Asymmetric Electric Field Screening in van der Waals Heterostructures

TL;DR

This study combines theoretical and experimental methods to reveal asymmetric electric field screening in MoS2/Graphene van der Waals heterostructures, highlighting thickness-dependent effects and interface dipolar contributions.

Contribution

It provides new insights into the intrinsic dielectric screening properties and asymmetric responses of vdW heterostructures, with implications for device engineering.

Findings

Asymmetric electric response observed under different field directions.

Screening is highly dependent on MoS2 layer thickness.

Interface dipolar contributions cause the asymmetric screening behavior.

Abstract

Electric field screening plays an important role in the physical and chemical properties of materials and their devices. Here, we use a compelling set of theoretical and experimental techniques involving van der Waals (vdW) ab initio density functional theory (DFT) simulations, quantum capacitance-based classical model and electric force microscopy (EFM) to elucidate the intrinsic dielectric screening properties of vdW heterostructures (vdWHs) formed by MoS2 and graphene layers. We experimentally observed an asymmetric electric response in the MoS2/Graphene vdWHs under different directions of the external electric field. That is, when the electric fields are shed towards graphene, a large amount of polarized charges screen the fields, but as the sign of the field was reversed, a strong depolarization field was present, and a partial screening was detected. This effect is thickness-dependent, in particular on the number of the MoS2 layers; whereas increased thickness of graphene showed a small effect on their electrical and screening behavior. Our results indicate that asymmetric dipolar contributions at the interface between graphene and MoS2 are the main cause to the unusual field-effect screening in the vdWHs. This work not only provides new insights on the screening properties of a vast amount of heterojunction fabricated so far, but also uncovers the great potential of controlling a fundamental property, such as screening, for device applications.