Spectroscopic evaluation of charge-transfer doping and strain in graphene/MoS2 heterostructures

It is important to study the van der Waals interface in emerging vertical\nheterostructures based on layered two-dimensional (2D) materials. Being\natomically thin, 2D materials are susceptible to significant strains as well as\ncharge transfer doping across the interfaces. Here we use Raman and\nphotoluminescence (PL) spectroscopy to study the interface between monolayer\ngraphene/MoS2 heterostructures prepared by mechanical exfoliation and\nlayer-by-layer transfer. By using correlation analysis between the Raman modes\nof graphene and MoS2 we show that both layers are subjected to compressive\nstrain and charge transfer doping following mechanical exfoliation and thermal\nannealing. Furthermore, we show that both strain and carrier concentration can\nbe modulated in the heterostructures with additional thermal annealing. Our\nstudy highlights the importance of considering both mechanical and electronic\ncoupling when characterizing the interface in van der Waals heterostructures,\nand demonstrates a method to tune their electromechanical properties.\n