Probing the interface strain in a 3D-2D van der Waals heterostructure

Abstract

The interaction at a van der Waals (vdW) epitaxial interface is perceived to be too weak to induce substantial elastic strain in films due to the weak nature of dipole-dipole interactions. Recent research on discovering giant strain in vdW heterostructures in 2D-2D configurations has reformed such an understanding. In this letter, the study on strain was extended to the regime of 3D-2D vdW heterostructures. Using temperature dependent Raman spectroscopy, the strain behaviors were revealed, through the change of phonon frequency, at a vdW epitaxial interface of CdS-mica. Although the interface was free of interactions for relatively thick CdS films, it was found that at least 0.4% strain can be borne at the interface when the film was only 6 nm thick and the strain was estimated to be 1.2% if a two-monolayer can be grown. The finding suggests that non-trivial strain could be enabled in 3D-2D vdW heterostructures if the thickness can be well-controlled, providing an avenue for strain engineering. This work also indicated a different changing tendency in the linewidth of phonon scattering as a function of temperature, which may be related to defects and serve as a reference for studying the linewidth of ultrathin films.