Dresden 2017 – scientific programme

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O: Fachverband Oberflächenphysik

O 108: Graphene: Adsorption, Intercalation and Other Aspects

O 108.7: Talk

Friday, March 24, 2017, 12:00–12:15, TRE Ma

Graphene phonons in inelastic electron tunnelling spectroscopy — •Johannes Halle¹, Nicolas Néel¹, Mads Brandbyge², and Jörg Kröger¹ — ¹Technische Universität Ilmenau, Ilmenau, Germany — ²Technical University of Denmark, Lyngby, Denmark

Graphene on Ir(111) was intercalated by Li, Cs, and Ni. Inelastic electron tunnelling spectroscopy (IETS) unraveled remarkably strong signatures of graphene phonons for Li and Cs intercalants. For Ni-intercalated graphene, in contrast, phonon signals stayed below the detection limit of the low-temperature scanning tunnelling microscope (STM). On the basis of previously determined phonon dispersion branches the IETS features were assigned to acoustic and optical graphene phonons at the M point of the surface Brillouin zone. Additional experiments unveiled that the IETS signal increased with increasing Li coverage. Moreover, decreasing the separation between STM tip and graphene from the tunnelling to contact ranges led to a significant lowering of the phonon spectroscopic signatures. Combining these results, and comparing to transport calculations based on density functional theory, we discuss possible mechanisms that appropriately describe inelastic excitations with non-zero wave vectors via electron injection from an STM tip. Financial support by the Deutsche Forschungsgemeinschaft through Grant No. KR 2912/10-1 is acknowledged.