Local tuning of WS2 photoluminescence using polymeric micro-actuators in a monolithic van der Waals heterostructure

TL;DR

This paper demonstrates a novel method for locally tuning the photoluminescence of monolayer WS2 using polymeric micro-actuators integrated into a van der Waals heterostructure, enabling precise strain engineering without fragile suspended structures.

Contribution

It introduces a new approach using electron-beam patterned polymeric actuators to locally apply strain to WS2, avoiding complex transfer or suspension processes.

Findings

Achieved a maximum PL redshift of 40 meV under local strain.

Demonstrated reversible and spatially controlled PL modulation.

Showed negligible friction allowing sliding of WS2 on graphene.

Abstract

The control of the local strain profile in 2D materials offers an invaluable tool for tailoring the electronic and photonic properties of solid-state devices. In this paper, we demonstrate a local engineering of the exciton photoluminescence (PL) energy of monolayer tungsten disulfide (WS2) by means of strain. We apply a local uniaxial stress to WS2 by exploiting electron-beam patterned and actuated polymeric micrometric artificial muscles (MAMs), which we implement onto monolithic synthetic WS2/graphene heterostructures. We show that MAMs are able to induce an in-plane stress to the top WS2 layer of the van der Waals heterostructure and that the latter can slide on the graphene underneath with negligible friction. As a proof of concept for the local strain-induced PL shift experiments, we exploit a two-MAM configuration in order to apply uniaxial tensile stress on well-defined micrometric regions of WS2. Remarkably, our architecture does not require the adoption of fragile suspended microstructures. We observe a spatial modulation of the excitonic PL energy of the WS2 monolayers under stress, which agrees with the expected strain profile and attains a maximum redshift of about 40 meV at the maximum strain intensity point. After the actuation, a time-dependent PL blueshift is observed in agreement with the viscoelastic properties of the polymeric MAMs. Our approach enables inducing local and arbitrary deformation profiles and circumvents some key limitations and technical challenges of alternative strain engineering methods requiring the 2D material transfer and production of suspended membranes.