Van der Waals heterostructures (vdWH), the nanoscale Lego built by 2D materials, enable the control of material properties with numerous combinations at atomic precision. Electric field screening is one of the key characteristics governing the performance of vdWH-based devices. Here, we use a compelling set of theoretical and experimental techniques to elucidate the intrinsic screening properties of vdW heterostructures (vdWHs) formed by MoS2 and graphene layers. Using electric force microscopy (EFM), we experimentally observed an asymmetric electric response in the MoS2/graphene vdWHs with respect to the polarity of the external electric field. When the electrostatic potential of graphene is higher than MoS2, the electric field is highly screened due to high density of polarized charges, while the electric field is only partially screened by reversing the polarity of the field. The asymmetric electric screening effect is thickness-dependent, in particular on the number of MoS2 layers, while increasing graphene layer number showed smaller influence on the electric field screening properties. The cause for the asymmetric screening behaviour is further studied by multiscale simulations combining van der Waals <i>ab initio </i>density functional theory (DFT) calculations and quantum capacitance-based electrostatic model. Our theoretical simulations indicate that asymmetric dipolar contributions at the heterostructure interface are responsible for the unusual field-effect screening, which further attributes such behaviour to the energy level alignment and distinct electronic structures between graphene and MoS2. The principles presented here can be readily applied to other type of vdWHs, which facilitate the engineering the fundamental property of screening in vdWHs, as well as optimized design of functional heterostructure devices.

Towards the understanding and engineering of the asymmetric electric field screening in van der Waals heterostructures

256th National Meeting (2018)

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