Observation of strain transfer in vertical van-der-Waals heterostructures

Strain is a powerful method to tune the properties of 2D materials. It has been widely applied both to study 2D monolayers and to modify their properties. The same approach also has great potential for van-der-Waals (vdW) heterostructures. To this end, however, we need to understand how strain can be applied to vertically stacked vdW structures, for which strain transfer from one layer to the next remains poorly understood.
In our experiment, we fabricated vertical heterostructures consisting of monolayers of the transition metal dichalcogenides (TMDCs) MoSe₂ and WS₂, which were deposited on a flexible substrate. The choice of these TMDC monolayers allowed us to read out separately and accurately the strain in each of monolayer by measurement of the energy of the respective exciton peak in the photoluminescence spectrum When we applied strain by bending the flexible substrate, we found that the strain transfer efficiency was linear in strain until slippage occurred. A strain transfer efficiency near unity could be achieved. We will describe our approach and results, as well as the influence of the presence of monolayers of hexagon BN.