Understanding and engineering phonon-mediated tunneling into graphene on metal surfaces

TL;DR

This study investigates how different metal intercalants affect phonon signatures in graphene on Ir(111), revealing tunable signals with intercalant type and coverage, and providing insights into electron-phonon interactions at the interface.

Contribution

It offers a detailed analysis of phonon signatures in metal-intercalated graphene, highlighting the influence of intercalant type and coverage, and combines experimental spectroscopy with transport calculations for comprehensive understanding.

Findings

Cs intercalation produces exceptionally strong phonon signals.

Li intercalation induces detectable but weaker phonon signatures.

Ni intercalation results in phonon signals below detection limit across all ranges.

Abstract

Metal-intercalated graphene on Ir(111) exhibits phonon signatures in inelastic elec- tron tunneling spectroscopy with strengths that depend on the intercalant. Extraor- dinarily strong graphene phonon signals are observed for Cs intercalation. Li interca- lation likewise induces clearly discriminable phonon signatures, albeit less pronounced than observed for Cs. The signal can be finely tuned by the alkali metal coverage and gradually disappears upon increasing the junction conductance from tunneling to con- tact ranges. In contrast to Cs and Li, for Ni-intercalated graphene the phonon signals stay below the detection limit in all transport ranges. Going beyond the conventional two-terminal approach, transport calculations provide a comprehensive understanding of the subtle interplay between the graphene{electrode coupling and the observation of graphene phonon spectroscopic signatures.