▎ 摘　　要

Molecular doping of graphene is intriguing since the electronic and vibrational properties of graphene are not only determined by the interfacial charge transfer process, but they can also be influenced by adsorbate-graphene hybridization, adsorbate-adsorbate interactions, as well as Fermi-level pinning of the molecule. In this work, we investigate the change in vibrational properties of graphene induced by an organic electron acceptor molecule in the presence of intervening spacers of ultra-thin molybdenum disulphide (MoS2) of variable thickness, down to a single layer. Mechanically exfoliated single-layer graphene and few-layer MoS2 crystals are combined to form heterostructures, which are then subjected to molecular doping by means of an organic hole-dopant, 7,7,8,8-tetracyanoquinodimethane (TCNQ). Variations in Raman G-peak parameters are discussed in terms of molecular doping of graphen e, when the dopant:graphene separation is controllably increased. We show that dopant-separation dependent Fermi level variations of graphene cannot be completely accounted within a simple charge transfer model. The additional mechanisms relevant to the complex nature of molecular doping are discussed.