Optical Detection of Passive Thermal Lattice Deformation of Monolayer WS2 in van der Waals Heterostructures of WS2/h-BN

Abstract

Van der Waals heterostructures (vdWHs) of the constituent two-dimensional (2D) layered materials are quickly emerging as functional structures for diverse novel electronic and optoelectronic devices. To further explore the device applications of the vdWHs, an open question, which is whether the lattice of atomic thin active layer follows the deformation of its neighboring thick layers in a vdWH, needs to be clarified. Herein, the thermal deformation of WS2 monolayers in vdWHs with and without hexagonal boron nitride (h-BN) layers on SiO2/Si substrates is investigated with combined optical spectroscopies of photoluminescence (PL) and Raman scattering. With a developed strategy extracting the pure strain-induced effects from the temperature-dependent PL and Raman scattering spectroscopic results, the relative deformations of the WS2 monolayers and the h-BN layers with respect to the substrate have been identified. Both the Raman and PL results consistently reveal that the lattice variation of the WS2 monolayers passively match the deformation of the h-BN layers, and the WS2 monolayer on the SiO2/Si substrate exhibits the largest strain. These findings have not only demonstrated the passive behavior of the thermal strain of 2D semiconductor monolayers in vdWHs heterostructures, but also paved a way to tailor the thermal strain via designing and constructing vdWHs.