Directly Probing Interfacial Coupling in a Monolayer MoSe₂ and CuPc Heterostructure

It is of great importance to develop useful methods to evaluate interfacial coupling strength noninvasively for exploring and optimizing heterointerface functionality. Recently, organic-inorganic van der Waals (vdW) heterostructures (HSs) composed of organic semiconductors and transition-metal dichalcogenides (TMD) have shown great potential for developing next-generation flexible optical, electrical, and optoelectrical devices. Since vdW coupling dominates the property of such a vdW HS, it is crucial to develop a method to evaluate its interfacial coupling strength noninvasively. In this work, by combining electrical force microscopy (EFM) and Raman and photoluminescence spectroscopic measurements, we were able to directly probe the coupling strength between monolayer MoSe₂ and a copper phthalocyanine (CuPc) thin film. Especially, we also found a new Raman mode in HS due to the Davydov splitting of the CuPc thin film via strong interfacial coupling between the two materials. This new Raman mode was thus utilized as a probe to reveal the modulation of the coupling strength by changing post-treatment conditions. All of these results indicate that the method developed here is capable of evaluating the coupling strength of the MoSe₂/CuPc HS effectively and innovatively, which aids in providing deep insights into such hybrid vdW HSs for future optical and optoelectrical applications.