Probing the interfacial coupling in ternary van der Waals heterostructures

Abstract

Good interfacial coupling between each constituent of van der Waals Heterostructures (vdWHs) is the prerequisite for the distinguished performance of related devices. Since vdWHs-based devices commonly consist of three or more constituents, an effective evaluation of interfacial coupling quality in multiple heterointerfaces is critical during the device fabrication process. Here, in ternary vdWHs composed of hBN, graphene (Gr) and transition metal dichalcogenide (TMD) flakes, which are essential building blocks for low-dimensional vdWHs-based electronic and optoelectronic devices, we realized probe and quantification of the interfacial coupling by low-frequency Raman spectroscopy under resonant excitation through the C exciton energy in TMD constituents. Based on the frequencies of emerging interlayer vibration modes in hBN/TMD/Gr ternary vdWHs, the interfacial coupling force constants of hBN/TMD and TMD/Gr interfaces are estimated as parameters to quantitatively evaluate the interfacial coupling strength at the corresponding interfaces. Moreover, the interfacial coupling strength at Gr/hBN interface is also successfully revealed in Gr/hBN/MoTe₂ ternary vdWHs, which cannot be directly characterized from Gr/hBN binary vdWH due to its unobservable interlayer modes with weak electron-phonon coupling. This general strategy can be further extended to probe and quantify the interfacial coupling quality in polynary vdWHs and related devices.