leads to instability. We showed that wide band gap BN and MoS2 slabs are metallized as a result of electron removal and their outermost layers are exfoliated once the charging exceeds a threshold value.