Evidence of Kohn anomalies in quasi-freestanding graphene on Pt(1 1 1)

High-resolution electron energy loss spectroscopy has been used to probe phonon dispersion in quasi-freestanding graphene epitaxially grown on Pt(1 1 1). We report direct evidence of the existence of Kohn anomalies in the image and image optical phonon modes. These findings contrast with previous results on graphene/Ni(1 1 1), for which no Kohn anomalies were detected. Thus, such dissimilarity arises from the different interactions existing between graphene/Pt(1 1 1) (quasi-freestanding graphene) and graphene/Ni(1 1 1) (strongly interacting with the substrate). Hence, the phonon spectrum can be used to finely study the graphene–substrate coupling.